Applied Mechanics and Materials Vols. 275-277

Abstract: When conducting modal analysis to the structure with crack defect using ansys finite element, we usually adopt the method of cutting a rectangular notch to simulate the crack on the model structure. As a result, the different crack simulation requires repeated modeling, which is a waste of time, and we cannot guarantee the accuracy of the calculation. In this paper, mathematical model between the local stiffness and crack size is established based on the finite element simulation of a diameter of 8mm steel bar. Thus, we can simulate varisized crack defects through a fixed crack notch by the method of modifying local stiffness. The method we used is more simple and accurate than the traditionary one by cutting a rectangular notch to form cracks, and reduces the workload, and has certain research significances.

Abstract: For solve efficiently the problem of crack propagation, the extended finite method(XFEM) was applied to analyse the problem. The extended finite method introduced nodal enrichment functions based on usual nodal shape functions, and traced crack propagation with the level set method. The extended finite method can model arbitrary crack growth without remeshing. This paper simulated the problem of the compact tension specimen with circular hole by extended finite method. The calculation results show that the extended finite method can solve efficiently the problem of crack growth , and the circular hole of compact tension specimen effect the trajectory of mode I crack propagation within certain distance.

Abstract: The influence of residual stesses must be considered in bending fatigue life prediction of fillet rolling crankshafts. In this paper, the stress/strain distributions near fillet during fatigue tests are calculated by finite element method. In residual stress computation, the three dimensional flexible contact model is adopted, and in bending strain computation, the static analysis are selected. Then, bending fatigue life prediction is performed by local stress-strain approach based on the residual stess and bending strain amplitude, and the results agree with the bending fatigue test.

Abstract: In order to investigate the ultra-long life fatigue properties of welded joints, ultrasonic fatigue tests of base material and welded joints were carried out using Q345q steel in ambient air at room temperature with a stress ratio R=-1. The results showed that the fatigue strength of specimens with welded joints dropped about 60% compared with that of base steel. To improve the fatigue properties of welded joints, two groups of specimens were treated by shot peening with different degrees which produced different compressive residual stresses on samples. It was found that the shot peening treatment could improve the fatigue strength of welded joints obviously. The fatigue fracture surface was analyzed by scanning electron microscopy. The fractography showed that there were two kinds of crack initiation mechanism in the Q345q base steel, crack inition from defects on the surface for high cycle fatigue failure and in the interior of the sample in very high cycle fatigue range. However, almost all cracks of welded joints initiated from defects caused by welding process. The failure of welded joints usually happened at the section of welded toes in the area of fusion or geometric discontinuity.

Abstract: Thin-walled tubes with origami patterns are popular design for the energy observing devices. However, less study has been done when they subjected to cracks. In this work, the origami square tube with different height to wall thickness ratio are first studied to investigate the collapse modes and deformation mode. Further more, stress concentration areas are identified by numerical simulations. Finally, horizontal and vertical crack was implemented in one of the side in order to study the effect on the deformation mode.

Abstract: Applied damage mechanics and coupled finite element method, to study the fatigue crack initiation life problem. Application of coupling finite element method, the damage coupling effect can be modified through the global stiffness matrix to achieve. The step length of the damage evolution is divided by the damage variable of the critical element, and then the damage evolution is analysised. The corresponding stiffness matrix and loading matrix can be obtained continually under the condition of increasing the damage evolution step of the critical element,then the equivalent stress can be calculated. The corresponding fatigue crack initiation life can be calculated by using the damage evolution equation, the progress will not stop until the damage degree of the critical element reaches to one. The fatigue crack initiation life is obtained by adding the fatigue crack initiation lives with different damage variable.

Abstract: This paper investigates the effect of various cycle counting correction factors in spectral fatigue damage calculations. Spectral fatigue calculations are based on complex stress transfer functions established through direct wave load analysis combined with stress response analysis. Cycle counting correction factors are introduced in the computation process to cater swell’s effect and to reduce the conservatism in the results due to narrow band approximation for a wide band random process. In this study, fatigue life of a ship structural detail is predicted by spectral method utilizing ANSYS software along with 3D liner sea-keeping code AQWA. Cumulative fatigue damage is calculated by a MATLAB program based on direct calculation procedure of spectral fatigue using cycle counting correction factors proposed by Wirsching, Rice and Dirlik. The results show an overall decrease in the computed fatigue damage and a corresponding increase in the expected fatigue life of the structure.

Abstract: The paper reviews the numerical methodology to investigate fracture parameter namely energy release rate, G, of a mixed mode crack. An inclined, through, centre crack is assumed in a ductile steel plate subjected to bi-axial tension. Applied stress and crack size are suitably selected to simulate small scale yielding (SSY) condition at the crack tips. The cracked plate is modelled by finite element method. Both plane stress and plane strain situations are examined. G value is found from J integral. Equations of transformation are employed to obtain normal and shear stress in the plane of the crack. G is then again determined for Mode I and Mode II cracks by modelling each case separately. The analysis is finally validated by fulfilment of the conservation of energy release rate criterion, G (Mixed mode) = G (Mode I) + G (Mode II).

Abstract: Energy release rate, G, of a Mode I crack is estimated numerically by load displacement procedure in the paper. A, through, edge crack is considered in a thin aluminum 2024-T3 alloy plate. The cracked plate is modeled by finite element method. Values of applied load and crack size are suitably selected to simulate LEFM and SSY regimes. Load line displacements are measured from finite element solution. Values of G are compared with J integral values that are obtained from finite element solution using stress and displacement fields near the crack tip.

Abstract: The problem of anti-plane crack in infinity orthotropic functionally graded materials is studied by using of integral transforms-dual integral equations. The shear modulus in the two principal directions of the functionally graded material was assumed to vary proportionately as gradient model of double parameters. And the variation curves of the dimensionless stress intensity factor with the orthogonal parameter and the crack length have been obtained by using the mathematical software .The results shows that stress intensity factor increases with the increasing of and a. It means that stress intensity factor decreases as the shear modulus of perpendicular to crack direction increased.