Papers by Keyword: Mixed-Mode Crack

Abstract: Concerning on the modelling of quasi-brittle fracture process zone at interface crack of quasi-brittle materials and structures, typical constitutive models of mixed mode interface cracks were compared. Numerical calculations of the constitutive behaviours of selected models were carried out at local level. Aiming at the simulation of quasi-brittle fracture of concrete-like materials and structures, the emphases of the qualitative comparisons of selected cohesive models are focused on: (1) the fundamental mixed mode fracture behaviours of selected interface crack models; (2) dilatancy properties of the selected models under mixed mode fracture loading conditions.

Abstract: Real-time displacement in stable crack tearing was measured by digital image correlation technique. Quantitative analyses were provided on mixed-mode Ⅰ/Ⅱ fracture and critical CTOA for recycled thin sheet metals. It is shown that the fracture of recycled thin sheet metals is tough due to the large plastic deformation, and mixed-mode crack is easier to extend than mode Ⅰ crack. The critical CTOA at stable crack tearing is constant and can be used as a fracture criterion for the thin sheet metals.

Abstract: In this study, the photoelastic experiment hybrid method was introduced and applied to the fracture problems of the isotropic polycarbonate plate with a central crack under the uniaxial and equibiaxial tensile load. The influences of equibiaxial tensile load on the isochromatic fringes and stress fields, stress intensity factors near the mixed mode crack-tip were investigated. As the results, without relation to the inclined angle of crack, the asymmetric isochromatic fringes around the crack propagation line under uniaxial tensile load has become symmetric and the slope of isochromatic fringe loop has inclined toward crack surface when an equal lateral tensile load was added. Furthermore, the distribution of all stress components have changed from asymmetric shape to symmetric shape, and only the range of compressive stress of σχ/σ0 have changed as compared with the mode I condition under unaxial load with β = 0°. When an equal lateral tensile load was added to uniaxial load, the value of stress intensity factors are little changed when β = 0° but the values of KI /K0 are increased and KII /K0 are become zero, that is, mode I situation when β = 15°~45°.

Abstract: Considering the SD effect, the parabolic-type yield criterion is obtained by using a new parameter. And by analogy with associated plastic flow rule, the ceramic phase transformation constitutive model is established. Under plane strain condition, the theoretical toughening expressions of mixed-mode I-II stationary cracks and steady-state growing cracks are developed by applying the weight function method. And the toughening effect is discussed under the influence of Poisson ratio, parameter and . The simulation results show that these phase transformation toughening effects are in good agreement with experimental results. And comparing with other yield criterions, it is more in line with actual characteristics of zirconia ceramic materials, when the expression of mixed I-II crack is reduced to mode I crack. And it also could provide theoretical support and reference for the further research of ceramic phase transformation toughening.

Abstract: The paper presents a numerical investigation of mixed-mode crack induced failure of concrete beam strengthened with steel plate. Both the cracking of the concrete and concrete-steel interfacial debonding can be observed. There is a shear stress concentration at the pre-existing crack or debonding tips, which is the root cause of the debonding. The results indicate that debonding only initiates and propagates along the left interface to the steel plate because that the normal stress along the left interface is tensile which make considerable contribution to the debonding and the normal stress along the right interface is compressive.

Abstract: Bamboo is a typical natural graded material, from the inner layer to the middle layer, and then to the outer layer. The elastic modulus is increasing gradually. The cracks grown on the inner layer and outer layer have different effects on the intensity. In this paper, the influence of the gradient distribution on the fracture behavior of the mixed-mode I and П cracks located in different layers is studied. The displacement measurement of bamboo specimens on asymmetric loading using digital speckle correlation method (DSCM) is performed and the crack tip opening displacement (COD), the stress intensity factor can be obtained. The results show that the COD of the crack in the outer layer is less than that of the crack in the inner layer, the stress intensity factor in the outer layer is greater than that of the crack in the inner layer, that means the property of the gradient distribution of bamboo has the protecting function for the static crack in the inner layer.

Abstract: This paper addresses the numerical simulation of mixed-mode crack propagation in Functionally Graded Materials (FGMs) by means of eXtended Finite Element Method (XFEM), endowed with elastic and toughness properties which gradually vary in space. The method allows to follow crack paths independently of the finite element mesh, this feature is especially important for FGMs, since the gradation of the mechanical properties may lead to complex propagation paths also in simple symmetric tests. Each step of crack growth simulation consists of the calculation of the mixed-mode stress intensity factor by means of a non-equilibrium formulation of the interaction integral method, determination of the crack growth direction based on a specific fracture criterion. A specific fracture criterion is tailored for FGMs based on the assumption of local homogenization of asymptotic crack-tip fields in FGMs. The present approach uses a user-defined crack increment at the beginning of the simulation. Crack trajectories obtained by the present numerical simulation agree well with available experimental results for FGMs. The computational scheme developed here serve as a guideline for fracture experiments on FGM specimens (e.g. initiation toughness and R-curve behavior).

Abstract: A numerical scheme is presented to predict crack trajectories in three dimensional components. First a relation between the curvature in mixed-mode crack propagation and the corresponding configurational forces based on the principle of maximum dissipation is reviewed. With the help of this, a numerical scheme is presented which is based on a predictor-corrector method using the configurational forces acting on the crack together with their derivatives along real and test paths. It is outlined how to extend the approach to three dimensional problems. With the help of this scheme it is possible to take bigger than usual propagation steps, represented by splines. Essential for this approach is the correct numerical determination of the configurational forces acting on the crack tip. An approach valid for arbitrary non-homogenous and non-linear materials with mixed-mode cracks is presented. Numerical examples show, that the method is able to predict the crack paths in components with holes, stiffeners etc. with good accuracy, saving much computational effort.

Abstract: In practical engineering, the cracks are always mixed mode. The research on the mixed fracture criterion has an important significance in fracture mechanics and engineering. Stress state of the mixed mode cracks is complicated. A new unified strength theory considering the effects of all the three principal stresses is generalized into the fracture mechanics in this paper. The complex stress states are common characteristics between the mixed mode cracks and the unified strength theory. A unified fracture function criterion is established by using the unified strength theory in this paper. In the unified fracture function, the difference between tension and pressure and the effect of the intermediate principal stress σ₂ are considered. With the variation of α = σ_t/ σ_c and failure parameter b , a series of mixed mode crack criteria are formed, and can be applied for many materials. The J-integral is calculated through FEM. According to the relation between the result and the stress intensity factor, K_lc can be obtained. Then it is used in the unified fracture function. The unified fracture criterion is compared with those of other mixed mode criterions.