Measurement of Interfacial Shear Strength in SiC‐Fiber/Si₃N₄ Composites

Abstract

An indentation method f o r measuring shear strength in brittle matrix composites w a s applied to S i Cf i be rlS i, N 4 -ma tr ix sump 1 e s . Three methods were used to manufacture the composites: reaction bonding of a Si / S i c preform, hot-pressing, and nitrogen-overpressure sintering. An indentation technique developed by Marshall for thin specimens was used to measure the shear strength of the interface and the interfacial friction stresses. This was done by inverting the sample after the initial p u s h through and retesting the pushed fibers. SEM observations showed that the shear strength was determined by the degree of reaction between the fiber and the matrix unless the fiber was pushed out of its (well-bonded) sheath. [

Finite element modelling of creep deformation in fibre-reinforced ceramic composites

“…19). These predictions, based upon the finite element results, are consistent with recent experimental results which show that the proportional limit increases, and the ultimate strength decreases, after long-duration fatigue testing of unidirectional HP-SiCf/Si3N 4 composites under a tensile mean stress [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. The present analysis also suggests that after tensile creep (or fatigue loading under a tensile mean stress), the proportional limit of HP-SiCf/Si3N4 will be lower than that for virgin material if significant recovery has occurred prior to reloading in monotonic tension (note that after unloading the compressive residual stress in the matrix rapidly relaxes, see Fig.…”

“…For example, initial debonding in reaction-bonded SiCr/Si3N4 composites was observed by Laughner and Bhatt [13]; whereas initial debonding was absent in hot-pressed SiCrSi3N4 composites investigated by Holmes [6]. Results obtained from fibre push-out tests show the existence of an interfacial shear stress in SiCr/Si3N4 composites, even after complete debonding along the interface has occurred [13,14]. As noted by Morscher et al [14], this interfacial shear stress is caused by surface roughness along the fibre-matrix interface.…”

“…The initial interfacial stress state which exists in a composite depends upon the fabrication route and interracial chemistry used to produce the composite. For example, initial debonding in reaction-bonded SiCr/Si3N4 composites was observed by Laughner and Bhatt [13]; whereas initial debonding was absent in hot-pressed SiCrSi3N4 composites investigated by Holmes [6]. Results obtained from fibre push-out tests show the existence of an interfacial shear stress in SiCr/Si3N4 composites, even after complete debonding along the interface has occurred [13,14].…”

Predicted Effects of Interfacial Roughness on the Behavior of Selected Ceramic Composites

“…Within this framework, fiber pushout and pullout experiments have been used to measure the interfacial friction coefficient and radial clamping stress in composites. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, attempts to extend these one or two parameters to a detailed understanding of the influence on macroscopic fracture behavior have had limited success. Qualitative inferences have been made and frictional shear stresses in the range of 2-50 MPa have been correlated with ''good'' composites.…”