• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1417-1424
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• 2006

In order to evaluate variation of fatigue life of mechanical components including engineering plastics, it is important to estimate probabilistic strain-life curves to accurately define the variation of fatigue characteristics. This paper intends to provide new assessment of P-$\varepsilon$-N (probabilistic strain-life curves) for considering the variation of fatigue characteristics in polyacetal. The fatigue strain controlled tests were conducted under constant 50% humidity and room temperature condition by a universal testing machine at strain ratio, R=0. A practical procedure is introduced to evaluate probabilistic strain-life curves. Three probabilistic distributions were used for generating P-$\varepsilon$-N curves such as normal, 2-parameter and 3-parameter Weibull. In this study, 3-parameter Weibull distribution was found to be most appropriate among assumed distributions when the probability distributions of the fatigue characteristic were examined using chi-square and Kolmogorov-Smirnov test. The more appropriate P-$\varepsilon$-N curves for these materials are generated by the proposed method considering 3-parameter Weibull distribution.

• The Journal of Engineering Geology
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• v.8 no.3
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• pp.215-224
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• 1998

In this study, total strain was measured by LVDTs and local strains on the surface of specimens were measured by strain gauges. And axi-symmetrically elastoplastic FEM analyses was carried out for cylindrical specimens. Considering the influence of the restraint induced by the loading platen, in the case of H/D=1, the strain distribution on the side of a specimen is obviously affected by the condition of platen contact. Furthermore, it is clear that the larger H/D ratio becomes, the smaller the influence to the strain distribution is. For the smooth contact condition, the strain on the side is not influenced by the stiffness of the specimen, the shape and the scale effect, the strain distribution coincides with the nominal total strain. Whereas, in the case of rough contact condition, the strain distribution is remarkably affected. It is made clear that strain responses of hard rock specimens may more sensitive than these of soft rock specimens as a results of interaction between loading platens and specimen and the uniaxial strength of specimens may strongly depends on this interaction and stress-strain relation is affected by the contact condition.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.04a
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• pp.97-100
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• 2000

A FEA(finite element analysis) model was proposed to study stress and strain distributions in thick composites with various types of fiber waviness under tensile and compressive loadings. Three types of model were considered in this study: uniform fiber waviness, graded fiber waviness and localized fiber waviness models. In the analysis, both material and geometrical nonlinearities due to fiber waviness were incorporated into the model utilizing energy density and incremental method. The strain distributions of uniform fiber waviness model were strongly influenced whereas the stress distributions were little influenced by fiber waviness. The stress and strain distributions of graded and localized fiber waviness models showed more complex distributions than those of uniform fiber waviness model due to the variation of fiber waviness along the thickness and length directions. It was concluded that the stress and strain distributions of composites with fiber waviness were significantly affected by types of fiber waviness.

• Transactions of Materials Processing
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• v.6 no.3
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• pp.250-256
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• 1997

Hammer forging was employed for Alloy 718 disk. The change in grain size during hot forging depends very much on dynamic recrystallization. The final grain size depends especially on the critical strain$($\varepsilon$_C)$/TEX> for dynamic recrystallization and Zener-Holloman parameter(Z). In this study, the critical strain$($\varepsilon$_C)$, the strain for 50 pct. recrystallization$($\varepsilon$_{0.5})$ and fraction of dynamic recrystallization(Xdyn) were measured by compression tests. FE simulation was also carried out ot predict the evolution of microstructure. The strain, strain rate and temperature distribution predicted by forging simulation can be effectively used to predict the distribution of grain sizes in the forged workpiece. The present model predictions showed an excellent agreement with the microstructural evolution of hammer-forged Alloy 718 disks.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.121-127
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• 2009

The failure behavior of RC structure was exceedingly affected by the size and the local strain distribution of the failure zone due to the strain localization behavior on the tension softening materials. However, it is very difficult to quantify and assess the local strain occurring in the failure zone by the conventional test method. In this study, image processing technology, which is available to measure the strain up to the complete failure of RC structures, was used to estimate the local strain distribution and the size of failure zone. In order to verify the reliability and validity for the image processing technology, the strain transition acquired by the image processing technology was compared with strain values measured by the concrete gauge on the uniaxial compressive specimens. Based on the verification of image processing technology for the uniaxial compressive specimens, the size and the local strain distribution of the failure zone of deep beam was measured using the image processing technology. With the results of test, the principal tensile/compressive strain contours were drawn. Using the strain contours, the size of the failure zone and the local strain distribution on the failure of the deep beam was evaluated. The results of strain contour showed that image processing technology is available to assess the failure behavior of deep beam and obtain the local strain values on the domain of the post-peak failure comparatively.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.120-125
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• 2007

Put Abstract text here The strain distribution measurement for wall thinned pipe bends by ESPI is presented. Defect types observed in the steel piping in the nuclear power plants (NPP) are the crack at the weld part and the wall thinning defect in the pipe bends. Especially, the wall thinning defects in the pipe bends due to the flow-accelerated corrosion (FAC) is a main type of defects observed in the carbon steel piping system. ESPI is one of the optical non-destructive testing methods and can measure the stress and the strain distribution of the object subjected by the tensile loading or the internal pressure. In this paper, the strain distribution of the wall thinned pipe bends due to the internal pressure will be measured by ESPI technique and the results are discussed. From the results, the size of the wall thinning defect can also be measured approximately.

• Computers and Concrete
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• v.7 no.5
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• pp.455-468
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• 2010

This paper presents a prediction and simulation method of tensile stress-strain curves of Engineered Cementitious Composites (ECC). For this purpose, the bridging stress and crack opening relations were obtained by the fiber bridging constitutive law which is quantitatively able to consider the fiber distribution characteristics. And then, a multi-linear model is employed for a simplification of the bridging stress and crack opening relation. In addition, to account the variability of material properties, randomly distributed properties drawn from a normal distribution with 95% confidence are assigned to each element which is determined on the basis of crack spacing. To consider the variation of crack spacing, randomly distributed crack spacing is drawn from the probability density function of fiber inclined angle calculated based on sectional image analysis. An equation for calculation of the crack spacing that takes into quantitative consideration the dimensions and fiber distribution was also derived. Subsequently, a series of simulations of ECC tensile stress-strain curves was performed. The simulation results exhibit obvious strain hardening behavior associated with multiple cracking, which correspond well with test results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.96-99
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• 2007

The microstructure with fine and uniform AGS(austenite grain size) along thickness direction over no recrystallization temperature is strongly required for production of the high strength steels. The previous AGS prediction only based on the average strain improves to find the rolling conditions for accomplishment of the fine grain, but cannot find those for uniform grain. In this paper, an integrated mathematical model for prediction of the strain distribution along thickness direction is developed by carrying out finite element simulation for a series of rolling conditions. Also, the AGS distribution after rough rolling is predicted by applying the proposed model with AGS prediction model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1207-1216
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• 1988

The most 3-Dimensional problems of composite materials, especially three-dimensional stress or strain distribution on jointed boundary in composite materials remains unsolved due to the limitations of analytic techniques. The purpose of this paper is to apply the Embedded Grid Method to model development to measure the three-dimensional strain distribution along the jointed boundary of composite materials which consist of two different materials. It was confirmed that the Embedded Grid Method was very useful in model development and measuring the three-dimensional strain distribution in a local region near the jointed boundary.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.202-212
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• 2000

This study investigates the ductility capacity of slender-wide reinforced concrete walls under predominant flexural moment loading. The experimental work for this study aims to provide design guidelines for bar detailing in critical regions under compressive stress in particular in case of slender-wide RC walls. According to the experimental observation the Bernoulli hypothesis of linear strain distribution is no longer valid and the ultimate compressive strain of concrete is significantly reduced, It is postulated that the nonlinear strain distribution causes the concentrated compressive stressed region and hence the premature crushing failure at the toe of walls. The reduced ultimate strain and nonlinear strain distribution need transverse reinforcement for confinement and more realistic models for the strength and displacement estimation of slender-wide RC wall.