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The compression-buckling tests performed so far have indicated, that along the loading path different kinds of defects can initiate and propagate. The most common type of defects is laminated composite structures is delamination. On the other hand, understanding the nature of general layups (neither symmetrical, nor asymmetrical) seems to be advantageous from the point of view of more effective tailoring the properties of composite structural members. The advance of delamination front can be described in terms of the strain energy release rate. The common experimental schemes, such as Double Cantilever Beam (DCB) test by assumption give information on a single fracture mode characteristic – GIc for Mode I. This is true for unidirectional specimens, but not for angle-ply ones, especially those with general layups, exhibiting mechanical couplings. In such cases the mode mixity along delamination front should be expected rather than the single fracture mode. This demands a definition of the circumstances of delamination initiation and propagation concerning the actual stress state in compressed composite columns at any stage of the loading and buckling process, as any defect can additionally weaken the load-bearing capacity of the column. Thus, numerical analyses preceding the experimental tests were performed in the ABAQUS Finite Element (FE) software environment in order to determine the variability of GIc along delamination front in DCB specimens with various general ply layups.
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