Survey of current fracture mechanics studies at AMMRC

Abstract

The fracture and fatigue studies at AMMRC encompass both experimental and analytical thrusts. This presentation will cover a few representative activities. The status of a test program on fracture behavior of unidirectionally reinforced composites using double cantilevered type specimens will be reported. Material systems include ‘S’ glass/epoxy and graphite/epoxy. Limited fracture toughness data is available. Additionally, some effort has been initiated on cross ply specimens. Fatigue studies at AMMRC in metals reflect a continuing interest in both initiation and propagation aspects. A technique has been developed for detection of crack initiation using an automated photographic process for recording, periodically, potential initiation sites. The observations are discussed in conjunction with damage criteria. Crack propagation studies have focussed in developing a ‘law’ which accounts for the extremes of propagation rates at threshold levels of stress intensity and at the higher levels associated with unstable growth. Additionally, crack propagation experiments are described which are aimed at exploring the transient effects on crack propagation of sudden changes in stress intensity levels. Supplementing these experimental studies are extensive analytical efforts directed toward defining the stress states in anisotropic material when used in lap and/or mechanical joint configurations. Additionally, extensive effort by one team of investigators has been devoted to analytical techniques for crack analysis. These techniques have been applied to a wide variety of geometric configurations and to a range of material types including anisotropic. This effort will be described briefly.