Chapter 30 Dynamic Triaxial Compression Experiments on Cor-Tuf Specimens Alex B. Mondal, Wayne Chen, Brad Martin, and William Heard Abstract A set of dynamic triaxial compression experiments at 50, 100, and 200 MPa confinement have been conducted with a modified Kolsky bar on cylindrical ultra-high strength concrete Cor-Tuf specimens of diameter 19 mm and length of 12.7 mm. The modified Kolsky bar utilized is capable of performing a triaxial compression test with a dynamic loading for a confining pressure of up to 400 MPa on specimens with 19.05 mm diameters. The experiment is composed of a hydrostatic phase which occurs at a quasi-static strain rate followed by a dynamic shear phase which occurs at a high strain rate. A set of 28 experiments were conducted at strain rates of 100 and 200 s 1. The experiments show that the fracture strength of the material increases under increasing pressure. The specimens showed higher strength in the dynamic confined experiments than both the quasi-static TXC experiments and the unconfined-uniaxial dynamic tests. The strength increase was in part caused by specimen size difference. Although the trend towards brittle ductile transition is observed the specimens were not loaded in a high enough confinement for the phase change to occur. Keywords Dynamic confined • Modified Kolsky bar • Split-Hopkinson pressure bar • Triaxial compression • Cor-Tuf 30.1 Introduction The dynamic response of materials can be drastically different than its response under quasi-static and intermediate strain rates. Modeling events like: earthquakes, explosions, drilling, and structural impact require an understanding of material response at high rates of loading [1]. Moreover, for events like earthquakes and explosions, the loading conditions are not uni-axial but multi-axial [2]. The dynamic triaxial compression experiment is a combination of two experiments: Kolsky bar experiments and triaxial compression tests. Conventional Kolsky bar tests, also known as split-Hopkinson bar (SHPB) tests, are experiments used to determine the dynamic properties of materials under uni-axial load. Conventional triaxial compression (TXC) tests on the other hand are quasi-static tests used to test pressure sensitive materials under a multi-axial stress state. Frew et al. [2], Lindholm et al. [3], Forquin et al. [4], Gary et al.[5], and Nemat-Nasser et al.[6] developed modified split Hopkinson bar techniques to allow for confinement following the first apparatus developed by Christensen et al. [7]. Christensen et al. [7] in 1972 were one of the first experimenters to modify a split Hopkinson pressure bar with confining pressure vessel capable of pneumatic pressures up to 206 MPa to test 19.05 mm diameter sand stone specimens. NematNasser et al. developed a 19 mm diameter Hopkinson bar that was capable of confining a specimen to 7 MPa with pneumatic pressure. Lindholm et al. [3] tested Dresser Basalt specimens under triaxial stress states from 0 to 690 MPa with dynamic loading along with formulating a fracture criterion. A.B. Mondal (*) •W. Chen Purdue University, West Lafayette, IN 47907, USA e-mail: amondal@purdue.edu B.Martin Air Force Research Laboratory, Eglin AFB, FL, USA W. Heard Engineer Research and Development Center, Vicksburg, MS, USA B. Song et al. (eds.), Dynamic Behavior of Materials, Volume 1: Proceedings of the 2013 Annual Conference on Experimental and Applied Mechanics, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-00771-7_30, #The Society for Experimental Mechanics, Inc. 2014 245
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