A Precision Experiment for the Deformation and Fracture of Blast Loaded Plates

Cloete, Trevor John

A Precision Experiment for the Deformation and Fracture of Blast Loaded Plates

Doctoral Thesis

2022

Abstract

The purpose of this thesis is to present a novel laboratory scale precision test [1] apparatus, developed specifically to study of the deformation and fracture of blast loaded plates. A review of published laboratory scale blast testing showed that classical ballistic pendulum techniques satisfy several precision testing criteria. However, specific aspects required improvement. Therefore, an instrumented ballistic pendulum has been developed, incorporating a central support, in the form of a Hopkinson bar, for use with a novel peripherally clamped centrally supported (PCCS) plate specimen, which allows the reaction force history at the inner boundary to be captured. Hence, in addition to the traditional impulse vs deflection data, this approach allows details such as the total deformation duration or the exact timing and magnitude of fracture processes to be captured. Furthermore, when used with a peripherally clamped annular (PCA) plate specimen, this approach allows the blast load pressure history to be captured. A literature review found several classical closed form solutions for the large deflection of impulsively loaded peripherally clamped solid (PCS) circular plates. However, several crucial aspects of the solutions were contradictory and/or incomplete. To address this a generalized energy method for modelling impulsively loaded axisymmetric plates was developed which subsumes previous solutions and facilitated novel analytical solutions that provide a theoretical framework for interpreting the experimental data. Extensive experimental results reported in this thesis provide a rich set of novel data for code validation. While the PCCS and PCA plate configurations require a refined definition of the observed failure modes, the transitions between the modes and the fracture behaviour are studied in great detail. The data is analysed using dimensionless impulse expressions obtained from the analytical solutions in this thesis. In addition to accurate deflection predictions, these solutions also provide improved deflection duration predictions using a novel two phase solutions that can also accommodate finite load duration. It is concluded that the instrumented ballistic pendulum, incorporating a central support in the form of a Hopkinson bar, in conjunction with the novel PCCS and PCA plate configurations and analytical solutions, satisfies all the requirement of a precision test.

Keywords

Mechanical Engineering

Reference:

Collections

PhD / Doctoral

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