George A. Hartman

Dual fatigue failure modes in Ti–6Al–2Sn–4Zr–6Mo and consequences on probabilistic life prediction

Abstract The variability in fatigue life of the Ti–6Al–2Sn–4Zr–6Mo (Ti-6-2-4-6) alloy was investigated. Cumulative life distribution plots were found to be composed of two failure mechanisms. The data could be closely represented by a cumulative distribution function (CDF) resulting from the superposition of the CDFs of the individual mechanisms. An approach for life prediction based on the data due to the worst-case mechanism is suggested.

Techniques for Mechanical and Thermal Testing of Ti 3 Al/SCS-6 Metal Matrix Composites

An integrated set of experimental techniques for mechanical and thermal testing of the Ti3Al/SCS-6 metal matrix composite is presented. Areas of discussion include gripping, specimen design, specimen heating, temperature measurement, and displacement measurement. The grip system was originally developed for use with ceramic composite materials and works well with the relatively brittle titanium-aluminide matrix composite used in this study. A modified version of an existing quartz lamp heating system allows temperature control at multiple points on the specimen. Results from baseline tension tests at various temperatures and post-thermal cycling tension tests are presented.

A Sampling of Mechanical Test Automation Methodologies Used in a Basic Research Laboratory

Basic research laboratories typically perform a variety of material tests and obtain the associated data to model material behavior phenomena and develop life prediction methodologies. In this research environment, a mechanical test automation system must meet challenges that are not always present in an industrial testing setting. For example, real-time crack closure load analyses, at the present time, are not widely performed in industrial crack propagation testing. In the research environment, however, on-line crack closure studies are used to make decisions in real-time about changes in test conditions. A previous paper described the overall system strategy and hardware and one of the crack propagation software modules from the fourth generation of the material analysis and testing environment (MATE) automation system. The present paper discusses selected methodologies that the current (fifth) generation of the MATE system uses to meet the challenges posed while automating research style mechanical tests. The methodologies addressed in this paper include waveform generation and synchronization for cyclic, monotonic, and thermomechanical (TMF) testing as well as specimen damage computation for self-similar cracked geometries.