• Advances in materials Research
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• v.11 no.4
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• pp.351-374
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• 2022

Softening function is the primary input for modeling the fracture of concrete when the cohesive crack approach is used. In this paper, based on the laboratory data on notched beams, an inverse algorithm is proposed that can accurately find the softening curve of the concrete. This algorithm uses non-linear finite element analysis and the damage-plasticity model. It is based on the kinematics of the beam at the late stages of loading. The softening curve, obtained from the corresponding algorithm, has been compared to other softening curves in the literature. It was observed that in determining the behavior of concrete, the usage of the presented curve made accurate results in predicting the peak loads and the load-deflection curves of the beams with different concrete mixtures. In fact, the proposed algorithm leads to softening curves that can be used for modeling the tensile cracking of concrete precisely. Moreover, the advantage of this algorithm is the low number of iterations for converging to an appropriate answer.

• Computers and Concrete
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• v.15 no.2
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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.

• Geomechanics and Engineering
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• v.8 no.1
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• pp.33-52
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• 2015

Based on the Mohr-Coulomb failure criterion, a gradient-dependent plastic model that considers the strain-softening behavior is presented in this study. Both triaxial shear tests on conventional specimen and precut-specimen, which were obtained from an ancient landslide, are performed to plot the post-peak stress-strain entire-process curves. According to the test results of the soil strength, which reduces from peak to residual strength, the Mohr-Coulomb criterion that considers strain-softening under gradient plastic theory is deduced, where strength reduction depends on the hardening parameter and the Laplacian thereof. The validity of the model is evaluated by the simulation of the results of triaxial shear test, and the computed and measured curves are consistent and independent of the adopted mesh. Finally, a progressive failure of the ancient landslide, which was triggered by slide of the toe, is simulated using this model, and the effects of the strain-softening process on the landslide stability are discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.04a
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• pp.179-182
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• 2000

The dynamic softening behavior of type 430 ferritic stainless steel could be characterized by the hot torsion test in the temperature range of 900-110$0^{\circ}C$ and the strain rate range of 0.05-5/sec. It is found that the continuous dynamic recrystallization (CDRX) was a major dynamic softening mechanism. The effects of process variables strain ($\varepsilon$) stain rate($\varepsilon$)and temperature (T) on CDRX could be individually established from the analysis of flow stress curves and microstructure. The effect of CDRX individually established from the analysis of flow stress curves and microstructure. The effect of CDRX increased with increasing strain rate and decreasing temperature in continuous deformation. The multipass deformation processes were performed with 10 pass deformations. The CDRX effect occurred in multipass deformatioon. The grain refinement could be achieved from multipass deformation The grain refinement increased with increasing strain rate and decreasing temperature. Also the CDRX in multipass deformation was affected by interpass time and pass strain. The total strain was to be found key parameter to occur CDRX.

• International Journal of Concrete Structures and Materials
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• v.18 no.3E
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• pp.191-198
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• 2006

The objective of this study is to examine fracture characteristics of concrete at early ages, i.g. critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of effective-elastic crack model and cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By experimenting with various strengths and ages, load-crack mouth opening curves were obtained, and the results were analyzed by linear elastic fracture mechanics and FEM(finite element method). The results from the test and analysis showed that critical stress intensity factor and facture energy increased while critical crack-tip opening displacement decreased with concrete aging from 1 day to 28 days. Four parameters of bilinear softening curve from 1 day to 28 days were obtained from a numerical analysis. The obtained fracture parameters and bilinear softening curves at early ages from this study are to be used as a fracture criterion and an input data for the finite element analysis of concrete at early ages.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.861-864
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• 2008

This study was performanced to investigate the fractural and fatigue behavior of ultra-strength steel fiber reinforcement concrete. The tension softening diagram can describe the post-cracking behavior of concrete in tension. In this paper, Three points bending tests with a notch have been carried out to investigate tensile properties of the steel fiber reinforced concrete(SFRC) according to variation of the height. Poly-linear approximation method combined with FEM analysis is applied to the steel fiber reinforced concrete to determine the tension softening diagrams and also to certify the validity of the method. The simulated load-CMOD curves using the determined softening diagrams though the poly-linear approximation method completely agree with the measured ones.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.417-420
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• 2006

For a better understanding of the fracture behavior of concrete structures, knowledge of the post-cracking behavior of concrete material is essential. The tension softening diagram can describe the post-cracking behavior of concrete in tension. In this paper, Four points bending tests with a notch have been carried out to investigate tensile properties of the steel fiber reinforced concrete(SFRC). Poly-linear approximation method combined with FEM analysis is applied to the steel fiber reinforced concrete to determine the tension softening diagrams and also to certify the validity of the method. The simulated load-CMOD curves using the determined softening diagrams though the poly-linear approximation method completely agree with the measured ones.

• Geomechanics and Engineering
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• v.3 no.4
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• pp.323-337
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• 2011

Israel's coastal region consists, mainly, of Pleistocene and Holocene sands with varying degrees of calcareous cementation, known locally as "kurkar". Previous studies of these materials emphasized the difficulty in their geotechnical characterization, due to their extreme variability. Consequently, it is difficult to estimate construction stability, displacements and deformations on, or within these soils. It is suggested that SPT and Menard pressuremeter tests may be used to characterize the properties of these materials. Values of elastic modulus obtained from pressuremeter tests may be used for displacement analyses at different strain levels, while accounting for the geometric dimensions (length/diameter ratio) of the test probe. A relationship was obtained between pressuremeter modulus and SPT blow count, consistent with published data for footing settlements on granular soils. Cohesion values, for a known friction angle, are estimated, by comparing field pressuremeter curves to curves from numerical (finite element or finite difference) analyses. The material analyzed in the paper is shown to be strain-softening, with the initial cohesion degrading to zero on development of plastic shear strains.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.121-124
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• 2004

In this paper, a series of fracture tests are performed for the chemically prestressed steel fiber reinforced concrete (SFRC) manufactured with addition of expansive additives for the study of fracture behavior and characteristics. Cracking loads of the chemically prestressed SFRC are greater than that of normal concrete and those are also increased by increasing of steel fiber volume. Thus, it is necessary to obtain optimum steel fiber volume to induce chemically prestressing effectively to concrete members. The result of three-points bending tests shows that early-cracking resistance of the chemically prestressed SFRC is increased without increase of fracture energy. From the test, the tension softening curves are also obtained by poly-linear approximation method and simulated behaviors by using the determined tension softening curves agree with experimental results. And it is confirmed that cracking and ultimate behaviors of chemically prestressed SFRC can be predicted by using obtained fracture characteristics.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.58-66
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• 2002

The objective of this study is to examine the fracture characteristics of concrete at early ages such as critical stress intensity factor, critical crack-tip opening displacement, fracture energy, and bilinear softening curve based on the concepts of the effective-elastic crack model and the cohesive crack model. A wedge splitting test for Mode I was performed on cubic wedge specimens with a notch at the edge. By taking various strengths and ages, load-crack mouth opening displacement curves were obtained, and the results were analyzed by linear elastic fracture mechanics and the finite element method. The results from the test and analysis showed that critical stress intensity factor and fracture energy increased, and critical crack-tip opening displacement decreased with concrete ages from 1 day to 28 days. By numerical analysis four parameters of bilinear softening curve from 1 day to 28 days were obtained. The obtained fracture parameters and bilinear softening curves at early ages may be used as a fracture criterion and an input data for finite element analysis of concrete at early ages.