40TH ANNIVERSARY The evolution of both types of damage with increasing applied AT can be seen in the sequence of reflected light microscopy images of Fig. 1 At the onset of fracture(△Te=400°C) nly visible in the central plies of this laminate PMCs in LI did not bridge the ply thickness while HMCs in TI were associated mainly with open pores. The application of temperature differentials up to AT 500C did not change the morphology of either type of matrix crack: they remained shallow surface features However PMCs were also visible in L2 and L3 and the presence of HMCs extended to T2.At△T=500°C HMCS of significant length could be seen originating either inside TI and T2 or from the ply edges running towards the centre of the specimen The length and depth of HMCs in Tl became much 9 SEM image showing deep HMC in the central transverse ply at a larger at AT=600oC. At this temperature differential, damage was detected in every ply of the laminate PMCS could be seen bridging the thicknesses of their respective 876 plies and some extended into adjacent transverse plies ( 0/90)s SICICAS The population of these cracks seemed higher the closer the longitudinal ply was located to the centreline(C-C)of the polished surface. The same was true for the transverse 国 plies Application of even higher temperature differentials re- sulted in long, deep HMCs in TI and T2(with depth always being larger in T1), longer HMCs in T3, and mul tiplication of PMCs in all longitudinal plies. However, 300 400 500 600 700 800 900 the depth of PMCs, even in Ll, did not increase In ad- Quenching Temperature Difference(C) dition, only short HMCs were visible in the outer T3 plies PMCs were distributed uniformly between longitu dinal plies with the same designation. By contrast, HMCS (o/90) SiC/CAS accumulated in the pairs of transverse plies in a more regular fashion. The differences in depth between HMCs in Tl, T2, and T3 can be clearly seen in the SEM images of Fig. 12 E15 The accumulation of damage in the 0 plies of this laminate at increasing thermal shocks can be seen in the graph of Fig. 13a. Significant increases in crack density are evident and at each temperature differen- 0 350400450500600700800 tial CDLI >CD 2>CDL3. The rate of increase in crack- ing for LI looks to be higher than the rates of in- Quenching Temperature Difference ('C) crease for L2 and l3. However the scatter of the perimental results does not allow safe conclusions to be reached DLI>CDL2>CD3 at all ATs and(b )Crack densities of PMCs and HMCs The accumulation of damage in the transverse plies of and total crack density at each AT this laminate is shown in Fig. 13b. The density of HMCs increases continuously with the application of higher tem- plies. Although they generally ran horizontally, succes- perature differentials. Note that only the total crack den- sive fibre-matrix interfaces deflected them continuously. that CDT1>CDT2>CDr3 at each temperature differential PMCs were also detected after quenching through the crit- However, whether CDTi or CDr was higher was mostly ical temperature differential, i.e. at ATc= 400C. They random result that depended on the point of origin of appeared only in 0 plies. Their advance was at right an- the respective HMCs. In general, HMCs emanating from gles to the longitudinal fibres, which remained unaffected ply edges ran for longer lengths From the comparison of since Pmcs were deflected at fibre-matrix interfaces crack densities of each type of damage at each AT it can40TH ANNIVERSARY Figure 9 SEM image showing deep HMC in the central transverse ply at a high temperature differential. Figure 10 (a) Crack density as a function of
T for PMCs for each set of longitudinal plies of (0/90)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. plies. Although they generally ran horizontally, succes￾sive fibre-matrix interfaces deflected them continuously. PMCs were also detected after quenching through the crit￾ical temperature differential, i.e. at
Tc = 400◦C. They appeared only in 0◦ plies. Their advance was at right an￾gles to the longitudinal fibres, which remained unaffected since PMCs were deflected at fibre-matrix interfaces. The evolution of both types of damage with increasing applied
T can be seen in the sequence of reflected light microscopy images of Fig. 11. At the onset of fracture (
Tc = 400◦C), damage was only visible in the central plies of this laminate. PMCs in L1 did not bridge the ply thickness while HMCs in T1 were associated mainly with open pores. The application of temperature differentials up to
T = 500◦C did not change the morphology of either type of matrix crack: they remained shallow surface features. However, PMCs were also visible in L2 and L3 and the presence of HMCs extended to T2. At
T = 500◦C, HMCs of significant length could be seen originating either inside T1 and T2 or from the ply edges running towards the centre of the specimen. The length and depth of HMCs in T1 became much larger at
T = 600◦C. At this temperature differential, damage was detected in every ply of the laminate. PMCs could be seen bridging the thicknesses of their respective plies and some extended into adjacent transverse plies. The population of these cracks seemed higher the closer the longitudinal ply was located to the centreline (C-C ) of the polished surface. The same was true for the transverse plies. Application of even higher temperature differentials re￾sulted in long, deep HMCs in T1 and T2 (with depth always being larger in T1), longer HMCs in T3, and mul￾tiplication of PMCs in all longitudinal plies. However, the depth of PMCs, even in L1, did not increase. In ad￾dition, only short HMCs were visible in the outer T3 plies. PMCs were distributed uniformly between longitu￾dinal plies with the same designation. By contrast, HMCs accumulated in the pairs of transverse plies in a more ir￾regular fashion. The differences in depth between HMCs in T1, T2, and T3 can be clearly seen in the SEM images of Fig. 12. The accumulation of damage in the 0◦ plies of this laminate at increasing thermal shocks can be seen in the graph of Fig. 13a. Significant increases in crack density are evident and at each temperature differen￾tial CDL1>CDL2>CDL3. The rate of increase in crack￾ing for L1 looks to be higher than the rates of in￾crease for L2 and L3. However, the scatter of the ex￾perimental results does not allow safe conclusions to be reached. The accumulation of damage in the transverse plies of this laminate is shown in Fig. 13b. The density of HMCs increases continuously with the application of higher tem￾perature differentials. Note that only the total crack den￾sity is plotted at each
T. Generally, it can be assumed that CDT1>CDT2>CDT3 at each temperature differential. However, whether CDT1 or CDT2 was higher was mostly a random result that depended on the point of origin of the respective HMCs. In general, HMCs emanating from ply edges ran for longer lengths. From the comparison of crack densities of each type of damage at each
T it can 958