Academic literature on the topic 'Viscoelastic creep law'
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Journal articles on the topic "Viscoelastic creep law"
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Dacol, Vitor, Elsa Caetano, and João R. Correia. "A Combined Exponential-Power-Law Method for Interconversion between Viscoelastic Functions of Polymers and Polymer-Based Materials." Polymers 12, no. 12 (December 16, 2020): 3001. http://dx.doi.org/10.3390/polym12123001.
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Understanding and modeling the viscoelastic behavior of polymers and polymer-based materials for a wide range of quasistatic and high strain rates is of great interest for applications in which they are subjected to mechanical loads over a long time of operation, such as the self-weight or other static loads. The creep compliance and relaxation functions used in the characterization of the mechanical response of linear viscoelastic solids are traditionally determined by conducting two separate experiments—creep tests and relaxation tests. This paper first reviews the steps involved in conducting the interconversion between creep compliance and relaxation modulus in the time domain, illustrating that the relaxation modulus can be obtained from the creep compliance. This enables the determination of the relaxation modulus from the results of creep tests, which can be easily performed in pneumatic equipment or simple compression devices and are less costly than direct relaxation tests. Some existing methods of interconversion between the creep compliance and the relaxation modulus for linear viscoelastic materials are also presented. Then, a new approximate interconversion scheme is introduced using a convenient Laplace transform and an approximated Gamma function to convert the measured creep compliance to the relaxation modulus. To demonstrate the accuracy of the fittings obtained with the method proposed, as well as its ease of implementation and general applicability, different experimental data from the literature are used.
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Sagar, Gautam, Dong Zheng, Anuwat Suwannachit, Maik Brinkmeier, Kristin Fietz, and Carsten Hahn. "On the Development of Creep Laws for Rubber in the Parallel Rheological Framework." Tire Science and Technology 47, no. 1 (March 1, 2019): 2–30. http://dx.doi.org/10.2346/tire.18.470104.
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ABSTRACT It is widely known that filler-reinforced rubber material in tires shows a very complicated material behavior when subjected to cyclic loadings. One of the most interesting effects for rolling tires is the nonlinear rate-dependent behavior, which is implicitly linked to the amplitude dependency of dynamic stiffness (Payne effect) at a given frequency and temperature. This effect, however, cannot be described by a conventional linear viscoelastic constitutive law, e.g., the Prony series model. Several nonlinear viscoelastic material models have been proposed in the last decades. Among others, Lapczyk et al. (Lapczyk, I., Hurtado, J. A., and Govindarajan, S. M., “A Parallel Rheological Framework for Modeling Elastomers and Polymers,” 182nd Technical Meeting of the Rubber Division of the American Chemical Society, Cincinnati, Ohio, October 2012) recently proposed a quite general framework for the class of nonlinear viscoelasticity, called parallel rheological framework (PRF), which is followed by Abaqus. The model has an open option for different types of viscoelastic creep laws. In spite of the very attractive nonlinear rate-dependency, the identification of material parameters becomes a very challenging task, especially when a wide frequency and amplitude range is of interest. This contribution points out that the creep law is numerically sound if it can be degenerated to the linear viscoelastic model at a very small strain amplitude, which also significantly simplifies model calibration. More precisely, the ratio between viscoelastic stress and strain rate has to converge to a certain value, i.e., the viscosity in a linear viscoelastic case. The creep laws implemented in Abaqus are discussed in detail here, with a focus on their fitting capability. The conclusion of the investigation consequently gives us a guideline to develop a new creep law in PRF. Here, one creep law from Abaqus that meets the requirements of our guideline has been selected. A fairly good fit of the model is shown by the comparison of the simulated complex modulus in a wide frequency and amplitude range with experimental results.
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Dai, H. L., and H. Y. Zheng. "Creep Buckling and Post-Buckling Analyses of a Viscoelastic FGM Cylindrical Shell with Initial Deflection Subjected to a Uniform In-Plane Load." Journal of Mechanics 28, no. 2 (May 8, 2012): 391–99. http://dx.doi.org/10.1017/jmech.2012.44.
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AbstractIn this paper, based on the viscoelastic theory, the creep buckling and post-buckling behaviors of a viscoelastic functionally graded material (FGM) cylindrical shell with initial deflection subjected to a uniform in-plane load are investigated. The material properties of the viscoelastic FGM cylindrical shell are assumed to vary through the structural thickness according to a power law distribution of the volume fraction of constituent materials and Poisson's ratio is assumed as a constant. Considering the transverse shear deformation and geometric nonlinearity, the constitutive relation of the viscoelastic FGM cylindrical shell is established. By means of the Newton-Newmark method and the Boltzmann superposition principle, the problem for the creep buckling and post-buckling of the FGM cylindrical shell is solved. The numerical results reveal that the transverse shear deformation, volume fraction and geometric parameters have significant effects on the creep buckling and post-buckling of the viscoelastic FGM cylindrical shell.
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Zou, Yong, Chin Jian Leo, and Henry Wong. "Time Dependent Viscoelastic Behaviour of EPS Geofoam." Applied Mechanics and Materials 330 (June 2013): 1095–99. http://dx.doi.org/10.4028/www.scientific.net/amm.330.1095.
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A series of laboratory tests was carried out to assess the time-dependent creep behaviour of EPS geofoam at room temperature (23°C) and at 40°C. The experimental data were then used to calibrate and to validate mechanical viscoelastic models along with an empirical Power Law model, at these two temperatures. The viscoelastic models examined were the 3-element (Maxwell-Kelvin), the 4-element (Burgers) and the Modified 4-element models. The modified 4-element model and the base case, the empirical power law model, were found to give the best predictions. As anticipated, the experimental results show that creep rate is higher at elevated temperatures. The results, at 23°C and 40°C, offer a means to assess and model creep behavior in geotechnical applications at normal, and at a practical elevated, temperature where use of EPS geofoam in warmer climate may be a concern.
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Pereira, Ayrton Alef Castanheira, José Roberto Moraes d'Almeida, and Thiago Motta Linhares Castro. "Evaluation of Short-term Creep Behavior of PE-HD after Aging in Oil Derivatives." Polymers and Polymer Composites 26, no. 3 (March 2018): 243–50. http://dx.doi.org/10.1177/096739111802600304.
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The creep behavior of a high density polyethylene (PE-HD) was evaluated before and after aging in contact with gasoline and diesel oil. Four viscoelastic models were used to assess changes in creep properties of the material: three parameters model, four parameters model, stretched Burgers model and Findley Law. Viscoelastic properties, stationary creep rate and compliance were used to analyze and compare the behavior between samples. A strain increase could be seen in aged samples in comparison with as-received ones, caused by plasticization due to aging effects. An increase in flexibility and decrease in stiffness in aged samples was also noted. This work also shows that the effects of aging on the creep response of a polymeric material can be analyzed using short term creep tests.
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Hagin, Paul N., and Mark D. Zoback. "Viscous deformation of unconsolidated reservoir sands—Part 2: Linear viscoelastic models." GEOPHYSICS 69, no. 3 (May 2004): 742–51. http://dx.doi.org/10.1190/1.1759460.
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Laboratory creep experiments show that dry unconsolidated reservoir sands follow a power law function of time (at constant stress), and cyclic loading tests (at quasi‐static frequencies of 10−6 to 10−2 Hz) show that the bulk modulus increases by a factor of two with increasing frequency while attenuation remains constant. In this paper, we attempt to model these observations using linear viscoelasticity theory by considering several simple phenomenological models. We investigated two classes of models: spring‐dashpot models, which are represented by exponential functions with a single relaxation time, and power law models. Although almost all of the models considered were capable of fitting the creep data with time, they result in very different predictions of attenuation and bulk modulus dispersion. We used the model parameters derived from fitting the creep strain to predict the bulk modulus dispersion and attenuation as a function of frequency, to find a single phenomenological model (and model parameters) that could explain the material's creep response with time as well as its dispersion and attenuation characteristics. Spring‐dashpot models, such as the Burgers and standard linear solid models, produce reasonable fits to the creep strain and bulk modulus dispersion data, but do not reproduce the attenuation data. We find that a combined power law–Maxwell creep model adequately fits all of the data. Extrapolating the power law–Maxwell creep model out to 30 years (to simulate the lifetime of a reservoir) predicts that the static bulk modulus is only 25% of the dynamic modulus. Including the instantaneous component of deformation into the previous prediction results in 2% total vertical strain at the wellbore, in good agreement with field observations.
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Osman, Ekhlas A., and Saad A. Mutasher. "Viscoelastic properties of kenaf reinforced unsaturated polyester composites." International Journal of Computational Materials Science and Engineering 03, no. 01 (March 2014): 1450004. http://dx.doi.org/10.1142/s2047684114500043.
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In order to quantify the effect of temperature on the mechanical and dynamic properties of kenaf fiber unsaturated polyester composites, formulations containing 10 wt.% to 40 wt.% kenaf fiber were produced and tested at two representative temperatures of 30°C and 50°C. Dynamic mechanical analysis was performed, to obtain the strain and creep compliance for kenaf composites at various styrene concentrations. It is possible to obtain creep curves at different temperature levels which can be shifted along the time axis to generate a single curve known as a master curve. This technique is known as the time–temperature superposition principle. Shift factors conformed to a William–Landel–Ferry (WLF) equation. However, more long term creep data was needed in order to further validate the applicability of time-temperature superposition principle (TTSP) to this material. The primary creep strain model was fitted to 60 min creep data. The resulting equation was then extrapolated to 5.5 days; the creep strain model of power-law was successfully used to predict the long-term creep behavior of natural fiber/thermoset composites.
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Alrubaie, Murtada Abass A., Roberto A. Lopez-Anido, Douglas J. Gardner, Mehdi Tajvidi, and Yousoo Han. "Modeling the hygrothermal creep behavior of wood plastic composite (WPC) lumber made from thermally modified wood." Journal of Thermoplastic Composite Materials 33, no. 8 (January 9, 2019): 1109–24. http://dx.doi.org/10.1177/0892705718820404.
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The viscoelastic behavior of an extruded wood plastic composite (WPC) made from thermally modified wood under hygrothermal treatment was studied and modeled. Multiple three-point bending creep/recovery tests were carried out using a dynamic mechanical thermal analyzer (DMTA) equipped with a submersible clamp. WPC specimens with a 15-mm span were subjected to two initial applied stresses; 9% and 14% of the flexural strength in 30 min of creep and 30 min of creep recovery under the combined effects of temperature (25°C, 35°C, and 45°C) and water immersion (saltwater (SW) and distilled water). A dry condition WPC control was used to compare the hygrothermal effects with respect to the control conditions. The WPC material in this article exhibited a linear viscoelastic behavior under the effect of temperature, whereas a nonlinear viscoelastic behavior was observed under immersion conditions. A power law model is considered a useful model to describe the creep behavior of WPC specimens with a 15-mm span in the control and the SW conditions and at 45°C. A power law model was used to describe 180-day creep deflection of WPC lumber beams with an 853-mm span subjected to 12 MPa of the flexural strength in four-point bending at 50% relative humidity and at 21°C. The power law model predicts that the WPC lumber will reach a flexural strain in outer fiber of 1% in approximately 150 years.
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Marklund, Erik, Janis Varna, and Lennart Wallström. "Nonlinear Viscoelasticity and Viscoplasticity of Flax/Polypropylene Composites." Journal of Engineering Materials and Technology 128, no. 4 (June 30, 2006): 527–36. http://dx.doi.org/10.1115/1.2345444.
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In tensile tests the flax/polypropylene composites clearly show nonlinear behavior in loading and hysteresis loops in unloading. In creep tests performed at different load levels the response was nonlinear viscoelastic, and after recovery, viscoplastic strains were detected. No degradation in stiffness could be seen and thus nonlinear viscoelasticity and viscoplasticity were assumed to be the main cause for the observed behavior. The fracture surface of a specimen that experienced creep rupture at 24 MPa was investigated using a scanning electron microscope. The viscoplastic response was studied experimentally and described by a power law with respect to time and stress level in the creep test. The nonlinear viscoelasticity was described using Schapery’s model. The application of Prony series and a power law to approximate the viscoelastic compliance was investigated. Both descriptions have accuracy sufficient for practical applications. However, at high stresses the attempts to describe the viscoelastic compliance by a power law with a stress-independent exponent failed and therefore stress dependence of this exponent was included in the data analysis. The accuracy within the considered stress range is good, but the thermodynamic consistency of this procedure has to be proven.
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Orlet, M. W., and C. E. Bakis. "Viscoelastic Characterization of High Fiber Content Filament Wound Polyurethane Matrix Composites." Rubber Chemistry and Technology 71, no. 5 (November 1, 1998): 1042–58. http://dx.doi.org/10.5254/1.3538509.
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Abstract Elastomeric matrix composites (EMCs) consisting of a polyurethane matrix unidirectionally reinforced with high volume fractions of high strength fibers have interesting and unique mechanical properties such as high strength and stiffness in the fiber direction and high ductility perpendicular to the fibers. The aim of this investigation is to explore the quasi-static mechanical properties of glass and carbon fiber EMCs in the direction transverse to the fibers and to measure and model the creep of the monolithic matrix material and the transverse creep of the glass EMC. In the quasi-static tests, glass and carbon EMCs followed a monotonic stress—strain curve that was essentially flat from approximately 1–2% to over 10% strain. The maximum stresses obtained in the quasi-static tests were approximately 3.5 and 7 MPa in the carbon and glass EMCs, respectively. The monolithic matrix and the glass EMC loaded transversely to the fibers both showed highly nonlinear creep behaviors. The former creep behavior was modeled successfully with a standard power law expression. The nonlinear creep behavior of the glass EMC cannot be modeled with a standard power law expression, possibly due to creep damage.
Dissertations / Theses on the topic "Viscoelastic creep law"
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Bouras, Yanni. "Thermal Stability of Concrete and Concrete-Filled Steel Tubular Arches." Thesis, 2020. https://vuir.vu.edu.au/40990/.
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The stability of arches is a classical mechanics and pragmatic engineering problem
that has been extensively studied by many researchers over the years. Despite the
comprehensive construction and research of arches throughout history, their complex
behaviour still presents a challenge to engineers and ensures they are the subject of
continual investigation. The problem of arch stability is of contemporary relevance
due to the surging popularity of concrete-filled steel tubular (CFST) arch bridges.
Hence, due to the inherent complex structural function of arches when coupled with
the increasing construction of CFST arches, research into the response and stability
of CFST arches under all possible environmental conditions is necessitated. However,
investigations into the effects of extreme temperatures on concrete and CFST arches
have not been conducted.
This thesis presents a comprehensive analytical and numerical investigation into the
stability of circular concrete and CFST arches subjected to combined mechanical and
thermal loading. Original models are derived for the non-linear prebuckling and buckling analysis including closed-form solutions for the in-plane elastic buckling loads of
concrete and CFST arches, and non-discretisation mechanically-based numerical models for their elastic and inelastic analysis prebuckling analysis. Additionally, a numerical
methodology to determine the elastic flexural-torsional buckling loads of CFST arches
is proposed. Furthermore, a novel fractional viscoelastic creep law is developed for
concrete at elevated temperatures in order to analyse the significance of basic creep
strain on thermal response and stability boundaries. The fractional-derivative creep
law proves to be a robust and compact method of modelling basic creep strain under
stress and temperature varying conditions. Finite difference schemes are employed to
numerically approximate the fractional derivative and incorporate basic creep into the prebuckling and stability analyses. Finite Element (FE) models are developed to verify the derived models and to also investigate the inelastic buckling strength and fire
performance of concrete and CFST arches.
The findings of this study provide a detailed understanding of the fundamental thermomechanical behaviour and failure modes of concrete and CFST arches. Consequently,
engineers may utilise the results detailed herein to assess and improve the fire resistance of concrete and CFST arch structures. Additionally, the developed creep law
has widespread application in the analysis of concrete structures under elevated temperatures. The proposed inelastic numerical models also provide efficient tools for the
analysis of other structures such as steel arches and beams.
Book chapters on the topic "Viscoelastic creep law"
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Kamil Hussein, Emad, Batool Mardan Faisal, Kussay Ahmed Subhi, Thiago Santos, Samir Ghouali, M. Asyraf, and Caroliny Santos. "Perspective Chapter: Viscoelastic Mechanical Equivalent Models." In Biomimetics - Bridging the Gap [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.108065.
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Today, we are living in a polymeric era where thousands of daily used products are manufactured from some polymeric materials with different tasks and under a wide range of ambient conditions, including time duration of loading and working condition temperature. This leads to focusing light spot on behavior of such specific materials and investigating the strain associated with the applied stress to understand both of creep and stress relaxation behavior of the loaded polymeric components. Hence, this chapter deals with the estimation of induced strain allied with the applied force on a polymeric material via establishing the so-called mechanical equivalent models starting from the simple elastic element (spring with a modulus of elasticity E), simple viscous element (damper or dashpot with fluid viscosity η), Maxwell model, Voigt model, modified Maxwell model, modified Voigt model, and Maxwell-Voigt model. The theoretical analysis was built on derivation of the prompted deformation, as a function of time in each of the employed models, as a result of the applied external load (force) and then by depending on Hook’s law transforming the gained expressions into stress (σ) and strain (ε) notation, followed by comparing the obtained equation with the general formula of the Hook’s law to find exact values of the constant and as coefficients of the stress and strain. Final theoretical analysis showed that Maxwell’s modified model was the best describing behavior of a loaded polymeric material to some extent followed by the other models.
Conference papers on the topic "Viscoelastic creep law"
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Diany, Mohammed, and Abdel-Hakim Bouzid. "Creep Constitutive Law of Packing Materials Based on Relaxation Tests." In ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57271.
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The tightness of valves, compressors and pumps is ensured by superposed braided rings installed in a system of stuffing-box. The nature of the packings material and structure, which is like a rectangular braided cord, influences the proper stuffing-box assembly behavior. During installation, a minimum compressive load is required to ensure a minimum level of tightness. A fairly large percentage of this axial compression load is transferred to the radial direction to generate the contact pressures at the packing-stem and packing-housing interfaces necessary for sealing. The packing is considered in several studies as a viscoelastic material with its creep-relaxation behavior assumed as one-dimensional rheological model. In the present work, relaxation tests in a test-bunch containing all the components of the packed stuffing-box, are carried out to define a creep constitutive law for packing braids of different materials. Based on three-dimensional compression tests the developed method is applied to three different packing materials.
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Lapczyk, Ireneusz, and Juan A. Hurtado. "A Viscoelastic-Elastoplastic Finite Strain Framework for Modeling Polymers." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36831.
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In this paper we present a new constitutive framework, the Parallel Rheological Framework (PRF), for modeling polymers that has been recently developed by the authors and implemented in the commercial finite element software Abaqus [1]. The framework is based on parallel finite-strain viscoelastic and elastoplastic networks. For each viscoelastic network a multiplicative split of the deformation gradient into elastic and viscous components is assumed. The evolution of the viscous component of the deformation gradient is governed by a flow rule obtained assuming the existence of a creep potential. The flow rule is expressed as a function of stress invariants and internal variables, and different evolution laws for the internal variables are allowed within the framework of the model. Similar to the viscoelastic networks, the deformation gradient in the elastoplastic network is decomposed into elastic and plastic components. The yield surface is defined assuming combined isotropic/kinematic hardening. The yield surface is a function of a scalar internal variable that describes isotropic hardening, and a tensorial internal variable (backstress) that describes the shift of the yield surface in the stress space. The evolution of the scalar variable is governed by associated flow rule, while the evolution of backstresses is determined by the Armstrong-Frederick law [2], which is extended to finite-strain deformations. Finally, stress softening is introduced into an elastoplastic network using a modified version of Ogden and Roxbourgh’s pseudo-elasticity model [3]. This paper presents an outline of the framework, including two recent enhancements: a new creep model (the power law model) and combined isotropic/kinematic hardening plasticity model. The framework is then applied to analyze numerically the uniaxial loading/unloading behaviors of filled natural rubber and an EPDM polymer. The results obtained using finite element simulations show very good correlation with experimental data.
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Shim, Do-Jun, Prabhat Krishnaswamy, Yunior Hioe, and Sureshkumar Kalyanam. "Viscoelastic Finite Element Modeling of Bimodal High Density Polyethylene (HDPE) Piping Materials for Nuclear Safety-Related Applications." In ASME 2010 Pressure Vessels and Piping Division/K-PVP Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/pvp2010-25715.
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The U.S. Nuclear Regulatory Commission (USNRC) has recently approved Relief Requests for the use of high density polyethylene (HDPE) piping in safety-related applications. The ASME Boiler and Pressure Vessel Code, meanwhile, has developed Code Case N-755 that defines the design and service life requirements for PE piping in nuclear plants though it has not as yet been approved by the USNRC. One of the issues of concern is premature failure of PE piping due to slow crack growth (SCG) that can initiate due to a combination of sustained loads, elevated temperatures, and a pre-existing defect. Understanding and predicting the SCG behavior is an essential step in developing a methodology for predicting the service life of PE piping. The first step in studying the failure process in a polymer under a constant sustained load is the selection of a suitable constitutive model to represent the time-dependent behavior of the material. In this paper, uniaxial tensile creep tests were performed for a bimodal HDPE (PE4710) piping material. This creep data was used to determine the viscoelastic material constants for this bimodal HDPE using a power-law creep model. These material constants were used in finite element (FE) analyses to study the viscoelastic behavior of the bimodal HDPE. As a first step, the FE model was verified by comparing the results from numerical simulations and experiments for a set of uniaxial tensile creep tests. The FE model was then applied to study the viscoelastic behavior of a SCG specimen. The time dependent stress and strain fields were investigated.
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Mandal, Partha Pratim, Joel Sarout, Reza Rezaee, and Mofazzal Hossain. "Can We Predict Primary Creep and Least Principal Stress Shmin at Depth Either from Specific Surface Area or Weak Phase of Gas Shales?" In International Petroleum Technology Conference. IPTC, 2022. http://dx.doi.org/10.2523/iptc-22212-ms.
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Abstract Recently short-term laboratory primary creep i.e., time-dependent deformation under triaxial in situ stress condition of ultra-low permeable gas shales have been utilized to work out geomechanical impacts of field development cycle such as modification of in situ stress state, prediction of production induced deformation, and understanding of fracture closure mechanism. However, obtaining creep data from the laboratory method is tedious, time-consuming, and costly. A simple power law model as a function of time involving instantaneous elastic compliance of the studied material B, and time dependent component n is used to describe creep and stress relaxation owing to the superposition principle of linear viscoelastic materials. Gas shales usually have a large specific surface area (SSA) because of the dominance of clay minerals (Illite, Smectite, Kaolinite, and Chlorite) and/or total organic carbon (TOC). Low-pressure nitrogen gas adsorption is a quick and cost-effective method to derive specific surface area value SN2 on powdered gas shale samples. From the observed strong empirical correlation between creep parameters and SN2value as well as with weak phase fraction ClayTocPHI (combination of clay, porosity, and TOC), a novel indirect approach is proposed to predict primary creep constitutive parameters either from the specific surface area (SSA) value SN2 or weak phase fraction ClayTocPHI of multiple gas shales at deeper subsurface formations (Figure 1). These gas shales cover a broad range of mineralogy, maturity, porosity, and depositional history. Through a case study, empirically derived creep parameters from SN2 are utilized to predict the least principal stress Shmin magnitude at depth of a six lithological layered gas shale formation with a viscoelastic stress relaxation approach. Direct field measurement validated the layered variation of the predicted Shmin magnitude.
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Aritan, Serdar, S. Olutunde Oyadiji, and Roger M. Bartlett. "A Mechanical Model Representation of the In Vivo Behaviour of Bulk Tissue." In ASME 7th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2004. http://dx.doi.org/10.1115/esda2004-58601.
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The aim of this study was to characterise the bulk modulus properties of the upper arm under relaxed and controlled contraction which is defined as 25% of the maximum voluntary contraction. A new testing machine was designed to generate constant load on the upper arm and measure the deformation over time. The machine consists of a device which is effectively a cuff that applies controllable pressure on a 47 mm wide band of the upper arm. Six different loads (10, 20, 30, 40, 50 and 60 kgf) were applied over a period of time of up to a maximum of 120 seconds. The deflection-time curves obtained show strongly non-linear response of the bulk tissue. The non-linearity manifested by these deflection-time curves is in terms of both time- and load-dependency. For each load, the creep behaviour follows an exponential law typical of viscoelastic materials. At low loads (below 30kgf), the creep response increases fairly linearly as the load is increased from 10 kgf to 30 kgf. But at high loads (above 30 kgf), the creep response increases only slightly as the load is increased from 30 kgf to 60 kgf. Beyond a load of 60 kgf, the deflection or creep becomes negligible. This implies that the upper arm has reached the state of incompressibility. The creep behaviour of the upper arm was simulated using four Voigt viscoelastic models in series. The three obvious soft tissues of the upper arm, namely skin, fat and muscle, were modelled in series. The effects of blood vessels and connective tissue were also modelled in series with the other tissues.
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Zhao, Ruogang, Kristine Wyss, and Craig A. Simmons. "Comparison of Three Material Models to Predict the Time-Dependent Deformation of a Single Cell Under Micropipette Aspiration." In ASME 2008 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2008. http://dx.doi.org/10.1115/sbc2008-192940.
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Micropipette aspiration is an experimental technique that is used widely to measure the mechanical properties of single cells [1]. The viscoelastic properties of the probed cell are often estimated by fitting experimental data to a three-parameter standard linear solid (SLS) half-space model (e.g., [1]). However, this analytical model does not account for the large strains that can occur with micropipette aspiration. This limitation has motivated the development of numerical methods to interpret the experimental data. For example, Zhou [2] implemented a material model combining a hyperelastic neo-Hookean material and a viscoelastic SLS material in an axisymmetric finite element (FE) model to simulate large strain micropipette aspiration of a suspended cell. The time-dependent creep deformation of cells has also been described by power-law rheology [3]; this material model has been applied to micropipette aspiration of nuclei [4], but not whole cells.
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Roy, Samit, Priyank Upadhyaya, Mohammad H. Haque, and Hongbing Lu. "A Multi-Scale Viscoelastic Cohesive Layer Model for Predicting Delamination in HTPMC." In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36397.
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In this paper, a novel numerical-experimental methodology is outlined to predict delamination in pristine as well as isothermally aged (in air) polymer matrix composites. A rate-dependent viscoelastic cohesive layer model was implemented in an in-house test-bed finite element analysis (FEA) code to simulate the delamination initiation and propagation in unidirectional polymer composites before and after aging. This unified model is fully rate-dependent and does not require a pre-assigned traction-separation law. The actual shape of traction separation law depends on: (a) the strain rate via the viscoelastic constitutive relationship, (b) the degree of thermo-oxidative aging via the changes in the experimentally measured creep compliance due to oxidation, and (c) the evolution of the internal state variable defining the state of damage. To determine the model parameters, double cantilever beam (DCB) experiments were conducted on both pristine and isothermally aged IM-7/bismaleimide (BMI) composite specimens. The J-Integral approach was adapted to extract cohesive stresses near the crack tip. A principal-stretch dependent internal damage state variable defines the damage in the cohesive layer. Within the cohesive layer, pristine and cohesive stresses were compared to estimate the damage parameters. Once the damage parameters had been characterized, the test-bed FEA code employed a micromechanics based viscoelastic cohesive layer model to simulate interlaminar delamination. From a numerical stability standpoint, the viscous regularization effect of the viscoelastic constitutive equations in the cohesive layer helps mitigate numerical instabilities caused by elastic energy released due to crack growth, thereby enabling the FEA model to simulate the load-deflection response of the composite structure well beyond peak load. The present cohesive-layer based FEA model was able to accurately predict not only the macro level load-displacement curve, but also the micro level crack growth history in IM-7/BMI laminate before and after thermal aging, using only three parameters.
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Chotpattananont, Datchanee, and Anuvat Sirivat. "Electrorheological Properties of Suspensions Prepared From Polythiophene Conductive Polymer." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79491.
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Electrorheological (ER) fluids are typically composed of polarizable particles dispersed in a non-conducting fluid. Upon the application of an electric field, chain-like or fibrillar aggregates of the suspended particles are oriented along the direction of the electric field, thereby inducing viscoelasticity and a drastic increase in viscosity. In our study, Poly(3-thiophene acetic acid), PTAA, has been developed for using as ER material. The rheological properties of this PTAA suspension upon the application of electric field were investigated under various deformations; oscillatory shear flow, steady shear, and creep. We found that PTAA based ER fluid exhibited viscoelastic behavior and showed the excellent responses under an applied electric field. Moreover, the ER response of this PTAA fluid was amplified with increases in electric field strength, particle concentration, and particle conductivity. Under the oscillatory shear, the dynamic moduli, G′ and G″, increased dramatically by 10 orders of magnitude, when the field strength was increased to 2 kV/mm. The suspensions exhibited a transition from fluid-like to solid-like behavior as the field strength increased. While under steady shear flow, the yield stress increased with electric field strength, E, and particle volume fraction, φ, according to a scaling law of the form, τy α Eαφγ. Furthermore, the creep curves of this ER fluid consisted of both elastic and viscous responses and this fluid exhibits partially elastic recovery after the removal of applied stress. The creep properties strongly depended on the magnitude of an applied stress.
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Dabiri, Arman, and Edgar Madril. "Isothermal Creep Behavior of 3M™ Scotch-Weld™ EC-2216 B\A in Single Lap Joints." 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/detc2016-60376.
Full textAbstract:
This paper studies the isothermal creep behavior of the 3M™ Scotch-Weld™ EC-2216 B\A Gray (EC-2216) epoxy in single lap joints subjected to a uniaxial tensile load. The time-independent mechanical properties of EC-2216 such as the Young’s modulus, shear modulus, and bulk modulus have been reported in the literature, but the results are not consistent. However, to the best knowledge of the authors its shear stress-strain constitutive equation has not been obtained yet. Thus, in this paper, we propose the shear stress-strain constitutive equation of the EC-2216 in single lap joints subjected to uniaxial tensile tests at room temperature (24±3°C). First, a viscoelastic model is estimated in short-term experiments within the viscoelastic regime. Second, the creep deformation of the EC-2216 is modeled by different conventional imperial models. Third, different conventional creep rate models are used to estimate the steady state creep rate of the third stage, which mainly indicates the longevity of the material. Moreover, the failure accumulate strain is obtained based on the maximum strain criterion, for different shear stress levels. Finally, the proposed models are compared to the current published data.
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Tate, Jitendra S., Ajit D. Kelkar, and Gary Beall. "Viscoelastic Effects on Fatigue Behavior of Braided Composites." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-14091.
Full textAbstract:
Textile composites include woven, braided, and knitted fabrics. Textile composites are considered when out-of-plane properties are also important. Textile composites generally have better dimensional stability, out-of-plane properties, and impact and delamination resistance. The natural conformability of biaxial braids makes them more cost competitive than woven fabric. These material systems are gaining popularity, in particular for the small business jets, where FAA requires take off weights of 5670 kgf or less. The vacuum assisted resin transfer molding (VARTM) process has proven to be low in cost compared to resin transfer molding (RTM). Thus, the combination of biaxial braids and the VARTM process is likely to considerably reduce overall costs. Before the braids can be confidently used in the primary structures, it is necessary to understand the performance of biaxial braided composites under various loading conditions and especially under fatigue. This will reduce uncertainty and hence reduce the factor of safety in the design This research addresses viscoelastic effects on fatigue behavior of carbon/epoxy braided composites. It is observed that braided composites exhibit creep and stress relaxation. Further it is observed that frequency in axial fatigue loading plays dominant role in fatigue life, but very little role in fatigue failure mechanisms. Rate of stiffness degradation is greatly affected by frequency. These entire phenomena such as creep, stress relaxation, frequency effect, and dependency of stiffness on rate of loading indicate the viscoelastic behavior of braided composites. In this research different tests were performed to confirm viscoelastic behavior of braided composites. Axial tension-tension fatigue tests were conducted at different frequencies and stiffness degradation was studied.