DEVELOPMENT OF A TIME-RESOLVED CATADIOPTRIC STEREO DIGITAL IMAGE CORRELATION TECHNIQUE FOR THE STUDY OF BLAST LOADING OF COMPOSITE MATERIAL STRUCTURES

Impingement of blast or shock waves on structures is characterized by a substantial transient aerodynamic load that develops over the short time associated with the shock reflection time scale. This mutual interaction between the shock wave and the structure can cause significant deformation of the structure and high strain rates within the material resulting in damage. While accelerometers, strain gages and other single point measurement probes and their corresponding techniques can provide valuable information of the local displacement and strain during blast loading, better understanding of the complex phenomena involved in these interactions require time dependent information acquired simultaneously from multi points on the structure. Digital Image Correlation is a full-field noncontact optical technique which can provide time dependent information of the displacement of the structure and the resultant high strain rates generated during the loading. The present setup consists of a single high-frame-rate camera which can accommodate two simultaneous stereo images of the deforming structure on its CMOS chip. Four different planar mirrors, appropriately positioned, provide the stereo views of the specimen captured on the chip. The present layout offers several advantages over traditional systems with two different cameras. First, it provides identical system parameters for the two views which minimizes their differences and thus facilitating robust stereo matching. Second, it reduces calibration time since only one camera is used and third its cost is substantially lower than the cost of a system with two cameras. The technique is being developed and tested in a large scale shock tube facility during loading by shock/blast wave of various impulses. The specimens used are flat plates made of high-alloy steel, aluminum or composite materials. In the present paper the development of the technique will be described and preliminary results of qualification tests will be presented and discussed.