Stress relaxation in discontinuously reinforced composites

Conference · Mon May 01 04:00:00 EDT 1995

OSTI ID:70790

Shi, N ^[1]; Arsenault, R J ^[2]

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1. Los Alamos National Lab., NM (United States)
2. Univ. of Maryland, College Park, MD (United States). Dept. of Materials and Nuclear Engineering

It has been observed that in discontinuously-reinforced Al{sub 2}0{sub 3}/NiAl composites that as the reinforcement size increases the average density of dislocations generated from the relaxation of the thermal stresses increases, and the corresponding thermal residual stresses slightly decrease. Similar changes result when the reinforcement morphology changes from spheres to short fibers to continuous filaments. The changes of dislocation density and thermal residual stresses with respect to particle size are in contrast to those observed in the SiC/Al counterpart A previously developed simple model used to explain the SiC/Al data, which was based on prismatic dislocation punching, suggested that the density of the misfit dislocations decreases when the reinforcement size increases. In this investigation, a simple model is proposed to explain the anomaly in the development of thermal residual stresses and the generation of misfit dislocations as a function of the particle size and shape in Al{sub 2}0{sub 3}/NiAl composites. As a result of a lack of sufficient independent-slip-systems in low symmetry materials such as NiAl, plastic relaxation of the thermal stresses is severely constrained as compared to fcc Al. As such, plastic relaxation requires collaborative slips in an aggregate of grains. This only occurs when the length scale of the varying misfit thermal stress field is much larger than the average grain size. That is, the mechanism of plastic relaxation becomes operative when the reinforcement size increases.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States); Department of Defense, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 70790
• Report Number(s): LA-UR--95-1168; CONF-9506181--1; ON: DE95010928; CNN: GRANT N00014-91-J-1353
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM ALLOYS
ALUMINIUM OXIDES
COMPOSITE MATERIALS
DISLOCATIONS
FIBERS
NICKEL ALLOYS
REINFORCED MATERIALS
SILICON CARBIDES
STRESS RELAXATION
THERMAL STRESSES