Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305559
Title: Crack initiation under shock loading : validation of a new testing technique
Author: Hernandez-Gomez, Luis Hector
ISNI:       0000 0001 3554 7530
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1992
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Abstract:
The evaluation of the dynamic fracture properties with the current impact testing techniques is subject of some controversy, because the crack initiation conditions cannot be established with accuracy. Besides, some of them are limited to low loading velocities and the evaluations are made following a static approach. In consequence, a fundamental study is required with two aims, namely, a development of a new impact testing technique and the analysis of the extension of the fracture mechanics concepts to crack initiation under dynamic loading. These are the objectives of this research project. The impact testing technique proposed is based on the shock tube technique and is capable to test the specimens, which are central cracked circular plates, under static and dynamic conditions. The findings show that the specimens are loaded uniformly with blast waves, which have an initial ramp that increases steadily without oscillations. The magnitude of the load is controllable and reproducible and the fracture analysis should be based on a dynamic calibration. This technique has been applied to the evaluation of the dynamic fracture toughness of PMMA following an experimental-numerical procedure. The crack initiation load and the strain rate were measured experimentally and the fracture toughness was calculated numerically with standard solutions and with numerical calculations of the J-Integral with the finite element code ABAQUS. The problem of crack initiation under pressure load has not been completely solved. Consequently, the significance of the static and dynamic test results was established with the findings of additional experimental and numerical work, which showed that the modulus of elasticity and fracture stress increases with the strain rate, that there is plastic deformation at the crack tip of those specimens tested under static conditions and that the dynamic calculations with ABAQUS involves the interaction of the stress waves with the boundaries. Furthermore, it has to be noticed that the crack tip is under bending stresses. Thus, this test is not a standard plane strain material dynamic test. Finally, conclusions are drawn on the use of the this experimental-numerical technique and its further application.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.305559  DOI: Not available
Keywords: Material degradation & corrosion & fracture mechanics
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