N. Petrinic

Measurements and micro-mechanical modelling of the response of sintered titanium foams.

Titanium foams of relative density in the range 0.35-0.50 are tested in quasi-static compression, tension and shear. The response is ductile in compression but brittle, and weaker, in shear and tension. Virtual foam microstructures are generated by an algorithm based on Voronoi tessellation of three-dimensional space, capable of reproducing the measured size distribution of the pores in the foam. Finite Element (FE) simulations are conducted to explore the mechanical response of the material, by analysing the elasto-plastic response of a statistical volume element (SVE). The simulations correctly predict the ductile compressive response and its dependence on relative density.

An Experimental Method for Dynamic Delamination Analysis of Composite Materials by Impact Bending

An improved experimental method for characterizing dynamic delamination growth in composite structures has been developed and verified using high speed photography and explicit finite element simulation. The method is based on a three-point bending device. End notch flexure carbon fiber composite beam specimens were subjected to both quasi-static and impact rates of Mode II loading. The experimental results showed no significant strain rate dependency of the delamination fracture toughness. This important result complements the scarce and conflicting data available in the literature, and serves as a reference for calibration of numerical modeling strategies.

A local optimisation method for obtaining material model parameters

A local optimisation method for obtaining material parameters in finite element simulations has been developed. The method is based on the minimisation of an error function which reflects the accuracy of a numerical prediction with respect to the results of simple specimen tests. The experimental data were obtained from high strain rate tensile tests on the alloy 90 per cent titanium – 6 per cent aluminium – 4 per cent vanadium (Ti6Al4V) using the tensile split‐Hopkinson pressure bar. The behaviour of the tensile specimen was monitored during the test using high‐speed photography and transient recorders. Finite element simulations were performed using ABAQUS/Explicit employing the Zerilli‐Armstrong material model for bcc metals).

Characterising the Effects of Strain Rate, Crystallographic Texture and Direction of Loading on the Mechanical Behaviour of Ti-6Al-4V

Abstract A cross-rolled plate of the industrially important titanium alloy, Ti-6Al-4V, has been microstructurally and mechanically characterised using a range of different experimental techniques. The microstructure of the material has been studied using backscatter electron (BSE) microscopy and electron backscatter diffraction (EBSD), with the crystallographic orientation data from the EBSD used to reconstruct the orientation distribution function of the dominant α phase. The mechanical behaviour of the material has been investigated at quasi-static and high strain rates in the three orthogonal material orientations in both tension and compression. A novel in situ optical measurement technique has been used to measure the geometry of the specimens during both quasi-static and high strain rate mechanical testing, improving the accuracy of the mechanical testing results and providing unprecedented information about the evolving geometries of the specimens. The macroscopic stress–strain response and the evolution of specimen cross-sectional profiles have been qualitatively linked to the macroscopic crystallographic texture in the plate.