Key Engineering Materials Vols. 297-300

Abstract: Although electrochemical transients can provide very sensitive indication about the onset of localized corrosion, including initiation of stress corrosion cracking (SCC), information on location of the initiation site is not available. In the present study, we proposed an estimation method of location and magnitude of SCC initiation events, where electrochemical transients associated with local anodic events are measured by multiple reference electrodes and location of the initiation sites are estimated based on relative magnitude of the electrochemical transients simultaneously measured at multiple locations.

Abstract: Zr-4 alloy is the material of nuclear fuel shell in nuclear power plant’s PWR. This paper presents this material’s general mechanical property and fatigue behavior that are tested in accordance with ASTM in room temperature and 380°C condition. The test results show that there is no cyclic hardening or cyclic softening phenomena for Zr-4 alloy applied by cyclic loading in room temperature condition. The fatigue design curve is obtained by processing fatigue test results with adopting ASME Sec.Ⅲ based on the test results of strain fatigue property. The research result shows the fatigue design data at different temperature may be corrected by elastic modulus with room temperature curve. This paper’s result may be used in PWR component design.

Abstract: Vanadium alloys in the composition range around V-4Cr-4Ti have been proposed as candidate materials for fusion reactor applications and structures. These applications will require detailed characterization of constitutive and fracture properties. This study is aimed at understanding the basic constitutive and fracture mechanisms in vanadium alloys. Understanding of the basic constitutive and fracture mechanisms is achieved through a series of mechanical tests. These test results are combined with quantitative models of the underlying macro- and micromechanics. In addition to these experimental studies, finite element analysis (FEA) techniques are used to determine stress and strain fields to verify the constitutive law used in the fracture specimens.

Abstract: Microscopic studies on the toughening mechanism of rubber-toughened PMMA (RTPMMA) were carried out using a polarizing optical microscope (POM) and a transmission electron microscope (TEM). POM result showed that in a typical RT-PMMA, a damage zone was developed in the vicinity of crack-tip, and therefore, it was considered that energy dissipation due to the damage zone development was the primary toughening mechanism. TEM result exhibited that the damage zone was a crowd of micro-crazes generated around rubber particles in the vicinity of notch-tip. Finite element analysis was then performed to simulate such damage formations in crack-tip region. Macro-scale and micro-scale models were developed to simulate damage zone formation and micro-crazing, respectively, with use of a damage model. It was shown that the damage model introduced was successfully applied to predict such kind of macro-damage and micro-craze formations.

Abstract: This short paper will present a two-dimensional (2D) model of masonry material. This mesoscopic mechanical model is suitable to simulate the behavior of masonry. Considering the heterogeneity of masonry material, based on the damage mechanics and elastic-brittle theory, the new developed Material Failure Process Analysis (MFPA2D) system was brought out to simulate the cracking process of masonry, which was considered as a three-phase composite of the block phase, the mortar phase and the block-mortar interfaces. The crack propagation processes simulated with this model shows good agreement with those of experimental observations. It has been found that the shear fracture of masonry observed at the macroscopic level is predominantly caused by tensile damage at the mesoscopic level. Some brittle materials are so weak in tension relative to shear that tensile rather than shear fractures are generated in pure shear loading.

Abstract: Low carbon TRIP steel shows quite complicated deformation behavior. The main purpose of this study is to clarify the deformation mechanism of low carbon TRIP steel by using a numerical simulation method. According to research works in the past, continuous transformation of retained austenitic phase is essential in order that TRIP steel may show favorable ductility, which implies that appropriate control of martensitic transformation is most important for improvement of ductility. Therefore, we built models for deformation-induced martensitic transformation and performed FEM analysis using homogenization method accounting for the chemical composition, temperature, and crystal orientation. As a result, the effects of chemical composition, temperature, and crystal orientation on the deformation and transformation behavior of low carbon TRIP steel were clarified quantitatively and the conditions to realize improved ductility in TRIP steel were suggested.

Abstract: The effects of the welding mechanical heterogeneity on the damage evolution of notched round-bar tensile specimens were investigated numerically using a fully coupled elastic-plastic damage finite element method. Some parameters reflecting the welding mechanical heterogeneity such as strength mismatching, rupture strain and weld metal width were taken into account to study their effects on the damage evolution of the weld metal. The calculation results show that the damage evolution of the weld metal is affected strongly by the welding mechanical heterogeneity. The damage evolution of the weld metal becomes larger with the decrease of both the rupture strain and yielding stress of the base metal. The effects of the mechanical properties of the base metal on the damage evolution of the weld metal decreases with the increase of the weld metal width.

Abstract: Using the method of mesomechanics, a represent volume element (RVE) with internal pressure acted on the inner wall of the void is suggested to simulate the hydrogen induced cracking (HIC) in porous ductile materials. Based on this RVE, yield criterion is derived and constitutive model is constructed. Simulations show that the hydrogen pressure intensively reduces the yield stress for porous ductile materials

Abstract: Nanoindentation data measured on the cell-wall of Al-alloy foams were analyzed to obtain the material properties of the cell wall. Using the obtained material properties, stress-strain curve of the foam in uniaxial compression was constructed by finite element modeling. The model developed for the analysis was a multiple cell model which utilized the unit cells as the basic building block of the foam. Both the in-plane and through-thickness density variations of the foam were considered in the model. The through-thickness density variation which is a function of casting or foaming process was represented using different densities for different foam layers, while the in-plane density variation which arises from internal defects (such as porosities, second phase particle, inclusions etc.) was assumed to follow a statistical probability distribution of Gaussian type. Uniaxial compression test was performed and the finite element analysis result was compared with the experimental result. The numerical model used in the study overpredicted the crushing strength of foams indicating that the model needs to be improved for predicting the real foam properties with better accuracy.

Abstract: In order to simulate the growth of arbitrarily shaped three dimensional cracks, the finite element alternating method is extended. As the required analytical solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear is used. In the study, a crack is modeled as distribution of displacement discontinuities, and the governing equation is formulated as singularity-reduced integral equations. With the proposed method several example problems for three dimensional cracks in an infinite solid, as well as their growth under fatigue, are solved and the accuracy and efficiency of the method are demonstrated.