In part one of this paper, the fracture processes of multiple transverse cracking and free edge delamination in composite laminates have been analyzed by an energy method. Numerical analyses and experimental examination using a series of T300/934 graphite epoxy laminates are pre sented in this part two. While part one is presented in a self-contained form, part two must be regarded as the continuation of part one.

Single crystals of tantalum carbide, up to 2 mm in size have been grown from solution in a bath of molten iron. The slip plane was found to be {1 11} using a two-surface analysis on etch-pitted crystals deformed by microindentation at room temperature. Observations of etch-pit patterns around inclusions suggest that slip occurs on other planes at elevated temperatures. Maximum microhardness values between 3800 and 5200 Knoop (100 gm load) were found at a composition TaC0.83• In regions of crystals with a carbon content less than TaC0.83 a phase transformation was seen close to microhardness indentations in samples decarburised below 2200 ~ C. The mechanical behaviour of tantalum carbide is discussed with reference to a general model for the electronic structure of carbides. IntroductionLike the other monocarbides of the Group IVA and VA transition metals, tantalum carbide possesses the rock salt structure and exists over a wide range of substoichiometry. The most recent phase diagram [1] indicates the composition limits for single-phase tantalum carbide as TaCo.75 to TaC0.9s below about 1500 ~ C. A maximum melting point of 3983 ~ C occurs at TaC0.98. Storms [2] has suggested that the maximum melting point might lie at TaC0.s but he also points out that the actual values of composition and temperature are subject to some uncertainty due to the experimental difficulties in making the measurements [3]. A number of authors have reported a zeta-phase tantalum carbide [4-6] which might be a metastable compound [2,4,5]. Its composition has been determined as TaCo.75 [5] or TaC0.r4 [6], but it also appears to exist over a range of substoichiometry [7]. Yvon and Parth6 [7] have recently shown that the structure of the zeta-phase consists of an arrangement of twelve close-packed metal atoms in a unit cell, with the carbon atoms in octahedral interstices. The arrangement of the metal atoms can be regarded as alternate layers of hcp and fcc stacking, i.e. a close-packed structure containing 50~ stacking faults. Such a structure with a high density of faults is in accord with recent electron microscope studies of *Present address:

Results of experiments to evaluate the degree of moisture-induced swelling and plasticization in T300/934, T300/5209, GY70/339 composites are described. Swelling was found to be a nonlinear reversible function of equilibrium moisture content. Out-of-plane swelling was several times larger than in-plane transverse swelling in the unidirectional composites. Equilibrium moisture content was found to vary with exposure temperature as well as humidity in the 339 and 5209 matrix systems. The in-plane shear properties were determined as a function of time, temperature, and equilibrium moisture content, and master curves of temperature and moisture-compensated modulus versus time were constructed for each material. Nonsymmetric (04/904)T cross-plied laminates were employed to study the alteration of residual stresses in T300/5209 and GY70/339 as a function of temperature and moisture content. The level of residual stresses measured for a given equilibrium moisture content was found to be a function of the temperature at which the moisture was absorbed.

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