Applications of Additive Manufacturing Techniques in Making Energetic Materials

Energetic materials are currently manufactured using methods such as casting, which can only produce certain geometries. Additive manufacturing enables more flexible fabrication and the potential for improved material consistency. Additive manufacturing has transformed many industries, but has only recently been applied to the manufacturing of energetic materials. This paper describes the development of two processes to apply additive manufacturing methods to energetic materials. Method one applies a fused deposition modelling approach (FDM). 5 µm aluminum powder and PVDF were mixed and made into filaments using a Filabot Original filament extruder. Energetic filaments were created composed of 90:10, 80:20, and 75:25 mixtures of PVDF:Al by mass. These filaments had reactive sections, but did not have consistent composition and could not sustain self-propagating reactions. The second method had the goal of mixing ammonium perchlorate (AP) into a curable polymer which solidifies under UV light. Powdered sugar was used in place of AP to simulate the viscosity while testing extrusion and printing capabilities. The powdered sugar and UV Cure mixture could be extruded using a syringe pump when the powdered sugar to UV Cure ratio was 3:1, but this mixture would not stick to the print bed. Both processes need refinement to produce functional energetic materials. This paper forms a foundation for further development of processes in which additive manufacturing can be safely used to produce energetic materials

SecureMEMS: Selective Deposition of Energetic Materials

There exists a pressing operational need to secure and control access to high-valued electromechanical systems, and in some cases render them inoperable. Developing a reliable method for depositing energetic materials will allow for the near-seamless integration of electromechanical systems and energetic material, and, in turn, provide the pathway for security and selective destruction that is needed. In this work, piezoelectric inkjet printing was used to selectively deposit energetic materials. Nanothermites, comprising of nanoscale aluminum and nanoscale copper oxide suspended in dimethyl-formamide (DMF), were printed onto silicon wafers, which enabled both thermal and thrust measurements of the decomposing energetic material. Various solids loadings were studied in order to optimize printing characteristics. Going forward, further studies will focus on the plausibility of inkjet printing other energetic materials for the purposes of the degradation of electromechanical systems

High Speed X-ray Phase Contrast Imaging of Energetic Composites under Dynamic Compression

Fracture of crystals and frictional heating are associated with the formation of “hot spots” (localized heating) in energetic composites such as polymer bonded explosives (PBXs). Traditional high speed optical imaging methods cannot be used to study the dynamic sub-surface deformation and the fracture behavior of such materials due to their opaque nature. In this study, high speed synchrotron X-ray experiments are conducted to visualize the in situ deformation and the fracture mechanisms in PBXs composed of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) crystals and hydroxyl-terminated polybutadiene binder doped with iron (III) oxide. A modified Kolsky bar apparatus was used to apply controlled dynamic compression on the PBX specimens, and a high speed synchrotron X-ray phase contrast imaging (PCI) setup was used to record the in situ deformation and failure in the specimens. The experiments show that synchrotron X-ray PCI provides a sufficient contrast between the HMX crystals and the doped binder, even at ultrafast recording rates. Under dynamic compression, most of the cracking in the crystals was observed to be due to the tensile stress generated by the diametral compression applied from the contacts between the crystals. Tensile stress driven cracking was also observed for some of the crystals due to the transverse deformation of the binder and superior bonding between the crystal and the binder. The obtained results are vital to develop improved understanding and to validate the macroscopic and mesoscopic numerical models for energetic composites so that eventually hot spot formation can be predicted

Epoxy–PCM Composites with Nanocarbons or Multidimensional Boron Nitride as Heat Flow Enhancers

The article of record as published may be found at https://doi.org/10.3390/molecules24101883The need for a ordable systems that are capable of regulating the temperature of living or storage spaces has increased the interest in exploring phase change materials (PCMs) for latent heat thermal energy storage (LHTES). This study investigates n-nonadecane (C19H40) and n-eicosane (C20H42) as alkane hydrocarbons/para ns for LHTES applications. An epoxy resin is used as the support matrix medium to mitigate para n leakage, and a thickening agent is utilized to suppress phase separation during the curing process. In order to enhance the thermal conductivity of the epoxy–para n composite, conductive agents including carbon nanofibers (CNFs), carbon nanotubes (CNTs), boron nitride (BN) microparticles, or boron nitride nanotubes (BNNTs) are incorporated in di erent gravimetric ratios. Enhancements in latent heat, thermal conductivity, and heat transfer are realized with the addition of the thermal fillers. The sample composition with 10 wt.% BN shows excellent reversibility upon extended heating–cooling cycles and adequate viscosity for template casting as well as direct three-dimensional (3D) printing on fabrics, demonstrating the feasibility for facile integration onto liners/containers for thermal regulation purposes.National Research Council Research Associateship Program (NRC-RAP)Office of Naval Research (ONR) through their Energy Systems Technology Evaluation Program (ESTEP)Naval Postgraduate School (NPS) Foundation seed fundin

The effect of interface shock viscosity on the strain rate induced temperature rise in an energetic material analyzed using the cohesive finite element method

The article of record as published may be found at https://doi.org/10.1088/1361-651X/ab2224In this work, shock induced failure and local temperature rise behavior of a hydroxyl-terminated polybutadiene (HTPB)—ammonium perchlorate (AP) energetic material is modeled using the cohesive finite element method (CFEM). Thermomechanical properties used in the model were obtained from four different experiments: (1) dynamic impact experimental measurements for fitting a viscoplastic constitutive model, (2) in situ mechanical Raman spectroscopy (MRS) measurements of the separation properties for fitting a cohesive zone model, (3) a pulse laser induced particle impact experiment combined with the MRS for measurement of the interface shock viscosity, and (4) Raman thermometry experiments for measurement of HTPB, AP, and HTPB-AP interface thermal conductivity. HTPB-AP interface regions with high density of particles were found to be more susceptible to local temperature rise due to the presence of viscoplastic dissipation as well as frictional heating. The increase in the interface shock viscosity lead to a decrease in both the viscoplastic and frictional dissipation. This resulted in a decrease in the maximum temperature and the density of local regions with a maximum temperature rise within the HTPB-AP microstructure. A power law relation for the decrease in viscoplastic energy dissipation, temperature rise and the density of the local temperature rise with the interface shock viscosity was obtained

Listen, Learn, Lead – Dr. Amela Sadagic, Dr. I Emre Gunduz and Dr. Geraldo Ferrer, Additive Manufacturing

Across the university, leaders in a wide range of disciplines are providing advanced, interdisciplinary education and secure research experiences that foster critical thinking and advance leadership skills in our graduates. Listen, Learn, Lead with NPS President retired Vice Adm. Ann E. Rondeau introduces these extraordinary campus leaders, and the invaluable contributions they make to the university, and to the Navy and nation.Episode #1

Simulation guided experimental interface shock viscosity measurement in an energetic material

The article of record as published may be found at http://dx.doi.org/10.1088/1361-651X/ab4148Experimental measurements of interface shock viscosity in hydroxyl-terminated polybutadiene (HTPB)-ammonium perchlorate (AP) material system are performed using mechanical Raman spectroscopy (MRS) combined with laser pulse shock loading. First, HTPB-AP interface level shock wave propagation is studied using the cohesive finite element method. The difference in the shock behavior of the analyzed HTPB-AP interfaces from that of the bulk AP and HTPB material is highlighted by numerical simulations of impacting a single AP particle in an HTPB-AP sample in three different ways: (1) a flyer plate is used to impact the whole HTPB-AP sample; (2) a flat impacter is used to impact the middle of AP particle embedded in HTPB matrix directly; and (3) a HTPB-AP interface is directly impacted with an impacter of radius 1 μm. Shock wave rise time at the interface is shown to differ for the three different impact modes. Based on the simulation results, a combined MRS and pulse laser-induced particle impact test is used for measuring shock viscosity at HTPB-AP interfaces. It is observed that by changing the chemical composition of the interface, shock viscosity can be altered. A modified finite element model with viscous stress based on shock viscosity values added to the stress equation is then used for the shock impact simulation of an HTPB-AP material system. A power law relation was obtained between shock wave rise time and the shock viscosity.Air Force Office of Scientific Research, Dynamic Materials and Interactions program (Grant No. FA9550-15-1- 0202

Simulation guided experimental interface shock viscosity measurement in an energetic material

The article of record as published may be found at https://doi.org/10.1088/1361-651X/ab4148Experimental measurements of interface shock viscosity in hydroxyl-terminated polybutadiene (HTPB)-ammonium perchlorate (AP) material system are performed using mechanical Raman spectroscopy (MRS) combined with laser pulse shock loading. First, HTPB-AP interface level shock wave propagation is studied using the cohesive finite element method. The difference in the shock behavior of the analyzed HTPB-AP interfaces from that of the bulk AP and HTPB material is highlighted by numerical simulations of impacting a single AP particle in an HTPB-AP sample in three different ways: (1) a flyer plate is used to impact the whole HTPB-AP sample; (2) a flat impacter is used to impact the middle of AP particle embedded in HTPB matrix directly; and (3) a HTPB-AP interface is directly impacted with an impacter of radius 1 μm. Shock wave rise time at the interface is shown to differ for the three different impact modes. Based on the simulation results, a combined MRS and pulse laser-induced particle impact test is used for measuring shock viscosity at HTPB-AP interfaces. It is observed that by changing the chemical composition of the interface, shock viscosity can be altered. A modified finite element model with viscous stress based on shock viscosity values added to the stress equation is then used for the shock impact simulation of an HTPB-AP material system. A power law relation was obtained between shock wave rise time and the shock viscosity

Epoxy–PCM Composites with Nanocarbons or Multidimensional Boron Nitride as Heat Flow Enhancers

The need for affordable systems that are capable of regulating the temperature of living or storage spaces has increased the interest in exploring phase change materials (PCMs) for latent heat thermal energy storage (LHTES). This study investigates n-nonadecane (C19H40) and n-eicosane (C20H42) as alkane hydrocarbons/paraffins for LHTES applications. An epoxy resin is used as the support matrix medium to mitigate paraffin leakage, and a thickening agent is utilized to suppress phase separation during the curing process. In order to enhance the thermal conductivity of the epoxy–paraffin composite, conductive agents including carbon nanofibers (CNFs), carbon nanotubes (CNTs), boron nitride (BN) microparticles, or boron nitride nanotubes (BNNTs) are incorporated in different gravimetric ratios. Enhancements in latent heat, thermal conductivity, and heat transfer are realized with the addition of the thermal fillers. The sample composition with 10 wt.% BN shows excellent reversibility upon extended heating–cooling cycles and adequate viscosity for template casting as well as direct three-dimensional (3D) printing on fabrics, demonstrating the feasibility for facile integration onto liners/containers for thermal regulation purposes

The role of microstructure in the impact induced temperature rise in hydroxyl terminated polybutadiene (HTPB)ﾖcyclotetramethylene- tetranitramine (HMX) energetic materials using the cohesive finite element method

This paper was Featured, and appeared on the cover of the JournalThe article of record as published may be found at https://doi.org/10.1063/5.0011264In this work, microstructure dependent impact-induced failure of hydroxyl-terminated polybutadiene (HTPB)ﾖcyclo-tetra-methylene-tetra- nitramine (HMX) energetic material samples is studied using the cohesive finite element method (CFEM). The CFEM model incorporates experimentally measured viscoplastic constitutive behavior, experimentally measured interface level separation properties, and phenomeno- logical temperature increase due to mechanical impact based on viscoplastic and frictional energy dissipation. Nanoscale dynamic impact experiments were used to obtain parameters for a strain-rate dependent power law viscoplastic constitutive model in the case of bulk HTPB and HMX as well as the HTPBﾖHMX interfaces. An in situ mechanical Raman spectroscopy (MRS) setup was used to obtain bilinear cohe- sive zone model parameters to simulate interface separation. During analyses, the impact-induced viscoplastic energy dissipation and the frictional contact dissipation at the failed HTPBﾖHMX interfaces is found to have a significant contribution toward local temperature rise. Microstructures having circular HMX particles show a higher local temperature rise as compared to those with diamond or irregularly shaped HMX particles with sharp edges indicating that the specific particle surface area has a higher role in temperature rise than particle shape and sharp edges. Regions within the analyzed microstructures near the HTPBﾖHMX interfaces with a high-volume fraction of HMX particles were found to have the maximum temperature increase.Financial support from the Air Force Office of Scientific Research (AFOSR), Dynamic Materials and Interactions Program (Grant No. FA9550-19-1-0318Financial support from the Air Force Office of Scientific Research (AFOSR), Dynamic Materials and Interactions Program (Grant No. FA9550-19-1-031