Thermal cycling-induced deformation of fibrous composites with particular reference to the tungsten-copper system

Role of interfacial and matrix creep during thermal cycling of continuous fiber reinforced metal–matrix composites

“…However, there is ample evidence in the literature that this condition is often violated, even in the absence of interfacial fracture. This is most clearly observed following thermal cycling of composites in the absence of any applied load [10,11]. For instance, Yoda et al [11] observed that the ends of W ®bers in a Cu matrix intruded into the matrix following thermal cycling, the extent of intrusion increasing with increasing number of cycles.…”

“…This is most clearly observed following thermal cycling of composites in the absence of any applied load [10,11]. For instance, Yoda et al [11] observed that the ends of W ®bers in a Cu matrix intruded into the matrix following thermal cycling, the extent of intrusion increasing with increasing number of cycles. Similar eects have been observed following slow thermal cycling of graphite ®ber reinforced aluminum composites [10], whereupon the matrix was observed to protrude past the ®ber-ends.…”

“…Similar eects have been observed following slow thermal cycling of graphite ®ber reinforced aluminum composites [10], whereupon the matrix was observed to protrude past the ®ber-ends. In both cases [10,11], the slow heating/cooling rates during cycling, in conjunction with the tensile matrix residual stress along the ®ber axes, allowed the matrix to elongate relative to the ®bers via creep. Here, no interfacial debonding occurs, and the dierential strain between the matrix and ®bers is accommodated by time-dependent diusional sliding at the interface close to the ®ber-ends, where large interfacial shear stresses exist.…”

“…This is very dierent from the eect observed during relatively rapid thermal cycling, where interfacial fracture, followed by frictional sliding at the debonded interface, results in the relief of axial tensile residual stresses in the matrix, allowing the matrix to shrink relative to the ®bers [9,17]. Frictional sliding is commonly observed in composites with weak interfaces which undergo debonding during cycling [9,12,17], whereas time-dependent sliding via interfacial creep occurs in the absence of debonding [10,11].…”

“…Although most studies of creep and thermal cycling of composites reported to date consider only one dominant matrix creep mechanism (e.g. Refs [5,10,11,14, 18±20]), it has been recognized that uni®ed creep laws are necessary to adequately describe the composite strain response when the temperature and matrix stress vary considerably, as during thermal cycling [29]. The role of mechanism transitions has been investigated in metal±ceramic multi-layers, where the dominant creep mechanism of the metallic layer(s) has been found to change continually during thermal cycling [30].…”