• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.313-330
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• 1993

The propagating crack problems under dynamic plane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems in orthortropic material, it is important to know the dynamic stress components and dynamic displacement components around the crack tip. Therefore the dynamic stress components of dynamic stress field and dynamic displacement components of dynamic displacement field in the crack tip of orthotropic material under the dynamic load and the steady state in crack propagation were derived. When the crack propagation speed approachs to zero, the dynamic stress component and dynamic displacement components derived in this study are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determinded by using the concept of crack closure closure energy with the dynamic stresses and represented according to physical properties of the orthotrophic material and crack speeds. The faster the crack velocity, the greater the stress value of stress components in crack tip. The stress value of the stress component of crack tip is greater when fiber direction coincides with the crack propagation than when fider direction is normal to the crack propagation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2220-2227
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• 2000

In this paper, dynamic photoelastic hybrid method is developed and its validity is certified. The dynamic photoelastic hybrid method can be used on the obtaining of dynamic stress intensity factors and dynamic stress components. The effect of crack length on the dynamic stress intensity factors is less than those on the static stress intensity factors. When structures are under the dynamic mixed mode load, dynamic stress intensity factor of mode I is almost produced. Dynamic loading device manufactured in this research can be used on the research of dynamic behavior when mechanical resonance is produced and when crack is propagated with the constant velocity.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.2
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• pp.331-341
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• 1993

The propagating crack problems under dynamic antiplane mode in orthotropic material is studied in this paper. To analyze the dynamic fracture problems by theoretical method or experimental method in orthotropic material, it is important to know the dynamic stress intensity factor in the vicinity of crack tip. Therefore the dynamic stress field and dynamic displacement field with dynamic stress intensity factor of orthotropic material in mode III were derived. When the crack propagation speed approachs to zero, the dynamic stress components and dynamic displacement components derived in this paper are identical to the those of static state. In addition, the relationships between dynamic stress intensity factor and dynamic energy release rate are determined by using the concept of crack closure energy with the dynamic stresses and dynamic displacements derived in this paper. Finally, the characteristics of crack propagation are studied with the properties of orthotropic material and crack speed. The variation of angle .alpha. between fiber direction and crack propagating direction and crack propagation speed fairly effect on stress component and displacement component in crack tip. The influence of crack propagation speed on the speed on the stress and displacement is greater in the case of .alpha.=90.deg. than in the case of .alpha.=0.deg. and the faster the crack propagation speed, the greater the stress value and displacement value.

• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.779-786
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• 2018

There have been previous attempts to observe the occurrence of dynamic ferritic transformation at temperatures even above $Ae_3$ in a low-carbon steel, and not only in steels, but recently also in titanium alloys. In this study, a new approach is proposed that involves treating true stress-true strain curves in uniaxial compression tests at various temperatures, and different strain rates in 0.1C-6Ni steel, which is a model alloy used to decelerate the kinetics of ferrite transformation from austenite. The initial flow stress up to peak stress was used to analyze the change in dynamic softening phenomena, such as dynamic recovery, dynamic recrystallization, and dynamic transformation. It is worth mentioning that for predicting the occurrence of dynamic transformation, flow stress before reaching peak stress is much more sensitive to the change in the dynamic softening rate due to dynamic transformation, compared to peak stress. It was found that the occurrence of dynamic ferritic transformation could be successfully obtained even at temperatures above $Ae_3$ once the deformation condition was satisfied. This deformation condition is a function of both the strain rate and the deformation temperature, which can be described as the Zener - Hollomon parameter. In addition, the driving force of dynamic ferritic transformation might be much less than that of the dynamic recrystallization of austenite at a given deformation condition. By applying this technique, it is possible to predict the occurrence of dynamic transformation more sensitively compared with the previous analysis method using peak stress during deformation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.381-386
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• 1993

This paper describes the dynamic fracture behavior of brittle materials under impact loading by using INSAMCR program with instrumented charpy test machine. To calculate the Dynamic Stress Intensity Factor The finite element analysis methods program, INSAMCR, was used. Dynamic fracture characteristic was researched to verify a relationship between Dynamic Stress Intensity Factor and crack tip propagation velocity in WC-6%Co. The relationship between Dynamic Stress Intensity Factor and crack tip velocity revealed typical .GAMMA. shape. INSAMCR was run to verify experimental results in WC-6%Co and shows a good coincidence.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.304-309
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• 2000

Strain gage method is used to evaluate the mode I dynamic stress intensity factor of marging steel(18Ni) and titanium alloy(Ti-6A1-4V). To decide the best strain gage position on specimen, static fracture toughness test was performed. Then instrumented charpy impact test and dynamic tensile test was performed by using strain gage method for evlauating dynamic stress intensity factor. Strain gage signals on the crack tip region are used to calculate the stress intensity factors. It is found that strain gage method is more useful than method by using load which is obtained from impact tup to assess dynamic characteristics such as dynamic stress intensity factor.

• 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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.8 s.179
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• pp.2007-2014
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• 2000

It has been reported that the dynamic stress intensity factor for a propagating crack is increasing or decreasing according to the increasement of the crack propagating velocity. It is confirmed in this study that the increasement or decreasement of stress intensity factor with crack growing velocity is accused by loading condition. When the crack propagates under a constant displacement along upper and lower boundary in finite plate, the dynamic stress intensity factor decreases according to the increasement of the propagating crack velocity. When the crack propagates under a constant stress along upper and lower boundary in finite plate, the dynamic stress intensity factor increases according to the increasement of the propagating crack velocity. The increasement or decreasement of stress intensity factor with crack growing velocity is greater in a fast crack propagation velocity than in a slow one.

• Geomechanics and Engineering
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• v.16 no.2
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• pp.113-124
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• 2018

Under repeated loading, the residual stresses within the subgrade and subsoil can accelerate the deformation of the road structures. In this paper, a series of laboratory cyclic loading model tests and small-scale model tests were conducted to investigate the dynamic stress response within soils under different loading conditions. The experimental results showed that a dynamic stress accumulation effect occurred if the soil showed cumulative deformation: (1) the residual stress increased and accumulated with an increasing number of loading cycles, and (2) the residual stress was superimposed on the stress response of the subsequent loading cycles, inducing a greater peak stress response. There are two conditions that must be met for the dynamic stress accumulation effect to occur. A threshold state exists only if the external load exceeds the cyclic threshold stress. Then, the stress accumulation effect occurs. A higher loading frequency results in a higher rate of increase for the residual stress. In addition to the superposition of the increasing residual stress, soil densification might contribute to the increasing peak stress during cyclic loading. An increase in soil stiffness and a decrease in dissipative energy induce a greater stress transmission within the material.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.7
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• pp.805-813
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• 2011

The dynamic stress of the diesel engine block is analyzed by using flexible-body dynamic analysis. Multiple loadings including the pressure load due to gas combustion, thermal load, and dynamic load are considered. Thermal load is assumed constant, however, pressure load and dynamic load are treated as time dependent. The present work is focused on the dynamic stress analysis, especially on finding critical points of the engine block. The analysis model includes four parts - engine block, generator, bed, and mounts. On the other hand, crank shaft, pistons, and main bearings are excluded from the model. However, their dynamic effects are applied by dynamic forces, obtained in the separate analysis. Dynamic stress is found by using flexible body dynamic analysis, and compared to the measured data.