• Journal of Welding and Joining
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• 제10권1호
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• pp.43-51
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• 1992

The plastic zone formed around a notch tip is important in analyzing the fracture toughness of structures and particularly weld cracks existed in the weld HAZ (heat affected zone) which produces local plastic deformation at the crack tip. Therefore, in order to analyze the fracture toughness in weld HAZ, it is necessary to investigate the new fracture toughness parameter $K_{c}$ $^{*}$ and critical plastic strain energy $W_{p}$ $^{c}$ according to the shape and size of the plastic zone. 1) If the temperature corresponding to $K_{c}$ $^{*}$=130kg-m $m^{-3}$ 2/ is determined, transition temperature $T_{tr}$ the magnitude of plastic zone size, and heat input change depending on the fracture toughness. The blunted amounts of the parent and weld HAZ show mild linear variation until .delta.=0.4mm and then increase very steeply there after. 2) The relation between the plastic strain energy( $W^{p}$ ) and transition temperature( $T_{*}$tr) in parent metal is more sensitive than that of weld HAZ. However, the plastic strain energy depends on the transition temperature, and thus the yield stress, .sigma.$_{ys}$ becomes an important parameter for plastic strain energy. 3) The critical plastic strain energy( $W_{p}$ $^{c}$ ) absorbed by the plastic zone at the notch tip indicated in case of parent metal: 60J/mm, in case of heat input(20KJ/cm): 75J/mm, in case of heat input(30KJ/cm); 50J/mmJ/mm.

• 한국정밀공학회지
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• 제6권4호
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• pp.94-102
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• 1989

The effect of plastic strain on the surface integrity of mild steel (SS 41) was studied. This paper shows that the recrystallization technique is adequate to evaluate the plastic strain in a machined surface experimentally. The relations between the plastic strain and the machining conditions are quantitatively evaluated by using the recrystallization technique. The obtained results are summarized as follows. 1. The surface integrity of steel is considerably influenced by the amount of surface region deformation produced by changes in cutting conditions. 2. The plastic strain in machined surface produced by changes of the cutting conditions is evaluated by the recyrstallization technique. 3. The plastic strain increases with the increase of depth of cut and the decrease of rake angle. 4. When the cutting force is high and the rake angle is small, the value of maximum true strain reaches to high. 5. The maximum true strain is related to the cutting energy, and the values increase with the increase of the unit shear and total engergy in constant depth with the increase of the energy values.

• Journal of Welding and Joining
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• 제7권4호
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• pp.38-45
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• 1989

In this study, in order to evaluate the shape and the size of the plastic zone at the notch tip before stable crack growth, a newly developed technique for plastic strain measurement, that is, the recrystallization-etching technique was applied to observe the intense strain zone at the notch tip of weld HAZ. 1) The recrystallized specimens showed that the amount of the intense strain zone, more than 20% plastic zone, was quantitatively observed as the plane strain state during the growth of the plastic zone. 2) The behavior of plastic deformation at midsection are different for parent and weld HAZ. In addition, the micro crack initiation occurs at midsection, parent and weld HAZ when the crack opening displacement(COD) value is .delta.$_{t}$=0.4mm. 3) The plastic zone for parent proceeds in the forward direction at notch tip and for weld HAZ in the right and left direction at the notch tip. 4) The relation between plastic strain energy(Wp) and COD(.delta.$_{t}$) depended on yield stress, gradient and plastic strain size.ize.

• 한국생산제조학회지
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• 제9권6호
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• pp.111-117
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• 2000

The plastically deformed layer in a machined surface must be considered in precision machining process. Therefore the analysis of the machined surface, including the plastic deformation and strain distribution should be carried out quantitatively. The subsequent recrystallization technique was presented for analysis of the plastically deformed layer in the machined surface, and the technique was successfully applied to determine the plastic strain in the machined surface. This investigation is to evaluate the plastic strain in the distance 0.1mm from the machined surface, and in particular, to find the effect of shear angle, shear strain, cutting energy etc. on the plastic strain.

• Advances in materials Research
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• 제2권2호
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• pp.111-118
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• 2013

The changes of plastic plateau in the stress-strain curves of annealed polypropylene (PP) films during stretching under room temperature were followed and the corresponding melting properties and microstructure were characterized by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). It was found that during stretching the plastic plateau disappeared progressively with the increase of drawing ratio. At the same time, the endotherm plateau in DSC curves also disappeared progressively. The presence of the plastic plateau was attributed to the stretching of unstable crystalline part which was formed by tie chains around initial row-nucleated lamellae structure during annealing. During stretching, the unstable part was stretched and converted to bridges connecting separated lamellae. There was direct relationship between the disappearance of plastic plateau and pore formation.

• Nuclear Engineering and Technology
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• 제38권7호
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• pp.619-638
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• 2006

Low temperature irradiation can significantly harden metallic materials and often lead to strain localization and ductility loss in deformation. This paper provides a review on the radiation effects on the deformation of metallic materials, focusing on microscopic and macroscopic strain localization phenomena. The types of microscopic strain localization often observed in irradiated materials are dislocation channeling and deformation twinning, in which dislocation glides are evenly distributed and well confined in the narrow bands, usually a fraction of a micron wide. Dislocation channeling is a common strain localization mechanism observed virtually in all irradiated metallic materials with ductility, while deformation twinning is an alternative localization mechanism occurring only in low stacking fault energy(SFE) materials. In some high stacking fault energy materials where cross slip is easy, curved and widening channels can be formed depending on dose and stress state. Irradiation also prompts macroscopic strain localization (or plastic instability). It is shown that the plastic instability stress and true fracture stress are nearly independent of irradiation dose if there is no radiation-induced phase change or embrittlement. A newly proposed plastic Instability criterion is that the metals after irradiation show necking at yield when the yield stress exceeds the dose-independent plastic instability stress. There is no evident relationship between the microscopic and macroscopic strain localizations; which is explained by the long-range back-stress hardening. It is proposed that the microscopic strain localization is a generalized phenomenon occurring at high stress.

• 한국정밀공학회지
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• 제15권4호
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• pp.141-147
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• 1998

A plastically deformed layer in the precision machined surface affects in various forms the physical properties of machined components such as the fatigue strength, the dimensional instability, microcracks and the stress corrosion cracking. These physical properties, so called surface integrity, are very important for designing highly stressed and critically loaded components. Typical plastic strains in the precision machined surface are very difficult to measure, since they are located within a very short distance from the surface and they change very rapidly. A new way is suggested to determine the residual strain in plastically deformed materials by analyzing the plastically deformed layer after a subsequent recrystallization process. This investigation is to explore a new technique for measuring plastic strain in machining applications, and in particular, to and the effect of cutting parameters(rake angle, depth of cut, specific cutting energy), on the plastic strains and strain energy.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.169-174
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• 2001

Low cycle fatigue tests are performed on high strength low alloy steels that be developed for submarine material. The relation between absorbed plastic strain energy and numbers of cycle to failure is examined in order to predict the low cycle fatigue life of structural steels by using plastic strain energy method. The cyclic properties are determined by a least square fit techniques. The life predicted by the plastic strain energy method is found to coincide with experiment data and results obtained from the Coffin-Manson method. Also the cyclic behavior of structural steels is characterized by cyclic softening with increasing number of cycle at room temperature. Especially, low cycle fatigue characteristics and microstructural changes of structural steels are investigated according to changing tempering temperatures. In the case of PFS steels, the $\varepsilon$-Cu is formed in 550C of tempering temperature and enhances the low cycle fatigue properties.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.183-190
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• 2000

Effective range of Hydraulic Hammer Compaction was studied by numerical analysis instead of empirical method. Numerical analyses were carried out with commercial FEM code, ABAQUS, and verified by comparing the numerical results with field tests of Hydraulic Hammer Compaction. Most of material properties were evaluated by data from laboratory and in-situ tests. Vertical effective range was estimated by distribution curve of plastic strain energy dissipated through soil layers under dynamic load and these results were in good agreement with field tests. Based on verification, the effects of governing properties of Hydraulic Hammer Compaction such as number of hit can be determined by numerical analyses. In addition, vertical effective range can also be determined by Menard's empirical equation using the external work at converging time of plastic strain energy in numerical analysis. This implies that the minimum energy of Hydraulic Hammer Compaction for improvement can be determined by Menard's equation.

• 국제강구조저널
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• 제18권4호
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• pp.1107-1124
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• 2018

The structural behavior of reinforced concrete coupled shear wall structures is greatly influenced by the behavior of their coupling beams. This paper presents a process of the seismic analysis of reinforced concrete coupled shear wall-frame system linked by hysteretic dampers at each floor. The hysteretic dampers are located at the middle portion of the linked beams which most of the inelastic damage would be concentrated. This study concerned particularly with wall-frame structures that do not twist. The proposed method, which is based on the energy equilibrium method, offers an important design method by the result of increasing energy dissipation capacity and reducing damage to the wall's base. The optimum distribution of yield shear force coefficients is to evenly distribute the damage at dampers over the structural height based on the cumulative plastic deformation ratio of the dissipation device. Nonlinear dynamic analysis indicates that, with a proper set of damping parameters, the wall's dynamic responses can be well controlled. Finally, based on the total plastic strain energy and its trend through the height of the buildings, a prediction equation is suggested.