Modified Crack Closure Integral Technique Research Articles

Modified crack closure integral technique for extraction of SIFs in meshfree methods

A new approach for extracting stress intensity factors (SIFs) by the element-free Galerkin (EFG) class of methods through a modified crack closure integral (MCCI) scheme is proposed. Its primary feature is that it allows accurate calculation of mode I and mode II SIFs with a relatively simple and straightforward analysis even when a coarser nodal density is employed. The details of the adoption of the MCCI technique in the EFG method are described. Its performance is demonstrated through a number of case studies including mixed-mode and thermal problems in linear elastic fracture mechanics (LEFM). The results are compared with published theoretical solutions and those based on the displacement method, stress method, crack closure integral in conjunction with local smoothing (CCI–LS) technique, as well as the M-integral method. Its advantages are discussed.

Application of the 3-D boundary element method to delaminated composite structures

A three-dimensional boundary element model for anisotropic solids is presented to study the fracture mechanics behavior of delaminated composite structures. The multi-domain technique is implemented to model the layered configurations and the cracks occurring at bi-material interface. The Modified Crack Closure Integral technique is implemented to characterize the fracture mechanics behavior of delaminations in terms of the total energy release rate and mode mix phase angles. Validating analyses, performed on different delaminated configurations, have shown the effectiveness of the proposed approach. Moreover, some original results are presented to investigate the effects of the stacking sequence on the fracture parameters.

Stress and Free Edge Delamination Analyses of Delaminated Composite Structure Using ANSYS

Laminated polymer composite structures manufactured using conventional layup technique, are prone to edge delamination, which can be suppressed by wrap-around technique. Present study is in regard to understanding of the interlaminar normal stress distribution ahead of the delamination front with respect to delamination suppression. An initial delamination of symmetric composite laminates with and without wrap-around is considered for performing static analysis of these laminated composites structures using finite element analyses. Understanding of delamination parameter was further extended in terms of strain energy release rate utilizing modified crack closure integral technique for various virtual crack extension sizes.

Crack growth in cylindrical aluminum shells with inner reinforcing foam layer

The occurrence of cracks in aging aircraft fuselage is major problem in the airline industry. The remaining life of the aircraft is strongly dependent on the residual strength of its structure. Residual strength is affected by crack sizes and their growth rates. In the case of a longitudinal crack in a pressurized cylinder (as in the case of an aircraft fuselage), the geometry and loading conditions cause the edges of the crack to bulge out generating a complex stress field around the crack tips; this is known as the ‘bulging effect’. The geometry of the shell, crack size and pressure contribute to this phenomenon. A proposed solution to reduce the effect of bulging for this type of crack is to apply a layer of polyisocyanurate (PIR) foam to the inner side of the fuselage near the crack site. This layer will bond to the shell and has the effect of reducing the bulge and consequently, the Stress Intensity Factor (SIF) at the crack tips. PIR foam is a lightweight material that adheres well to the shell and provides additional stiffness around the crack area. In the present study the effect of applying a PIR foam layer to a longitudinal crack in a pressurized cylindrical shell is assessed. Nonlinear Finite Element Analysis (FEA) is used in conjunction with the Modified Crack Closure Integral technique (MCCI) in order to evaluate the effect of bulging on the crack’s SIF. Parameters considered in this study include shell radius, shell thickness, crack length, foam thickness and pressure. Numerical results are compared with existing experimental data and the effect of foam thickness for several shell configurations is presented. Results indicate that the bulge factor (BF) could be reduced by as much as 45% depending on shell configuration, foam thickness and pressure.

Characterization of Curing Stress Effects on Fracture Behavior of FRP Laminated Composites with Embedded Delaminations

A detailed study on the effect of curing stresses on interlaminar delamination crack growth behavior in fiber-reinforced polymeric (FRP) composites is presented. At a given applied load or displacement, the strain energy release rate distribution along the delamination front with and without considering the effects of curing stresses are compared. In this analysis, results are presented for elliptical delaminations embedded between plies of different orientations in the laminate. A full three-dimensional coupled-field finite element analysis has been conducted to study the delamination crack growth behavior due to curing stress effects. A superposition procedure along with the modified crack closure integral technique based on the concepts of linear elastic fracture mechanics is employed to evaluate the individual modes of strain energy release rates during delamination propagation. It has been observed that the residual thermal stresses developed during the curing stages in manufacturing of FRP laminated composites significantly affect the onset and growth of delamination. The asymmetric behavior of interlaminar fracture energy along the delamination front is found to depend upon the stacking sequence, neighboring ply orientation, thermoelastic anisotropy, and material heterogeneity at the interface of laminated composites.

Fracture analysis of an adhesively bonded sandwich beam under Mode-I loading

In this paper, an analytical closed-form solution for Mode-I energy release rate of an adhesively bonded sandwich beam is derived from the modified elastic foundation model. For validation purpose, a model based on the finite element method (FEM) was also constructed using the modified crack closure integral technique to calculate the compliance and Mode-I energy release rate of the sandwich beam. Comparison between the closed-form solution and the FEM solution showed a good agreement. The results of calculations also showed a significant effect of the adhesive layer of the sandwich beam on fracture analysis. This means that the effect of the adhesive layer of the sandwich beam cannot be ignored.

BEM based evaluation of SIFs using modified crack closure integral technique under remote and/or crack edge loading

This paper deals with the boundary element method based evaluation of stress intensity factors for mode I and mixed mode problems under remote and/or crack edge loading. The modified crack closure integral technique has been used to enhance the accuracy of the computed stress intensity factors. Simple, ready to use, relations for the strain energy release rate have been obtained corresponding to linear, quadratic and quarter point elements surrounding the crack tip. The boundary element method is employed by breaking a domain into two subregions for the mixed mode problems. Case studies involving remote or crack edge loading for both mode I and mixed mode problems are presented to demonstrate the accuracy of the new scheme. The stress intensity factors based on the proposed scheme show better agreement with the standard solutions available in the literature than those obtained directly through the displacement method.

Further considerations in modified crack closure integral based computation of stress intensity factor in bem

This paper deals with modified crack closure integral based computation of stress intensity factors in a boundary element method for problems with mechanical loading remote from the crack edges. The modified crack closure integral technique has been coupled with the local smoothing scheme to obtain simple relations for energy release rates for linear, quadratic and quarter point elements around the crack tip. Stress intensity factors calculated through the proposed formulation and the displacement method for a number of examples are compared, wherever possible, with data available in the literature. The results based on the proposed scheme are more accurate than those obtained by the displacement method.

Boundary element method based computation of stress intensity factor by modified crack closure integral

The local smoothing scheme in conjunction with the modified crack closure integral technique has been adopted in the boundary element method to improve the accuracy of computed stress intensity factors. Simple relations have been derived for the case of linear, quadratic and quarter point elements around the crack tip. Case studies are presented to demonstrate improvement in the accuracy. While the displacement method gives a difference with the standard handbook solution up to 26%, the suggested method helps to reduce it to within 2%.