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Title: The response of CVD diamond and other brittle materials to multiple liquid impacts
Author: Coad, E. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1997
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The development of the multiple liquid impact jet apparatus (MIJA) for the laboratory simulation of rain erosion has allowed accurate and reproducible examination of many infra-red (IR) materials. Such materials are used as "window" materials allowing (IR) optics but many have poor rain erosion resistance. The liquid impact response of this class of brittle materials has been studied and the growth of damage successfully modelled. The development of chemical vapour deposited (CVD) diamond technology has offered the possibility of both fully coated and free-standing domes. This offers a very attractive alternative to conventionally used materials due to the exceptional material properties and erosion resistance of diamond. The first samples of free-standing CVD diamond studied have shown a number of significant damage mechanisms relating to the dimensions of the sample and the difficulty of acoustically matching the rear of the sample with the mounting. These modes of failure are examined and shown to rely upon shock wave interaction resulting from the high wave velocity (≈18 mm μs-1) and the low attenuation of diamond. A comparison of the rain erosion resistance between CVD diamond, natural and high temperature high pressure (HTHP) diamond is also made. The effects of high moduli coatings to enhance the erosion resistance of conventional materials have been studied for a range of substrate materials and various diamond and non-diamond coatings. The observed damage mechanisms and optimum coating thicknesses are discussed. Surface preparation and surface toughening, by either thermal or chemical processes, can have a large effect on both the nucleation of damage and its growth. All of these factors have been considered in detail and optimum procedures identified. Finally, a components response can be affected by both its temperature and its stress state. Equipment for producing chosen temperatures and for adding controlled stress states into the sample have been developed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available