Accession Number : ADP004978

Title :   Effects of Shear Lag on Thermal Expansion of 3D Carbon-Carbon Composites,

Corporate Author : JORTNER RESEARCH AND ENGINEERING INC COSTA MESA CA

Personal Author(s) : Jortner,J.

Report Date : DEC 1984

Pagination or Media Count : 13

Abstract : Thermal expansion of coupons of 3D carbon-carbon is analyzed in terms of the thermo-elastic properties of the mini-constituents (yarn bundles and matrix pockets) and the stress transfer across their interfaces. The weakness of the interfaces limits the stress transfer by shear. When the shear strength of the interface is exceeded and debonding occurs, stress transfer in the de-bonded region is assumed to be frictional. The frictional shear capability is estimated as a function of the inter-constituent stresses that occur on heating. The analysis, which deals with the stress-transfer using a shear-lag approach, provides estimates of the displacements between mini-constituents. Numerical results are presented to show how elastic and frictional shear lag influences measurements of thermal expansion. The relation of specimen dimensions to the geometry of the composite's unit cell, and details of the measurement technique, are predicted to influence the measured expansions; for some techniques, the measured expansion is predicted to differ significantly from the true expansion of the bulk composite material. Analytical predictions are shown to compare reasonably well to Lander's data on end effects, up to about 4000 F, beyond which the likelihood of cree/relaxation phenomena makes the analysis in applicbale.

Descriptors :   *CARBON CARBON COMPOSITES, *THERMAL EXPANSION, TRANSFER, STRESS ANALYSIS, THREE DIMENSIONAL, THERMOELASTICITY, INTERFACES, SHEAR STRENGTH, BONDING, FRICTION, SHEAR PROPERTIES, DELAY, CARBON YARN, THERMAL STRESSES

Distribution Statement : APPROVED FOR PUBLIC RELEASE