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Applied Composite Materials: An International Journal for the Science and Application of Composite Materials (v.5, #6)
Standard Test Methods for Delamination Resistance of Composite Materials: Current Status by P. Davies; B. R. K. Blackman; A. J. Brunner (pp. 345-364).
This paper presents a survey of the current status of test methods for the measurement of delamination resistance of composite materials, with particular emphasis on the work performed in this area by ESIS, the European Structural Integrity Society. First, existing mode I fracture test standards are described. We then present work currently underway, both to extend the range of application of these mode I tests and to standardise mode II, mixed mode (I/II) and mode III tests. Finally, we discuss tests to characterise fatigue crack propagation.
Keywords: fibre reinforced composites; delamination resistance; fracture; standardisation
Stress Distributions around Holes in Composite Laminates Subjected to Biaxial Loading by C. Soutis; C. Filiou (pp. 365-378).
An approximate solution has been derived for the in-plane stresses near a circular hole, in an orthotropic composite laminate under biaxial loading. The derived stresses were found to be in good agreement with the exact analytical solution, for a series of laminates investigated. However, the degree of accuracy of the approximate stress distribution is strongly influenced by the laminate lay-up and the biaxiality ratio. The resultant stresses could be employed in stress based fracture models to investigate the notch sensitivity and fracture mechanisms of composite plates with an open-hole subjected to biaxial loading.
Keywords: composites; laminates; biaxial loading; open hole; stress analysis; notch sensitivity; stress concentration factors; exact stress distribution; approximate solution
Non-Axisymmetric Matrix Cracking and Interface Debonding with Friction in Ceramic Composites by F. S. Ji; L. R. Dharani (pp. 379-397).
A three-dimensional analytical model based on the principle of minimum potential energy is developed and applied to determine the stress state in a discrete fiber/matrix composite cylinder subjected to axial tensile loading in the fiber direction and containing a non-axisymmetric transverse matrix crack and an interface debond. The friction over the debonded interface is incorporated into the analysis. The strain energy release rates associated with the matrix crack and the interface debonding under the combination of the applied load and the interface frictional force are computed. The strain energy release rate criterion has been employed to evaluate the critical applied loads for the two fracture modes and to assess the competition between propagation of a matrix crack and growth of interface debonding. A parametric study has been carried out. The computed results show that the interface friction plays an important role in the failure of brittle matrix composites.
Keywords: matrix cracking; interface debonding; interface friction; strain energy release rate
Effect of Through-Thickness Stitching on the Fatigue Life of Composite Single-Lap Joints by Lalit K. Jain; K. H. Leong; Yiu-Wing Mai; Liyong Tong (pp. 399-409).
An exploratory experimental evaluation has been undertaken to investigate the effect of through-thickness stitching on the fatigue life of composite single lap joints. Balanced single lap joints were considered, and the lay-up for the adherends was (0/±45/90)s Specimens were stitched transversely and through-the-thickness with Kevlar® thread in a zigzag pattern and were manufactured using the resin transfer moulding (RTM) technique. Preliminary experimental results have indicated that stitches remain intact when the crack starts growing from either side of the overlap. This consequently imparts a significant improvement in the fatigue life of stitched versus unstitched counterparts.
Keywords: single lap joints; resin transfer moulding; through-thickness stitching; fatigue life; strength; cycles to failure