Stresses in Composite Building Reinforcement due to Differences in Poisson's Ratios

The aim of the work is the calculation assessment of stresses in the elements of composite building reinforcement caused by differences in the Poisson’s ratios of reinforcing fibers and polymer binders. The research methodology is based on the development of a micromechanical model of the interphase interaction of the reinforcing fiber and a polymer matrix in an elementary cell, which is a hollow polymer micro-cylinder in which a fibrous reinforcing filler is located in the form of a connection with a deformation tension changing under load. The transformation of the Lame problem to the calculation assessment of the effect of differences in the values of the Poisson’s ratios of the reinforcing fibers and the polymer matrix, as well as nominal tensile stresses and the volumetric content of fibers in the composite reinforcement on changes in local stresses in the reinforcing fibers and polymer matrix is made. Analytical dependencies are obtained linking the parameters of the local stress-strain state of the walls of an elementary cylinder in the vicinity of a fibrous filler with a set of indices of the physical and mechanical properties of polymer matrix materials and fibrous filler (moduli of elasticity and Poisson's ratios), as well as the volume content of the filler. As an example, these parameters are calculated for a wide range of degrees of filling with glass and basalt fiber for a number of polymer matrices (epoxy and polyester). It is shown that in the range of the volumetric filler content of 0.5–0.7, contact pressures at the interface of the reinforcing fibers with the polymer matrix are from 2 to 6 % of the nominal tensile stresses in the polymer matrix, depending on the combination of Poisson ratios of the fibers and the matrix. In this case, the circumferential tensile stresses in the polymer matrix at the interface with the fiber are from 11.6 to 19.2 % of the nominal axial tensile stresses in the polymer matrix for fiberglass and from 10.6 to 17.1 % for basalt-plastic reinforcement. The research results can be used in scientific research and educational activities.