Accounting nonlinear strain components in mechanical tests (bending) of the composite material

When analyzing the damage composite materials (in particular, laminates) during mechanical testing shows that fracture occurs from deviations from the theoretically defined principal stress trajectories. The trajectories of principal stresses at the same time are defined by the resistance of materials. This fact is explained by the authors test the actions of unaccounted geometrical factors, residual stresses, etc.

In most cases, the model corresponds to the loading plane bending of the beam.
The article gives evidence of the shear stresses in the plane bending beam, which, applying the formula of resistance of materials can be determined.
These unaccounted invaluable and stress, affecting trajectories of principal stresses, baffled many testers.

See. Also "Accounting for heterogeneity in mechanical tests (bending) of layered composite materials."