Fracture and Damage Mechanics V

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Authors: Xiang Guo Wu, Sang Mook Han, Sung Wook Kim, Su Tae Kang
Abstract: This paper concerns the theoretical research of shear failure load of steel fiber reinforced ultra high performance cement composites (SFR-UHPCC) beam. Based on test investigation, an analytical model of prestressed SFR-UHPCC beam is constituted. Two formulae of ultimate failure load, i.e. the upper bound and the lower bound of shear loading capacity, all have been obtained according to the limit analysis of concrete plasticity. In the process of upper bound analysis, uniform distribution of steel fiber has been assumed, and virtual work induced by steel fiber has been divided into two parts, i.e. pulling-out virtual work and debonding virtual work. Five coefficients are introduced considering some defects. Twelve SFR-UHPCC beams with three kinds of shear span ratio i.e. 2.7, 5.6 and 8.5 are tested and compared with the results from the proposed equations.
Authors: Ying Liu, Ling Tian Gao
Abstract: In this paper, a new algorithm based on Meshless Local Petrov-Galerking (MLPG) method is presented for analyzing the crack dynamic propagation. A new modified Moving Least Squares approximation is proposed to simplify the treatment of essential boundary conditions. Explicit central difference with lumped mass matrix is adopted for the time integral. Visibility criterion with crack edge node adding technique and the maximum hoop stress criterion are used to describe the crack propagation and forecast the crack propagation direction. Based on this algorithm, three-point bend specimen for impact fracture test is investigated. Comparing the results with those obtained by the laser caustic method and high-speed photographs, the accuracy of the present algorithm is proved.
Authors: Ze Sheng Ji, Mao Liang Hu, Xiao Yu Chen
Abstract: AZ91D magnesium alloy is prepared by hot extrusion of recycled machined chips and its fractures and mechanical properties are investigated at various extrusion conditions. Cold-press is employed to prepare extrusion billets of AZ91D magnesium alloy chips, and then the billets are hot extruded at 573K-723K with an extrusion ratio of 11:1. The results show that tensile strength and elongation of the extrusion magnesium alloy with the extrusion temperature of 673K and the extrusion rate of 0.08mm/s can reach 380MPa and 6%, respectively. Fracture surface presents a mix mechanism of dimple-like fracture and gliding fracture. Due to grain refinement by cold-press and hot extrusion, mechanical properties of extruded rods are much higher than those of as-cast AZ91D magnesium alloy. Also, much lower energy consumption is necessary for this recycling compared to the conventional casting process. Solid state recycling is an efficient method for magnesium alloy chips recycling.
Authors: You Tang Li, Ping Ma, Chang Feng Yan
Abstract: The eigen-equation of bi-materials cracks was founded on the basis of the stress field and displacement field. The influence of shearing modulus and Poisson’s ratio of matrix material and additive material to eigen-values were analyzed through the results of calculating. The stress intensity factors at the tip of matrix crack were calculated. The suitable parameters of bi-steel materials crack in fracture design were obtained. The results show that the effect of Poisson’s ratio on eigen-values is not obviously and the effect of shearing modulus is obviously. The shearing modulus of additive material should bigger than that of matrix material.
Authors: You Tang Li, Zhi Yuan Rui
Abstract: The applied investigation of regular fracture for low carbon steel under extra-low cycle inverse rotating bending fatigue was studied in this paper. The principle of inverse rotating bending fatigue was explained at first. The effect of experimental parameters on cycle times of fracture, such as the relations of presetting deflection to quality of blanking and cycle times of fracture were discussed through the experiments. The effects of geometrical parameters of notch, such as tip radius, depth and open angle, on cycle times of fracture were studied. The results show that low carbon steel can be regular fractured through inverse rotating bending fatigue. The quality of blanking is depended on presetting deflection of inverse rotating bending.
Authors: Shou Fan Rong, Jing Qiang Zhang, Ze Sheng Ji
Abstract: α-Al2O3 powders, a small amount of 3Y-TZP and Cu powders were used as principle materials in which adequate amount of TiO2-MgO-CAS system additives were added by wet grinding .The compacts were prepared by hot-pressed sintering. The results showed that the fracture toughness was significantly enhanced by synergistic toughening of in-situ growth abnormal grain, phase transformation and metal particles. Under the sinter condition of 30MPa and 1550 for 1h, the maximum fracture toughness reached to 7.90MPa·m1/2 and the bending strength is in advance of 600Mpa, which was one time higher than un-toughen alumina ceramics. The effects of multiphase synergistic toughening on the fracture toughness of alumina ceramic were investigated; meanwhile, the fracture behavior and the mechanisms of toughening were analyzed.
Authors: Yu Ting He, Hong Peng Li, Rong Shi, Feng Li, G.Q. Zhang, L.J. Ernst
Abstract: The passivation cracking of Micro-structures of IC packages is studied by maximum principal stress theory using a certain 2D FEM model with different design parameters, pitch of lines, width of line, thickness of epoxy, thickness of dielectric layer, thickness of glue, the glue material’s yielding stress and Aluminium yielding stress (following as “d”, “w”, “t_epo”, “t_Teos”, “t_glue” “sy_glue” and “sy_al” respectively). For different critical process steps, the final process temperature is acted as a representative parameter to analyze its impact. Furthermore, Response Surface Model (RSM) of principal stress is established using any two design parameters. Results show that “d”, “w”, “t_epo”, “sy_glue” and “sy_al” will have great influence on passivation cracking while “t_Teos” have a little impact.
Authors: Min Xia Fan, He Jun Li, Yi Dong Yuan, Ke Zhi Li
Abstract: Tensile properties and fracture morphologies of C/C composites used as aircraft brake disc at different heat treatment temperature have been studied. Fracture morphologies characteristics of tensile sample were observed with scanning electron microscope (SEM), and fracture mechanism was analyzed. The test results show that, with increase of heat treatment temperature, tensile strength of C/C composites has a descend trend, whereas, breaking strain has an upward trend, and failure mode changes from brittle fracture into “pseudo-plasticity” fracture. Destructional form includes interface debonding, extraction, break and matrix damage and so on, among which interfacial failure is principal fracture mechanism.
Authors: Gang Chen, Qing Ping Zhang, Zhong Fu Chen, Si Zhong Li, Yu Ze Chen
Abstract: Cylindrical shell is a kind of common used structure in engineering. Interest in the response of cylindrical shells to local impact loading has increased over the last few years. A structure always endures working load more or less. For a cylindrical shell, the working load commonly is internally pressure. In this paper, a numeral simulation of wedge block impact internally Pressured cylindrical shell was carried out. The dynamic failure process of the structure was obtained. The consistency between experimental observation and numerical simulation is satisfactory.
Authors: Yong Qi Liu, Yan Xia Wang, Xiu Hua Men, Feng Hua Lin
Abstract: Mechanical fatigue experiments are performed for piston pin seat, and the stress-strain response of the piston overall structure is analyzed by the elastic-plastic FEA. An estimated formula of the fatigue life is put forward by amending the Manson-Coffin formula on the basis of studying the fatigue behavior of piston pin seat. The Newton iterative algorithm is applied to calculate the modified formula, and the mechanical fatigue life of piston pin seat is obtained. By comparison the predicted value with the experimental results, the feasibility of estimated formula is validated.

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