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Ultrasonic characterisation of rolled aluminium and steel sheet correlated with electron backscatter diffraction measurements

By Stephen Essex


This thesis is based on the characterization of material properties of interest in rolled aluminium and steel sheet, both popular materials used across a wide-range of applications. The forming processes involved in producing rolled sheet metal depend on plastic deformation, inducing elastic anisotropy as a consequence. These changes result in a variation from the simple isotropic and cubic symmetry systems possessed by steel and aluminium prior to cold-working. The most significant changes include the introduction of crystallographic texture and the morphology of the crystallographic grains in size and shape to accommodate the plastic deformation.\ud It is desirable in industries that use rolled product for manufacturing components to quantify such changes. The literature has postulated links between plastic and elastic properties, and hence any quantification of the elasticity, crystallographic texture and grain morphology can aid in the prediction of future formability behaviour.\ud This thesis presents non-destructive, rapid ultrasonic measurements to characterize some of the changes that are evident in rolled aluminium and steel sheet. These ultrasonic results have then been correlated to crystallographic orientation measurements generated from using a microscopic technique called electron backscatter diffraction (EBSD). The level of agreement between the two contrasting methods has been analysed and is presented here.\ud The non-destructive ultrasonic measurements include quantifying crystallographic texture utilising theory linking the S0 Lamb wave velocity and the direction of propagation in a rolled sheet with respect to the rolling direction. This leads to the determination of texture coefficients known as orientation distribution coefficients (ODC). Through-thickness linearly polarized SH waves have then been used to analyse grain morphology using attenuation data, and elasticity measurements from velocity data.\ud EBSD datasets have been manipulated to produce predictions of the effective elastic stiffness constants, which in turn can be used to generate comparable S0 Lamb wave velocity predictions to be directly compared to the ultrasonic measurements. This process has required a novel method to generate such ultrasonic velocity predictions as a function of angle, together with predictions for the nine effective elastic stiffness constants inherent to rolled orthorhombic sheet. The facility to measure grain size and shape accurately from EBSD data has been utilized.\ud The thesis starts with a general introduction in non-destructive testing and microscopy, with focussed discussion on ultrasound, electromagnetic acoustic transducers (EMATs), EBSD and metallurgy in the subsequent chapters. Chapter 6 introduces the development of correlation methods between the ultrasound and EBSD results, with chapters 7 and 8 displaying the empirical ultrasound and EBSD data respectively. Chapter 9 compares the data from the two methods, with the final conclusions given in chapter 10

Topics: QC
OAI identifier: oai:wrap.warwick.ac.uk:3147

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  1. (1999). Ultrasonic waves in solid media, doi

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