Composite crack-growth curve

It should be noted that a mode 11 crack-resistance R-curve may also be obtained for some fiber-matrix systems (Vu-Khanh, 1987). In conjunction with the mode 1 R-curve the additional information of a mode 11 R-curve will be of great use to the composite design engineers. This is increasingly the view of the ESIS task group on delamination crack growth resistance. 

We now turn our attention from considerations of stiffness to stress-strain and tensile behavior. Variations in strength and modulus as a function of direction (Broutman and Krock, 1967, Chapter 12) have been treated by several investigators for example, Tsai (1965) and Brody and Ward (1971). Even though the polymer matrix typically has such a low modulus that it does not contribute much overall to the composite modulus, the matrix can by no means be neglected, because failure often involves catastrophic crack growth in the matrix (see below). Stress-strain curves for unidirectional composites are typically fairly linear up to failure for loading in the direction of the fibers (Broutman and Krock, 1967, p. 370), but quite nonlinear transverse to the fiber direction. The stress to rupture is also very low in the latter case, presumably due to a high concentration of stress in the matrix. 

European Structural Integrity Society (ESIS) Testing Committee protocol for conducting J-crack growth resistance curve tests on plastics, in D. R. Moore, B. R. K. Blackman, P. Davies, A. Pavan, P. Reed, J. G. Williams, eds., Experimental Methods in the Application of Fracture Mechanics Principles to the Testing of Polymers, Adhesives and Composites, Elsevier, London, 2000, p. 140. 

ESIS Technical Committee on Rolymers and Composites, A Testing Protocol for Conducting J Crack Growth Resistance Curve Tests on Plastics, May 1995. 

Herrmann, K., Curved thermal crack growth in the interfaces of a unidirectional Carbon-Aluminum composite- In Mechanics of Composite Materials. Recent Advances, eds. Z. Hashin and C-T. Herakovich, Pergamon Press, New York/Oxford, 1983, 383-397. 

Vesely, V., Kersner, Z. (2006) R-curves from equivalent elastic crack approach effect of structural growth on fracture behaviour, in Proc. Int. Symp. Brittle Matrix Composites 8, A. M. Brandt, V. C. Li and I. H. Marshall eds, Warsaw Woodhead Publishing and ZT RSI pp. 527-36. 

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