3. Investigating Dynamic Fracture Parameters for Al7075-T651 Using Modified Hopkinson Pressure Bar (MHPB)

Dynamic fracture toughness of engineering materials is an important parameter in damage evaluation and safety assessment of the structures that are often subjected to impact loading. In the current work, dynamic initiation fracture toughness has been experimentally evaluated at different loading rates for a aluminium alloy Al7075-T651. It was observed that dynamic fracture toughness increases with the loading rates. The experimental set up used in this study is a Modified Hopkinson Pressure Bar consisting of the incident bar, a projectile, and a adjustable three-point bend fixture. Specimens used in the experiments are machined according to ASTM-E399 standard. Two different sets of experiments were conducted at projectile velocities of 12.7 m/s and 13.9 m/s with corresponding launch pressure of 1 bar and 1.5 bar respectively. Stress intensity factor was evaluated using a established load point displacement technique, while the time of initiation of fracture (t_f) was obtained using a stereo-configuration of high speed cameras in conjunction with 3D Digital Image Correlation. The dynamic initiation fracture toughness was evaluated and was found to be 18.48 MPa\( \sqrt{m} \) and 21.68 MPa\( \sqrt{m} \) for the given boundary conditions respectively.