Academic literature on the topic 'Flexure criteria'
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Journal articles on the topic "Flexure criteria"
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Simpson, A. "On flexure-torsion flutter criteria." Aeronautical Journal 103, no. 1028 (October 1999): 457–74. http://dx.doi.org/10.1017/s0001924000064411.
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Abstract The classical criteria of the 1920s for the avoidance of flexure-torsion flutter were based on parameters such as stiffness ratio and the position across the typical chord of the aerodynamic, elastic and mass centres. In more recent times, and in the context of aeroelastic tailoring of lifting surfaces constructed with composite materials, a new terminology has emerged — as evident from technical papers produced in the USA over the past decade. The prevention of flexure-torsion flutter, or the raising of the critical speed, is now achieved by providing more wash-in or less wash-out , where these terms do not have their established aeronautical meanings — and for this reason (and other, non-semantic ones) are to be deprecated. By recourse to a typical section model (with quasi-steady and unsteady compressible aerodynamics), the writer argues that, for conventionally constructed wings, the new criteria are ‘fuzzy’ and incomplete versions of the earlier criteria in respect of the positioning of the various ‘centres’ (i.e., elastic, mass and aerodynamic) across the typical chord, and therefore that the new terminology is redundant in this context. For laminated composite wing structures, even when the construction is uniform and the fiexural axis straight, it is established that the inclination of this axis with respect to the CG and aerodynamic axes may be so large that the fiexural and shear centres at the tip could be several chords forward or aft of the mid-chord axis; the criteria of the 1920s are then irrelevant. The wash-in/wash-out criteria may then be said to ‘come into their own’, albeit that it is shown herein that they remain fuzzy and incomplete — even for quasisteady binary problems. A crude modal binary model of a rudimentary laminated composite wing is included to illustrate this and other features. By recourse to a higher-order flutter formulation, the writer demonstrates that the wash-in/wash-out criteria are, in certain respects, unreliable.
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KIRCHNER, H. P., and J. C. CONWAY. "Criteria for Crack Branching in Cylindrical Rods: II, Flexure." Journal of the American Ceramic Society 70, no. 6 (June 1987): 419–25. http://dx.doi.org/10.1111/j.1151-2916.1987.tb05662.x.
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Grammatikou, Sofia, Dionysis Biskinis, and Michael N. Fardis. "Ultimate Strain Criteria for RC Members in Monotonic or Cyclic Flexure." Journal of Structural Engineering 142, no. 9 (September 2016): 04016046. http://dx.doi.org/10.1061/(asce)st.1943-541x.0001501.
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Nowakowski, Michał, Piotr Małczak, Magdalena Mizera, Mateusz Rubinkiewicz, Anna Lasek, Mateusz Wierdak, Piotr Major, Andrzej Budzyński, and Michał Pędziwiatr. "The Safety of Selective Use of Splenic Flexure Mobilization in Sigmoid and Rectal Resections—Systematic Review and Meta-Analysis." Journal of Clinical Medicine 7, no. 11 (October 27, 2018): 392. http://dx.doi.org/10.3390/jcm7110392.
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Background: According to traditional textbooks on surgery, splenic flexure mobilization is suggested as a mandatory part of open rectal resection. However, its use in minimally invasive access seems to be limited. This stage of the procedure is considered difficult in the laparoscopic approach. The aim of this study was to systematically review literature on flexure mobilization and perform meta-analysis. Methods: A systematic review of the literature was performed using the Medline, Embase and Scopus databases to identify all eligible studies that compared patients undergoing rectal or sigmoid resection with or without splenic flexure mobilization. Inclusion criteria: (1) comparison of groups of patients with and without mobilization and (2) reports on overall morbidity, anastomotic leakage, operative time, length of specimen, number of harvested lymph nodes, or length of hospital stay. The outcomes of interest were: operative time, conversion rate, number of lymph nodes harvested, overall morbidity, mortality, leakage rate, reoperation rate, and length of stay. Results: Initial search yielded 2282 studies. In the end, we included 10 studies in the meta-analysis. Splenic flexure is associated with longer operative time (95% confidence interval (CI) 23.61–41.25; p < 0.001) and higher rate of anastomotic leakage (risk ratios (RR): 1.02; 95% CI 1.10–3.35; p = 0.02), however the length of hospital stay is shorter by 0.42 days. There were no differences in remaining outcomes. Conclusions: Not mobilizing the splenic flexure results in a significantly shorter operative time and a longer length of stay. Further research is required to establish whether flexure mobilization is required in minimally invasive surgery.
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Bai, J. B., R. A. Shenoi, X. Y. Yun, and J. J. Xiong. "Progressive damage modelling of hybrid RTM-made composite Π-joint under four-point flexure using mixed failure criteria." Composite Structures 159 (January 2017): 327–34. http://dx.doi.org/10.1016/j.compstruct.2016.09.083.
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Molina-Cerrillo, Javier, María San Román, Javier Pozas, Teresa Alonso-Gordoa, Miguel Pozas, Elisa Conde, Marta Rosas, Enrique Grande, María Laura García-Bermejo, and Alfredo Carrato. "BRAF Mutated Colorectal Cancer: New Treatment Approaches." Cancers 12, no. 6 (June 14, 2020): 1571. http://dx.doi.org/10.3390/cancers12061571.
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Colon cancer is one of the most frequently diagnosed malignancies in adults, considering both its incidence and prevalence. Anatomically, the right colon is considered as being from the cecum to the splenic flexure, and the left colon is from the splenic flexure to the rectum. Sidedness is a surrogate of a wide spectrum of colorectal cancer (CRC) biology features (embryology, microbiome, methylation, microsatellite instability (MSI), BRAF, aging, KRAS, consensus molecular subtypes (CMS), etc.), which result in prognostic factors. Different molecular subtypes have been identified, according to genomic and transcriptomic criteria. A subgroup harboring a BRAF mutation has been described, and represents approximately 10% of the patients diagnosed with colon cancer. This subgroup has morphological, clinical, and therapeutic characteristics that differ substantially from patients who do not carry this genetic alteration. Unfortunately, there is no established standard of care for this particular cohort of patients. This manuscript aims to study the biology of this subgroup of colon cancer, to understand the current approach in clinical research.
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Kelly, Trevor. "Nonlinear analysis of reinforced concrete shear wall structures." Bulletin of the New Zealand Society for Earthquake Engineering 37, no. 4 (December 31, 2004): 156–80. http://dx.doi.org/10.5459/bnzsee.37.4.156-180.
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Although shear walls are a widely used system for providing lateral load resistance, nonlinear analysis procedures for this type of element are much less well developed than those for frame and truss elements. Equivalent flexural models do not include shear deformation and are only suited for symmetric, straight walls. This paper describes the development of an analysis model which includes nonlinear effects for both shear and flexure. The formulation is based on a "macro" modelling approach which is suitable for complete building models in a design office environment.
An analysis methodology is developed using engineering mechanics and experimental results and implemented in an existing nonlinear analysis computer program. A model is developed and validated against test results of solid walls and walls with openings. This shows that the model can capture the general characteristics of hysteretic response and the maximum strength of the wall. Results can be evaluated using acceptance criteria derived from published guidelines. An example shear wall building is then evaluated using both the nonlinear static and the nonlinear dynamic procedures. The procedure is shown to be a practical method for implementing performance based design procedures for shear wall buildings.
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Lisowski, Bartłomiej. "Impact of Fiber Metal Laminates - Literature Research." Mechanics and Mechanical Engineering 22, no. 4 (September 2, 2020): 1355–70. http://dx.doi.org/10.2478/mme-2018-0106.
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AbstractThe paper refers the general idea of composite materials especially Fiber Metal Laminates (FMLs) with respect to low-velocity impact incidents. This phenomenon was characterized by basic parameters and energy dissipation mechanisms. Further considerations are matched with analytical procedures with reference to linearized spring-mass models, impact characteristics divided into energy correlations (global flexure, delamination, tensile fracture and petaling absorbed energies) and set of motion second order differential equations. Experimental tests were based on analytical solutions for different types of FML - GLARE type plates and were held in accordance to ASTM standards. The structure model reveals plenty of dependences related to strain rate effect, deflection represented by the correlations among plate and intender deformation, separate flexure characteristics for aluminium and composite, contact definition based on intender end-radius shape stress analysis supported by FSDT, von Karman strains as well as CLT. Failure criteria were conformed to layers specifications with respect to von Misses stress-strain criterion for aluminium matched with Tsai-Hill or Puck criterion for unidirectional laminate. At the final stage numerical simulation were made in FEM programs such as ABAQUS and ANSYS. Future prospects were based on the experiments held over 3D-fiberglass (3DFG) FMLs with magnesium alloy layers which covers more favorable mechanical properties than FMLs.
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Schmieder, Annett, Thorsten Heinze, and Markus Michael. " Failure Analysis of High-Strength Fiber Ropes." Materials Science Forum 825-826 (July 2015): 891–98. http://dx.doi.org/10.4028/www.scientific.net/msf.825-826.891.
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Until the present days, in discontinuous conveyor systems, e.g. cranes and elevators, steel wire ropes and steel chains are the exclusively used tension members. Nevertheless, these tension members are exhibiting essential disadvantages, e.g. high dead weight, low bending flexure and high susceptibility to corrosion. For fulfilling the steadily increasing requirements especially in running ropes, alternative tension members have to be developed and approved concerning their series-production readiness by utilization of new technologies and new materials. High-strength fiber ropes are demonstrating promising mechanical properties, regarding tensile strength, vibration behavior and bending fatigue life. Still, the application of such high-strength fiber ropes is limited, due to unavailable systematic investigations and insufficient guidelines for dimensioning and processes for determination of discard criteria. With the help of new technologies and procedures, e.g. multi-zone cyclic bend-over-sheave (CBOS) test machinery and computer-assisted tomography, new knowledge concerning the wear behavior of fiber ropes is to be gained and new discard criteria are to be developed.
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Joseph, Thomas K., K. Renji, and Kartik Venkatraman. "On the Region for the Application of Passive Damping Treatment and Loss Factor Enhancement." International Journal of Acoustics and Vibration 24, no. 4 (December 31, 2019): 693–700. http://dx.doi.org/10.20855/ijav.2019.24.41432.
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The loss factor of a structure is significantly improved by using constrained damping treatment. For a mass efficient design, the damping material is to be applied at suitable locations. The studies reported in literature use the modal strain energy distribution in the viscoelastic material or the strain energy distribution in the base structure as tools to arrive at these suitable locations for the damping treatment. It is shown here that the regions identified through the above criteria need not be suitable for certain bending modes of vibration. A new approach is proposed in which the strain in the viscoelastic material and the angle of flexure are shown to be more reliable in arriving at the locations for the damping treatment. Providing damping layers at identified locations using these parameters results in significant loss factors with minimal added mass.
Dissertations / Theses on the topic "Flexure criteria"
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Ferrell, Devin Bradley. "Development of Criteria for Lamina Emergent Mechanism Flexures with Specific Application to Metals." Diss., CLICK HERE for online access, 2010. http://contentdm.lib.byu.edu/ETD/image/etd3549.pdf.
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Erguner, Kamil. "Analytical Examination Of Performance Limits For Shear Critical Reinforced Concrete Columns." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12611220/index.pdf.
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Most of the older reinforced concrete (RC) buildings have columns that are deficient
when the current code requirements are considered. Therefore, performance of the columns
determines the performance of the structure under the effects of earthquake induced lateral
loads. It is recognized that no provision is proposed in TEC2007 to estimate the failure type
called flexure-shear. Behavior of columns having probability of failing in flexure-shear
failure mode is mostly underestimated by TEC2007 procedures. In addition, failure type
classification of columns performed according to the linear and nonlinear procedures of
TEC2007 needs to be examined with respect to the test results to cover all failure types
including flexure-shear failure in order to lead the engineers develop economical and
realistic retrofit solutions.
In this study, different methods are explored to obtain reliable estimates for the
performance of code deficient shear critical RC columns. Special considerations are given to
Axial-Shear-Flexure interaction (ASFI) approach due to its mechanical background.
After examination of different approaches, ASFI method with proposed
modifications was selected as the most reliable model and lateral load-displacement analyses
were performed on a database of shear critical columns. Findings were compared with the
estimations of the nonlinear procedure given in Turkish Earthquake Code (TEC2007) for
database columns. In addition, drift capacity equations and simplified safe drift capacity
equations are proposed in light of statistical studies on the selected column specimens.
In the last part of the study, performance evaluation of columns according to
nonlinear procedures of FEMA 356, TEC2007, ASCE/SEI 41 update supplement, and
EUROCODE 8 were conducted.
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Zhang, Xuesong, and n/a. "Punching Shear Failure Analysis of Reinforced Concrete Flat Plates Using Simplified Ust Failure Criterion." Griffith University. School of Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20051104.153239.
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Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.
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Souza, Gilberto Pereira de. "Avaliação de critérios de falhas de compósitos poliméricos reforçados aplicados a vigas sob carregamento de flexão." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-10042017-130608/.
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Este trabalho apresenta um estudo de aplicabilidade de diferentes critérios de falhas para materiais compósitos poliméricos reforçados, especificamente laminados compostos de fibras unidirecionais, submetidos a carregamento de flexão. Consiste inicialmente de um levantamento bibliográfico para descrever os principais mecanismos de falhas e como estes podem ser analisados. É realizada uma avaliação dos principais critérios de falhas existentes, em estudos de casos de vigas do material submetidas a esforços de flexão três pontos. Para tal avaliação utilizou-se o método dos elementos finitos, devido à complexidade da análise de tensões em compósitos poliméricos reforçados. Posteriormente foram implementadas rotinas computacionais para o cálculo de alguns dos critérios de falhas encontrados na literatura. Assim, analisou-se as potencialidades e limitações desses critérios nos estudos de caso abordados.This work presents a study about the applicability of different failure criteria for laminated reinforced composite materials made of unidirectional fibers, under flexural loads. First, it is described the failure mechanisms of this material, and how this can be evaluated. Some of the most important failure criteria are tested for beams under flexural loads. Because of the complexity of composite stress analysis, it was used the Finite Element Method. After that, some computational routines were implemented to calculate the failure criteria. The advantages and limitations of these theories could be verified for the flexural case studies.
Books on the topic "Flexure criteria"
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Keshav, Satish, and Alexandra Kent. Inflammatory bowel disease. Edited by Patrick Davey and David Sprigings. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780199568741.003.0203.
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Inflammatory bowel disease (IBD) encompasses ulcerative colitis (UC) and Crohn’s disease (CD). Both conditions cause chronic relapsing inflammation in the gastrointestinal (GI) tract, but have different characteristics. UC causes diffuse mucosal inflammation limited to the colon, extending proximally from the anal verge, with the rectum involved in 95% of patients. UC is described in terms of the disease extent: proctitis (confined to the rectum), proctosigmoiditis (disease confined to the recto-sigmoid colon), distal disease (distal to the splenic flexure), and pan-colitis (the entire large intestine). The extent of disease can change, with proximal extension seen in approximately a third of patients with proctitis, although there is great variation between studies. CD causes inflammation that can affect the entire thickness of the wall of the intestine, and is not confined to the mucosa. CD can affect any part of the GI tract. The terminal ileum is affected in approximately 80% of cases, the colon in approximately 60% of cases, and the rectum and perianal region in approximately 40% of cases. CD is classified by location (ileal, colonic, ileocolonic, upper GI tract), by the presence of stricturing or penetrating disease, and by the age of onset (before or after the age of 40). Penetrating disease refers to the development of fistulae, which can lead to complications such as abscesses or perforations. An earlier age at onset is associated with more complicated disease. The diagnosis of UC or CD is established through a combination of clinical, endoscopic, radiological, and histological criteria rather than by any single modality. Occasionally, it is not possible to establish an unequivocal diagnosis of CD or UC in IBD, and a third category, accounting for nearly 10% of cases, is used, termed IBD unclassified.
Book chapters on the topic "Flexure criteria"
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Bochkarev, Andrey V., Vladimir I. Erofeev, and Alexander I. Zemlyanukhin. "Modulation Instability of Flexural Waves in Cylindrical Shells: Modified Criterion." In Dynamical Processes in Generalized Continua and Structures, 119–32. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-11665-1_6.
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Kerstein, DMD, Robert B. "Employing the T-Scan/BioEMG III Synchronized Technologies to Diagnose and Treat Chronic Occluso-Muscle Disorder." In Advances in Medical Technologies and Clinical Practice, 362–514. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-5225-9254-9.ch007.
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This chapter discusses chronic occluso-muscle disorder, which is a myogenous subset of temporomandibular disorder (TMD) symptoms resultant from occlusally activated muscle hyperactivity. It also describes the computer-guided occluso-muscle disorder treatment known as disclusion time reduction (DTR), that studies repeatedly show reduces many common muscular temporomandibular disorder symptoms. T-Scan-based research since 1991 has determined that a significant etiologic component of occluso-muscle disorder is prolonged (in time) occlusal surface friction shared between opposing posterior teeth during mandibular excursions, that occurs in both normal chewing function and during parafunction. This friction results in prolonged compressions of the periodontal ligament (PDL) fibers of the involved teeth, which when in excursive opposing occlusal contact, also experience pulpal flexure that leads to pulpal neural activation, which together with the periodontal ligament compressions, trigger excess muscle contractions within the masticatory muscles. It is this unique neuroanatomy that incites and perpetuates many chronic muscular TMD symptomatology, that can be readily resolved in patients that meet the diagnostic criteria for DTR candidacy, using the ICAGD coronoplasty that is performed in the maximum intercuspal position (MIP), without employing treatment splints, deprogrammers, appliances, orthotics, or mandibular repositioning. Additionally, this chapter will highlight the newest disclusion time reduction therapy (DTR) studies that support the clinical implementation of this highly effective measured occlusal treatment for occluso-muscle disorder.
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Mohamed, Ashraf Ragab. "Reliability-Based Criteria for the Decision of the Compensation of Corroded Flexural Reinforcement." In Advances in Computer and Electrical Engineering, 364–80. IGI Global, 2016. http://dx.doi.org/10.4018/978-1-4666-9479-8.ch014.
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Corrosion of reinforcement is considered as the major cause of most deteriorated concrete structures. As reinforcement corrodes, the load carrying capacity is affected and hence, the probability of failure increases. At the time of inspection of deteriorated structures, engineers are faced with the problem whether the available steel is enough to secure the safety of the structural member. This chapter addresses this problem based on reliability-based approach to evaluate the safety of the deteriorated members due to uniform corrosion under bending. A methodology is proposed to facilitate the determination of the member reliability index based on basic material properties and current loading. A step-by-step procedure is proposed based on charts developed in this study according to the Egyptian code provisions.
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Mohamed, Ashraf Ragab. "Reliability-Based Criteria for the Decision of the Compensation of Corroded Flexural Reinforcement." In Civil and Environmental Engineering, 1336–51. IGI Global, 2016. http://dx.doi.org/10.4018/978-1-4666-9619-8.ch060.
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Corrosion of reinforcement is considered as the major cause of most deteriorated concrete structures. As reinforcement corrodes, the load carrying capacity is affected and hence, the probability of failure increases. At the time of inspection of deteriorated structures, engineers are faced with the problem whether the available steel is enough to secure the safety of the structural member. This chapter addresses this problem based on reliability-based approach to evaluate the safety of the deteriorated members due to uniform corrosion under bending. A methodology is proposed to facilitate the determination of the member reliability index based on basic material properties and current loading. A step-by-step procedure is proposed based on charts developed in this study according to the Egyptian code provisions.
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Majid, D. L., Nor Hafizah Manan, and Yee Ling Chok. "Honeycomb Composite Structures of Aluminum: Aerospace Applications." In Encyclopedia of Aluminum and Its Alloys. Boca Raton: CRC Press, 2019. http://dx.doi.org/10.1201/9781351045636-140000279.
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A honeycomb composite structure is usually composed of a lightweight hexagonal core sandwiched between two thin face sheets that are adhesively joined. Both the core and the face sheets can be combinations of many types of materials depending on the application. In this article, an overview of the design and manufacturing process of aluminum honeycomb composite structures particularly for aerospace application is presented. Aluminum honeycomb composite structures are lightweight constructions with high specific strength and stiffness that are applied mainly in the aerospace industry. An aluminum honeycomb panel is typically made up of the secondary structural components and interiors of an aircraft such as the wing skin, trailing edge, control surface, flooring, partitions, aircraft galleys, and overhead bins, to name a few. Other applications are in the spacecraft, helicopter, missile, and satellite. Owing to its honeycomb design peculiar to the hexagonal beehives, it can reach more than 30 times higher in stiffness and 10 times higher in flexural strength compared to its solid counterpart of the same weight. The mechanical properties of the honeycomb composite structure hinge on the materials of the core and face sheets, the core geometries, and the thickness of the face sheets. Designed for superior flexural and shear loading, the selection of the optimal honeycomb design will depend on the application requirements. The principal design criterion of a sandwich structure in aerospace applications is weight saving, and there is a trade-off between performance and cost. In terms of manufacturing of the honeycomb composite sandwich structure, the two main processes are the expansion process commonly used for low-density cores and the corrugation process for higher density cores.
Conference papers on the topic "Flexure criteria"
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Naves, M., D. M. Brouwer, and R. G. K. M. Aarts. "Multibody-Based Topology Synthesis Method for Large Stroke Flexure Hinges." In ASME 2016 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/detc2016-59287.
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Large stroke flexure mechanisms inherently lose stiffness in supporting directions when deflected due to load components in compliant bending and torsion directions. To maximize performance over the entire range of motion, a topology optimization suited for large stroke mechanisms is required. In this paper a new multibody-based topology synthesis method is presented for optimizing large stroke flexure hinges. This topology synthesis consists of a layout variation strategy based on a building block approach combined with a shape optimization to obtain the optimal design tuned for a specific application. A derivative free shape optimization method is used to optimize high complexity flexure mechanisms in a broad solution space. To obtain the optimal layout, three predefined “building blocks” are proposed which are consecutively combined to find the best layout with respect to a specific design criteria. More specifically, this new method is used to optimize a flexure hinge aimed at maximizing the first disturbing eigenfrequency. The optimized topology shows an increase in frequency of a factor ten with respect to the customary three flexure cross hinge, which represents a huge improvement in performance. The numerically predicted natural frequencies and mode shapes have been verified experimentally.
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Mirnajafi, Ali, Leigh McClure, Jeremy Raymer, and Michael S. Sacks. "Flexural Rigidity of the Commissure Region of the Aortic Valve Leaflet." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43141.
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Flexure is a major deformation mode of the aortic valve (AV) leaflet during valve function [1]. The structure of the AV must thus allow for low flexural rigidity yet also be of sufficient strength to support large tensile loads during valve closure. It well known that the AV is a heterogeneous structure uniquely adapted to provide efficient valve function. Yet, unlike the trilayered central leaflet region, the commissural region commissural region of the AV leaflet (Fig. 1) is composed of only a single layer of collagen fibers. The effect of this structural difference in the AV leaflets flexural rigidity and hence its function is unknown. Also, knowledge of the flexural rigidity of the AV leaflets can be used as design criteria in fabricating bioprosthetic and tissue engineered heart valve considering the fact that the commissural region is known to be a major site for porcine bioprosthetic failure [2]. Yet, to our knowledge the mechanical properties of the AV leaflet in the commissural area have never been measured, due to its small size (3–5 mm).
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Garcia, Ephrahim, Yoonsu Nam, and Nicolae Lobontiu. "Architectures for Integration of Cellular Microscale Actuator Arrays." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-43050.
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The paper proposes the design of several amplification microelectromechanical devices formed of many identical micro-units that are connected in a serial-parallel configuration, each being individually actuated and amplifying its own input motion. The micro-devices realize the border-crossing from the micro- to the meso-scale displacement domain as they combine the micron-level individual inputs into millimeter-range output levels. The base structural unit is a flexure-based compliant device that is capable of transforming the input from a thermoactuator into an amplified displacement, about a direction perpendicular to the input one. The base unit is designed based on performance criteria such as displacement amplification, input stiffness and output stiffness by utilizing finite element simulation and an algorithm based on closed-form compliance equations of the incorporated flexure hinges. The microelectromechanical amplification device is monitored by means of embedded capacitive displacement sensors, for both the input and output ports. This preliminary analysis will be further utilized to produce and analyze several micro-scale amplification devices.
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Steinthorsson, Asthor T., Milton E. Aguirre, Gerard Dunning, and Just L. Herder. "Review, Categorization and Comparison of 1 DOF Static Balancers." In ASME 2015 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/detc2015-47217.
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A static balancer is a mechanism used to force compensate mechanical systems and has been used in applications such as improving haptic feedback in surgical instruments and lowering motor loads in robotic systems. Currently no complete overview exists of all SB methods, this paper can be seen as an extension to earlier work by introducing more static balancing categories and methods. The goal is to have a comprehensive overview of state-of-the-art to aid designers in selecting the appropriate static balancer technology for mechanical systems. Existing designs are categorized based on the energy storage mechanism, e.g. elastic energy storage mechanisms. Critical design parameters are extracted from published literature to form the basis of comparison of the different categories. A performance criterium is defined to illustrate balancing capabilities as a function of system size. The three comparison parameters are: CompensatedForceVolume,SBStrokeVolume,EnergyVolume The comparison results show that compliant flexure balancers are the best selection for balancing systems while keeping minimal size. Theoretical calculations show that there is still ample room to improve current balancers with regard to the chosen balancer criteria.
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Parmar, G., D. B. Hiemstra, Y. Chen, and S. Awtar. "A Moving Magnet Actuator for Large Range Nanopositioning." In ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control. ASMEDC, 2011. http://dx.doi.org/10.1115/dscc2011-6153.
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In this paper, we present the design, fabrication, and testing of a moving magnet actuator (MMA) for large range (∼10mm) nanopositioning. MMAs are direct-drive, single-phase electromagnetic linear actuators that provide frictionless and backlash-free motion. These qualities, along with an adequate motion range, make MMAs promising candidates for large range nanopositioning. In this work, we identify actuator- and system-level performance criteria and associated design tradeoffs, and use this knowledge to systematically and concurrently design an MMA and a double parallelogram flexure bearing. The resulting actuator provides a force output per unit square root power of 4.56N/W, better than 9% force uniformity with respect to stroke, and a low moving mass of 106g. An integrated thermal management system is also incorporated as part of the actuator in order to mitigate the heat dissipated from the MMA coils. The overall single-axis motion system was fabricated and tested to demonstrate a 36Hz open-loop bandwidth and less than 4nm (RMS) steady-state positioning noise over a 10mm motion range. Preliminary closed-loop design and testing highlight the potential of the proposed actuator in nanopositioning.
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Lin, Chen-Chi, and Clayton D. Mote. "The Criteria Predicting Wrinkling of Thin, Flat, Rectangular Webs." In ASME 1995 Design Engineering Technical Conferences collocated with the ASME 1995 15th International Computers in Engineering Conference and the ASME 1995 9th Annual Engineering Database Symposium. American Society of Mechanical Engineers, 1995. http://dx.doi.org/10.1115/detc1995-0148.
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Abstract A web is termed wrinkled when one of the in-plane principal stresses is tensile and the other is sufficiently compressive. A criterion is derived that predicts wrinkling of isotropic, compressible rectangular webs under uniform in-plane principal stresses. The compressive stress at impending wrinkling depends on the flexural stiffness, and it equals zero in the case of a membrane. A criterion of wrinkling is also derived using isotropic, incompressible membrane theory. This criterion predicts an infinite number of wrinkle waves in a wrinkled region. With small flexural stiffness, the number of wrinkle waves becomes finite at wrinkling and it is predictable along with the shape and the size of the wrinkled region. The number of the wrinkle waves increases as the aspect ratio of the rectangular web increases, as the in-plane principal tension increases, and as the flexural stiffness decreases. Analyses of wrinkling of a rectangular web under simple shear and uniform longitudinal stretching illustrate the above predictions.
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Gandhi, Prasanna, Vaibhav Soni, Kaustubh Sonawale, and Naved Patanwala. "Assembly Guidelines for High Performance Meso-Flexure Linkage Mechanisms." In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-64594.
Full textAbstract:
Flexure mechanism systems with ultra-high precision motion are increasingly being used for several applications including micro-measurement, micro/nano manipulation, microfabrication, data reading, writing on CD, and so on. Flexure linkages offer inherent advantages of being frictionless, highly repeatable, and having great design flexibility. Monolithic fabrication of these mechanisms limits use of multiple materials in the system and becomes expensive especially for three dimensional mechanisms. Alternative method of assembling various components of flexure mechanism is considered in this paper. Assembly guidelines for building flexure mechanisms from separately machined components are arrived at. It is found that if each of the fixed ends of the flexure mechanism is located perfectly using two pins, internal stresses are generated in the linkages and their warping does not allow the desired operation. The proposed guidelines which are based on criterion similar to Grubler’s include a very simple formulation to determine number of location pins to be used in assembly. Further guidelines are laid down to determine locations of these pins. Two flexure mechanisms, one planar and other 3D based on double parallelogram flexure linkage mechanisms are fabricated and assembled using these guidelines and found to be working with repeated assembly and disassembly.
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Lotti, Fabrizio, Andrea Zucchelli, Barbara Reggiani, and Gabriele Vassura. "Evaluating the Flexural Stiffness of Compliant Hinges Made With Close-Wound Helical Springs." In ASME 2006 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2006. http://dx.doi.org/10.1115/detc2006-99042.
Full textAbstract:
Advantages and problems related to the use of compliant hinges in articulated robotic structures are briefly discussed. A novel kind of elastic joint made with close-wound helical springs is then described. It is capable of large angular displacement so that it can be conveniently applied in manipulation devices like the humanoid robot hand developed at the University of Bologna. The results of this application encourage a systematic investigation on the properties of this kind of joints, not previously described in the literature, aiming at mechanical characterization and definition of design criteria. To this purpose, the paper outlines a general investigation programme, where theoretical models, Finite Elements analysis and experiments jointly contribute to the evaluation of the hinge stiffness and to the identification of influential design parameters. Preliminary results related to evaluation of the stiffness about the principal bending axis are then examined and discussed, comparing the results obtained from experiments with those achieved by means of a simplified mathematical model and the correspondent FE analysis. An auxiliary parameter is finally introduced in order to define a general criterion for the design of spring-based hinges subjected to large deflection.
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Qiu, C., J. J. Yu, S. Z. Li, Hai-jun Su, and Y. Z. Zeng. "Synthesis of Actuation Spaces of Multi-Axis Parallel Flexure Mechanisms Based on Screw Theory." In ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/detc2011-48252.
Full textAbstract:
This paper introduces an approach for synthesis of actuation spaces of multi-axis parallel flexure mechanisms. The concept of actuation space, first proposed by J. Hopkins and M. Culpepper, is developed from constraint and freedom space, which are two fundamental concepts in constraint-based method. Within the framework of screw theory, actuation and constraint can be represented mathematically by a wrench, and freedom can be depicted by a twist. A Compliance matrix is provided to set the relationship between constraint wrenches and actuation forces in view that such an important rule as “actuation forces are linear independent of constraint wrenches”. Developed from this design rule, a synthesis criterion of actuation space of flexure systems is promoted to select suitable actuators. As a result, this synthesis criterion enable designers to (i) formulate the actuation space systematically in the format of screws or screw system, (ii) determine actuator placement according to the requirement of minimizing the interference between actuation forces and constraint wrenches. Synthesis procedures and selective examples are discussed in details.
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Blattau, Nathan J., Donald B. Barker, and Craig D. Hillman. "Preventing Ceramic Chip Capacitor Cracking During Printing Wiring Board Bending." In ASME 2003 International Mechanical Engineering Congress and Exposition. ASMEDC, 2003. http://dx.doi.org/10.1115/imece2003-42256.
Full textAbstract:
The purpose of this study is to investigate the possibility of using finite element models of varying complexities to better understand and predict the durability of multi-layer ceramic chip capacitors subjected to printed wiring board flexure. This study covers low voltage capacitors (0805, 1206, 1812, 2220 sizes) constructed from X7R ceramic mounted on FR-4 printed wiring boards. Existing failure data obtained from Kemet’s experiments on 0805 and 1206 capacitors is used to establish and verify the failure criterion, which is based upon the tensile stresses in the capacitor. This failure limit is determined by performing a finite element analysis that adequately represents the experiments performed by Kemet. The failure limit (overstress) is then extended to a family of capacitors to predict their durability with regard to printed wiring board flexure. Guidelines can then be established to aid designers in preventing failures of capacitors due to printed wiring board flexure.