Micromodelling of effective stress intensities for bridged cracks in fibre-reinforced titanium metal-matrix composites

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“…The value of τ deduced (4.7-20 MPa) in this study compares well with that reported in the literature [9][10][11][14][15][16][17][18][20][21][22][23]25,26], but it is lower than the results generally reported from push-out tests [16][17][18]20,23]. The effect of fatigue loading has been suggested as a possible reason for the low value of τ [14,34].…”

“…The measured average crack length as a function of the number of applied cycles and the corresponding σ a,max is shown in Figures 2(a) and 2(b) for the specimens 93411 and 93413, respectively. The crack length versus cycle count response is typical of fully bridged crack growth exhibiting decreasing crack growth rate (da/dN) with increasing crack length [9,10,11,14,[16][17][18][20][21][22][23][24][25][26]. The specimen 93411 was stopped at ≈ 7.87 x 10 6 cycles, COD profiles measured, and the matrix removed using an etchant.…”

“…This format follows from the original work of Kitagawa and Takahashi [22]. These authors identified an apparent "safe region", shown schematically in Fig.…”

“…The fiber bridging models commonly used to describe crack growth perpendicular to fibers in MMC are either shear lag models [9,[10][11][12][14][15][16][17][18][19][20][21][22][23][24][25][26] or constant bridging stress models [11,17,18]. These shear lag models assume that the fiber/matrix interface has negligible debonding energy, initial stresses are zero and the sliding stress, τ is constant.…”

“…In CMC and MMC systems, the bridging mechanisms were modeled as a distributed closing pressure exerted on the crack surface with the applied load in the direction of the fibers (Figure 1). The models used to describe crack growth in continuously reinforced CMC and MMC include shear lag [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][19][20][21][22][23][24][25][26], constant bridging stress distributions [11,17,18] and fiber pressure models [17]. These fiber bridging models for continuously reinforced CMC and MMC predict a wide range of bridging stress distributions.…”