• 한국안전학회지
• /
• 제19권4호
• /
• pp.8-13
• /
• 2004

The purpose of this paper is to investigate the welding residual stress distribution according to the constraint or non-constraint welding condition with titanium commonly using power station, aircraft, and ship. The measuring method of the residual stress was applied stress release rating method with strain gages and a potable strain meter. The x direction residual stress generally showed the tensile residual stress in case of res03int welding. On the other hand, the x direction residual stress under non-restraint welding were changed tensile stress into compressive stress on 15mm away from welding bead center. Also, the y direction residual stress generally showed the tensile residual stress in case of non-restraint welding and the y direction residual stress under restraint welding were changed tensile stress into compressive stress about 60mm away from welding bead center.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.247-254
• /
• 2003

The lightness of components required in automobile and machinery industry is requiring high strength of components. In particular manufacturing process and new materials development for solving the fatigue fracture problem attendant upon high strength of suspension of automobile are actively advanced. In this paper, the effect of compressive residual stress of spring steel(JISG SUP-9) by shot-peening on fatigue crack growth characteristics in high temperatures($100^{\circ}$, $150^{\circ}$, $180^{\circ}$) was investigated with considering fracture mechanics. So, we can obtain followings. (1)Compressive residual stress decreases in high temperature, that is, with increasing temperature. (2)The effect of compressive residual stress on fatigue crack growth behavior in high temperature increases below ${\Delta}K=17{\sim}19MPa$ (3)It was investigated by SEM that the constraint of compress residual stress for plastic zone of fatigue crack tip was decreased in high temperature as compared with room temperature.

• 대한기계학회논문집A
• /
• 제30권5호
• /
• pp.528-532
• /
• 2006

In the aerospace industry, Cold expansion has been used the most important method that is retarded of crack initiation from fastener hole surface. Cold expansion method(CEM) is that a oversized tapered mandrel goes through the hole in order to develop a compressive residual stress as the passing of the mandrel around the hole. Therefore, because of characteristic of mandrel inserting, Residual Stress Distributions (RSD) are differently generated form Entry, Mid and Exit position of the plate. Also, it is respected that RSD are changed as distances between holes. In this paper, It is performed a FE analysis of RSD by CEM and it is respectively shown RSD in the Entry, Mid and Exit position. It is compared residual stress results form the cold expansion in these two cases: the concurrent CEM and the sequential CEM. From this research, it has been found that compressive residual stress of Entry position is lower than other positions. Also, the concurrent CE of adjacent holes leads to much higher compressive residual stress than the sequential CE. In addition, in the sequential CE case, a compressive RSD of 1 step's hole around is lower than compressive RSD of 2 step's hole around.

• 대한기계학회논문집A
• /
• 제35권11호
• /
• pp.1369-1375
• /
• 2011

쇼트피닝 공정은 쇼트볼이 소재에 충돌을 일으킬 때 생기는 압축잔류응력에 의해 소재의 피로 강도를 향상 시키는데 그 목적이 있다. 본 연구는 변형률 속도 민감도 변화가 압축잔류응력에 미치는 영향을 분석하기 위해서 수행되었다. 본 연구자는 변형률 속도 민감도의 영향을 고려한 쇼트피닝 다중 충돌을 ABAQUS 6.9-1 를 사용하여 모사하였다. 사용된 소재는 AISI 4340 강종이다. 본 연구자는 변형률 속도 민감성이 높은 재료와 낮은 재료를 비교하였다. 결과적으로 변형률 속도 민감성이 증가하면 압축 잔류응력은 감소하였다. 또한 경도가 낮은 소재의 압축잔류응력이 경도가 높은 소재보다 더 크게 발생 하였다.

• 한국안전학회지
• /
• 제19권4호
• /
• pp.20-24
• /
• 2004

Antifatigue failure technology take an important the part of current industries. Currently, the shot peening is used for removing the defect from the surface of steel and improving the fatigue strength on surface. Therefore in this paper the effect of compressive residual stress by shot peening on fatigue crack growth characteristics in stress ratio(R=0.1, 0.3, 0.6)was investigated with considering fracture mechanics. There is difference between shot peening specimen and unpeening specimen. Fatigue crack growth rate of shot peening specimen was lower than that of unpeening specimen. Fatigue lift shows more improvement in the shot peening material than in the unpeening material. And compressive residual stress of surface on the shot peening processed operate resistance force of fatigue crack propagation. That is the constrained force about plasticity deformation was strengthened by resultant stress, which resulted from plasticity deformation and compressive residual stress in the process of fatigue crack propagation.

• 대한기계학회논문집A
• /
• 제30권9호
• /
• pp.1110-1115
• /
• 2006

Cold expansion of fastener holes has been successfully used for many years to impart beneficial compressive residual stresses. Beneficial compressive residual stress of fastener hole that has been cold expanded before is reduced by using of materials for a long time. As a result, fatigue life of material is reduced. So, compressive residual stresses of material have to regenerate by re-cold expansion method. In this paper, it was carried out a finite element analysis about variation of residual stress due to tensile stress and residual stress distribution that was regenerated by re-cold expansion method in the fastener hole. Here, a diversity tensile stress was used. Also, it was performed a finite element analysis according to cold expansion rate of re cold expansion in order to obtain a beneficial compressive residual stress.

• 대한기계학회논문집
• /
• 제15권2호
• /
• pp.693-702
• /
• 1991

The existence of residual stress in the circumferential butt welded pipes is one of the most important problems concerning stress corrosion cracking in service. In this paper, the residual stress distributions in three kinds of circumferential butt welded pipes were measured by the hole drilling strain gage method and calculation using finite element method is performed and its results are compared with the experiments. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed rom compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self restraint bending force in the pipe welding.

• 한국압력기기공학회 논문집
• /
• 제17권2호
• /
• pp.145-156
• /
• 2021

Ultrasonic Nanocrystal Surface Modification (UNSM) is a peening technology that generates elastic-plastic deformation on the material surface to which a static load of a air compressor and a dynamic load of ultrasonic vibration energy are applied by striking the material surface with a strike pin. In the UNSM-treated material, the structure of the surface layer is modified into a nano-crystal structure and compressive residual stress occurs. When UNSM is applied to welds in a reactor coolant system where PWSCC can occur, it has the effect of relieving tensile residual stress in the weld and thus suppressing crack initiation and propagation. In order to quantitatively evaluate the compressive residual stress generated by UNSM, many finite element studies have been conducted. In existing studies, single-path UNSM or UNSM in a limited area has been simulated due to excessive computing time and analysis convergence problems. However, it is difficult to accurately calculate the compressive residual stress generated by the actual UNSM under these limited conditions. Therefore, in this study, a minimum finite element peening analysis area that can reliably calculate the compressive residual stress is proposed. To confirm the validity of the proposed analysis area, the compressive residual stress obtained from the experiment are compared with finite element analysis results.

• 한국정밀공학회지
• /
• 제8권1호
• /
• pp.41-49
• /
• 1991

A knowledge of the resdual stress distribution at circumferential weldments can normally increase the accuracy of a fracture assessment in pipe line. In this paper, we present the measurements about the residual stress distributions at three kinds of circumferential butt welded pipes using the holl drilling strain gage method. By this experiment, we have obtined the following characteristics. At the inner surface of the pipe region near the center line of welding is under high tensile residual stress. However, as the distance from the center line of welding increases, the tensile component decreases and finally becomes compressive residual stress at region far away from the center line of welding. The longitudinal residual stress at the outer surface is compressive regardless of the diameter of pipe and the circumferential stress is changed from compressive to tensile as pipe diameter increases. The results also demonstrate that the residual stress is mainly caused by self-restraint bending force in the pipe welding.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2003년도 추계학술대회 논문집
• /
• pp.138-144
• /
• 2003

Rencentely, the request for the light weight is more incresed in the area of industrial environment and machinery and consistent effort is needed to accomplish high strength of material for the direction of light weight. we got the following characteristic from crack growth test carried out in the range of stress ration of 0.1, 0.3 and 0.6 by means of opening mode displacement. At the content stress ratio, the threshold stress intensity factor crack range ${\Delta}K_{th}$in the early stage of fatigue crack growth (Region I) and dtress intensity factor range ${\Delta}K$ in the stable of fatigue crack growth (Region II) with an increase in ${\Delta}K$. Fatigue life shows more improvement in the Shot-peened material than in the Un-peening material. And compressive residual stress of surface on the Shot peening processed operate resistance force of fatigue. So we can obtain fallowings. (1) The fatigue crack growth rate on stage II is conspicuous with the size of compressive residual stress and is depend on Paris equation. (2) Although the maxium compressive residual stress is deeply and widely formed from surface, fatigue life does not improve than when maxium compressive residual stress is formed in surface. (3) The threshold stress intensity factor range is increased with increasing compressive residual stress.