Department of Mechanical and Aerospace Engineering

D.K. Wright Jr. Dynamic Inelasticity Laboratory

D.K. Wright Jr. Laboratory, which is the primary experimental facility in the area of mechanics of materials in the Department of Mechanical and Aerospace Engineering at CWRU. During his tenure at CWRU, he has upgraded this facility into a state-of-the-art laboratory with a vision that it will serve a major interdisciplinary instructional and research need on campus.

The laboratory houses a newly built 82.5 mm bore single stage gas gun capable of accelerating 0.75 Kg projectiles to speeds of 1 Km/s. The gas gun has a broached key-way along the entire length of the 18 feet gun barrel for conducting normal plate impact and pressure-shear plate impact experiments. High-speed and wide bandwidth Hewlett Packard and Tektronix digitizing oscilloscopes are available for data acquisition. Facilities have also been established for preparing specimens for plate impact experiments, including thin, flat specimens (down to thickness of 50 m m), and flatness within 1-2 wavelengths of light over the diameter of the specimens. Equipment for polishing and metallographic work is also available.

Besides the gas gun facility, the D. K. Wright Jr. Laboratory has been equipped with compression-tension Hopkinson bar and torsional Kolsky bar apparatus. All necessary strain gage conditioners and amplifiers required for data recording and subsequent processing are available. Recently we have also added the capability of measuring real time temperature rise during dynamic deformation using High speed HgCdTe infra-red detectors. The system has a linear array of five mercury cadmium telleride cells mounted on a Dewar cooled with liquid nitrogen. Also, an Ealing microscope reflective objective is available for the collection of the infra-red radiation from the specimen surface and focusing it on to the detector array.

The laboratory also houses a fully computer controlled servo-hydraulic Schenck Pegasus testing machine equipped with servo-hydraulic grips and various load cells for low strain-rate mechanical testing of materials. In conjunction with the Schenck Pegasus servo-hydraulic machine, CCD camera and appropriate software and hardware is available for image acquisition and analyzing experimental data from optical interferometers such as high sensitivity Moiré microscope, photo-elasticity, Michelson interferometry, etc. Amongst the various interferometers the unique piece of apparatus in our laboratory is the Moiré Microscope. The moiré microscope is based on a novel use of a transmission diffraction grating for generating the moiré fringes, and allows the full field mapping of deformation fields on a micron level length scales. An in-house developed image analysis program allows us to obtain the experimental fringe data to provide quantitative information of the Eulerian deformation fields, including local material rotations, stretches etc. The algorithms used to calculate these quantities are based on large deformation analysis enabling accurate evaluation of finite elastic-plastic deformation fields.

Along with the laboratory development, efforts have also been devoted towards the development of computational capabilities that are vital for the interpretation of the experimental results. Efficient algorithms for transient, large deformation elastic-plastic response of solids including temperature effects, have been implemented into computer codes in an appropriate finite-element setting. Appropriate subroutines for pre- processing and post processing of computational data have also been developed. A unique feature of the computational algorithms is that they allow the implementation of constitutive equations of a variety of engineering materials over a wide range of strain rates. Material failure involving both the ductile failure as well as brittle failure can be implemented.