Experimental Study on Behind-Plate Overpressure Effect by Reactive Material Projectile

The effect of particle size and mass ratio on the mechanical response of Al/PTFE/SiC composite with a 23 factorial design

In order to study the effects of different SiC mass ratios, SiC particle sizes and Al particle sizes on the mechanical response of Al/PTFE/SiC, an experiment was conducted through the full 23 factorial design. The specimens were prepared by means of molding-vacuum sintering, while the mechanical response of the materials was measured through quasi-static compression. The regression models between failure stress, failure strain and various factors were established respectively and then verified through the analysis of variance (ANOVA) and residual analysis. Besides, the relationship between factors and response as well as that between factors were analyzed using response surface plots. According to the analytical results, the ultimate compressive strength of the material can be improved either by reducing the particle size of SiC and Al or increasing the mass ratio of SiC, while the ductility of the material can be enhanced by maintaining the interaction between SiC mass ratio and SiC particle size at high levels. The interaction effects are significant and can not be ignored, especially the interaction between SiC mass ratio and SiC particle size has an important impact on the mechanical responses, which shows that SiC has a greater influence than Al particles in the material system.

Impact-Initiation Sensitivity of High-Temperature PTFE-Al-W Reactive Materials

Drop-weight tests were conducted to investigate the impact-initiation sensitivity of high-temperature PTFE-Al-W reactive materials. The test results show that the impact-initiation sensitivity of the materials more than doubles with increasing the sample temperature from 25 to 350 °C. Combined with the impact-induced initiation process recorded by high-speed video and the difference between reacted and unreacted residues, the crack-induced initiation mechanism was revealed. The rapid propagation of crack provides a high-temperature and aerobic environment where Al reacts violently to PTFE, which induces the initiation. Moreover, the influence of sample temperature on the sensitivity was discussed and analyzed. The analysis results indicate that the sensitivity shows a temperature interval effect, and 127 and 327 °C are the interval boundaries where the sensitivity changes significantly. The sensitivity may leaps at 127 °C and increases more rapidly in the temperature interval from 127 to 327 °C, but hardly changes after the temperature reaches 327 °C.

Mechanism of Pyrolysis Reaction of Al-Rich Al/PTFE/TiH2 Active Material

In order to obtain the chemical reaction mechanism of Al-rich Al/PTFE/TiH₂ composites in argon and oxygen atmosphere, Al/PTFE, PTFE/TiH₂, Al/TiH₂ and Al-rich Al/PTFE/TiH₂ with different contents of TiH₂ composites were prepared by using the wet mixing method. The pyrolysis behavior of the above composites was investigated by thermogravimetric differential scanning calorimeter (TG-DSC). In addition, the calorific value of the above composite was measured by an oxygen bomb calorimeter. The compositions of TG-DSC residues at different peak temperatures and 1000 °C and the residues of oxygen bomb experiment were analyzed by X-ray diffraction (XRD), The results show that the pyrolytic products of Al-rich Al/PTFE/TiH₂ materials under argon atmosphere can be divided into four stages. In the first stage (328.6–378.6 °C), the products are TiH_1.924, (C₂F₄)_n, (CF₂)_n, H₂(g), Al and TiH₂; in the second stage (510.8–534.3 °C), the products are Al, TiH_1.924, (C₂F₄)_n, (CF₂)_n, Ti, AlF₃, TiF₃, TiF₄(g), C and H₂(g). In the third stage (540.8–618.1 °C), the products are Al, C, Ti, (C₂F₄)_n, (CF₂)_n, AlF₃, TiF₃, TiF₄, CF₄(g), C₃F₆(g), C₄F₈(g), C₂F₆(g), Al₅Ti₂ and H₂(g); in the fourth stage (918.5–1000 °C), the products are AlCTi₂, Al₂Ti, AlTi, TiC, AlF₃, Al, TiF₃, TiC_0.957, TiC_0.981 and TiC_0.95. The calorific value of the combustion of Al-rich Al/PTFE/TiH₂ composite with 10% the content of TiH₂ is the highest and is 19,899 J/g, which is 3.776% higher than that of Al-rich Al/PTFE composite. When TiH₂ content is greater than zero and not more than 10%, the chemical reaction mechanism of Al-rich Al/PTFE/TiH₂ is almost the same under oxygen atmosphere. When the content of TiH₂ is higher than 10%, the mechanism of this material is different.

Bulk Density Homogenization and Impact Initiation Characteristics of Porous PTFE/Al/W Reactive Materials

In this research, the bulk density homogenization and impact initiation characteristics of porous PTFE/Al/W reactive materials were investigated. Cold isostatic pressed (CIPed) and hot temperature sintered (HTSed) PTFE/Al/W reactive materials of five different theoretical maximum densities were fabricated via the mixing/pressing/sintering process. Mesoscale structure characteristics of the materials fabricated under different molding pressures were compared while the effect of molding pressures on material bulk densities was analyzed as well. By using the drop weight testing system, effects of the theoretical maximum densities (TMDs), drop heights and molding pressures on the impact initiation characteristics were studied. Quantitatively, characteristic drop heights (H₅₀) for different types of materials were obtained. The two most significant findings of this research are the density homogenization zone and the sensitivity transition zone, which would provide meaningful guides for further design and fabrication of reactive materials.

A Study on the Mechanical Properties and Impact-Induced Initiation Characteristics of Brittle PTFE/Al/W Reactive Materials

Polytetrafluoroethylene/aluminum/tungsten (PTFE/Al/W) reactive materials of three different component mass ratios (73.5/26.5/0, 68.8/24.2/7 and 63.6/22.4/14) were studied in this research. Different from the PTFE/Al/W composites published elsewhere, the materials in our research were fabricated under a much lower sintering temperature and for a much shorter duration to achieve a brittle property, which aims to provide more sufficient energy release upon impact. Quasi-static compression tests, dynamic compression tests at room and elevated temperatures, and drop weight tests were conducted to evaluate the mechanical and impact-induced initiation characteristics of the materials. The materials before and after compression tests were observed by a scanning electron microscope to relate the mesoscale structural characteristics to their macro properties. All the three types of materials fail at very low strains during both quasi-static and dynamic compression. The stress-strain curves for quasi-static tests show obvious deviations while that for the dynamic tests consist of only linear-elastic and failure stages typically. The materials were also found to exhibit thermal softening at elevated temperatures and were strain-rate sensitive during dynamic tests, which were compared using dynamic increase factors (DIFs). Drop-weight test results show that the impact-initiation sensitivity increases with the increase of W content due to the brittle mechanical property. The high-speed video sequences and recovered sample residues of the drop-weight tests show that the reaction is initiated at two opposite positions near the edges of the samples, where the shear force concentrates the most intensively, indicating a shear-induced initiation mechanism.