Reinforced Carbon-Carbon Research Articles

Finite Element Analysis of the Carbon Fiber Reinforced Polymers (CFRP) With Epoxy Resin

The class of materials known as carbon fibre or graphite reinforced polymers is one in which carbon fibre is most frequently employed to strengthen composite materials. The matrix for carbon fibres can also be made of non-polymer materials. Carbon has had very modest success in metal matrix composite applications because of the development of metal carbides and concerns about corrosion. In high-temperature applications, reinforced carbon-carbon (RCC), which is made of graphite reinforced with carbon fibres, is employed structurally.
 
 The use of CFRP has grown since its inception because it provides classic metals like cast iron with considerably improved characteristics at a lower weight. Due to its unparalleled potential, this discovery has emerged as the new spearhead of material technology. In this study, the relationship between variations in the fibre mass and CFRP characteristics is examined. The test is conducted using ASTM standard test specimens and software from Ansys 2022 R1. Evaluating equivalent stress, strain, and total deformation of the composite under the same load is the main goal of this research.

Model for the Effect of Fiber Bridging on the Fracture Resistance of Reinforced-Carbon-Carbon

A micromechanical methodology has been developed for analyzing fiber bridging and resistance-curve behavior in reinforced-carbon-carbon (RCC) panels with a 3D composite architecture and a SiC surface coating. The methodology involves treating fiber bridging traction on the crack surfaces in terms of a weight function approach and a bridging law that relates the bridging stress to the crack opening displacement. A procedure has been developed to deduce material constants in the bridging law from the linear portion of the K-resistance curve. This approach has been applied to analyzing R-curves of RCC generated using double cantilever beam and single cantilever bend specimens to establish a bridging law for RCC. The bridging law has been implemented into a micromechanical code for computing the fracture response of a bridged crack in a structural analysis. The crack geometries considered in the structural analysis include the penetration of a craze crack in SiC into the RCC as a single-edge crack under bending and the deflection of a craze crack in SiC along the SiC/RCC interface as a T-shaped crack under bending. The proposed methodology has been validated by comparing the computed R-curves against experimental measurements. The analyses revealed substantial variations in the bridging stress (σo ranges from 11 kPa to 986 kPa, where σo is the limiting bridging stress) and the R-curve response for RCC due to the varying number of bridging ligaments in individual specimens. Furthermore, the R-curve response is predicted to depend on crack geometry. Thus, the initiation toughness at the onset of crack growth is recommended as a conservative estimate of the fracture resistance in RCC. If this bounding structural integrity analysis gives unacceptably conservative predictions, it would be possible to employ the current fiber bridging model to take credit for extra fracture resistance in the RCC. However, due to the large scatter of the inferred bridging stress in RCC, such an implementation would need to be probabilistically based.

Simulation of the Stagnation Region Microcrack Growth During Space Shuttle Reentry

The newly developed reinforced-carbon―carbon damage assessment model is applied to a micrometeoroid crack at the stagnation point of a sphere for a space shuttle reentry trajectory. The model, which has been validated against arcjet tests (Titov, E., Zhong, J., Levin, D., and Picetti, D., of Carbon―Carbon Crack Growth due to Carbon Oxidation in High Temperatures, Journal of Thermophysics and Heat Transfer, Vol. 23, No. 3, July― Sept. 2009, pp. 489―501.) (Titov, E., Levin, D., Picetti, D., and Anderson, B. P., Thermal Protection System Crack Growth Simulation Using Advanced Grid Morphing Techniques, Journal of Thermophysics and Heat Transfer, Vol. 24, No. 4, 2010, pp. 708―720.), predicts the microhole wall material response to the high-energy, atomic oxygen rich flow to simulate a micrometeoroid impact of the space shuttle nose cap shield during the STS-5 mission reentry. The extent of the crack damage site hole diameter was found to grow by a factor of 2.7, which agrees within about 30% of the NASA Johnson Space Center reinforced-carbon―carbon damage growth tool, version 2, a semi-empirical approach developed through extensive arcjet testing.

Thermal Protection System Crack Growth Simulation Using Advanced Grid Morphing Techniques

An extension of previous [Titov, E., Zhong, J., Levin, D., and Picetti, D., Simulation of RCC Crack Growth Due to Carbon in High-Temperature Gas Environments, Journal of Thermophysics and Heat Transfer, Vol. 23, No. 3, July-Sept. 2009, pp. 489-501.] modeling of crack damage growth in reinforced carbon-carbon specimens is presented in this work. The specimens were studied in an arcjet and represented a portion of the space shuttle wing [Lewis, R., Quick Look Report, Atmospheric Reentry Materials and Structures, 2004.] and a high-velocity meteoroid impact [Curry, D. M., Pham, V. T., Norman, I., and Chao, D. C., Oxidation of Reinforced Carbon-Carbon Subjected to Hypervelocity Impact, NASA TP 2000-209760, March 2000.]. The test geometry and flow conditions rendered the flow regime as transitional to continuum; therefore, a Navier-Stokes-based gas-dynamic approach with the temperature jump and velocity slip correction to the boundary conditions was used. The modeled mechanism for wall material loss was atomic oxygen reaction with the bare, exposed carbon surface. The purpose of this work is to improve the predictive modeling of crack growth damage assessment by developing procedures that use coupled, advanced topology-based surface and grid-meshing tools. A recessing three-dimensional surface morphing procedure was developed and tested by comparison with arcjet experimental results. A multiblock structured adaptive meshing was used to model the computational domain changes due to the wall recession. This approach made it possible to model full three-dimensional crack growth scenarios as well as to include the presence of realistic reinforced carbon-carbon material features such as delamination, both of which affect damage growth because they enable higher atomic oxygen penetration. Comparison with the arcjet data show that the inclusion of these two factors further improves the comparison between modeling and data. The predicted channel growth and shape change were found to agree with arcjet observations, and local gas flowfield results were found to affect the oxidation rate in a manner that cannot be predicted by previous mass loss correlations. The method holds promise for future modeling of materials gas-dynamic interactions for hypersonic flight.

Characterization and Oxidation Behavior of Rayon-Derived Carbon Fibers

Rayon-derived fibers are the central constituent of reinforced carbon/carbon (RCC) composites. Optical, scanning electron, and transmission electron microscopy were used to characterize the as-fabricated fibers and the fibers after oxidation. Oxidation rates were measured with weight loss techniques in air and oxygen. The as-received fibers are ~10 μm in diameter and characterized by grooves or crenulations around the edges. Below 800 °C, in the reaction-controlled region, preferential attack began in the crenulations and appeared to occur down fissures in the fibers.

Editorial: Ultra High Temperature Ceramics for Aerospace Applications

Improved interest in ultra-high-temperature ceramics (UHTCs) is being animating the scientific community. This emerging attention is driven by the demand of developing re-usable hot structures as thermal protection systems of aerospace vehicles, able to re-enter in planetary atmospheres at relatively high speed (order of 8-11 Km/s). In contrast to traditional blunt capsules or Shuttle-like vehicles, characterised by poor gliding capabilities and complex thermal protection systems, the future use of UHTCs opens new horizons for the development of spaceplanes with slender fuselage noses and sharp wing leading edges. Advanced aerodynamic configurations reduce the vehicles drag, enhance the vehicles performances, due to a larger manoeuvrability resulting in larger down range, cross range and abort windows, and reduce electromagnetic interferences and communications black-out. Analysis has shown that materials with temperature capability approaching 2000°C and above will be required for these space vehicles, but the state of the art Reinforced Carbon-Carbon (RCC) material, currently used on the Space Shuttle, have maximum use temperatures of approximately 1650°C. The articles collected in this issue provide state-of-art scientific advancements on the subject with particular attention to the potential technological applications. The papers specifically deal with research studies on monolithic ceramic materials, composed primarily of Zirconium and Hafnium Diborides with different additives. The activities are carried out at materials level, with furnace or arc-jet testing, or include developments of UHTC-based hot structures at sub-component level. In the latter case, ultra-high temperature ceramic prototype structures have been developed and tested with embedded structural health monitoring systems. I want to thank all the article contributors for their manuscripts. I hope they will be useful for future basic and applied researches on the subject.

Data Mining and Complex Problems: Case Study in Composite Materials

Data mining is defined as the discovery of useful, possibly unexpected, patterns and relationships in data using statistical and non-statistical techniques in order to develop schemes for decision and policy making. Data mining can be used to discover the sources and causes of problems in complex systems. In addition, data mining can support simulation strategies by finding the different constants and parameters to be used in the development of simulation models. This paper introduces a framework for data mining and its application to complex problems. To further explain some of the concepts outlined in this paper, the potential application to the NASA Shuttle Reinforced Carbon-Carbon structures and genetic programming is used as an illustration.

Oxidation of Carbon/Carbon through Coating Cracks

Reinforced carbon/carbon (RCC) is used to protect the wing leading edge and nose cap of the Space Shuttle Orbiter on re-entry. It is composed of a lay-up of carbon/carbon fabric protected by a SiC conversion coating. Due to the thermal expansion mismatch of the carbon/carbon and the SiC, the SiC cracks on cool-down from the processing temperature. The cracks act as pathways for oxidation of the carbon/carbon. A model for the diffusion controlled oxidation of carbon/carbon through machined slots and cracks is developed and compared to laboratory experiments. A symmetric cylindrical oxidation cavity develops under the slots, confirming diffusion control. Comparison of cross sectional dimensions as a function of oxidation time shows good agreement with the model. A second set of oxidation experiments was done with samples with only the natural craze cracks, using weight loss as an index of oxidation. The agreement of these rates with the model is quite reasonable.

Nondestructive Evaluation (NDE) for Characterizing Oxidation Damage in Cracked Reinforced Carbon–Carbon

In this study, coated reinforced carbon–carbon (RCC) samples of similar structure and composition as that from the NASA space shuttle orbiter's thermal protection system were fabricated with slots in their coating simulating craze cracks. These specimens were used to study oxidation damage detection and characterization using nondestructive evaluation (NDE) methods. These specimens were heat treated in air at 1143°C and 1200°C to create cavities in the carbon substrate underneath the coating as oxygen reacted with the carbon and resulted in its consumption. The cavities varied in diameter from approximately 1 to 3 mm. Single‐sided NDE methods were used because they might be practical for on‐wing inspection, while X‐ray micro‐computed tomography (CT) was used to measure cavity sizes in order to validate oxidation models under development for carbon–carbon materials. An RCC sample having a naturally cracked coating and subsequent oxidation damage was also studied with X‐ray micro‐CT. This effort is a follow‐on study to one that characterized NDE methods for assessing oxidation damage in an RCC sample with drilled holes in the coating.

Permanent set of the Space Shuttle Thermal Protection System Reinforced Carbon–Carbon material

The objective of this paper is to provide an interpretation and understanding of the permanent set (or deformation) phenomenon observed from debris impacts on Space Shuttle Thermal Protection System (TPS) Reinforced Carbon–Carbon (RCC) panels. Deflection test results for static and dynamic loadings of RCC material will be presented. Permanent set has been observed for both the static and dynamic loading onto RCC material, even for cases where no damage was detected using conventional Non-Destructive Evaluation (NDE) techniques. Although, the RCC material is considered to be brittle, the evidence of permanent set indicates a tough-brittle material behavior with plasticity. The post-test observation of permanent set, without NDE-detectable damage, indicates an opportunity for an alternative method for assessing debris impacts.

On-orbit passive thermography

On July 12, 2006, British-born astronaut Piers Sellers became the first person to conduct thermal nondestructive evaluation experiments in space, demonstrating the feasibility of a new tool for detecting damage to the reinforced carbon–carbon (RCC) structures of the Shuttle. This new tool was an extravehicular activity (EVA, or spacewalk) compatible infrared camera developed by NASA engineers. Data was collected both on the wing leading edge of the orbiter and on pre-damaged samples mounted in the Shuttle's cargo bay. A total of 10 infrared movies were collected during the EVA totaling over 250 MB of data. Images were downloaded from the orbiting Shuttle to Johnson Space Center for analysis and processing. Results are shown to be comparable to ground-based thermal inspections performed in the laboratory with the same type of camera and simulated solar heating. The EVA camera system detected flat-bottom holes as small as 2.54 cm in diameter with 50% material loss from the back (hidden) surface in RCC during this first test of the EVA IR Camera. Data for the time history of the specimen temperature and the capability of the inspection system for imaging impact damage are presented.

Use of focused pulse-echo ultrasonics for non-destructive inspection of thick carbon-carbon structures

The reinforced carbon-carbon (RCC) heat shield components on the Space Shuttle's wings must withstand harsh atmospheric re-entry environments where the wing leading edge can reach temperatures of 3000°F (about 1650°C). Potential damage includes impact damage, micro cracks, oxidation in the silicon carbide-to-carbon-carbon layers, and interlaminar disbands. The thick, carbon-carbon and silicon-carbide layers in the heat shield panels are difficult to inspect and existing techniques were deemed to be inadequate. Since accumulated damage in these structures can lead to catastrophic failure of the Shuttle's heat protection system, it became imperative for NASA to develop quickly an acceptable health monitoring programme. NASA selected a multi-method approach for inspecting the wing leading edge which includes eddy current, thermography, and ultrasonics. Sandia Labs produced the in-situ ultrasonic pitch-catch inspection method. Optimum combinations of custom ultrasonic probes and data analysis were merged into the overall inspection method needed to properly survey the heat shield panels. Comprehensive validation tests revealed that the ultrasonic pitch-catch inspection system is capable of reliably finding flaws of 0.25 diameter or less in the heat shields. The inspection system is now in use at NASA to complete 'Return-to-Flight' certification inspections prior to each Shuttle launch.

On the Use of the Transient Hot-Strip Method for Measuring the Thermal Conductivity of High-Conducting Thin Bars

The thermal conductivity of thin, high-conducting ceramic bars—commonly used in mechanical tensile testing—is measured using a variant of the short transient hot-strip technique. As with similar contact transient methods, the influence from the thermal contact resistance between the sensor and the sample is accurately recorded and filtered out from the analysis—a specific advantage that enables sensitive measurements of the bulk properties of the sample material. The present concept requires sensors that are square in shape with one side having the same width as the bar to be studied. As long as this requirement is fulfilled, the particular size of the thin bar can be selected at will. This paper presents an application where the present technique is applied to study structural changes or degradation in reinforced carbon–carbon (RCC) bars exposed to thermal cycling. Simultaneously, tensile testing and monitoring of mass loss are conducted. The results indicate that the present approach may be utilized as a non-destructive quality control instrument to monitor local structural changes in RCC panels.

Failure analysis of the space shuttle Columbia RCC leading edge

Failure analysis of the Columbia shuttle left T-seal 9 and an unidentified fragment of leading edge reinforced carbon-carbon (RCC) composite material was carried out to determine the causes of failure. Standard metallographic and microscopy procedures were employed to identify and characterize the failure mode. The results indicate that erosion and cracking occurred. Erosion was caused by the extreme temperatures and stress conditions experienced during the shuttle breakup in the upper atmosphere. Porosity, glassy phase, pinholes, and cracking in the silicon carbide (SiC) layer of the RCC material accelerated erosion and mass loss. Brittle cracking was also found in the SiC layer, and crack propagation was apparently enhanced by the flaws in the microstructure.

Oxidation microstructure studies of reinforced carbon/carbon

Laboratory oxidation studies of reinforced carbon/carbon (RCC) are discussed with particular emphasis on the resulting microstructures. This study involves laboratory furnace (500–1500 °C) and arc-jet exposures (1538 °C) on various forms of RCC. RCC without oxidation protection oxidized at 800 and 1100 °C exhibits pointed and reduced diameter fibers, due to preferential attack along the fiber edges. The 800 °C sample showed uniform attack, suggesting reaction control of the oxidation process; whereas the 1100 °C sample showed attack at the edges, suggesting diffusion control of the oxidation process. RCC with a SiC conversion coating exhibits limited attack of the carbon substrate at 500, 700 and 1500 °C. However samples oxidized at 900, 1100, and 1300 °C show small oxidation cavities at the SiC/carbon interface below through-thickness cracks in the SiC coating. These cavities at the outer edges suggest diffusion control. The cavities have rough edges with denuded fibers and can be easily distinguished from cavities created in processing. Arc-jet tests at 1538 °C show limited oxidation attack when the SiC coating and glass sealants are intact. When the SiC/sealant protection system is damaged, attack is extensive and proceeds through cracks, creating denuded fibers in and along the cracks. Even at 1538 °C, where diffusion control dominates, attack is non-uniform with fiber edges oxidizing preferentially.

Materials analysis: A key to unlocking the mystery of the Columbia tragedy

Materials analyses of key forensic evidence helped unlock the mystery of the loss of space shuttle Columbia that disintegrated February 1, 2003 while returning from a 16-day research mission. Following an intensive four-month recovery effort by federal, state, and local emergency management and law officials, Columbia debris was collected, catalogued, and reassembled at the Kennedy Space Center. Engineers and scientists from the Materials and Processes (M&P) team formed by NASA supported Columbia reconstruction efforts, provided factual data through analysis, and conducted experiments to validate the root cause of the accident. Fracture surfaces and thermal effects of selected airframe debris were assessed, and process flows for both nondestructive and destructive sampling and evaluation of debris were developed. The team also assessed left hand (LH) airframe components that were believed to be associated with a structural breach of Columbia. Analytical data collected by the M&P team showed that a significant thermal event occurred at the left wing leading edge in the proximity of LH reinforced carbon carbon (RCC) panels 8 and 9. The analysis also showed exposure to temperatures in excess of 1,649°C, which would severely degrade the support structure, tiles, and RCC panel materials. The integrated failure analysis of wing leading edge debris and deposits strongly supported the hypothesis that a breach occurred at LH RCC panel 8.