• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2017.05a
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• pp.111-111
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• 2017

쇼트피닝 기술은 크게 피로강도 향상을 위한 쇼트피닝(shot peening), 재료의 청정 및 도장 품질 향상을 위한 쇼트블라스트(shot blast) 그리고 쇼트피닝 시 판재의 변형되는 성질을 이용한 핀포밍(peen forming) 등으로 구분할 수 있다. 그 중 본 연구에서는 해양산업 분야에서 널리 사용되는 회주철의 효과적인 내구성 향상을 위해 쇼트피닝 기술을 적용하였다. 그러나 쇼트피닝 기술 적용에 있어서 가장 중요한 것은 제품의 균일성, 정확성, 신뢰성을 확보하기 위해 쇼트피닝 강도를 제어하는 여러 가지 변수들에 대하여 최적 상태를 유지하는 것이다. 따라서 회주철에 대한 최적 쇼트피닝 분사조건 규명작업은 반드시 쇼트피닝 가공 전에 수반되어야만 한다. 그 일환으로 실험은 쇼트피닝 분사시간과 분사압력을 변수로 하여 회주철 표면에 적용하였으며, 기계적 특성 평가를 통해 최적의 쇼트피닝 조건을 규명하고자 하였다. 쇼트피닝 분사조건에 따른 회주철의 내구성을 평가하기 위해 캐비테이션 실험을 실시하였으며, 경도 측정, 횡단면 관찰 및 표면의 3D 현미경 관찰 등을 통해 기계적 특성을 분석하였다. 캐비테이션 실험은 ASTM G32 규정에 의거하여 천연해수 내 $30^{\circ}C$에서 $50{\mu}m$의 진폭으로 실시하였다. 실험 후에는 주사전자현미경으로 손상표면을 관찰하였으며, 손상 정도를 비교하기 위해 무게 감소량을 계측하여 상호 비교/분석하였다.

• Journal of the Korean Society for Railway
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• v.12 no.6
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• pp.895-901
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• 2009

Fatigue fracture of the welded joints of bogie frames is one of unsolved problems. To improve the fatigue strength of the welded joints, various techniques have been applied. In this study, we have investigated the effect of shot peening on the fatigue characteristics of SS400 welded specimens. The fatigue lives of four kinds of welded specimens were examined; welded, PWHT, shot peened, and shot peened after PWHT. The results of the fatigue tests show that the fatigue limit of the shot-peened specimens is higher than that of the welded specimens, and the PWHT specimens have a lower fatigue limit than the welded specimens. It was found that shot peening is a very effective method to improve the fatigue strength of SS400 welded joints.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.1119-1129
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• 2011

Shot-peening effects on the fatigue behavior of bearing steel were investigated under the high cyclic loading. Hourglass shape specimens were made of bearing steel(JIS-SUJ2) for rotary bending fatigue tests. Two kinds of treatments were performed : a heat treatment and a shot-peened surface treatment after the heat treatment. The fracture surfaces of specimens were classified into two types of fracture mode : the surface fracture mode induced by a surface defect and the internal fracture mode induced by a nonmetallic inclusion. Inclusion depth and shape affected considerably the fatigue life. Shot-peening treatment improved much the fatigue life of the bearing steel under low and high levels of cyclic loads. Probabilistic-stress-life (P-S-N) curves were suggested for the reliable fatigue life estimation of the improved bearing steel.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3227-3235
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• 1994

This paper deals with an evaluation of the residual stress due to shot peening induced in a carburized gear tooth and its application to the fatigue crack propagation problem. A practical method is proposed on the basis of the assumption that the residual stress is caused by the difference of volume expansion in the case and the core, and the influence of both the reduction of retained austenite and the strain due to shot peening are considered. The evaluated residual stress is close to the measured stress, though the surface stress is rather overestimated. The stress intensity factor is computed by the influence function method, and it is shown that the factor is decreased by the residual stress in shot peened gear tooth. The shot peening is fairly effective to the reduction of fatigue crack growth rate. The crack propagation is simulated and the resistance due to shot peening is quantitatively demonstrated and discussed.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.9
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• pp.61-67
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• 1997

Hardened layer and compressive residual stress created by carburized treatment effect on bending strength of gear massively. Also, shot peening treatment improves the strength of carburized gear as it does the hardness and residual stress of surface layer. In these days shot peening techniques are welcomed as one of physical improvement ways around the surface of materials. It is used widely because qualitative analysis of shot peening has become possible and surface treatment can be done with very little costs comparaed to other surface improvement methods. Therefore this study investigates the effect of shot peening in surface shape and bending fatigue strength after doing many kinds of shot peening treatments, then doing fatigue test and also explained characteristics of shot peening gear.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.12
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• pp.987-995
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• 2016

In this study, the effects of shot peening (SP) on the Vickers hardness of $ZrO_2$ were studied. The size of the shot balls were ${\phi}180{\mu}m$ and ${\phi}300{\mu}m$. The Vickers hardness was measured using an indentation load of 98 N and 294 N. The Vickers hardness was evaluated using Weibull statistical analysis. The scale parameters were significantly evident from the indentation load of 98 N and the shot ball of ${\phi}180 {\mu}m$. Generally, the shape parameters were also evident from the small short ball (180sp). Thus, it is shown that the introduction of a compressive residual stress by SP is an effective technique for increasing the mechanical properties of $ZrO_2$.

• Journal of Industrial Technology
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• v.26 no.A
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• pp.69-73
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• 2006

Mach peening treatment is one of the various kinds of techniques to improve the fatigue properties. The mach peening process gives high-level work hardening and compressive residual stress near the surface layer, improving the fatigue strength. In addition, this treatment reduces slip bands that initiate the fatigue cracks near the surface. During impingement, a plastic indentation surrounded by a plastic zone is formed. Mach peening treatment characteristic is less energy consumption and is an environmental friendly processing methods that is not accompanied by pollution. It is machining process that can prevent fatigue fracture beforehand in structure using already as well as process of production. The test results showed that fatigue crack propagation delay appeared by drilling type 43%, mach peening type 110%.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.04a
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• pp.697-703
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• 1996

Fatigue strength of high strengthsteels are variable with many different surface treatment. It is well known that residual compressive stress retard fatigue crack growth rate(or arrest crack). High strngth steels are manufactured by following process. Heat treatment, shot peening and chromium plating process. High strength steel(HRC40 or above) which are subjected to fatigue load and dynamic load, chromium plated parts shall be peened in accordance with requirements and baked after plating. The purpose of this paper is to compare and discuss the influence of surface treatment and hydrogen embrittlement on fatigue strength of high strength steel. Therefore, fatigue test was performed to investigate influence of surface treatment. The results shows that shot peening is very effect method in creasing fatigue life and after plating, baking process is essential to prevent hydogen failure. In this paper, the experimental investigation is made to clarify the influence of shot peening conditions and baking process on fatigue strength of high strength steel.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.65-70
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• 2007

Welding is the most commonly used method to produce bogie and carbody of Electrical Multiple Units(EMU), because it increases the strength and lowers the weight of EMU. Since bogies are constantly exposed to repeated reacting load during acceleration and deceleration, it is also true that crack normally occurs at welding parts. In this study, we have investigated the fatigue strength of SS400 on welded parts in order to find efficiency of treatment after welding by shot peening and Post-Weld heat treatment(PWHT) with butt welded specimens. The results of fatigue test indicate that the measurement of base material specimen is 236MPa, welded specimen is 132MPa and the specimen of PWHT is 107MPa approximately. We concluded that the measurement of welded specimen and PWHT is approximately 44 and 54 percents lower than the base material specimen, respectively. Another finding is that the peened specimen is approximately 23 and 61 percents higher than the base material specimen in terms of the fatigue in strength of specimens.