The Mechanical Properties of Metal Matrix Composites Subjected to Cyclic Temperature Changes.
Technical rept. 1 Jul 74-30 Jun 75,
TENNESSEE UNIV SPACE INST TULLAHOMA DEPT OF METALLURGICAL ENGINEERING
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Part I The strength of metal matrix materials reinforced with unidirectional brittle fibers is shown to be best described in terms of upper and lower bounds. Tensile strength and fracture toughness values were obtained from 6061 aluminum reinforced with boron or silicon carbide fibers. The as-received, heat treated and thermally fatigued conditions were investigated and similar tests were carried out on cross-plied, 090 degrees, boron reinforced material. The failure of the slotted specimens is discussed in terms of strength bounds similar in concept to those proposed to describe the tensile strength results. Part II The mechanical properties of various boron and silicon carbide fiber reinforced 6061 aluminum matrix specimens were measured both before and after subjecting the specimens to repeated cyclic temperature variations between room temperature and 698 K. The results of dilatometer experiments are discussed in terms of creep at the elevated temperatures and the generation of large tensile internal stresses in the matrix at room temperature. It is hypothesized that these effects degrade the strength of the fiber-matrix bond and eventually cause breakage of individual fibers.
- Laminates and Composite Materials