Behavior of Nonlinear Viscoelastic Material Under Simultaneous Stress Relaxation in Tension and Creep in Torsion

1969 ◽  
Vol 36 (1) ◽  
pp. 22-27 ◽  
Author(s):  
J. S. Y. Lai ◽  
W. N. Findley
Keyword(s):  
Stress Relaxation ◽  
Multiple Integral ◽  
Analytical Investigation ◽  
Integral Approach ◽  
Successive Approximations ◽  
Tension Stress ◽  
Creep Tests ◽  
Direct Inversion ◽  
Nonlinear Viscoelastic ◽  
Shearing Strain

An experimental and analytical investigation is presented for simultaneous stress relaxation in tension and creep in torsion of polyurethane in the nonlinear range of stresses. The method employed a multiple integral approach with an assumed product form of kernel function to describe creep behavior. The required constants were determined from pure creep experiments on polyurethane. The tension stress and shearing strain versus time for simultaneous stress relaxation and creep were computed from results of these pure creep tests alone, and the results were compared with experiments on the same polyurethane under simultaneous stress relaxation and creep. In the method of analysis, direct inversion of the equation for creep was used as a first approximation for relaxation. Means for obtaining successive approximations and for accounting for cross effects are described. The second approximation was found to be adequate to describe the observed behavior very satisfactorily.

Effect of Cure State on Stress Relaxation in 3501-6 Epoxy Resin

1997 ◽  
Vol 119 (3) ◽  
pp. 262-265 ◽  
Author(s):  
S. R. White ◽  
A. B. Hartman
Keyword(s):  
Stress Relaxation ◽  
Epoxy Resin ◽  
Creep Compliance ◽  
Numerical Technique ◽  
Matrix Material ◽  
Relaxation Modulus ◽  
Master Curves ◽  
Creep Tests ◽  
Three Point Bending ◽  
Direct Inversion

Little experimental work has been done to characterize how the viscoelastic properties of composite material matrix resins develop during cure. In this paper, the results of a series of creep tests carried out on 3501–6 epoxy resin, a common epoxy matrix material for graphite/epoxy composites, at several different cure states is reported. Beam specimens were isothermally cured at increasing cure temperatures to obtain a range of degrees of cure from 0.66 to 0.99. These specimens were then tested in three-point bending to obtain creep compliance over a wide temperature range. The master curves and shift functions for each degree of cure case were obtained by time-temperature superposition. A numerical technique and direct inversion were used to calculate the stress relaxation modulus master curves from the creep compliance master curves. Direct inversion was shown to be adequate for fully cured specimens, however it underpredicts the relaxation modulus and the transition for partially cured specimens. Correlations with experimental stress relaxation data from Kim and White (1996) showed that reasonably accurate results can be obtained by creep testing followed by numerical conversion using the Hopkins-Hamming method.

A Linear Compressibility Assumption for the Multiple Integral Representation of Nonlinear Creep of Polyurethane

1970 ◽  
Vol 37 (2) ◽  
pp. 441-448 ◽  
Author(s):  
K. G. Nolte ◽  
W. N. Findley
Keyword(s):  
Integral Representation ◽  
Multiple Integral ◽  
Kernel Functions ◽  
Nonlinear Creep ◽  
Volume Changes ◽  
Creep Tests ◽  
Third Order ◽  
Nonlinear Viscoelastic ◽  
Different Order ◽  
Order Kernel

The assumption that volume changes associated with creep of a nonlinear viscoelastic material are only linearly dependent on the stress history is incorporated into a third-order multiple integral representation. This assumption reduces the number of independent kernel functions in the representation from 12 to 7. The traces of these independent kernels may be determined from two tension, two torsion, and one combined tension and torsion creep tests. Experiments on polyurethane are well represented by this method. The time-dependence of the kernel functions is expressed by time raised to a power with the power differing for different-order kernel functions.

Uniaxial and biaxial mechanical behavior of human amnion

2005 ◽  
Vol 20 (11) ◽  
pp. 2902-2909 ◽  
Author(s):  
Michelle L. Oyen ◽  
Robert F. Cook ◽  
Triantafyllos Stylianopoulos ◽  
Victor H. Barocas ◽  
Steven E. Calvin ◽  
...  
Keyword(s):  
Energy Dissipation ◽  
Stress Relaxation ◽  
Mechanical Behavior ◽  
Biaxial Tension ◽  
Relaxation Times ◽  
Small Strain ◽  
Integral Approach ◽  
Nonlinear Viscoelastic ◽  
Pregnancy And Delivery ◽  
Tension Testing

Chorioamnion, the membrane surrounding a fetus during gestation, is a structural soft tissue critical for maintaining a successful pregnancy and delivery. However, the mechanical behavior of this tissue membrane is poorly understood. The structural component of chorioamnion is the amnion sublayer, which provides the membrane’s mechanical integrity via a dense collagen network and is the focus of this investigation. Amnion uniaxial and planar equi-biaxial tension testing was performed using cyclic loading and stress-relaxation. Cyclic testing demonstrated dramatic energy dissipation in the first cycle followed by less hysteresis on subsequent cycles. Fractional energy dissipation per cycle was strain dependent, with greatest dissipation at small strain levels. Stress-relaxation testing demonstrated a level-dependent response and continued relaxation after long relaxation times. A nonlinear viscoelastic (separable) hereditary integral approach was inadequate to model the amnion response due to intrinsic coupling of the strain- and time-dependent responses.

Modeling of Nonlinear Viscoelastic Creep of Polycarbonate

e-Polymers ◽  
2007 ◽  
Vol 7 (1) ◽  
Author(s):  
Wenbo Luo ◽  
Said Jazouli ◽  
Toan Vu-Khanh
Keyword(s):  
Creep Behavior ◽  
Room Temperature ◽  
Multiple Integral ◽  
Model Fit ◽  
Viscoelastic Creep ◽  
Commercial Grade ◽  
Nonlinear Viscoelastic ◽  
Schapery Model ◽  
Special Case ◽  
Better Than

AbstractThe creep behavior of a commercial grade polycarbonate was investigated in this study. 10 different constant stresses ranging from 8 MPa to 50 MPa were applied to the specimen, and the resultant creep strains were measured at room temperature. It was found that the creep could be modeled linearly below 15 MPa, and nonlinearly above 15 MPa. Different nonlinear viscoelastic models have been briefly reviewed and used to fit the test data. It is shown that the Findley model is a special case of the Schapery model, and both the Findley model and the simplified multiple integral representation are suitable for properly describing the creep behavior of the polycarbonate investigated in this paper; however, the Findley model fit the data better than the simplified multiple integral with three terms.

Micromechanical Analysis of Nonlinear Viscoelastic Unidirectional Fiber-Reinforced Composites

2011 ◽  
Vol 110-116 ◽  
pp. 1166-1170 ◽  
Author(s):  
Hasan Behzadpoor ◽  
Saeed Masoumi ◽  
Manouchehr Salehi
Keyword(s):  
Three Dimensional ◽  
Fiber Reinforced Composites ◽  
Elastic Fibers ◽  
Reinforced Composites ◽  
Fiber Reinforced ◽  
Creep Tests ◽  
Unidirectional Fiber ◽  
Viscoelastic Matrix ◽  
Nonlinear Viscoelastic ◽  
Micromechanical Approach

The micromechanical approach of Simplified Unit Cell Method (SUCM) in closed-form three dimensional solutions is used for predicting creep response of unidirectional fiber reinforced composites. The composite consist of elastic fibers reinforcing nonlinear viscoelastic resin. The nonlinear viscoelastic matrix behavior is modeled by using Schapery single integral viscoelastic constitutive equation. Off-axis specimens of graphite/epoxy with 45 and 90 fiber orientations were subjected to 480 minutes creep tests and the results is compared with experimental data and MOC results available in the literature. There is good agreement with experimental results due to using SUCM.

scholarly journals Nonlinear Viscoelastic–Plastic Creep Model Based on Coal Multistage Creep Tests and Experimental Validation

Energies ◽  
2019 ◽  
Vol 12 (18) ◽  
pp. 3468 ◽  
Author(s):  
Junxiang Zhang ◽  
Bo Li ◽  
Conghui Zhang ◽  
Peng Li
Keyword(s):  
Creep Behavior ◽  
Physical Property ◽  
Creep Model ◽  
Creep Process ◽  
Creep Tests ◽  
Model Based ◽  
Nonlinear Viscoelastic ◽  
Improved Model ◽  
And Control ◽  
Plastic Creep

The development of fractures, which determine the complexity of coal creep characteristics, is the main physical property of coal relative to other rocks. This study conducted a series of multistage creep tests to investigate the creep behavior of coal under different stress levels. A negative elastic modulus and a non-Newtonian component were introduced into the classical Nishihara model based on the theoretical analysis of the experimental results to propose a nonlinear viscoelastic–plastic creep model for describing the non-decay creep behavior of coal. The validity of the model was verified by experimental data. The results show that this improved model can preferably exhibit decelerating, steady state, and accelerating creep behavior during the non-decay creep process. The fitting accuracy of the improved model was significantly higher than that of the classical Nishihara model. Given that acceleration creep is a critical stage in predicting the instability and failure of coal, its successful description using this improved model is crucial for the prevention and control of coal dynamic disasters.

Tensile and Compressive Creep Behavior of IN718 Alloy Manufactured by Selective Laser Melting

2020 ◽  
Vol 986 ◽  
pp. 102-108 ◽  
Author(s):  
Zhen Xu ◽  
Chuan Guo ◽  
Zhen Rong Yu ◽  
Xin Li ◽  
Xiao Gang Hu ◽  
...  
Keyword(s):  
Creep Behavior ◽  
Chemical Potential ◽  
Creep Process ◽  
Tension Stress ◽  
Creep Tests ◽  
Compressive Creep ◽  
Large Size ◽  
Stress Orientation ◽  
Evolution Of Microstructure ◽  
Tension Compression Asymmetry

Tensile and compressive creep behavior of SLMed IN718 alloy under 973K (700°C) were investigated. Crept samples were analyzed by SEM and TEM to expose evolution of microstructure, precipitates and dislocation structure during the creep process. Results show that initial creep rate under compression is higher than under tension for the same creep conditions. Minimum creep rates are approximately the same both in tensile and compressive creep tests. The different creep behaviors may be related to the fact that tension stress promotes precipitations of fine needle-like γ′′ phases, while compression stress promotes precipitations of large size δ phases. The tension-compression asymmetry owns to the increment of chemical potential varying with the stress orientation.

Fourth-order fractional diffusion model of thermal grooving: integral approach to approximate closed form solution of the Mullins model

2018 ◽  
Vol 13 (1) ◽  
pp. 6 ◽  
Author(s):  
Jordan Hristov
Keyword(s):  
Integration Method ◽  
Closed Form Solution ◽  
Multiple Integral ◽  
Fractional Diffusion ◽  
Form Solution ◽  
Balance Method ◽  
Integral Approach ◽  
Integration Technique ◽  
Multiple Integration ◽  
Space Coordinate

A multiple integration technique of the integral-balance method allowing solving high-order subdiffusion diffusion equations is presented in this article. The new method termed multiple-integral balance method (MIM) is based on multiple integration procedures with respect to the space coordinate. MIM is a generalization of the widely applied Heat-balance integral method of Goodman and the double integration method of Volkov. The method is demonstrated by a solution of the linear subdiffusion model of Mullins for thermal grooving by surface diffusion.

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