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C. M. Sayers

Bio: C. M. Sayers is an academic researcher. The author has contributed to research in topics: Crystallite & Deep drawing. The author has an hindex of 1, co-authored 1 publications receiving 4 citations.

Papers
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Book ChapterDOI
01 Jan 1987
TL;DR: In this paper, the long wavelength limit of a polycrystalline aggregate is modelled as an elastic continuum with elastic constants determined by the elastic constants of the grains and the crystallite orientation distribution function (CODF).
Abstract: In a polycrystalline aggregate the elastic constants in the specimen reference frame vary from grain to grain due to the random orientation of the grains. Polycrystalline metals are therefore elastically inhomogeneous, and the elastic constant mismatch at the grain boundaries leads to scattering of the ultrasonic wave. In the long wavelength limit, however, the metal can be modelled as an elastic continuum with elastic constants determined by the elastic constants of the grains and the crystallite orientation distribution function (CODF). This function gives the probability of a crystallite having a given orientation with respect to the specimen frame, and gives a quantitative description of the texture, or crystallographic alignment, of the material. In a strongly textured metal the yield stress varies as a function of direction and this can lead to non-uniform flow in deep drawing for example. As a result there is a need for a non-destructive measurement of texture in process control, and there is considerable interest in the use of ultrasonics for this purpose. In section 2 it is shown how information on the CODF can be obtained from ultrasonic velocity measurements.

4 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a simple micromechanical model of a prestressed polycrystalline aggregate was developed, in which the texture-induced and stress-induced anisotropies of the aggregate were precisely defined.
Abstract: In this paper we develop a simple micromechanical model of a prestressed polycrystalline aggregate, in which the texture-induced and stress-induced anisotropies of the aggregate are precisely defined; here the word ‘texture’ always refers to the texture of the aggregate at the given prestressed configuration, not to that of a perhaps fictitious natural state of the aggregate. We use this model to derive, for a prestressed orthotropic aggregate of cubic crystallites, a birefringence formula which shows explicitly the effects of the orthotropic texture on the acoustoelastic coefficients. From this formula we observe that, generally speaking, we cannot separate the total birefringence into two distinct parts, one reflecting purely the influence of stress on the birefringence, and the other encompassing all the effects of texture. The same formula, on the other hand, provides for each material specific quantitative criteria under which the ‘separation of stress-induced and texture-induced birefringence’ would become meaningful in an approximate sense.

35 citations

Journal ArticleDOI
TL;DR: In this paper, the authors measured the birefringence and the difference between Poisson's ratios measured using a shear wave polarized along the length of a plate and another wave polarized on the width of the plate, linearly related to the degree of deformation and hardness.
Abstract: Poisson's ratio and birefringence, both measured by ultrasound, are used to follow the evolution of the anisotropy in ASTM A-36 steel plates cold-rolled between 5 and 50% deformation, and then subjected to recrystallization at 900 and 1000 oC. Times of flight of longitudinal and shear waves along the thickness of the plates were measured. As orthotropy increases, both birefringence and the difference between Poisson's ratios measured using a shear wave polarized along the length and another wave polarized along the width of the plate, are linearly related to the degree of deformation and cold-rolled hardness. In addition, the ultrasonic methods used clearly detected the complex changes in anisotropy produced by the austenization and recrystallization heat treatments. Thus, Birefringence or Poisson's ratio, measured by ultrasound, can be used to follow-up nondestructively changes in the anisotropy of rolled plates as a function of both, degree of deformation and recrystallization heat treatment.

4 citations