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An operationally simple strength criterion for anisotropic materials is developed from a scalar function of two strength tensors. Differing from existing quadratic approximations of failure surfaces, the present theory satisfies the invariant requirements of coordinate transforma tion, treats interaction terms as independent components, takes into account the difference in strengths due to positive and negative stresses, and can be specialized to account for different material symmetries, multi-dimensional space, and multi-axial stresses. The measured off-axis uniaxial and pure shear data are shown to be in good agreement with the predicted values based on the present theory.

The high-order theory of plate deformation developed in Part 1 of this work is extended here to model the behavior of laminated plates. Through comparison with elasticity solutions, it is shown the present theory correctly models effects not attainable from the classical theory.

A theory of plate deformation is derived which accounts for the effects of transverse shear deformation, transverse normal strain, and a nonlinear distribution of the in-plane displacements with respect to the thickness coordinate. The theory is compared with lower-order plate theories through application to a particular problem involving a plate acted upon by a sinusoidal surface pressure. Comparison is also made with the exact elasticity solution of this problem. It is found that when the ratio of the characteristic length of the load pattern to the plate thickness is of the order of unity, lower-order theories are inadequate and the present high-order theory is required to give meaningful results. The present work treats homogeneous plates while Part 2 involves laminated plates.

The conditions necessary for the application of fracture mechanics to anisotropic materials were examined and verified experimentally on orthotropic plates. It was observed that crack extension, by opening and forward sliding, occurred independently and the associated stress-intensity factors at the state of incipient fracture are material constants. An empirical relation (k1/k1c) + (k2/k2c)2 = 1 was found to be a fracture criterion for both balsa wood and fiber-glass-reinforced plastic plates, inferring the existence of a general law of fracture for orthotropic materials.