Journal articles: 'Stress relaxation model'

1

Guo, Jin Quan, Wu Zhou Meng, Fei Li, and Li Xin Wang. "Creep Prediction From Stress Relaxation Coupled With Equivalent Relaxation Rate." Applied Mechanics and Materials 644-650 (September 2014): 1382–85. http://dx.doi.org/10.4028/www.scientific.net/amm.644-650.1382.

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Several stress relaxation and creep tests of high temperature material are performed. According to the characteristics of stress relaxations and the superposition equation of diffusion and Maxwell equations of two stages, equivalent relaxation time and equivalent relaxation rate are proposed. Considering equivalent relaxation rate as the creep rate under constant stress, the relaxation-creep conversion model is built up and presented. Then the steady-state creep curve and creep rate are calculated. The results show that the numerical results are in good agreement with the experimental data. It indicates that equivalent relaxation rate can be employed for the analysis of steady-state creep rate. The conversion model and method can be used to design the creep strength and predict the life of the component at high temperature.

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Raza, S. M., N. Farooqui, S. B. H. Abidi, S. A. Raza, and S. M. M. R. Naqvi. "Self-consistent stress relaxation model." Physica Status Solidi (a) 100, no. 2 (April 16, 1987): K149—K153. http://dx.doi.org/10.1002/pssa.2211000246.

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Duan, Xiaochang, Hongwei Yuan, Wei Tang, Jingjing He, and Xuefei Guan. "An Engineering Prediction Model for Stress Relaxation of Polymer Composites at Multiple Temperatures." Polymers 14, no. 3 (January 30, 2022): 568. http://dx.doi.org/10.3390/polym14030568.

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This study develops an engineering prediction model for stress relaxation of polymer composites, allowing the prediction of stress relaxation behaviour under a constant strain, over a range of temperatures. The model is based on the basic assumption that in the stress relaxation process the reversible strain is transformed to irreversible strain continuously. A strain-hardening model is proposed to incorporate nonlinear elastic behaviour, and a creep rate model is used to describe the irreversible deformation in the process. By using stress relaxation data at different temperatures, under different strains, the dependence on temperature and initial strain of the model parameters can be established. The effectiveness of the proposed model is verified and validated using three polymer composite materials. The performance of the model is compared with three commonly used stress relaxation models such as the parallel Maxwell and Prony series models. To ease the use of the proposed model in realistic structural problems, a user subroutine is developed, and the stress relaxation of a plate structure example is demonstrated.

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Liu, Q., W. Chen, J. K. Guo, R. F. Li, D. Ke, Y. Wu, W. Tian, and X. Z. Li. "Fractional Stress Relaxation Model of Rock Freeze-Thaw Damage." Advances in Materials Science and Engineering 2021 (February 13, 2021): 1–8. http://dx.doi.org/10.1155/2021/3936968.

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Freeze-thaw cycle is a type of fatigue loading, and rock stress relaxation under freeze-thaw cycles takes into account the influence of the freeze-thaw cycle damage and deterioration. Rock stress relaxation under freeze-thaw cycles is one of the paramount issues in tunnel and slope stability research. To accurately describe the mechanical behaviour of stress relaxation of rocks under freeze-thaw, the software element is constructed based on the theory of fractional calculus to replace the ideal viscous element in the traditional element model. The freeze-thaw damage degradation of viscosity coefficient is considered. A new three-element model is established to better reflect the nonlinear stress relaxation behavior of rocks under freeze-thaw. The freeze-thaw and stress relaxation of rock are simulated by ABAQUS, the relevant model parameters are determined, and the stress relaxation equation of rock under freeze-thaw cycle is obtained based on numerical simulation results. The research shows that the test results are consistent with the calculated results, indicating that the constitutive equation can better describe the stress relaxation characteristics of rocks under freeze-thaw and provide theoretical basis for surrounding rock support in cold region.

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Nonnenmacher, T. F., and W. G. Glöckle. "A fractional model for mechanical stress relaxation." Philosophical Magazine Letters 64, no. 2 (August 1991): 89–93. http://dx.doi.org/10.1080/09500839108214672.

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Guo, Jin Quan, Wei Zhang, and Xiao Hong Sun. "Stress Relaxation Continuum Damage Constitutive Equations for Relaxation Performance Prediction." Advanced Materials Research 455-456 (January 2012): 1434–37. http://dx.doi.org/10.4028/www.scientific.net/amr.455-456.1434.

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Stress relaxation constitutive equations based on Continuum Damage Mechanics, Kachanov-Robatnov creep model, and stress relaxation equation has been developed by analyzing stress relaxation damage mechanisms and considering the relationship that stress relaxation is creep at various stresses. And, the constitutive differential equations were integrated to predict stress relaxation performance by using numerical analysis technique. In order to validate the approach, the predicted results are compared to the experimental results of uni-axial isothermal stress relaxation tests conducted on 1Cr10NiMoW2VNbN steel with the same temperature of creep tests. Good agreement between results of relaxation tests and the predicted results indicates that the developed constitutive models can be used in the relaxation behavior evaluation of high temperature materials.

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Liao, Chuanjun, Hongrong Fang, Hongrui Wang, and Man Man. "Study on characteristics and mathematical models of stress relaxation for metal O-rings." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 231, no. 7 (December 1, 2016): 826–37. http://dx.doi.org/10.1177/1350650116682152.

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The metal O-ring is effectively applied to extreme conditions and long-term uses for several decades, where conventional seals cannot meet the requirements. During the long-time service, the stress relaxation of the metal O-ring has been confirmed to be a potential damage to the sealing performance. By analyzing the sealing mechanism and the problem of the stress relaxation of the metal O-ring, a model has been developed to study its stress relaxation. The model includes the contact model, the stress–strain model, and the dynamic equation of stress relaxation. Based on the classical elastic-plastic model for two contact rough surfaces, the contact model of sealing zone is developed, by which the mechanical and geometric parameters of the sealing zone can be obtained for the initial state after the assembling. In the stress–strain model, the determination of stress and strain in the metal O-ring is performed by means of a simplified closed-form solution. The dynamic equation of stress relaxation using the stress-creep rate equation is developed, and is solved by combination of the contact model and the stress–strain model. The equation can be adopted for stress relaxation analysis of the metal O-ring at any time. After a validation of the model by comparison with experiments, a parametric study is presented. Simulation results corresponding with the mathematical models explain how the stress relaxation characteristic of the metal O-ring is influenced by a number of parameters.

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LI, W. H., G. CHEN, S. H. YEO, and H. DU. "STRESS RELAXATION OF MAGNETORHEOLOGICAL FLUIDS." International Journal of Modern Physics B 16, no. 17n18 (July 20, 2002): 2655–61. http://dx.doi.org/10.1142/s0217979202012803.

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In this paper, the experimental and modeling study and analysis of the stress relaxation characteristics of magnetorheological (MR) fluids under step shear are presented. The experiments are carried out using a rheometer with parallel-plate geometry. The applied strain varies from 0.01% to 100%, covering both the pre-yield and post-yield regimes. The effects of step strain, field strength, and temperature on the stress modulus are addressed. For small step strain ranges, the stress relaxation modulus G(t,γ) is independent of step strain, where MR fluids behave as linear viscoelastic solids. For large step strain ranges, the stress relaxation modulus decreases gradually with increasing step strain. Morever, the stress relaxation modulus G(t,γ) was found to obey time-strain factorability. That is, G(t,γ) can be represented as the product of a linear stress relaxation G(t) and a strain-dependent damping function h(γ). The linear stress relaxation modulus is represented as a three-parameter solid viscoelastic model, and the damping function h(γ) has a sigmoidal form with two parameters. The comparison between the experimental results and the model-predicted values indicates that this model can accurately describe the relaxation behavior of MR fluids under step strains.

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9

Szot, Wiktor. "Stress relaxation in samples made of acrylonitrile butadiene styrene material manufactured by fused deposition modelling." Mechanik 94, no. 12 (December 8, 2021): 46–50. http://dx.doi.org/10.17814/mechanik.2021.12.16.

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Increased interest in fused deposition modeling (FDM) resulting, for example, from its use in the production of utility models determines the undertaking of research on mechanical and rheological properties of materials. Mechanical and rheological properties of models made of materials used in FDM technology depend on technological parameters. In this paper, the effect of 0° and 90° print orientation on stress relaxation was analyzed. Additionally, the usefulness of the rheological model to describe the relaxation curve was evaluated. Stress relaxation tests were performed by tensile testing. The five-parameter Maxwell-Wiechert model was used to describe stress relaxation. The tests showed little effect of print orientation on the rheological parameters of the five-parameter model. The Maxwell-Wiechert model showed a very good approximation to the stress relaxation curves.

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10

Guo, Jin Quan, Li Xin Wang, and Fu Zhen Xuan. "Creep Based Prediction Model of Stress Relaxation Behavior for High Temperature Materials." Advanced Materials Research 139-141 (October 2010): 356–59. http://dx.doi.org/10.4028/www.scientific.net/amr.139-141.356.

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An average creep rate conversion model based on Schlottner-Seeley creep assessment procedure and creep damage equation has been developed by considering the relationship that two stages of stress relaxation are corresponding to the first and the second creep stage respectively and the effect of these two kinds of creep rate on relaxation, and stress relaxation is creep at various stresses. And an incremental calculation prediction methodology of stress relaxation performance was established. The predicted results are compared with the data of stress relaxation tests conducted on bolting steel 1Cr10NiMoW2VNbN used in ultra-supercritical turbines. Validation results indicate that the developed model has led to better consistent results with the measured data and thus can be recommended in stress relaxation behavior prediction of high temperature materials.

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Cai, Tingting, Lei Shi, Yulong Jiang, and Zengchao Feng. "A Core Damage Constitutive Model for the Time-Dependent Creep and Relaxation Behavior of Coal." Energies 15, no. 11 (June 6, 2022): 4174. http://dx.doi.org/10.3390/en15114174.

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The creep and stress relaxation behaviors of coal are common in coal mining. The unified constitutive model is suitable to describe and predict both the creep and relaxation evolution characteristics of rocks. The generalized Kelvin model is the core element for traditional and improved component models to reflect both the nonlinear creep and relaxation. In this paper, an improved core damage model, which could both reflect the creep and stress relaxation in relation to the damage evolution, was established based on a comparison of the traditional and improved component models, and the responding constitutive equations (creep and stress relaxation equation) at constant stress/strain were deduced. Then, the core damage model was validated to the uniaxial compressive multistage creep and stress relaxation test results of coal, showing that the model curves had great accordance with the experimental data. Moreover, the model comparisons on accuracy, parameter meaning, and popularization among the core damage model, hardening-damage model, and the fractional derivative model were further discussed. The results showed that the parameters in the core damage model had clear and brief physical significances. The core damage model was also popularized to depict the time-dependent behaviors of other rocks, showing great accuracy.

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12

Wu, Yunyun, Chunjie Yin, Xianlei Zhang, and Xiaoyu Gu. "Fractional Order Viscoelastic Model for Stress Relaxation of Polyvinyl Chloride Geomembranes." Applied Sciences 13, no. 3 (January 26, 2023): 1582. http://dx.doi.org/10.3390/app13031582.

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Stress relaxation properties have a significant impact on the performance of polyvinyl chloride (PVC) geomembranes (GMBs) at the peripheral joints of the membrane faced rockfill dam (MFRD). This paper presents a fractional order viscoelastic model (FOVM) to measure the relaxation stress as a function of time. Model parameters were obtained by best fit to results from wide-width strip tensile tests conducted at three tensile rates and three initial strains for 48 h. The results of a 90 d stress relaxation test demonstrate the applicability of the model to describe the stress relaxation behavior of PVC GMBs. The tensile rate and initial strain marginally influenced the relaxation modulus rate, while having no effects on the fractional derivative order. Residual stress could account for the difference in relaxation stress between the longitudinal and transverse specimens. Finally, the FOVM could be used for predicting the service cycle under specifying failure stress criteria. Furthermore, it has great potential for applications in predicting the long-term deformation of PVC GMBs at the peripheral joints of MFRD. Furthermore, it has great potential for applications in predicting the long-term deformation of PVC GMBs at the peripheral joints of MFRD.

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Fyhrie, D. P., and J. R. Barone. "Polymer Dynamics as a Mechanistic Model for the Flow-Independent Viscoelasticity of Cartilage." Journal of Biomechanical Engineering 125, no. 5 (October 1, 2003): 578–84. http://dx.doi.org/10.1115/1.1610019.

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The initial, rapid, flow independent, apparent stress relaxation of articular cartilage disks deformed by unconfined compressive displacement is shown to be consistent with the theory of polymer dynamics. A relaxation function for polymers based upon a mechanistic model of molecular interaction (reptation) appropriately approximated early, flow independent relaxation of stress. It is argued that the theory of polymer dynamics, with its reliance on mechanistic models of molecular interaction, is an appropriate technique for application to and the understanding of rapid, flow independent, stress relaxation in cartilage.

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14

Raza, S. M., S. B. H. Abidi, and N. Farooqui. "Proposed model for stress relaxation at low temperatures." Applied Physics Letters 46, no. 1 (January 1985): 34–35. http://dx.doi.org/10.1063/1.95840.

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15

Borja, Ronaldo I. "Generalized Creep and Stress Relaxation Model for Clays." Journal of Geotechnical Engineering 118, no. 11 (November 1992): 1765–86. http://dx.doi.org/10.1061/(asce)0733-9410(1992)118:11(1765).

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16

Tsakiris, N., P. Argyrakis, I. Avramov, C. Bocker, and C. Rüssel. "Crystal growth model with stress development and relaxation." EPL (Europhysics Letters) 89, no. 1 (January 1, 2010): 18004. http://dx.doi.org/10.1209/0295-5075/89/18004.

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Stein, Judith, and Lori C. Prutzman. "Stress relaxation studies of model silicone RTV networks." Journal of Applied Polymer Science 36, no. 3 (July 20, 1988): 511–21. http://dx.doi.org/10.1002/app.1988.070360305.

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18

Lei, Junle, Dingyuan Lei, Shuaiwei Wang, and Zhaochong Liu. "Stress relaxation characteristics of crushed cane tail straw." BioResources 18, no. 1 (November 3, 2022): 143–60. http://dx.doi.org/10.15376/biores.18.1.143-160.

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To gain insight into the mechanical properties of crushed sugarcane tail leaves during stress relaxation, a self-made compression equipment was used in this study. The variation law of different factors on the stress relaxation process of crushed cane tail was explored and a stress relaxation model was established. The three-element and five-element generalized Maxwell models were selected to fit the regression analysis of the stress relaxation curve of the crushed cane tail. The comparison showed that the determination coefficient R2 of the five-element stress relaxation model was higher, and a three-factor and three-level response surface test was designed. Following the quadratic regression polynomial of the stress rapid decay time and the equilibrium elastic modulus, the final optimization results obtained are as follows: The moisture content was 60.8%, the crushing particle size was 45 mm, the feeding amount was 150 g, and the stress rapid decay time was 14.0 s. The equilibrium elastic modulus was 129 kPa.

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Yang, W., T. C. Fung, K. S. Chian, and C. K. Chong. "Viscoelasticity of Esophageal Tissue and Application of a QLV Model." Journal of Biomechanical Engineering 128, no. 6 (May 11, 2006): 909–16. http://dx.doi.org/10.1115/1.2372473.

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The time-dependent mechanical properties of the porcine esophagus were investigated experimentally and theoretically. It was hypothesized that the viscoelasticity was quasilinear, i.e., the time and strain effects were independent. In order to verify the separability of time and strain effects, the stress-relaxation test was conducted at various strains and the data were fitted with the Fung’s quasilinear viscoelastic (QLV) model. By using the material parameters obtained from the stress relaxation test, the cyclic peak stress and hysteresis were predicted. Results showed that the stress relaxed by 20–30% of the peak stress within the first 10s and stabilized at ∼50% at the time of 300s. The relative stress relaxation R2 (i.e., the difference of stress at a particular time to the final equilibrium stress normalized by the total difference of the peak and final stress) was not different significantly for various strains. It was also found that, by using the stress-time data during both the ramp and relaxation phases, the correlation between parameters was substantially reduced. The model could also predict the cyclic peak stress and hysteresis except for the underestimate of valley stress. We conclude that the QLV model could be used as the material characterization of the esophageal tissue.

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Wang, Dan, Kun Wu, Guanlin Li, and Lifeng Wang. "The viscoelastic mechanical property and constitutive models of 3D printed photopolymer." Rapid Prototyping Journal 27, no. 2 (January 13, 2021): 346–54. http://dx.doi.org/10.1108/rpj-07-2020-0163.

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Purpose The purpose of this paper is to study the mechanical property of three-dimensional (3D) Printed photopolymer (Vero Yellow and Tango Black) with different constant strain rate. According to the experimental results, three constitutive models are used to describe the stress-strain and stress-time relation in the tension and stress relaxation process. Design/methodology/approach The Stratasys Objet 260 was used to prepare the four groups of samples with different photopolymers (Vero Yellow and Tango Black). The stress-strain and stress-time relations are obtained by the uniaxial tensile tests and relaxation tests performed at room temperature with different constant strain rates. The generalized Kelvin model (GKM), standard linearized model (SLM) and fractional order model (FOM) are used to describe experimental data by means of the curve-fitting approach. Findings Experimental results show that the tension stress increases faster at a higher strain-rate for tensile tests. Relaxation stress is influenced by the preload strain-rate for relaxation tests. For the theoretical fitting, the error comparison between three constitutive models and experimental data are calculated to demonstrate the high accuracy in describing the stress-strain relationship for tension. For stress relaxation, the error comparison confirms higher accuracy of FOM with the largest error within 3%, while the error of GKM and SLM up to 10%. Originality/value The paper confirms the viscous-elastic mechanical property of 3D printed photopolymer composites (Vero Yellow and Tango Black) for Stratasys PolyJet. As FOM shows high accuracy both in describing stress-strain and stress-time relation for tension and stress relaxation process, it can be directly used as a constitutive model to predict mechanical properties for engineering application.

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Guo, Wenbin, Fan Hu, Xuehong De, Zhibo Hou, Zhipeng Wang, and Xinyang Jiang. "Description of the instantaneous stress drop behavior of a cornstraw-potato residue mixture based on stress relaxation models." BioResources 17, no. 3 (July 26, 2022): 5255–67. http://dx.doi.org/10.15376/biores.17.3.5255-5267.

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Studying the stress relaxation characteristics can provide important process parameters for the granulation and briquetting of biomass materials. In this study, a generalized Maxwell model and fractional model were established to describe and analyze the stress instantaneous drop behavior of a cornstraw-potato residue mixture during the stress relaxation process. Stress relaxation characteristic parameters, e.g., the stress instantaneous drop time, were obtained. Using this information, the influence of the compression speed on the stress instantaneous drop time, stress relaxation time ratio, and other parameters were analyzed. In addition, the regression model of the compression frequency and compression speed was established, which provided a method for determining the appropriate compression frequency of the molding equipment according to the compression speed.

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Krečmer, Norbert, Marek Liška, Josef Chocholoušek, and Peter Vrábel. "Measurement and Calculation of Residual Stress in Axi-Symmetric Glass Sample Using Structural Relaxation Theory." Advanced Materials Research 39-40 (April 2008): 529–34. http://dx.doi.org/10.4028/www.scientific.net/amr.39-40.529.

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Consistent model including structural relaxation is necessary for correct glass stress calculation in numerical computations of glass forming processes. Calculation of glass relaxation phenomena is often done by combining independent empirical formula on stress relaxation (for a simple temperature regime) and independent model of time-temperature dependence on Tool fictive temperature, Tf. Another approach was developed and verified here. Tool-Narayanaswamy and Moynihan/Mazurin relaxation model was adopted. Relaxation was obtained not from empirical model, but from calculated time-temperature dependence of Tool fictive temperature (Tf), dynamic viscosity, heat capacity and coefficient of thermal expansion. Heat conduction in a glass probe of known temperature history, structural relaxation and stress calculation were used in one computation scheme using Matlab. The stress of glass probe was measured using polarized light (Senarmont method). Rather high stress computation accuracy was obtained in comparison to stress experimental results. The applied model approach is being to be extended for application in commercial finite element codes for modeling of glass forming processes.

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Guo, Jin Quan, Xiao Hong Sun, and Hui Chao Shi. "Stress Relaxation Damage Analysis for High Temperature Bolting." Advanced Materials Research 455-456 (January 2012): 1429–33. http://dx.doi.org/10.4028/www.scientific.net/amr.455-456.1429.

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The paper analyzes the stress relaxation damage mechanisms of high temperature (HT) bolts of ultra-supercritical steam turbine units. Based on creep damage mechanisms and relaxation characteristics, the paper proposes a life prediction model, and by which to predict relaxation damage life of HT bolting material 1Cr10NiMoW2VNbN. Validation results indicate that the developed model has led to better consistent results with experimental data and thus can be recommended in relaxation life evaluation of HT materials.

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Dehkordi, Yousef Ghaderi, Ali Pourkamali Anaraki, and Amir Reza Shahani. "Comparative study of the effective parameters on residual stress relaxation in welded aluminum plates under cyclic loading." Mechanics & Industry 21, no. 5 (2020): 505. http://dx.doi.org/10.1051/meca/2020061.

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The prediction of residual stress relaxation is essential to assess the safety of welded components. This paper aims to study the influence of various effective parameters on residual stress relaxation under cyclic loading. In this regard, a 3D finite element modeling is performed to determine the residual stress in welded aluminum plates. The accuracy of this analysis is verified through experiment. To study the plasticity effect on stress relaxation, two plasticity models are implemented: perfect plasticity and combined isotropic-kinematic hardening. Hence, cyclic plasticity characterization of the material is specified by low cycle fatigue tests. It is found that the perfect plasticity leads to greater stress relaxation. In order to propose an accurate model to compute the residual stress relaxation, the Taguchi L18 array with four 3-level factors and one 6-level is employed. Using statistical analysis, the order of factors based on their effect on stress relaxation is determined as mean stress, stress amplitude, initial residual stress, and number of cycles. In addition, the stress relaxation increases with an increase in mean stress and stress amplitude.

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Eden, O. R., A. J. C. Lee, and R. M. Hooper. "Stress relaxation modelling of polymethylmethacrylate bone cement." Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 216, no. 3 (March 1, 2002): 195–99. http://dx.doi.org/10.1243/0954411021536405.

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This paper describes tests that were carried out to model the stress relaxation behaviour of polymethylmethacrylate (PMMA) bone cement. Stress relaxation of bone cement is believed to be a significant factor in the mechanism of load transfer in the femoral stem of a polished, collarless taper-fit replacement hip joints. It is therefore important that this condition and its implications are understood. Stress relaxation was carried out on PMMA samples of varying age in four-point bending configuration. It was shown that the samples stiffened with age and that the amount of stress relaxation reduced as the samples aged. The experimental results of the stress relaxation were accurately modelled on the double exponential of the Maxwell model so that long-term predictions of the stress condition could be made from short-term mechanical tests.

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Ristaniemi, Aapo, Dristi Regmi, Diponkor Mondal, Jari Torniainen, Petri Tanska, Lauri Stenroth, Mikko A. J. Finnilä, Juha Töyräs, and Rami K. Korhonen. "Structure, composition and fibril-reinforced poroviscoelastic properties of bovine knee ligaments and patellar tendon." Journal of The Royal Society Interface 18, no. 174 (January 2021): 20200737. http://dx.doi.org/10.1098/rsif.2020.0737.

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Tissue-level stress-relaxation of ligaments and tendons in the toe region is characterized by fast and long-term relaxations and an increase in relaxation magnitude with strain. Characterizing the compositional and structural origins of these phenomena helps in the understanding of mechanisms of ligament and tendon function and adaptation in health and disease. A three-step tensile stress-relaxation test was conducted on dumbbell-shaped pieces of bovine knee ligaments and patellar tendon (PT) ( n = 10 knees). Their mechanical behaviour was characterized by a fibril-reinforced poroviscoelastic material model, able to describe characteristic times and magnitudes of fast and long-term relaxations. The crimp angle and length of tissues were measured with polarized light microscopy, while biochemical contents were determined by colorimetric biochemical methods. The long-term relaxation time was longer in the anterior cruciate ligament (ACL) and PT compared with collateral ligaments ( p < 0.05). High hydroxyproline content predicted greater magnitude and shorter time of both fast and long-term relaxation. High uronic acid content predicted longer time of long-term relaxation, whereas high crimp angle predicted higher magnitude of long-term relaxation. ACL and PT are better long-term stabilizers than collateral ligaments. The long-term relaxation behaviour is affected or implied by proteoglycans and crimp angle, possibly relating to slow structural reorganization of the tissue.

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Makarov, P. V. "The Model of Dynamic Stress Relaxation of Elastoplastic Materials." Russian Physics Journal 63, no. 11 (March 2021): 1876–84. http://dx.doi.org/10.1007/s11182-021-02245-1.

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Chen, Xiaoshuai, Atsushi Konno, Kazuya Sase, Akito Ema, and Teppei Tsujita. "A Model of Stress Relaxation for Brain Retraction Simulation." Journal of Japan Society of Computer Aided Surgery 20, no. 1 (2018): 22–32. http://dx.doi.org/10.5759/jscas.20.22.

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Ko, Sun-Chien, Sanboh Lee, and Chun-Hway Hsueh. "Viscoelastic stress relaxation in film/substrate systems—Kelvin model." Journal of Applied Physics 93, no. 5 (March 2003): 2453–57. http://dx.doi.org/10.1063/1.1541108.

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Masoori, Mohammad, and Michael L. Greenfield. "Frequency analysis of stress relaxation dynamics in model asphalts." Journal of Chemical Physics 141, no. 12 (September 28, 2014): 124504. http://dx.doi.org/10.1063/1.4895972.

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You, Gexin, Chunyan Wang, Shuqin Mei, Bo Yang, and Xiuwen Zhou. "Model and prediction of stress relaxation of polyurethane fiber." Materials Research Express 5, no. 3 (March 14, 2018): 035308. http://dx.doi.org/10.1088/2053-1591/aab230.

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Bates, Jason H. T., and Baoshun Ma. "A Progressive Rupture Model of Soft Tissue Stress Relaxation." Annals of Biomedical Engineering 41, no. 6 (March 19, 2013): 1129–38. http://dx.doi.org/10.1007/s10439-013-0789-3.

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Bal, Burak. "Numerical Investigation of the Role of Volumetric Transformation Strain on the Relaxation Stress and the Corresponding Hydrogen Interstitial Concentration in Niobium Matrix." Advances in Materials Science and Engineering 2017 (2017): 1–7. http://dx.doi.org/10.1155/2017/2036516.

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The effects of relaxation stress on the hydrogen concentration in Niobium- (Nb-) H media were investigated by iterative numerical modeling approach. To calculate the transformation strain, relaxation stress, and corresponding relaxed hydrogen concentration around an edge dislocation, a new third-order polynomial formulation was utilized in the model. With the aid of this polynomial, hydrogen induced relaxation stress never exceeds the dislocation stress, which indicates that the total stress field never turns to compressive state and diverges the results. The current model calculates the hydrogen concentration not only in the vicinity of an edge dislocation but also far away from the dislocation. Furthermore, the effect of relaxation stress on the interaction energy was also captured in the model. Overall, the current findings shed light on the complicated hydrogen embrittlement mechanisms of metallic materials by demonstrating that hydrogen induced relaxation has a significant effect on the hydrogen atom concentration and the interaction energy between the existing internal stress field and the solute hydrogen atom.

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Schiffmann, Kirsten Ingolf. "Nanoindentation creep and stress relaxation tests of polycarbonate: Analysis of viscoelastic properties by different rheological models." International Journal of Materials Research 97, no. 9 (September 1, 2006): 1199–211. http://dx.doi.org/10.1515/ijmr-2006-0189.

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Abstract Feedback-controlled nanoindentation with a Berkovich diamond tip has been used to perform creep and stress relaxation tests on polycarbonate at room temperature for a wide range of loads (10 – 30000 μN) and indentation depths (30 – 3000 nm). The creep compliance J(t) and relaxation modulus G(t) have been calculated from experimental data as a function of time in the range t = 0.1 – 100 (1000) s. The data are analysed by different rheological models which are compared: (1) the Burgers model, (2) the generalised Maxwell/generalised Kelvin model, and two empirical approaches: (3) a logarithmic model, and (4) a power law model. The Burgers model gives a poor description of the material behaviour since it assumes a steady-state flow of material which is not observed in the experimental time range. The generalised models yield a set of discrete relaxation- and retardation time constants. It is shown that these time constants do not correlate with specific molecular moving processes in the polymer, but are only one of several possible parameterisations of the creep and relaxation curves. Numerical differentiation of G(t) and J(t) shows that polycarbonate has continuous relaxation- and retardation time spectra, respectively, and the dynamic viscosity η(t) of the material increases linearly with time. The behaviour of polycarbonate is best represented by the empirical power law model, which allows optimum fit of creep/relaxation curves, relaxation and retardation time spectra and time-dependent viscosity.

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Stropek, Zbigniew, Zbigniew Stropek, Krzysztof Golacki, and Krzysztof Golacki. "Stress Relaxation of Apples at Different Deformation Velocities and Temperatures." Transactions of the ASABE 62, no. 1 (2019): 115–21. http://dx.doi.org/10.13031/trans.12993.

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ABSTRACT. Stress relaxation tests on apples (‘Beni Shogun’ variety) were performed at different velocities in the range of 0.0002 to 1 m s-1 and at three temperatures (2°C, 10°C, and 20°C). The generalized Maxwell model was used to describe the experimental stress relaxation curves. The two relaxation times of the model decreased with an increase in the deformation velocity. The relaxation times were related to the processes of gas and liquid flows in the intercellular spaces. This research showed the critical velocity associated with the weakness of the apple structure to lie between deformation velocities of 0.0002 and 0.002 m s-1, where a rapid decrease in the two relaxation times occurred. An increase in the peak force response with increasing deformation velocity showed the viscoelastic behavior of apple flesh. The equilibrium modulus describing the material condition after deformation was much larger under the quasi-static loading condition than the impact loading condition at all deformation velocities. The temperature did not seem to affect the Maxwell model parameters and peak force response for all deformation velocities under both loading conditions. Keywords: Apple, Generalized Maxwell model, Impact loading, Quasi-static loading, Stress relaxation, Viscoelasticity.

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Kundera, Czesław, and Jerzy Bochnia. "Investigating the stress relaxation of photopolymer O-ring seal models." Rapid Prototyping Journal 20, no. 6 (October 20, 2014): 533–40. http://dx.doi.org/10.1108/rpj-04-2013-0043.

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Purpose – This paper aims to investigate the suitability of additive manufacturing to produce O-ring seals. Design/methodology/approach – The O-rings were made by the PolyJet-Matrix technology using four different digital materials and then tested for relaxation properties under static and dynamic (sliding) conditions. The approximation of the relaxation curves involved modelling with a Prony series. Findings – The PolyJet-Matrix technology offers new opportunities to model elastomeric elements, with examples being the O-rings produced and tested for their relaxation properties. Describing the behaviour of the particular materials fabricated with this technology by using relaxation functions will extend the knowledge base on digital materials. Research limitations/implications – The four types of photopolymers used in the experiment differed in viscoelastic properties. The analysis of the stress relaxation of the O-ring models was performed at four different step displacements of the loading element. Practical implications – The test results may be useful for the design of O-ring seals made of new elastomeric materials. The relaxation properties of the O-rings made of such materials can be applied to analyse the dynamics of seals, for instance, face seals. Originality/value – The originality of the work lies in the use of digital materials to design and produce elastomeric elements with different relaxation properties, which was confirmed by the test results. This paper presents results of a relaxation analysis for a ring model and the material that the ring is made of. It also discusses how 3D printing and digital materials can be applied in practice.

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Chen, Rui, and B. Stimpson. "Triaxial stress relaxation tests on Saskatchewan potash." Canadian Geotechnical Journal 32, no. 1 (February 1, 1995): 11–21. http://dx.doi.org/10.1139/t95-002.

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Relative to the study of creep, the stress relaxation phenomenon has been overlooked in research on salt rocks, especially with respect to the behavior of salt in deep underground mining environments. In the laboratory tests described in this paper, deformational properties of potash were first studied by performing reverse-loading tests that approximately simulate in situ loading paths during excavation of underground cavities. Potash relaxation properties were then investigated by multiple-stage, repeated relaxation tests along the reverse-loading path. Results show that potash behavior along a reverse-loading path is highly stress rate dependent and is reflected in the dependence of the initial axial deformation modulus, ductile point, and post-yield behavior on the rate at which the deviatoric stress is applied to the specimen. The inserted relaxation phases did not significantly affect the subsequent behavior of the potash, and therefore inserted relaxation tests are useful for investigating time-dependent behavior at various stages of deformation. A linear relationship exists between normalized stress drop and logarithm of time, which might imply that potash has no creep limit. Finally, an attempt was made to extend a uniaxial strain hardening constitutive law postulated by another researcher to include confining pressure, and the experimental data were found to approximately fit the proposed constitutive model. Key words : potash, stress relaxation, triaxial tests, constitutive model.

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Friedrich, Chr. "Mechanical stress relaxation in polymers: fractional integral model versus fractional differential model." Journal of Non-Newtonian Fluid Mechanics 46, no. 2-3 (April 1993): 307–14. http://dx.doi.org/10.1016/0377-0257(93)85052-c.

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Wang, Y.-Q., J.-K. Wu, H.-B. Liu, and S.-T. Xu. "Modeling and numerical analysis of multi-bolt elastic interaction with bolt stress relaxation." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 230, no. 15 (August 8, 2016): 2579–87. http://dx.doi.org/10.1177/0954406215615155.

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Multi-bolt joint distributed around the connecting members are generally adopted to meet the high-performance assembly requirements in aerospace, energy and power industries. However, the initial preload could be low due to non-optimized preload sequence and bolt stress relaxation, especially at elevated temperature. Thus, it is necessary to take elastic interaction and bolt stress relaxation into account before jointing. In this article, a general multi-bolt elastic interaction with bolt stress relaxation is modelled analytically. First, the multi-bolt joint is characterized by ‘spring-node’ model and elastic interaction stiffness. Second, the bolt residual preload can be estimated according to linear superposition of elastic interaction and bolt stress relaxation under the condition of node displacement equilibrium. Further, the influence of preloading sequence and bolt stress relaxation on residual preload distribution was numerically analyzed using a typical circular ring with 8-bolt joint. Two bolts’ preloading sequences were planned, star sequence and counterclockwise sequence, respectively. The bolt creep simulation time was set as 10 h using the power-model at intermediate temperature. From comparison, the predicted results using the developed model were consistent with the FE simulations both with and without bolt stress relaxation.

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Su, Yong Lei, Ai Lun Wang, and Xue Peng Li. "Degradation Characteristics of Combined Rotor for Turbine Considering Stress Relaxation of Rod." Applied Mechanics and Materials 387 (August 2013): 168–73. http://dx.doi.org/10.4028/www.scientific.net/amm.387.168.

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Considering stress relaxation of rod under high temperature, pretightening force of rod changing with time was obtained. A finite element contact model with interface was analyzed and contact stiffness under different loads was concluded. Combining contact stiffness of the microscopic model with the stress analysis result of turbine interface, a calculating method for dynamic characteristic of combined rotor considering contact stiffness was presented, effect of rod relaxation on dynamic characteristic of combined rotor was obtained. The results showed that pretightening force of rod was decreasing due to stress relaxation, degradation of combined rotor that natural frequency drift caused by the stress relaxation of rod.

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Bao, Yidong, Dongmei Wu, Zhiyuan Yan, and Zhijiang Du. "A New Hybrid Viscoelastic Soft Tissue Model based on Meshless Method for Haptic Surgical Simulation." Open Biomedical Engineering Journal 7, no. 1 (November 15, 2013): 116–24. http://dx.doi.org/10.2174/1874120701307010116.

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This paper proposes a hybrid soft tissue model that consists of a multilayer structure and many spheres for surgical simulation system based on meshless. To improve accuracy of the model, tension is added to the three-parameter viscoelastic structure that connects the two spheres. By using haptic device, the three-parameter viscoelastic model (TPM) produces accurate deformationand also has better stress-strain, stress relaxation and creep properties. Stress relaxation and creep formulas have been obtained by mathematical formula derivation. Comparing with the experimental results of the real pig liver which were reported by Evren et al. and Amy et al., the curve lines of stress-strain, stress relaxation and creep of TPM are close to the experimental data of the real liver. Simulated results show that TPM has better real-time, stability and accuracy.

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Ingman, D., and Y. Michlin. "Damage Accumulation During Stress Relaxation of Polymer Films in Bending." Journal of Electronic Packaging 124, no. 3 (July 26, 2002): 260–65. http://dx.doi.org/10.1115/1.1463731.

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A nonlinear viscoelastic damage accumulation model with a physical approach is presented with a view to describing stress relaxation in amorphous and partially crystalline polymers. The deformation is represented as stress-aided transition through a series of symmetrical energy barriers. There is also a stress threshold, introduced by the authors and representing an asymptotic residual stress below which relaxation does not occur. The model comprises three parameters: an activation volume, V; a product of several parameters with physical meaning, A (only the combination of A and V in the form of the relaxation time constant can be reconstructed from the present set of experiments); and the relaxation threshold. It allows a practically unlimited number of energy barriers. The damage depends on the stress history. Experimental data were collected on stress relaxation of three polymers at different temperatures. The experiments involved bending of a polymer strip within a metal cylinder and measurement of the radius of curvature after removal of the strip from the cylinder, using a specially-developed method. The measured radii ranged from infinity to 1.5 cm, and the obtained data were fitted to the model. The results show that the residual stress and other model parameters are temperature-dependent.

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Davis, T., J. Ding, W. Sun, and S. B. Leen. "Computational simulation of the relaxation of local stresses due to foreign object damage under cyclic loading." Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 224, no. 2 (April 1, 2010): 41–50. http://dx.doi.org/10.1243/14644207jmda286.

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In this study, the phenomenon of residual stress relaxation from foreign object damage (FOD) is numerically simulated using a hybrid explicit—implicit finite-element method. The effects of cycle fatigue loadings on stress relaxation were studied. FOD is first simulated by firing a 3mm cube impacting onto a plate made of titanium alloy Ti-6Al-4V at 200m/s. The FOD impact produces two distinct stress concentrations: one is compressive directly beneath the impact site; the other is tensile around the outer edge of the impact. The plate was then assumed to be subjected to a cyclic fatigue loading. The stress relaxation was investigated under a range of stress ratios and maximum applied stresses. Two different material models were considered for the simulations, namely an elastic—perfectly plastic model and a non-linear kinematic hardening model.

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Wang, René, Dinesh Ram, Bernhard Stauder, Ricardo Fernández Gutiérrez, Elisabetta Gariboldi, and Maria Cecilia Poletti. "Stress Relaxation during Artificial Aging of an AlSi7Cu0.5Mg Cast Alloy." Crystals 12, no. 8 (August 19, 2022): 1168. http://dx.doi.org/10.3390/cryst12081168.

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After casting and solidification, Al cast cylinder heads undergo a sequence of heat treatments to achieve the desired material properties. This sequence comprises solution heat treatment (SHT), quenching, and artificial aging. Internal stresses are formed due to temperature gradients in the complex geometry of the cylinder heads during quenching from the SHT temperature to room temperature. Especially high tensile stresses can produce damage during service. However, part of these internal stresses relaxes during the aging treatment. This work aims to systematically measure the relaxation of the stresses, as well as to phenomenologically model the amount and rate of relaxation. Cast specimens of AlSi7Cu0.5Mg are heat-treated in a furnace before relaxation in a creep testing machine. SHT and SHT plus aging at 180, 200, and 230 °C for 0 h, 0.5 h, 1 h, 4 h, and 6 h are carried out before testing. The relaxation of the stress at constant temperature and strain over 5 h is recorded at three different testing temperatures (180 °C, 200 °C, and 230 °C). The relaxation process is strongly dependent on the testing temperature: at 180 °C and 200 °C the equilibrium stress was already reached after around 1 h, and at 230 °C the equilibrium was reached after 3.5 h. The initial stress values do not influence the relaxation rate. A phenomenological relaxation model is developed to calculate the stress decrement over time and the equilibrium stress in the AlSi7Cu0.5Mg-alloy. The model allows for calculating the levels of residual stress at any time during artificial aging as a function of the thermal history of the alloy, the relaxation temperature, and the initial stress level. Complete relaxation of the initial stress is not reached within 5 h.

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Li, Yongfeng, and Francis A. Cucinotta. "Mathematical Model of ATM Activation and Chromatin Relaxation by Ionizing Radiation." International Journal of Molecular Sciences 21, no. 4 (February 12, 2020): 1214. http://dx.doi.org/10.3390/ijms21041214.

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We propose a comprehensive mathematical model to study the dynamics of ionizing radiation induced Ataxia-telangiectasia mutated (ATM) activation that consists of ATM activation through dual mechanisms: the initiative activation pathway triggered by the DNA damage-induced local chromatin relaxation and the primary activation pathway consisting of a self-activation loop by interplay with chromatin relaxation. The model is expressed as a series of biochemical reactions, governed by a system of differential equations and analyzed by dynamical systems techniques. Radiation induced double strand breaks (DSBs) cause rapid local chromatin relaxation, which is independent of ATM but initiates ATM activation at damage sites. Key to the model description is how chromatin relaxation follows when active ATM phosphorylates KAP-1, which subsequently spreads throughout the chromatin and induces global chromatin relaxation. Additionally, the model describes how oxidative stress activation of ATM triggers a self-activation loop in which PP2A and ATF2 are released so that ATM can undergo autophosphorylation and acetylation for full activation in relaxed chromatin. In contrast, oxidative stress alone can partially activate ATM because phosphorylated ATM remains as a dimer. The model leads to predictions on ATM mediated responses to DSBs, oxidative stress, or both that can be tested by experiments.

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Boyle, J. T. "Stress relaxation and elastic follow-up using a stress range-dependent constitutive model." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, no. 6 (October 21, 2011): 1472–83. http://dx.doi.org/10.1177/0954406211425766.

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Despite the availability of detailed non-linear finite element analysis (FEA), some aspects of high-temperature design can still be best addressed through more simplified methods. One such simplified method relates to the problem of elastic follow-up where, typically in strain-controlled situations, elastic behaviour in one part of a structure can lead to large strain accumulation in another. Over the past 30 years, it has been shown that in regions with significant elastic follow-up, a plot of maximum stress against strain (a ‘stress-strain trajectory’) is virtually independent of the constitutive relation – a characteristic which can be used to estimate elastic follow-up for design purposes without detailed non-linear FEA. The majority of studies which have reported this independence on material behaviour have used simple constitutive models for creep strain, primarily based on power-law creep or variations. Recently, studies of the behaviour of high-temperature structures with a stress range-dependent constitutive law have begun to emerge. This article examines the problem of elastic follow-up using such a constitutive law for a classic two-bar structure and for a more complex structure using FEA. It is found that the independence of the stress–strain trajectory on constitutive equation is lost with a stress range-dependent relation.

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Milenin, A., R. Kuziak, V. Pidvysots'kyy, P. Kustra, Sz Witek, and M. Pietrzyk. "Model Of Relaxation Of Residual Stresses In Hot-Rolled Strips." Archives of Metallurgy and Materials 60, no. 3 (September 1, 2015): 1935–40. http://dx.doi.org/10.1515/amm-2015-0329.

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Abstract Residual stresses in hot-rolled strips are of practical importance when the laser cutting of these strip is applied. The factors influencing the residual stresses include the non uniform distribution of elastic-plastic deformations, phase transformation occurring during cooling and stress relaxation during rolling and cooling. The latter factor, despite its significant effect on the residual stress, is scarcely considered in the scientific literature. The goal of the present study was development of a model of residual stresses in hot-rolled strips based on the elastic-plastic material model, taking into account the stress relaxation. Residual stresses in hot-rolled strips were evaluated using the FEM model for cooling in the laminar cooling line and in the coil. Relaxation of thermal stresses was considered based on the creep theory. Coefficients of elastic-plastic material model and of the creep model for steels S235 and S355 were obtained from the experiments performed on the Gleeble 3800 simulator for the temperatures 35-1100°C. Experiments composed small tensile deformations of the sample (0.01-0.02) and subsequent shutter speed without removing the load. Model of the thermal deformation during cooling was obtained on the basis of the dilatometric tests at cooling rates of 0.057°C/s to 60°C/s. Physical simulations of the cooling process were performed to validate the model. Samples were fixed in the simulator Gleeble 3800, then heated to the temperature of 1200°C and cooled to the room temperature at a rate of 1-50°C/s. Changes of stresses were recorded. Good agreement between calculated and experimental values of stresses was observed. However, due to neglecting the effect of stress relaxation the stress at high temperatures was overestimated. Due to the change of their stress sign during the unloading process the resulting residual stresses were underestimated. Simulation of residual stresses in rolling and cooling were performed on the basis of the developed model. It was shown that the effect of stress relaxation and phase transformations on the distribution of residual stresses in strips is essential and neglecting these factors could lead to an underestimation of residual stresses.

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Zhang, Xingzhen, Ying Deng, Tian Liang, Shihan Jin, and Weidong Li. "Modeling and Verification of Stress Relaxation Behavior of Ti-6Al-4V." MATEC Web of Conferences 321 (2020): 11076. http://dx.doi.org/10.1051/matecconf/202032111076.

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The phenomenon of gradual decrease of internal stress with the deformation of material maintained under the precondition of certain temperature and initial stress or pre-strain is called stress relaxation. Due to that, the flow stress of the metal material falls rapidly when the hot forming process pauses, and then the required forming load. In this paper, the experiment was carried out to study the stress relaxation property of Ti-6Al-4V, in the temperature range of 1023K~1123K and with the pre-tension strain 0.7%, 4% and 10%. The quartic delay function was used to describe the stress relaxation behavior. The predicted value of stress relaxation equation is in good agreement with the experimental data, and the correlation coefficient is above 0.99. Arrhenius creep constitutive equation embedded in CAE software was derived. The finite element model of stress relaxation process of test bar was builded, and the tensile-relaxation experiment was performed under the loading condition of 1:1 part forming process. The forming force results agree well, and the validity and accuracy of the constitutive model are verified, laying a foundation for the subsequent process simulation and optimization.

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Kourousis, Kyriakos I. "A Cyclic Plasticity Model for Advanced Light Metal Alloys." Applied Mechanics and Materials 391 (September 2013): 3–8. http://dx.doi.org/10.4028/www.scientific.net/amm.391.3.

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Advanced light metals have recently attracted the interest of the aerospace and automotive industry. The need for accurate description of their cyclic inelastic response under various loading histories becomes increasingly important. Cyclic mean stress relaxation and ratcheting are two of the phenomena under investigation. A combined kinematic isotropic hardening model is implemented for the simulation of the behavior of Aluminum and Titanium alloys in uniaxial mean stress relaxation and ratcheting. The obtained results indicate that the model can perform well in these cases. This preliminary analysis provides useful insight for the evaluation of the models capabilities.

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Malmelöv, Andreas, Martin Fisk, Andreas Lundbäck, and Lars-Erik Lindgren. "Mechanism Based Flow Stress Model for Alloy 625 and Alloy 718." Materials 13, no. 24 (December 9, 2020): 5620. http://dx.doi.org/10.3390/ma13245620.

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To predict the final geometry in thermo-mechanical processes, the use of modeling tools is of great importance. One important part of the modeling process is to describe the response correctly. A previously published mechanism-based flow stress model has been further developed and adapted for the nickel-based superalloys, alloy 625, and alloy 718. The updates include the implementation of a solid solution strengthening model and a model for high temperature plasticity. This type of material model is appropriate in simulations of manufacturing processes where the material undergoes large variations in strain rates and temperatures. The model also inherently captures stress relaxation. The flow stress model has been calibrated using compression strain rate data ranging from 0.01 to 1 s−1 with a temperature span from room temperature up to near the melting temperature. Deformation mechanism maps are also constructed which shows when the different mechanisms are dominating. After the model has been calibrated, it is validated using stress relaxation tests. From the parameter optimization, it is seen that many of the parameters are very similar for alloy 625 and alloy 718, although it is two different materials. The modeled and measured stress relaxation are in good agreement.

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Journal articles on the topic 'Stress relaxation model'

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