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Title: Dynamic fracture and fragmentation : studies in Ti-6Al-4V
Author: Jones, David
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2014
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This study concentrates on the development of experimental techniques that are of benefit to research into high strain rate fracture and fragmentation. Two main areas are pursued, namely the effect of the stress state in the sample and the initial temperature of the sample on the resulting fracture mechanism and fragmentation behaviour when under tensile loading at strain rates of 10^4 s^-1. Both areas use expanding rings and cylinders to achieve this. Experiments are designed and fielded on explosively loaded Ti-6Al-4V rings where the aspect ratio (sample wall thickness to height) is adjusted to create stress states ranging from uniaxial stress to plane strain with velocimetry and fragment recovery used to measure the expansion and failure processes. A transition to necking before failure under uniaxial stress was observed, as opposed to ductile tearing under shear loading in plane strain conditions. Intermediate geometries were found to undergo massive internal damage not seen in the other experiments, leading to premature failure and smaller fragments. Temperature dependence was investigated using a new gas gun driven expanding cylinder technique with Ti-6Al-4V cylinders 150 mm long, 50 mm inner diameter and 4 mm wall thick- ness reaching temperatures between 150 K and 800 K before expansion. The loading mechanism was found to be highly repeatable and independent of sample temperature, providing a robust platform for generating high strain rate tensile and failure test data at temperatures unob- tainable by other means. A full suite of velocimetry, high speed imaging, fragment recovery and microscopy techniques were used to fully characterise the material during and after defor- mation. At elevated temperatures adiabatic shear banding was found to be an active failure mechanism. The fragmentation toughness parameter Kf was found to be 101 ± 13 MPa m^1/2 under these conditions.
Supervisor: Eakins, Daniel; Proud, William Sponsor: Atomic Weapons Establishment
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available