Ablator Research Articles

Multi-physical analysis of ablation for C/C composites based on peridynamics

C/C composite material is one of the most widely used thermal protection materials for hypersonic vehicles. As coupled with fluid dynamics, chemical reaction, heat transfer and ablation recession, its numerical simulation is challenging and complicated. In this study, a multi-physical analysis approach for the stripping process during ablation based on peridynamics is proposed. Aerodynamic parameters and heat flux distribution are determined by empirical formulas. The energy balance on the ablative wall has been taken into account for the thermal boundary conditions and the temperature field is obtained by using bond-based peridynamics. Then, the temperature-dependent dimensionless mass flux and surface recession rate are evaluated by solving the equations involving mass conservation of surface elements and chemical equilibrium of reactions. Meanwhile, considering the breaking of bonds and the deletion of material points in this model, the phenomenon of ablation and stripping process of material on the surface can be simulated. A C/C one-dimensional model is built to verify the effectiveness of the methodology, and the peridynamic results agree with the experimental observation from literatures well. Finally, after combining fluid dynamics, chemical reaction, heat transfer and ablation recession, the exterior shape and temperature field at a nose tip of a hypersonic vehicle are predicted.

Determination of tin in geological materials using LA-ICP-MS: Seemingly simple analysis?

Laser ablation inductively coupled plasma mass spectrometry is a unique technique designated for in situ analysis of a wide variety of solid samples. Nowadays, LA-ICP-MS is almost routinely used to study chemical and isotopic composition of geological materials. This paper reviews our experience with the analysis of tin in geological samples and comprehensively summarizes the limitations that may lead to inaccurate and imprecise outcomes. Experimental results show the extent of cross-contamination given by the ablation of materials containing tenths and tens of %m/m of Sn, and elucidate the impact of contamination on a background progress. Moreover, an analysis is also jeopardized by the occurrence of doubly charged ions of uranium as well as by the matrix effect amplified with operating conditions. Finally, the inhomogeneity of NIST SRM 614 is highlighted via 2D mapping especially within the rim area where tin content reaches up to 8 mg kg−1. Furthermore, a real quartz sample is subjected to LA-ICP-MS analysis to demonstrate the manifestation of discussed negative effects. The true tin content in quartz sample and NIST 614 is verified via GF-AAS. The result of NIST 614 bulk analysis is in a good agreement with GeoReM value.

Oxy-Butane Ablation Testing of Thermal Protection Systems Based on Nanomodified Phenolic Resin Matrix Materials.

Two classes of thermal protection systems composed of a carbon-fibre-reinforced (CFRP) layer and an ablative material layer joined with a thermo-resistant ceramic adhesive were developed. The two classes differ in the composition of the ablative material reinforcing compound. In the first class, the ablative material is based on micronic-sized cork granules, and in the second class, the ablative material is reinforced with carbonic felt. For both classes of thermal protection systems, the reinforcement material was impregnated in simple phenolic resin, and nanometric additive, consisting of silicon carbide nanoparticles added in two different weight contents (1 and 2% by weight) relative to the resin. The thermal conductivity for the ablative materials in the thermal protection systems structure was determined. A test facility using oxy-butane flame was developed through which the thermal protection systems developed were tested at extreme temperatures, to simulate some thermal conditions in space applications. The materials were characterised from a morphostructural point of view using optical and scanning electron microscopy after thermal testing. The TPS composed of the carbon-felt-based ablative layer showed improved behaviour compared to the cork-based ablative ones in terms of the temperature increase rate during thermal conductivity testing, mass loss, as well as morphostructural appearance and material erosion after oxy-butane testing. The nSiC-based samples in both sets of TPSs showed improved behaviour compared to the un-filled ones, considering the temperature increase, mass loss, and morphostructure of the eroded material.

Lightweight, strong, and thermally insulating polybenzoxazine aerogel thermal protection composites for antioxidant ablation long to 1800 s

The lightweight ablation materials that have been successfully applied in thermal protection systems (TPS) are the focus of attention owing to the urgent demand for aerospace vehicles to have efficient thermal insulation materials with lightweight, long-term antioxidant, and micro-ablation. However, improving the antioxidant ablation properties in a long-term aerobic atmosphere is still a significant challenge. Herein, a novel strategy to fabricate needle quartz fiber (NQF) reinforced SiO2 aerogel interpenetrating polybenzoxazine (PBO) aerogel thermal protection composites (NQF/SiO2–PBOs) with a binary network structure is proposed. The as-prepared NQF/SiO2–PBOs perfectly inherited their porous nanostructure and captivating properties, including lightweight (0.53 g/cm3), high mechanical strengths, and low thermal conductivity of 0.048 W/(m·K) at 25 °C and 0.079 W/(m·K) at 1100 °C. Moreover, the NQF/SiO2–PBOs exhibited outstanding high-temperature thermal insulation and long-time antioxidant ablation with low linear and mass ablation rates. The cold surface temperature peaked at approximately 307.2 °C within 1800 s when the hot surface temperature exceeded 1100 °C. The ablation/thermal insulation mechanism was also discussed through the analysis of the microstructure, chemical structure, and crystal structure. This research provides a meaningful reference for the development and exploitation of new advanced lightweight, long-term antioxidant, and micro-ablative thermal protective materials.

Reinforced compressive and ablative properties of phenolic aerogel by in-situ polycarbosilane-derived ceramic

Lightweight ablative materials owing to their low density, high efficiency heat insulation and excellent designability, which are considered as the most promising candidate materials in the field of aerospace ablative thermal protection. In this work, a polycarbosilane (PCS) in-situ reinforced carbon felt/phenolic (PR/Cf) aerogel composite is reported. The surface of aerogel and carbon fiber was coated with PCS protective layer by sol gel method and secondary vacuum impregnation process. The aerogel composite material possesses low density (0.264–0.307 g/cm3), hydrophobic, low thermal conductivity (0.121–0.178 W/(m·K)) and significant high compressive strength (12.89 MPa). When the oxygen acetylene flame with high heat flow density ablates for 20 s, it shows high efficiency in heat protection and insulation, and the linear ablation rate is as low as 0.089 mm/s. The PL/PR/Cf aerogel composite shows competitive and broad application prospects in the field of ablation heat protection in the future.

Analysis and Optimization of Contact Material Ablation under the Cumulative Effect of the Number of Breakings of OLTC.

Vacuum on-load tap-changers (OLTC) for converter transformers have a much higher number of breakings than conventional circuit breakers. Contact ablation after several breakings will affect the stability and life of the device. This paper establishes the electromagnetic thermal multi-physical field coupling model of the vacuum interrupter for OLTC based on the finite element analysis method. The thermal field distribution of normal and ablative contact materials during the breaking process was analyzed. The key parameters affecting the contact temperature under the cumulative number of breakings are analyzed and the optimized design is completed. The simulation results show that the contact surface reaches a maximum temperature of 1390 K at 8 ms. There is a significant increase in the area of the high-temperature area on the contact surface. The possibility of re-ignition of the interrupter is increased. Based on the judgment matrix method, the key influencing parameters of the contact temperature rise are analyzed. The final parameters are selected as follows: contact material-CuCr8 alloy, contact seat thickness-2 mm, contact thickness-10 mm, and contact diameter-40 mm.

Surface Laser Micropatterning of Polyethylene (PE) to Increase the Shearing Strength of Adhesive Joints

In the introduction, we present an overview of previous research on this subject in order to help the reader review possible technological solutions regarding the joining of construction materials. The original research presented in this article concerns the results of increasing the shear strength of adhesive joints of plastics using various types of surface preparation (laser texturing). Laser texturing consists in developing the surface by applying various geometric patterns of appropriate shapes and depths, as well as its density on the surface. The above parameters are currently selected in an empirical way as research is still being developed as part of a research project. The textures obtained in this way are subjected to microscopic examination. Then, a layer of glue is applied, and the samples prepared in this way, after drying, are subjected to various destructive tests, e.g., tensile, shear, and bending. In this article, we attempted to test the strength of the bonded joint of polyethylene (PE). The impact of a laser beam with ultrashort picosecond pulses was used in the research. Tools in the form of a TRUMPF TruMicro 5325c device integrated with a SCANLAB GALVO scanning head were used. This enabled ablative material removal without the presence of a heat affected zone (HAZ) in the non-laser part. Ultrashort laser pulses remove material without melting the non-exposed area by the laser beam. On the basis of the tests performed (in this article and previous research works of the authors), it was shown that the method increases the shear strength of the glued joints made in the tested construction materials. This is confirmed by laboratory results of tribological tests. The laser treatment parameters used, which are shown in this article, did not lead to the appearance of cracks in the micromachined materials. Research has shown that the connections between elements with a properly selected micropattern are characterized by a several-fold increase in the strength of joints, unlike materials without a micropattern. The presented method may be helpful for use as a technology for joining plastics.

Experiments of ablation characteristics for different nozzle materials and transient simulations on thermochemical erosion in hybrid rocket motors

This paper focuses on investigating ablation characteristics of different nozzle materials in hybrid rocket motors by firing tests and numerical simulations. Hybrid rocket nozzles with different ablation materials are designed and manufactured. Four firing tests with working time of 40 s are conducted, and 90% hydrogen peroxide and polyethylene are adopted. The test results indicate that erosion rates of T705 graphite, whole felt C/C composite, axial rod braided C/C composite, and carbon/ceramic composite are 0.045 mm/s, 0.022 mm/s, 0.03 mm/s, and 0.01 mm/s. Circumferentially uneven ablation is found in the nozzle throat of T705 graphite and C/C composite, and this is mainly due to asymmetric oxidizer injection, asymmetric combustion, and uneven material properties. Transient numerical simulations of 40 s on nozzle thermochemical erosion are carried out, and the regression process of fuel wall and nozzle wall is solved by a dynamic grid technique. The error of average throat erosion rate between simulation results and test results is only 1.82%. The evolution process of nozzle profile and flow field structure are exhibited, and coupling effects between the erosion rate and nozzle profile are obtained. Simulation results show that as the working time increases, protrusions and pits appear on the nozzle inner wall and gradually extend. The temperature of nozzle wall and nozzle erosion rate on the windward side is higher, while they are lower on the leeward side. Nozzle throat erosion rate history is divided into four stages, and time nonlinear characteristics of the throat erosion rate are revealed.

Tensile behaviors of nanoporous phenolic composites reinforced by 3D needle-punched preforms with different weave patterns

Needle-punched preform reinforced nanoporous phenolic composite (NPC) is a cost-effective lightweight ablative material for thermal protection systems. It consists of a needle-punched preform composed of alternating stacked fiber felt and stacked woven fabric, which plays a crucial role in the thermal insulation efficiency and mechanical properties. Herein, needle-punched preforms with different types of fabrics, including plain, twill, and satin, are deliberately designed for the reinforcement of NPC, and their tensile properties and fracture mechanism are investigated through experimentation and the CT image-based finite element method. At the same preform density, the composite with plain fabric exhibits the highest tensile strength of 146 ± 6.3 MPa, a tensile modulus of 8.2 ± 0.2 GPa, and an elongation of 2.1 ± 0.1%, due to having the highest number of crossover points and the largest undulation of fiber yarns. Furthermore, the CT image-based simulation reveals the failure mechanism of NPC. The von mises stress of woven fabric is higher than that of fiber felt, which demonstrates the woven fabric is the main load-bearing structure and determines the mechanical of composite. These results will provide useful guidance for the structural design and optimization of needle-punched preform reinforced composites.

Photocatalytic activity of hybrid Ag/Er:ZnO nanoparticles synthesized by pulsed laser ablation in distilled water

We have studied the photocatalytic performance of ZnO, Er:ZnO, hybrid Ag/ZnO, and Ag/Er:ZnO colloidal nanoparticles (NPs) synthesized by pulsed laser ablation of stoichiometric targets and silver plate in double distilled water. The x-ray diffraction (XRD) analysis revealed the polycrystalline structure of the ablated NPs. The morphology of the nanoparticles was examined by the transmission electron microscope (TEM). The optical properties of the prepared colloidal NPs were investigated by the UV-visible absorption and photoluminescence spectroscopies. The photodegradation of the Rhodamine 6G organic dye was utilized to evaluate the photocatalytic activity of the produced colloidal NPs under illumination by UV light. The hybrid Ag/Er:ZnO colloidal NPs showed enhanced photodegradation efficiency of 96.4%, after 45 min of UV irradiation, compared to 79.7% of the pristine ZnO NPs. The obtained results point out the enhancing effect of the dopants on the photocatalytic performance of ZnO, and further demonstrate the pulsed laser ablation of bulk materials in pure water as a fast and eco-friendly technique for producing efficient nanoparticle photocatalysts.

An open carbon–phenolic ablator for scientific exploration

Space exploration missions rely on ablative heat shields for the thermal protection of spacecraft during atmospheric entry flights. While dedicated research is needed for future missions, the scientific community has limited access to ablative materials typically used in aerospace. In this paper, we report the development of the HEFDiG Ablation-Research Laboratory Experiment Material (HARLEM), a carbon–phenolic ablator designed to supply the need for ablative materials in laboratory experiments. HARLEM is manufactured using polyacrylonitrile-based carbon fiber preforms and a simplified processing route for phenolic impregnation. We characterized the thermal protection performance of HARLEM in arcjet experiments conducted in the plasma wind tunnel PWK1 of the Institute of Space Systems at the University of Stuttgart. We assessed the performance of the new material by measuring surface recession rate and temperature using photogrammetry and thermography setups during the experiments, respectively. Our results show that HARLEM’s thermal protection performance is comparable to legacy carbon–phenolic ablators that have been validated in different arcjet facilities or in-flight, as demonstrated by calculations of the effective heat of ablation and scanning electron microscopy of as-produced samples. In-house manufacturing of carbon–phenolic ablators enables the addition of embedded diagnostics to ablators, allowing for the acquisition of data on internal pressure and more sophisticated pyrolysis analysis techniques.

Ab initio calculated dynamic structural factors and optical properties of beryllium along the Hugoniot

Beryllium is an ablator material used in inertial-confinement fusion and hypervelocity impact studies. The thermoelastic properties, structural factors, and optical properties of beryllium are important in these studies. In this paper, the static structural factors, ion–ion dynamic structural factors, adiabatic velocity, and optical properties of beryllium along the Hugoniot were calculated by ab initio simulations. The static structural factors show that beryllium atoms were randomly distributed. The dynamic structural factors extracted the dispersion relation for collective excitation via the scattering function. By collecting the peak position of the dynamic structural factors, the dispersion relation and adiabatic sound velocity were derived by definition. Using the calculated equation of state, the thermoelastic properties and adiabatic sound velocity have been derived. The two calculated methods for adiabatic sound velocity were verified to be equivalent.

Identifying the influence of bubble size and position on crater formation during underwater nanosecond laser ablation of stainless steel

Underwater laser ablation can be employed both as a means to produce nanoparticles and to texturize surfaces of various materials. In this approach, a stationary or flowing water layer above the target surface confines laser induced plasma which cools to form short lived cavitation bubbles, positively influencing the amount of removed material per laser pulse. Plasma and cavitation bubble evolution additionally give rise to bubbles which may persist in the water throughout the ablation process. These bubbles are known to have a detrimental effect on material removal rates particularly in stationary water, but the quantitative influence of bubble dimensions and position on removed material volume is currently unknown. Here we show the laser intensity profile changes induced by bubbles located at 0–0.4 Rayleigh lengths above a stainless steel surface and couple these changes to removed crater volume. Our results show that water flowing at Reynolds numbers in the range of 1–100 positively contribute to crater volumes for pulse frequencies up to 1 kHz. At 1 kHz, it was found bubbles have insufficient time to flow from the vicinity of the laser spot, regardless of the Reynolds number within the range investigated. These conclusions assist in selecting an appropriate combination of laser and flow conditions to optimize laser ablation material removal rate.

Effects of hydrogen concentration in ablator material on stimulated Raman scattering, two-plasmon decay, and hot electrons for direct-drive inertial confinement fusion

Effects of hydrogen concentration in ablator material on stimulated Raman scattering, two-plasmon decay, and hot electrons for direct-drive inertial confinement fusion

An improved theory of thermoelasticity for ultrafast heating of materials using short and ultrashort laser pulses

This paper introduces an improved thermoelastic theory designed specifically to address the challenges posed by fast and ultrafast heating of materials. The proposed theory incorporates a time delay in the temperature gradient and introduces the rate of temperature gradient as an additional term in the heat equation. This term accounts for the phase lag and the precedence of the temperature gradient and heat flux vector. By leveraging the sign of the temperature gradient rate, the theory automatically determines the precedence of either the temperature gradient or the heat flux vector. To verify the effectiveness of the proposed theory, experiments reported in the literature were simulated using several theories, namely the classical, Lord-Schulman (LS), Green-Lindsay (GL), dual-phase-lag (DPL), and the presented theory. The simulations considered the effects of relaxation times and pulse duration on the results. The findings reveal that for pulse durations shorter than 50 ps, the second-order time derivative of the temperature gradient becomes a crucial term in the energy equation for accurately predicting temperature profiles. Additionally, as the pulse duration decreases, the sensitivity to relaxation times increases. Regarding the surface temperature corresponding to the material ablation threshold, it is observed that for an 80 fs laser pulse, the ablation temperature falls between the boiling and critical temperatures, significantly higher than the boiling temperature associated with the ablation by a 270 ps pulse duration. Lastly, the simulation results exhibit a high level of agreement with the experimental data, particularly in terms of displacements, further validating the accuracy of the presented simulations.

Application of the Markov chain Monte Carlo analysis through a lumped model in ablation test results of ablative and reradiative materials

High heat fluxes generated by aerodynamic heating or rocket propellant burning create a high demand for the use Thermal Protection Systems (TPS) to prevent damage or malfunctioning in payloads and rocket parts. Thermophysical and ablative properties of TPS materials are needed for their design, but are commonly unavailable or difficult to access experimentally. Besides, materials present different responses to high heat fluxes according to their composition and manufacturing process. Inverse heat transfer problems were initially studied to determine not known variables in thermal behavior of space vehicles and have proven to reach reliable properties values of ablative materials. This work applies an already validated methodology, using the Markov chain Monte Carlo (MCMC) method applied to a lumped physical model of ablation, to determine thermophysical and ablation properties of different composite materials starting from arc-jet ablation results. The direct problem with a more refined mesh and the obtained values of these properties was used and the numerical results were compared to the experiments, presenting good agreement and resulting in lower rms values, when compared to original values extracted from literature.

Modeling of Electron and Lattice Temperature Distribution Through Lifetime of Plasma Plume

When employing shorter (sub picosecond) laser pulses, in ablation kinetics the features appear which can no longer be described in the context of the conventional thermal model. Meanwhile, the ablation of materials with the aid of ultra-short (sub picosecond) laser pulses is applied for micromechanical processing. Physical mechanisms and theoretical models of laser ablation are discussed. Typical associated phenomena are qualitatively regarded and methods for studying them quantitatively are considered. Calculated results relevant to ablation kinetics for a number of substances are presented and compared with experimental data. Ultra-short laser ablation with two-temperature model was quantitatively investigated. A two-temperature model for the description of transition phenomena in a non-equilibrium electron gas and a lattice under picosecond laser irradiation is proposed. Some characteristics are hard to measure directly at all. That is why the analysis of physical mechanisms involved in the ablation process by ultra-short laser pulses has to be performed on the basis of a theoretical consideration of `indirect' experimental data. For Copper and Nickel metal targets, the two-temperature model calculations explain that the temperature of the electron subsystem increased suddenly and approached a peak value at the end of laser pulse. In addition, the temperature profile of lattice temperature subsystem evolution slowly, and still increasing after the end of laser pulse. A good agreement prevails when a comparison between the present results and published results.

Study on surface quality and mechanical properties of micro-milling WE43 magnesium alloy cardiovascular stent

Traditional laser processing technique is mainly applied for cardiovascular stent manufacture, especially for materials with high mechanical properties and high melting point, while it usually produces problems such as material ablation and defects during finish machining process. Magnesium alloy, as material candidate for bioresorbable cardiovascular stent, has low melting and ignition point, high oxidizability property. Laser processing technique scarcely meets the requirements of high surface quality of magnesium alloy cardiovascular stents, this paper firstly develops a five-axis micro-milling technique to fabricate magnesium alloy cardiovascular stents. Milling orthogonal test was carried out to obtain the optimal finish machining parameters, and then a novel stent machining process was established. The processed stent has an inner diameter of 1.5 mm, a thickness of 80 μm and a length of 8 mm with a U-bend width of 100 μm and a link strut width of 70 μm, and the optimal finish processing parameters was set up with the main spindle speed of 30,000 rpm, feed speed 200 mm/min, cutting width 50 μm and cutting depth 40 μm. The dimensional accuracy and surface topography of the magnesium alloy stent were measured and characterized, and results showed that the dimensional accuracy was within 0.01 mm, and the machined stent achieved better surface quality without obvious processing defects such as pits, grooves and pores while comparing with the stent under original processing parameters. In order to evaluate the radial support performance of the stent, the radial compression and expansion experiments and simulations were conducted, respectively. Results showed that the maximum diameter error in the experiment and simulation was 13.35 %, and the radial recoiling error was 16.79 %. This work provides a potential stent manufacture technique in the development and clinical application of bioresorbable magnesium alloy stent.

Fully Coupled Material Response and Internal Radiative Heat Transfer for Three-Dimensional Heat Shield Modeling

A material response code is strongly coupled with a radiative transfer equation (RTE) to evaluate the effect of a spectrally resolved heat flux on the thermal response of a heat shield. A P1 approximation model of RTE is used to account for radiation heat transfer within the material. First, the RTE model is verified by comparing the numerical results with the analytical solution. Next, the coupling scheme is verified by comparing the temperature histories computed by the pure conduction scheme with the ones computed by conduction coupled with radiative emission. The verification study is conducted using test cases from the literature (radiant heating, arc jet heating, and space shuttle entry) as well as on a 3D Block, a 2D IsoQ sample, and the Stardust Return Capsule. The verification results are satisfactory for all cases. Thus, the verification results indicate that the coupling approach can accurately simulate the thermal response of the material. The coupling scheme was then used to simulate a laser heating experiment that studied the impact of spectral radiative heat transfer on ablative material. The results from the laser ablation simulations exhibit a behavior analogous to the experimental observations, indicating the importance of spectral radiative flux on the material response.

Thermal oxidation and compressive failure behavior of ZrSi2–B4C modified phenolic resin-based composite

Phenolic resin-based ablative materials have gained significant attention in the aerospace sector in recent years. In this study, TGA-DSC, FT-IR, XRD and XPS were employed to the thermal stability and phase transformation of the ZrSi2–B4C modified quartz fiber/boron containing phenolic resin (QF/BPR) composite. The compressive failure behavior of the composite at 600–1200 °C was studied through SEM and high-speed camera techniques. The results indicated that the compression strength of the composite decreased to a minimum at 600 °C and increased at 800–1200 °C. The composite exhibited different failure modes at different temperature: shear fracture at room temperature (RT), debonding of the fiber bundles at 600 °C, fiber buckling and fiber shear fracture at 800 °C, fiber buckling and delamination at 1000–1200 °C. The improvement in thermal stability of composite was primarily attributed to the formation of ZrO2, SiO2 and B2O3, which covered the fiber and effectively transmitted the load, leading to an enhanced strength of the interface between the fiber and resin.