Three-dimensional Image Correlation System Research Articles

Three-dimensional shear angle determination with application to shear-frame test

The shear frame test is very often used in the context of plastics engineering to examine only the fiber construction for its deformability. Here, it is common to assume a homogeneous deformation, which apparently exists as a global deformation due to the shear frame. This results in the assumption of a constant overall shear angle. In this paper, we compare two analytical approaches to describe the deformation and the resulting strains in detail, particularly, the local shear angle calculation. As a second step, the extension of the shear angle computation based on curvilinear, three-dimensional surface deformations is applied to optical results of the experimental deformation behavior. For this purpose, a three-dimensional image correlation system is drawn on to determine the local, tangential shear angle even for folded fabrics. This requires an approach which is different to the classical digital image correlation method since the speckle varnish influences the deformation of the very compliant fiber bundles. In a third step, the same procedure is applied to the results of three-dimensional finite element computations since the programs do not provide the shear angle measure. The shear angle determination is discussed at various examples. As a side result of the investigations, the material parameters for orthotropic elasticity are determined using a representative volume element approach exploiting μ-CT data. Although the wrinkling prediction calculations depend on the pre-deformation, finite element discretization, and uncertainties of the specimens, calculation results might be used as an indicator to improve the specimen geometries.

Strain Measurement in Local Volume by Non-Contact Videoextensometric Technique on Ultra High Strength Steels

The paper presents the results of strain measurement using two methods: videoextensometry (ME46) and digital image correlation (DIC)-ARAMIS. ME46 - allows measuring and monitoring the major and minor strain on a planar surface of a loaded object [1]. Experimental equipment uses a CCD camera for monitoring the process. The software calculates the displacements of contrast dots and subsequently the strain components are obtained. Another method for non-contact measurements is DIC technique; the measurements are done using three-dimensional image correlation system. The system uses two digital high-speed cameras providing a synchronized stereo view of the specimen where speckles are arranged on the surface. The results show the complete strain field during the tests, including details of the strain field when necking develops prior to the failure [2]. Experimental results obtained on ultra high strength automotive steels DP 1000 and 1400M grades during static tensile test are presented in the paper. The outputs of both are deformation maps. Advantages and disadvantages of both methods are compared.

Full field strain measurement during a tensile split Hopkinson bar experiment

A method for full field measurement of strain (and strain rate) during a tensile split Hopkinson bar test is introduced. The measurements are done by using the ARAMIS three-dimensional image correlation system. The system uses two digital high-speed cameras that provide a synchronized stereo view of the specimen. Depending on the number of pixels used, the system is capable of recording frames at a rate of up to 250,000 per second. The results show the complete strain field during the tests, including details of the strain field when necking develops prior to the failure. Before necking, when the deformation is homogeneous, the strains from the ARAMIS system agree with the strain that is determined from the elastic waves that are recorded in the incident and transmitter bars.