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Although latency measurements were consistent with previous studies, the plyometric training program did not cause significant change in the peroneus longus reaction time.

Thick three-dimensional (3-D) finite element models of centre cracked plates are used to study the variation in the biaxiality factor ,L3 with the crack aspect ratio a/w. The use of two widely accepted methods to evaluate the T-stress in two-dimensions, namely the boundary layer method and the displacement field method, to calculate the T-stress in three-dimensions is studied. It is shown that the boundary layer method gives results that compare rather well with the two-dimensional plane strain values (maximum difference of 6 percent), while the displacement field method results are about 15 percent lower. Two parameters are shown to affect the threedimensional evaluation of the biaxiality factor, namely the material's Poisson's ratio v and the specimen's thickness t. The biaxiality factor is directly proportional to u and inversely proportional to t. Three-dimensional analysis is required to assess correctly the effect of u and t on ,B. Nomenclature Abbreviations: 2-D = two-dimensional 3-D = three-dimensional b.1. = boundary layer f.e. = finite element f.m. = full model LEFT = linear elastic fracture mechanics SSY = small scale yielding Latin symbols: a = half crack length a/w = crack aspect ratio E = Young's modulus h = half of cracked plate height J = J-integral Irl = stress intensity factor for mode I K/Kc = normalised stess intensity factor r, 0 = cylindrical co-ordinates centred at the crack tip T = T-stress t = model thickness 36 B.S. Henry and A.R. Luxmoore u, v = displacement in the x-direction and y-direction respectively w = half of cracked plate width Greek symbols: /3 = biaxiality factor u = Poisson's ratio p = notch diameter 0"ij = stress tensor 0"us = yield stess of material

The fracture toughness of AISI 304 and 316L stainless steels and their welds irradiated to 7 × 1025 neutrons (n)/m2 (50 percent of this was at E > 0.1 MeV) was investigated on 10- and 20-mm-thick three-point bend specimens. Measurements of critical values of the J-integral, Jc, and the crack-opening displacement, δc, defined at the onset of stable crack growth, were performed at 20 and 400°C. The electric potential method was adapted to hot-cell operation for the detection of the initiation point. Drastic reductions of fracture toughness occur when combining welding, irradiation, and high temperature. As an example, the value δc = 0.51 mm of base-material nonirradiated specimens tested at 20°C drops to 0.011 mm for welded irradiated specimens tested at 400°C. The consequences on liquid metal fast breeder reactor (LMFBR) structural design are illustrated in the case of the French LMFBR Super Phénix.

Recent studies have shown that the near crack-tip stress field at a given J value is dependent on geometry. This dependence has been linked to the degree of constraint in the geometry, with low constraint geometries losing J dominance at very low deformation levels. New approaches centred on the use of a two-parameter description (e.g.J-T and J-Q) of the crack-tip stress-strain state have emerged. However, there is a serious lack of experimental and numerical results for low constraint geometries to quantify the 7,-stress and Q-value in the literature. This paper describes details of an experimental and numerical program carded out on low and high constraint geometries (CCT and TPB) fabricated from an aluminium alloy. The results show that the experimental and numerical fracture toughness values (Jc) agree within 4-10 percent. The T-stress and Q-value two-parameter methodologies are successful at indexing the fracture toughness, ordering the data into a systematic trend of decreasing fracture toughness with increasing 7" or Q, albeit with some scatter. This allows the use of practical two-parameter failure criteria, in the form of J-T and J-Q loci, to predict the behaviour of cracked components, without the conservatism associated with the use of high constraint test geometries. Nomenclature Abbreviations:ASTM American society for testing and materials BSI British standards institute CCT centre cracked specimen in tension CT compact tension specimen HRR Hutchinson, and Rice and Rosengren fields LEFM linear elastic fracture mechanics SSY small-scale yielding TPB three point bend specimen Latin symbols:a half-crack length (CCT specimens) crack length (TPB specimens) E Young's modulus J J-integral Jc critical J-integral K stress intensity factor Q Q-value S span between centre line of two rollers applying load on a TPB specimen t specimen's thickness 7, T-stress