Experiment- and computation-based identification of mechanical properties of fiber reinforced polymer composites

Based on testing angle-ply composite specimens with different lay-ups, the lamina elastic properties are defined by minimization of the error function determining the differences between the predicted and measured strains. The problem that a number of the measured values obtained as a result of testing exceeds that of the lamina elastic constants is resolved by using the linear algebra methods with assessment of stability of the solutions against random perturbations of the matrix and/or column of free terms. Based on the lamina elastic constants defined, an analysis of the lamina nonlinear and time-depended properties is carried out and the lamina in-plane shear creep is described, the weak singular Abel's operator and matrix algorithms being used. To obtain the explicit forms of stiffness and compliance matrices of laminated composites on the basis of classical lamination theory relations, the assumption that their physical nonlinearity and rheological characteristics are substantially determined by the corresponding lamina in-plane shear properties is used, and the corresponding constitutive equations are derived to describe the anisotropy of their nonlinear and time-dependent properties. Testing a number of angle-ply polymer composite specimens under time variable loading shows the applicability of the approach elaborated. The satisfactory agreement between experimental and predicted data is observed.