B. Dattaguru

Finite element estimates of strain energy release rate components at the tip of an interface crack under mode I loading

The strain energy release rate components

A general procedure for modified crack closure integral in 3D problems with cracks

G_{I}

Cracks emanating from pin-loaded lugs

and

Finite element analysis of an interface crack with large crack-tip contact zones

G_{II}

Modified crack closure integral using six-noded isoparametric quadrilateral singular elements

in mode I and mode II at the tip of an interface crack in a bimaterial plate under tension in a direction normal to the interface were evaluated using finite element analysis and Modified Crack Closure Integral (MCCI) technique. Three models, namely the bare interface model, the resin layer model and the subinterface crack model were studied with two different material combinations with progressively decreasing crack tip element size Aa which is also the virtual crack extension considered in the MCCI evaluation. The finite element results for all the models show increasing mode II dominance as

A comprehensive study of interference and clearance fit pins in large plates

\Delta a \rightarrow 0

The fatigue crack growth rate in L-72 Al-alloy plate specimens with cold worked holes

. Interpretation of these results is meaningful if the virtual crack extension Au is identified as crack growth step size.

A Method for Estimation of the Radius of Elastic-Plastic Boundary Around Cold-Worked Holes

In linear elastic fracture mechanics (LEFM), Irwins crack closure integral (CCI) is one of the signficant concepts for the estimation of strain energy release rates (SERR) G, in individual as well as mixed-mode configurations. For effective utilization of this concept in conjunction with the finite element method (FEM), Rybicki and Kanninen [Engng Fracture Mech. 9, 931 938 (1977)] have proposed simple and direct estimations of the CCI in terms of nodal forces and displacements in the elements forming the crack tip from a single finite element analysis instead of the conventional two configuration analyses. These modified CCI (MCCI) expressions are basically element dependent. A systematic derivation of these expressions using element stress and displacement distributions is required. In the present work, a general procedure is given for the derivation of MCCI expressions in 3D problems with cracks. Further, a concept of sub-area integration is proposed which facilitates evaluation of SERR at a large number of points along the crack front without refining the finite element mesh. Numerical data are presented for two standard problems, a thick centre-cracked tension specimen and a semi-elliptical surface crack in a thick slab. Estimates for the stress intensity factor based on MCCI expressions corresponding to eight-noded brick elements are obtained and compared with available results in the literature.

Fracture mechanics based design procedures for pressurized components having part-through cracks

Pin-loaded lugs were analysed in the presence of cracks emanating from circular holes. The analysis presents a unified treatment of interference, push or clearance fit pins. Both metallic (isotropic) and composite (orthotropic) plates were dealt with. The finite element model used special singular six-noded quadrilateral elements at the crack tip. The non-linear load contact behaviour at the pin-hole interface was dealt with by an inverse technique. A modified crack closure integral (MCCI) technique was used to evaluate the strain energy release rates (SERRs) and stress intensity factors (SIFs) at the crack tips. Numerical results are presented showing the non-linear variation of SIF with applied stress, and the influence of the amount of interference or clearance and the interfacial friction on SIF.

An economic finite element strategy for LEFM problems

Abstract There is considerable ambiguity regarding the limiting values of the strain energy release rate (SERR) components at the tips of a crack lying along the interface between two dissimilar isotropic media. In this paper this aspect is examined using finite element analysis and Modified Crack Closure Integral (MCCI) for a problem in which the material properties are chosen so as to cause a large size crack-tip contact zone. By careful choice of this problem, interpenetration of the crack faces in the crack-tip contact zones is observed for the first time in the finite element analysis. Earlier solutions primarily on remote mode 1 loading reported that SERR components do not converge as the virtual crack extension Δa → 0 and that these components show an oscillatory nature when Δa is less than the contact zone size rc. In the present work, multipoint constraints are imposed on crack face normal displacements in the contact zone and meaningful results are generated for both remote tension and shear loading cases. The apparent nonconvergence of the SERR components as Δa → 0 can be explained if these components are considered as functions of Δa, and Δa is considered as the actual crack growth step size.