Advances in Fracture and Materials Behavior

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Authors: Zong De Liu, Bin Li, Zhang Qi Wang, Jing Jing Liu, W. Ji
Abstract: In this work, a new method, electro-thermal explosion ultra-high speed spraying (EEUSS), was utilized to synthesize the titanium carbide based and nickel bonded (TiC-xNi) coatings. The nickel content was varied at the weight percents of 5, 10, 15 and 20%. The microstructure and properties of the coatings were studied by means of scanning electron microscope (SEM), X-ray diffraction (XRD) and microhardness tester, respectively. The TiC-xNi coatings had the metallurgical bonding with the substrate, and consisted of submicron grains. The grain abrasion tests results showed that the abrasion resistance of the coatings was affected by the contents of Ni.
Authors: Hai Jun Su, Jun Zhang, Lin Liu, Heng Zhi Fu
Abstract: Directionally solidified oxide ceramic eutectic composites with superior strength, oxidation resistance, creep resistance, structural stability and low sensitivity to crack at high temperature have aroused much attention in recent years, and various preparation techniques have been developed. In situ fabrication of ceramic eutectic composites by laser rapid solidification is a cheap and quick method compared to conventional multi-step fabrication methods of fiber reinforced composites for high temperature use. In this paper, Al2O3/YAG/ZrO2 ternary eutectics are rapidly prepared from melt by directional solidification using laser zone remelting technique, the growth characteristic and fracture toughness are investigated. The results show that: (1) Laser rapidly solidified Al2O3/YAG/ZrO2 ceramic eutectic in situ composite presents a fine interpenetrating network structure, in which Al2O3, YAG and ZrO2 phases are continually interconnected and finely coupled without pores, colonies and grain boundaries between interfaces. (2) Laser scanning rate and power density strongly affect the eutectic growth. With the processing parameters adjusted properly, the eutectic shows homogeneous and coupled lamellar microstructure. The characteristic dimensions of the microstructure are around 2~3 1m for Al2O3 and YAG phases, and around 0.2~1 1m for ZrO2 phases, respectively. (3) The hardness and fracture toughness of the rapidly solidified Al2O3/YAG/ZrO2 eutectic are 16.7 GPa and 8.0 MPa.m1/2, respectively.
Authors: Shi Rong Li, Wen Shan Yu
Abstract: Based on Brinson’s one-dimensional thermo-mechanical constitutive relations of shape memory alloys and the theory of thin plates in the von Kármán sense, the response of bending of a uniform heated circular plate embedded with SMA fibers in the radial directions and subjected to a uniform distributed mechanical load is studied. The characteristic curves of the central deflection versus temperature rise of the circular plate with both clamped and simply supported boundary conditions are obtained. The numerical results show that, the recovery forces of the pre-strained SMA caused by the phase transformation from martensite to austenite can modify the bending deformation significantly. So, it can be concluded that the bending deformation can be adjusted effectively and actively by embedment of the SMA fibers into the circular plates
Authors: J.H. Xie, Pei Yan Huang, Jun Deng, Yi Yang
Abstract: Reinforced concrete (RC) beams strengthened with prestressed fiber-reinforced polymer (FRP) laminates has been proved to be a rather effective strengthening technique in the field of bridge engineering. However, debonding failure usually occurs at the end of FRP in the strengthened beams on releasing the prestress due to the high interfacial shear stress. Analytical method to calculate the interfacial stress is developed in this paper. Through the establishment of mathematical model for the interfacial shear stress, the distribution of the interfacial shear stress and the longitudinal stress of FRP are presented explicitly in an analytical way. Moreover, the maximum prestress level is estimated to prevent debonding failure on releasing the prestress. Finally, experimental results of eight strengthened beams validate the analytical solution for the FRP longitudinal stress.
Authors: Kyung Seok Oh, S.I. Heo, J.C. Yun, Kyung Seop Han
Abstract: Conductive polymer composites (CPCs) consisting of expanded graphite (EG), flake-type graphite (FG) and thermalsetting resin were fabricated by means of a preform molding technique. Conductive fillers, EG and FG, were mechanically mixed with the phenol resin to provide an electrical property to composites. The filler loadings were fixed at 75wt.% to obtain a high electrical conductivity. The mechanical and electrical properties of CPCs were optimized according to the weight ratio and the particle size of FG. As the weight ratio increased, the flexural strength increased, however, the electrical conductivity decreased for both cases of CPCs using different sizes of FG. The particle size was an important parameter to change the mechanical and electrical behaviors. The flexural strength was sensitive to the particle size due to the different level of densification. The electrical conductivity also showed size-dependent behavior because of the different contribution to the conductive networking.
Authors: Xue Ping Mao, Hong Xu, Gang Wang, Zhi Yong Ma
Abstract: Softening, namely degradation, is an important characteristic for the components long-termly operating in high temperature environment. In this article, hardness is adopted to indicate this effect. In order to study the independent effect of high temperature and stress on the material properties, the zero-stress ageing experiments at 540 oC, 565 oC, 660 oC and the stress-accelerating softening experiments (i.e. creep experiment) at 540 oC, 565 oC with interruption were carried out in steel 30Cr1Mo1V, respectively. The stress range tested was from 240MPa to 320MPa. The Vicker’s hardness was measured. The relationship between Larson-Miller parameter and the Vicker’s hardness under zero-stress softening condition and under stress-accelerating softening condition is obtained. Based on the extraction of the effects of temperature and time, the stress softening effect formulae are established.
Authors: Dong Yu Liu, Shi Xiang Hou, Ye Yuan, Bing Zhe Bai, Zong De Liu, Hong Xu, Jian Chao Peng
Abstract: The air cooling rate of the Low Carbon Mn-Si-Cr steel bar with different diameter after austenitizing at 910oC and 960oC was simulated by Formaster-F Phase transforming instrument and Gleeble-1500 thermal /mechanical simulating machine. Microstructure of the specimen was observed by OLYMPUS PME3 optical microscope and FEI QUANTA200F scanning electron microscope. The hardness and impact toughness of the steel was tested by HBRV-187.5 hardness tester and JCSJ300-I instrumented Charpy impact tester. The experimental result showed that with the amount of CFB in CFB+M mixed microstructure increasing the combination of strength and toughness of the steel was improved. The higher the austenitizing temperature of the steel, the wider the air-cooling rate range obtaining CFB+M mixed microstructure. However, the steel produces mixed grain after austenitizing at 960 oC. For obtaining fine prior austenite grain size, Ti and Nb alloying element need to be added.
Authors: Shu Hong Liu, Yan Liang Du, Yue Qin Qi, Cong Juan Yang
Abstract: A two-dimensional electromechanical analysis is performed on a transversely isotropic piezoelectric material containing a line crack of length 2a, which is subjected to uniform distributed forces with intensity q along the crack faces and uniform electric displacement fields at infinity. Based on the impermeable electric boundary conditions, the closed complex form expression for the electromechanical fields are deduced in the vicinity of the crack. Taking PZT-4 ceramic into consideration, electromechanical fields under different loads are illustrated through several examples. It can be seen that electromechanical fields show 1/2 order singularity at the crack tip, and the piezoelectric effect can’t be negelected.
Authors: Yan Liang Du, Shu Hong Liu, Shi Jie Duan, Yan Qiang Li
Abstract: A two-dimensional electromechanical analysis is performed on a transversely isotropic piezoelectric material containing an elliptical hole, which is subjected to uniform compressive forces with intensity q acting on the edge of the hole and uniform electric displacement fields at infinity. Based on the impermeable electric boundary conditions, general electromechanical fields solution are obtained in the form of complex potentials.
Authors: Yong Yu Zhang, Xiao Yang Chen, Ling Sha
Abstract: This work reports on strength behaviour of polysilicon thin film flexure hinge. In order to develop a microscopic modelling of thin film flexure hinge for microstructures, in situ test benches have been designed and fabricated. The experiment demonstrated that a deviation between the macroscopic theory value and experimental result. A model similar to that used for rotational stiffness in macroscopic steel is used to fit testing data for polysilicon film flexure hinge. The dynamic characteristic and fatigue behaviour of the thin film flexure hinge were also investigated. The hinge was excited by an integrated electro-thermal microactuator that could be self-heated and driven. Resonant frequency of the polysilicon flexure hinge test benches is 6.5 Hz, and the maximum operating frequency reached 1KHz. When a cyclic loading of 1μN.μm was exerted to the micromachining flexure hinge, the limit stress alternation number exceed 1.0×108. When the stress alternation number exceeded 1.0×109, the polysilicon beam of microactuator would lost its elastic character. If the micro hinge operated at high temperature (exceed 200/), the lifetime would decreased. If the working temperature were too high, the micro hinge would be burned out.

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