• Nuclear Engineering and Technology
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• v.48 no.5
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• pp.1252-1263
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• 2016

This paper presents a numerical method to simulate ductile tearing in cracked components under high strain rates using finite element damage analysis. The strain rate dependence on tensile properties and multiaxial fracture strain is characterized by the model developed by Johnson and Cook. The damage model is then defined based on the ductility exhaustion concept using the strain rate dependent multiaxial fracture strain concept. The proposed model is applied to simulate previously published three cracked pipe bending test results under two different test speed conditions. Simulated results show overall good agreement with experimental results.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.137-142
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• 2001

In structural applications, brittle materials such as soda-lime glasses and ceramics are often subjected to multiaxial stress. Brittle materials with crack or damaged by foreign object impacts are abruptly fractured from cracks, because of their properities of very high strength and low fracture toughness. But in most cases, the residual strength has been derived from tests under uniaxial stress such as a 4-point bend test. The strengths under multiaxial stresses might be different from the strength. In comparable tests, the residual strength under biaxial stress state by the ball-on-ring test was greater than that under the uniaxial one by the 4-point bend test. In the case that crack having 90deg. to loading direction, the ratio of biaxial to uniaxial flexure strength was 1.12. At a different crack angle to loading direction when it was evaluated by the 4-point bend test, the residual strength was different and the ratio of 45deg. to 90deg. was 1.16.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.1341-1342
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• 2011

• Journal of the Korean Society for Precision Engineering
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• v.22 no.12 s.177
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• pp.149-155
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• 2005

The rotating components such as turbine rotors in service are generally subjected to multiaxial cyclic loading conditions. The prediction of fatigue lift for turbine rotor components under complex multiaxial loading conditions is very important to prevent the fatigue failures in service. In this paper, axial and torsional low cycle fatigue tests were preformed for 3.5NiCrMo steels serviced low pressure turbine rotor of nuclear power plant. Several methods to predict biaxial fatigue life such as Tresca, von Mises and Brown & Miller's critical plane approach were evaluated to correlate the experimental results for serviced NiCrMoV steel. The fracture mode and fatigue characteristics of NiCrMoV steel were discussed based on the results of fatigue tests performed under the axial and torsional test conditions. In particular, the Brown and Miller's critical plane approach was found to best correlate the experimental data with predictions being within a factor of 2.

• International Journal of Automotive Technology
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• v.6 no.3
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• pp.285-291
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• 2005

In this paper, the author proposes a fatigue damage parameter of spot welded joints under proportional loading. The proposed fatigue damage parameter is developed based on von Mises' equivalent stress and local structural stress at the edge of spot weld nugget. The structural stress at the edges of the weld nugget in each sheet is calculated using the forces and moments that are determined by finite element analysis. A structural equivalent stress is then calculated by von Mises' equivalent stress equation. The structural equivalent stresses are correlated to experimental fatigue life of the spot welded joints. The proposed parameter is evaluated with fatigue test data of spot welds subjected to multi axial and tensile-shear loads. Sheppard's parameter and Rupp and co-workers' parameter are also evaluated with the same test data to compare with the author's parameter. This proposed parameter presents a better correlation with experimental fatigue data than those of Sheppard's and Rupp and co-workers' parameter. The proposed parameter should be very effective for durability calculations during the early design phase since coarsely meshed finite element models can be employed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.932-938
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• 2002

In structural applications, brittle materials such as soda-lime glasses and ceramics are usually subjected to multiaxial stress state. Brittle materials with cracks or damage by foreign object impacts are apt to fracture abruptly from cracks, because of their properities of very high strength and low fracture toughness. But in most cases, the residual strength of structural members with damage has been tested under uniaxial stress condition such as the 4-point bend test. Depending upon the crack pattern developed, the strength under multiaxial stress state might be different from the one under uniaxial. A comparative study was carried out to investigate the influence of stress state on the residual strength evaluation. In comparable tests, the residual strength under biaxial stress state by the ball-on-ring test was greater than that under the uniaxial one by the 4-point bend test, when a small size indendation crack was introduced. In the case that crack having an angle of 90deg. to the applied stress direction, the ratio of biaxial to uniaxial flexure strength was about 1.12. The residual strength was different from crack angles to loading direction when it was evaluated by the 4-point bend test. The ratio of residual strength of 45deg. crack to 90deg. one was about 1.20. In the case of specimen cracked by a spherical impact, it was shown that an overall decrease in flexure strength with increasing impact velocity, and the critical impact velocity for formation of a radial and/or cone crack was about 30m/s. In those cases that relatively large cracks were developed as compared with the case of indented cracks, the ratio of residual strength under biaxial stress state to one uniaxial became small.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.5
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• pp.133-138
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• 2007

Surface pitting is a major failure mode for gears. The contact fatigue life analysis of transmission gear considering running-in process is presented in this paper. Surface roughness change of rolling test is used in a life analysis. Contact stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions; the subsurface stress field is obtained using rectangular patch solutions. Mesoscopic multiaxial fatigue criterion which can yield satisfactory results for non-proportional loading is then applied to predict fatigue damage. Suitable counting method and damage rule were used to calculate the fatigue life of random loading caused by rough surface. The life analysis considering running-in is in good agreement with the experimental results.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2004.10a
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• pp.180-183
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• 2004

Superplastic formability depends on flow parameters such as temperature, strain rate, strain and stress, microstructures. Usually, superplastic properties of materials are characterized with using a uni-axial tension testing. However, superplastic sheet is formed under mutiaxial loading condition in most forming practices. In the present study, superplastic characteristics of A15083 alloys were determined with using both a uni-axial and biaxial bulging tests. Specially, cone-type die was used to achieve constant strain rate under constant pressure condition. Even though constant strain rate under a certain pressure was achieved only approximately, a cone-type bulging test was found to be quite beneficial to get a multiaxial formability of superplastic materials.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.612-617
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• 2014

It is generally known that the automotive road wheel involves the non-proportional multiaxial loading condition, therefore the measuring dynamic stress and strain in driving state is very important to predict an endurance characteristic of the automotive road wheel. In this study, the ultimate driving test using F1 circuit with respect to 2 kinds of velocity conditions have been carried out in order to measure dynamic stress, strain of the wheel and acceleration of a vehicle. Based on the measured results, the characteristics of dynamic stress generation have been analyzed, and factors which have effect on the dynamic stress generation have been studied.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.2
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• pp.33-56
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• 2001

It is well known fact that all rocks exhibit brittle properties and time depends strain properties (creep). An understanding of the time dependent deformation behaviour of rocks is believed to be essential in the field of civil and tunnelling. The rock and concrete creep in various forms of loading conditions and physical environment are reviewed. A comparison of creep behaviour between rocks and concrete is provided, in order to bring two existing relatively independent methods of predicting creep strain closer together. It was felt that the physical process in the creep of rocks would be similar to the process in creep of concrete. Since experiments and observations have shown that non-elastic (creep) mechanical behaviour of all crystalline solids (i.e., concrete, rocks, ceramics and refractories) and single materials have a common base. Also a comparison of the results for the accepted methods of estimating creep in rocks and concrete under - multiaxial loading was attempted to extend the knowledge of deformational characteristics of these two materials.