Fracture Criteria for Matrix and Fibers in Unidirectional Polymeric Composites at Static Loadings

When analyzing the strength of structures made of layered fibrous polymer composite materials; the criteria for failure of a monolayer – a unidirectional reinforced composite – are used. A criterion of strength according to the conditions of matrix fracture is formulated, corresponding to conical limiting surfaces and the lowest destructive loads. The criterion of strength according to the condition of fiber failure, which does not allow the paradox of increasing strength in the region of transition from fiber destruction to matrix failure, is given. Experimental verification of the criteria for volumetric, planar, and one-dimensional loads is carried out. Their better correspondence to empirical data is shown and their advantages in comparison with known criteria are marked. A small number of easily detectable parameters of these criteria contribute to their reliability and stability in strength calculations of composite structural elements.