Maurizio Natali

Development of an Experimental Apparatus for Ablative Nanocomposites Testing

This study involves the design of a small scale apparatus to test ablative materials, which are commonly used to provide thermal protection to key structural components of solid rocket motors (SRMs). The testing of these materials involves subjecting them to extreme heat and fluid velocities while measuring the resulting temperature on various points of the sample. Observation of the front and back face temperatures during testing, as well as post test analysis of material erosion and mass loss, can provide a quick assessment of the efficacy of newly developed ablative materials. The setup developed through this project is designed to be a small-scale device with quantified heat input and temperature values for the testing of ablatives such as carbon/phenolic composites, C/C composites, conventional polymer composites, and polymer nanocomposites. This device will perform tests on small samples of ablative materials with a front face of roughly 12.7 x 12.7mm (0.5 x 0.5 in.) and 15-50mm thickness. A high temperature flame produced through the use of an oxyacetylene torch system will be directed and focused on this small sample face through the use of a welding nozzle, which will accelerate the flame towards the sample at high velocity. Prior to testing and in order to properly quantify the heat flux generated by this device, a slug calorimeter is used to calibrate the flame by measuring the rate of change of temperature for a slug of material at different distances from the nozzle exit. Data is gathered during testing through the use of multiple thermocouples to measure the back face and/or heat soak temperatures of the sample. These readings are obtained using a data acquisition (DAQ) card and recorded over time using a LabView VI. Due to a specific procedure required to light the oxyacetylene torch, the testing method for this device involves first lighting the torch and adjusting it to the proper fuel ratio, then moving the torch along a single axis slide up to the specified testing distance (used to determine input flux). The data of initial material testing with this apparatus are compared to knowledge of the materials tested, as well as data from tests with a similar apparatus to determine the overall validity of the results gathered from the developed apparatus.

Inelastic Takahashi hard-rod gas.

We study a one-dimensional fluid of hard rods interacting with each other via binary inelastic collisions and a short-ranged square-well potential. Upon tuning the depth and the sign of the well, we investigate the interplay between dissipation and cohesive or repulsive forces. Molecular-dynamics simulations of the cooling regime indicate that the presence of this simple interparticle interaction is sufficient to significantly modify the energy dissipation rates expected by Haffs law for the free cooling. The simplicity of the model makes it amenable to an analytical approach based on the Boltzmann-Enskog transport equation which allows deriving the behavior of the granular temperature. Furthermore, in the elastic limit, the model can be solved exactly to provide a full thermodynamic description. A meaningful theoretical approximation explaining the properties of the inelastic system in interaction with a thermal bath can be directly extrapolated from the properties of the corresponding elastic system, upon a proper redefinition of the relevant observables. Simulation results both in the cooling and driven regimes can be fairly interpreted according to our theoretical approach and compare rather well to our predictions.

In-situ ablation recession sensor based on ultra-miniature thermocouples - part a: 0.25 mm diameter thermocouples

In this research, a break-wire like recession sensor based on commercial, ultra-small thermocouples (250 μm diameter) was designed and tested. A series of thermocouples (TCs) are embedded in the thermal protection systems (TPS), perpendicularly at the ablator surface. Each sensing head of the TC is positioned at a well-established depth from the surface. During the heating of the ablator, the TCs would first work as a temperature sensor providing precious information about the state of the TPS. When the temperature rises above the melting point of the metal sheath and of the Seebeck junction, the TC would break. Due to this double nature of the sensing heads – as a traditional Seebeck junction and as a position marker it would be possible to obtain a wide range of data on the recession state of the TPS. The proposed ablation recession sensor was tested on carbon/carbon (CC) composites and it was tested under a severe hyperthermal environment produced using an oxy-acetylene test bed. Two types of CC materials with different densities (LDCC=1.34 g/cc and HDCC=1.70 g/cc) were considered. At the same time, two different configurations were tested (4 levels and 8 levels). The obtained results were quite encouraging showing the TCbased approach can provide accurate data on the recession rate of the TPS material. Due to the uniqueness of the proposed sensing technique, it can be applied both on TPS of spacecraft as well as on rocket nozzles. Moreover, the proposed approach uses low cost, commercially available TCs and processing techniques.

An investigation of compressive and shear strength of char from polymer nanocomposites for propulsion applications

Ablative material is used in solid rocket motors (SRMs), since the formation of a char layer provides thermal protection to key structural components during motor firings. The char strength of thermoplastic polyurethane elastomer nanocomposites (TPUNs) is of particular interest due to its potential as a replacement for the current industry standard, Kevlar®-filled EPDM. TPUNs are being considered to replace Kevlar®-filled EPDM for a number of reasons, primarily because: TPUNs exhibit superior ablation and insulative characteristics, easy fabrication, and are recyclable. Due to the fragile nature of the charred TPUNs, ordinary testing methods (e.g., Rockwell hardness) are not feasible; thus necessitating the creation of a testing protocol and sensor. This study encompasses the improvement of a compressive testing protocol and sensor for evaluating the strength of the char layer of SRM insulation materials and also the early stages of a shear testing protocol. The compression protocol that was developed is the continuation of previous work which has shown potential in determining the comparative strengths between different SRM insulation materials. Building on prior art, a crushing test method was further developed and a sensor platform was assembled to perform crushing tests as well as the addition of a shear test. The test procedure consists of measuring the amount of force required to crush an area of the charred sample for a specified penetration depth. The shear test involves shearing off the char from a horizontal direction. During the shear test, the force required to shear off the char completely is measured. The test is repeated for different types of TPUNs that consist of carbon nanofibers, montmorillonite organclays, and multi-walled carbon nanotubes; and the current industry standard Kevlar®-filled EPDM. For both the crushing and shearing tests, the energy dissipated is quantified to determine which TPUN exhibited the best performance. The test is fully automated to ensure repeatability of each measurement and to remove the potential for human-induced error.

PHENOLIC MATRIX NANOCOMPOSITES BASED ON COMMERCIAL GRADE RESOLS SYNTHESIS, CHARACTERIZATION AND COMPARISON WITH MICROCOMPOSITES

Polymer layered silicate nanocomposites based on a commercial grade resol were produced using a simple, low labor cost mechanical approach, providing an effective alternative to the more traditional technique based on the use of the intercalative polymerization of phenol and formaldehyde monomers. The matrix was a resol diluted in methanol. The selected nanoclay was Cloisite® 30B. Two kind of nanocomposites were studied: the first one prepared at a nanoclay percentage equal to 5% and, the second one, produced at 20% nanoclay percentage. Finally, a comparison between these nanocomposites and a blend loaded with 20% of micrometric silica, was performed. The produced materials were studied by means of X‐ray diffraction, SEM and thermogravimetric analysis. The first nanocomposite showed a good degree of dispersion as well as distribution of the nanoclay platelets. SEM images even showed that high loaded nanocomposite exhibited a morphology very similar to a porous media. According to thermogravimetric analysi...

Thermoset Nanocomposites as ablative materials for rocket and military applications

Abstract Ablative materials are at the base of entire aerospace industry; these sacrificial materials enable the production of propulsion devices [such as liquid and solid rocket motors (SRMs)] or protect vehicles and probes during the hypersonic flight through a planetary atmosphere. They are also known as thermal protection system (TPS) materials. Some nonpolymeric materials have been successfully used as ablatives; however, due to their versatility, polymeric ablative materials (PAMs) represent the widest family of sacrificial TPS materials. In fact, when compared with nonpolymeric ablatives such as high-melting-point metals and inorganic polymers (or metal oxides or carbides), PAMs have some intrinsic advantages such as tunable density, higher heat shock resistance, and lower cost. This chapter covers all main areas related to the science and technology of military PAMs based on thermoset matrices.

MWNT‐Doped Epoxy Matrix for Detecting Impact Damages in Fiber Reinforced Composites by Electrical Resistance Measurements

In this paper, we report the development of a glass fiber reinforced composite based on a MWNT‐doped epoxy matrix. The intrinsic electrical conductivity of carbon nanotubes has allowed the production of a nanocomposite with enhanced electrical properties, respect the neat matrix. Due to the high aspect ratio of carbon nanotubes, very small amounts of these particles were enough for modifying the electrical properties of the obtained glass fiber composites. A low‐velocity impact was created on the surface of the laminate, in order to produce a damage, which not involved the catastrophic failure of the sample. In order to evaluate the damage level, a mechanical characterization was performed on pristine samples, on one hand, and impacted The measurement of the electrical resistance, before and after the impact, was exploited as a way for detecting the presence of the damage produced. The results have shown that it is possible to associate the increase in electrical resistance of the composite with the forma...