Scaling, characterization, and application of gram-range explosive charges to blast testing of materials
Open Access
- Author:
- Hargather, Michael John
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- February 25, 2008
- Committee Members:
- Gary Stuart Settles, Committee Chair/Co-Chair
James Bernhard Anderson, Committee Member
Panagiotis Michaleris, Committee Member
Robert John Santoro, Committee Member
Gita Talmage, Committee Member - Keywords:
- schlieren
shadowgraph
TNT equivalence
laboratory-scale explosives
explosive
material blast testing - Abstract:
- Laboratory-scale experiments with gram-range explosive charges were performed. Optical shadowgraphy and high-speed digital imaging were used to measure the explosive-driven shock wave position versus time from varying explosive charges. From this, shock Mach number versus distance from the explosion center can be found. These data then yield explosive overpressure and duration, thus explosive impulse. Explosive impulse is a key parameter in explosive characterization and in determining potential damage to structures. High-speed digital cameras and three-dimensional digital image correlation software were then used to measure aluminum panel deflections due to measured explosive impulse impingement. Explosive characterization was performed on two explosives, pentaerythritol tetra-nitrate (PETN) and triacetone triperoxide (TATP). The characterization included optical measurements of shock wave position versus time and piezo-pressure measurements of explosive overpressure duration versus distance. Experimental results were supported computationally by simulations performed using the commercial computational fluid dynamics code AUTODYN. Results show the importance of the shock Mach number versus radius profile, since all other pertinent information can be derived from it. These data show that the characterization procedure developed here is effective for both a traditional explosive, PETN, and for an exotic, non-ideal explosive, TATP. Gram-scale-explosive blast tests were performed on aluminum panels using the above characterized explosives. Typically, material blast testing is conducted at full-scale, but these tests are expensive, dangerous, and difficult to instrument effectively in the field. The present laboratory experiments performed with gram-scale explosive charges show that laboratory-scale testing can be repeatable and effective for documenting material responses to an explosive impulse. A "shock-hole" fixture was developed to allow panel boundaries to be effectively clamped, yet provide optical access to the deforming panel surface, which was measured by high-speed digital imaging and image correlation. Results of parametric experiments show that panel deformation is a function of explosive impulse, independent of explosive charge type. Dynamic and permanent plastic deformation of the aluminum panels is also dependent on fixture design, with the permanent plastic deformation being highly influenced by boundary conditions. The gram-scale explosive testing procedures developed here show the benefits of laboratory-scale explosive testing: high repeatability and advanced instrumentation, along with relatively low resource costs and minimal danger to researchers. Explosive scaling procedures developed previously allow gram-scale blast information to be extrapolated to full-scale test parameters. Small-scale material testing can be more difficult to scale appropriately, yet it can still be used to validate computational models and to experimentally determine physical properties of materials. The techniques developed here form a basis for future laboratory-scale explosive materials testing. The scientific understanding of gram-range explosions and blast scaling has also benefited.