• Transactions of the Korean Society of Automotive Engineers
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• v.12 no.1
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• pp.196-202
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• 2004

The development of new materials with light weight and high strength has become vital to the machinery, aircraft and auto industries. However, 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 adopting residual stress(in this thesis). The compressive residual stress was imposed on the surface according to each shot velocity(57, 70, 83, 96 m/sec) based on Shot-peening, which is the method of improving fatigue life and strength. By using the methods mentioned above, the following conclusions have been drawn. 1. The fatigue crack growth rate(da/dN) of the Shot-peened material was lower than that of the Un-peened material. And in stage I, ΔKth, the threshold stress intensity factor, of the shot-peen processed material is high in critical parts unlike 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. 2. Fatigue life shows more improvement in the Shot-peened material than in the Un-peened material. And compressive residual stress of surface on the Shot-peen processed operate resistance force of fatigue crack propagation.

• Journal of the Korean institute of surface engineering
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• v.37 no.6
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• pp.350-359
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• 2004

Stress corrosion cracking(SCC) characteristics of shot-peened stainless steel containing Ti (0.09 wt%-0.92 wt%) fabricated by the vacuum furnace were investigated using SCC tester and potentiostat. The homogenization and the sensitization treatment were carried out at $1050^{\circ}C$ for 1hr and $650^{\circ}C$ for 5 hr. The samples for SCC were shot-peened using $\Phi$0.6 mm steel ball for 4 min and 10 min. Intergranular and pitting corrosion characteristics were investigated by using EPR and CPPT. SCC test was carried out at the condition of$ 288^{\circ}C$, 90 kgf pressure, water with 8 ppm dissolved oxygen, and $8.3xl0^{-7}$/s strain rate. After the corrosion and see test, the surface of the tested specimen was observed by the optical microscope, TEM and SEM. Specimen with Ti/C ratio of 6.14 showed high tensile strength at the sensitization treatment. The tensile strength decreased with the increase of the Ti/C ratio. Pitting and intergranular corrosion resistance increased with the increase of Ti/C ratio. Stress corrosion cracking strength of shot-peened specimen was higher than that of non shot- peened specimen. Stress corrosion cracking strength decreased with the increase of the Ti/C ratio.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.677-682
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• 2002

Break-in is an intentional treatment to enhance the performance life of machinery parts and to maintain static friction behavior. Most studies on break-in have concerned only about surface conditions such as roughness or film formation. But the exact mechanism of break-in has not been found yet. Friction, scuffing behavior and wear of AISI 1045 were studied in relation to break-in and residual stress. The cylinder-on-disk type tribometer was used with the line-contact geometry. Scuffing tests were carried out using a constant load of 730N. In the break-in procedure the step load was applied from 100N to 200N. In this experiment, it was found that the break-in helps compressive residual stress to be formed well enough to enhance the scuffing life during the scuffing test. Specimens that had high compressive residual stress induced by shot-peening show better wear resistance than those were not shot-peened. Results of scuffing test, break-in procedure and wear amount in relation to residual stress have been discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.193-193
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• 2000

박막 내의 잔류 응력은 막의 기계적 전기적 물성을 변화시키는 등 박막에 많은 영향을 끼치는 것으로 알려져 있다. 이러한 응력은 박막의 증착 공정중 여러 가지 증착 조건에 의해서 변화하게 되는데, 특히 스퍼터링 시스템의 경우에는 증착 압력과 사용하는 가스, 인가되는 전력 등 기본적인 증착조건들에 상당한 영향을 받는다. 이러한 영향은 금속 박막의 경우 상당히 잘 알려져 있다. 또한 반도체 공정에서 금속화 과정중 금속 전극의 단락등을 막기 위해 많은 연구가 진행되어 왔다. 본 논문에서는 고주파 마그네트론 스퍼터링 시스템을 사용하여 산화 아연(ZnO)을 증착하고 여러 공정 변수들에 따른 응력의 변화를 관찰하였다. 실험에서 ZnO 타겟을 사용하였으며, 작동 가스로는 아르곤과 산소를 사용하였다. 증착한 박막들은 모두 압축 응력을 보였으며, 박막의 응력에 가장 큰 영향을 미치는 요소들은 압력, 산소와 아르곤의 비, 기판과 타겟과의 거리 등이었는데, 인가 전력에는 거의 영향을 받지 않았다. 일반적으로 스퍼터링 시스템에서의 압축응력은 atomic peening에 의해서 형성되는데, 박막을 두드리는 높은 에너지의 아르곤이나 산소의 유량과 에너지의 1/2승에 비례하는 것으로 알려져 있다. 그러나 본 시스템에서는 인가 전력을 높여도 응력이 증가하지 않았고, 타겟과의 거리를 줄이면 오히려 응력이 감소함을 보였다. 이는 박막의 응력이 peening 하는 입자의 에너지뿐만이 아니라 증착되는 물질의 증착 속도와도 밀접한 관련이 있음을 보여준다. 즉, 증착속도가 증가하면 peening하는 입자가 끼치는 응력의 효과가 반감되기 때문으로 수식을 통해 증명할 수 있었다.진탄화 처리시간을 변화시켰을 때 화합물층의 생성은 ${\gamma}$'상으로부터 시작되고 $\varepsilon$상은 즉시 ${\gamma}$'상을 소모하면서 생성되어 일정시간이 지난 후 $\varepsilon$상은 안정화되며 질소가스농도가 증가할수록 화합물 층내의 $\varepsilon$상분율은 역시 증가하였다. 한편 CH4 가스농도는 처리되는 강종에 따라 차이를 보이며 적정 CH4 가스농도를 초과시에는 $\varepsilon$상 생성은 억제되고 시멘타이트상이 생성되었다.e에서 발생된 질소 플라즈마를 구성하는 이온들의 종류와 그 구성비율을 연구하였다.여러 가지 응용으로의 가능성을 가지고 있다. 그 예로 plasma processing, plasma wave에 의한 입자 가속, 그리고 가스 레이저 활성 매질 발생 등이 있다. 특히 plasma processing의 경우 helicon plasma는 높은 밀도, 비교적 낮은 자기장, remote operation 등이 가능하다는 점에서 현재 연구가 활발히 진행되고 있다. 상업용으로도 PMT와 Lucas Signatone Corp.에 서 helicon source가 제작되었다. 또한 높은 해리율을 이용하여 저유전 물질인 SiOF의 증착에서 적용되고 있다. 이 외에도 다수의 연구결과들이 발표되었다. 잘 일치하였다.ecursor 분자들이 큰 에너지를 가지고 기판에 유입되어 치밀한 박막이 형성되었기 때문으로 사료된다.을수 있었다.보았다.다.다양한 기능을 가진 신소재 제조에 있다. 또한 경제적인

• Journal of the Korean Society of Industry Convergence
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• v.26 no.6_2
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• pp.1011-1017
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• 2023

In this study, the harmless crack size (a_hml) by double shot peening (DSP) using shot balls with different diameters was evaluated on carburized, quenched-tempered SCM822H steel. The minimum crack size (a_NDI) detectable by non-destructive inspection was also evaluated. The relationship between the crack size (a_25,50) that reduces the fatigue limit by 25% and 50% and a_hml was evaluated. The residual stress of DSP was greater in SP_(0.6+0.08) than SP_(0.8+0.08) and appeared deeper in the depth direction. In addition, the hardness below the surface appeared larger. The fatigue limit of DSP increased 2.07 times and 1.95 times compared to non-SP. All a_hml of the DSP specimen was determined at the depth (a). The compressive residual stress distribution affects a_hml, and the a_hml of SP_(0.6+0.08), which has a large compressive residual stress and a high fatigue limit, appeared large. a_hml of SP_(0.6+0.08) introduced deeper than the residual stress of SP_(0.8+0.08) is larger in the range of As=1.0-0.3. Since the residual stress in the thickness direction has a greater effect on a_hml than the residual stress at the surface, it is necessary to introduce it more deeply. The relation of a_hml, a_25,50, and a_NDI were evaluated in the point for safety and reliability.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.789-790
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• 2009

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.207-209
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• 2003

In FE analysis for residual stress of a casting, contact force between mould and casting material and gravity force must be considered for exact simulation. Preheating of a repair weldment had a little effects on the reduction of residual stress. However, preheating with hammer peening had a great deal of effects on the reduction of residual stress. A method for estimation of fatigue life for a repair weldment has been established.

• Proceedings of the KWS Conference
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• 2004.05a
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• pp.240-242
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• 2004

Effect of post treatment on the fatigue strength of a box weldment was investigated in order to improve fatigue life of the weldment. The post treatment applied were the smooth grinding of weld bead, weld toe grinding and hammer peening at the weld toe. The fatigue strength of the weldment after post treatment clearly increased, compared with that of the weldment in as-welded condition. After smooth grinding of weld bead, fatigue crack initiated at the root of the weldment, while fatigue crack initiated at the weld toe for the other methods.

• Proceedings of the Korean Nuclear Society Conference
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• 2005.05a
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• pp.1032-1033
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• 2005

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2008.11a
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• pp.138-138
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• 2008

H13강에 대해 이온질화에 대한 쇼트피닝의 효과를 살펴보았다. 쇼트피닝을 이온질화는 기존이온질화에 비해 높은 경도와 깊은 경화층을 얻을 수 있었다. 이는 쇼트피닝에 의해 결정립계와 전위밀도가 증가함에 따라 질화공정이 가속화된 것으로 보인다.