日本金属学会誌

J. Japan Inst. Metals, Vol. 59, No. 8 (1995),
pp. 869-877

Fracture Strength Evaluation of Zirconia Particle-ReinforcedNickel Matrix Composites by Disk-Bending Tests

Takehiro Ishizuka, Yoriko Ohta and Kenji Wakashima

Precision and Intelligence Laboratory, Tokyo Institute of Technology, Yokohama

Abstract:

In an effort to obtain a reasonable fracture criterion necessary for a micromechanics-based approach to the design of ceramic-metal ``functionally graded materials,'' disk-bending tests have been carried out for a series of zirconia (PSZ: ZrO2-2 mol%Y2O3) particle-reinforced nickel (Ni) matrix composites fabricated by hot-press consolidation of PSZ-Ni powder mixtures with several different compositions (0, 20, 40, 60, 80 and 100 vol% PSZ). Disk-shaped samples of typical dimensions 20 mm dia.{×}1 mm are radially ``four-point'' bent at room temperature; it is thereby found that the samples containing PSZ over 40 vol% fracture by radial cracking under equibiaxial loading. The convex-face tensile strains at fracture of these samples are determined by assuming a simple geometry of spherical bending; the corresponding fracture stresses in PSZ particles are calculated with a micromechanics-based method which takes account of the plasticity of the Ni matrix. The results are analyzed on the basis of a fracture-mechanics criterion in terms of the energy release rate for a penny-shaped crack under multiaxial loading. An equivalent normal stress σneq is then defined as σneq=√σn22/(1-0.5{ν)2}, where σn and τ are the normal and shear stresses acting on the crack surface and ν is Poission's ratio. It is found that fracture occurs when the maximum value of σneq in PSZ particles reaches a constant level. Scanning electron microscopic observations give evidence of this particle cracking-controlled fracture.


(Received January 27, 1995)

Keywords:

functionally graded materials, zirconia-nickel composites, powder metallurgy, disk-bending test, elastoplastic analysis, micromechanics, residual stress, fracture criterion


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