Yielding in Unidirectional Composites Under External Loads and Temperature Changes*

Abstract

Initial yield surfaces were constructed for the boron-aluminum composite under arbitrary combinations of applied composite stresses and temperature changes, by means of a finite element analysis of a regular hexagonal array model.The results suggest that with regard to initial yielding, the macroscopic transverse isotropy of the composite is approximately retained on the microscale. Therefore, the general isothermal yield surface can be constructed as a function of four composite stresses. Yielding in the transverse plane is controlled mainly by matrix properties, whereas yielding under normal composite stresses applied in the fiber direction is controlled by the ratio E f /E m of the Young's moduli of the constituents. In general, high magnitudes of this ratio, as well as higher fiber volume fractions make yielding more difficult.It was found that yielding takes place both under hydrostatic composite stresses, and as a consequence of uniform temperature changes. Therefore, these effects must be accounted for in macroscopic yield criteria and flow rules for composites. It is shown that a uniform temperature increase causes an approximate translation of the yield surfaces in the negative hydrostatic stress direction. Relatively small temperature changes can cause yielding in most composite systems. The typical values were found in the interval of 50° to 100°F, when the tensile yield stress of the matrix was taken as Y = 10,000 psi, and were proportional to Y. *Sponsored by the U.S. Army Research Office-Durham.

More on the effects of thermal residual and hydrostatic stresses on yielding behavior of unidirectional composites

“…Previous investigations on the subject of the influence of residual stresses on yielding behavior of composites include studies carried out by Dvorak et al [24,25], Zahl and McMeeking [1] and Aghdam et al [26]. Dvorak et al [24,25] obtained initial yield surfaces for unidirectional boron-aluminum composite system under various applied stresses and a temperature change.…”

Deformation and fracture properties of damage tolerant in-situ titanium matrix composites

“…(b) Classical composite strengthening through load transfer between the titanium alloy metal matrix and the discontinuous whisker reinforcements [39,40]. Load transfer is largely dependent on the bond integrity at the interfaces of the whisker reinforcement and the metal matrix.…”

A generalized plane strain meshless local Petrov–Galerkin method for the micromechanics of thermomechanical loading of composites

“…Though approaches based on the finite difference and boundary element methods can be found in the literature (see [Adams and Doner 1967] and [Eischen and Torquato 1993], respectively), most numerical approaches rely on the finite element method [Nimmer 1990;Nimmer et al 1991;Wisnom 1990;Durodola and Derby 1994;Shaw and Miracle 1996;Zhang et al 2004;Dvorak et al 1973;Zahl and McMeeking 1991;Aghdam et al 2000;Aghdam and Khojeh 2003;Gentz et al 2004;Zhao et al 2007;Shen 1998;Haktan Karadeniz and Kumlutas 2007], and have been used for predicting various elastic, elastoplastic and thermoelastic characteristics of composites. Some of these models include the effect of thermal stress on the mechanical behavior of composite materials.…”

“…Shaw and Miracle [1996] used the finite element method to study the effects of interfacial region on the thermal residual stress and transverse behavior of a SiC/Ti metalmatrix composite. The influence of residual stresses on the yielding behavior of composite materials was studied in [Dvorak et al 1973;Zahl and McMeeking 1991;Aghdam et al 2000;Aghdam and Khojeh 2003], while [Gentz et al 2004] and [Zhao et al 2007] studied the effects of the residual stresses on the behavior of polymer-matrix composite. In addition, the overall coefficient of thermal expansion of composite materials was studied using micromechanical finite element [Shen 1998;Haktan Karadeniz and Kumlutas 2007], approximate closed-form models [Van Fo Fy 1965;Rogers et al 1977;Chamis 1984], and experimental methods [Sideridis 1994].…”