Progresses in Fracture and Strength of Materials and Structures

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Authors: Guo Zheng Kang, Zhao Li, Yu Jie Liu
Abstract: The cyclic deformation behaviors of 42CrMo steel with different heat treatments were observed by uniaxial cyclic straining and stressing tests at room temperature. The cyclic softening/ hardening features of the tempered or annealed 42CrMo steel and their effects on the uniaxial ratcheting produced in asymmetrical cyclic stressing were discussed. It is concluded that the tempered 42CrMo steel shows significantly cyclic softening feature, but the annealed one is cyclic stabilizing. Different ratcheting behaviors are also observed. For the tempered 42CrMo steel, a special tertiary ratcheting behavior is observed and the previous cyclic straining greatly accelerates the evolution of ratcheting strain in subsequent cyclic stressing. In contrast, the annealed sample presents a stabilized ratcheting with nearly constant ratcheting strain rate after certain cycles, and the previous cyclic straining slightly influences the ratcheting in subsequent cyclic stressing.
Authors: Seok Hwan Ahn, Kum Cheol Seok, Ki Woo Nam
Abstract: The experimental and the analysis for effects of circumferentially local wall thinning on the fracture behavior of pipes were carried out. Local wall thinning for experimental was machined on the outside of pipes in order to simulate the metal loss due to erosion/corrosion. In addition, the pipes with local wall thinning on the inside were carried out FE analysis, and it made a comparative study with that of outside. Failure mode could be classified into ovalization, local buckling and crack initiation depending on the thinned length and thinned ratio. Three-dimensional elasto-plastic analyses were able to accurately simulate fracture behaviors of inner/outer local wall thinning. Therefore the fracture behavior of the inner local wall thinning can be estimated with the outer local wall thinning.
Authors: Qin Zhi Fang, Tie Jun Wang, Hui Min Li
Abstract: Large deformation performances of polycarbonate (PC) and PC/ABS (Acrylonitrile Butadiene Styrene) have been investigated experimentally in this paper. The displacement fields of these polymers are measured with a system based on digital image correlation (DIC) method. The variations of strains during tension are measured and the true stress-strain curves are presented. For these materials, it is observed that the contraction in thickness is larger than that in width during tension. No obvious stress softening is observed in the true stress-strain curves. The true stress-strain curves can be fitted well with three-stage model.
Authors: Wen Zhong Cai, Shan Tung Tu, Yang Yan Zheng, Jian Ming Gong
Abstract: A new methodology of computer simulation is proposed to perform finite element (FE) calculations of uniaxial tensile deformation on the three-dimensional (3D) complex microstructures, through its application to the microstructure of aluminum matrix containing randomly distributed and oriented SiC particles of highly variable and angular geometry. Compared with the simplified microstructure model, the complex microstructure model shows significant differences in terms of micromechanical fields and macroscopic uniaxial deformation. The results reveal that a quantitative and convenient reconstruction of microstructure of particulate composites is crucial for both the prediction and design of material properties.
Authors: Yu Ming Li, Hong Bai Bai, Jian Zheng
Abstract: Analysed the stress-strain test in the pressing direction of metal rubber specimen, the deformation process can be divided into three stages. Used the accumulative method of high step polynomial, the experience formula of metal rubber’s deformation character can be simply and effectively established. With the fabrication and formation technology, the microscopic physics mechanism has been analyzed in these deformation stages.
Authors: Bin Xu, Le Yang, Shi Bo Xing, Li Li
Abstract: In order to increase boronizing speed without decreasing the hardness of boride layer, the effect of plastic deformation at room temperature on powder RE-chrome-boronizing for a medium carbon steel (steel 45), in which boronizing plays a main role, was studied in this paper. The cold plastic deformation (CPD), whether compressing or shot-peening, can increase boronizing speed. Meanwhile, the boride layer can also retain its high microhardness (1 300―1 900HV0.1) with low brittleness. The layer depth achieved for a given heating time increases with increasing CPD degree on the steel. The analyses show that boronizing kinetics in the RE-chrome-boronizing (RE-Cr-B) samples with CPD can be enhanced.
Authors: Kee Joo Kim, Joo Sung Kim, Cheol Woong Kim, Il Seon Sohn, Jin Yi Lee, Joong Bae Kim
Abstract: To fabricate the aluminum alloys with good drawability, the textures evolution of the 3003 aluminum alloy sheets after rolling and subsequent annealing was studied. The measurement of the deformation textures was carried out for the sheets in which were cold rolled with high reduction ratio by using the symmetric roll. In addition, the change of the recrystallization texture was investigated after heat-treatments of the rolled sheets with various heat treatment conditions. Rolling without lubrication and subsequent annealing led to the formation of favorable rot-CND {001}<110> and γ-fiber ND//<111> textures in 3003 aluminum alloy sheets. From the results, the γ-fiber ND//<111> component well evolved during rolling at high reduction ratio (reduction over 90%, l/d parameter over 6.0). Among shear deformation textures, the γ-fiber ND//<111> was not rotated during recrystallization (350°C) in special condition.
Authors: Dai Okumura, Atsushi Okada, Nobutada Ohno
Abstract: In this study, the elastic buckling strength of cubic open-cell foams subjected to uniaxial compression is investigated using the homogenization framework developed by the present authors (Ohno et al., JMPS 2002; Okumura et al., JMPS 2004). First of all, based on the framework, the microscopic bifurcation and macroscopic instability of cubic open-cell foams are numerically analyzed by performing finite element analysis. It is thus shown that long wavelength buckling is the primary mode and occurs just after the onset of macroscopic instability. Then, a solution for predicting the stress of long wavelength buckling is analytically derived from the onset condition of macroscopic instability. The validity of this analytical solution is demonstrated by the finite element results.
Authors: Katsuhiko Sasaki, Terumitsu Imanishi, Kazuaki Katagiri, Atushi Kakitsuji, Toyohiro Satoh, Akiyuki Shimizu, Nobuhito Nakama
Abstract: In this paper, carbon nanotube (CNT) containing aluminum composite materials, which have good thermal conductivity, are made by the plasma activated sintering. CNT and vapor-grown carbon fiver (VGCF) as a super multi-wall CNT are used for the composite materials. To clarify the deformation and thermal characteristic of the composite materials, Young’s modulus and thermal conductivity are measured. Finally, the micromechanical discussion is also conducted using Mori-Tanaka model.
Authors: Xin Lei Gao, Jian Li, Wan Zhen Gao, Xiang Pei Qin
Abstract: Ultra high molecular weight polyethylene (UHMWPE) is a kind of non-polar polymer with a crystalline structure. Its failure appeared usually as a type of wire drawing when it was used as a material of rubbing pairs. By a designed heating test, the thermal damage phenomena of UHMWPE were observed by SEM. Its thermal damage model during the process of wire drawing damage was assumed that when the thermal energy was accepted by the UHMWPE, its volume expanding and its surface melting into a viscous fluid proceeded from its elevated temperature, and then the viscous fluid flowed according with non-Newtonian fluid model; after cooling, the melt re-crystallized and gathered again and at the same time many obvious cavities with phenomena of wire drawing appeared in the re- crystalline polymer. As a result the material of UHMWPE shrank to porosint from the congeries with the small uniform particles.

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