Fracture Resistance of SiC‐Fiber‐Reinforced Si₃N₄ Composites at Ambient and Elevated Temperatures

Abstract

The crack growth behavior in unidirectional SiC‐fiber‐rein‐forced Si3N4‐matrix composites fabricated in our laboratories was investigated as a function of fiber volume fraction and temperature. Both the stress‐intensity factor and an energy approach were adopted in the characterization of the crack growth behavior. Crack resistance increased with crack extension (R‐curve or T‐curve) as a result of bridging effects associated with the intact fibers. Large‐scale bridging was observed, and was considered in the determination of the R‐curves. Temperature and fiber volume fraction affected the crack propagation behavior. At room temperature a single crack was initiated at the notch tip; it then branched and delaminated upon further loading. In contrast, at 1200°C, little crack branching was observed. Increasing fiber volume fraction increased the degree of crack branching. Temperature and fiber volume fraction also affected the R‐curve behavior. Raising the temperature to 1200°C did not significantly degrade the room‐temperature R‐curve effect. Increasing the fiber volume fraction from 14% to 29% substantially enhanced the toughening effect and the R‐curve behavior.

Electrospun nylon 6 nanofiber reinforced BIS-GMA/TEGDMA dental restorative composite resins

“…With the unit of A being J (Joules), the unit of WOF (or fracture resistance) is J/m 2 or more conveniently, kJ/m 2 [20,21]. Eight specimens, approximately 25 mm in length, 2 mm in width and thickness were prepared and tested.…”

Reinforcement of a self-setting calcium phosphate cement with different fibers

“…where A is the area under the load-displacement curve, which is the work done by the applied load to deflect and fracture the specimen. With the unit of A being J (Joules), the unit of WOF (or fracture resistance 40 ) is J/m 2 or more conveniently, kJ/m 2 (k = 10 3 ). 30,39 After the matrix had cracked, most of the fiber-reinforced specimens were still intact, due to fibers bridging the cracks and supporting the applied load.…”

Silicon Nitride/Silicon Carbide Nanocomposite Materials: II, Hot Strength, Creep, and Oxidation Resistance

“…Second-phase inclusions of various shapes have been tested in Si 3 N 4 , such as particles, 12 fibers, 13,14 whiskers, [15][16][17][18][19][20][21][22] and platelets, 1,[23][24][25][26][27][28][29] most of which were made of SiC. A beneficial effect of fibers and whiskers on the fracture toughness at ambient temperature was found in some cases; 14,15,21 however, in most of the investigations, no increase in strength or even a strength degradation was observed. 19,21 The only exception is the work of Buljan et al, 15 who reported a 25% strength increase due to whiskers.…”