<title>Active control of interlaminar stresses in laminated composites by through-thickness thermal gradients</title>

Abstract

In this paper, we propose a method to actively control interlaminar stresses near the free edges of laminated composites by though-thickness thermal gradients. Theoretical solutions are given for optimal steady-state through-thickness temperature distributions under uniaxial loading that are required to eliminate or reduce the interlaminar stresses below a prescribed level. The optimal solutions are obtained by minimizing appropriate performance indices that are functions of the far-field properties, with respect to the through-thickness temperature differences. In the second part, an experimental investigation is conducted on a glass/epoxy cross-ply laminate with embedded piezoelectric sensors and a thermal heater. Through the experiment, a feasibility of the thermal control of interlaminar stresses is demonstrated.

Optimal through-thickness temperature gradients for control of interlaminar stresses in composites

“…where e° and K, can be obtained by inverting the force resultant-strain relation (1). It is recalled that the /th temperature difference (or gradient) is defined as (8) Therefore, the actual temperature differences that must be applied with respect to ambient temperature are…”

“…Thus, in practice the presently determined optimal temperature gradients through the laminate thickness would be inputs to an inverse problem of heat conduction, to determine the heat input at one or more interfaces. Our experience in the lab indicates 8 that the heat input at interface, although not necessarily leading to temperature gradients that are mathematically optimal, would still lead to temperature gradients of a qualitative nature that are close enough to the optimum values to reduce the interlaminar stresses. Thus, until the inverse problem of heat conduction is solved, the present theoretical results provide guidelines as to where the heat should be introduced to reduce the interlaminar stresses, even in a nonoptimum way.…”

Piezoelectric Control of Edge Debonding in Beams Strengthened with Composite Materials: Part II - Failure Criteria and Optimization

“…In addition, shear lag effects associated with the adhesively bonded actuators, interaction with the host structure, and weight considerations further limit the efficiency of the control system. Kim et al [9,10] examined the feasibility of using thermally induced strains (which, in some cases, may be considered analogous to the piezoelectrically induced strains) to control the interlaminar stresses near the strait free edges of composite laminates. Although the analytical and experimental investigations confirmed that the stresses could be effectively controlled, application of this method in practice is rather complicated and limited.…”