Energy Dissipation of a Cohesive Soil by the Fourier Transformation of Stress Relaxation Response

Polymer composites have a characteristic, composition specific visco-elastic property which influences the damage progression during fatigue cycling. While some researchers have studied the time dependent constitutive response of polymer composites during the first cycle of fatigue loading, very few have experimentally investigated the dependence of visco-elastic response of built-up polymer composite materials at various stages of fatigue cycling [1]. Our earlier studies on fatigue response of polymer composites focused primarily on the stiffness degradation as a function of applied cycles of loading, which represents the gross response of the material [2]. While doing such an experiment, complimentary experimental techniques to measure the temperature evolution was attempted through the use of infrared thermal imaging technique, which gave some insight into the change in temperature response as a function of fatigue cycling. However, there was no systematic measurement of creep and stress relaxation response of the composite material as a function of induced fatigue damage. The present paper describes the results of creep and stress-relaxation obtained during uni-axial fatigue loading of a hybrid polymer composite material. For this purpose, a woven carbon fiber mat was chosen as the synthetic fiber and Flax fiber in the unidirectional form was chosen as the natural fiber that is laid between the two layers of woven carbon fiber mat. Epoxy LY 556 and hardener Araldite® was used for building up of composite laminate by hand-lay-up technique. Dog-bone shaped tensile specimens with a gage width of 13 mm and gage length of 57 mm were extracted from the 250 × 250 mm sq. plate laminate of 2.1 mm thickness using a numerical controlled milling machine. The specimens were tested at 35% of their median tensile strengths under fatigue at a positive stress ratio (Pmin/Pmax) of 0.1 in tension-tension loading. Prior to start of fatigue loading, the specimens were held in load control and the strain in the gage length was measured for understanding the creep response over 2500 seconds. For stress-relaxation characterization, the specimens were held in extensometer control over a period of 2500 sec. The creep and stress relaxation tests were carried out after periodic intervals of fatigue cycling. It was observed that in the case of un-impacted specimens, the creep rate is consistent with the stiffness variation, which in turn, is dependent on the number of fatigue cycles - till it showed signs of de-lamination. Thereafter it was governed by the woven synthetic fiber response. Similarly, the stress relaxation response was found to decrease with increasing fatigue cycles. In case of impacted specimens, the local deformation had a prominent role in terms of creep and stress relaxation response.

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Influence of cooling rate on stress relaxation response of strained PVDF film

Materials Research Innovations ◽

10.1179/143307507x199443 ◽

2006 ◽

Vol 10 (4) ◽

pp. 428-433 ◽

Cited By ~ 2

Author(s):

P. Lee-Sullivan

Keyword(s):

Stress Relaxation ◽

Cooling Rate ◽

Relaxation Response ◽

Pvdf Film

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Stress relaxation response of active fiber composites

10.1117/12.883429 ◽

2011 ◽

Cited By ~ 3

Author(s):

Hassene Ben Atitallah ◽

Anastasia Muliana ◽

Zoubeida Ounaies

Keyword(s):

Stress Relaxation ◽

Fiber Composites ◽

Relaxation Response ◽

Active Fiber ◽

Active Fiber Composites

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Modeling Stress Relaxation Response of Wheat En Masse Using the Triaxial Test

Transactions of the ASAE ◽

10.13031/2013.31210 ◽

1989 ◽

Vol 32 (5) ◽

pp. 1701-1708 ◽

Cited By ~ 5

Author(s):

R. G. Bock ◽

V. M. Pari ◽

H. B. Manbeck

Keyword(s):

Stress Relaxation ◽

Triaxial Test ◽

Relaxation Response ◽

Modeling Stress

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Stress-relaxation response of human menisci under confined compression conditions

Journal of the Mechanical Behavior of Biomedical Materials ◽

10.1016/j.jmbbm.2013.05.027 ◽

2013 ◽

Vol 26 ◽

pp. 68-80 ◽

Cited By ~ 43

Author(s):

Andreas Martin Seitz ◽

Fabio Galbusera ◽

Carina Krais ◽

Anita Ignatius ◽

Lutz Dürselen

Keyword(s):

Stress Relaxation ◽

Relaxation Response ◽

Confined Compression

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Dynamic Response of Immature Bovine Articular Cartilage in Tension and Compression, and Nonlinear Viscoelastic Modeling of the Tensile Response

Journal of Biomechanical Engineering ◽

10.1115/1.2206201 ◽

2006 ◽

Vol 128 (4) ◽

pp. 623-630 ◽

Cited By ~ 46

Author(s):

Seonghun Park ◽

Gerard A. Ateshian

Keyword(s):

Articular Cartilage ◽

Stress Relaxation ◽

Tensile Stress ◽

Dynamic Modulus ◽

Relaxation Function ◽

Tensile Modulus ◽

Relaxation Response ◽

Unconfined Compression ◽

Tensile Response ◽

Cyclical Loading

Very limited information is currently available on the constitutive modeling of the tensile response of articular cartilage and its dynamic modulus at various loading frequencies. The objectives of this study were to (1) formulate and experimentally validate a constitutive model for the intrinsic viscoelasticity of cartilage in tension, (2) confirm the hypothesis that energy dissipation in tension is less than in compression at various loading frequencies, and (3) test the hypothesis that the dynamic modulus of cartilage in unconfined compression is dependent upon the dynamic tensile modulus. Experiment 1: Immature bovine articular cartilage samples were tested in tensile stress relaxation and cyclical loading. A proposed reduced relaxation function was fitted to the stress-relaxation response and the resulting material coefficients were used to predict the response to cyclical loading. Adjoining tissue samples were tested in unconfined compression stress relaxation and cyclical loading. Experiment 2: Tensile stress relaxation experiments were performed at varying strains to explore the strain-dependence of the viscoelastic response. The proposed relaxation function successfully fit the experimental tensile stress-relaxation response, with R2=0.970±0.019 at 1% strain and R2=0.992±0.007 at 2% strain. The predicted cyclical response agreed well with experimental measurements, particularly for the dynamic modulus at various frequencies. The relaxation function, measured from 2% to 10% strain, was found to be strain dependent, indicating that cartilage is nonlinearly viscoelastic in tension. Under dynamic loading, the tensile modulus at 10Hz was ∼2.3 times the value of the equilibrium modulus. In contrast, the dynamic stiffening ratio in unconfined compression was ∼24. The energy dissipation in tension was found to be significantly smaller than in compression (dynamic phase angle of 16.7±7.4deg versus 53.5±12.8deg at 10−3Hz). A very strong linear correlation was observed between the dynamic tensile and dynamic compressive moduli at various frequencies (R2=0.908±0.100). The tensile response of cartilage is nonlinearly viscoelastic, with the relaxation response varying with strain. A proposed constitutive relation for the tensile response was successfully validated. The frequency response of the tensile modulus of cartilage was reported for the first time. Results emphasize that fluid-flow dependent viscoelasticity dominates the compressive response of cartilage, whereas intrinsic solid matrix viscoelasticity dominates the tensile response. Yet the dynamic compressive modulus of cartilage is critically dependent upon elevated values of the dynamic tensile modulus.

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