Fracture Control in Composite Materials Using Integral CrackArresters

Abstract

Damage tolerance and survivability have become important design criteria for future military aircraft structures. The inherent flaws which exist in a structural material or the damage sustained in combat, if uncontrolled, can grow to critical sizes and lead to failure of a component or, possibly, the entire aircraft. The objective of this study has been to investigate and develop crack arrester designs for composite materials which will contain cracks and damage locally, thereby allowing an aircraft and crew to return safely to base for repair or replacement of damaged parts. This is accomplished by using crack arrester strips which form a barrier and prevent a crack from propagating beyond them. This paper presents the results obtained in the first phase of these studies, in which it has been shown that crack arrester strips do stop and contain the damage, and that the use of these strips will provide survivability at significantly less weight than designs in which survivability is achieved by limiting the operating strain. These conclusions are based on both analysis and tests performed on specimens of variable thickness, size, and laminate configuration in which failure modes and critical conditions have been characterized.