• 연구논문집
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• 통권34호
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• pp.59-68
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• 2004

The hot spot stress approach and the notch strain approach are discussed with some results of them. And a stress model that can be applicable to several types of weld joints with single S-N curve of the base material. The stress model uses the geometric characteristics of the stress distribution vicinity of weld joints. The model was applied to five different weld joins(the base material is SM490B). By the representative stress, the experimental fatigue data are plotted very closely to the S-N curve of the base material.

• Biomolecules & Therapeutics
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• 제6권3호
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• pp.232-241
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• 1998

This study was done to investigate whether cholic acid derivatives have anti-stress activity in various stress models. Two cholic acid derivatives, ursodeoxycholic acid (UDCA) and tauroursodeoxycholic acid (WDCA), were used. physical, psychological, chemical and environmental stress models were performed. Adrenal weight, serum glucose levels and ALP activity were elevated in restraint stress model, but this elevation was prevented by UDCA treatment. Moreover, UDCA and TUDCA inhibited exploratory and spontaneous movements in oscillation stress model. In alcohol-induced stress model, TUDCA improved rotarod performance. UDCA and TUDCA significantly reduced the involution of lymphoid organs and the increment of WBC counts in cold stress model. These findings suggest that choric acid derivatives have antistress effects in various stress models.

• 대한기계학회논문집
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• 제19권5호
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• pp.1190-1201
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• 1995

Photoelastic experiment has been restricted by three significant problems such as the problems of modeling for a complicated body, of development of experimental model material, and of residual stress in photoelastic specimen. The residual stress in photoelastic model materials is caused by molding, cutting and time effects, etc.. Especially, large residual stress exists on the interface of photoelastic model material for bi-material. Small residual stress occurred in the photoelastic model materials is usually neglected in the photoelastic experiments. But the residual stress provides some errors in the results of photoelastic experiments. In this paper, the stress optic law which can be effectively applied to the phtoelastic model materials with residual stress is developed. By using this stress optic law, we can obtain good results from isochromatic fringe patterns of photoelastic experiment specimen in which residual stress are involved. The stress optic law can be applied to obtain good results of photoelastic experiment from composite materials or bimaterials.

• 소성∙가공
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• 제24권1호
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• pp.52-61
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• 2015

Evaluation of the elevated temperature flow stress for thermoplastic fiber metal laminates(TFMLs) sheet, comprised of two aluminum sheets in the exterior layers and a self-reinforced polypropylene(SRPP) in the interior layer, was conducted. The flow stress as a function of temperature should be evaluated prior to the actual forming of these materials. The flow stress can be obtained experimentally by uniaxial tensile tests or analytically by deriving a flow stress model. However, the flow stress curve of TFMLs cannot be predicted properly by existing flow stress models because the deformation with temperature of these types of materials is different from that of a generic pure metallic material. Therefore, the flow stress model, which includes the effect of the temperature, should be carefully identified. In the current study, the flow stress of TFMLs were first predicted by using existing flow stress models such as Hollomon, Ludwik, and Johnson-Cook models. It is noted that these existing models could not effectively predict the flow stress. Flow stress models such as the modified Hollomon and modified Ludwik model were proposed with respect to temperatures of $23^{\circ}C$, $60^{\circ}C$, $90^{\circ}C$, $120^{\circ}C$. Then the stress-strain curves, which were predicted using the proposed flow stress models, were compared to the stress-strain curves obtained from experiments. It is confirmed that the proposed flow stress models can predict properly the temperature dependent flow stress of TFMLs.

• 소성∙가공
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• 제22권8호
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• pp.450-455
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• 2013

In the current study, a new dynamic recrystallization model for predicting high temperature flow stress is developed based on a physical model and the mean field theory. In the model, the grain aggregate is assumed as a representative volume element to describe dynamic recrystallization. The flow stress and microstructure during dynamic recrystallization were calculated using three sub-models for work hardening, for nucleation and for growth. In the case of work hardening, a single parameter dislocation density model was used to calculate change of dislocation density and stress in the grains. For modeling nucleation, the nucleation criterion developed was based on the grain boundary bulge mechanism and a constant nucleation rate was assumed. Conventional rate theory was used for describing growth. The flow stress behavior of pure copper was investigated using the model and compared with experimental findings. Simulated results by cellular automata were used for validating the model.

• 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.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.644-655
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• 2008

Conventional hyperbolic model does not satisfactorily predict the overall stress-strain behaviors of various geomaterials. Tatsuoka and Shibuya(1992) suggest the generalized hyperbolic equation(GHE) considering strain dependency and calculated performance is in good agreement with precise triaxial compression test results of stress-strain relations over wide range of strains before peak stress condition in some cases, but GHE model also does not satisfactorily predict stress-strain relations as strain goes on state of peak stress in most cases. For improve a weak point of the GHE, in this study, modified form of generalized hyperbolic equation (MGHE model) is proposed which can predict highly nonlinear stress-strain behavior for various geomaterials from small strain to peak stress condition.

• 한국농공학회논문집
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• 제48권4호
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• pp.33-40
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• 2006

In present study, the principal stress condition needed to conduct cubical large-scale triaxial test which can reflect three dimensional stress condition (or plain strain condition) in a dam was investigated by performing model test and numerical analysis and the principal stress ratio varying with the height of CFRD was examined. Also, the principal stress ratio in CFRD body was investigated from the monitoring results of horizontal and vertical earth pressure gages, installed in the center zone and lower part of transition zone of the dam body, respectively, in order to consider the principal stress condition in the large-scale triaxial test to model the behavior of CFRD. The result of the study indicated that the principal stress ratio decreased gradually from the lower to the upper part in the dam body for its center axis and was about 0.5 and 0.2 in the lower and upper part, respectively.

• 한국농공학회지
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• 제38권2호
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• pp.133-144
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• 1996

To get accurate results, the realistic stress-strain relationships of soils are dependent on a number of factors such as soil types, density, stress levels and stress path. Such attempts are continuously being made by the developement of analytical models for soils incorporating all such factors. Isotropic compression-expansion test and a series of drained conventional triaxial tests with several stress path for Baekma river sand were performed to investigate parameters characteristics of Lade's single work hardening model dependant on the stress path. Using the computer program based on the regression analysis, the values of parameters for the model were determined. In conclusion, the parameters of Lade's model are little influenced by the stress paths. Though yield criterion parameters ( h, ${\alpha}$a) are much influenced by stress level and stress path, the parameters don't have influence on stress-strain behavior.

• 한국의류산업학회지
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• 제7권1호
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• pp.33-40
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• 2005

This study is to develope the job stress model for workers in fashion and textile industries and to investigate the effect of job stressors on stress symptom and its effect on job performance. The structural equation model analysis was performed for examining the relationship among job stressors, stress symptom and job performance. Environmental factors, task factors, role factors and organizational climate factors were identified as job stressors. Task characteristics and role characteristics were positively related to job stress symptom. Environmental factors and organizational climate factors were negatively related to job stress symptom. Also, job stress symptom was negatively related to job performance. The findings suggest some implications on how to improve job performance or to reduce job stress.