• Coupled systems mechanics
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• v.7 no.1
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• pp.27-42
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• 2018

Behavior of soil is usually described with continuum type of failure models such as Mohr-Coulomb or Drucker-Prager model. The main advantage of these models is in a relatively simple and efficient way of predicting the main tendencies and overall behavior of soil in failure analysis of interest for engineering practice. However, the main shortcoming of these models is that they are not able to capture post-peak behavior of soil nor the corresponding failure modes under extreme loading. In this paper we will significantly improve on this state-of-the-art. In particular, we propose the use of a discrete beam lattice model to provide a sharp prediction of inelastic response and failure mechanisms in coupled soil-foundation systems. In the discrete beam lattice model used in this paper, soil is meshed with one-dimensional Timoshenko beam finite elements with embedded strong discontinuities in axial and transverse direction capable of representing crack propagation in mode I and mode II. Mode I relates to crack opening, and mode II relates to crack sliding. To take into account material heterogeneities, we determine fracture limits for each Timoshenko beam with Gaussian random distribution. We compare the results obtained using the discrete beam lattice model against those obtained using the modified three-surface elasto-plastic cap model.

• Journal of Industrial Technology
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• v.19
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• pp.269-278
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• 1999

When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.1
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• pp.171-178
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• 2002

An effect is made in this study to deepen understanding of small punch(SP) creep testing which has been a round for about 10 years as a substitute for the conventional uniaxial creep testing. Even though considerable numbers of SP creep test program have been performed, most of the tests were aimed at measuring creep rupture lives only. Very flew studies showed interest on the meaning of what we were really measuring during the SP creep tests. In this paper meanings of the parameters measured during the SP creep testing, such as punch load and punch displacement rate are investigated using finite element analysis. It was shown that the measured parameters must represent the stress and strain rates of the material at the annular region located at about 0.65 mm from the center of the SP specimen. The material in this location would go through constant maximum stress and strain rate during the testing. Experimental verification is also discussed.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.2
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• pp.112-120
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• 1993

Variable thickness plates are commonly encountered in the majority of mechanical/structural components of industrial applications. And, as a result of the unsymmetry of the structure or the load and the anisoptropy of the materials, the cracks in engineering structures are generally subjected to combined stresses. In spite of considerable practical interest, however, a few fracture mechanics study on combined mode crack in a variable thickness plate have carried out. In this respect, combined mode 1/3 stress intensity factors $K_{1}$ and $K_{3}$ at the crack tip for a variable thickness plate were obtained by 3-dimensional finite element analysis. Variable thickness plates containing a central slant crack were chosen. the parameters used in this study were dimensionless crack length .lambda. crack slant angle .alpha, thickness ratio .betha. and width ratio .omega. Stress intensity factors were calculated by crack opening displacement(COD) and crack tearing displacement(CTD) method proposed by Ingraffea and Manu. The effect of thickness ratio .betha. on $K_{1}$ is relatively great in comparison to $K_{3}$.

• Journal of Welding and Joining
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• v.3 no.2
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• pp.52-63
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• 1985

Fillet welded joints, specially in ship structure, are well known the critical part where stress concentrate or crack initiates and grows. This paper is concerned with the study of the behavior of fatigue crack growth t the root and toe of load carrying cruciform fillet welded joints under three points bending by the determination of stress intensity factor from the J-Integral, using the Finite Element Method. The stress intensity factor was investigated in accordance to the variation of the weld size (H/Tp). weld penetration (a/W) and plate thickness (2a'/Tp). As mixed mode is occurred on account of shearing force under the three points bending, Stern's reciprocal theory is applied to confirm which mode is the major one. The main results may be summarized as follows 1) The calculation formula of the stress intensity factor at the both of root and toe of the joint was obtained to estimate the stress intensity factor in the arbitrary case. 2) The change of stress field around crack tip gives much influence on each other at the roof and toe as H/Tp decreases. 3) Mode I is a major mode under the three points bending.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.610-616
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• 1990

The fracture mechanics analysis of surface cracks in plates and cylindrical geometries is important in the integrity evaluation of flawed structural components. The objective of this paper is, thus, to numerically investigate an interaction effect of two surface cracks in plate and cylindrical geometries. The effect of crack spacing on the magnitude of the stress intensity factor(K) is investigated using the line-spring model. For the case of a finite plate under uniaxial loading, the effect of crack spacing on the K values is negligible. However, for the case of a cylinder under moderate internal pressure, a significant increase in K values is observed at the deepest point of the surface crack.

• Proceedings of the KSR Conference
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• 2004.10a
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• pp.982-987
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• 2004

Most design practices have not taken advantage of the advanced theories in the modern fracture mechanics and finite element analysis due to complexity of analysis as well as the large quantity of vaguely defined parameters in actual designs. This paper considers fatigue problems in bridge structures using effective analytical and design tools from the field of qualitative constraint reasoning. A set of software modules was developed for fatigue analysis ,and evaluation, which is easily applicable in engineering practices of bridge designers. The software modules integrate techniques in the field of knowledge representation and qualitative reasoning, into the conventional fatigue analysis. The techniques enable the use complex analysis formulations to tackle practical problems with uncertainties, and present the design outcome in two-dimensional design space. Appropriate engineering assumptions and judgments in carrying out these procedures, often the most difficult part for practicing engineers, can be partially produced by using qualitative reasoning to define the trends and ranges, interval constraint analysis to derive the controlling parameters, as well as design space to account for practical experience. This paper depicts a way of complex analysis to practical engineering designs with qualitative reasoning.

• International Journal of High-Rise Buildings
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• v.3 no.4
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• pp.243-254
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• 2014

In this study, a demolition analysis code using the adaptively shifted integration (ASI)-Gauss technique, which describes structural member fracture by shifting the numerical integration point to an appropriate position and simultaneously releasing the sectional forces in the element, is developed. The code was verified and validated by comparing the predicted results with those of several experiments. A demolition planning tool utilizing the concept of a key element index, which explicitly indicates the contribution of each structural column to the vertical load capacity of the structure, is also develped. Two methods of selecting specific columns to efficiently demolish the whole structure are demonstrated: selecting the columns from the largest index value and from the smallest index value. The demolition results are confirmed numerically by conducting collapse analyses using the ASI-Gauss technique. The numerical results suggest that to achieve a successful demolition, a group of columns with the largest key element index values should be selected when explosives are ignited in a simultaneous blast, whereas those with the smallest should be selected when explosives are ignited in a sequence, with a final blast set on a column with large index value.

• Structural Engineering and Mechanics
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• v.19 no.6
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• pp.639-652
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• 2005

In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axial and in-plane bending loads. In the fatigue test, the crack developments were monitored step by step using the alternating current potential drop (ACPD) technique. Using Paris' law, stress intensity factor, which is a fracture parameter to be frequently used by many designers to predict the integrity and residual life of tubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, a scheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stress intensity factor for the K-joint specimen has then been carried out. In the finite element analysis, J-integral method is used to estimate the stress intensity factors along the crack front. The numerical stress intensity factor results have been validated through comparing them with the experimental results. The comparison shows that the proposed numerical model can produce reasonably accurate stress intensity factor values. The effects of different crack shapes on the stress intensity factors have also been investigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numerical analysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be used for estimating the stress intensity factor values of cracked tubular K-joints for design purposes.

• Computers and Concrete
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• v.5 no.2
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• pp.117-134
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• 2008

An experimental and numerical research was conducted to gain a deeper insight on the structural behaviour of deep-beams with indirect supports and to assess the size effects in the ultimate state behaviour. The experimental campaign focused on the influence of the reinforcement tie distribution height on the compression check of the support region and on the benefits of using unbonded prestressing steel. Three reduced scale specimens were tested and used to validate the results obtained with a nonlinear finite element model. As a good agreement could be found between the numerical and the experimental results, the numerical model was then further used to perform simulations in large scale deep-beams, with dimensions similar to the ones to be adopted in a practical case. Two sources of size effects were identified from the simulation results. Both sources are related to the concrete quasi-brittle behaviour and are responsible for increasing failure brittleness with increasing structural size. While in the laboratory models failure occurred both in the experimental tests as well as in the numerical simulations after reinforcement yielding, the numerically analysed large scale models exhibited shear failures with reinforcement still operating in the elastic range.