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Measuring the stress-bridging law of a heterogeneous material

Description: In this investigation, fracture experiments on a high explosive material (PBX 9501) were conducted using the digital image correlation technique. From the experimental measurement, we are able to determine quantitatively the stress-bridging law (or decohesion law), which characterizes the relationship between the bridging stress and the opening displacement cross the bridging zone. The plastic bonded HMX (PBX) high explosives are composed of the energetic crystal (HMX) and a polymeric binder. Previous experimental observations showed that the fracture process in the sugar mock, a simulant of the PBX 9501 high explosive, is very different from that in brittle solids, even though the high explosive material PBX 9501 is quite brittle under tension. A close examination of the fracture surface revealed that before crack initiation and propagation, a very large damage region is developed ahead of the crack tip. Since such a damage region is very narrow, it can be modeled as a stress bridging zone. Due to the presence of the sizable bridging zone, conventional fracture mechanics is no longer applicable. Stress bridging has to be considered explicitly in order to understand of fracture processes in the PBX 9501 high explosive and the sugar mock. The model, which explicitly incorporates stress-bridging mechanism, is shown in Fig.1. In describing the model, one would need the following quantities, bridging zone length R, bridging stress {sigma}(x{sub 1}), bridging-zone opening displacement {sigma}(x{sub 1}), and the critical stress, {sigma}{sub C}, at which bridging zone starts to develop. Among these quantities, the key element for the bridging model is the relationship between the bridging stress {sigma} and the opening displacement cross the bridging zone {sigma}, i.e., {sigma}({delta}), or the stress-bridging law that can only be determined through experimental measurement. In this study, fracture experiments on PBX 9501 high explosive using the digital image correlation technique were conducted. ...
Date: January 1, 2002
Creator: Liu, C. (Cheng)
Partner: UNT Libraries Government Documents Department

Experimental investigation of the representative volume element size.

Description: In this investigation, the minimum size of the representative volume element (RVE) of a heterogeneous material is determined experimentally using the digital image correlation (DIC) technique. The uniaxial compression experiment was conducted on the PBS 9501, a high explosive simulant material. The minimum size of the representative volume element (RVE) of the PBS 9501 heterogeneous material, where the average crystal diameter of the material is around 100{micro}m, was determined experimentally to be 1.5mm. This result is consistent with those numerical calculations on polycrystalline materials and some other composites.
Date: January 1, 2002
Creator: Liu, C. (Cheng); Stout, M. G. (Michael G.) & Asay, B. W. (Blaine W.)
Partner: UNT Libraries Government Documents Department

Compressive Properties of a Closed-Cell Aluminum Foam as a Function of Strain-Rate and Temperature.

Description: The compressive deformation behavior of a closed-cell Aluminum foam (ALPORAS) manufactured by Shinko Wire. Co. in Japan was evaluated under static and dynamic loading conditions as a function of temperature. High strain rate tests (1000 - 2000/s) were conducted using a split-Hopkinson pressure bar(SHPB). Quasi-static and intermediate strain rate tests were conducted on a hydraulic load frame. Little change in the flow stress behavior as a function of strain rate was measured. The deformation behavior of the Al-foam was however found to be strongly temperature dependent under both quasistatic and dynamic loading. Localized deformation and stress state instability during testing of metal foams will be discussed in detail since the behavior over the entire range of strain rates indicates nonuniform deformation.
Date: January 1, 2001
Creator: Gray, G. T. (George T.), III; Liu, C. (Cheng); Trujillo, C. P. (Carl P.); Jacquez, B. (Benito); Mukai, T. & Cady, C. M. (Carl McElhinney)
Partner: UNT Libraries Government Documents Department