The out-of-plane compressive response of Dyneema® composites

Out-of-plane compression tests were conducted on six grades of ultra high molecular weight polyethylene fibre composites (Dyneema (R)) with varying grades of fibre and matrix, ply thickness, and ply stacking sequence. The composites with a [0 degrees/90 degrees] lay-up had an out-of-plane compressive strength that was dictated by in-plane tensile fibre fracture. By contrast, the out-of-plane compressive strength of the uni-directional composites was significantly lower and was not associated with fibre fracture. The peak strength of the [0 degrees/90 degrees] composites increased with increasing in-plane specimen dimensions and was dependent on the matrix and fibre strength as well as on the ply thickness. A combination of micro X-ray tomography and local pressure measurements revealed the existence of a shear-lag zone at the periphery of the specimens. Finite element (FE) and analytical micromechanical models predict the compressive composite response and reveal that the out-of-plane compression generates tensile stresses along the fibres due to shear-lag loading between the alternating 0 degrees and 90 degrees plies. Moreover, the compressive strength data suggests that the shear strength of Dyneema (R) is pressure sensitive, and this pressure sensitivity is quantified by comparing predictions with experimental measurements of the out-of-plane compressive strength. Both the FE and analytical models accurately predict the sensitivity of the compressive response of Dyneema (R) to material and geometric parameters: matrix strength, fibre strength and ply thickness. (C) 2014 Elsevier Ltd. All rights reserved.