• 한국안전학회지
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• 제13권1호
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• pp.19-25
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• 1998

In this study, proper injection molding condition has been studied through stress relaxation tests in order to experimentally investigate the effect of the condition on softening of mold product, using specimens produced under the different conditions according to the recommendation of resin manufactures. As a result, softening of the specimens was found to be strongly influenced by material melting temperature. The specimen with higher material melting temperature is found to have lower softening. However, softening of the specimen with lower mold temperature has an decrement, compared with other specimens. In particular, specimen with notch is influenced by mold temperature. The softening increase with higher injection speed and pressure. Finally in order to improve softening, material melting temperature, injection speed and injection pressure were found to be increased with low mold temperature.

• Computers and Concrete
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• 제15권2호
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• pp.199-213
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• 2015

The residual fracture toughness of post-fire normal-strength concrete subjected up to $600^{\circ}C$ is considered by the wedge splitting test. The initial fracture toughness $K_I^{ini}$ and the critical fracture toughness $K_I^{un}$ could be calculated experimentally. Their difference is donated as the cohesive fracture toughness $K_I^c$ which is caused by the distribution of cohesive stress on the fracture process zone. A comparative study on determining the residual fracture toughness associated with three bi-linear functions of the cohesive stress distribution, i.e. Peterson's softening curve, CEB-FIP Model 1990 softening curve and Xu's softening curve, using an analytical method is presented. It shows that different softening curves have no significant influence on the fracture toughness. Meanwhile, comparisons between the experimental and the analytical calculated critical fracture toughness values further prove the validation of the double-K fracture model to the post-fire concrete specimens.

• Coupled systems mechanics
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• 제4권2호
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• pp.115-136
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• 2015

We present for one-dimensional model for elastoplastic bar with combined hardening in FPZ - fracture process zone and softening with embedded strong discontinuities. The simplified version of the model without FPZ is directly compared and validated against analytical solution of Bazant and Belytschko (1985). It is shown that deformation localizes in an area which is governed by the chosen element size and therefore causes mesh sensitivity and that the length of the strain-softening region tends to localize into a point, which also agrees with results obtained by stability analysis for static case. Strain increases in the softening domain with a simultaneous decrease of stress. The problem unloads elastically outside the strain-softening region. The more general case with FPZ leads to more interesting results that also account for induced strain heterogeneities.

• Structural Engineering and Mechanics
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• 제32권3호
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• pp.459-475
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• 2009

This paper presents analytical methodologies for remaining life prediction of plain concrete structural components considering tension softening and size effects. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. Size effect has been accounted for by modifying the Paris law, leading to a size adjusted Paris law, which gives crack length increment per cycle as a power function of the amplitude of a size adjusted stress intensity factor (SIF). Details of tension softening effects and size effect in the computation of SIF and remaining life prediction have been presented. Numerical studies have been conducted on three point bending concrete beams under constant amplitude loading. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature for all the tension softening models.

• Computers and Concrete
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• 제5권3호
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• pp.261-277
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• 2008

This paper presents methodologies for remaining life prediction of plain concrete structural components considering tension softening effect. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. A methodology to account for tension softening effects in the computation of SIF and remaining life prediction of concrete structural components has been presented. The tension softening effects has been represented by using any one of the models mentioned above. Numerical studies have been conducted on three point bending concrete structural component under constant amplitude loading. Remaining life has been predicted for different loading cases and for various tension softening models. The predicted values have been compared with the corresponding experimental observations. It is observed that the predicted life using bi-linear model and power curve model is in close agreement with the experimental values. Parametric studies on remaining life prediction have also been conducted by using modified bilinear model. A suitable value for constant of modified bilinear model is suggested based on parametric studies.

• 한국결정성장학회지
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• 제8권4호
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• pp.619-625
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• 1998

저온소성용 글라스/세라믹 복합체 제조시 사용되는 유리 프릿트의 연화점과 유리의 함량이 소결특성에 미치는 영향에 대해 고찰하였고, 이에 따라 고밀도의 저온소성용 글라스/세라믹 복합체를 제조하였다. 유리의 함량이 증가함에 따라 복합체의 소결밀도는 증가하였고, 이때 사용되는 유리의 연화점이 낮을 경우 유리의 함량이 적은 시현의 경우에도 변형이 일어남을 알수 있었다. 유리의 연화점이 높은 유리를 사용한 시편의 경우, 유리의 함량을 증가시켜도 시편의 변형은 일어나지 않았으며, 소결밀도는 계속적으로 증가하여 치밀화가 하고 있음을 알수 있었다. 이러한 유리함량과 유리의 연화점이 소결특성에 미치는 영향을 고찰함으로써 높은 밀도의 동시소성용 글라스/세라믹을 제조할 수 있는 유리의 연화점과 유리함량을 예측할 수 있었고, 이에따라 $790^{\circ}C$의 연화점을 갖는 유리를 유리 프릿트로 사용함으로써 $900^{\circ}C$의 소성온도에서 소결밀도 97%이상의 고밀도의 저온소성용 글라스/세라믹 복합체를 제조할 수 있었다.

• Coupled systems mechanics
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• 제4권3호
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• pp.211-235
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• 2015

In this work we present a one-dimensional damage model capable of representing the dynamic fracture for elastodamage bar with combined hardening in fracture process zone - FPZ and softening with embedded strong discontinuities. This model is compared with another one we recently introduced (Do et al. 2015) and it shows a good agreement between two models. Namely, it is indicated that strain-softening leads to a sensitivity of results on the mesh discretization. Strain tends to localization in a single element which is the smallest possible area in the finite element simulations. The strain-softening element in the middle of the bar undergoes intense deformation. Strain increases with increasing mesh refinement. Strain in elements outside the strain-softening element gradually decreases to zero.

• Structural Engineering and Mechanics
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• 제5권6호
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• pp.785-801
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• 1997

Reinforced Concrete beams with tension and compression softening material constitutive laws are studied. Energy-based and non-local regularisation techniques are presented and applied to a R.C. element. The element characteristics (sectional tangent stiffness matrix, element tangent stiffness matrix restoring forces) are directly derived from their symbolic expressions through numerical integration. In this way the same spatial grid allows us to obtain a non-local strain estimate and also to sample the contributions to the element stiffness matrix. Three examples show the spurious behaviors due to the strain localization and the stabilization effects given by the regularisation techniques, both in the case of tension and compression softening. The possibility to overestimate the ultimate load level when the non-local strain measure is applied to a non softening material is shown.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1995년도 추계학술대회논문집
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• pp.172-180
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• 1995

Isothermal interrupted deformation behavior of 10vol.%SICp/AI-Si composites was investigated by hot torsion test at the temperature ranges from 27$0^{\circ}C$ to 43$0^{\circ}C$ and at strain rate range of 1.26X10-2~2.16X10-1/sec. With increasing pass strain, flow stresses were high compared to continuous deformation condition. Fractional softening was increased with temperature imterruption time and pass strain. Fractional softening of 10vol.%SiCp/AI-Si composites was lower than that of AI-Si matrix at 37$0^{\circ}C$. However at high temperature of 43$0^{\circ}C$, SiC particle promoted static softening, diminishing the dislocation density at the interface of AI-Si matrix and reinforcements, then this resulted in higher fractional softening in composites. Both of failure strain improved reducing the fracture of SiC particle and Si precipitates above 32$0^{\circ}C$, however at low temperature of 27$0^{\circ}C$, the softening effect by interrupted deformation was found to be negligible.

• 소성∙가공
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• 제30권3호
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• pp.134-141
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• 2021

In order to improve excessive spring-back behavior as a result of the roll forming process using ultra high strength steel (UHSS) sheet, local softening in region of a partial area expected to be deformed on an initial blank is considered in this study. With SPFC1470 UHSS sheet with initial blank thickness of 1.20mm, the local softening is performed with the following conditions: temperatures of 500℃, 550℃, 600℃ and 650℃, and holding time of 20s, 40s, 80s and 160s. Mechanical properties, such as yield stress and tensile strength, as well as elongation, are evaluated through uniaxial tensile tests, while the microstructural characteristics as a result of local softening are also investigated using the heat-treated specimens. As a result, it is shown that the spring-back behavior of the roll-formed prototype was reduced about by 78.9%, when the local softening at about 500℃ was performed for 160s considering the practical manufacturing condition.