The financial support provided by a consortium of Manitoba aerospace industries and the Natural Science and Engineering Research Council (NSERC) of Canada is gratefully acknowledged. The authors thank Messrs. J. Van Dorp;
D;
Mardis;
I;
Penner;
X.Y;
Li;
W.J;
Fan;
and X. Meng for their assistance in the machining of test specimens and in the experimental work;