Key Engineering Materials Vols. 353-358

Abstract: A new method of parameter determination in the fatigue residual strength degradation model is proposed. The new method and minimization technique are compared experimentally to account for the effect of tension-compression fatigue loading on structural materials. It is shown that the correlation between experimental results and the theoretical prediction of the fatigue life, fatigue life distribution obtained by the proposed method is very reasonable.

Abstract: By the test of rotational bending for bar of 45 steel with V notch in low cycle fatigue, the bar’s fatigue life is studied under strain-controlled condition. The characteristics of several kinds of specimens' crack propagations are analyzed. The accumulative effect of crack propagation is discussed to find the appropriate load for quick fracture. Based on the theory of continuum medium damage mechanics, the damage evolution model in low cycle fatigue is obtained. The predicted curves and strain-life curves agree with experimental data for medium carbon steel well in this work. These results are very important for the life estimation of medium carbon steel.

Abstract: An Elastic Plastic-Damage (EPD) model is developed to model the softening behaviour of the cement-soil admixture based on continuous damage mechanics. The softening behaviour is considered to be characteristic outcome of the material degradation due to damage in material. Material degradation is modelled by reducing progressively the stiffness and yield stress of the material when the damage variable has attained a critical index. The basic equations of the model are derived and presented. A Fortran program for this model has been developed and implemented into a finite element code ABAQUS. In order to evaluate the applicability of this model, several unconfined compression tests are simulated using ABAQUS with this model. The computed results are compared with measured data and good agreement is achieved.

Abstract: Based on the Lord and Shulman generalized thermo-elastic theory, the dynamic thermal and elastic responses of a piezoelectric rod fixed at both ends and subjected to a moving heat source are investigated. The generalized piezoelectric-thermoelastic coupled governing equations are formulated. By means of Laplace transformation and numerical Laplace inversion the governing equations are solved. Numerical calculation for stress, displacement and temperature within the rod is carried out and displayed graphically. The effect of moving heat source speed on temperature, stress and temperature is studied. It is found from the distributions that the temperature, thermally induced displacement and stress of the rod are found to decrease at large source speed.

Abstract: two-dimensional problem in electromagneto-thermoelasticity for a thermally and electrically conducting half-space solid whose surface is subjected to a time-dependent heat is studied in the context of Lord and Shulman theory. The solid is placed in an initial magnetic field parallel to the plane boundary of the half-space. The normal mode analysis is used to obtain the exact expressions for the considered variables. The results of the considered variables are represented graphically. From the distributions it can be found the coupled effect and thermal wave effect.

Abstract: In order to study the damage mechanism under different stress states of aluminum alloy components, two kinds of representative triaxial stress states were adopted, namely notch tensile and pure shear. The results of study showed: During the notch tensile test, stress triaxiality in the least transverse-section was relatively higher. With increasing applied stress, the volume fraction of the microvoid in notch root was increasing constantly. When microvoid volume fraction reached the critical value, the specimen fractured. During the pure shear test, stress triaxiality almost came up to zero, and there was almost no micro-void but localized shear bands within the specimen. The shear bands resulted from non-uniform deformation constantly under the shear stress. With stress concentrating, the cracks were produced in the shear bands and later coalesced. When the equivalent plastic strain reached the critical value, the specimen fractured. The modified Gurson damage model and the Johnson-Cook model were used to simulate the notch tensile and shear test respectively. Simulated engineering stress-strain curves fit the measured engineering stress-strain curves very well. In addition, the empirical damage evolution equation for the notch specimen was obtained from the experiment data and FEM simulations.

Abstract: Geometrically nonlinear bending and buckling of circular sandwich plates subjected to transversely non-uniform temperature rise is investigated in this paper. On the basis of sandwich plate theory, nonlinear equations governing the large thermal axis-symmetric deformations of circular sandwich plate in terms of the middle plane’s displacements are derived. Numerical solutions of the nonlinear boundary value problem are obtained by using the shooting method. Equilibrium paths and configurations for different boundary conditions and different values of materials and geometry parameters are illustrated. Numerical results show that the boundary conditions and the stiffness greatly effect critical buckling loads.

Abstract: The influences of crystallographic and geometric parameters such as grain misorientation on the performance of short cracks are illustrated based on FEM in this paper. Firstly, the microstructure is simulated to account for the effects of grain misorientation on the performance of short cracks and the short cracks are initiated within the microstructure for the further investigation. The influence of grain misorientation is demonstrated by the change of neighboring grain orientations with an initiated short crack from 0° to 180°. The effects of the grain boundary on the short crack with the crack arrested or retarded are described by the crack propagation until it approached the grain boundary. The results will give more useful information such as crack arrested and retardation to the further research on the characteristics and evolution of short cracks.

Abstract: PLA/PCL and PLA/PCL/LTI blends were developed to improve the fracture properties of biodegradable PLA. LTI was blended to improve the miscibility of PLA and PCL. It was shown that the fracture toughness values were dramatically increased due to LTI addition. SEM results also exhibited that PCL spherulites decreases due to LTI addition and therefore, void formation is reduced and local stress concentration is suppressed, resulting in the improvement of the toughness values. The improved miscibility is also closely related to the enhancement of ductile deformation; as a result, the fracture toughness is increased.

Abstract: Biaxial compression model tests on rockmass containing intermittent joints under plane stress condition were carried out in this study, where the laser speckle photo technique was used for measuring the displacement field. The results obtained have indicated that the laser speckle method was effective and the measuring value was about 14% less than the measuring value of dial gauges. Based on the displacement field and the principal stress field which were measured by laser speckle photo technique, dial gauges and strain gauges, the angle of wing incipient crack, the evolution of stress field at the joint tip and the path of crack extension were deeply studied. The deformation and failure characteristics, including the fracture mechanism of rockmass, were also analyzed in this study.