Estimation of the energy of detonation initiation in a hydrogen-oxygen mixture by a high-velocity projectile

The paper presents the results of a numerical study of the initiation of oblique detonation modes by a high-velocity projectile moving in an argon-diluted hydrogen?oxygen mixture. The simulation of oblique detonation wave modes showed that calculated and experimental flow patterns agree. The calculated detonation cell size agreed with experimental data. For the initial pressure Pst = 121 kPa and Pst = 141 a series of calculations were carried out for a different projectile diameters. The detonation initiation energy was estimated, and the results were compared with theoretical models.

Investigation of Composite Materials Impact Damage by a Computer Tomography

In this paper, a complex study of composite materials of different nature for the presence of internal defects after the application of impact damage was carried out. The dependence of the initiation energy on material damage from the magnitude of the impact energy is obtained. The areas of sample bundles were investigated by ultrasonic testing (UT). The structure of samples from composite materials was monitored using an industrial microtomography system. A technique was developed that allows highly accurate determining the size of internal sample defects by means of computed tomography (CT).

Effects of Hydrogen-Air Gas Mixture Volume and Initiation Type and Energy on the Propagation of a Spherical Flame Front

The investigation considered a spherical flame front propagating in free space filled with a hydrogen-air mixture containing 15 % hydrogen. The experiments were conducted inside latex shells. We initiated combustion in the centre of the volume, using either a 1 mJ spark or a nichrome wire explosion releasing 5 J of energy. In the case of the 7 m3 and larger shells, we recorded video data on the flame front using an InfraTec ImageIR 8320 infrared camera featuring a 2.0--5.7 μm spectral ranges and a rate of 300 frames per second. In the case of the 0.003 m3 and smaller shells, we visualised the processes by means of an IAB-451 schlieren system. We recorded these images using a Videosprint G/2 visible-wavelength camera at a rate of 1000 frames per second. We identified the differences in flame front acceleration dynamics for the same combustible mixture composition and flame initiation energy. We found that the distribution function specifics concerning the pre-exponential factors in the power law of flame front acceleration indicate that individual random perturbations have a considerable effect at the initial stage of quasi-spherical flame front formation. We compared flame front propagation for the cases when the initiation energy was 1 mJ and 5 J respectively and determined that the initiation energy also affects the process

Cracking Resistance Characterization of Asphalt Concrete Containing Reclaimed Asphalt Pavement at Intermediate Temperatures

The cracking resistance of asphalt concrete (AC) that contains reclaimed asphalt pavement (RAP) was evaluated in this study with a fracture energy approach. Monotonic and cyclic semicircular bending (SCB) tests were performed with the digital image correlation to correlate crack length with fracture energy. Five types of AC that contained various RAP content (0%, 15%, 30%, 40%, 50%) were evaluated at two intermediate temperatures (15°C and 25°C). On the basis of the relationship between fracture energy and crack extension length, several performance indicators for cracking were proposed: fracture energy and crack initiation energy in monotonic and cyclic SCB tests, an energy cumulative rate in monotonic SCB tests, a fatigue accumulation index (FAI), a fracture energy index, and the slope of the crack steady propagation stage (SOCSP) in cyclic SCB tests. The effects of the RAP content on these indicators were investigated. It was observed from the test results that RAP reduced the fracture energy and crack initiation energy in the monotonic and the cyclic SCB tests. RAP led to a lower energy cumulative rate than an AC mix without RAP in the monotonic SCB tests. Similarly, the FAI and SOCSP values were found to decrease with an increase in RAP content in the cyclic SCB tests. These results indicated that, in general, the addition of RAP reduced the cracking resistance at intermediate temperatures.

Mechanical Performance of Polymer-Matrix Laminate Reinforced with 3D Fabric during Three-Point Impact Bending

The paper presents the analysis of course and the results of impact 3-point bending tests conducted with use of instrumented Charpy hammer (CEAST RESIL 50 hammer + MC101 registrator + CALKA J computer program) on GFRP laminate specimens cut of the panels manufactured by RTM method on base of classic plain-woven fabric preform and 3D fabric. The specimens of the 3D laminate were cut alternatively along (W direction) and transverse (P direction) to the translaminar interweave strands. It was found that maximum force obtained in the tests is comparable for both the classic and the 3D laminates. Deformability of the 3D (W) specimen is by about 20% higher than those of the classic laminate, whereas it is higher by even 75% for 3D (P). The trend of deformability observed for the tested laminates differs from known trends characteristic for static conditions what confirms different material response mechanisms at low and higher load rate. Failure energy in the classic and in the 3D (W) specimen is on comparable level. However, 3D (P) specimen showed slightly lower summary failure energy than the classic one and almost twice a high failure initiation energy (first effects of failure occur before maksimum load is gained).