Cross-section reconstruction during uniaxial loading

Abstract

The inelastic response of materials to applied uniaxial loading is typically measured using tensile or compressive specimens of an initially circular cross-section. Under deformation, this cross-section may become elliptical due to anisotropic material behaviour. An optical technique for measuring the elliptical deformation of anisotropic, homogeneous cylindrical specimens undergoing uniaxial deformation is presented. It enables the quantification of anisotropic deformation in situ and provides data for material characterization. Three or more silhouette views of a specimen are obtained using multiple cameras or mirrored views. The positions of the edges are computed using a sub-pixel edge detection method, and 3D tangent rays from the camera through these positions are calculated. These bounding tangents are used as the basis for an elliptical fit by least squares at cross-sections along the length of the specimen. Stochastic error estimates are performed by simulation of the experiment. Error estimates, for the experimental set-up used, are also calculated by reconstructing elliptical prisms of precisely measured dimensions. Example reconstructions from specimens of rolled titanium deformed plastically in tension at quasi-static (7 × 10−4 s−1) and high strain rates (3 × 103 s−1) are presented.

Characterising the Effects of Strain Rate, Crystallographic Texture and Direction of Loading on the Mechanical Behaviour of Ti-6Al-4V

“…Recent papers have described and validated the reconstruction process in detail [20,21], and also shown it's utility when applied to Taylor impact experiments on commercially pure zirconium [22] and Ti-6Al-4V [19].…”

“…The setup used in these experiments was identical to that described in [20], the only difference being that the illumination set-up was modified such that all pictures of the Fig. 8 Tensile specimen design, used for both quasi-static and high strain rate testing Fig.…”

Increasing data from high rate characterization experiments using optical reconstruction

“…In particular, by imaging the specimen from different angles using three cameras, six tangent lines are produced, which is one more than required, for each cross-section. The ellipse parameters can be calculated using a least-squares approach [6].…”

A method for the in situ measurement of evolving elliptical cross-sections in initially cylindrical Taylor impact specimens

“…2 Experimental set-up Fig. 3 Cross-sectional view of the experimental set-up Cross-sections in initially cylindrical Taylor impact specimens from the specimen, as validated by Arthington et al [18]; their paper contains a full description of the edge detection and geometry reconstruction techniques used in the current study.…”