A new material degradation model only with fundamental material properties required is proposed for composite progressive damage analysis based on micromechanics. For different failure modes, the effects of fiber and/or matrix damage on the composite material properties are explored, from which the material degradation factors for these failure modes are deduced. The material degradation model is then implemented for progressive damage analyses, using user subroutines in the commercial code ABAQUS®, accompanying with a modified Hashin type failure criterion and finite element models for six commonly used double-lap composite bolted joints with various layups, geometry dimensions, and fasteners. The numerical predictions of failure loads, failure patterns, and load–displacement curves are compared with results obtained from static tests and further ultrasonic C-scan detection. Good agreements between numerical failure predictions and experimental outcomes indicate the effectiveness and suitability of the proposed model for progressive damage analyses of composite bolted joints.

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To explore the physical effect of end distances on mechanical behaviors of composite bolted joints, series of single-bolt composite joints designed with different end distances were tested. In conjunction with the experimental work, a numerical progressive damage method is introduced to trace the damage process from the onset and propagation up to ultimate failure of the joints. A group of material degradation factors is presented by a trial-and-error method to establish three-dimensional progressive damage models of the bolted joints. The progressive damage analyses show that the predicted load-displacement curves, failure loads, and failure patterns of bolted joints with different end distances are in good agreements with the related experimental outcomes. From the experimental and numerical results, it follows that the cleavage failure gradually switches to the bearing failure with the increasing ratio of E/D ranged from about 2 to 4. An economic and suitable ratio of E/D & 3 is provided for the bolted joints made of X850 carbon/epoxy composites with balanced and symmetric layups [45/0/À45/0/90/0/45/0/À45/0] s . The understanding of the effect of E/D on the mechanical behaviors including the strength, stiffness, and failure patterns of single-bolt joints is strengthened.

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