• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.38 no.7
• /
• pp.809-815
• /
• 2014

The induction heating bending process, which has been recently applied to nuclear piping, can generate residual stresses due to thermomechanical mechanism during the process. This residual stress is one of the crack driving forces that have important effects on crack initiation and propagation. However, previous studies have focused only on geometric shape variations such as the change in thickness and ovality. Moreover, very few studies are available on the effects of process variables on residual stresses. This study investigated the effects of process variables on the residual stress distributions of induction heating bended austenitic stainless steel (316 series) piping using parametric finite element analysis. The results indicated that the heat generation rate and feed velocity have significant effects on the residual stresses whereas the moment and bending angle have insignificant effects.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1997.05b
• /
• pp.110-117
• /
• 1997

Alloy 690 제1열 시제 전열관을 U 굽힘 가공할 시 전열관에 도입된 표면 잔류응력 및 굽힘 단면에서 치수변화 (벽두께, 진원도)를 위치별로 측정하여 평가하였다. 외측호(extrados)의 표면 잔류응력은 $\psi$=0$^{\circ}$에서 축 방향 응력이 -319 MPa (압축)로 가장 높았으며, 내측호(intrados)는 $\psi$=0$^{\circ}$, 160$^{\circ}$ 위치인 천이영역 부관에서 응력 변화가 크게 되는 경향을 보였다 측면(flank)은 인장 잔류응력으로 $\psi$=90$^{\circ}$(apex)에서 최대 190 MPa 로 축방향 응력으로 나타났다. 잔류응력치는 벽두께 보다는 진원도 변화와 일치되어 나타났으며, 시제 전열관의 벽두께 및 진원도는 ASTM의 치수 허용치 내에 포함되는 것으로 평가되었다. 잔류응력 측정은 스트레인 게이지를 이용한 구멍뚫기 방법 (Hole-Drilling Method)을 사용하였다.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.4
• /
• pp.761-768
• /
• 1990

본 연구에서는 4-점 굽힘시험 장치를 이용하여 구멍의 표면에서 응력구배를 발생시켰을 때 (구멍의 깊이 방향으로는 응력구배가 없음), 구멍을 뚫기전 표면의 응 력구배를 고려하여 산정한 하중상태와 구멍을 뚫은 후 이완되는 잔류응력을 비교하였 다. 또한 잔류응력 측정시 구멍의 진원도에 대하여 실험적으로 연구하였으며, 구멍 직경의 측정오차가 잔류응력 측정에 미치는 영향을 분석하였다. 연구결과 4-점 굽힘 시험시 하중상태는 응력구배를 고려하여 계측되어야 하며, 응력구배장에서의 잔류응력 을 로젯트 게이지 중심에 존재하는 균일응력으로 나타낼 수 있다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.3
• /
• pp.341-346
• /
• 2010

The effect of specimen geometry on the bending and tensile strengths of dissimilar joints ($\beta-Si_3N_4/S45C$) with copper interlayers was evaluated. The average bending strength of specimens with circular cross sections was higher than that of specimens with rectangular cross sections. The crack initiation stress ($\sigma_i$) was successfully determined by the acoustic emission (AE) method and was approximately 60~80% of the bending strength. The residual stresses near the interfaces on the ceramic side were measured by X-ray diffraction before conducting the bending test. The bending strength and the crack initiation stress decreased with an increase in the residual stresses. The effect of the bending strain component was evaluated by the tensile testing; the tensile strength decreased with an increase in the bending strain component and was approximately 80% of the bending strength.

• Composites Research
• /
• v.22 no.2
• /
• pp.24-29
• /
• 2009

This study aims to investigate the residual strength of sandwich composites with Al honeycomb core and carbon fiber face sheets after the quasi-static indentation damage by the experimental investigation. The 3-point bending test and the edge-wise compressive strength test were used to find the mechanical properties, and the quasi-static point load was applied to introduce the simulated damage on the specimen. The damaged specimens were finally assessed by the 3-point bending test and the compressive strength test. The investigation results revealed the residual strength of the damaged specimens due to the quasi-static indentation. The both test results showed that the residual strength of the damaged specimen was decreased according to increases of the damaged depth.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.9
• /
• pp.1059-1064
• /
• 2012

In this study, tensile tests were performed on specimens that simulated the cold-bending and heat-treatment of pipe bends to understand the mechanical properties of pipe bends manufactured by cold-bending followed by heat-treatment for relieving residual stress. The strength and ductility of cold-worked materials were respectively found to be higher and lower than those of the parent material although heat-treatment was carried out to relieve residual stress. In addition, the increase in strength and decrease in ductility were proportional to the applied strain levels for cold-working. It was thus inferred that the intrados and extrados regions of pipe bends that were cold-bended and heat-treated show higher strength and lower ductility compared to the parent straight pipe and that the mechanical properties at the crown region are nearly the same as those of the parent straight pipe.

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

• Composites Research
• /
• v.27 no.2
• /
• pp.77-81
• /
• 2014

In this study, it was performed damage assessment and repair of small scale aircraft adopted on composite. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole were compared with the results of no damaged specimen test. In addition, The damaged composite structure was repaired using external patch repair method after removing damaged area. After that, this study presents comparison results of the experimental investigation between the damaged and the repaired specimen. It was found that the bending strength of repaired specimen was recovered up to 95% of undamaged specimen.

• Journal of Ocean Engineering and Technology
• /
• v.9 no.2
• /
• pp.133-140
• /
• 1995

This paper deals with the residual strength characteristics of composite materials under the environment of high temperature and humidity. Two types of GFRP, one with unidirection and randomly oriented, are used to investigate the features of moisture absorption and the residual strength. The results show that, when exposed longterms in high temperature and humidity, the randomly oriented composites is more stable than the unidirection one.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.23 no.7 s.166
• /
• pp.1085-1093
• /
• 1999

Thickness effects of coupling agent on residual bending stress were investigated in $Polyimide/SiO_2$ joints during thermal cycling. Thickness and peel strength of $\gamma$-APS coupling agent were measured and correlated with solution concentration and residual bending stress. The variation of residual bending stress with temperature was also measured for various thicknesses of the coupling agent. Finite element results were compared with experimental data for residual bending stress in $Polyimide/SiO_2$ joints.