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Title: A new technique for tensile testing of high performance engineering material
Author: Zhou, Junyi
ISNI:       0000 0005 0287 2491
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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The thesis describes a new test technique and an associated bespoke apparatus to conduct tensile testing at high strain rates and in environmentally-controlled conditions. The technique is suitable to measure the dynamic tensile response of brittle materials difficult to grip (brittle solids and materials in the form of fibre yarns or tapes) and of ring-shaped specimens. The apparatus is compact in size and shape, and this facilitates testing in a conditioned atmosphere. The method also offers the advantage that identical specimens are used in all tests (across wide ranges of strain rate and temperature). The technique allows the measurement of the tensile response of monolithic poly(methyl methacrylate) (PMMA) and unidirectional composites based on Dyneema® tape, Dyneema® SK75 yarn and Kevlar® 49 yarn. The measurements are conducted in a wide range of strain rate (0.0001-323/s ) and yield valid dynamic stress versus strain histories, including part of the elastic material response. Valid stress-strain curves for Dyneema® tape and Dyneema® SK75 yarn are obtained for the first time. We then extend this technique to conduct experiments at low strain rates and at temperatures in the range -40 to 70°C. The sensitivities of the tensile properties to strain rate and temperature are effectively correlated using the time-temperature equivalence principle. A numerical investigation is conducted to assess the suitability of this technique for both Hopkinson bar tests and projectile impact experiments, allowing tests at ultra-high strain rates (> 1000/s).
Supervisor: Tagarielli, Vito Sponsor: Defence Science and Technology Laboratory
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral