Detonation loading of tubes in the modified shear wave speed regime
We performed experiments and numerical simulations on a thin-wall aluminum tube with internal gaseous detonation loading in the modified shear wave speed regime. Strain gauges were used to determine the time-dependent hoop strain on the surface of the tube. The experimental results were compared with analytical models and numerical simulations with explicit finite element computation treating the detonation as a traveling load. Hoop strain amplification factors (defined as the ratio of the dynamic strain to the equivalent static strain) close to two were obtained both in the present experiments and simulations. No resonance phenomena in the hoop strain were found in either experiments or simulations. Computations reveal the existence of a resonance in the shear strain.
LINEAR ELASTIC RESPONSE OF TUBES TO INTERNAL DETONATION LOADING
This paper deals with the structural response of a tube to an internal gaseous detonation. An internal detonation produces a pressure load that propagates down the tube. Because the speed of the gaseous detonation can be comparable to the flexural wave group speed, excitation of flexural waves in the tube wall must be considered. Flexural waves can result in much higher strains and stresses than static loading with the same loading pressures. Experiments and numerical simulations were used to determine the structural response. In the experiments, a detonation tube was instrumented with a number of strain gages. A series of experiments was carried out under different conditions. Strains were measured that exceeded the equivalent static strain by up to a factor of 3·9. Special attention was paid to the influence of the detonation speed, reflection and interference of structural waves at flanges and also at the tube end, the linearity of the response, the transient development of the deflection profile, and the influence of detonation cell size. Analytical models and finite element models were used to interpret the observations and to make quantitative predictions of the peak strain.
Measurements of normal detonation wave structure using Rayleigh imaging
Normal detonation waves have been studied using Rayleigh scattering to obtain two-dimensional density images surrounding the wave front. The detonations were generated in mixtures of H 2 , O 2 and Ar with [O 2 ]/[Ar] held at 0.21/0.79, equivalence ratios varying between 0.6 and 1.4 and initial pressures set between .272 and .578 atm. The fourth harmonic of a Nd:YAG laser provided a pulsed sheet, of UV laser light which cut through the detonation wave front as it traversed the test section to generate the Rayleigh scattering. An intensified CID camera was used to acquire and image the resulting signals. Schlieren images were acquired simultaneously for comparison. Cellular structure was clearly visible in the images and cell sizes have been correlated with detonation parameters for comparison with measurements and analyses by earlier investigators. The progression of wave front structure could be understood by observing images which were each acquired from different runs and at random times in the wave front development. Rayleigh signal ratios, comparing reactant and product densities were quantified at various locations within the wave front. They were compared with calculated values based on shock theory and equilibrium analysis and were found to be in good agreement.