Abstract:In this paper, the microstructure characteristics, fatigue properties and fracture mechanism of 95 mm Al-Cu-Li alloy hot-rolled thick plates in different orientations were studied by fatigue testing machine, scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the mechanical properties and fatigue properties of Al-Cu-Li alloy hot-rolled thick plate were both anisotropic. The mechanical properties of the L direction are better than those of the ST direction, but the fatigue properties are worse than those of the ST-direction. The fatigue crack sources of Al-Cu-Li alloy thick plates mainly appear on the surface of the sample, near the surface of the inclusions and grain boundaries. During the crack propagation process, the crack propagation path in the LT direction was more tortuous than that in the L direction, and the ST direction had a typical cleavage characteristic. The morphology of the instantaneous fracture zone was similar to that of the tensile fracture. The more grain boundaries, the greater the crack propagation resistance, and the undissolved second phase in the LT direction and ST direction can effectively hinder the crack propagation, resulting in better fatigue performance than that in the L direction.

Abstract:The fatigue properties of RPC (Reactive Powder Concrete) with different steel fiber ratios of 0%, 1.5% and 3% in volume were investigated with the uniaxial compressive fatigue test.The results showed that the splitting failure mode appeared for pure RPC specimens without steel fiber, but the shear failure mode occurred for those specimens with steel fiber of 1.5% or 3% in volume.The fatigue life and strength increased with the increase of steel fiber ratio; the macroscopic damage, ε-n/Nf curves and the evolution of the fatigue deformation modulus of tested RPC experienced three stages.With the increase of steel fiber ratio, the first and third stages of ε-n/Nf curves lengthened，and the fatigue deformation modulus significantly increased with the increase of the steel fiber ratio corresponding to the same n/Nf.It is suggested that the ratio of fatigue deformation modulus to the initial elastic modulus should be 0.7 and 0.75 for the RPC with a steel fiber ratio of 1.5% and 3%, respectively.