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40TH ANNIVERSARY Figure I The nomenclature used to describe damage due to thermal shock on a(0/90)s laminate. Figure 2 Photomicrograph of shallow, hair-like HMC on TI at AT=450.C. exclusively in the thick, central 90 ply (T1)and each one At AT=450-5000C, only a small number of HMCs was deflected at the successive fibre-matrix interfaces it were observed in Tl. They did not penetrate deep into encountered on its path. For this reason Graham et al. [10], the matrix and had short lengths. The small number(1-2 who observed similar crack patterns on the transverse of PMCs that were seen in LI at AT=500C exhibited faces of UD Nicalon/lithium aluminosilicate(LAs)II af- similar characteristics. In addition, they did not span the ter thermal shock, termed themthermal debond cracks. entire 0o ply thickness but arrested at fibre-matrix inter- HMCs seemed to appear randomly on the ply surface, al- faces inside the ply though most of them could be seen towards the centreline At AT=600C a number of short, random HMCs were (C-C)of the ply. again observed in Tl. while some PMCs in Ll could be PMCs were detected on the surfaces of thermally- seen to extend and bridge the whole 0o ply thickness shocked specimens of this laminate after quenching Some HMCs seemed to connect and form 1-2 longer through AT= 500C, exclusively in the two 0 plies cracks in TI at AT= 700oC. At the same temperature (LI) adjacent to the thick, central 90 ply. These cracks differential, some PMCs not only bridged the 0o ply thick ran across the ply thickness, leaving the fibres on their ness but also extended into the adjacent 90 ply. Almost h unaffected(Fig 3). all PMCs, which had increased significantly in numbe40TH ANNIVERSARY Figure 1 The nomenclature used to describe damage due to thermal shock on a (0◦/90◦)s laminate. Figure 2 Photomicrograph of shallow, hair-like HMC on T1 at T = 450◦C. exclusively in the thick, central 90◦ ply (T1) and each one was deflected at the successive fibre-matrix interfaces it encountered on its path. For this reason Graham et al.[10], who observed similar crack patterns on the transverse faces of UD Nicalon/lithium aluminosilicate (LAS) II after thermal shock, termed them ‘thermal debond’ cracks. HMCs seemed to appear randomly on the ply surface, although most of them could be seen towards the centreline (C-C ) of the ply. PMCs were detected on the surfaces of thermallyshocked specimens of this laminate after quenching through T = 500◦C, exclusively in the two 0◦ plies (L1) adjacent to the thick, central 90◦ ply. These cracks ran across the ply thickness, leaving the fibres on their path unaffected (Fig. 3). At T = 450–500◦C, only a small number of HMCs were observed in T1. They did not penetrate deep into the matrix and had short lengths. The small number (1–2) of PMCs that were seen in L1 at T = 500◦C exhibited similar characteristics. In addition, they did not span the entire 0◦ ply thickness but arrested at fibre-matrix interfaces inside the ply. At T = 600◦C a number of short, random HMCs were again observed in T1, while some PMCs in L1 could be seen to extend and bridge the whole 0◦ ply thickness. Some HMCs seemed to connect and form 1–2 longer cracks in T1 at T = 700◦C. At the same temperature differential, some PMCs not only bridged the 0◦ ply thickness but also extended into the adjacent 90◦ ply. Almost all PMCs, which had increased significantly in number, 953