Papers by Keyword: Crack Tip

Abstract: Metallic implants should have the following basic characteristics as excellent biocompatibility, high corrosion resistance, suitable mechanical properties (strength, fracture toughness...) and high wear resistance in order to serve safely and adequately for a long-time period without rejection. Austenitic stainless steels are popular for implant applications because of their availability, lower cost, excellent fabrication properties, accepted biocompatibility and toughness. The mechanical working conditions within human body are tough, because surgical implants are subjected to static and dynamic mechanical loading and exposed to surrounding aggressive environment such as human body. As the material is subjected to cyclic loading, micro-plastic deformation occurs around the crack [1,2]. The aim of this paper is to observe the area around the originated crack on the testing bar. The microstructural analysis of initial state and after three-point bending was performed by optical and scanning electron microscopy. Hardness measurement was performed under the crack originated after cyclic loading.

Abstract: K-criterion that is used to boundary line and brittle fracture is presented when the size of plastic zone around crack-tip is less than that of adaptive zone of K-criterion by comparison adaptive zone of K-criterion with plastic zone around crack-tip in this paper. Finally numerical examples are given to illustrate the applications of the present method by comparison with other methods.

Abstract: The tearing mechanical properties and the deformation field distribution of 45 degree oblique direction of the crack tip was studied on the stratospheric airship envelope reinforced by plain woven Kevlar-fiber composite. Here, the material samples were prefabricated with the initial length of 20mm unilateral incision, and the digital speckle correlation experimental method was used to obtain the perpendicular crack tip displacement and strain fields with artificial spots under mono-axial tear test. The results show the deformation field changes with the characteristic of discrete step and the strain concentration phenomenon, and the strain concentration zone expands as increasing tensile load. The warp and weft step maximum displacement reaches 6.00mm and 1.7mm, and deformation in every step exhibits a diminishing step law, the warp deformation in the rear area of the crack tip are evenly, while the shear and weft strain volatile in a wide range

Abstract: This report is mainly performed to investigate finite element (FE) modeling and post-processing capacities for fracture mechanics analyses characterized by the stress intensity factor (SIF) at successively stationary crack tip positions. As part of a linear elastic fracture mechanics (LEFM) analysis, the determination of stress intensity factor distribution can also be adopted by J-integral approach. The aim of this report is to review three papers related to estimate J-integrals through FE study and represent the theoretical backgrounds. Furthermore, the technical details for both FE modeling and SIF evaluation will be described in this report based on complete understanding of three reference papers. These numerical approaches to deal with SIF evaluation of general cracks can be applied in 2D and 3D FE models.

Abstract: The relationship between stress and crack growth was studied. Applying the software ANSYS, the method of calculating stress intensity factor of composite mode cracks was built. At the same time, the stress intensity factor of mode I crack was calculated and the influence of crack size and loading on the stress intensity factor was studied. The results show that the results of ANSYS are almost the same to analytic results, which proves that the method is feasible. When the crack is quite big or quite small, the result of ANSYS’ error is comparatively obvious, which is due to the problem of the refinement of meshing. When the crack is too big, the dense of meshing is inadequate.

Abstract: Based on Numerical Manifold Method (NMM), a novel method is presented for computing Stress Intensity Factor (SIF) of cracks. The Williams expansions are employed as the analytical solutions in the mesh containing the crack tip. And high-order polynomial functions are used as the numerical solutions in the surrounding meshes. Then the SIFs are computed via combination of the numerical solutions and the analytical solutions. Meanwhile, the meshes in NMM need not conform to the physical boundaries including the crack edges, allowing the cracks arbitrarily align within the meshes. The given example shows the validity of the method.

Abstract: This paper focuses on the thermo-mechanical behaviors of shape memory alloy (SMA) board with a crack subjected to bending load. The stress field near the crack tip of SMA board is described according to the solution of linear elastic mechanics. The phase transformation behaviors of SMA board are formulated based on Zhou’s one-dimensional phase transformation model. The phase transformation zone equation is derived to describe the phase transformation zone near the crack tip.

Abstract: The finite element method is adopted to simulate the whole process of electromagnetic acoustic emission in this paper. The effects of different voltage on distribution of displacement and temp at the tip of the crack are discussed. The simulation results show that, above voltage loading on the metal plate, the value of the temp around the crack tip can be up to the melting point , which will melt the tip of crack. Larger melting sizes are obtained when loading voltage is increased. At the same case, the displacement duo to electromagnetic force at crack tip is much larger than this induced by thermal expansion

Abstract: The failure components made of silicon is an important issue in the electronic and nano-technological developments. A study on the near-crack-tip deformation of single-crystal silicon wafer under tensile load was presented. The strain formulas around the crack tip of mode I crack were deduced from linear elastic fracture mechanics. The strain fields around the crack tip were simulated and analyzed in detail.

Abstract: An analysis of residual stress, one of the contributory factors to the crack tip driving force, is extremely important to probe the fatigue crack growth mechanism and to further develop the life prediction methodology. Since fatigue crack growth is governed by crack-tip plasticity and crack closure in the wake of the crack tip, the investigation of residual stain/stress field in both behind and in front of the crack tip is crucial. In the current work, a 304L stainless steel compact-tension specimen is pre-cracked under constant-amplitude cyclic loading. Neutron diffraction is employed to directly measure the three orthogonal residual strain fields with 1-mm spatial resolution as a function of distance from the crack tip. The mapping results show that the three orthogonal residual-strain distributions around the crack tip depend on the stress multiaxiality, not following a single Poisson relationship to each axis.