Study On Dynamic Tensile Fracture Behaviors Of Selected High Strength、Toughness Aluminum Alloy

Dynamic tensile fracture behaviors of the extruded rods of2024-T4and7075-T6aluminumalloys were experimentally investigated under varying loading conditions. The main contents areasfollows:1) The initial yield stress and fracture strain of7075-T6alloy obtained in spilt Hopkinsontension bar (SHTB) tests is higher than that of2024-T4alloy. But the initiation fracture toughnessand spall strength of2024-T4alloy are higher than those of7075-T6alloy in three-point bending(TPB) and plate impact experiments, which indicates that2024-T4alloy has better crack initiationtoleranceandstrongerspallfailureresistance.2) Based on metallurgical investigations by using optical and scanning electron microscopes,it is revealed that the microstructure has a profound effect on the dynamic tensile fracturemechanism of each aluminum alloy.2024-T4alloy is relatively brittle due to voids or cracksnucleated at many coherent precipitate phases in the grain interiors, and the fracture mode ispredominantly transgranular.7075-T6alloy exhibits relatively ductile fracture because voids orcracks growth is partly intergranular along the grain boundaries and partly transgranular by voidformation aroundcoarseintermetallicparticles.3) The effects of temperature on the dynamic yield and spall behaviors were studied for twoaluminum alloys,2024-T4and7075-T6by a series of pre-heating plate-impact spall experiments.Hugoniot elastic limit (HEL) strength and spall strength are calculated by the free surface velocityprofiles. Experimental results show that whether normalized HEL strength or normalized spallstrength linearly decline for both2024-T4alloy and7075-T6alloy with the same slope over thetested temperature range. Comparison between aluminum alloys and pure aluminums indicatedthat the apparent difference observed in the correlation between HEL strength and spall strengtharelinkedwith thedifferent dominantmechanism ofdamageevolution.4) A cohesive element model has been developed to predict the rear free surface velocityprofile in a flyer plate impact tests on aluminum alloy under the different temperatures. Thesimulation’s material parameters is almost the same with experimental material parameters,and wefound the main characteristics of the free surface velocity profile history is affected by the initial dynamic yield strength, kinematic hardening flow stress, cohesive strength, cohesive viscosityparameterandthreshold failuredisplacement.