The split Hopkinson bar bulge setup: a novel dynamic biaxial test method

In sheet metal forming, very often, large plastic deformations are imposed to a thin plate. An accurate description of the material’s elastoplastic response is therefore of paramount importance to perform finite element (FE) simulations of an actual forming operation. Reliable stressstrain data till significantly larger strains compared to tensile tests can be identified by means of bulge test. In this work, a dynamic hydraulic bulge test is proposed. The novel split Hopkinson bar bulge setup, combines features of classical split Hopkinson pressure bar (SHPB) and hydraulic bulge tests. The special configuration of the Hopkinson bars leaves the sample surface fully accessible. As such, high-speed optical measurements can be performed on the sample surface allowing the application of, for instance, digital image correlation (DIC) for full-field displacement strain mapping. The potential of the facility is explored by performing experiments on 0.8mm thick Al2024-T3 sheet.

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Compression, Tension and Shear Testing of Fibrous Composite with the Split Hopkinson Bar Technique

EPJ Web of Conferences ◽

10.1051/epjconf/201818302006 ◽

2018 ◽

Vol 183 ◽

pp. 02006 ◽

Cited By ~ 1

Author(s):

Amos Gilat ◽

Jeremy D. Seidt

Keyword(s):

Strain Rate ◽

High Speed ◽

Fibrous Composite ◽

Hopkinson Bar ◽

Image Correlation ◽

Compression Tests ◽

Strain Rate Effects ◽

Full Field ◽

Split Hopkinson Bar ◽

Split Hopkinson

The Split Hopkinson Bar (SHB) technique is used for high strain rate testing of T800/F3900 composite in compression, tension and shear. Digital Image Correlation (DIC) is used for measuring the full-field deformation on the surface of the specimen by using Shimadzu HPV-X2 high-speed video camera. Compression tests have been done on specimens machined from a unidirectional laminate in the 0°and 90° directions. Tensile tests were done in the 90° direction. Shear tests were done by using a notched specimen in a compression SHB apparatus. To study the effect of strain rate, quasi-static testing was also done using DIC and specimens with the same geometry as in the SHB tests. The results show that the DIC technique provides accurate strain measurements even at strains that are smaller than 1%. No strain rate effect is observed in compression in the 0° direction and significant strain rate effects are observed in compression and tension in the 90° direction, and in shear.

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Full Field Strain Measurement in Split Hopkinson Bar Experiments

Volume 1: Advanced Energy Systems; Advanced and Digital Manufacturing; Advanced Materials; Aerospace ◽

10.1115/esda2008-59198 ◽

2008 ◽

Author(s):

Amos Gilat ◽

Tim Schmidt ◽

John Tyson ◽

Andrew Walker

Keyword(s):

High Speed ◽

Three Dimensional ◽

Hopkinson Bar ◽

Image Correlation ◽

Full Field ◽

Split Hopkinson Bar ◽

Strain And Strain Rate ◽

Full Field Measurement ◽

Split Hopkinson ◽

Correlation System

A method for full field measurement of strain (and strain rate) in split Hopkinson bar experiments (compression, tensile, and shear) 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 or recording frames at a rate of up to about 110,000 per second. Before conducting a test, a random dot pattern is applied to the surface of the specimen. The image correlation algorithm uses the dot pattern to define a field of overlapping virtual gage boxes. The 3-D coordinates of the center of each gage box is determined at each frame, interpolated to better than 1/100 of a pixel. The coordinates are then used for calculating the deformations, strains, and strain rates throughout the surface of the specimen.

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High Strain Rate Torsion and Bauschinger Tests on Ti6Al4V

Materials Science Forum ◽

10.4028/www.scientific.net/msf.706-709.774 ◽

2012 ◽

Vol 706-709 ◽

pp. 774-779 ◽

Cited By ~ 3

Author(s):

Jan Peirs ◽

Patricia Verleysen ◽

Kim Verbeken ◽

Frederik Coghe ◽

Joris Degrieck

Keyword(s):

High Strain Rate ◽

Strain Rate ◽

High Strain ◽

Kinematic Hardening ◽

Hopkinson Bar ◽

Image Correlation ◽

Material Behaviour ◽

Split Hopkinson Bar ◽

Strain And Strain Rate ◽

Split Hopkinson

An accurate isotropic and kinematic hardening model and description of the strain rate dependent material behaviour is necessary for simulation of fast forming processes. Consequently, the material model parameter identification requires experiments where large strains, high strain rates and strain path changes can be attained. Usually, quasi-static tension-compression Bauschinger tests are used to assess the materials kinematic hardening. Hereby it’s important to have the same specimen geometry and boundary conditions in the forward and reverse loading step which is not easily achieved in high strain rate testing techniques. In this work, high strain rate split Hopkinson bar torsion experiments on Ti6Al4V are carried out to study the constitutive material behaviour at large plastic strain and strain rate. In torsion experiments, due to the absence of cross sectional area reduction, higher strains than in tensile tests can be obtained. In addition, a modified torsional split Hopkinson bar setup is developed to perform dynamic Bauschinger tests. A shear reversed-shear load is applied instead of the classical tension-compression load cycle. The test results are analysed to find out if the technique can be used for characterisation of the kinematic material behaviour. Digital image correlation and finite element simulations are used to improve the interpretation of the experimental results.

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