40TH ANNIVERSARY (90/0)s SIC/CAS Perpendicular Matrix Cracking 543210 300400500600700800900 Quenching Temperature Difference(c) 4 3.5 (a) 3 2 15 0 40045050060 700 Quenching Temperature Difference (C) Figure 13(a) Crack density as a function of AT for PMCs for each set of longitudinal plies of (90/0)3s Nicalon/CAS laminate. Note that CDLI>CDL?>CDL3 at all ATs and (b) Crack densities of PMCs and HMCs and total crack density at each AT. Relevant trends for each damage mode even higher quenching temperature differences, damage became more extensive, especially the PMCs in longi tudinal plies. However, HMCs in transverse plies were observed, apart from increasing in length, to penetrate deeper and deeper into the matrix. The extent of ther mal shock damage exhibited a gradient across the ma- terial surface: higher crack densities and deeper HMCs were located at or close to the centreline. On moving to- wards the outer plies the extent of the damage reduced significantly In terms of the number of cracks and their measured length as a function of the surface area, damage in the form of PMcs was found to be much more extensive compared with that in the form of HMCs, especially at severe thermal shocks. However, whereas PMCs propa- gated only at the surface of the laminate, HMCs could be seen to extend deeply into the matrix for△T≥600°C Figure /2 SEM images of HMCs in(a)T1, (b)T2, and(c)T3 at AT= was evident from their increased opening. Unfortunately, 800C. The differences in depth can be clearly observed. the depth they penetrated could not be determined with any particular accuracy experimentally. However, judging in the case of the(90%/0%)3s system, in those adjacent to from the openings of the crack surfaces at the surface, the them. With the application of higher differentials, damage extent of their propagation on the surface(from edge to extended to the outer plies until, at intermediate shocks edge for some specimens at severe shocks), and the fact (AT=600C), the surfaces of all plies were fractured. At that in these configurations they cannot meet any ply inter40TH ANNIVERSARY Figure 12 SEM images of HMCs in (a) T1, (b) T2, and (c) T3 at
T = 800◦C. The differences in depth can be clearly observed. in the case of the (90◦/0◦)3s system, in those adjacent to them. With the application of higher differentials, damage extended to the outer plies until, at intermediate shocks (
T = 600◦C), the surfaces of all plies were fractured. At Figure 13 (a) Crack density as a function of
T for PMCs for each set of longitudinal plies of (90◦/0◦)3s Nicalon/CAS laminate. Note that CDL1>CDL2>CDL3 at all
Ts and (b) Crack densities of PMCs and HMCs and total crack density at each
T. Relevant trends for each damage mode are also shown. even higher quenching temperature differences, damage became more extensive, especially the PMCs in longi￾tudinal plies. However, HMCs in transverse plies were observed, apart from increasing in length, to penetrate deeper and deeper into the matrix. The extent of ther￾mal shock damage exhibited a gradient across the ma￾terial surface: higher crack densities and deeper HMCs were located at or close to the centreline. On moving to￾wards the outer plies the extent of the damage reduced significantly. In terms of the number of cracks and their measured length as a function of the surface area, damage in the form of PMCs was found to be much more extensive compared with that in the form of HMCs, especially at severe thermal shocks. However, whereas PMCs propa￾gated only at the surface of the laminate, HMCs could be seen to extend deeply into the matrix for
T ≥ 600◦C as was evident from their increased opening. Unfortunately, the depth they penetrated could not be determined with any particular accuracy experimentally. However, judging from the openings of the crack surfaces at the surface, the extent of their propagation on the surface (from edge to edge for some specimens at severe shocks), and the fact that in these configurations they cannot meet any ply inter- 960