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The failure of fiber reinforced composites under transverse loading is investigated on a
representative volume element. The volume element is composed of a twelve fiber hexagonal
array. The debonding of the central fiber is studied under transverse shear as well as under
transverse compressive loading by calculating the mode I and mode II part of the energy
release rate. The initiation of failure is assumed to take place at the location of maximum
tensile or maximum shear stresses, respectively. In order to determine the failure initiation
point, the stress field in the interface before crack initiation is calculated.
Off-axis tests are widely used for the determination of the anisotropic mechanical properties of composite materials, this is, the longitudinal E-modulus and the strength. The mechanical properties are evaluated from the test data under idealising assumptions such as homogeneity of the material as well as a homogeneous stress distribution. In real off-axis tests, however, significant deviations from the idealising assumptions are present. The reduction of the accuracy of the results strongly depends on the off-axis angle.
In this paper a series of off-axis tests is analysed. The stresses on potential failure plane are calculated by finite element analyses. By varying the geometrical parameters it is shown how small deviations from the ideal case influence the measured elastic constants and the strength. Especially at low off-axis angles the mechanical properties strongly vary with the angle. In addition, fracture surfaces for different shear/normal stress combinations are studied and typical phenomena are identified.