Experimental Mechanics in Nano and Biotechnology

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Authors: Shahrum Abdullah, Ahmad Kamal Ariffin
Abstract: This paper describes the laboratory accelerated fatigue tests of BS 080A42 steel using the shortened variable amplitude (VA) loading produced by the Wavelet Bump Extraction (WBE) algorithm. In this study, a VA strain loading which was measured on the lower suspension arm of a vehicle while driven over a pavé road surface was used. The WBE shortened loading was validated based on the fatigue life comparison to the original loading using four strain-life fatigue damage models. Experimental fatigue tests were performed using a cylindrical shape specimen with the 6- mm gauge length smooth surface made from BS 080A42 steel. The experimental findings showed that the fatigue tests were accelerated from 78.8 hours to 32.5 hours, preserving at least 99% of the original fatigue damage in the mission loadings. Finally, it is suggested that the WBE algorithm is suitable for the application of automotive accelerated fatigue tests.
Authors: Seung Kee Koh, Eui Gyun Na, Tae Hyun Baek, K.J. Kang, S.T. Ahn, T.H. Han
Abstract: In order to evaluate the structural integrity of the breech system used for a thick-walled cylinder subjected to pulsating high internal pressure, fatigue life simulation of a breech system was performed. A stress analysis of the breech was performed to locate the critical region vulnerable to crack initiation. Low-cycle fatigue behavior of the breech material was investigated to obtain the fatigue crack initiation properties. Elastic-plastic finite element stress analysis resulted in a stress concentration at the breech ring groove root. Strains at the breech ring and block were experimentally measured using strain gages and resulted in similar values compared to the calculated strains. Local strain approach was employed to estimate the fatigue life of the breech system for crack initiation at the groove root of the breech ring. Fatigue tests using simulation specimens were performed and an averaged fatigue life was obtained, showing a very good agreement with the calculated fatigue life within a factor of two.
Authors: Shun Fa Hwang, Yi Der Su
Abstract: Composite materials using polymer resins as matrices have viscoelastic behavior. This behavior has effects on the fatigue properties of composite materials. Therefore, one can accelerate the fatigue testing if the loading frequency or temperature is changed. The purpose of this work is to investigate the accelerated fatigue properties of glass/fiber composites. In order to establish the accelerated fatigue properties of glass/epoxy composites, the fatigue testing of unidirectional specimens with different angles is conducted at room temperature under different stresses, stress frequencies, and stress ratios. The results indicate that the fatigue life increases with the increasing of stress frequency or stress ratio for the three types of unidirectional specimens. The reasons for these increasing effects are also discussed.
Authors: Takehiko Takahashi, Susumu Hioki, Ikuo Shohji, Osamu Kamiya
Abstract: The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s at room temperature, 80 and 120oC. In addition, the fatigue life was estimated by using the surface deformation of the solders, and image processing. And also, it was compared with Coffin-Manson type of fatigue behavior. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder at temperatures, 80 and 120oC. The fatigue life determined by surface deformation indicated a close behavior to Coffin-Manson type fatigue behavior in those solders. Therefore the low-cycle fatigue life of solders could be estimated by the surface deformation.
Authors: Sung Choong Woo
Abstract: The objective of this study is to investigate the tensile behavior and fracture toughness of glass fiber reinforced aluminum hybrid laminates (GFAL) in association with the fracture process using plain coupon and single-edge-notched specimens. The tensile properties of GFAL, such as elastic modulus and ultimate tensile strength, were clearly dependent on the fiber orientations. In particular, the superiority of GFAL0 in KIC and GIC was much more pronounced than that of monolithic Al 1050. However, a transverse crack parallel to the fiber orientation reduced the toughness of GFAL considerably. Microscopic observations of the fracture zone in the vicinity of the crack tip exhibited various modes of micro-fracture in the respective layers as well as fiber fractures and interface delamination between fiber composite and Al layers. Such a damage evolution in GFAL depending on the fiber layer orientation had strongly influence upon the tensile behavior and the toughness of GFAL.
Authors: Ki Weon Kang, Hee Jin Shim, C.M. Kim, Jung Kyu Kim
Abstract: The study aimed at the failure analysis and strength evaluation of brazed joints used in household air conditioner. For these goals, the failure modes were investigated through the fractographic analysis and micro-Vickers hardness test. The failure modes were classified into two different types and their mechanism was influenced by heat and internal flaws such as incomplete penetration and pin holes. Also, a finite element analysis was performed to evaluate the strength behavior of the brazed joints according to the heat and internal flaws.
Authors: Seok Jin Kwon, Jung Won Seo, Dong Hyung Lee, Chan Woo Lee
Abstract: The majority of catastrophic wheel failures are caused by surface opening fatigue cracks either in the wheel tread or wheel flange areas. The inclined cracks at railway wheel tread are initiated and the cracks are caused by wheel damage-spalling after 60,000 km running. Because the failured railway wheel is reprofiled before regular wheel reprofiling, the maintenance cost for the railway wheel is increased. Therefore, it is necessary to analyze the mechanism for introduction of crack. In the present paper, the combined effect on railway wheels of a periodically varying contact pressure and an intermittent thermal braking loading is investigated. To analyze damage cause for railway wheels, the measurements for replica of wheel surface and effect of braking application in field test are carried out. The result shows that the surface cracks in railway wheel tread are due to combination of thermal loading and ratcheting.
Authors: Hyeon Chang Choi, Hyeon Ki Choi
Abstract: The relationship between fatigue crack growth behavior and cyclic crack tip opening displacement is studied. An elastic-plastic finite element analysis (FEA) is performed to examine the growth behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. We investigate the relationship between the reversed plastic zone size and the changes of the cyclic crack tip opening displacement along the crack growth. The cyclic crack tip opening displacement is related to fatigue crack opening behavior.
Authors: Kil Sung Lee, In Young Yang
Abstract: Currently, stacking condition related to the energy absorption of composite materials is being considered as an issue for the structural efficiency and safety of automobiles, aerospace vehicles, trains, ships even elevators during collision. In particular, CFRP (carbon fiber reinforced plastics) composite materials have found wide applicability because of their inherent design flexibility and improved material properties. The most important objective in designing automobiles is currently to focus on environment-friendly aspect and safety performance aspect. Therefore, the designing automobile should be more concerned on the aspect of securing safety performance, but at the same time, it also should consider reducing weight of automobile structural member. In this study, CFRP (Carbon Fiber Reinforced Plastics) side members with single-hat-section shaped were manufactured. The axial static collapse tests were performed for the members using universal testing machine, and the collapse mode and energy absorption characteristics were analyzed according to stacking condition such as fiber orientation angle and shape of the section.
Authors: Byeong Choon Goo
Abstract: In general, structural integrity of rolling stock structures should last more than 25 years. During the lifetime corrosive degradation occurs. For structural design and diagnosis, quantitative relationship between corrosive degradation and variation of mechanical properties such as tensile strength and fatigue strength is needed. In this study, electrochemical corrosion tests, atmospheric corrosion tests and fatigue tests of corroded specimens were carried out. The electrochemical characteristics of SS400, SM490A, SUS205L and SUS304 were examined. At regular intervals tensile and fatigue tests were carried out by using specimens of SM490A and SS400 on the atmospheric corrosion test bed. The fatigue strength decreases as the atmospheric corrosion period increases. In addition, the effect of heat treatment on the tensile and fatigue behavior was studied.

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