Fracture of Structural Materials under Dynamic Loading
Abstract
Classical concepts of Griffith-Irwin fracture mechanics were extended to include time effects and hence to apply to crack instability under dynamic loads. Theoretical considerations of the stress intensity histories experienced by cracks subjected to short pulse loads suggested that instability requires the crack tip stress intensity to exceed the dynamic toughness for a minimum time. This postulate was checked by experiments. Impact techniques were used to produce well-defined stress pulses in specimens of an epoxy, 4340 steel, 1018 steel, and 6061-T6 aluminum containing cracks of several lengths to observe crack instability behavior. The experimental results were not well described by static fracture mechanics, but were in accord with the minimum time postulates deduced from stress intensity histories. The understanding gained from the research program promises to be useful in assessing the safety of structures under dynamic loads, in characterizing the dynamic fracture resistance of materials, and in designing equipment and procedures for measuring dynamic fracture toughness. The relationship between dynamic initiation toughness and dynamic propagation toughness was addressed. The temperature histories in material near a rapidly propagating crack in a steel plate were measured and used to compute the heat of fracture and the dynamic propagation toughness. Simultaneous measurements of the dynamic stress intensity were made using the shadow optical method of caustics and high speed photography.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 25, 1981
- Accession Number
- ADA098791
Entities
People
- Donald A. Shockey
Organizations
- SRI International