Critical Strength Parameters Research Articles

Principles of certification of metals for susceptibility to brittleness by the criterion of critical strength

Problem definition. Existing evaluation system of liability to brittle fracture is based on specifying the critical temperature Tc of ductile/brittle transition for specimens with stress concentrator (SC) and uses relative values of impact toughness (KCV, KCU) and widening (ψк). Thus the Tc becomes relative and it is not possible to measure brittleness or embrittlement degree for specimens with SC. Paper purpose. Neutralize the system faults of evaluation system of liability to brittle fracture of constructional alloys with SC. The concept is to change the KCV (KCU) or ψк parameters by critical strength parameter (ϭ0,2с at Tc). Conclusions. Fracture of the specimen with SC (ϭNF) on YTS (ϭ0,2с) at Tc (or room TR) as embrittlement criterion is proposed instead of relative values of (KCV, KCU) and (ψк). The ϭNF / ϭ0,2 = BrNF ratio is a degree of reliability for specimen with SC (BrNF > 1) or embrittlement measure (BrNF < 1). The BrNF value is a quantitative measure of the fracture resistivity of the specimen with SC or crack. Correlation ratio between Br and BrNF for each type of SC has been found. It allows to use the calculation of embrittlement liability based on metal strength for test of metals without full scale tests of metal specimens with SC. Keywords: embrittlement; fracture degree; fracture resistivity; critical temperature; critical strength; strengthreliability of the specimen with SC

Anisotropic Behaviour of Knitted Glass Fibre/Epoxy Composites under Compressive and Shear Loading

Te authors have investigated the anisotropic properties of plain weft knitted glass fibre fabric reinforced epoxy composites oriented at different off-axial angles and subjected to compressive and shear loads. The compression test results in the off-axial angles of 0°, 30°, 45°, 60° and 90° indicated that the ultimate compressive strength and compressive modulus were greatest at 0° but decreased at other off-axial angles. The compressive strength was higher than the tensile strength for the knitted fabric composite at any offaxial angle. On the other hand, the shear test results for the same off-axial angles showed that the ultimate shear strength and shear modulus were greatest at the off-axial angle of 60°. A simple analytical model was applied to calculate the compressive strength at any off-axial angle, by using three critical strength parameters, i.e. the compressive strengths of 0° and 90° and the shear strength of 0°. The theoretical strength data agree favourably with our experiments.

Coupled-field description of zero-average dispersion management.

Using a coupled-field formalism and a standard perturbation analysis, we analyze a dispersion-managed system under zero-average dispersion conditions. A nonlinear integral equation in the spectral domain allows the determination of the critical strength parameter of a two-step dispersion map. Higher-order correction terms confirm the difference observed in the pulse shapes in each fiber and comparisons with fully numerical results reveal a good agreement. The existence of an antisymmetric dispersion-managed soliton is also confirmed.