Key Engineering Materials Vols. 324-325

Abstract: To research the creep behavior of salt rock, the uniaxial and triaxial creep experiments were carried out under different deviatoric stresses and same confining pressure or different confining pressures and same deviatoric stress. The experiment results showed that the analysis on the creep damage of salt rock should consider the influence of confining pressure and deviatoric stress. By introducing the damage variable to the Norton Power law of salt rock, a new constitutive law of salt rock was presented. The damage equivalent stress was the function of the confining pressure and the deviatoric stress in the new constitutive law. The constitutive law can embody the steady creep and accelerative creep of salt rock, in which the parameters are obtained by simulating the experimental data of salt rock in some salt mine. The theoretic results are in good agreement with the experimental results. The new constitutive law was embedded in the three dimension numerical codes. The natural gas storage in the salt mine was analyzed by the new constitutive law. The evolvement law of damage bound and the displacement law around the natural gas storage were studied under the minimal natural gas storage pressure. The continuous operating time of the natural gas storage was also analyzed under the pressure. The research conclusions are expected to be applied in the natural gas storage projects in salt rock layer.

Abstract: Based on the theory of thermo-elasticity mechanics, the finite element numerical simulation models have been established for the package bulging process. The mechanism of the interfacial void evolution is postulated. By taking the interface strength as function of process (moisture and temperature), it shows that the critical stress that results in the unstable void growth and delamination at the interface is significantly reduced and becomes comparable to the magnitude of the vapor pressure. The simulation result can make us understand the mechanism of the void-growth at the interface framework and provide data base for improving reliability of package and optimum design

Abstract: In steel structure systems such as plate girder bridges and framed structures, fatigue damage used to occur at welded areas rather than primary structural members. These damages and behaviors of the welded attachments need to be extensively investigated so that the fatigue design criterion can effectively control the fatigue damage of steel structure systems. This study utilized a full-scale plate girder on which various welding attachments were mounted. The welded attachments investigated herein included flange gussets, web gussets, vertical stiffeners, and cover plates. The fatigue cracks initiated at the longitudinal end of joint area of the weld bead and the parent metal where stress was significantly concentrated. The initiated fatigue cracks developed along the weld path and then, propagated to the parent metal in the direction perpendicular to the principal stress. The fatigue cracks developed even under a compressive stress when a significant residual stress was experienced from the welding. The fatigue strengths of the each welded attachment were evaluated and compared with the current fatigue design specifications in AASHTO [1] and JSSC [2].

Abstract: The effect of ageing treatment and coarse intermetallic particles on the compromise between the toughness and the yield strength of 7010 and 7150 aluminum alloys (Al-Zn-Mg-Cu alloys) are investigated. Plane-strain fracture toughness tests were performed on the compact-tension specimens of L-T orientation. The fracture toughness of 7010 alloy was higher than that of 7150 alloy at the same ageing treatment. The 7150 alloy contain a greater amount of coarse Cu-bearing particles, which deteriorate the fracture behavior and decrease the ageing hardening ability of the alloy. The toughness of the both alloys increased greatly for the overaged condition as compared to that for the T6 condition. Two dominant mechanisms of failure occur: microvoid-induced transgranular fracture and intergranular fracture modes, and the former becomes more important in the overaged ageing conditions.

Abstract: The effects of multiple repairing-weld and TIG-dressing on the fatigue property of high strength steel weld joints used in platform have been investigated. Through the fatigue tests on high strength steel welded joint samples, the life estimating formula is obtained after each time of repairing weld and TIG-dressing. The S-N curve and the equation after repairing weld and TIG-dressing are given. The work in this paper offers an important basis for the multiple repairing-weld of platforms.

Abstract: The cohesive zone interface model was used to calculate 90o peel in the ACF bonding samples. The constitutive equation for the interface model was modified by introduction a damage factor χ . The thermal damage factor and humidity damage factor can be derived from the experiment data. The interfacial model with damage factor can change the maximal peel stress and the delamination length. The calculation result of the interfacial model with damage factor agreed well to the experiment of the 90o peeling.

Abstract: The authors have studied and clarified that ion nitriding was able to improve the fatigue properties of tool steel. Five kinds of ion nitriding methods (ion nitriding condition is different) were used in this study. The fatigue test had been performed using a rotating bending fatigue testing machine to investigate the effects of ion nitriding on fatigue properties of tool steel. The fractography was analyzed using a scanning electron microscope (SEM), and hardness distribution was also investigated using a microhardness tester. As a result, the fatigue strength and hardness of the ion nitrided specimen increased after ion nitriding processing. It is considered that the compressive residual stress which produced by ion nitriding processing in the layer reduced fatigue fracture, and the altered surface composition improved surface hardness. According to the results of the fatigue test, the optimal ion nitriding method on improving the fatigue limit of tool steel was determined. The hardness of the specimens remarkably increased after ion nitriding processing.

Abstract: On the basis of the anisotropic damage theory and piezoelectric theory, the nonlinear free vibration governing equations for cross-ply laminated damaged plates with piezoelectric actuators are established. The Galerkin procedure furnishes an infinite system of equations for time functions which are solved by the method of harmonic balance. In the numerical results, the influences of damage parameters and piezoelectric effect on the nonlinear amplitude-frequency response curves of the laminated plates are discussed, which results reveal the inherent features about the coupled mechanics and electricity.

Abstract: Experiments show that the failure of ductile materials can be characterized by a rate-independent parameter, relative spacing d defined as the ratio of the distance between two voids and the radius of voids. In this study, this experimental phenomenon is analyzed via numerical simulations using 3-D finite element model. Considering that hydrostatic stress is a dominant factor in the evolution of microvoid nucleation, growth and coalescence in ductile materials, numerical simulations are performed to obtain the relationship between relative spacing d and hydrostatic stress in the ligament between voids. Numerical results show that hydrostatic stress along matrix ligament is sensitive to the change of the relative spacing. Further analysis shows that the failure of ductile materials can modeled by using a criterion of the threshold of local hydrostatic stress in the ligament. Based on such a criterion, a curve displaying the relationship between the strength of ductile material and strain rate is obtained numerically. It is concluded that the failure criterion of ductile materials can be described by using local hydrostatic stress and relative spacing between two voids, which is not sensitive to strain rates.

Abstract: This paper reports on the mechanical properties and plastic shrinkage crack of concrete containing modified polypropylene fiber
a kind of new porous polypropylene fiber. Results of crack properties tests show that after adding modified polypropylene fiber, crack area, maximum crack width and average crack width of concrete decreased markedly. Results of mechanical properties show that flexural and splitting tensile strength of concrete with 1.0‰ modified polypropylene fiber volume fraction at 28 days increased 24% and 28% respectively compared to the reference concrete; Reticulate polypropylene fiber has less effects than modified polypropylene fiber on flexural and splitting tensile strength. Compressive strength of fiber reinforced concrete changed slightly, but flexural strength and splitting tensile strength increased, and the ratio of splitting tensile strength to compressive strength decreased.