Aluminum Polytetrafluoroethylene Research Articles

Dynamic Constitutive Model of Tungsten‐Whisker‐Reinforced Aluminum/Polytetrafluoroethylene Composite Material and Quantitative Determination of Impact Reaction Release Energy in Vacuum Environment

To meet the strength requirements of aluminum/polytetrafluoroethylene (Al/PTFE) in practical applications, tungsten (W) whisker is added into the traditional formula Al/PTFE (26.5%/73.5%) to improve the dynamic compressive strength of the reactive material. Mechanical properties of reactive material specimens prepared by sintering are tested. In the results, it is shown that the dynamic compressive strength of Al/PTFE‐reactive material reinforced by tungsten whisker with volume fraction of 13.1% can reach 141 MPa at strain rate of 1800 s−1. The constitutive model of dynamic compression for tungsten‐whisker‐enhanced Al/PTFE‐reactive material is constructed, and the results are basically consistent with the experimental results. The quantitative impact energy release of reactive material specimens under vacuum environment are performed by using the two‐stage light gas gun loading system, and the quantitative impact release energies of Al/PTFE‐reactive material reinforced by tungsten whisker under different whisker percentage content and diameter are obtained.

PTFE-modified Al through bridging approach to enhance combustion reaction and energetic performance

Aluminum/Polytetrafluoroethylene (Al/PTFE) composites have attracted a great deal of attention due to their remarkable energy density and wide range of applications. Unfortunately, the inert oxide layer (Al2O3) on the surface of Al and the interfacial contact area between PTFE and Al seriously impact the combustion reaction kinetics and energy output efficiency. Here, an approach is utilized to significantly enhance the interfacial contact area between Al and PTFE through F2601 serving as the bridging agent. The ignition, combustion reaction, and energetic performance (pressure and combustion heat) can be adjusted by varying the particle size of Al and PTFE content. The energy release efficiency of bridging Al/PTFE has been improved significantly as PTFE content increases and the particle size of Al decreases. The bridging Al/PTFE with 10 μm Al and nano Al exhibit a bright and wide flame, and a fierce flame propagation process, as well as much high pressure output (167.73 kPa and 199.92 kPa) and heat release (11879 J/g and 12322 J/g). Furthermore, the critical mass ratio (approximately 88/12) of bridging Al/PTFE for self-sustained combustion has been obtained for the first time. The improvement of energy output performance is attributed to the interfacial contact between PTFE and Al and the reaction of fluorine and Al2O3 resulted from bridging Al/PTFE through F2601. The prepared bridging Al/PTFE with high energy output characteristics holds great potential in solid propellants, reactive materials, and other high-energy fuels.

Combustion characteristics of Al/PTFE materials with different microstructures

The microstructures play a crucial role in the combustion of aluminum/polytetrafluoroethylene (Al/PTFE) materials. Mechanically activated Al/PTFE typically demonstrates higher reactivity but a lower combustion rate compared to physically mixed Al/PTFE. Recently, the combustion performance of fuel-rich Al/PTFE has been well explained by the microexplosion mechanism. In this study, the combustion characteristics of stoichiometric Al/PTFE (26.5:73.5 wt%) materials with varying microstructures were investigated to further the understanding of their combustion mechanism and offer insights for their potential applications in metal cutting. The Al/PTFE materials with different microstructures were prepared using sonication and ball milling methods. The results of scanning electron microscope (SEM) analysis suggest that the sonicated Al/PTFE (s-Al/PTFE) containing spherical Al particles displayed a loosely dispersed structure, while the milled Al/PTFE (m-Al/PTFE) exhibited a densely layered structure with flake-like Al particles coated by the PTFE matrix. The milled Al/PTFE was found to be mechanically activated. Combustion in quartz tubes was recorded using a high-speed camera and a video. Combustion of s-Al/PTFE demonstrated a high-temperature flame (∼2346 K) and obvious microexplosions featuring hot particles ejection, while combustion of m-Al/PTFE showed a weak flame (∼2037 K) and slow-burning, featuring dense carbon smoke. Increasing the powder density was observed to slightly decrease (∼100 K) flame temperature. Microstructure and phase analysis of combustion products were systematically conducted to elucidate the combustion behaviors. The results suggest that the residue of s-Al/PTFE contained high AlF3 and low carbon content, whereas the residue of m-Al/PTFE exhibited the opposite condition. The results of the combustion tests suggest that microexplosions promoted the oxidation of hot Al particles and carbon products, consequently leading to a fast reaction, high flame temperature, and enhanced heat transfer capability.

Investigation on the microstructures, mechanical properties and impact initiation characteristics of Al/PTFE reactive materials reinforced by TiH2 particles

Aluminum/Polytetrafluoroethylene (Al/PTFE) is a representative energetic material, which can be used in many fields including defense weapon fragments, insensitive penetrator or oil-well perforation. However, the insufficient mechanical strength of traditional ingredient has seriously restricted its penetration ability, and traditional additives improve its compressive strength at the expense of reactivity. Hence, innovative component design and advanced manufacturing technology should be applied to Al/PTFE composite. In this investigation, TiH2 as a new reinforcement is introduced into Al/PTFE to improve both strength and reactivity. Quasi-static and dynamic compressive tests were conducted, and the impact reaction process was recorded by high-speed camera. The results shown Al/PTFE/TiH2 composites are all elasto-plastic materials, significant strain hardening and strain rate hardening phenomenon were observed. The compressive strength increased first and then decreased with increase in TiH2 content, reached the maximum of 185.1 MPa at the strain rate of 5000 s−1 when TiH2 content was 30 %, which increased by 30.4 % compared to traditional Al/PTFE. A newly-developed drop-weight device was used to quantitatively characterize reactivity, and the reaction efficiency reached 8.2 % when TiH2 content was 30 %, increased by 43.2 % compared to Al/PTFE. The formation of oriented PTFE nano-fibers was considered the important strengthening mechanism. The established Johnson–Cook model was agreed well with experimental results. Combining the results of thermogravimetry-differential scanning calorimetry (TG-DSC) tests with X-ray diffraction (XRD) analysis of reaction residues, the reaction mechanism was clarified. The impact initiation reaction was in a mechano-chemical manner and the reactivity was speculated to be the results of multiple actions between Al/PTFE and TiH2.

On Aftereffects of Shaped Charge Comprised of Reactive Material Liner

Two types of shaped charge comprised of reactive material liner, which can generate exothermal reaction by certain external action, were designed to promote the aftereffect. One design contained two layers of liners, which can form a short and wide explosive formed penetrator (EFP). The other design contained three layers of liners, which can form a long and thin EFP. The composition of reactive material is aluminum/polytetrafluoroethylene (AL/PTFE) mixtures. The results of numerical simulation and experiments show that, for steel target with a thickness of 45 millimeter (mm), the EFP generated by the reactive shaped charge comprised with three layers of liners can penetrate more deeply than that with two layers of liners. The former can also perforate two 500 mm spaced steel targets with a thickness of 5 mm, then the residual EFP delivered the reactive material into the oil box. The reactive material released its energy, and ignited the oil.

Effect of Confining Pressure on Impact Reaction Threshold of Aluminum/Polytetrafluoroethylene Reactive Material

An impact reaction experiment is conducted with a modified split Hopkinson pressure bar (SHPB) apparatus to study the reaction threshold of aluminum/polytetrafluoroethylene (Al/PTFE) reactive materials under confining pressure. The dynamic compression behavior, impact damage characteristics, and impact reaction threshold of the Al/PTFE reactive material under the confining pressure are investigated. The results have presented that confining pressure makes the specimens suffer triaxial loading and improves the dynamic compressive strength of Al/PTFE reactive materials from 36.8 MPa (impact velocity is 14.64 m s−1) to 62.7 MPa (14.80 m s−1). Besides, the fractal dimension of the posttest specimen is decreased by confining pressure, which has proved that the confining pressure hinders damage under impact loading. Moreover, the impact reaction experiment demonstrates that the confining pressure increases the threshold of Al/PTFE, and the minimum specific incident energy for the reaction of the T10 (molding pressure is 10 MPa) specimen increases from to . This research not only reveals that Al/PTFE can be reacted by impact loading at confining pressure but also clarifies that confining pressure limits the impact damage of the Al/PTFE reactive material and increases the reaction threshold.

Force chains behaviours of Al-PTFE granular composite under elevated strain rates

This study proposed a simulation method to characterize the influence of mesostructural force chains on the dynamic response of aluminum-polytetrafluoroethylene(Al-PTFE) granular composite under strain-controlled compression. The model was developed followed real Al particle size distribution. Based on the analysis of force chains, the global deformation, mechanical strength, and failure behaviour for the material were investigated. The results indicate that, with the increasing of strain rates, the yield strength of the Al-PTFE increases, but it is inversely proportional to the ultimate compressive strength. The stability of force chains accounts for the phenomenon that a higher strength is observed in the material under lower strain-rate impact. Particularly, an angle of force transmission is introduced to quantitatively explain the evolution mechanism of force chains.

Force chains behaviours of Al-PTFE granular composite under elevated strain rates

This study proposed a simulation method to characterize the influence of mesostructural force chains on the dynamic response of aluminum-polytetrafluoroethylene(Al-PTFE) granular composite under strain-controlled compression. The model was developed followed real Al particle size distribution. Based on the analysis of force chains, the global deformation, mechanical strength, and failure behaviour for the material were investigated. The results indicate that, with the increasing of strain rates, the yield strength of the Al-PTFE increases, but it is inversely proportional to the ultimate compressive strength. The stability of force chains accounts for the phenomenon that a higher strength is observed in the material under lower strain-rate impact. Particularly, an angle of force transmission is introduced to quantitatively explain the evolution mechanism of force chains.

Dynamic simulation and model of laser ablation of Al/PTFE material in the vacuum

Despite in-depth investigations on the chemical reaction mechanism of Al/PTFE (aluminum/polytetrafluoroethylene), the research on the heat and mass transfer process of the Al/PTFE material itself is still lacking. Based on the previous study on the reaction mechanism of Al/PTFE, this paper theoretically analyzes and summarizes the dynamic multi-physical processes between the laser-Al/PTFE interactions. With the theoretical analysis and some hypotheses, a mathematical model, which considers the phase transition, moving recessive interface, thermal decomposition, chemical reactions, laser heat conduction, and the target material's temperature-dependent material and optical properties, is established in the one-dimensional domain to capture the dynamic interaction between laser and Al/PTFE. The robust coupling scheme utilized in the model enables us to track the moving interface recession, and predict the temperature distributions and ablation zone profiles. The proposed model has been validated by comparing the predictions of the ablation depths with those obtained using other simplified models and experimental results.

Explosion characteristics of aluminum-based activated fuels containing fluorine

Measuring the dust explosion characteristics of aluminum-based activated fuels was a prerequisite for developing effective prevention and control measures. In this paper, ignition sensitivity, flame propagation behaviors and explosion severity of aluminum/polytetrafluoroethylene (Al/PTFE) compositions including 2 PT (2.80 wt.% F), 4 PT (7.18 wt.% F) and 8 PT (11.90 wt.% F) were studied. When the content of F increased from 2.80 wt.% to 11.90 wt.%, the minimum explosive concentration MEC decreased from 380 g/m3 to 140 g/m3, due to the dual effects of increased internal active aluminum and enhanced reactivity. The average flame propagation velocities increased as the percentage of F increased. The maximum explosion pressure Pm of 500 g/m3 aluminum-based activated fuels increased from 247 kPa to 299 kPa. Scanning electron microscopy demonstrated that with the increase of PTFE content, the reaction was more complete. On this basis, the explosion mechanism of aluminum-based activated fuels was revealed.

Dynamic characteristics of enhanced Al/PTFE and real-time quantitative evaluation of impact release energy under vacuum environment

Aluminum/Polytetrafluoroethylene (Al/PTFE) reactive material occurs chemical reaction and release a large amount of energy under the impact load, which has the dual characteristics of strength and energy release, so it can be applied to the attack of confined space targets to enhance the damage effect on the target. In order to study the dynamic strength of enhanced Al/PTFE and the real-time impact release energy, based on the traditional formula Al/PTFE (26.5%/73.5%), enhanced Al/PTFE reactive material specimens were prepared by cold pressing and rapid cooling processes, and the dynamic mechanical properties of the specimens were tested by the Split Hopkinson Pressure Bar (SHPB) testing system. The experiments have been conducted by using two-stage light gas gun loading system combining with the impact release energy related testing system under vacuum condition. Meanwhile, the evolutionary process of reaction product was numerically simulated by ANSYS/Fluent, and the boundary conditions of the numerical simulation were defined by self-programmed UDF subroutine. Experiments, theoretical analysis and numerical simulation were adopted to obtain the real time energy release of Al/PTFE reactive materials at different impact velocities. The results show that the maximum dynamic failure strength of the enhanced Al/PTFE reactive projectile is 126 MPa, and the strain rate hardening phenomenon and viscoelastic effect are exhibited when the strain rate is in the range of 1500 ∼ 3000 s−1. When the strain rate is in the range of 3000 ∼ 4000 s−1, the specimen is insensitive to strain rate. When the impact velocities are 2.30 km/s and 2.54 km/s, the energies that the reactive projectiles release are 8.36 kJ/g and 8.38 kJ/g, respectively, and the reactive material reacts completely. When the impact velocities are 1.64 km/s, 1.80 km/s and 1.94 km/s, the projectiles have not fully reacted. The reactive degree of the reactive projectile increases with the increase of the impact velocity. For the complete reaction of Al/PTFE reactive projectile, the critical impact velocity of the enhanced reactive material is between 1.94 km/s and 2.30 km/s.

Mesoscale study on the shock response and initiation behavior of Al-PTFE granular composites

A combination of mesoscale simulations and explosive loading experiments is used to investigate the shock response and shock-induced initiation behavior of aluminum-polytetrafluoroethylene (Al-PTFE) granular composites. A two-dimensional model following the random distribution of real Al particle sizes is developed and validated against experiments. The model is employed to investigate the effect of Al mass fractions on shock characterizes as well as Hugoniot relationships, and noticeable differences are visualized at the grain-level in the pressure, temperature, and strain response. Systematic shock structures in metals have been identified, and the underlying mechanisms of deformation and energy dissipation are discussed respectively. Results demonstrate that the high pressure is concentrated in the wave front, but a much greater heat and larger strain exhibit along grain/matrix interfaces that enable the friction dissipation the main mechanism of hot-spots formation. Specific quantities of critical temperature to initiate are obtained based on basic microstructure attributes to analyze the influence on hot-spots distribution by mass fractions. The interaction of shock wave with mesoscale heterogeneities accounts for the stochastic nature of the initiation process.

Heat conduction and deflagration behavior of Al/PTFE induced by thermal shock wave under temperature gradient

In order to reveal the influence of sintered and unsintered aluminum/polytetrafluoroethylene (Al/PTFE) reactive material on heat conduction, ignition and deflagration characteristics under the condition of thermal loading, the sintered and unsintered samples prepared by molding process are heated by acetylene flame as heat source. The heat conduction and deflagration behaviors of samples are measured synchronously by infrared thermal imager and high-speed camera before and after ignition. Meanwhile, combining with the three-dimensional differential equation of heat conduction in cylindrical coordinate system, the temperature gradient, heat flux and ignition moments during the process of heat conduction are solved by numerical simulation. The results show that the two kinds of samples both undergo the evolutions of temperature gradient and thermal shock wave induced by temperature gradient. The instantaneous energy accumulation caused by thermal shock wave promotes the samples to deflagrate, and the heat conduction durations before ignition, ignition temperature of sintered sample are both smaller than that of unsintered sample. The micro-morphologies before ignition indicate that the unsintered sample needs to accumulate more energy to achieve deflagration. The deflagration reaction extent of unsintered sample is more intense than that of sintered sample, however, the deflagration durations of sintered sample lasts longer. The maximum flame area of unsintered sample is 30.6% larger than that of the sintered sample, and the maximum temperatures of the flame core of sintered and unsintered sample are 1284 K and 1425 K, respectively.

Cathodic electrophoretic deposition and thermal properties of nano aluminum/fluoropolymer metastable intermolecular composite

ABSTRACT One challenge in the application of traditional metastable intermolecular composite (MIC) material is that MIC particles are not compatible with micro-electro-mechanical system (MEMS) based pyrotechnic device. The preparation of MIC film material can solve such problem. In this paper, we applied electrophoretic deposition method to prepare aluminum/polyvinylidene fluoride (Al/PVDF) and aluminum/polytetrafluoroethylene (Al/PTFE) MIC films. The morphological, structural and compositional information of the film samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and energy dispersive spectrometer (EDS). The energy-release characteristics of Al/PVDF and Al/PTFE MIC films were analyzed by thermogravimetric (TG) analysis and differential scanning calorimetry (DSC). Micromorphology results show that the components of the films were evenly distributed but there were a few holes. DSC curves of both Al/PVDF and Al/PTFE films show that there was only one major exothermic peak and the exothermic temperature of Al/PTFE was 63°C higher than that of Al/PVDF. Kinetic analysis of main exothermic peaks indicates that the apparent activation energies (E a) calculated by Ozawa, Flynn-Wall-Ozawa and Starink methods were reliable. And E a of Al/PTFE is higher than that of Al/PVDF, implying that Al/PVDF is prone to react. The kinetics results of electrophoretic deposition for both Al/PVDF and Al/PTFE show that the parabolic relationship between deposition mass and deposition time exist in all experiments.

Modified model of Al/PTFE projectile impact reaction energy release considering energy loss

Aiming at the evaluation model of Aluminum/Polytetrafluoroethylene (Al/PTFE) impact reaction energy release established by Ames R G, the factors that have great influence on reaction energy release, such as vessel wall energy absorption and ejected gas energy, are ignored in the model. In fact, the sum of the initial kinetic energy and the impact reaction energy release should include the increase of target internal energy, the enthalpy of gas products, the thermal radiation energy, the kinetic energy of gas products and the energy absorbed by the vessel wall. The evolutionary rules of each part energy are quantitatively evaluated by quasi-closed vessel experiments at different impact velocities combining with various measured methods such as overpressure sensor, high speed camera, instantaneous optical pyrometer and infrared thermal imager. The Ames R G model is modified based on the results of reaction energy release at different impact velocities, and a modified model of reaction energy release considering temperature is established. The results show that with the increase of impact velocity, the enthalpy of gas products and the energy absorbed by the vessel wall increase greatly. The energy absorbed by the vessel wall accounts for most of the projectile impact energy release. The impact reaction energy release of unit mass projectile increases with the increase of impact velocities. When the impact velocities are in the range of 389–509 m/s, the increase of reaction release energy is significantly lower than that of 509–596 m/s. The modified model considering energy loss can be used to quickly evaluate and characterize the reaction energy release characteristics of active materials under impact load.

Quasi-static mechanical behaviors of different inert particle reinforced Al/PTFE reactive composites

In this paper, the quasi-static mechanical behaviors of particle reinforced aluminum/polytetrafluoroethylene (Al/PTFE) reactive composites are studied. The mechanical behaviors of composites with the volume fraction of 30% W, WC, SiC and SiO2 respectively are compared by the quasi-static compression test, and the failure mechanism is analyzed. Test results show that SiC/SiO2 particle reinforced composites show better toughness, while W/WC particle reinforced composites show more brittleness. The failure mechanism analysis indicates that the failure of particle reinforced composites is mainly caused by matrix fracture and particle spalling from the matrix.

Force chains based mesoscale simulation on the dynamic response of Al-PTFE granular composites

Force chains based mesoscale simulation is conducted to investigate the response behavior of aluminum-polytetrafluoroethylene (Al-PTFE) granular composites under a low-velocity impact. A two-dimensional model followed the randomly normal distribution of real Al particles size is developed. The dynamic compressive process of Al-PTFE composites with varied Al mass fraction is simulated and validated against the experiments. The results indicate that, force chains behavior governed by the number and the size of agglomerated Al particles, significantly affects the impact response of the material. The failure mode of the material evolves from shear failure of matrix to debonding failure of particles with increasing density. A high crack area of the material is critical mechanism to arouse the initiation reaction. The damage maintained by force chains during large plastic strain builds up more local stresses concentration to enhance a possible reaction performance. In addition, simulation is performed with identical mass fraction but various Al size distribution to explore the effects of size centralization and dispersion on the mechanical properties of materials. It is found that smaller sized Al particle of composites are more preferred than its bulky material in ultimate strength. Increasing dispersed degree is facilitated to create stable force chains in samples with comparable particle number. The simulation studies provide further insights into the plastic deformation, failure mechanism, and possible energy release capacity for Al-PTFE composites, which is helpful for further design and application of reactive materials.

The Influence of Initial Defects on Impact Ignition of Aluminum/Polytetrafluoroethylene Reactive Material

Aluminum/polytetrafluoroethylene (Al/PTFE) reactive material is a typical multifunctional energetic material, which can release enormous energy under impact loading. To clarify its ignition mechanism, a Split Hopkinson pressure bar (SHPB) is used to conduct the impact ignition experiment on reactive materials with different initial defects. The experimental results show that the measured minimum specific incident energy that can cause the ignition for the specimen without pre‐impact (MSed specimen) increases slowly from 97.5 to 101 Jcm−2 with the molding pressure first, but drops substantially to 83.3 Jcm−2 as the molding pressure increases to 100 MPa. In addition, only the MSed specimens with the molding pressure above 100 MPa are ignited at the third stress pulse. Combined with the results of scanning electron microscopy, it is found that the existence of local larger pores inside the MSed specimens with high molding pressures (100, 120, and 150 MPa) contributes to the increase in damage level under impact and thus reduces the ignition threshold. The impact ignition experiment on the pre‐impacted specimens (MSed + PIed specimens) indicates that a phenomenon of damage sensitization exists in Al/PTFE reactive materials, confirming that the initial defects and damage evolution have significant effects on the impact ignition of the material.

Influence of Temperature on the Mechanical Properties and Reactive Behavior of Al-PTFE under Quasi-Static Compression.

Al-PTFE (aluminum-polytetrafluoroethylene) is a typical kind of Reactive Material (RM), which has a variety of potential applications in weapon systems. In this paper, quasi-static compression experiments were carried out for a pressed and sintered mixture of Al and PTFE powders using a microcomputer-controlled electronic universal testing machine. The results show that both the mechanical property and reactive behavior of Al-PTFE are strongly temperature-dependent. The material undergoes a brittle-ductile transition associated with a temperature-induced crystalline phase transformation of the PTFE matrix. At low temperatures (−18, 0, and 16 °C), samples of Al-PTFE failed with shear crack and no reaction was observed. As the temperature increased (22, 35, and 80 °C), Al-PTFE exhibited a high toughness and violent reaction occurred in all of the tested samples. Scanning electron microscope observations showed different fracture mechanisms of the PTFE matrix and the increase in toughness was due to the formation of PTFE fibrils which could dissipate energy and bridge crack plane during plastic deformation.

Investigation on Mechanical Properties and Reaction Characteristics of Al‐PTFE Composites with Different Al Particle Size

Al‐PTFE (aluminum‐polytetrafluoroethylene) serves as one among the most promising reactive materials (RMs). In this work, six types of Al‐PTFE composites with different Al particle sizes (i.e., 50 nm, 1∼2 μm, 6∼7 μm, 12∼14 μm, 22∼24 μm, and 32∼34 μm) were prepared, and quasistatic compression and drop weight tests were conducted to characterize the mechanical properties and reaction characteristics of Al‐PTFE composites. The reaction phenomenon and stress‐strain curves were recorded by a high‐speed camera and universal testing machine. The microstructure of selected specimens was anatomized through adopting a scanning electron microscope (SEM) to correlate the mesoscale structural characteristics to their macroproperties. As the results indicated, in the case of quasistatic compression, the strength of the composites was decreased (the yield strength falling from 22.7 MPa to 13.6 MPa and the hardening modulus declining from 33.3 MPa to 25 MPa) with the increase of the Al particle size. The toughness rose firstly and subsequently decreased and peaked as 116.42 MJ/m3 at 6∼7 μm. The reaction phenomenon occurred only in composites with the Al particle size less than 10 μm. In drop weight tests, six types of specimens were overall reacted. As the Al particle size rose, the ignition energy of the composites enhanced and the composites turned out to be more insensitive to reaction. In a lower strain rate range (10−2·s−1∼102·s−1), Al‐PTFE specimens take on different mechanical properties and reaction characteristics in the case of different strain rates. The formation of circumferential open cracks is deemed as a prerequisite for Al‐PTFE specimens to go through a reaction.