Accession Number : ADA192021

Title :   Fracture Physics of Delamination of Composite Materials.

Descriptive Note : Final technical rept. 1 Feb 84-30 Jun 87,

Corporate Author : TEXAS A AND M UNIV COLLEGE STATION MECHANICS AND MATERIALS CENTER

Personal Author(s) : Bradley, W L ; Corleto, C R ; Goetz, D P

PDF Url : ADA192021

Report Date : Oct 1987

Pagination or Media Count : 267

Abstract : Real time observations in the scanning electron microscope have delineated the details of the fracture processes that result in mode I and mode II delamination of composite materials. These observations give clear explanation of why GII/GIC ratio for brittle materials is three times that for ductile materials. These in situ observations of fracture also indicate that distinctively different damage zone develops ahead of growing cracks for mode I and mode II delamination. Two techniques have been developed to measure the strain field around a crack tip. Stero imaging and direct measurement of distortion of a fine array of dots placed on the surface. Both are effective in measuring the strain field around a crack tip. A surprising result which emerged from these measurements is that the local strain to failure at the crack tip is much greater than the elongation measured in a tensile test (up to six times as high). A linear, orthotropic finite element code has been used to calculate the stress fields around the crack tip for mode I and mode II loading. A J-integral approach for mode I has been used to investigate the delamination of multi directional composites. Initial results using this approach look very promising for characterizing systems which can not be characterized with conventional analysis.

Descriptors :   *FRACTURE(MECHANICS), *BONDING, *LAMINATES, BRITTLENESS, COMPOSITE MATERIALS, CRACKS, DAMAGE, DUCTILITY, ELECTRONIC SCANNERS, ELONGATION, J INTEGRALS, MATERIALS, MEASUREMENT, PHYSICS, TENSILE TESTERS, COMPUTER AIDED DIAGNOSIS, STEREOMAPPING, REPRINTS, NOTCH SENSITIVITY

Subject Categories : Laminates and Composite Materials

Distribution Statement : APPROVED FOR PUBLIC RELEASE