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a b s t r a c tThe impact toughness of two highly textured rolled plates of Ti-6Al-4V alloy with an α equiaxed and an α lamellar microstructures has been investigated.The results show a strong anisotropy of the fracture energy for both materials and underline that a coincidence of the prismatic planes with the shear bands at the notch tip is favorable for higher fracture energies. Moreover, it is pointed out, as it was already done by previous studies, that the α lamellar microstructure presents higher fracture energy than the α equiaxed one.Thanks to electron back scattering diffraction, and tensile tests, local microstructure heterogeneities, called macrozones, have been observed and characterized. Their size depends on microstructure element and is larger for α lamellar microstructure than for the α equiaxed. High strain is localized on the macrozones favorably oriented for prismatic slip with respect to the direction of impact and leads to a particular dimple free zone on the fracture surface.The contribution of these macrozones in the fracture behavior, and more precisely on the crack propagation rate was evaluated; thus the effects of the macroscopic texture and of the microstructure element on the impact toughness are discussed separately.

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The damage mechanisms under transverse creep of two unidirectionalmetal matrix composites are investigated. This paper is based on a two-scale approach, and on experimental and numerical studies. On the macroscopic scale, the global response of the composite subjected to aconstant transverse load is analyzed. On the microscopic scale, the influence of each component (matrix, fibre and interface) on the global behavior is investigated. In the experimental part of the study, creep tests have been performed at different temperatures under vacuum, and scanning electron microscope (SEM) observations have allowed the investigation of the damageevolution under different applied loads. In the numerical work, the creep tests were simulated on a representative unit cell using the finite element method and taking into account the various nonlinearities (matrix viscoplasticity coupled with interface damage). The experimental and numerical results show that the global behavior of the composite depends on the local interfacial behavior. Two domains are evidenced as a function of the applied stress, a critical stress being thus determined. Below the critical stress, the interfaces remain undamaged, leading to a low creep rate and a long duration test. Above the critical stress, the interfaces are totally debonded, thereby increasing the secondary creep rate and leading to a possible specimen failure.