Matrix-dominated failure

If a composite with unidirectional fibres is loaded in tension or compression perpendicular to the fibre direction or in axial shear in fibre direction, it can fail without failure of the fibres by fracture, buckling, or kinking. These cases are therefore called matrix-dominated failure. 

Fracture process in multidirectional composite laminates subjected to in-plane static or fatigue tensile loading involves sequential accumulation of damage in the form of matrix cracks that appear parallel to the fibres in the off-axis plies, edge delamination and local delamination long before catastrophic failure. These resin dominated failure modes significantly reduce the laminate stiffness and are detrimental to its strength. 

The standard mechanical tests, as described in Section 7. can normally be undertaken with care for composites as a function of temperature. The difference between fiber- and matrix-dominated properties can result in different temperature dependencies. Changes in the residual thermal stresses present can occur both between the fibers and the resin, and between layers, in particular between 0" and 90 orientated unidirectional layers. Care needs to be taken in assessing the failure mode, particularly in flexural and compressive tests where there can be changes, particularly at elevated temperatures, due to the matrix providing a lower degree of support to the fibers, thus encouraging compression failure. 

The ultimate tensile strength of a fibrous composite a depends on whether failure is fiber-dominated or matrix-dominated. The latter is common when Vt is small. One result of such treatment is... 

Brinson, H.F. Matrix Dominated Time Dependent Failure Predictions in Polymer Matrix Composites , J. of Composite Structures, 47 (1999), p. 445-456. 

One can conclude that the shear and tension/compression type debonding is also one of the dominant failure mechanisms in the case of AP-fiber orientation. According to the results, the AP-fiber orientation produces lower fiber and matrix stresses than the P-fiber orientation. This would imply a lower probability for wear failure under AP- compared to P-fiber orientation. This is, however, opposite to the impression one has from the scratch experiments, and also in contrast to previous sliding wear studies on this material. Probably, in terms of the complete wear process and the complexity of wear mechanisms, the AP-fiber orientation is less advantageous, i.e., the wear debris as a third abrasive have a more dominant effect on the wear process than in the case of P-fiber orientation. 

In this paper, the failure criterion developed in [1] was employed to study failure in a number of matrix-dominated laminates, such as [ 0]2s [i0/9O]s and some fiber-dominated 7t/4 laminates. For some 7t/4 laminates, test results showed that open-mode delamination could occur along interfaces adjacent to the 90° layer. Such failure of delamination depends on the stacking sequence of the laminate. Results indicated that the present method can also be used to predict the onset of open-mode delamination. 

For the fiber-dominated laminate (0 = 0°) and highly matrix- dominated laminates (0 > 30°), failure initiates from the interior of the laminate and the classical Tsai-Hill criterion is accurate. 

Failure of matrix-dominated ( [ 0]2s [ 0/9O]g ) laminates and fiber- dominated tc/4 laminates has been studied. A new multiple-mode failure criterion was proposed. This new criterion, which took the free-edge effect into account, was found capable of predicting laminate strengths for the matrix-dominated laminates and delamination on-set stress for tc/4 laminates. 

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