: An overview of the virtual crack closure technique is presented. The approach used is discussed, the history summarized, and insight into its applications provided. Equations for two-dimensional quadrilateral elements with linear and quadratic shape functions are given. Formula for applying the technique in conjuction with three-dimensional solid elements as well as plate/shell elements are also provided. Necessary modifications for the use of the method with geometrically nonlinear finite element analysis and corrections required for elements at the crack tip with different lengths and widths are discussed. The problems associated with cracks or delaminations propagating between different materials are mentioned briefly, as well as a strategy to minimize these problems. Due to an increased interest in using a fracture mechanics based approach to assess the damage tolerance of composite structures in the design phase and during certification, the engineering problems selected as examples and given as references focus on the application of the technique to components made of composite materials.

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Virtual crack closure technique: History, approach, and applications

Fracture toughness of the tensile and compressive fibre failure modes in laminated composites

An intralaminar damage model, based on a continuum damage mechanics approach, is presented to model the damage mechanisms occurring in carbon fibre composite structures incorporating fibre tensile and compressive breakage, matrix tensile and compressive fracture, and shear failure. The damage model, together with interface elements for capturing interlaminar failure, is implemented in a finite element package and used in a detailed finite element model to simulate the response of a stiffened composite panel to low-velocity impact. Contact algorithms and friction between delaminated plies were included, to better simulate the impact event. Analyses were executed on a high performance computer (HPC) cluster to reduce the actual time required for this detailed numerical analysis. Numerical results relating to the various observed interlaminar damage mechanisms, delamination initiation and propagation, as well as the model’s ability to capture post-impact permanent indentation in the panel are discussed. Very good agreement was achieved with experimentally obtained data of energy absorbed and impactor force versus time. The extent of damage predicted around the impact site also corresponded well with the damage detected by non destructive evaluation of the tested panel.

Predicting low-velocity impact damage on a stiffened composite panel

https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1083&context=mechengfacpub

Peridynamic model for dynamic fracture in unidirectional fiber-reinforced composites

A status report on delamination resistance testing of polymer-matrix composites

Intralaminar fracture toughness of a cross-ply laminate and its constituent sub-laminates

Thermo-structural analyses of passive and active hot composite structures considering temperature dependent material properties under thermal and mechanical loads are carried out. The behaviour of the composite material under thermal, thermo-chemical and mechanical loads is studied. A general approach to carry out thermo-structural analysis and how the behaviour is incorporated in the modelling are briefly discussed. Thermo-structural analysis shows that thermal stresses are very much predominant when compared to stresses due to mechanical loads. A parametric study on variation of coefficient of thermal expansion (α) due to change in fibre orientation of carbon–carbon cap type structure is studied and it is concluded that one of the critical design variables identified is the α value across the thickness of the laminate.

M.K. Jana

Papers

Intralaminar fracture toughness of a cross-ply laminate and its constituent sub-laminates

Thermo-structural analysis of composite structures

Accurate evaluation of strain-energy release rate in unidirectional FRP compact-tension specimen