Tensile fracture toughness of ceramic materials: Effects of dynamic loading and elevated temperatures

Technical Report · Mon Jan 01 00:00:00 EST 1990

DOI:https://doi.org/10.2172/7249840· OSTI ID:7249840

Suresh, S.; Duffy, J.; Yeshurun, Y.; Yang, K. ^[1]; Nakamura, T. ^[2]

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1. Brown Univ., Providence, RI (USA). Div. of Engineering
2. State Univ. of New York, Stony Brook, NY (USA). Dept. of Mechanical Engineering

Experimental methods are presented for the determination of fracture initiation toughness of ceramics and ceramic composites in pure tension under quasi-static and dynamic loading conditions over a range of temperature spanning 20{degree}C to 1300{degree}C. Circumferentially notched and cyclic fatigue pre-cracked rods of a variety of ceramic materials were subjected to quasi-state tensile fracture (Stress intensity factor loading rate, {dot K}{sub I} {approx} 0.1 MPa{radical}m{center dot}s{sup -1}) in an electro-servohydraulic test machine and to dynamic tensile fracture ({dot K}{sub I} {approx}10{sup 6}MPa{radical}m{center dot}s{sup -1}) using a modified tensile Kolsky (split-Hopkinson) bar. Dynamic finite element analyses of the circumferentially notched cylindrical rod have been conducted to develop the optimum specimen dimensions and tests procedures for ambient and elevated temperature dynamic fracture initiation toughness measurement. Experiments conducted on Al{sub 2}O{sub 3}, Si{sub 3}N{sub 4} and SiC, and an Al{sub 2}O{sub 3}--25 volume% SiC whisker composite at room temperature indicate that the dynamic to quasi-state fracture initiation toughness ratio K{sub Id}/K{sub Ic} is in the range of 1.1--1.4. Scanning electron microscopy observations show that failure above 1100{degree}C usually evolves by the nucleation, growth and coalescence of cavities. The mechanisms of elevated temperature quasi-state and dynamic fracture in polycrystalline Al{sub 2}O{sub 3} are examined and possible causes for the apparently higher dynamic fracture initiation resistance are discussed. The significance and limitations of the proposed experimental techniques are highlighted. 25 refs., 14 figs., 3 tabs.

• Research Organization: Brown Univ., Providence, RI (USA). Div. of Engineering
• Sponsoring Organization: DOE/ER; National Science Foundation (NSF)
• DOE Contract Number: FG02-84ER45167
• OSTI ID: 7249840
• Report Number(s): DOE/ER/45167-T1; ON: DE90008329; CNN: DMR-8714665
• Country of Publication: United States
• Language: English

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SILICON NITRIDES
TEMPERATURE EFFECTS
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