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In Wang et al. (2002), the mode I crack problem has been analyzed for a functionally graded material strip with arbitrarily distributed properties. For the completeness of the research, this paper provides an analysis method for the mode II in plane and mode III anti-plane elastic crack problems for a functionally graded material (FGM) strip containing a crack along the gradient direction. In the analysis, the gradient region is treated as a number of homogeneous layers stacked along the gradient direction. The analytical models developed in this paper for the modes II and III problems, together with the model developed in Wang et al. (2002) for the mode I crack problem complete the analysis of the mixed-mode crack problem for functionally graded materials with a crack parallel the gradient direction. Those analytical models allow the material properties be any continuous functions along the thickness direction of the strip. [ABSTRACT FROM AUTHOR]

The paper addresses special features of nonlocalized and localized fatigue damage in metals and alloys. The sizes of maximum fatigue cracks at a fatigue limit in metals and alloys of various grain sizes and strengths are analyzed. The authors discuss the linear and nonlinear fracture mechanics criteria that relate the fatigue crack sizes and the fatigue limits. The experimental values of the fatigue crack size are compared to those calculated by different criteria. Special features of initiation of nonpropagating fatigue cracks in the presence of stress concentrators are studied. [ABSTRACT FROM AUTHOR]

Abstract  Dynamic failure events such as armor penetration and explosive fragmentation are too complex to be treated by classical single-crack continuum fracture mechanics. In such cases deformation and fracture result from multiple cracks, voids, and shear bands acting simultaneously and influencing one another’s evolution. An alternative “meso” fracture mechanics is needed that treats microfailure activity while permitting fast and inexpensive predictive computations. This paper discusses the approach and experiments that elucidate and quantify failure physics on the micron level. “Rosetta Stone” experiments that isolate a damage mode, produce statistical distributions of damage features, and “freeze in” damage at various stages of development are described and illustrated. The observations and data lead to equations describing nucleation and growth of cracks, voids, and shear bands. The resulting mesomechanical material failure models link the microworld with the macroworld and can be used in continuum hydrocodes for fast, efficient simulations of dynamic fracture scenarios. [ABSTRACT FROM AUTHOR]

In order to avoid introduction of an error when a local crack growth criterion is used in an incremental crack growth formulation, each straight crack extension would have to be infinitesimal or have its direction corrected. In this paper a new procedure to correct the crack extension direction is proposed in connection with crack growth analyzed by the Dual Boundary Element Method (DBEM). The proposed correction procedure and a reference correction procedure already described in the literature are evaluated by solving two different computational crack growth examples. In the two examples it is found that analyses of the crack paths performed with the proposed crack correction procedure using big increments of crack extension are in excellent agreement with analyses of the crack paths performed by using very small increments of crack extension. Furthermore, it is shown that the reference correction procedure has a tendency to overcorrect the crack growth direction if the stop criterion for the iterative correction procedure is not calibrated in each new crack growth analysis. [ABSTRACT FROM AUTHOR]

A general numerical tool for the analysis of three–dimensional bimaterial interface cracks is presented in this paper. The proposed tool is based on a multidomain formulation of the Boundary Element Method (BEM), with the crack located at the interface of the domain. Mixed mode stress intensity factors are computed along the three-dimensional crack fronts using the Energy Domain Integral (EDI) methodology and decoupled via the Interaction Integral. The capability of the procedure is demonstrated by solving a number of examples. The last of these examples consists in a thick centre cracked panel for which the behaviour of the J-integral and the mixed-mode stress intensity factors along the crack front is studied as a function of the material mismatch. [ABSTRACT FROM AUTHOR]

Weld bead geometry cannot, by its nature, be precisely defined. Parameters such as bead shape and toe radius vary from joint to joint even in well-controlled manufacturing operations. In the present paper the weld toe region is modelled as a sharp, zero radius, V-shaped notch and the intensity of asymptotic stress distributions obeying Williams’ solution are quantified by means of the Notch Stress Intensity Factors (NSIFs). When the constancy of the angle included between weld flanks and main plates is assured and the angle is large enough to make mode II contribution non-singular, mode I NSIF can be directly used to summarise the fatigue strength of welded joints having very different geometry. By using a large amount of experimental data taken from the literature and related to a V-notch angle of 135°, two NSIF-based bands are reported for steel and aluminium welded joints under a nominal load ratio about equal to zero. A third band is reported for steel welded joints with failures originated from the weld roots, where the lack of penetration zone is treated as a crack-like notch and units for NSIFs are the same as conventional SIF used in LEFM. Afterwards, in order to overcome the problem related to the variability of the V-notch opening angle, the synthesis is made by simply using a scalar quantity, i.e. the mean value of the strain energy averaged in the structural volume surrounding the notch tips. This energy is given in closed form on the basis of the relevant NSIFs for modes I and II and the radius RC of the averaging zone is carefully identified with reference to conventional arc welding processes. RC for welded joints made of steel and aluminium considered here is 0.28 mm and 0.12 mm, respectively. Different values of RC might characterise welded joints obtained from high-power processes, in particular from automated laser beam welding. The local-energy based criterion is applied to steel welded joints under prevailing mode I (with failures both at the weld root and toe) and to aluminium welded joints under mode I and mixed load modes (with mode II contribution prevailing on that ascribable to mode I). Surprising, the mean value of ΔW related to the two groups of welded materials was found practically coincident at 2 million cycles. More than 750 fatigue data have been considered in the analyses reported herein. [ABSTRACT FROM AUTHOR]

The paper reports on the results from analysis of some nonclassical fracture problems that allow for stresses along cracks. The results have been obtained by the author and his collaborators at the Institute of Mechanics (Kiev) since 1980 [ABSTRACT FROM AUTHOR]

The present paper deals with the measurements of the critical Crack Tip Opening Angle by using an instrumented test. There is a comparison between the analysis of results made by a well known kinematic model and those given by finite element analysis based on a cohesive model for node release. Analysis is performed both on simple specimens and on back slotted ones. [ABSTRACT FROM AUTHOR]

The sectional thickness of plate-like components has a significant influence on the fatigue and fracture properties. This effect is primarily due to the differences in the through-the-thickness stresses prevailing at the tip of a crack in a finite-thickness plate or shell. Characterization of this effect to date has remained largely empirical. The current paper presents new analytical results for CTOD for the through-the-thickness crack in infinite plates with various thicknesses. These results are based on a recently developed solution for an edge dislocation in infinite plate of arbitrary thickness. The analytical predictions of the CTOD and the constraint factor are compared with the three-dimensional FE results. It is shown that the analytical and the numerical results are in good agreement when the numerical calculations are not affected by the size of the FE mesh and by the boundaries of the FE model. [ABSTRACT FROM AUTHOR]