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Journal articles on the topic 'Off-axis stiffness'
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1
Heslehurst, Rikard B. "Off-axis transformation of the composite laminate stiffness properties." Composite Structures 35, no. 4 (August 1996): 369–74. http://dx.doi.org/10.1016/s0263-8223(96)00042-6.
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Garner, Amy, Moneeb Genedy, Usama Kandil, and Mahmoud Reda Taha. "Controlling off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer using alumina nanoparticles." Journal of Composite Materials 52, no. 18 (December 21, 2017): 2483–91. http://dx.doi.org/10.1177/0021998317748466.
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This investigation experimentally examines the effect of incorporating alumina nanoparticles on the off-axis stiffness and stress-relaxation of carbon fiber-reinforced polymer composites. Four epoxy–alumina nanoparticle nanocomposites incorporating 0.0, 1.0, 2.0, and 3.0 wt% alumina nanoparticles of the total weight of epoxy are examined. Off-axis tension stiffness and stress-relaxation tests were performed on carbon fiber-reinforced polymer coupons fabricated with alumina nanoparticles–epoxy nanocomposites. Dynamic mechanical analysis testing of neat epoxy and epoxy nanocomposites incorporating alumina nanoparticles was used to identify the stiffness and relaxation behavior of the alumina nanoparticles–epoxy nanocomposite matrix. Fourier transform infrared spectroscopy was used to observe chemical changes when alumina nanoparticles are mixed with epoxy. It is shown that using alumina nanoparticles at a concentration close to 2.0 wt%, can reduce the off-axis stiffness by ∼30% and increase the off-axis stress-relaxation of carbon fiber-reinforced polymer by ∼10%.
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Montesano, John, Zouheir Fawaz, Kamran Behdinan, and Cheung Poon. "Fatigue Damage in On-Axis and Off-Axis Woven-Fiber/Resin Composite." Key Engineering Materials 488-489 (September 2011): 230–33. http://dx.doi.org/10.4028/www.scientific.net/kem.488-489.230.
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In this study the tensile static and fatigue behaviour of a woven-fabric laminate is investigated in both the on-axis and off-axis material directions. Emphasis is placed on the development of damage and its influence on the stress-strain behaviour of the laminate. The test results illustrate that there is a high degree of anisotropic behaviour due to anisotropic damage development, which is evident by the variation of the material behaviour between the on-axis and off-axis test specimens. The fatigue tests also suggest that the on-axis specimens exhibit noticeable stiffness degradation, while the off-axis specimens do not. The qualitative results provide significant insight into the type of damage mechanism responsible for the observed behaviour.
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Naves, M., R. G. K. M. Aarts, and D. M. Brouwer. "Large stroke high off-axis stiffness three degree of freedom spherical flexure joint." Precision Engineering 56 (March 2019): 422–31. http://dx.doi.org/10.1016/j.precisioneng.2019.01.011.
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Kashtalyan, Maria, and Costas Soutis. "Stiffness and fracture analysis of laminated composites with off-axis ply matrix cracking." Composites Part A: Applied Science and Manufacturing 38, no. 4 (April 2007): 1262–69. http://dx.doi.org/10.1016/j.compositesa.2006.07.001.
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Trease, Brian P., Yong-Mo Moon, and Sridhar Kota. "Design of Large-Displacement Compliant Joints." Journal of Mechanical Design 127, no. 4 (November 7, 2004): 788–98. http://dx.doi.org/10.1115/1.1900149.
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This paper investigates the drawbacks of typical flexure connectors and presents several new designs for highly effective, kinematically well-behaved compliant joints. A revolute and a translational compliant joint are proposed, both of which offer great improvements over existing flexures in the qualities of (1) a large range of motion, (2) minimal “axis drift,” (3) increased off-axis stiffness, and (4) a reduced stress-concentrations. Analytic stiffness equations are developed for each joint and parametric computer models are used to verify their superior stiffness properties. A catalog of design charts based on the parametric models is also presented, allowing for rapid sizing of the joints for custom performance. A joint range of motion has been calculated with finite element analysis, including stress concentration effects.
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Katerelos, D. G., L. N. McCartney, and C. Galiotis. "Effect of Off – Axis Matrix Cracking on Stiffness of Symmetric Angle-Ply Composite Laminates." International Journal of Fracture 139, no. 3-4 (June 2006): 529–36. http://dx.doi.org/10.1007/s10704-006-0100-9.
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Barret, C., and S. Baste. "Effective Elastic Stiffnesses of an Anisotropic Medium Permeated by Tilted Cracks." Journal of Applied Mechanics 66, no. 3 (September 1, 1999): 680–86. http://dx.doi.org/10.1115/1.2791562.
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This paper is concerned with the relationship between the effective stiffness tensor and the intensity of damage in individual modes for an anisotropic material with tilted cracks. The predictions are compared favorably with the experimentally measured load-induced changes of the 13 stiffnesses of a two-dimensional C/C-SiC ceramic matrix composite subjected to an off-axis solicitation. By taking into account the thickness of the cracks, it is possible to understand the change of the elastic anisotropy of the material and of its inelastic strain.
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Zhou, Qing Kun, Zhi Yong Zhang, Da Peng Fan, and Hua Jie Hong. "Transverse Stiffness and Guiding Characteristics Analysis of Compliant Linear Guided Mechanism." Applied Mechanics and Materials 34-35 (October 2010): 1941–45. http://dx.doi.org/10.4028/www.scientific.net/amm.34-35.1941.
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This paper presents a novel compliant linear guided mechanism (CLGM) to replace traditional spring and translation joint to transfer motion and force with its advanced guiding characteristics. In view of the incompatible relationship between axial stiffness and transverse stiffness of CLGM, eight kinds of CLGMs were developed by using building block approach based on fixed-guided flexure beam. The finite element analysis (FEA) models of eight CLGMs were built to complete numerical analysis on the force-displacement in axis and off-axis direction with same geometric sizes. The FEA results show that the structure configuration of Type 2-Type 8 can achieve a larger axial travel, Type 2 and Type4 have the advanced guiding characteristic with higher ratio of axial/transverse stiffness. Analysis indicates that the building block approach is an efficient method to complete the conceptual synthesis of compliant mechanism and FEA is effective on the structure optimization for the required compliance and stiffness in axial and transverse direction.
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Wang, Y. H., Zheng Dao Wang, and X. X. Zhao. "Prediction of the Fatigue Life Based on Stiffness Degradation Concept." Advanced Materials Research 33-37 (March 2008): 199–204. http://dx.doi.org/10.4028/www.scientific.net/amr.33-37.199.
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In order to predict the fatigue life of matrix-dominated polymer composites, a new model based on stiffness degradation concept was proposed. The effect of off-axis was considered by defining a non-dimensional modified stress level, and the expression of fatigue stress limit could be provided in the new model. Based on the fatigue tension-tension experiment of PI/SiO2 hybrid thin films under different stress levels, the simulated results was confirmed to be well agreeable with the experimental data.
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Mahieux, C. A., and K. L. Reifsnider. "Thermally Activated Mechanical Composite Switches." Advanced Composites Letters 8, no. 3 (May 1999): 096369359900800. http://dx.doi.org/10.1177/096369359900800302.
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A model describing the stiffness-temperature relationship of polymers was recently developed1,2. The present paper focuses on the integration of this model into classical lamination theory3. The computer simulations revealed that the stresses in off axis laminates are non-monotonic when temperature increases, i.e., continuous fibre reinforced polymer matrix composites seem to behave as thermally activated mechanical switches.
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Hao, Guangbo, and John Mullins. "On the comprehensive static characteristic analysis of a translational bistable mechanism." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 230, no. 20 (August 9, 2016): 3803–17. http://dx.doi.org/10.1177/0954406215616418.
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Bistable mechanisms have two stable positions and their characteristic analysis is much harder than the traditional spring system due to their postbuckling behaviour. As the strong nonlinearity induced by the postbuckling, it is difficult to establish a correct model to reveal the comprehensive nonlinear characteristics. This paper deals with the in-plane comprehensive static analysis of a translational bistable mechanism using nonlinear finite element analysis. The bistable mechanism consists of a pair of fixed-clamped inclined beams in symmetrical arrangement, which is a monolithic design and works within the elastic deformation domain. The displacement-controlled finite element analysis method using Strand7 is first discussed. Then the force–displacement relation of the bistable mechanism along the primary motion direction is described followed by the detailed primary translational analysis for different parameters. A simple analytical (empirical) equation for estimating the negative stiffness is obtained, and experimental testing is performed for a case study. It is concluded that (a) the negative stiffness magnitude has no influence from the inclined angle, but is proportional to the product of the Young’s modulus, beam depth, and cubic ratio for in-plane thickness to the beam length; (b) the unstable position is proportional to the product of the beam length and the Sine function of the inclined angle, and is not affected by the in-plane thickness and the material (or the out-of-plane thickness). The in-plane off-axis (translational and rotational) stiffness is further analysed to show the stiffness changes over the primary motion and the off-axis motion, and a negative rotational stiffness domain has been obtained.
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Kejun, Wang, Xuan Ming, Dong Jihong, Chi Chunyan, and Zhang Huanhuan. "Design and Research of Off-Axis Three-Mirror Space Remote Sensor Structure." Open Mechanical Engineering Journal 9, no. 1 (September 28, 2015): 744–51. http://dx.doi.org/10.2174/1874155x01509010744.
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On the basis of characteristics of optical system of three-mirror off-axis, with the method of topology optimization, the mirrors’ support structure and the frame structure which is a truss structure of the optical system were designed and investigated, the lightweight of the support structure and the truss structure are important, the structure optimization design of the system was completed, which quality is very light, by means of the finite element analysis techniques, we know that the shape error variation RMS and PV of optical mirror which are important indexes of image quality. The modal analysis and dynamic simulation calculation were carried out and the response character of the structure under dynamic environment was solved. Finally, the correctness of the finite element analysis results and the rationality of the design are validated by environmental testing. the analysis and test results indicate that the PV and RMS meet the design indexunder the comprehensive influence of gravity and thermal load which is in the control range, the overall structure have a high enough dynamic stiffness and reasonable distribution of modal, and the dynamic response of Space Remote Sensor was within the allowable range, which meet the use requirement.
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Philippidis, T. P., and A. P. Vassilopoulos. "Stiffness Reduction of Composite Laminates under Combined Cyclic Stresses." Advanced Composites Letters 10, no. 3 (May 2001): 096369350101000. http://dx.doi.org/10.1177/096369350101000302.
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Stiffness reduction due to fatigue of a [0/(±45)2/0]T Glass/Polyester (GRP) laminate under combined cyclic stress is investigated in this experimental study. Stress states combining all three components of in-plane stress tensor are induced by uniaxially testing specimens cut off-axis at various angles from the principal material coordinate system. Modulus reduction is related to the various failure modes exhibited under different states of combined stress. It is verified that shear and transverse normal stress induce more severe stiffness degradation compared to stress states where normal stress in the main fibre direction is dominant. For every loading condition and stress state, it is observed in general that stiffness decrease is more pronounced under lower stress levels than these inducing low cycle fatigue.
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Fletcher, Lloyd, Jared Van-Blitterswyk, and Fabrice Pierron. "Combined shear/tension testing of fibre composites at high strain rates using an image-based inertial impact test." EPJ Web of Conferences 183 (2018): 02041. http://dx.doi.org/10.1051/epjconf/201818302041.
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Testing fibre composites off-axis has been used extensively to explore shear/tension coupling effects. However, off-axis testing at strain rates above 500 s-1 is challenging with a split Hopkinson bar apparatus. This is primarily due to the effects of inertia, which violate the assumption of stress equilibrium necessary to infer stress and strain from point measurements taken on the bars. Therefore, there is a need to develop new high strain rate test methods that do not rely on the assumptions of split Hopkinson bar analysis. Recently, a new image-based inertial impact test has been used to successfully identify the transverse modulus and tensile strength of a unidirectional composite at strain rates on the order of 2000 -1. The image-based inertial impact test method uses a reflected compressive stress wave to generate tensile stress and failure in an impacted specimen. Thus, the purpose of this study is to modify the image-based inertial impact test method to investigate the high strain rate properties of fibre composites using an off-axis configuration. For an off-axis specimen, a combined shear/tension or shear/compression stress state will be obtained. Throughout the propagation of the stress wave, full-field displacement measurements are taken. Strain and acceleration fields are then derived from the displacement fields. The kinematic fields are then processed with the virtual fields method (VFM) to reconstruct stress averages and identify the in-plane stiffness components G12 and E22.
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Kesba, Mohamed Khodjet, A. Benkhedda, E. A. Adda bedia, and B. Boukert. "Effect of high temperature on the stiffness properties of cracked composite laminates with different off-axis angles." Procedia Structural Integrity 28 (2020): 864–72. http://dx.doi.org/10.1016/j.prostr.2020.11.055.
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Abrahamsson, T. J. S., and J. H. Sa¨llstro¨m. "A Spinning Finite Beam Element of General Orientation Analyzed With Rayleigh/Timoshenko/Saint-Venant Theory." Journal of Engineering for Gas Turbines and Power 118, no. 1 (January 1, 1996): 86–94. http://dx.doi.org/10.1115/1.2816554.
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Linear vibrations are studied for a straight uniform finite beam element of general orientation spinning at a constant angular speed about a fixed axis in the inertial space. The gyroscopic and circulatory matrices and also the geometric stiffness matrix of the beam element are presented. The effect of the centrifugal static axial load on the bending and torsional dynamic stiffnesses is thereby accounted for. The Rayleigh/Timoshenko/Saint-Venant theory is applied, and polynomial shape functions are used in the construction of the deformation fields. Nonzero off-diagonal elements in the gyroscopic and circulatory matrices indicate coupled bending/shearing/torsional/tensional free and forced modes of a generally oriented spinning beam. Two numerical examples demonstrate the use and performance of the beam element.
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Xie, Junbo, Guodong Fang, Zhen Chen, and Jun Liang. "High-temperature constitutive model for three-dimensional needled C/C-SiC composite under tensile loading." Journal of Composite Materials 51, no. 18 (November 13, 2016): 2619–29. http://dx.doi.org/10.1177/0021998316674350.
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Tensile experiments of three-dimensional needled C/C-SiC composite from room temperature to 1800℃ were performed to investigate tensile behavior. The damage characteristics and macroscopic mechanical behavior of the composite are relevant to the testing temperature and off-axis angles of the tensile loading. The tensile strength increased while the modulus decreased with the increase of temperature. A high-temperature nonlinear constitutive model was established to analyze the nonlinear stress–strain relationship of the composite. Plastic strain accumulation and stiffness degeneration were described by the plasticity and damage theories. The effect of temperature on the tensile behavior of the composite was particularly considered in this model by introducing a thermal damage variable. The proposed constitutive model can predict the stress–strain behavior of the material subjected to different off-axis tensile load, and at different temperatures. Fairly good agreement was achieved between the predicted and experimental results.
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Měšťánek, Petr, and Vladislav Laš. "Stress-Controlled Fatigue Testing of E-Glass Epoxy Composite: Monitoring of Micro-Damage." Applied Mechanics and Materials 732 (February 2015): 143–46. http://dx.doi.org/10.4028/www.scientific.net/amm.732.143.
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The paper deals with progressive and fatigue damage of long fiber E-glass epoxy composite, its residual stiffness degradation and corresponding transverse matrix crack density induced by load-controlled tension. Constant-amplitude fatigue tests in repeated tension of plain [±60]S; [±30]S; [0]8 and [0/902/±45/90]S samples were performed. Sudden onset of transverse matrix cracking and consequent gradual increase of its density has been observed in off-axis plies. The crack density increases with increasing number of cycles or load. Consequently, residual stiffness of the laminate decreases. It has been concluded that progressive/fatigue damage of the laminate is not a continuous homogenous process but the series of discrete sudden events emerging at ply level.
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Loukil, Mohamed Sahbi, and Janis Varna. "Effective shear modulus of a damaged ply in laminate stiffness analysis: Determination and validation." Journal of Composite Materials 54, no. 9 (September 23, 2019): 1161–76. http://dx.doi.org/10.1177/0021998319874369.
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The concept of the “effective stiffness” for plies in laminates containing intralaminar cracks is revisited presenting rather accurate fitting expressions for the effective stiffness dependence on crack density in the ply. In this article, the effective stiffness at certain crack density is back-calculated from the stiffness difference between the undamaged and damaged laminate. Earlier finite element method analysis of laminates with cracked 90-plies showed that the effective longitudinal modulus and Poisson’s ratio of the ply do not change during cracking, whereas the transverse modulus reduction can be described by a simple crack density dependent function. In this article, focus is on the remaining effective constant: in-plane shear modulus. Finite element method parametric analysis shows that the dependence on crack density is exponential and the fitting function is almost independent of geometrical and elastic parameters of the surrounding plies. The above independence justifies using the effective ply stiffness in expressions of the classical laminate theory to predict the intralaminar cracking caused stiffness reduction in laminates with off-axis plies. Results are in a very good agreement with (a) finite element method calculations; (b) experimental data, and (c) with the GLOB-LOC model, which gives a very accurate solution in cases where the crack face opening and sliding displacements are accurately described.
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Azevedo, Cristiano B., José Humberto S. Almeida Jr, Heitor F. Flores, Frederico Eggers, and Sandro C. Amico. "Influence of mosaic pattern on hygrothermally-aged filament wound composite cylinders under axial compression." Journal of Composite Materials 54, no. 19 (January 21, 2020): 2651–59. http://dx.doi.org/10.1177/0021998319899144.
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The mechanical response of composite structures may be affected by harsh environments, particularly when the matrix has a major contribution, e.g. with off-axis plies. This study aims at investigating the influence of the winding pattern on the axial compressive behavior of filament wound composite cylinder under hygrothermal conditioning. Carbon fiber-reinforced epoxy cylinders were manufactured via filament winding with 1/1, 3/1, and 5/1 mosaic winding patterns and submitted to distilled and artificial seawater environmental conditioning. Water uptake for each hygrothermal conditioning was periodically monitored. The winding pattern influenced both compressive strength and stiffness, and the environmental conditioning decreased strength up to ≈10%. The winding pattern with three diamonds around the circumference of the cylinders provides the properties in term of compressive strength and stiffness.
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Tu¨rkay, O. S., I. T. Su¨mer, A. K. Tugˇcu, and B. Kiray. "Modeling and Experimental Assessment of Suspension Dynamics of a Horizontal-Axis Washing Machine." Journal of Vibration and Acoustics 120, no. 2 (April 1, 1998): 534–43. http://dx.doi.org/10.1115/1.2893862.
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In this paper a nonlinear time variant rigid body dynamic model of the suspension system of an horizontal-axis washing machine is derived using Newton-Euler method, programmed for simulation, and assessed experimentally. The model includes the shock absorbers, the non-linear stiffness of the bellows and also the decoupled spinup motor dynamics. The simulation model predicted the transient and steady-state vertical and horizontal amplitudes of the tub within acceptable errors for a prototype suspension system design. The lift-off and the sliding phenomena of the cabinet have been assessed experimentally using four triaxial piezoelectric force transducers. These were found to be in very good agreement with the theoretical predictions. The model and the simulation code are thus validated experimentally for suspension design optimization of horizontal-axis washing machines.
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Wood, Zach, Lisa Lynn, Jack T. Nguyen, Margaret A. Black, Meha Patel, and Meir M. Barak. "Are we crying Wolff? 3D printed replicas of trabecular bone structure demonstrate higher stiffness and strength during off-axis loading." Bone 127 (October 2019): 635–45. http://dx.doi.org/10.1016/j.bone.2019.08.002.
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Luo, Yi, Olivier Gibaru, and Adel Olabi. "Dynamic Simulation of the Six Axis Machining Robot for Trajectory Planning in CATIA-LMS." Applied Mechanics and Materials 163 (April 2012): 74–78. http://dx.doi.org/10.4028/www.scientific.net/amm.163.74.
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Nowadays six axis machining robots are widely used in many fields of industry. Compared to machine tools, industrial robots offer a cheaper yet more flexible alternative to the machine-tools in the cleaning and pre-machining applications of aluminum castings. But the low stiffness has limited the application of industrial robots to the machining tasks with very low precision requirement. This paper presents a practical approach to improve the robot-machining accuracy by developing an off line simulation tool. Firstly we will complete the dynamic simulation of the 6-axis stiff model in CATIA-LMS for trajectory planning. Secondly we will set flexible joints and balancing system for the industry machining robot in LMS. Finally we will make some compare with the position trajectories generated by flexible joint and stiff joint, and then adjust the parameters under the references of the simulation result before the industry machining.
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Zhai, Zhanyu, Bingyan Jiang, and Dietmar Drummer. "Nonlinear Material Model for Quasi-Unidirectional Woven Composite Accounting for Viscoelastic, Viscous Deformation, and Stiffness Reduction." Polymers 10, no. 8 (August 11, 2018): 903. http://dx.doi.org/10.3390/polym10080903.
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To clarify the individual contribution of viscoelastic and viscous deformation to the global nonlinear response of composites, multilevel cyclic loading-unloading recovery tensile tests were carried out. The experimental results show that there is a linear relationship between the viscous strain and viscoelastic strain of composites, regardless of the off-axis angle or loading stress level. On the basis of experimental results, a coupled damage-plasticity constitutive model was proposed. In this model, the plasticity theory was adopted to assess the evolution of viscous strains. The viscoelastic strain was represented as a linear function of viscous strains. Moreover, the Weibull function of the effective stress was introduced to evaluate the damage variables in terms of stiffness reduction. The tensile stress-strain curves, predicted by the proposed model, showed a good agreement with experimental results.
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Derouin, Aaron, and Jim R. Potvin. "The Effect of Functional Knee Braces on Muscular Contributions to Joint Rotational Stiffness in Anterior Cruciate Ligament–Deficient and –Reconstructed Patients." Journal of Applied Biomechanics 35, no. 5 (October 1, 2019): 344–52. http://dx.doi.org/10.1123/jab.2018-0227.
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Functional knee braces are frequently prescribed by physicians to ameliorate the function of individuals with anterior cruciate ligament (ACL) injuries. These braces have been shown in the literature to potentially enhance knee stability by augmenting muscle activation patterns and the timing of muscle response to perturbations. However, very few techniques are available in the literature to quantify how those modifications in lower-limb muscle activity influence stability of the knee. The aim of the present study was to quantify the effect of an off-the-shelf functional knee brace on muscle contributions to knee joint rotational stiffness in ACL-deficient and ACL-reconstructed patients. Kinematic, electromyography, and kinetic data were incorporated into an electromyography-driven model of the lower extremity to calculate individual and total muscle contributions to knee joint rotational stiffness about the flexion–extension axis, for 4 independent variables: leg condition (contralateral uninjured, unbraced ACL injured, and braced ACL injured); knee flexion (5°–10°, 20°–25°, and 30°–35°); squat stability condition (stable and unstable); and injury status (ACL deficient and ACL reconstructed). Participants had significantly higher (P < .05,η2 = .018) total knee joint rotational stiffness values while wearing the brace compared with the control leg. A 2-way interaction effect between stability and knee flexion (P < .05,η2 = .040) for total joint rotational stiffness was also found.
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Loukil, Mohamed Sahbi, and Janis Varna. "Crack face sliding displacement (CSD) as an input in exact GLOB-LOC expressions for in-plane elastic constants of symmetric damaged laminates." International Journal of Damage Mechanics 29, no. 4 (July 27, 2019): 547–69. http://dx.doi.org/10.1177/1056789519866000.
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The crack opening and crack sliding displacements of both faces of an intralaminar crack are the main parameters defining the significance of each crack in laminate stiffness degradation, according to the previously published GLOB-LOC approach for symmetric laminates with an arbitrary number of cracks in all plies. In the exact stiffness expressions of this approach, the crack density is always multiplied by crack opening displacement and crack sliding displacement. The dependence of crack opening displacement on geometrical and elastic parameters of adjacent plies was studied previously and described by simple fitting functions. The crack sliding displacement has been analyzed for low-crack densities only and the proposed finite element method-based fitting expressions are oversimplified not including the out-of-plane ply stiffness effects. Based on finite element method analysis, more accurate expressions for so-called non-interactive cracks are suggested in the presented article. For the first time the shear stress perturbations are analyzed and interaction functions are presented with the feature that they always lead to slightly conservative predictions. The presented simple fitting functions, when used in the GLOB-LOC model, give predictions that are in a good agreement with finite element method results and with experimental data for laminates with damaged off-axis plies in cases when crack face sliding is of importance. The significance of including crack sliding displacement in stiffness predictions is demonstrated.
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Salzar, R. S., M. J. Pindera, and F. W. Barton. "Elastoplastic Analysis of Layered Metal Matrix Composite Cylinders—Part I: Theory." Journal of Pressure Vessel Technology 118, no. 1 (February 1, 1996): 13–20. http://dx.doi.org/10.1115/1.2842155.
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An exact elastic-plastic analytical solution for an arbitrarily laminated metal matrix composite tube subjected to axisymmetric thermo-mechanical and torsional loading is presented. First, exact solutions for transversely isotropic and monoclinic (off-axis) elastoplastic cylindrical shells are developed which are then reformulated in terms of the interfacial displacements as the fundamental unknowns by constructing a local stiffness matrix for the shell. Assembly of the local stiffness matrices into a global stiffness matrix in a particular manner ensures satisfaction of interfacial traction and displacement continuity conditions, as well as the external boundary conditions. Due to the lack of a general macroscopic constitutive theory for the elastic-plastic response of unidirectional metal matrix composites, the micromechanics method of cells model is employed to calculate the effective elastic-plastic properties of the individual layers used in determining the elements of the local and thus global stiffness matrices. The resulting system of equations is then solved using Mendelson’s iterative method of successive elastic solutions developed for elastoplastic boundary-value problems. Part I of the paper outlines the aforementioned solution strategy. In Part II (Salzar et al., 1996) this solution strategy is first validated by comparison with available closed-form solutions as well as with results obtained using the finite-element approach. Subsequently, examples are presented that illustrate the utility of the developed solution methodology in predicting the elastic-plastic response of arbitrarily laminated metal matrix composite tubes. In particular, optimization of the response of composite tubes under internal pressure is considered through the use of functionally graded architectures.
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Socci, Carlo Alberto, and Christos Kassapoglou. "Prediction of matrix crack initiation and evolution and their effect on the stiffness of laminates with off-axis plies under in-plane loading." Composites Science and Technology 200 (November 2020): 108427. http://dx.doi.org/10.1016/j.compscitech.2020.108427.
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Padovan, Joe, Mark Schrader, and Joel Parris. "Buckling and Postbuckling of Elastomeric Components: Tactile Feel in Electric Switches." Rubber Chemistry and Technology 63, no. 1 (March 1, 1990): 135–48. http://dx.doi.org/10.5254/1.3538237.
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Abstract Within the range of the parameters of the switch designs considered, only very slight cocking of the switch structure occurred. Thus, with minimal off-axis cocking, the axisymmetric assumption remained valid, resulting in a considerable finite-element economization when compared to a full three dimensional model. Some switch designs encounter localization problems, such as surface folding and stiffness mismatches. Mesh refinement is not a general panacea for these localization problems. Regardless, a fold of this type or stiffness mismatch is generally indicative of a potentially poor switch design, with the possibility of associated fatigue problems. For the switch designs considered, the peak strains were found to be less than 70 percent; thus the Mooney-Rivlin and Ogden material models yielded essentially similar results. Furthermore, a Hookean material model may be adequate for some purposes, because the tactile-feel response was found to be dominated more by switch geometry than anything else. Overall, we have seen that combining FE analysis together with the full continuum-constitutive-boundary formulation can successfully address the problem of buckling and postbuckling of elastomeric structures. In the case of switches, such behavior is an intrinsic property. This is an interesting contrast with traditional structures.
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Chamieh, Dimitri S., Allan J. Acosta, Christopher E. Brennen, and Thomas K. Caughey. "Experimental Measurements of Hydrodynamic Radial Forces and Stiffness Matrices for a Centrifugal Pump-Impeller." Journal of Fluids Engineering 107, no. 3 (September 1, 1985): 307–15. http://dx.doi.org/10.1115/1.3242482.
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The present work is an experimental investigation of the possible forces of fluid dynamic origin that can act on a turbomachine rotor particularly when it is situated off its normal center position. An experimental facility, the Rotor Force Test Facility, has been designed and constructed in order to measure these kinds of forces acting on a centrifugal pump impeller when the latter is made to whirl in a slightly eccentric circular orbit. The scope of the present experimental work consists of measuring quasi-steady forces on the impeller as it whirls slowly about the axis of the pump rotation. These forces are due to interaction between the impeller and volute; they are decomposed into force components relative to the geometric center of the volute and to those proportional to displacement from this center. These latter are interpreted as stiffness matrices. Such matrices were obtained for two different volutes and both were found to be the sum of a diagonal and a skew-symmetric matrix. It can be shown that a stiffness matrix of this type can lead to dynamic instability of impeller shaft system in certain circumstances. This new experimental finding may explain some operational problems of “high-speed” hydraulic machinery. Comparison is made with various existing theoretical and experimental results.
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Hajishafieiha, Peiman. "Fuzzy Logic Controller Designing of an Active Roll Control System for Medium and Large Size Vehicles." Applied Mechanics and Materials 110-116 (October 2011): 4845–55. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.4845.
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The roll / ride trade-off is a long-standing challenge to vehicle dynamicists. Achieving better ride performance almost inevitably leads to increased roll of the vehicle. This roll motion, mostly induced by maneuvering, leads to undesirable handling characteristics and subsequently higher risk of rollover. This paper analyses the use of an Active Roll Control (ARC) system with a Fuzzy Logic Controller (FLC) for improving the handling without sacrificing the ride comfort. The logic for reducing the roll angle of the vehicle is to have some forces exerted by linear actuators on the suspension system, depending on the velocity and steering angle of the vehicle. These forces create a moment about the roll axis which decreases the roll angle. The proposed Fuzzy logic controller is a feedback controller which outputs the correcting roll moment about the roll axis. The effects of employing such a control system are evaluated through computer simulation. Torsional stiffness of the chassis is then taken into consideration to account for unique properties of large-size vehicles. Simulation results with Fuzzy logic controller are very promising and show that the roll performance is significantly improved compared to the vehicle without ARC.
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Pindera, M. J., and M. S. Lane. "Frictionless Contact of Layered Half-Planes, Part I: Analysis." Journal of Applied Mechanics 60, no. 3 (September 1, 1993): 633–39. http://dx.doi.org/10.1115/1.2900851.
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A method is presented for the solution of frictionless contact problems on multilayered half-planes consisting of an arbitrary number of isotropic, orthotropic, or monoclinic layers arranged in any sequence. A displacement formulation is employed and the resulting Navier equations that govern the distribution of displacements in the individual layers are solved using Fourier transforms. A local stiffness matrix in the transform domain is formulated for each layer which is then assembled into a global stiffness matrix for the entire multilayered half-plane by enforcing continuity conditions along the interfaces. Application of the mixed boundary condition on the top surface of the medium subjected to the force of the indenter results in an integral equation for the unknown pressure in the contact region. The integral possesses a divergent kernel which is decomposed into Cauchy type and regular parts using the asymptotic properties of the local stiffness matrix and the ensuing relation between Fourier and finite Hilbert transform of the contact pressure. For homogeneous half-planes, the kernel consists only of the Cauchy-type singularity which results in a closed-form solution for the contact stress. For multilayered half-planes, the solution of the resulting singular integral equation is obtained using a collocation technique based on the properties of orthogonal polynomials. Part I of this paper outlines the analytical development of the technique. In Part II a number of numerical examples is presented addressing the effect of off-axis plies on contact stress distribution and load versus contact length in layered composite half-planes.
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Raghavendra, Sunil, Alberto Molinari, Vigilio Fontanari, Michele Dallago, Valerio Luchin, Gianluca Zappini, and Matteo Benedetti. "Tension-compression asymmetric mechanical behaviour of lattice cellular structures produced by selective laser melting." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 234, no. 16 (March 24, 2020): 3241–56. http://dx.doi.org/10.1177/0954406220912786.
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Additive manufacturing is an evolving technology for fabricating porous structures used in a broad array of applications, ranging from the aerospace industry to biomedical engineering. Porous titanium alloy (Ti6Al4V) structures play a major role in biomedical implants and are preferred over conventional solid implants because their properties can be tailored to obtain the stiffness required to avoid stress shielding and improve osteointegration. The mechanical properties of these structures are dependent on unit cell topology and overall porosity. In the present work, three open cellular configurations were studied, namely regular (square), irregular (skewed square) and fully random structures, at three different porosity levels. The samples were manufactured using the selective laser melting of spherical Ti6Al4V powder. The deviations of manufactured samples from as designed were assessed using morphological characterisations and porosity analyses. The mechanical characterisations of the samples included monotonic and cyclic tensile tests, along with conventional compression tests under monotonic and cyclic conditions. The results from the study indicate a clear deviation of thickness values from as-designed values. The effect of inclination of the strut with respect to the loading axis has been studied in compression samples. The off-axis loading in compression led to the asymmetry in the Young's modulus in compression and tension. These led to finite element modelling of structures in the elastic regime and its validation using Gibson–Ashby model for cellular structures.
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Cao, Yin Ping, and Xiu Hua Shi. "The Research of SOL Treated Cantilever Beam Based on Analytical Methods and ANSYS." Advanced Materials Research 79-82 (August 2009): 1663–66. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.1663.
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SOL (stand-off layer) damping treatment is the most effective method to improve the damping characteristics of the base structure compared with unconstrained and constrained layer damping treatment. In this case, the viscoelastic layer is sandwiched between the SOL and the constraining layer. During vibration, the SOL acts as a strain magnifier which magnifies the shear strain in the viscoelastic layer by increasing the distance between the viscoelastic layer and the neutral axis of the base structure thus dissipates more vibration energy. The equations of motion root in kinematic equations, constitutive equations and equilibrium equations of force and moment, and constitute one variable (lateral deflection) with order differential equation and two variables (axial deflections of the base beam and the constraining layer) with order differential equation of motion. Together with the boundary conditions, the transfer function method and the finite element method are adopted to analyze the damping characteristics of the composite structure. In distributed function method, the equations are transferred to state space form. In finite element method, the lateral deflection is interpolated by Hermite interpolation function and the axial deflections of the base layer and the constraining layer are interpolated by Lagrange interpolation function. At last, the predictions of the two analytical methods are validated against the commercial software ANSYS. Close agreements are found among the three methods. To achieve the expected effect, the SOL must have high shear stiffness and low bending stiffness so it does not significantly influence the flexural rigidity of the base structure but does not absorb the shear stress desired to be passed on to the viscoelastic layer. This paper is focus the application of SOL damping treatment on cantilever beam model, but it is essential to note that the model can be extended to complex structures such as plates and shells. We can select the slotted SOL damping treatment which could effectively avoid the increase in bending stiffness but also maintain high shear stiffness as the substitute.
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Agostoni, Piergiuseppe, Susanna Sciomer, Pietro Palermo, Mauro Contini, Beatrice Pezzuto, Stefania Farina, Alessandra Magini, et al. "Minute ventilation/carbon dioxide production in chronic heart failure." European Respiratory Review 30, no. 159 (February 2, 2021): 200141. http://dx.doi.org/10.1183/16000617.0141-2020.
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In chronic heart failure, minute ventilation (V′E) for a given carbon dioxide production (V′CO2) might be abnormally high during exercise due to increased dead space ventilation, lung stiffness, chemo- and metaboreflex sensitivity, early metabolic acidosis and abnormal pulmonary haemodynamics. The V′Eversus V′CO2 relationship, analysed either as ratio or as slope, enables us to evaluate the causes and entity of the V′E/perfusion mismatch. Moreover, the V′E axis intercept, i.e. when V′CO2 is extrapolated to 0, embeds information on exercise-induced dead space changes, while the analysis of end-tidal and arterial CO2 pressures provides knowledge about reflex activities. The V′Eversus V′CO2 relationship has a relevant prognostic power either alone or, better, when included within prognostic scores. The V′Eversus V′CO2 slope is reported as an absolute number with a recognised cut-off prognostic value of 35, except for specific diseases such as hypertrophic cardiomyopathy and idiopathic cardiomyopathy, where a lower cut-off has been suggested. However, nowadays, it is more appropriate to report V′Eversus V′CO2 slope as percentage of the predicted value, due to age and gender interferences. Relevant attention is needed in V′Eversus V′CO2 analysis in the presence of heart failure comorbidities. Finally, V′Eversus V′CO2 abnormalities are relevant targets for treatment in heart failure.
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Ratner, Alon, Richard Beaumont, and Iain Masters. "Dynamic Mechanical Compression Impulse of Lithium-Ion Pouch Cells." Energies 13, no. 8 (April 23, 2020): 2105. http://dx.doi.org/10.3390/en13082105.
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Strain rate sensitivity has been widely recognized as a significant feature of the dynamic mechanical properties of lithium-ion cells, which are important for their accurate representation in automotive crash simulations. This research sought to improve the precision with which dynamic mechanical properties can be determined from drop tower impact testing through the use of a diaphragm to minimize transient shock loads and to constrain off-axis motion of the indenter, specialized impact absorbers to reduce noise, and observation of displacement with a high speed camera. Inert pouch cells showed strain rate sensitivity in an increased stiffness during impact tests that was consistent with the poromechanical interaction of the porous structure of the jellyroll with the liquid electrolyte. The impact behaviour of the inert pouch cells was similar to that of an Expanded Polypropylene foam (EPP), with the exception that the inert pouch cells did not show hysteretic recovery under the weight of the indenter. This suggests that the dynamic mechanical behaviour of the inert pouch cells is analogous to a highly damped foam.
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Just, Koch, Brod, Jansen, Gude, and Rolfes. "Influence of Reversed Fatigue Loading on Damage Evolution of Cross-Ply Carbon Fibre Composites." Materials 12, no. 7 (April 9, 2019): 1153. http://dx.doi.org/10.3390/ma12071153.
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Microcrack formation and delamination growth are the main damage mechanisms in thefatigue of composites. They lead to significant stiffness loss, introduce stress concentrations andcan be the origin of subsequent damage events like buckling or fibre breakage, especially in case ofshear and compression stresses during load reversal. Fatigue experiments of carbon fibre reinforcedlaminates were conducted at several stress ratios and analysed in terms of crack and delaminationgrowth. These investigations were accompanied by microscopic imaging, digital image correlationand finite element modelling to take into account the effects of residual stresses and crack closure.It was found that residual stresses significantly change the local stress ratio in off-axis layers andlead to residual crack opening of inter fibre cracks. These cracks remain open and close under highcompression loadings only. Furthermore, crack formation under pulsating compression loadingturned out to be driven by residual stresses leading to perpendicular cracks as observed underpure tension loading. The experimental findings further confirm the severe detrimental effect oftension-compression loading on crack formation and delamination growth compared to pulsatingtension-tension or compression-compression loads.
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Pindera, M. J., and M. S. Lane. "Frictionless Contact of Layered Half-Planes, Part II: Numerical Results." Journal of Applied Mechanics 60, no. 3 (September 1, 1993): 640–45. http://dx.doi.org/10.1115/1.2900852.
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In Part I of this paper, analytical development of a method was presented for the solution of frictionless contact problems of multilayered half-planes consisting of an arbitrary number of isotropic, orthotropic, or monoclinic layers arranged in any sequence. The local/global stiffness matrix approach similar to the one proposed by Bufler (1971) was employed in formulating the surface mixed boundary condition for the unknown stress in the contact region. This approach naturally facilitates decomposition of the integral equation for the contact stress distribution on the top surface of an arbitrarily laminated half-plane into singular and regular parts that, in turn, can be solved using a numerical collocation technique. In Part II of this paper, a number of numerical examples is presented addressing the effect of off-axis plies on contact stress distribution and load versus contact length in layered half-planes laminated with unidirectionally reinforced composite plies. The results indicate that for the considered unidirectional composite, the load versus contact length response is significantly influenced by the orientation of the surface layer and the underlying half-plane, while the corresponding contact stress profiles are considerably less affected.
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Ravve, Igor, and Zvi Koren. "Slowness vector versus ray direction in polar anisotropic media." Geophysical Journal International 225, no. 3 (February 13, 2021): 1725–54. http://dx.doi.org/10.1093/gji/ggab061.
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SUMMARY The inverse problem of finding the slowness vector from a known ray direction in general anisotropic elastic media is a challenging task, needed in many wave/ray-based methods, in particular, solving two-point ray bending problems. The conventional resolving equation set for general (triclinic) anisotropy consists of two fifth-degree polynomials and a sixth-degree polynomial, resulting in a single physical solution for quasi-compressional (qP) waves and up to 18 physical solutions for quasi-shear waves (qS). For polar anisotropy (transverse isotropy with a tilted symmetry axis), the resolving equations are formulated for the slowness vectors of the coupled qP and qSV waves (quasi-shear waves polarized in the axial symmetry plane), and independently for the decoupled pure shear waves polarized in the normal (to the axis) isotropic plane (SH). The novelty of our approach is the introduction of the geometric constraint that holds for any wave mode in polar anisotropic media: The three vectors—the slowness, ray velocity and medium symmetry axis—are coplanar. Thus, the slowness vector (to be found) can be presented as a linear combination of two unit-length vectors: the polar axis and the ray velocity directions, with two unknown scalar coefficients. The axial energy propagation is considered as a limit case. The problem is formulated as a set of two polynomial equations describing: (i) the collinearity of the slowness-related Hamiltonian gradient and the ray velocity direction (third-order polynomial equation) and (ii) the vanishing Hamiltonian (fourth-order polynomial equation). Such a system has up to twelve real and complex-conjugate solutions, which appear in pairs of the opposite slowness directions. The common additional constraint, that the angle between the slowness and ray directions does not exceed ${90^{\rm{o}}}$, cuts off one half of the solutions. We rearrange the two bivariate polynomial equations and the above-mentioned constraint as a single univariate polynomial equation of degree six for qP and qSV waves, where the unknown parameter is the phase angle between the slowness vector and the medium symmetry axis. The slowness magnitude is then computed from the quadratic Christoffel equation, with a clear separation of compressional and shear roots. The final set of slowness solutions consists of a unique real solution for qP wave and one or three real solutions for qSV (due to possible triplications). The indication for a qSV triplication is a negative discriminant of the sixth-order polynomial equation, and this discriminant is computed and analysed directly in the ray-angle domain. The roots of the governing univariate sixth-order polynomial are computed as eigenvalues of its companion matrix. The slowness of the SH wave is obtained from a separate equation with a unique analytic solution. We first present the resolving equation using the stiffness components, and then show its equivalent forms with the well-known parametrizations: Thomsen, Alkhalifah and ‘weak-anisotropy’. For the Thomsen and Alkhalifah forms, we also consider the (essentially simplified) acoustic approximation for qP waves governed by the quartic polynomials. The proposed method is coordinate-free and can be applied directly in the global Cartesian frame. Numerical examples demonstrate the advantages of the method.
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Alm, Lena, Jannik Frings, Matthias Krause, and Karl-Heinz Frosch. "Intraarticular osteotomy of malunited tibial plateau fractures: an analysis of clinical results with a mean follow-up after 4 years." European Journal of Trauma and Emergency Surgery 46, no. 6 (July 25, 2020): 1203–9. http://dx.doi.org/10.1007/s00068-020-01440-y.
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Abstract Purpose Malunions are a common complication after tibial plateau fractures (TPF), leading to stiffness, pseudo-instability and posttraumatic osteoarthritis. The purpose of this study was to analyse the clinical outcome after intraarticular osteotomy of malunited TPF and to perform a failure analysis. Methods Between 2013 and 2018, 23 patients (11 males, 12 females; 43.8 ± 12.8 years) with intraarticular osteotomy after malunited TPF were included in the retrospective study. Clinical examination and postoperative scores were collected with a minimum follow-up of 24 months. Malunion was measured on pre- and postoperative CT scans and localized according to the 10-segment classification while the leg axis in the frontal plane was measured pre- and postoperatively on long leg standing radiographs. Results Excellent and good clinical outcome was achieved in 73.9% (n = 17) of the cases and patient related outcome improved significantly (Tegner 3.3 ± 1.6–5 ± 1.8, p < 0.001; clinical Rasmussen 14.6 ± 3.8–24.9 ± 4.4, p < 0.001). Radiological parameters also improved as an intraarticular step-off was reduced from 9 ± 3.8 to 0.6 ± 0.8 mm (p < 0.001) and a lower limb malalignment from 7.2 ± 4.8° to 1.5 ± 1.9° (p = 0.003). Failure analysis showed that an impaired clinical result correlated with a postoperative extension (n = 3, p < 0.001) and flexion deficit (n = 4, p = 0.035). Conclusion Intraarticular osteotomy of malunited TPF lead to good clinical results with significant clinical and radiological improvement in most cases while an impaired patient outcome correlated with a limited range of motion. This study is the first failure analysis of intraarticular osteotomy after malunited TPF published up to now.
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Melcher, David, Moritz Bätge, and Sebastian Neßlinger. "A novel rotor blade fatigue test setup with elliptical biaxial resonant excitation." Wind Energy Science 5, no. 2 (May 28, 2020): 675–84. http://dx.doi.org/10.5194/wes-5-675-2020.
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Abstract. The full-scale fatigue test of rotor blades is an important and complex part of the development of new wind turbines. It is often done for certification according to the current IEC (2014) and DNV GL AS (2015) standards. Typically, a new blade design is tested by separate uniaxial fatigue tests in both main directions of the blade, i.e. flapwise and lead lag. These tests are time-consuming and rather expensive due to the high number of load cycles required, up to 5 million. Therefore, it is important to run the test as efficiently as possible. During fatigue testing, the rotor blade is excited at or near its resonant frequency. The trend for new rotor blade designs is toward longer blades, leading to a significant drop in their natural frequencies and a corresponding increase in test time. To reduce the total test time, a novel test method aims to combine the two consecutive uniaxial fatigue tests into one biaxial test. The biaxial test excites the blade in both directions at the same time and at the same frequency, resulting in an elliptical deflection path of the blade axis. Using elliptical loading, the counting of damage equivalent load cycles is simplified in comparison to biaxial tests with multiple frequencies. In addition, the maximum loads in both main directions remain separated, while off-axis loading is introduced. To achieve such a test, specific load elements need to be arranged so as to equalize the natural frequencies of the test setup for both test directions. This is accomplished by adding stiffness or inertial effects in a specific direction. This work describes a new method to design suitable test setups. A parameterized finite element (FE) model of the test with beam elements for the blade represents the test setup. A harmonic analysis on the FE model can identify the load distribution and the test conditions of a specific test setup within seconds. An optimization algorithm that varies parameters of the model and searches for the optimal setup is then applied to the analysis. This approach allows the efficient determination of a test setup, suited to the predefined requirements. The method is validated by applying it to three different test scenarios for a modern rotor blade: (a) state-of-the-art uniaxial setups, (b) uniaxial setups including springs and (c) a biaxial setup. In conclusion, the resulting setups are evaluated in terms of test quality and efficiency.
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Helbig, Klaus. "Longitudinal directions in media of arbitrary anisotropy." GEOPHYSICS 58, no. 5 (May 1993): 680–91. http://dx.doi.org/10.1190/1.1443452.
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A longitudinal direction is one in which three pure modes can propagate. It is known that every medium has at least three longitudinal directions. Every axis of symmetry is such a “bound” longitudinal direction, but in most media there are additional “free” longitudinal directions which do not coincide with symmetry directions. In particular, there are longitudinal directions even in triclinic media that possess no symmetry except the point symmetry. The maximum number of distinct longitudinal directions is thirteen. In a longitudinal direction the wave propagation is particularly simple: for the longitudinal mode, wave normal, displacement direction, and ray direction are identical, while for the two transverse modes the deviation of the ray direction from that of the wave normal depends on the type of longitudinal direction and the relative magnitude of a few stiffnesses expressed in a coordinate system aligned with the longitudinal direction. Similarly, the polarization pattern in the vicinity of a longitudinal direction depends strongly on the type of the longitudinal direction and on the relative magnitude of some off‐diagonal stiffnesses. Since the polarization pattern can be observed in suitable vertical seismic profiling (VSP) surveys, it might be inverted to obtain information on elastic parameters that is difficult to obtain by other means. For orthorhombic symmetry, there are always the three bound longitudinal directions coinciding with the axes. In each plane of symmetry a pair of free longitudinal directions can exist, and there can be four symmetrically disposed free longitudinal directions outside the planes of symmetry. Existence and direction of these free directions follows from simple expressions in the elastic stiffnesses.
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Mackay, Allen B., David G. Smith, Spencer P. Magleby, Brian D. Jensen, and Larry L. Howell. "Metrics for Evaluation and Design of Large-Displacement Linear-Motion Compliant Mechanisms." Journal of Mechanical Design 134, no. 1 (January 1, 2012). http://dx.doi.org/10.1115/1.4004191.
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This work introduces metrics for large-displacement linear-motion compliant mechanisms (LLCMs) that evaluate the performance tradeoff between displacement and off-axis stiffness. These metrics are nondimensionalized, consisting of relevant characteristics used to describe displacement, off-axis stiffness, actuation force, and size. Displacement is normalized by the footprint of the device, transverse stiffness by a new performance characteristic called virtual axial stiffness, and torsional stiffness by the characteristic torque. These metrics account for the variation of both axial and off-axis stiffness over the range of displacement. The metrics are demonstrated for several microelectromechanical systems (MEMS) that are sensitive to size because of high cost and off-axis stiffness because of function. The use of metrics in design is demonstrated in the design of an LLCM; the resulting design shows increased values for both the travel and transverse-stiffness metrics.
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Carraro, P. A., L. Maragoni, and M. Quaresimin. "Stiffness degradation of symmetric laminates with off-axis cracks and delamination: an analytical model." International Journal of Solids and Structures, December 2020. http://dx.doi.org/10.1016/j.ijsolstr.2020.12.013.
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Li, Canran, Nianfeng Wang, Fan Yue, and Xianmin Zhang. "Optimization of Translational Flexure Joints Using Corrugated Units Under Stress Constraints." Journal of Mechanisms and Robotics 13, no. 6 (June 1, 2021). http://dx.doi.org/10.1115/1.4050763.
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Abstract When optimizing corrugated flexure (CF) joints, most approaches for calculating the maximum stress on the CF beam depend on finite element analysis (FEA). The current paper introduces the design optimization for joints using CF units under stress constraints. The stress state is solved; based on that, the maximum displacement under stress constraints is deduced. The natural frequency formula of the translational joint is further derived from the results of the stiffness matrix. The stage configurations corresponding to the maximum displacement are optimized by restricting the off-axis/axial stiffness ratio and natural frequency of the joint. The optimal results of different types are validated by FEA and experiments.
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Jiang, Dajun, Shi Zhan, Qianying Cai, Hai Hu, and Weitao Jia. "Enhanced interfragmentary stability and improved clinical prognosis with use of the off-axis screw technique to treat vertical femoral neck fractures in nongeriatric patients." Journal of Orthopaedic Surgery and Research 16, no. 1 (July 31, 2021). http://dx.doi.org/10.1186/s13018-021-02619-8.
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Abstract Background The optimal internal fixation strategy for vertical femoral neck fractures (VFNFs) in nongeriatric patients remains uncertain. Therefore, the purpose of this study was to compare the clinical prognoses and underlying mechanical characteristics of a novel off-axis screw technique with dynamic hip screws (DHSs) and three traditional parallel screws. Methods This study included a clinical investigation and a patient-specific finite element analysis (FEA). In the clinical investigation, VFNF patients were grouped by fixation type: (1) use of three parallel screws (G-TRI); (2) augmentation with an off-axis screw (G-ALP); and (3) DHS with an anti-rotational screw (G-DHS). Fixation failures (nonunion, femoral neck shortening (FNS), varus deformation, screw cut-out) and avascular necrosis (AVN) consequent to the three types of fixations were compared. In the FEA, twenty-four fixation models with the three fixation types were created based on the data of eight healthy volunteers. Models were assessed under walking conditions. Stiffness, interfragmentary motion (IFM), and implant stress were evaluated. Results In the clinical investigation, the fixation failure rate was significantly (p < 0.05) lower in G-ALP (18.5%) than in G-DHS (37.5%) and G-TRI (39.3%). No significant difference in AVN was observed among the three fixation groups. In the FEA, stiffness and implant stress in the G-DHS models were significantly (p < 0.05) higher, and the IFM of G-ALP was significantly (p < 0.05) lower among the groups. Conclusions Among fixation types for VFNFs, the off-axis screw technique exhibited better interfragmentary stability (lowest IFM) and a lower fixation failure rate (especially FNS). Analyzing interfragmentary stability in biomechanical experiments is more consistent with clinical prognosis than construct stability for VFNFs, suggesting that internal fixations should aim for this outcome.
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Mizzi, Luke, Andrea Sorrentino, Andrea Spaggiari, and Davide Castagnetti. "A comparison between rotating squares and anti-tetrachiral systems: Influence of ligaments on the multi-axial mechanical response." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, September 2, 2021, 095440622110431. http://dx.doi.org/10.1177/09544062211043145.
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Rotating unit systems are one of the most important and well-known classes of auxetic mechanical metamaterials. As their name implies, when loaded, these systems deform primarily via rotation of blocks of material, which may be connected together either directly through joints (or ‘joint-like’ connections made by overlapping vertices of the rotating units) as in the case of rotating rigid polygonal-unit systems or by ligaments/ribs as in the case of chiral honeycombs. In this work, we used Finite Element Analysis to investigate the effect which the presence/absence of ligaments has on the on-axis and off-axis mechanical properties of these systems by analysing two of the most well-known structures which characterise these two cases: the rotating square system and the anti-tetrachiral honeycomb. It was found that while the presence of ligaments has a negligible effect on the on-axis Poisson’s ratio of these systems, it has a profound influence on nearly all other mechanical properties as well as on the off-axis loading behaviour. Systems with ligaments were found to exhibit a high level of anisotropy and also a severely reduced level of stiffness in comparison to their non-ligamented counterparts. On the other hand, the rotating square system suffers from high localized stress-intensities and has a very low strain-tolerance threshold. In addition, an optimized ‘hybrid’ geometry which is specifically designed to capture the best features of both the anti-tetrachiral and rotating square system, was also analysed. This work shows the main differences between ligament-based and non-ligament-based auxetic structures and also highlights the importance of considering the off-axis mechanical response in addition to the on-axis properties when investigating such systems.
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Wang, Nianfeng, Zhiyuan Zhang, Fan Yue, and Xianmin Zhang. "Exploration of Translational Joint Design Using Corrugated Flexure Units With Bézier Curve Segments." Journal of Mechanical Design 141, no. 5 (January 11, 2019). http://dx.doi.org/10.1115/1.4042366.
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In order to satisfy particular design specifications, shape variation for limited geometric envelopes is often employed to alter the elastic properties of flexure joints. This paper introduces an analytical stiffness matrix method to model a new type of corrugated flexure (CF) beam with cubic Bézier curve segments. The cubic Bézier curves are used to depict the segments combined to form CF beam and translational joint. Mohr's integral is applied to derive the local-frame compliance matrix of the cubic Bézier curve segment. The global-frame compliance matrices of the CF unit and the CF beam with cubic Bézier curve segments are further formed by stiffness matrix method, which are confirmed by finite element analysis (FEA). The control points of Bézier curve are chosen as optimization parameters to identify the optimal segment shape, which maximizes both high off-axis/axial stiffness ratio and large axial displacements of translational joint. The results of experimental study on the optimum translational joint design validate the proposed modeling and optimization method.
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Schmitt, François, Olivier Piccin, Bernard Bayle, Pierre Renaud, and Laurent Barbé. "Inverted Honeycomb Cell as a Reinforcement Structure for Building Soft Pneumatic Linear Actuators." Journal of Mechanisms and Robotics 13, no. 1 (November 16, 2020). http://dx.doi.org/10.1115/1.4048834.
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Abstract In this article, the inverted honeycomb cell, known to exhibit an auxetic behavior, is considered to design two pneumatic linear actuators. The actuators are built using a combination of soft and rigid structures. They present complementary performances in terms of displacement, force, and stiffness. Experimental evaluations are conducted using prototypes produced using multimaterial additive manufacturing to combine soft and rigid materials with freedom of shape. The first actuator is inspired by origami structures. The possibility to obtain large deformations under low pressure is observed. The second actuator is based on a cylindrical auxetic structure based on the inverted honeycomb cell. Smaller deformation is reached but the design favors the off-axis stiffness, so the component can be integrated without any additional mechanical joint for translation. A discussion on the relative performances of these two actuators and their possible uses conclude the paper.