Papers by Keyword: Strain Energy Release Rate (SERR)

Abstract: The aim of this paper is to introduce a virtual crack closure technique based on EFG method for thread-shape crack. The cracked component is discretized and the displacement field is determined using a coupled FE/EFG method, by which EFG nodes are arranged in the vicinity of crack tip and FE elements in the remain part in order to improve computational efficiency. Two typical parameters, nodal force and crack opening displacement attached to crack tip are calculated by means of setting up an auxiliary FE zone around crack tip. Strain energy release rate (SERR), further stress intensity factor (SIF) are determined by the two parameters. The method to calculate SIF is named as virtual crack closure technique based on EFG method. It is showed by several numerical examples that using the method presented in this paper, SIF on the crack tip can be obtained accurately.

Abstract: Material flaws, pre-cracks and crack initiation due to cyclic loading often lead to undetected crack propagation in commercial structures like aircraft components, automotive parts and computer motherboard. Cyclic loading can make the crack grow large into any shape with an arbitrary orientation, depending on the structure geometry, boundary and loading conditions. Since crack propagation in many cases may lead to catastrophic failure with human and monetary loss as a result, it is important to enable crack growth prediction at all stages of development and during maintenance in order to prevent such scenarios. Micro mechanical approach is used for modelling the crack in composite materials. Crack propagation in a single edge crack plate is carried out by using FEM analysis. 2D model is analysed to determine the crack growth. The crack propagation rate, stress intensity factor and strain energy release rate are predicted by varying the crack length in fiber reinforced epoxy composite using NISA/ENDURE.

Abstract: Past and on-going research works on adhesive bonding in composite and sandwich were reviewed. Discussion was emphasized on critical failure mechanisms (e.g. mechanism of peel fracture) to enhance the performance of the bonding. This paper also focused on the application of good adhesive bonding in the application of sandwich structures. Debonding between skin and core is one of the failure mechanisms that should be given more attention in fabrication of sandwich structures. Incorporating fillet in composite bonding is one of the alternative ways to reduce the stress concentration at the edges of overlap length and to produce high peel strength for bonding. Basic understanding of the designs, theories and manufacturing of adhesive bonding were also presented. Several important parameters in the design such as the strain energy release rate (SERR) and formation of fillet also discussed. The analysis of SERR using virtual crack closure technique (VCCT) has also been highlighted to achieve high strength of adhesive bonding, providing the key element for optimization of the delamination resistance in maximizing energy absorption during fracture. Significant challenges or limitations in improving and optimizing the design were also highlighted.

Abstract: Some results of 3D finite element analyses of the all fracture modes (AFM) specimen on mixed-mode II and III fracture are presented in this paper. The computational fracture analysis is based on the calculation of separated strain energy release rates (SERRs) along the crack front by the modified virtual crack closure integral (MVCCI)-method and the commercially available FE-code ANSYS. Calculation results show that under pure in-plane shear loading (mode II), not only the mode II, but also the mode III loading conditions, are generated owing to the Poission’s ratio effects. Similarly, under pure out-of-plane shear loading (mode III), besides the mode III, the mode II loading conditions are induced due to the global deformation. Nevertheless, once in-plane and out-of-plane shear loadings are superimposed, the fracture behavior appears more complex. Further discussion is given associate with some previous study.

Abstract: This research aims to investigate the effects of particle size, volume fraction and dispersion on the tensile strengths of particulate nanocomposites with an embedded crack. The finite element micromechanical model in conjunction with linear elastic fracture mechanics (LEFM) was used to study the particle effect on the fracture behavior of nanocomposites. Results indicated that the tensile strength of particulate composites increases when the particle size is decreasing, however it can be deduced dramatically by the local aggregation of particles. The simulation results are in good agreement with the experimental observation. In addition, the predictions show that the tensile strength decreases with the increase of volume fraction of nanoparticles. So far, no consistent experimental data can be found to validate the above results and thus further study in this issue is required.

Abstract: The interfacial property between graphite/epoxy laminate and multi-walled carbon nanotubes (MWNTs)/polymer nanocomposites was investigated. For the graphite/epoxy laminate, the fiber orientations were varied. For the MWNTs/polymer nanocomposites, the epoxy resins were used as the matrix material and the MWNTs were used as the reinforcement. The weight percentage of MWNTs in the MWNTs/polymer nanocomposites beam specimen was varied. The graphite/epoxy laminate and the MWNTs/polymer nanocomposite beam were glued together by epoxy to make the test specimens. To determine the interfacial property, the end notch flexure (ENF) method was used, and the specimen was placed in a three-point bending test to evaluate the critical strain energy release rate Gc. In analysis, the finite element method was used to obtain the numerical values of the critical strain energy release rate Gc and compared with the experimental ones.

Abstract: Steel-concrete composite structures are widely used in high buildings for its excellent seismic behaviors, whereas faults or cracks, which have great influence on interfacial mechanical behaviors of structural members, inevitably form near the interface between steel and concrete during the process of molding. Therefore, it is necessary to study the mechanical characteristics of the crack tip near the interface. In this paper, the application scope of the path-independence of J-integral in steel-concrete composite structure with a crack is discussed. According to the conservation law of J-integral for the steel-concrete composite structure with a crack parallel to the interface, a hypothesis that the value of strain energy release rate (SERR) of the mode-I fracture is independent of the crack location when the crack is parallel and close to the interface is put forwarded. And this hypothesis is verified through finite element method (FEM). A schematic model for a skew crack near the steel-concrete interface is provided. The variation law of SERR with the Dundur’s parameters and the angle between crack direction and interface are calculated by FEM. At last, calculating method of the stress intensity factor as well as the SERR for a skew crack near the interface is suggested. All these may contribute to further investigation on interfacial mechanical behaviors for steel-concrete composite structure.

Abstract: The paper presents results of studies into the effect of repetitive low-energy impacting (known as impact fatigue) on reliability and crack growth in adhesively bonded joints. This type of loading is compared to the standard tensile fatigue in order to assess severity of such loading regime. Another loading type studied is a combination of a small portion of repetitive impacts with tensile fatigue. Crack propagation in a joint exposed to these types of loading is studied experimentally and numerically (with finite elements). This analysis is accompanied by microstructural studies of various damage processes, active at different stages of the crack growth process.

Abstract: Steel-concrete composite structures are widely used in high buildings for its excellent seismic behaviors, whereas faults or cracks, which have great influence on interfacial mechanical behaviors of structural members, inevitably form near the interface between steel and concrete during the process of molding. Therefore, it is necessary to study the mechanical characteristics of the crack tip near the interface. In this paper, the application scope of the path-independence of J-integral in steel-concrete composite structure with a crack is discussed. According to the conservation law of J-integral for the steel-concrete composite structure with a crack parallel to the interface, a hypothesis that the value of strain energy release rate (SERR) of the mode-$fracture is independent of the crack location when the crack is parallel and close to the interface is put forwarded. And this hypothesis is verified through finite element method (FEM). A schematic model for a skew crack near the steel-concrete interface is provided. The variation law of SERR with the Dundur’s parameters and the angle between crack direction and interface are calculated by FEM. At last, calculating method of the stress intensity factor as well as the SERR for a skew crack near the interface is suggested. All these may contribute to further investigation on interfacial mechanical behaviors for steel-concrete composite structure.

Abstract: Multi-layer structures are common in electronic package especially for the micro devices manufactured via the semi-conductor processes or MEMS processes. Interfacial crack due to the delamination significantly weakens the multi-layer structure. It is desired to understand the interfacial fracture properties of the electronic packaging materials. In this research, three specimens named Doubled Cantilever Beam (DCB), End-Notched Flexure (ENF), and Four-Point-Bending are proposed to investigate the fracture toughness associated with mode I, mode II and mixed mode. Basing on the Euler-Bernoulli beam theory, the strain energy in a bi-layer beam is derived. The strain energy before and after the propagation of the interfacial crack are calculated, lead to the determination of the strain energy release rate. The analytical results of strain energy release rate derived in this investigation are compared with the numerical results obtained from finite element method. The effects of material properties and thickness between the adjacent layers of interfacial crack are examined through the parametric study.