[en] In this study, the effects of surface oxide film formation on the fatigue behavior of 7075-T6 aluminum alloy were analyzed in terms of the corrosion time of the alloy. The aluminum material used is known to have high corrosion resistance due to the passivation phenomenon that prevents corrosion. Aluminum alloys have been widely used in various industrial applications such as aircraft component manufacturing because of their lighter weight and higher strength than other materials. Therefore, studies on the fatigue behavior of materials and passivation properties that prevent corrosion are required. The fatigue behavior in terms of the corrosion time was analyzed by using a four pointing bending machine, and the surface corrosion level of the aluminum material in terms of the corrosion time was estimated by measuring the surface were studied by scanning electron microscopy (SEM). The results indicated that corrosion actively progressed for four weeks during the initial corrosion phase, the fatigue life significantly decreased, and the surface roughness increased. However, after four weeks, the corrosion reaction tended to slow down due to the passivation phenomenon of the material. Therefore, on the basis of SEM analysis results, it was concluded that the growth of the surface oxide film was reduced after four weeks and then the oxide film on the material surface served as a protection layer and prevented further corrosion

[en] As the industrial society develops rapidly, the weight reduction and high strength are gradually demanded . In case of the welded joint for the rolling stock which receives the repeated load, the fracture can be easily occurred. However, the durability and fatigue characteristics can be improved if the shot peening technique is applied. The optimal peening process should be applied to the metal surface because the over peening can lower the durability of parts. Thus, the fatigue characteristics and Fractography of welded A6061-T6 alloy for a rolling stock were studied in the paper. The optimal peening condition and Fractography were examined. The experimental result show that over peening can lower fatigue life caused by micro crack, fold and incrustations. The fatigue life of welded A6061-T6 was tremendously improved

[en] The object of this study considers corrosion fatigue improvement of 7075-T6 aluminum by using shot peening treatment on 3.5% NaCl solution at room temperature. Aluminum alloy is generally used in aerospace structural components because of the light weight and high strength characteristics. Many studies have shown that an aluminum alloy can be approximately 50% lighter than other materials. Mostly, corrosion leads to earlier fatigue crack propagation under tensile conditions and severely reduces the life of structures. Therefore, the technique to improve material resistance to corrosion fatigue is required. Shot peening technology is widely used to improve fatigue life and other mechanical properties by induced compressive residual stress. Even the roughness of treated surface causes pitting corrosion, the compressive residual stress, which is induced under the surface layer of material by shot peening, suppersses the corrosion and increases the corrosion resistance. The experimental results for shot peened specimens were compared with previous work for non treated aluminum alloy. The results show that the shot peening treatment affects the corrosion fatigue improvement of aluminum alloys and the induced compressive residual stress by shot peening treatment improves the resistance to corrosion fatigue

[en] This paper investigates the characteristics of friction and wear of shot peened AI 7075. Three types of specimens were used to get the experimental results. One type of specimen was made by machining and polishing. Another type of specimen was made by machining, shot peening. The other type of specimen was made by machining, shot peening, and polishing. TE77(PLINT) friction and wear tester was used to obtain the experimental data under 100N and 3Hz. The experimental results show that the shot peening process enhances the hardness near the surface of specimens and improves the wear resistance

[en] 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

[en] 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 peended material

[en] Micro shock waves are induced in laser shock peening and their effect on metal samples is presented. Laser shock peening produces maximized internal compressive stress on metal surfaces. This research evaluated the effects of micro shock waves from laser shock peening with a pulsed Nd:YAG laser on steel samples, through the analysis of the mechanical properties of the samples. In the experiments, a piezo material was applied to measure the micro shock waves and the hardnesses and micro tensile strengths of the samples were evaluated

[en] In this study, the improvement of fatigue life in Al7075-T6 specimen with a circular hole-notch was investigated. Optimum-peening intensity was applied to the specimen and the fatigue test was accomplished at the room and high temperature environment. A circular hole-notch with the diameter d = 0.6mm and the depth h = 0.6mm was artificially made on the surface of the center of the specimen. The optimum-peening intensity was 0.341mmA. Fatigue test was performed by 4-point rotary bending, and applied stress was 260MPa. The fatigue lives of shot peened specimens were about 5 times, 8 times, and 4 times longer than unpeened specimens under the room temperature, the high temperature of 100 .deg. C, and the high temperature of 200 .deg. C, respectively. From the experimental results, the improvement of fatigue life of Al7075-T6 specimens with a circular hole-notch was confirmed by shot peening. It is expected the shot peening effect on notched structures in various industries will be excellent.

[en] The shot peening process is most often used to improve fatigue properties of metal parts. The single most critical parameter of the shot peening process is the shot ball itself. Without the correct quality media, all other shot peening parameters are extraneous and the desired fatigue improvement and consistency of improvement will not be achieved. shot peening involves modifications of the surface and subsurface condition of a material that can be described by the change of the residual stresses, the hardness, and the surface roughness. This paper presents the shot peening to optimize the shot ball parameters. The effect of shot peening parameter on the surface roughness, surface hardness and residual stress are investigated

[en] In this paper, artificial and real defects(delamination and debond) in composite structures were detected by using ESPI system. Three types of specimens, that is, composite laminates, honeycomb structures, and adhesive joints, were used to study the applicability of ESPI to composite structures. To detect defects in specimens, we selected thermal loading method that can easily induce the surface deformation of specimen. Experimental results show that defects in composite structures could be easily detected by ESPI. Moreover, it shows that ESPI could be usefully applied to the detection of defects in various composite structures