A shock tube facility will be designed and built, with the capability of simulating explosions of various sizes. The blasts will be imparted to standing plates of varying geometries and boundary conditions. The tests will first be performed on homogeneous structures, such as the metals or plastics currently used in transportation containers. They will then be followed by evaluation of composite materials subjected to the same rigorous blasts. Of particular interest are 3D woven S-2 glass fabric preforms and composites, developed and manufactured by 3TEX, Inc. (Cary, North Carolina), that offer high strength in three directions, excellent crack suppression, damage tolerance, ballistic impact resistance and blast mitigation properties. The use of composites is also particularly useful in that were the material be found to be stronger, it would result in lighter weight of the vehicles, and therefore present the additional benefit of saving energy.
Following, are the major objectives to be accomplished in the first year of this endeavor:
(i) Design shock tube facility for blast loading
(ii) Fabricate and experimentally calibrate the shock tube facility
(iii) Develop and fabricate S-2 glass fabric preforms and composite panels
(iv) Conduct experiments to determine effect of blast loading on panels
(v) Correlate advanced 3-D dynamic numerical models subjected to the same sudden transient loadings with the experiments.
Highway
At both the state and national levels, there exists a desire to improve highway safety. This is indeed essential in light of the well publicized number of human casualties quoted each year. Added to the already existing problems are new threats brought about by criminal elements skilled in the use of explosives. It is purported in this study to partially remedy against this new safety hazard by seeking materials that might shield transportation vehicles against shattering of their containers, resulting in these shattered pieces flying off and further endangering bystanders, or lose their cargo as a result of nearby explosions. The facilities will be established to implement blast testing of materials advanced for that purpose.
Task 1. Design of Shock Tube Facility
A shock tube will be designed with helium as the driving gas, and with the secondary chamber open to atmospheric air. A two diaphragm system will also be implemented in order to take advantage of elevated temperature within the intermediate chamber. Also, a converging driven section will be considered, to impart an additional thrust to the flow.
Several materials are listed in the literature as appropriate for diaphragms. They include cellophane, cellulose acetate, mylar, scored copper, scribed aluminum, each having its distinct characteristics. For instance, for a tube of diameter 3 inches (75 mm), a 0.02 inch thick cellulose acetate plate bursts at pressure equal to 10 times that of atmospheric pressure, whereas for the same dimensional parameters, the scribed aluminum burst at 14.5 to 50 times atmospheric pressure. The latter, therefore, provides more pressure to be applied to the driven section. Several sheets of these materials can also be sandwiched, providing cumulative resistance to pressure. Mylar is readily available commercially, is easy to handle, and provides a very clean break. It will be used in the first trials of the apparatus.
Finally, the tube will be made of aluminum 6061-T6511, because of its relatively low density. In addition, it can be readily purchased in several standard sizes, ranging from 2 to 6 inches (50 to 150 mm) in diameter, with minimum yielding pressure of 2000 psi (14 MPa). Several shorter sections will be used, and will be joined with threaded flanges. The flanges, in turn, will be bolted together, with o-rings providing a leak-free connection. Also, the internal surfaces of the tubes will be honed to obtain smooth finishes that should minimize wall viscous effects.
Task 2. Fabrication and Calibration of the Facility
All major parts necessary for fabrication of the shock tube are readily available commercially. They consist mainly of tubes, flanges, diaphragm sheets, o-rings, nuts, bolts, and valves.
The shock tube will be calibrated against theoretical predictions. This will be accomplished by use of pressure transducers that can be linked to electronic devices such as oscilloscopes, to record the entire pressure history of the shock. Several recording systems have been developed specifically to measure the progression of pressure during an explosion. These include the piezoelectric side-on blast gage and the pencil blast gage, among others. These will be installed at the exit of the shock tube to register its pressure output. Adjustments can then be made to the driver pressure, or length of the various sections to optimize the shock strength. Also, variation of outgoing pressure with compression chamber pressure will be traced such as to obtain a design chart to be used during testing. Piezo-electric transducer and micro transducers will be affixed to the internal surface of the tube to monitor pressure, temperature, velocity, or density.
Task 3. Design and fabrication of fabric preforms and composite materials
The design and fabrication of composite materials will take place at 3TEX Inc. Composites will be designed and fabricated from 3-D Woven S-2 Glass Fabrics and Dow Derakane 8084 Epoxy-Vinyl Ester resin. These composite are expected to have superior properties and structural integrity when subjected to blast loadings than homogeneous materials or 2D woven composites.
Task 4. Experiments
Experiments will be carried out first, on
homogeneous panels, then with the 3D Woven composites.
Strain gages will be placed on both the front and the back of the specimens, either at the center or at the location of highest stress, where failure is expected to initiate. The strain gage located on the front face of the panel may incur damage upon impact, but will at least provide information concerning the initiation of the event, from a structural standpoint. As the first stress waves reach the back face, they will trigger the associated strain gage, thus immediately providing information concerning wave speeds in the material. In addition, the back strain gages give a detailed account of the strain (or stress) history pertinent to the outer layer of the material. A study of the stress history will be used to identify instances of failure.
Post-mortem analysis will be conducted using the Split Hopkinson Pressure Bar (SHPB) technique in compression, to assess
the internal damage to the specimens following impact.
Task 5. Mathematical and Numerical Simulations
An effort will be made during the first year of this project to implement a mathematical model and 3-D dynamic numerical analysis code to simulate blast loading on structural panels, particularly those made from 3-D woven fabric composites. This effort will be led by 3TEX Inc.
Schock design and manufacture: 9/31/03
Assembly and instrumentation: 10/31/03
Manufacture of homogeneous specimens: 10/31/03
First tests and calibration: 11/31/03
Manufacture of 3Weave: 6/31/04
Preliminary Testing of 3Weave: 7/31/04
SHPB testing: 7/31/04
Calibration of FEM and experiments: 7/31/04
$179,266.00 ($179,266.00 Yearly)
At least two Master's sudents will derive their theses from this project.
University of Rhode Island (under leadership of Dr. Arun Shukla) serves as Research Institution in US ARMY STTR Phase II contract “3-D Orthogonal Woven Composites in Armor Systems”, awarded to 3TEX, Inc. (effective March 2002-March 2004), Dr. Alexander Bogdanovich is Principal Investigator.
3TEX, Inc. is working on US Army SBIR Phase II contract “Innovative Materials for Lightweight Armor” (effective July 2001-July 2003), Dr. Alexander Bogdanovich is Principal Investigator.
3TEX is working on US Navy SBIR Phase I contract “3WEAVE Multi-Functional Composites: Load Bearing and Armor Protection” (effective November 2002-May 2003), Dr. Mansour Mohamed is Principal Investigator.
3TEX is working on US Navy SBIR Phase I contract “3WEAVE-Composite/Cellular-Metal Blast Protection” (effective January 2003-June 2003), Dr. Mansour Mohamed is Principal Investigator.
All four aforementioned research contracts are directly related to the problems of impact, ballistic and blast mitigating 3-D woven composite materials for human, vehicle and military ship protection against broad variety of threats, including those used or possibly could be used in terrorist attacks.
Results of the research will be published in technical journals, conference proceedings, and student theses. In addition, the results of this investigation will be published or posted on a URITC web page for world wide dissemination. Finally, oral presentations will be conducted as needed to US DOT and URITC personnel. The results will be of direct relevance to participating and other industry.
The results from this project will have direct application to the transportation industry. It is a very focused and specific research, aimed at improving the safety of transportation vehicle carrying explosive, inflammable materials, or unstable chemical substances. It will also be beneficial from the standpoint of homeland security, since the research may potentially result in the development of a material that could mitigate the effect of roadside explosions on transportation trucks.
Blast Loading, Impact Loading, Composite Panel, Armor, Wave Propagation, Fracture, Split Hopkinson Pressure Bar, Finite Element Modeling, Discrete Element Modeling.