• Journal of the Korean Wood Science and Technology
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• 제26권4호
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• pp.13-19
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• 1998

Stress relaxation tests have been performed under five different tensile strain levels and five different bending strain levels. Three different theoretical models have been developed based on four-element Burger's model, viscoelastic theory and viscous-viscoelastic theory. Experimental data were used to obtain parameters of the models and to verify accuracy of the models. Among the three theoretical models developed in this study, three-integral model (Model 3) based on viscous-viscoelastic theory showed the most exact estimations of stress relaxation under both tensile and bending strains and their correlation coefficients were greater than 0.99 for all the strain levels. Model 1 showed little initial stress relaxation. Model 2 showed excessive initial relaxation and, then, no relaxation after about 20 minute of strain application. Stress retention under strain decreased as strain increased, which means increased stress relaxation as strain increases. When the strain level was less than proportional limit, the effect of strain level on stress relaxation was not clearly shown. However, this effect was increased as strain level increased when strain level was greater than proportional limit.

• Geomechanics and Engineering
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• 제32권5호
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• pp.495-502
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• 2023

In this study, stress relaxation tests were carried out by keeping silt type soil specimens under different strain levels. Decreases in the stress values with time data was collected to better understand the effect of the strain level on the relaxation properties of soil specimens. In addition, the stress relaxation effect on the uniaxial compressive strength (UCS) values of the specimens was investigated with a series of tests. According to the results obtained from this study, the UCS values of the silt specimens significantly vary as a result of the stress relaxation effect. The UCS values were determined to increase with an increase of relaxation strain level to a threshold value. On the other hand, the UCS values were found to be affected adversely in case of high stress levels at the initiation of the relaxation, which are close to the peak level.

• 소성∙가공
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• 제17권8호
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• pp.579-585
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• 2008

Numerous experimental investigations on metallic materials and solid polymers have shown that relaxation behavior is nonlinearly dependent on prior strain rate. The stress drops in a constant time interval nonlinearly increase with an increase of prior strain rate. And the relaxed stress associated with the fastest prior strain rate has the smallest stress magnitude at the end of relaxation periods. This paper deals with the performance of three classes of unified constitutive models in predicting the characteristic behaviors of relaxation. The three classes of models are categorized by a rate sensitivity of kinematic hardening rule. The first class uses rate-independent kinematic hardening rule that includes the competing effect of strain hardening and dynamic recovery. In the second class, a stress rate term is incorporated into the rate-independent kinematic hardening rule. The final one uses a rate-dependent format of kinematic hardening rule.

• Coupled systems mechanics
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• 제11권6호
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• pp.543-556
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• 2022

Delamination of multilayered inhomogeneous beam that exhibits non-linear relaxation behavior is analyzed in the present paper. The layers are inhomogeneous in the thickness direction. The dealamination crack is located symmetrically with respect to the mid-span. The relaxation is treated by applying a non-linear stress-straintime constitutive relation. The material properties which are involved in the constitutive relation are distributed continuously along the thickness direction of the layer. The delamination is analyzed by applying the J-integral approach. A time-dependent solution to the J-integral that accounts for the non-linear relaxation behavior is derived. The delamination is studied also in terms of the time-dependent strain energy release rate. The balance of the energy is analyzed in order to obtain a non-linear time-dependent solution to the strain energy release rate. The fact that the strain energy release rate is identical with the J-integral value proves the correctness of the non-linear solutions derived in the present paper. The variation of the J-integral value with time due to the non-linear relaxation behavior is evaluated by applying the solution derived.

• 한국농공학회지
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• 제30권3호
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• pp.38-50
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• 1988

carried out to present a rheology model which is able to treat time-dependent properties of clay. The results were summarized as follow ; 1. The slope (a(e1)) of deviator stress in strain rate test was independent on axial strain, and pore water pressure was decreased with increment of strain rate. 2. The pore water pressure in a stress relaxation condition was not changed when the strain rate before stress relaxation was 0.05%/min., but it was increased with increment of time when the strain rate before stress relaxation was 0.2%/min 3. The greater the stress condition (q/qmax) and the strain rate before creep test became, the greater the increment rate of axial strain in creep test became. 4. SEKIGUCHI's constitutive equation was slightly overpredicted while empirical equation proposed in the study was well coincided with measured values. 5. The constitutive equation induced by a strain function could be dealed with a behavior of the pore water pressure increased with increment of elapsed time after primary consolidation.

• Journal of Biosystems Engineering
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• 제17권3호
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• pp.260-271
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• 1992

Fruits are generally subjected to mechanical forces during harvesting, handling, and transportation that may cause damage in the form of bruises, punctures, and cracks. In order to prevent damage, and insure better quality fruits for consumers, it is very essential to study physical properties of these materials. The studies were conducted to examine the effect of storage period, storage condition, and other factors, such as loading rate and initial strain, on the stress relaxation behavior of the fruit flesh, and develop nonlinear viscoelastic models to represent its stress relaxation behavior. The following results were obtained from the study : 1. Since the viscoelastic behavior of the fruits flesh was nonlinear, the behavior was satisfactorily modelled as follows ; $${\delta}({\varepsilon},\;t)={\varepsilon}^A[B\;{\exp}(-Ct)+D\;{\exp}(-Ft)+G(-Ht)]$$ But, for the every strain applied, the stress relaxation behavior of the fruit flesh, such as apple and pear, could be well described by the Generalized Maxwell model, respectively. 2. The effect of loading rate on the stress relaxation behavior was remarkable. The higher loading rate resulted in the higher initial stress, and the faster stress relaxation. 3. The higher initial strain resulted in the higher initial stress, and stress relaxed at the large initial strain was also much higher than at the small initial strain. 4. Stress relaxation rate and quantity stored in the fruits at the low temperature storage were much higher than those at the normal temperature storage in the same storage period. Also, in all fruits tested, the longer storage period was the more relaxation rate and quantity were shown. These trends in the normal temperature condition was the more significant than in the low temperature condition.

• 한국지반공학회논문집
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• 제15권6호
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• pp.17-28
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• 1999

본 연구에서는 자연점토의 압밀에 대한 변형률속도의 영향을 해석하기 위하여 비선형 점탄소성 모델을 제안하였다. 연약지반의 점소성 거동은 유일한 유효응력-변형률-변형률속도 (equation omitted)의 관계식으로부터 구할 수 있다. Berthierville 점토에 대한 크리프실험, 다단계 하중실험, Relaxation실험과 같은 실내실험결과와 수치해석결과를 비교하였다. 제안된 점탄소성 모델을 사용하여 자연점토의 압밀거동을 비교적 정확히 예측할 수 있다.

• 한국지반신소재학회논문집
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• 제5권3호
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• pp.31-36
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• 2006

본 연구에서는 보호, 여과, 차수기능을 갖는 부직포 지오텍스타일과 지오멤브레인의 응력완화거동을 각각 고찰하였다. "두 가지 지오신세틱스 제품의 응력완화거동을 해석하는데 "전이현상이론"이 적용되었다. 이들 지오신세틱스 제품의 응력완화거동에서 초기 및 후기 완화시간은 구성방정식으로부터 구하였다. 이들 지오신세틱스 제품의 초기완화거동은 부가변형률에 대한 의존성이 있으며, 특히 온도가 증가 할수록 증가하였다. 끝으로, 이들 지오신세틱스 제품의 초기 및 후기 완화시간은 부가변형률 및 온도가 커질수록 짧아졌으며, 완화시간 감소는 지오멤브레인보다 부직포 지오텍스타일의 경우가 더 큼을 알 수 있었다.

• 소성∙가공
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• 제16권2호
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• pp.101-106
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• 2007

Uniaxial displacement controlled tests were performed on annealed Type 304 stainless steel at room temperature. A servo-controlled testing machine and strain measurement on the gage length were employed to measure the response to a given input. The test results exhibit that the flow stress increases nonlinearly with the strain rate and the relaxed stress at the end of the relaxation periods depends strongly on the strain rate preceding the relaxation test. The rate-dependent inelastic deformation behavior is simulated using a new unified viscoplasticity model that has the rate-dependent format of nonlinear kinematic hardening rule, which plays a key role in modeling the rate dependence of relaxation behavior. The model does not employ yield or loading/unloading criteria and consists of a flow law and the evolution laws of two tensor and one scalar-valued state variables.

• Structural Engineering and Mechanics
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• 제18권5호
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• pp.565-589
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• 2004

The present paper concerns the macroscopic overall description of rheologic properties for steel wire and synthetic fibre cables under variable loading actions according to non-linear creep and/or relaxation theory. The general constitutive equations of non-linear creep and/or relaxation of tension elements - cables under one-step and the variable stress or strain inputs using the product and two types of additive approximations of the kernel functions are presented in the paper. The derived non-linear constitutive equations describe a non-linear rheologic behaviour of the cables for a variable stress or strain history using the kernel functions determined only by one-step - constant creep or relaxation tests. The developed constitutive equations enable to simulate and to predict in a general way non-linear rheologic behaviour of the cables under an arbitrary loading or straining history. The derived constitutive equations can be used for the various tension structural elements with the non-linear rheologic properties under uniaxial variable stressing or straining.