Predicting strength of fibrous laminates under triaxial loads only upon independently measured constituent properties

The stress concentration factor in the matrix of a fibrous composite reinforced with transversely isotropic fibers is determined upon constituent elastic properties as well as the fiber volume frac...

Stress concentration factor in matrix of a composite reinforced with transversely isotropic fibers

Bridging Model is an efficient micromechanical theory which can be used to predict the effective thermomechanical as well as strength properties of a fiber reinforced composite. The key to the Bridging Model is a bridging tensor, which was obtained on Eshelby's inclusion method [Huang and Zhou, Strength of Fibrous Composites, Vol. 53, Zhejiang University Press, Springer, Hangzhou, (2011)]. A different approach to the closed-form expressions for the elements of a bridging tensor is presented in this work. The method is based on averaging the stress fields of a single-fiber inclusion embedded within an infinite matrix subjected to various load conditions. By solving the bridging equations between the averaged stress components in the fiber and those in the matrix, the exact expressions for the bridging tensor elements are obtained. The Bridging Model can be established by neglecting some small quantities in the bridging tensor elements. Effective elastic moduli of a unidirectional (UD) composite are expressed as functions of a bridging tensor. Comparisons of predicted elastic properties of a total number of 18 UD composites on simplified and the exact bridging tensors are made. POLYM. COMPOS., 36:1417–1431, 2015. © 2014 Society of Plastics Engineers

A new approach to a bridging tensor

This paper attempts to estimate the ultimate strength of a laminated composite only based on its constituent properties measured independently. Three important issues involved have been systematically addressed, i.e., stress calculation for the constituent fiber and matrix materials, failure detection for the lamina and laminate upon the internal stresses in their constituents, and input data determination of the constituents from monolithic measurements. There are three important factors to influence the accuracy of the strength prediction. One is the stress concentration factor (SCF) in the matrix. Another is matrix plasticity. The third is thermal residual stresses in the constituents. It is these three factors, however, that have not been sufficiently well realized in the composite community. One can easily find out the elastic and strength parameters of a great many laminae and laminates in the current literature. Unfortunately, necessary information to determine the SCF, the matrix plasticity, and the thermal residual stresses of the composites is rare or incomplete. A useful design methodology is demonstrated in the paper.

Assessment of composite failure and ultimate strength without experiment on composite

Constitutive relation, deformation, failure and strength of composites reinforced with continuous/short fibers or particles

An elastic analysis of fiber-reinforced composites subjected to normal or/and shear stress in planes normal to the fiber direction is presented The effect of material properties on the stress distribution is studied and a stress concentration factor valid for all the laminae presently used in industry is obtained It is found that this factor is essentially unaffected by the substantial variation of the ratio of the elastic moduli of the fiber and the epoxy of the various laminae considered herein This result is of theoretical interest and also useful in composites design

D. Chen

Papers

On the Stress Distribution in Laminae