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Effect of mixed mode loading on ply crack development in laminated composites: theory and application.

McCartney, L N (2004) Effect of mixed mode loading on ply crack development in laminated composites: theory and application. NPL Report. MATC(A)167

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Mixed mode loading is always encountered near stress concentrations in composite components, such as holes in general symmetric laminates. The stress concentration effects lead to stress states that are a combination of biaxial and shear loading modes so that a mixed mode situation must be taken into account when considering the formation of ply cracking near the stress concentrations. This report is concerned with a proposed methodology for the development of a technique that can account for the effects of mixed mode loading on ply crack development in general symmetric laminates. The approach will indicate how the methodology, already developed to predict the effects of ply cracking on laminate properties when ply crack growth occurs in mode I loading, can be extended to deal with ply crack growth in the mixed mode situations. These arise in practical applications, where combined mode I and mode II deformations are encountered at ply crack tips. The problem splits into two distinct stages. The first concerns the estimation of the availability of energy for ply crack development under mixed mode conditions that is addressed in this report. The second involves understanding the factors that control the resistance of the material in mixed mode situations (i.e. its effective fracture toughness).
The criterion for first ply failure is based on a general form of energy balance that is designed to be flexible. It is clear from the preliminary results presented in this report that the choice of ply cracking criterion has a significant effect on the predictions for first ply failure. In particular it has been shown that the use of a total energy release rate criterion, in situations where ply crack growth is mixed mode, leads to predictions that are physically unreasonable, thus indicating the importance of deriving a physically realistic criterion for ply cracking.
The analysis presented in this report is to be the basis of modifications to a software system that has recently been developed using homogenisation techniques to take account of ply crack formation in more than one orientation in any general symmetric laminate. The inclusion of mixed mode effects are expected to lead to more accurate simulations of both damage development and strength predictions. The software will also be used to upgrade the PREDICT module of the NPL Composites Design Analysis (CoDA) software system.

Item Type: Report/Guide (NPL Report)
NPL Report No.: MATC(A)167
Subjects: Advanced Materials
Advanced Materials > Composites
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/2951

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