Initiation stress of delamination cracking in A2091 AI-Li alloy

The measurement of the velocities of ultrasonic waves has been used to detect the delamination cracking during tensile tests in an A2091 A1–Li alloy at both liquid helium and room temperatures. The measured tensile far–field stresses at the onset of the delamination cracking are 335 and 357 MPa, at cryogenic and room temperatures, respectively. The density of delamination cracks in the alloy is estimated from the reduction in the ultrasonic wave velocity and resultant decrease in modulus of elasticity. It is estimated that the interfacial bonding strengths normal to a grain boundary are 116 and 113 MPa, at cryogenic and room temperatures, respectively. Fracture mechanics analysis has been used to estimate the onset of delamination cracking in fracture toughness tests on the basis of the results of the tensile tests. The predicted levels of far field applied stresses are much lower than those for macroscopic crack initiation at both temperatures.