• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.5
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• pp.1-7
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• 2008

A study of new materials that are light-weight, high in strength has become vital to the machinery of auto industries. But then, there are a lot of problems with developing such materials that require expensive tools, and a great deal of time and effort. Therefore, the improvement of fatigue strength and fatigue life are mainly focused on by adopting residual stress. And Influence of corrosive condition for corrosion fatigue crack was investigated, after immersing in 3.5%NaCl, $10%HNO_3$+3.5%HF, $6%FeCl_3$. The immersion period was performed for 365days. The compressive residual stress was imposed on the surface according to each shot velocity based on shot peening, which is the method of improving fatigue life and strength. Fatigue life shows more improvement in the shot peened material than in the un peened material in corrosion conditions. The threshold stress intensity factor range was decreased in corrosion environments over ambient. Compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation. The fatigue crack growth rate of the Shot-peened material was lower than that of the un peened material. Also m, fatigue crack growth exponent and number of cycle of the shot peened material was higher than that of the un peened material. That is concluded from effect of da/dN.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.4
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• pp.67-72
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, crack growth tests are conducted on spring steel and shot peened specimens. And then the residual stresses and fractographs are examined. The crack growth equation that can describe the whole crack growth behavior is used to evaluate the experiment results. The results show that fatigue crack glows slowly in the shot peened specimen than in the unpeened. And in the case of the 2-step shot peened specimen the initial stress intensity factor range and the fracture toughness is higher than the unpeened specimen due to the compressive residual stress. Fractographs show that the compressive residual stress of the surface suppress the fatigue crack opening and consequently slow crack growth rates.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.325-330
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• 2004

Recently, the request for the high strength of material is more and more increased in the area of industrial environment and machinery. To accomplish the high strength of materials, carbonizing treatment, nitrifying treatment, shot-peening method are representatively applied, however, shot-peening method is generally used among the surface processes. Shot peening is a cold working process used to impact Compressive residual stressed in the exposed surface layers. Benefits due to shot peening are increase in resistance to fatigue, stress corrosion cracking, fretting, galling, erosion and closing of pores. In this study, the influence of shot peening on the corrosion was investigated on spring steel immersed in 3.5% NaCl. The immersion test as performed on the two kinds of specimens. Corrsion potential, polarization curve, residual stress and etc, were investigated from experiment results. From test result the effect of shot peening on the corrosion was evaluated. The important results of the experimental study on the effects of shot peened on the environment corrosion of spring steels are as follows; In case of corrosion potential, shot peened specimen shows more activated negative direction as compared with parent mental. Surface of specimen, which is treated with the shot peened is placed as more activated state against inner base metal. It can cause t도 anti-corrosion effect on the base metal.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.184-189
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• 2004

Shot peening process is used as one of the various kinds of techniques to improve the fatigue properties. However, to obtain fatigue properties of metal materials, many efforts and time are needed. Because the fatigue life of shot peened metals increases highly. In this paper, fatigue properties of shot peened Al 7075-T6 are estimated using the fundamental of accelerated life test to reduce the experimental. Experimental results show that the estimated life data almost agree with actual rotary bending fatigue test data within 7% error.

• Transactions of the Korean Society of Automotive Engineers
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• v.13 no.1
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• pp.159-165
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• 2005

Shot peening can be defined as the process of work hardening of the surface of components by means of propelled stream of spherical shot. Benefits due to shot peening are increase in resistance to fatigue, stress corrosion cracking, fretting, galling, erosion and closing of pores. In this study, the influence of shot peening on the corrosion was investigated on spring steel immersed in $3.5\%\;NaCl$. The immersion test was performed on the two kinds of specimens. Corrosion potential, polarization curve, residual stress and etc. were investigated from experimental results. From test results, the effect of shot peening on the corrosion was evaluated. The important results of the experimental study on the effects of shot peened spring steels on the environment corrosion are as follows; In case of corrosion potential, shot peened specimen shows more activated negative direction as compared with parent metal. Surface of specimen, which is treated with the shot peened, is placed as more activated state against inner base metal. It can cause the anti-corrosion effect on the base metal.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.322-327
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• 1997

This paper investigates the effects of shot peening on mechanical properties of SAE 9254, which is a spring steel used for the suspension system of automobiles. Rotary Bending Fatigue test is accomplished and the results are summarized as fellows : 1. The tensile strength and the hardness do not change so much. 2. The layer of highly residual stress is obtained by multi-stage shot peening. 3. The fatigue strength seems to be improved by residual stress. 4. The fatigue strength of un-peened and multistage shot peened material are 425 MPa and 756 MPa, respectively.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.12 s.255
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• pp.1534-1542
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• 2006

In this paper, the concept of accelerated life test, which is a popular research field nowadays, is applied to the shot peened material. To predict the efficient and exact room temperature fatigue characteristics from the high temperature fatigue data, the adequate accelerated model is investigated. Ono type rotary bending fatigue tester and high temperature chamber were used for the experiment. Room temperature fatigue lives were predicted by applying accelerated models and doing reliability evaluation. Room temperature fatigue tests were accomplished to check the effectiveness of predicted data and the adequate accelerated life test models were presented by considering errors. Experimental result using Arrhenius model, fatigue limit obtain almost 5.45% of error, inverse power law has about 1.36% of error, so we found that inverse power law is applied well to temperature-life relative of shot peened material.

• Corrosion Science and Technology
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• v.12 no.5
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• pp.239-244
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• 2013

Marine equipment exposed to harsh environments requires not only excellent corrosion resistance but also improvement of physical characteristics against natural material degradation. With growing interests in ocean energy resources, the higher reliability for marine equipment has become more important in terms of material characteristics. ALBC3 alloy represents excellent corrosion resistance and is widely used in corrosive environments. However, cavitation damage occurs frequently due to its poor durability in high flow rate of marine environment. In this research, shot peening technology was employed as a surface modification with shot peening stand-off distance to mitigate cavitation damage. The effects of shot peening on extent of cavitation damage and weight loss were evaluated for both shot peened and non-peened specimens. The results revealed that the application of shot peeing decreased cavitation damage for all experimental conditions in comparison with the non-peened specimens. The optimum stand-off distance was determined to be 10 cm, since more than 35 % of cavitation damage reduction was observed.

• 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.

• Journal of the Korean institute of surface engineering
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• v.36 no.6
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• pp.475-479
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, tests are conducted on spring steel and shot peened specimens. Various tests are accomplished to evaluate mechanical properties influenced by shot peening process, and fatigue tests are also performed to evaluate the improvement of fatigue strength. And then the residual stresses are examined. The mechanical properties of material did not change so much by shot peening. However, the fatigue strength of notched specimen remarkably increased. In the case of 1-step shot peening, fatigue strength increased by about 20％ than unpeened specimen. Especially, in the case of 2-step shot peening, fatigue strength increased by about 40％, because the residual compressive stress at surface was higher than that of 1-step shot peened specimen. The fatigue strength and life are closely related to the value and position of maximum compressive residual stress by shot peening.