Low-Velocity Spall Testing of Ti-6Al-4V Alloy and a New Spall Critterion Based on Meso-Scale

摘要

During the contract period the spall testing of Ti-6Al-4V has been completed. The series of tests (total 11 tests) at different impact velocities (from 290 m/s to 460 m/s) have been performed and the level of the normal stress sigma (sub F) for the incipient spall as a function of the incident pulse duration tau(Sub C) has been determined. Such analysis has yielded the preliminary data in the form of the critical tensile stress versus the pulse duration, sigma(sub F). The Scanning Electron Microscopy (SEM) observation of the spalled surfaces was performed showing microdimples. Optical microscopy observation of the specimen cross-sections demonstrated presence on the me so- scale a combination of microcracks and adiabatic shearing. Those observations are very helpful to identify the physical mechanism of fracture development. The relief of the material separation leads to a new failure criterion on the mesoscale 1,2. The quantitative statistical analysis of the pictures needs more time and is in progress. A new model of spalling based on two meso- mechanisms of material separation has recently been developed and verified for martensitic armor steel and hard aluminum alloy, 1,2, it confirms all findings by experiment. In order to gain more deep insight on the material behavior during spalling the initial microstructure of the Ti-6Al-4V alloy has been examined by microscopy observation, including chemical treatment of the surfaces. The literature survey on high strain rate behavior and spalling of Ti-6Al-4V alloy is included in this Report.