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Surface cracks are the most common defects in solar silicon wafers. The stress intensity factors (SIFs) calculated by the semi-analytical equation derived by Newman and Raju have been compared with results of 3D finite element analysis for a wide range of semi-elliptical surface crack configurations in thin silicon wafer subjected to bending. It has been shown that the geometrical nonlinearity of silicon wafers significantly influences the SIF values. The discrepancy between nonlinear and linear models is 19% for a surface crack with 20 μm depth and 1 mm length, while it is 74% for a surface crack with 160 μm depth and 100 mm length. Furthermore, the results show that for long surface cracks ( a / c ⩽ 0.01 ) finite element models should be used to calculate the SIF and the existing semi-analytical solution is not reliable.

This paper illustrates an efficient contour integral procedure to obtain stress intensity factors in combination of the asymptotic analysis with finite element analysis. Note that this set-up is very general: the material can be anisotropic elastic, and the specimen can be built as a bi-material system, notches of arbitrary opening angle can be analyzed (γ = 0 → crack, γ = 180° → free edge). The purpose of this technical note is to comment on three issues in the notch mechanics: the interpretation of the eigenvalue equation, the definition of stress intensity factors, and the effect of the outer contour location on H-integral evaluations.

In this study we focus on the fracture behavior of two types silicon-thin film glass-silicon (Si-Glass-Si) triple stacks specimens with a sharp corner. We determine the notch stress intensity factor K n for both specimens using a combination of the Williams eigenfunction expansion method, Stroh’s sextic formalism, finite element analysis, and the path-independent H-integral. Empirical solutions of dimensionless stress intensity factors are proposed for two typical specimens, and the dependence of geometry is analyzed. Furthermore, the effect of glass thickness on stress intensity is explored for anodic-bonded Si-Glass-Si triple stacks. We discuss the feasibility of using a critical value of K n to correlate the failure results for both specimens with various bond area and glass thickness.

A procedure for constraint correction of crack growth resistance curves for single edge notched specimens and for pipe geometries is presented. The procedure is based on FE models with the combination of shell- and line-spring finite elements. Crack tip opening displacement and T-stress are employed, and ductile crack growth is accounted for. Experimental crack growth resistance curves are obtained for both single edge notched tension- and bending-specimens for different crack depths to cover significantly different constraint levels. To account for different constraint levels, a method to scale the resistance curve using the T-stress is implemented. The analyses include ductile crack growth in both the circumferential and thickness directions. The effect of circumferential crack growth with biaxial loading is also presented. The results from the line-spring model are compared with detailed 3D-models for verification of the implementation of circumferential crack growth. The importance of including crack growth in circumferential direction is discussed based on numerical parametric studies. A measure to quantify the importance of circumferential crack growth is proposed.

The present study addresses the use of CTOD and T-stress in fracture assessments of surface cracked shell structures. A new software is developed for this purpose, denoted LINKpipe. It is based on a combination of a quadrilateral assumed natural deviatoric strain thin shell finite element and an improved linespring finite element. Plasticity is accounted for using stress resultants. A power law hardening model is used for shell and linespring materials. A co-rotational formulation is employed to represent nonlinear geometry effects. With this, one can carry out nonlinear fracture mechanics assessments in structures that show instabilities due buckling (local/global), ovalisation and large rigid body motion. Many constraint-measuring parameters have been proposed, with the Q-parameter or the T-stress being the most popular ones. Solid finite element meshing for complex structures such as pipes containing semi-elliptical surface cracks in order to compute Q is at present not a feasible approach. However, shell structures are most conveniently meshed with shell finite elements, and the linespring finite element is a natural way of accounting for surface cracks. The T-stress is readily obtained from the linespring membrane force and bending moment along the surface crack. In this study we present a new approach to analyse cracked shell structures subjected to large geometric changes. By numerical examples it is shown how geometric instabilities and fracture compete as governing failure mode.

This study presents a practical procedure for application of constraint correction of high strength steels and its weldments. Tests have been carried out on single edge notch bend (SENB) specimens with shallow and deep notch and SENT (single edge notch tensile) specimen with shallow notch, to cover the constraint effect. The yield strength of the material was 700 MPa. In order to apply the results on real structures it is crucial that the constraint correction procedures are made available to designers. The procedures must be easy to perform, have high accuracy and low costs. In order to meet these requirements the concept of linespring has been applied for performing direct calculations of components.

Higher utilization of structural materials leads to a need for accurate numerical tools for reliable prediction of structural response. Analysis with line spring finite elements is efficient in performing approximate fracture mechanics analysis of surface cracked shells. The present study addresses the performance of the line spring finite element utilized for describing a surface crack in a bimaterial elastic plastic wide plate structure. Some outlines for the application of the line spring in a yield strength mismatch situation are obtained from a parameter study, and utilized for the two-dimensional (2D) discretization of welded wide plates. Large scale test results are compared to the results obtained from both a 2D and 3D numerical analysis.

Reeling has proven to be an efficient and cost effective method for offshore pipelaying. During the reeling process the pipe undergoes deformation that can strain the material by 1–2%. The existing failure assessment methods often turn out to be too conservative to allow such a strain level in the structure. The amount of conservatism can be significantly reduced by using a new failure assessment approach developed by SINTEF. This approach depends on finite element calculations for establishing the non-linear fracture mechanics parameters and the stress and strain distributions in the pipe. The present study addresses the performance of shell and line spring finite elements as a cost effective tool for performing such numerical calculations.

The fatigue lifetimes of cylindrical aluminum specimens containing shrinkage cavities were measured. The results were compared with those of specimens without macroscopic cavities (DC cast). Two different heat treatments were considered: T4 (naturally aged) and T6 (near peak aged). The pore shape and distribution in the specimens were complex. Pores with a maximum diameter larger than 0.2 mm resulted in a significant reduction of the lifetime. Numerical calculations were carried out to predict the fatigue life and crack growth model taking crack closure effects into account was used. This model tended to give somewhat nonconservative results when compared with test results. Modification of the model, taking a short crack effect into account, gave conservative results.

A two-surface stress space material model for cyclic plasticity simulations is presented. The model takes into account the transient effects of cyclic hardening/softening and mean stress relaxation by means of exponential relationships that are functions of number of reversals and current strain level. By updating the size/location of a bounding surface at each point of strain reversal, the transient behaviour is simulated in a simplified manner. The increased hardening due to nonproportional loading is accounted for. The transient material model and two similar, but stabilized, models are applied in calculating the accumulated damage in biaxial low cycle fatigue loading. The plastic work per reversal is employed as damage parameter. The differences in the computed accumulated damage obtained by using the three different constitutive equations are clearly illustrated, hence indicating which type of material model may be sufficient for different types of loading.