The diffraction of elastic waves by an imperfect fusion bond

We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material.     

The energy dependence of 18O(π+, π−)18Ne(gs)

Eight angular distributions measured for ¹⁸(π⁺, π^?)¹⁸Ne(gs) across the Δ₃₃ resonance show the details of the energy dependence of the reaction. At higher energies, the maximum is at q ? 0.85 fm^?1, in agreement with simple sequential scattering models, but a lower energies it is at q ? 0.5 fm^?1, with the transition occuring over a narrow energy range.