Combined Mode I‐Mode III Fracture of Fatigue‐Precracked Alumina

The mixed-mode fracture behavior of (cyclic) fatigue pre-cracked ceramic specimens was studied in combined tension-torsion loading. Circumferentially notched cylindrical rods of polycrystalline alumina were precracked in uniaxiai cyclic compression to introduce a concentric mode I fatigue crack. Subsequently, the rods were quasi-statically fractured in pure tension, pure torsion, and various combinations of tensile and torsional stresses to obtain the mode I-mode III fracture envelope. The introduction of torsional loads promotes severe abrasion between the crack faces. The critical stress intensity factor for fracture initiation increases by a factor of °2.3 as the loading mode is changed from pure tension to pure torsion. Fracture surface tortuosity and abrasion “shield” the crack-tip from the far-field tensile and torsional loads to cause an apparent toughening effect. The mechanisms of mixed-mode fracture in alumina are examined and consequences of the breakdown of the similitude concept implicit in the nominal use of fracture mechanics are discussed.

[1]  E. Tschegg,et al.  Torsional fracture of fatigue pre-cracked ceramic rods , 1987 .

[2]  L. Ewart,et al.  Crack propagation in ceramics under cyclic loads , 1987 .

[3]  S. Suresh,et al.  Tensile fracture toughness measurements in ceramics , 1987 .

[4]  S. Suresh,et al.  Room temperature fatigue crack growth in cemented carbides , 1986 .

[5]  S. Suresh,et al.  Dynamic fatigue crack growth in polycrystalline alumina under cyclic compression , 1986 .

[6]  A. R. Rosenfield,et al.  Mixed-Mode Fracture of Ceramics in Diametral Compression , 1986 .

[7]  T. Gross.  Frictional effects in mode III fatigue crack propagation , 1985 .

[8]  J. Petrovic.  Mixed‐Mode Fracture of Hot‐Pressed Si3N4 , 1985 .

[9]  D. Marshall.  Mechanisms of Failure from Surface Flaws in Mixed‐Mode Loading , 1984 .

[10]  E. Tschegg,et al.  Sliding mode crack closure and mode III fatigue crack growth in mild steel , 1983 .

[11]  J. Petrovic,et al.  Fracture of A12O3 in Combined Tension/Torsion: I, Experiments , 1981 .

[12]  D. Shetty,et al.  Biaxial Fracture Studies of a Glass‐Ceramic , 1981 .

[13]  J. J. Mecholsky,et al.  Mixed‐Mode Fracture in Soda‐Lime Glass , 1979 .

[14]  J. Petrovic,et al.  Correction of Mixed‐Mode Fracture from Controlled Surface Flaws in Hot‐Pressed Si3N4 , 1977 .

[15]  B. Lawn,et al.  Indentation fracture: principles and applications , 1975 .

[16]  G. Sih.  Strain-energy-density factor applied to mixed mode crack problems , 1974 .

[17]  B. Cotterell.  Brittle fracture in compression , 1972 .

[18]  F. Erdogan,et al.  On the Crack Extension in Plates Under Plane Loading and Transverse Shear , 1963 .

[19]  Subra Suresh,et al.  Constitutive behavior of a microcracking brittle solid in cyclic compression , 1987 .