Elastodynamic Crack Analysis by Boundary Element Method Using Numerical Inversion of Laplace Transform.

A boundary element method using Laplace transform in time domain is developed for the analysis of fracture mechanic under coupled thermoelastic assumption. The transient coupled thermoelastic field is solved without need for domain discretization. The singular behavior of the temperature and displacement fields in the vicinity of the crack tip is modeled by quarter-point elements. Thermal dynamic stress intensity factors for mode I are evaluated from computed nodal values, using the well-known displacement and traction formulas. The accuracy of the method is investigated through comparison of the results with the available data in literature. The conditions where the inertia term plays an important role is discussed and variations of the dynamic stress intensity factor is investigated.

In this paper, the fracture problem of functionally graded material (FGM) was studied, and the shear modulus was assumed to be an exponential function. The influences of inhomogeneous parameter, crack size and crack angle on the stress intensity factors have been analyzed by the finite element method. The results indicated that the stress intensity factors of mode I decreased with the increasing of the crack angle, the stress intensity factors of mode II increased with the increasing of the crack angle, and the crack stress intensity factor of mode I and mode II decreased with the increasing of the inhomogeneous parameters at crack tips, which was of certain directive significance for the FGM design and manufacture in the actual engineering.

Due to a very short time span of dynamic fracture event, it is quite difficult to experimentally measure dynamic stress field near the crack tip. Node-based finite element method (NBFEM) developed by Yagawa et al was extended to solve dynamic crack propagation problems by modifying the original NBFEM and three schemes of crack tip node separation during crack propagation are examined. A dynamic stress intensity factor in mode I, KdynI, is calculated for fast propagating crack at a constant speed. Three different schemes of the crack tip node separation were considered. Comparing the numerical results with those analytically obtained by Freund showed that the condition of zero initial velocity and nonzero acceleration gives the highest accuracy of three conditions with only 0.91% error.

The principles of physical mesomechanics and synergetics, provides for a measure of energy involved in the ability of a material to resist deformation and fatigue cracking used for introducing a concept of equivalent stress and stress intensity factor in Mode I crack opening of fatigued metals. Acquired under the standard test conditions, the curves of unidirectional tension and those of fatigue duration and of crack-growth kinetics show themselves applicable as universal master-diagrams descriptive of the material behavior though under multiparametric loading. Specimen patterns of fracture, revealed by the test pieces of metallic alloys given to asymmetrical biaxial loading or multiparametric loading, passed careful research. In the biaxial case, this research facilitated finding of the view of the correction function for the level of equivalent stress and, in the multi-axial case, employing of the above subject ideas to ascertain the very level of equivalent stress.

Cracks around railway wheel flats exposed to rolling contact loads and residual stresses

Dynamic stress intensity factor K III and dynamic crack propagation characteristics of anisotropic materials

Real-time measurement of shear fatigue crack propagation at high-temperature using the potential drop technique

AerMet 100 exhibits excellent mechanical properties, proven in previous studies; however, defects may greatly influence the mechanical behavior during the service of the material, which serves as one of the major challenges in the wider application of the material. To quantify the crack evolution process, the in-plane type I crack propagation behavior is comprehensively investigated based on the extended finite element method (XFEM). The crack growth is characterized in terms of the extracted crack propagation angle, stress intensity factor (SIF) in the crack tip, and stress field profiles during the crack propagation process. An extrapolation method is adopted to calculate the SIF, followed by a series of parametric studies on the influence of the governing factors, i.e., initial crack length, initial crack location, initial crack angle, and the crack number through numerical investigation. It is found that the crack propagation angle enlarges monotonously with the increase of the initial crack location, the initial crack length, and the crack number, increases slowly with the growth of initial crack angle, and rapidly enlarges in reverse at about 45°. The SIF in Mode I, KId, gradually decreases with the increase of the initial crack location and the crack number, and nearly keeps steady when the initial crack length and initial crack angle varies. Results provide further understanding of the failure and fracture behavior of AerMet 100 and guide the future application and design of the structures.

Mixed-mode fracture mechanics analysis of an embedded arbitrarily oriented crack in a two-dimensional functionally graded material using plane elasticity theory is considered. The material properties are assumed to vary exponentially in two planar directions. Then, employing Fourier integral transforms with singular integral equation technique, the problem is solved. The stress intensity factors (SIFs) at the crack tips are calculated under in-plane mechanical loads. Finally, the effects of crack orientation, material non-homogeneity, and other parameters are discussed on the value of SIF in mode I and mode II fracture.

The problem of a kinked crack is analysed for the most general case of elastic anisotropy. The kinked crack is modelled by means of continuous distributions of dislocations which are assumed to be singular both at the crack tips and at the kink vertex. The resulting system of singular integral equations is solved numerically using Chebyshev polynomials and the reciprocal theorem. The stress intensity factors for modes I, II and III and the generalised stress intensity factor at the vertex are obtained directly from the dislocation densities.

Parametric features of an UIC60 rail at weld bottom crack in transverse direction under weld-wheel contact forces

The transient elastodynamic response of a transversely isotropic material containing a semi-infinite crack under uniform impact loading on the faces is examined. The crack lies in a principle plane of the material, but the crack front does not coincide with a principle direction. Rather, the crack front is at an angle to a principle direction and thus the problem becomes more three-dimensional in nature. Three loading modes are considered, i.e., opening, in-plane shear and anti-plane shear. The solutions for the stress intensity factor history around the crack tip are found. Laplace and Fourier transforms together with the Wiener-Hopf technique are employed to solve the equations of motion directly. The asymptotic expression of stress near the crack tip leads to a closed-form solution for the dynamic stress intensity factor for each loading mode. It is found that the stress intensity factors are proportional to the square root of time as expected. Results given here converge to known solutions in transversely isotropic materials with a crack oriented along a principle direction and isotropic materials as special cases. The results of this analysis are used to find approximate strain energy release rates for dynamically loaded penny shaped cracks.

Analytical stress intensity factors for edge-cracked cylinder

Two-dimensional time-harmonic BEM for cracked anisotropic solids

Applications of the fast multipole fully coupled poroelastic displacement discontinuity method to hydraulic fracturing problems