This document summarizes a study on the ablation behavior of carbon/carbon (C/C) composites under different temperature conditions simulated using an arc plasma heater. Three key points:
1) C/C composite samples were tested in oxygen-lean (~4750 K) and oxygen-rich (~2467 K) temperature regimes in the plasma heater to study the effects of sublimation and oxidation on ablation rates. Ablation rate increased with higher oxygen conditions.
2) Back-face temperatures and residual compressive strength were tested on samples exposed to the extreme temperature conditions. The 4750 K sample showed toughening in the affected zone while the 2467 K sample showed lower strength and modulus.
Simulation of curing process of carbon/epoxy composite during autoclave degas...Darkdragon766
Simulation of curing process of carbon/epoxy composite during
autoclave degassing molding by considering phase changes of epoxy
resin
Seong-Hwan Yoo a, b
, Min-Gu Han a
, Jin-Ho Hong a
, Seung-Hwan Chang a, *
a School of Mechanical Engineering, Chung-Ang University (CAU), 221, Huksuk-Dong, Dongjak-Gu, Seoul 156-756, Republic of Korea
b Korea Photonics Technology Institute Lighting Solution R&BD Center, Gwangju, Republic of Korea
Effect Of Curing Temperature And Curing Hours On The Properties Of Geo-Polyme...ijceronline
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
A Result Paper on Experimental Investigation on CMAijtsrd
There are various roadway construction activities and plans that involve the use of flexible pavement having hot mix technique. This hot mix technique is a traditional method for the construction of road that has fulfilled the performance evaluation from infrastructure point of view throughout the past years. The various processes which are involved in this technique are providing heat to the aggregate and binder, proper mixing, provision of tack coat as per the specifications, laying of the mixed, the process of compaction. The cold mixed technique having use of bitumen emulsion on large scale should be epicenter of the study such that this technology may advance its application in present as well as future with proper specifications, testing throughout. The Hot mixed based techniques have gone through the significant advancements with time. The Cold mixed based technology is somewhere lagging in terms of applications which might be observed in the developing countries. In the present study, it has been the primary motivation that underlies the selection of cold mixed technique. Manoj Sheoran | Ms. Shivani "A Result Paper on Experimental Investigation on CMA" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-5 , August 2021, URL: https://www.ijtsrd.com/papers/ijtsrd45179.pdf Paper URL: https://www.ijtsrd.com/engineering/other/45179/a-result-paper-on-experimental-investigation-on-cma/manoj-sheoran
Simulation of curing process of carbon/epoxy composite during autoclave degas...Darkdragon766
Simulation of curing process of carbon/epoxy composite during
autoclave degassing molding by considering phase changes of epoxy
resin
Seong-Hwan Yoo a, b
, Min-Gu Han a
, Jin-Ho Hong a
, Seung-Hwan Chang a, *
a School of Mechanical Engineering, Chung-Ang University (CAU), 221, Huksuk-Dong, Dongjak-Gu, Seoul 156-756, Republic of Korea
b Korea Photonics Technology Institute Lighting Solution R&BD Center, Gwangju, Republic of Korea
Effect Of Curing Temperature And Curing Hours On The Properties Of Geo-Polyme...ijceronline
International Journal of Computational Engineering Research (IJCER) is dedicated to protecting personal information and will make every reasonable effort to handle collected information appropriately. All information collected, as well as related requests, will be handled as carefully and efficiently as possible in accordance with IJCER standards for integrity and objectivity.
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology
A Result Paper on Experimental Investigation on CMAijtsrd
There are various roadway construction activities and plans that involve the use of flexible pavement having hot mix technique. This hot mix technique is a traditional method for the construction of road that has fulfilled the performance evaluation from infrastructure point of view throughout the past years. The various processes which are involved in this technique are providing heat to the aggregate and binder, proper mixing, provision of tack coat as per the specifications, laying of the mixed, the process of compaction. The cold mixed technique having use of bitumen emulsion on large scale should be epicenter of the study such that this technology may advance its application in present as well as future with proper specifications, testing throughout. The Hot mixed based techniques have gone through the significant advancements with time. The Cold mixed based technology is somewhere lagging in terms of applications which might be observed in the developing countries. In the present study, it has been the primary motivation that underlies the selection of cold mixed technique. Manoj Sheoran | Ms. Shivani "A Result Paper on Experimental Investigation on CMA" Published in International Journal of Trend in Scientific Research and Development (ijtsrd), ISSN: 2456-6470, Volume-5 | Issue-5 , August 2021, URL: https://www.ijtsrd.com/papers/ijtsrd45179.pdf Paper URL: https://www.ijtsrd.com/engineering/other/45179/a-result-paper-on-experimental-investigation-on-cma/manoj-sheoran
Stabilization or solidification of iron ore mine tailings using cementeSAT Journals
Abstract Current research emphasis is more on the utilization of materials that are considered as waste. Tailings and fly ash are major category of industrial wastes, whose disposal is problematic from environmental point of view. In this present research, Industrial byproducts, namely, lime (CaO) and class F type fly ash have been used as candidate materials along with the partial addition of ordinary Portland cement (OPC) in the Stabilization/solidification (S/S) of polymetallic iron ore mine tailings (TM). The effectiveness of S/S was assessed by comparing laboratory experimental values obtained from unconfined compressive strength (UCS), hydraulic conductivity and leaching propensity tests of S/S samples with regulatory standards for safe surface disposal of such wastes. Some S/S cured matrices were found unable to provide the required immobilization of pollutants. S/S and 28 days cured mine tailing specimens made with composite binders containing TM/10/0/0, TM/5/0/20, TM/10/0/40 and TM/0/10/40 significantly impaired the solubility of all contaminants investigated and proved successful in fixing metals within the matrix, in addition to achieving adequate UCS and hydraulic conductivity values, thus satisfying regulatory norms (U.S. EPA). Laboratory investigations revealed the TM blends (stabilized materials) were non-hazardous. The test results of this study are encouraging and it may be possible to undertake large-scale fill construction with stabilized tailing material that is sustainable and cost effective. Keywords: Tailing materials, Laboratory study, Compaction characteristics, unconfined compressive strength, Hydraulic conductivity, Heavy metal content.
This ppt is about the cold mix asphalt. Some of its advantages and disadvantages over hot mix asphalt. Also some discussion about the test conducted on the cold mix asphalt and the result of it. And also discuss about the conclusion of above.
Employing of novel poly (amine-ester) with Pentaerithritol core as a new poly...IJERA Editor
A novel hyperbranched poly (amine-ester) (HBPAE) with a high number of hydroxyl end groups has been prepared and successfully applied as new polymeric admixture for ordinary Portland cement (OPC) after its complete characterization via GPC, IR, 1H-NMR, TGA and DSC. The effect of polymer addition on the cement paste was investigated by measuring the effect of 1, 3 and 5 wt. % HBPAE solutions on the properties of OPC. The results clarified that the addition of HBPAE to OPC pastes decreased the water of consistency while increased the compressive strength with no effect on the chemical composition of the cement phase. The SEM images indicated that the incorporation of HBPAE in cement phase affected the physical state, shape, size, morphology and microstructure of the formed hydrates. Generally, the addition of hyperbranched poly amine-ester (HBPAE) improved the physico-mechanical properties of cement.
The concrete being widely consumed material in the construction industry has severe concern with the environment. The need of the time is to find some alternative material to save the environment.
The concrete has to sustain a very high temperature, when any fire accident occurs. The properties of the concrete are to be studied when exposed to the heat in order to understand effect of temperature on the concrete. Authors have presented the experimental results for the reinforced concrete of different grades at different temperatures.
Influence of various parameters of cryogenic treatment on performance of tun...vivatechijri
Cryogenic treatment is supplementary thermal treatment done after conventional hardening
process, wherein hardened material is further cooled till cryogenic temperatures which may range from -80°C
to -196°C. In the case of various grades of steel, the cryogenic treatment process has proved to have improved
mechanical properties significantly through conversion of retained austenite to martensite and refinement of
grain structure of steel. However, the effect of cryogenic treatment on high hardness material like tungsten
carbide is still in research and results are uncertain. Ongoing research have suggested that cryogenic treatment
may result into improvement of hardness and wear resistance of tungsten carbide tools which in turn may
improve tool life and efficiency of the cutting operation. But, the amount of improvement in properties majorly
depends of various parameters of cryogenic treatments. This paper deals with reviewing various parameters of
cryogenic treatment like cooling cooling rate, soaking temperature, soaking time, tempering temperature,
tempering time and its effect on performance of tungsten carbide tool
Numerical study on heat transfer and densification for SiC composites during ...ZAHER RAMADAN
Abstract
In this study, a thermal-gradient chemical vapor infiltration (TG-CVI) process was numerically
studied in order to enhance the deposition uniformity within the preform. The computational
fluid dynamics technique was used to solve the governing equations for heat transfer
and gas flow during the TG-CVI process for two- and three-dimensional (2-D and 3-D)
models. The temperature profiles in the 2-D and 3-D models showed good agreement with
each other and with the experimental results. The densification process was investigated in
a 2-D axisymmetric model. Computation results showed the distribution of the SiC deposition
rate within the preform. The results also showed that using two-zone heater gave better
deposition uniformity.
PUBLICATION OF MATERIAL SCIENCE AND ENGINEERING RESEARCH PAPERThe House of Perle
POST GRADUATE LEVEL OF WRITING AND COMMUNICATION SKILLS
Required the understanding and application of scientific methods, including forming hypotheses, designing experiments to test hypotheses, and collecting, analyzing, interpreting, and reporting data.
The Northwestern University Materials Research Science & Engineering Center offers a Research Experience for Undergraduates (REU) program over a 9-week period each summer. Most accepted students are exceptional rising junior and seniors. The NU-MRSEC is an interdisciplinary program focused on multi-functional nanoscale material structures. I had the opportunity to contribute to 2 research projects led by a faculty member and was assigned to a post-doctoral associate mentor worked closely with me. I participated in interdisciplinary research group meetings, expanding my science and engineering experience into a range of fields. Required the understanding and application of scientific methods, including forming hypotheses, designing experiments to test hypotheses, and collecting, analyzing, interpreting, and reporting data.
Deposition of ni ti n coatings by a plasma assisted mocvd using an organometa...tshankar20134
Titanium nitride (TiN)/nickel (Ni) composite coatings were synthesized by plasma assisted metal-organic
chemical vapour deposition (PAMOCVD) using organo-metallic and metal-organic complexes namely dichlorobis(5-
cyclopentadienyl)titanium (IV) for titanium and N,N'-ethylene-bis(2,4-pentanedion-iminoato)nickel(II) for nickel. The
growth of such films was investigated in nitrogen (N2) plasma environment in the substrate temperature range of 450-
550ºC at a deposition pressure of 0.5-1 mbar. Prior to the deposition of films, the Ti precursor was subjected to the
equilibrium vapour pressure measurements by employing TG/DTA in transpiration mode, which led to the value of 109.2
± 5.6 kJ mol-1 for the standard enthalpy of sublimation (Ho
sub). The phase identification using glancing incidence x-ray
diffraction showed Ni/TiN is a nanocomposite coating containing nanocrystals of Ni and TiN with face centered cubic
structure. Scanning electron microscopy revealed a uniform surface morphology of the films, while chemical analysis by
energy dispersive analysis confirmed the presence of titanium, nickel and nitrogen in the composite films.
A collection of alternative vehicles including:
- Gas/Electric Hybrid Motorbikes & 3-Wheelers
- All-Electric ATV's
- Electric Bicycles
- All Electric Motorbikes
- Mobility Dcooters Sv=
Stabilization or solidification of iron ore mine tailings using cementeSAT Journals
Abstract Current research emphasis is more on the utilization of materials that are considered as waste. Tailings and fly ash are major category of industrial wastes, whose disposal is problematic from environmental point of view. In this present research, Industrial byproducts, namely, lime (CaO) and class F type fly ash have been used as candidate materials along with the partial addition of ordinary Portland cement (OPC) in the Stabilization/solidification (S/S) of polymetallic iron ore mine tailings (TM). The effectiveness of S/S was assessed by comparing laboratory experimental values obtained from unconfined compressive strength (UCS), hydraulic conductivity and leaching propensity tests of S/S samples with regulatory standards for safe surface disposal of such wastes. Some S/S cured matrices were found unable to provide the required immobilization of pollutants. S/S and 28 days cured mine tailing specimens made with composite binders containing TM/10/0/0, TM/5/0/20, TM/10/0/40 and TM/0/10/40 significantly impaired the solubility of all contaminants investigated and proved successful in fixing metals within the matrix, in addition to achieving adequate UCS and hydraulic conductivity values, thus satisfying regulatory norms (U.S. EPA). Laboratory investigations revealed the TM blends (stabilized materials) were non-hazardous. The test results of this study are encouraging and it may be possible to undertake large-scale fill construction with stabilized tailing material that is sustainable and cost effective. Keywords: Tailing materials, Laboratory study, Compaction characteristics, unconfined compressive strength, Hydraulic conductivity, Heavy metal content.
This ppt is about the cold mix asphalt. Some of its advantages and disadvantages over hot mix asphalt. Also some discussion about the test conducted on the cold mix asphalt and the result of it. And also discuss about the conclusion of above.
Employing of novel poly (amine-ester) with Pentaerithritol core as a new poly...IJERA Editor
A novel hyperbranched poly (amine-ester) (HBPAE) with a high number of hydroxyl end groups has been prepared and successfully applied as new polymeric admixture for ordinary Portland cement (OPC) after its complete characterization via GPC, IR, 1H-NMR, TGA and DSC. The effect of polymer addition on the cement paste was investigated by measuring the effect of 1, 3 and 5 wt. % HBPAE solutions on the properties of OPC. The results clarified that the addition of HBPAE to OPC pastes decreased the water of consistency while increased the compressive strength with no effect on the chemical composition of the cement phase. The SEM images indicated that the incorporation of HBPAE in cement phase affected the physical state, shape, size, morphology and microstructure of the formed hydrates. Generally, the addition of hyperbranched poly amine-ester (HBPAE) improved the physico-mechanical properties of cement.
The concrete being widely consumed material in the construction industry has severe concern with the environment. The need of the time is to find some alternative material to save the environment.
The concrete has to sustain a very high temperature, when any fire accident occurs. The properties of the concrete are to be studied when exposed to the heat in order to understand effect of temperature on the concrete. Authors have presented the experimental results for the reinforced concrete of different grades at different temperatures.
Influence of various parameters of cryogenic treatment on performance of tun...vivatechijri
Cryogenic treatment is supplementary thermal treatment done after conventional hardening
process, wherein hardened material is further cooled till cryogenic temperatures which may range from -80°C
to -196°C. In the case of various grades of steel, the cryogenic treatment process has proved to have improved
mechanical properties significantly through conversion of retained austenite to martensite and refinement of
grain structure of steel. However, the effect of cryogenic treatment on high hardness material like tungsten
carbide is still in research and results are uncertain. Ongoing research have suggested that cryogenic treatment
may result into improvement of hardness and wear resistance of tungsten carbide tools which in turn may
improve tool life and efficiency of the cutting operation. But, the amount of improvement in properties majorly
depends of various parameters of cryogenic treatments. This paper deals with reviewing various parameters of
cryogenic treatment like cooling cooling rate, soaking temperature, soaking time, tempering temperature,
tempering time and its effect on performance of tungsten carbide tool
Numerical study on heat transfer and densification for SiC composites during ...ZAHER RAMADAN
Abstract
In this study, a thermal-gradient chemical vapor infiltration (TG-CVI) process was numerically
studied in order to enhance the deposition uniformity within the preform. The computational
fluid dynamics technique was used to solve the governing equations for heat transfer
and gas flow during the TG-CVI process for two- and three-dimensional (2-D and 3-D)
models. The temperature profiles in the 2-D and 3-D models showed good agreement with
each other and with the experimental results. The densification process was investigated in
a 2-D axisymmetric model. Computation results showed the distribution of the SiC deposition
rate within the preform. The results also showed that using two-zone heater gave better
deposition uniformity.
PUBLICATION OF MATERIAL SCIENCE AND ENGINEERING RESEARCH PAPERThe House of Perle
POST GRADUATE LEVEL OF WRITING AND COMMUNICATION SKILLS
Required the understanding and application of scientific methods, including forming hypotheses, designing experiments to test hypotheses, and collecting, analyzing, interpreting, and reporting data.
The Northwestern University Materials Research Science & Engineering Center offers a Research Experience for Undergraduates (REU) program over a 9-week period each summer. Most accepted students are exceptional rising junior and seniors. The NU-MRSEC is an interdisciplinary program focused on multi-functional nanoscale material structures. I had the opportunity to contribute to 2 research projects led by a faculty member and was assigned to a post-doctoral associate mentor worked closely with me. I participated in interdisciplinary research group meetings, expanding my science and engineering experience into a range of fields. Required the understanding and application of scientific methods, including forming hypotheses, designing experiments to test hypotheses, and collecting, analyzing, interpreting, and reporting data.
Deposition of ni ti n coatings by a plasma assisted mocvd using an organometa...tshankar20134
Titanium nitride (TiN)/nickel (Ni) composite coatings were synthesized by plasma assisted metal-organic
chemical vapour deposition (PAMOCVD) using organo-metallic and metal-organic complexes namely dichlorobis(5-
cyclopentadienyl)titanium (IV) for titanium and N,N'-ethylene-bis(2,4-pentanedion-iminoato)nickel(II) for nickel. The
growth of such films was investigated in nitrogen (N2) plasma environment in the substrate temperature range of 450-
550ºC at a deposition pressure of 0.5-1 mbar. Prior to the deposition of films, the Ti precursor was subjected to the
equilibrium vapour pressure measurements by employing TG/DTA in transpiration mode, which led to the value of 109.2
± 5.6 kJ mol-1 for the standard enthalpy of sublimation (Ho
sub). The phase identification using glancing incidence x-ray
diffraction showed Ni/TiN is a nanocomposite coating containing nanocrystals of Ni and TiN with face centered cubic
structure. Scanning electron microscopy revealed a uniform surface morphology of the films, while chemical analysis by
energy dispersive analysis confirmed the presence of titanium, nickel and nitrogen in the composite films.
A collection of alternative vehicles including:
- Gas/Electric Hybrid Motorbikes & 3-Wheelers
- All-Electric ATV's
- Electric Bicycles
- All Electric Motorbikes
- Mobility Dcooters Sv=
Amy Desel is one of the highly experienced and reputed dieticians with the expertise in crafting healthful lifestyles for the clients of every background.
Amy desel is actively involved in various charitable causesAdolph Scutt
Amy Desel is a seasoned Residential Real Estate Agent who serves her clients by providing them personalized service in the buying and selling process. She is a member of the Al Filippone Associates Team in Southport, CT.
Development of Nanocomposite from Epoxy/PDMS-Cyanate/Nanoclay for Materials w...IJMER
Dicyanate monomer viz bis-4-cyanato-polydimethylsiloxane(PDMS-CY) containing
siloxane known as thermally stable structural unit was prepared. The PDMS-CY/DGEBA-stability, thermal degradation kinetics and microstructures
An experimental and analytical study to show the effect of theOzyegin University
The main purpose of this paper is showing the enhancement of thermal conductivity
of the epoxy with many percentages of carbon fiber into it. In addition to pure epoxy and pure
carbon fiber, three percentages of carbon fiber are used in this study, which are 20, 40, and 60%,
respectively. All of these samples are tested at different values of applied powers (input power)
(10, 25, 40, 55, and 70 W). A comparison between pure epoxy, pure carbon fiber and the
composites that involve all these percentages is done. In addition, the study involves the effect of
these simples on the performances of both Aluminum and cooper heat sinks.
It is shown from the results that increasing in fiber carbon percentage leads to increase in
thermal conductivity of composite, heat sink junction temperature, overall heat sink efficiency,
and density of composite. The increasing in overall heat sink efficiency leads to decrease the
height of heat sink, and consequently decreasing its cost. For instance at 70 W power input,
increasing the fiber carbon percentage(from 0 to 100%) for each material of heat sink, leads to
decrease the average fin length by 48% ,decrease the manufacturing cost by 47%, increase in
junction temperature by 65 %, and increase fin efficiency by 2.5 %.
Experimental Investigation on Adsorption Capacity of a Variety of Activated C...IJERA Editor
This study aims to develop a device with minimum heat and mass transfer limitations between adsorbent and
adsorbate, and subsequently to obtain practically applicable adsorption capacity data. Also, 5 kW adsorption
chillers (evaporators, condensers and adsorbers) are designed based on the experimental output data of the whole
tested pairs. A finned-tube heat exchanger was employed and installed at the center adsorber, and each employed
adsorbent was immobilized on its surfaces by using an adhesive agent. A variety of pairs: are activated carbon
powder (ACP)/R-134a, ACP/R-407c, ACP/R-507A, activated carbon granules (ACG)/R-507A, ACG /R-407c
and ACG /R-134a, were examined at different adsorption temperatures of 25, 30, 35 and 50°C. It was found that,
at the adsorption temperature of 25°C the maximum adsorption capacity was 0.8352 kg kg-1 for ACP/R-134a,
while at the adsorption temperature of 50°C the maximum adsorption capacity was 0.3207 kg kg-1 for ACP/R-
134a. Therefore, the ACP/R-134a pair is highly recommended to be employed as adsorption refrigeration
working pair because of its higher maximum adsorption capacity higher than the other examined pairs.
Heat Transfer in Porous Media With Slurry of Phase Change MaterialsCSCJournals
3-D laminar model of a rectangular porous channel with high thermal conductivity and constant wall heat flux is chosen to investigate the enhancement of heat transfer when used in conjunction with the phase change material slurry. Numerical simulations for various wall heat fluxes and inlet velocities are carried out. The slurry consist of microencapsulated octadecane and water. The heat transfer coefficient of the porous channel with pure water and with micro-encapsulated phase change material are calculated and compared. The effect of porosity and permeability of the porous medium on the heat transfer coefficient while using a slurry of phase change material are studied. The results show that the heat transfer coefficient of the porous channel can improve by introducing phase change material slurry, but only under certain heat fluxes, inlet velocities, and porous media properties.
Phase change material (PCM) thermal composites consisting of porous aluminium/stearic acid phase change material have been produced for heat storage applications. Porous aluminium/stearic acid composite structures were produced by infiltrating stearic acid PCM into open- cell porous aluminium materials prepared by using dissolvable spherical salt beads in combination with vacuum casting process. Scanning electron microscopic analysis has been used to characterize the empty porous aluminium materials and the results reveal a cellular structure consisting of spherical pores which are interconnected with smaller windows. The thermal response of empty porous aluminium structures and those infiltrated with stearic acid was measured using an infrared camera. The result showed that the heat transfer performance of the PCM thermal composites was significantly improved and largely dependent on the relative density of the porous structures.
Improvement of Tensile Properties of Recycled Low-Density Polyethylene by Inc...Dr. Amarjeet Singh
Plastics are used in versatile applications including
automobile, packaging, piping and house goods, these huge
uses attribute in the consumption of the oil reserves and the
emerged waste harm the environment when it disposed
irregularly. Recycling of plastics is one of the realistic
solutions to the aforementioned problems and to reduce
production cost. However, the reduction in mechanical
properties of recycled plastics limit their use and thus
reinforced plastics become popular because of their high
mechanical, physical and thermal properties. The effects of
calcium carbonate content from 0 to 15 wt.% on the tensile
properties of recycled low-density polyethylene (RLDPE)
were tested, the addition of calcium carbonate particles up to
15 wt.% was found to enhance the tensile strength and
modulus of elasticity of RLDPE samples. Three calcium
carbonate particle sizes (80, 200 and 500 µm) were mixed
with RLDPE to investigate the effect of particles size on the
tensile properties of RLDPE, it was found that the addition of
small filler particles resulted in a noticeable improvement of
tensile strength and modulus of elasticity of RLDPE
compared with large filler particles. It was also observed that
the addition of stearic acid slightly improves tensile
properties of RLDPE which may be related to improvement
of the interfacial adhesion between the filler and RLDPE. The
crystallization temperature and the degree of crystallinity of
RLDPE were increased by the addition of 7.5 wt.% calcium
carbonate particles because they act as nucleating agents.
As a part of course on Environments and Energy Materials, this was presented to explain the various areas (materials, manufacturing, testing) of advancement in turbines used for applications such as power generation and jet engines.
1. CERAMICS
INTERNATIONAL
Available online at www.sciencedirect.com
Ceramics International 41 (2015) 13751–13758
Sublimation and oxidation zone ablation behavior
of carbon/carbon composites
Shameel Farhana
, Rumin Wanga,n
, Kezhi Lib
, Chuang Wangb
a
School of Science, Northwestern Polytechnical University, Xi’an 710072, China
b
School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an 710072, China
Received 21 July 2015; received in revised form 31 July 2015; accepted 7 August 2015
Available online 18 August 2015
Abstract
Three-dimensional carbon/carbon (C/C) composites comprising four reinforcement directions (4D) were fabricated using intermediate modulus
carbon fibers and densified using a hybrid process. This consists of a pre-densification step using a thermal-gradient chemical vapor infiltration
process followed by a high-pressure pitch impregnation and carbonization process. The specimens machined along Z-axis of the preform
architecture were tested in an arc plasma heater for studying its ablation behavior at different temperatures. Regimes from ultra-high temperature
(4750 K) sublimation to high-temperature (2467 K) oxidation zones were created by varying the mass flow rate of secondary air in the heater. The
ablation rate showed a progressive increase as the environment changed from oxygen-lean sublimation to oxygen-rich oxidation conditions while
the back-face temperature showed a similar temperature profile during the plasma exposure period. The thermal diffusivity value decreased with
the rise in temperature till 1173 K and later on became fairly flat till 1523 K and onwards. In the compression test, 4750 K exposed specimen
showed toughening in the plasma-affected zone and crushed with shear mode from the opposite face while the 2467 K exposed specimen showed
end brushing in the plasma heat-affected face with a lower residual strength and Young’s modulus.
& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: E. Thermal applications; Carbon/carbon composites; Plasma arc-heater; Ablation; Oxidation
1. Introduction
Carbon/carbon (C/C) composites are materials of choice in
aerospace industry due to their outstanding thermostability and
thermomechanical properties at a very high temperature [1–5].
C/C composites were originally used on ablative structures
(e.g., rocket nozzles, re-entry nose tips & leading edges) in
which the material has to endure high thermal gradient and is
mainly ablated by some gasification processes like oxidation
and sublimation [6]. The re-entry conditions vary with the type
of mission: temperature up to 5000 K and pressure up to
100 bar, and a heat flux received by the protection ranging
from 0.1 to 500 MW/m2
[7]. Under such conditions, a
considerable part of the heat flux is consumed by mass
transfer, which has two principal forms: oxidation and
sublimation. These phenomena are grouped under the generic
name of ablation [8]. By definition, ablation is a process of
elimination of a large amount of thermal energy by sacrificing
a portion of mass of the ablative material. General physio-
chemical reactions containing this process are phase changes,
conduction, convection, radiation, diffusion and exothermic/
endothermic chemical reactions [9]. Chemical reactions play a
significant role in establishing ablation rates of most of the
resultant material-environment combinations. Ultra high tem-
perature ceramics are the potential candidates for thermal
protection of reentry vehicles because of their very high
melting points. The major hurdle in the development of these
materials is that their manufacturing techniques are not mature
until now [10]. High density of the material as well as
machining problems is another reason to search for alternative
www.elsevier.com/locate/ceramint
http://dx.doi.org/10.1016/j.ceramint.2015.08.043
0272-8842/& 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
n
Correspondence to: Department of Applied Chemistry, School of Science,
NWPU, Youyi West Road 127, Xi’an 710072, Shaanxi, China.
Tel.: þ86 29 88492947.
E-mail addresses: shameelfarhan@yahoo.com (S. Farhan),
rmwang@nwpu.edu.cn (R. Wang).
2. materials overcoming aforementioned problems with addi-
tional advantages apart from the uniform thermo-mechanical
properties, low erosion and high thermal stability. The material
studied in this research is three-dimensional and four-
directional (4D) in structure. The 4D C/C composites are well
known for their excellent thermo-physical and thermo-
mechanical properties in short-term, high-temperature applica-
tions [11–14]. Due to the high interlaminar shear strength, they
exhibit high performance with respect of shape stability and
anti-ablation [15].
Many experimental characterizations of C/C composites
have been reported in literature [16–19]. The oxyacetylene
flame ablation and plasma arc ablation are the most widely
used methods to study the ablation behavior of C/C composites
[20–24]. Oxyacetylene flame does not simulate the actual
reentry conditions due to limited heat flux and flow species
[25]. Only plasma arc heater can produce nearly similar reentry
conditions. Moreover, these experiments include micro, meso
and macroscopic observations of the ablated surface and
measurements of the recession rates. The ablated surface
morphology generally consists of fiber denudation and block
denudation and the recession rates can be expressed in terms of
the linear erosion rate and the mass ablation rate. The testing
temperature is around 3200 K similar to the temperature in the
nozzle of solid rocket motor.
To the authors’ knowledge, no one has done such kind of
work in which operating parameters of an arc heater were
changed with regard to chemical reactivity of C/C composites.
The purpose of this research is to differentiate the two main
chemical reaction regimes: oxidation dominant and sublima-
tion dominant and compare the effects of these regimes on the
ablation behaviour of a 4D C/C composite. The temperature
was adjusted by controlling the mass flow rate of the
secondary air (plasma cooling gas) so that the oxygen-rich
high temperature ($2500 K) and oxygen-lean ultra-high
temperature ($ 4500 K) were created in the plasma flow
field. Moreover, the effect of plasma stream temperatures,
stagnation enthalpies, gaseous velocities, and cooling (second-
ary) air flow rate on the ablation behavior of the 4D C/C
composite was also studied. The stagnation-point ablation rates
were measured with different mix ratios of primary and
secondary air working as the test gas. Air was chosen as a
testing media for the simulation of the reentry condition. Air
having a mixture of O2 and N2, dissociates into N, O, NO,
when it passes through the shock wave created arc in the
plenum chamber of arc heater. The composite studied was
prepared by a hybrid process and six samples of similar
density and fiber orientation were machined out for testing. To
examine the effect of hostile environment on the virgin
material, back-face temperature and the residual compressive
strength of the two specimens that experienced extreme
conditions were also tested. The two extreme conditions were
ultra-high temperature (4750 K) oxygen-lean and high tem-
perature (2467 K) oxygen-rich environment respectively. The
resulting back-face temperature, crushing behavior and load–
displacement plot were also discussed in relation to the
ablation test conditions.
2. Experimental
2.1. Preform fabrication
A 4D preform was fabricated by the insertion of stiffened
carbon rods in four directions in an orthogonal plane. TC 42S
carbon fiber (Tairyfil Co., China) bundles with 5.7 μm
diameter, 5150 MPa ultimate tensile strength and 290 GPa
Young’s modulus were used in the dry weaving process.
Multiple fiber bundles were combined and passed through a
8–15% binder solution in a standard pultrusion machine. The
binder can be any kind of organic polymer like polyvinyl
chloride, polyvinyl alcohol, epoxies and resins that are used in
the manufacture of advanced fiber reinforced composites. Here
solid novolac dissolved in organic propanol was chosen as a
novel choice. The excessive resin was squeezed by passing
through a series of nozzles and the coated rods were dried in a
tube-heating oven. The maximum fiber preheating and the
pultruded rods post-treatment temperatures were 653 K (opti-
mum for removing coatings from the carbon fiber) and 523 K
(curing temperature of novolac), respectively. The diameter of
the pultruded rod was controlled within 1.0 to 1.30 mm
depending upon the number of tows and weaving geometry
requirements. After rigidization, novolac binder in the pultrur-
ods was about 5% by weight. Fiber volume fraction (Vf) was
maintained in the range of 8–9% in the XY-plane and 13–14%
in the Z-axis. Total Vf of the preform was about 40% and the
bulk density was almost 0.69 g/cm3
. Further details about the
preform employed can be found in [26,27].
2.2. Densification process
The preform was densified using a hybrid process which is a
combination of two processes. A pre-densification step with a
thermal-gradient chemical vapor infiltration (TCVI) process
and a high-densification using a high pressure pitch impreg-
nation and carbonization (HiPIC) process. The preform was
first high temperature (HT) treated at 1873 K to convert the
fiber coating and resin into the carbon. The HT process was
conducted at a very slow rate with the aid of graphitic holding
plates to avoid the collapse of the preform. Pyrolytic carbon
from the natural gas (98% CH4, 0.3% C3H8, 0.3% C4H10,
0.4% other hydrocarbon, 1% N2) was deposited on the carbon
fibers in a TCVI furnace at temperature range of 1350–1450 K
[28]. At a deposition rate of 0.5 mm/h, a bulk density of
1.70 g/cm3
was achieved in 80 h. It was further increased to
1.86 g/cm3
by three successive HiPIC cycles. Intermediate heat
treatment at 2500 K after TCVI process was used for pore
opening, graphitization and strength enhancement [29]. High
softening (HS) pitch (399 K softening point, 1.30 g/cm3
density, 490% carbon contents, 4.5% hydrogen, 455%
carbon yield) was poured on the pre-densified C/C composite
under vacuum and stabilized for 5 h at 573 K. As shown by
studies [30] on wetting and impregnation of carbon fibers by
HS pitches, no impregnation of the inter-filamentary porosity
occurs even at high temperature and therefore, pressure turns
out to be necessary for the densification of C/C composites. It
S. Farhan et al. / Ceramics International 41 (2015) 13751–1375813752
3. was further carbonized at 1100–1200 K and 80 MPa isostatic
pressure.
2.3. Characterization
2.3.1. Density and porosity
The geometric density of 4D C/C specimens
(ø¼22 mm  50 mm) after final HT treatment was measured
by the ratio of mass of the sample to the total apparent volume.
True density and apparent porosity of carbon foam were
examined by helium gas displacement pycnometer (Pentapyc
5200e Quantachrome Instruments, Florida, USA). True density
is the mass per unit volume of material, which exclude all
voids or pores. Open porosity was calculated using the
following expression:
%P ¼
ρt Àρa
ρt
 100 ð1Þ
where %P is the bulk open porosity, ρt and ρa are true and
apparent densities of the samples respectively. The true density
of the composite was found to be 1.9070.01 g/cm3
while the
final open porosity of the composite was 3.2570.25%.
2.3.2. Electric arc plasma testing
The 4D C/C composite block was cut along the Z-axis of the
fiber architecture forming a cylindrical geometry with outer
diameter of 22.5À0.5
mm and length of 50 mm. The length (or
thickness) of the specimens is not so important because only
the blunt face was exposed to air plasma and thus, the exposed
area was kept fixed at 3.97 Â 10À4
m2
. Fibers in the XY-plane
were oriented in 01 (U-direction), þ601 (V-direction) and
À601 (W-direction) angles whereas Z-directional fibers were
along the Z-axis. In the testing, Z-axis fibers were at 901 to the
blunt face (face exposed to plasma stream). The ablation
experiments were performed on a Huels type arc heater. Two
tandem cylindrical electrodes were separated by a central
copper tube and insulated from each other. Primary air was
injected tangentially to the wall of the heater from four
different points in a manner to encircle the plasma jet along
the centerline and to stabilize it with the minimum contact with
the inner surfaces. A magnetic coil was used on the anode to
rotate the arc termination and prevent arc backfire to the rear
plug. The heater was ignited by a high-voltage breakdown with
Ar gas filling the chamber. Within one second, after the arc
breakdown, the gas supply was switched from Ar to air. The
plasma expanded as it passed through a converging–diverging
nozzle to a low supersonic Mach number. The secondary air
was injected into the upstream end of the constrictor at various
flow rates for the adjustment of final temperature and velocity
of spurting plasma stream. To ensure quasi-one dimensional
heat flow, a silica/phenolic holder was used to hold and protect
the samples from side-wall heating at a length of 15 mm from
the exposed face. The planar surface of the specimen and the
holder were flushed and grinded using SiC emery papers with
360 down to 1200 grit. The following parameters listed in
Table 1 were either fixed or varied for the study of their effect
on the ablation behavior of the 4D C/C composite.
A small hole (ø¼3 mm  35 mm) was drilled in the speci-
mens from the backside for the insertion of a thermocouple.
Because C/C composites have good electrical conductivity, the
compacted mineral-insulated metal-sheathed, K type thermo-
couple with a range of À73 to 1550 K was used following
ASTM E235 M-23 test method. The distance between the
thermocouple and the exposed surface was fixed at almost
15 mm. The centers of the plasma and the specimen were
aligned horizontally. A microbalance (1 mg precision) and a
0.1 mm precise caliper gauge were used for the pre- and post-
test evolution of samples. After attaining the required condi-
tions of static chamber pressure and heat flux, the sample was
moved into the sputtering plasma flow with the help of
pneumatically-drive trolley. After the test, ablated mass was
divided by the exposed surface area and test duration and the
results were expressed with a unit of kg/m2
-s. Fig. 1 shows the
schematic of the experimental set up fitted with a specimen and
a back-face thermocouple.
2.3.3. Thermal diffusivity
The thermal diffusivity of 4D C/C composite cut into disk
geometry (ø¼12.5 mm  2.5 mm) was measured by the flash
diffusivity method, which basically consists of subjecting one
side of a sample to a single laser flash and then monitoring the
transient temperature response on the other side. A Netzsch
LFA 457 Micro-Flash instrument with the guidelines of ASTM
E-1461 standard was operated from room temperature to
1250 1C under Ar atmosphere. The uncertainty of the mea-
surements was 75%.
2.3.4. Compression after ablation (CAA)
The compression-after-ablation (CAA) [26] of the material
was studied using the SANS CMT 5105 (100 kN) mechanical
testing machine. The vertical moving speed of the crosshead
was set at 0.5 mm/min with the load and displacement being
recorded and were in the direction parallel to Z-axis carbon
fiber rods. The specimens were cut using a diamond saw to a
height of about 30 mm. To create a smooth surface, thin layers
of ablated surface were removed using 600 sand papers. The
specimens were dried in a drying oven at 110 1C for 120 min
before the compressive tests. The compressive strength was
calculated according to the following equation:
σc ¼
Ρ
Α
ð2Þ
where P was the maximum loading of fracture (N); A was the
cross-sectional area of the specimen (mm2
).
3. Results and discussion
3.1. Electric arc plasma testing
Fig. 2 shows the macro-morphologies of the samples after
exposure to high-energy reactive air plasma test in an ambient
atmosphere. The recession rates along with different arc heater
parameters are summarized in Table 2. The ablation rate and
temperature as a function of the ratio of secondary to primary
S. Farhan et al. / Ceramics International 41 (2015) 13751–13758 13753
4. air are plotted in Figs. 3 and 4. The ablation rate came out to be
2.17 kg/m2
-s for the initial flow ratio of 1.01, and increased to
2.62 kg/m2
-s when the ratio exceeded to 2.62. Such an
increase was attributed to the strong oxidizing condition in
the plasma flow resulting from the increase in mass flow rate of
the secondary air. The flow enthalpy of the plasma stream also
decreased with the increase in secondary air flow rate. The
back-face temperatures of the specimen 1 and 6 were recorded
during the ablation testing to see the effect of ultra-high
temperature (4750 K) and high temperature (2467 K) environ-
ments on the back-face temperature. From specimen 1 to 6, the
temperature and stagnation enthalpy gradually decreased from
4750 to 2467 K and 5750 to 2819 kJ/kg, respectively, by
increasing the mass flow rate of the secondary air. The
secondary air was injected upstream before the nozzle and
acted as a cooling gas. The ablation rate increased with
decreasing the temperature of plasma stream, which was
nearly in a reverse order. The highest ablation rate of
2.62 kg/m2
-s was observed in case of the lowest temperature
of 2467 K, the highest air mass flow rate (15.8þ41.42 g/s) and
the plasma stream velocity of 630 m/s. Virtually all oxygen in
the plasma stream reacted with the carbon atoms, irrespective
of the heating rate, to form CO2 and CO when the temperature
was r3000 K. The enthalpies of these species are negative
with respect to that of un-dissociated air. In specimen 6, the
conditions were favorable for oxidation reaction dominance
(excess secondary air) and mechanical denudation due to the
shear forces of high plasma velocity. Macro-morphology of the
specimen 6 also revealed excessive oxidation pits on the
Table 1
Arc-heater parameters during sublimation and oxidation zone ablation testing of 4D C/C composites.
Fixed parameters Variable parameters
Primary air flow
rate (g/s)
Distance of
specimen (mm)
Ablation
time (s)
Secondary air flow
rate (g/s)
Hot chamber
pressure (bar)
Thermal enthalpy
(kJ/kg)
Velocity of plasma
stream (m/s)
Temperature
(K)
15.8570.10 1070.10 15 15.85–38.70 4.2–5.6 3200–5766 574–628 4750–2500
Holder Thermocouple
SpecimenPlasma Stream
Arc Heater
W-direction V-direction
U-directionZ-direction
Fig. 1. Arc heater testing; (a) Schematic of experimental set up and (b) test specimen along Z-axis with reinforcement directions highlighted by bold lines.
5 mm5 mm
Fig. 2. Macro-morphologies of specimens after plasma arc heater test; speci-
men 1 (sublimation regime) to 6 (oxidation regimes) from left to right.
0.8 1.2 1.6 2.0 2.4 2.8
2.0
2.2
2.4
2.6
2.8 Ablation rate
Temperature
Mass flow ratio (Sec. Air / Pri. Air)
Ablationrate(kg/m2-s)
2400
3000
3600
4200
4800
Temperature(K)
Fig. 3. Effect of mass flow ratio on ablation rate and exposure temperature of
plasma arc heater (sublimation to oxidation regimes).
S. Farhan et al. / Ceramics International 41 (2015) 13751–1375813754
5. surface and specially at the peripheral area which is compara-
tively weaker against the strong shear forces.
C(s) þO2-CO2 þ395 kJ/mol (3)
CO2þC(s)-2CO–142.5 kJ/mol (4)
CO formed is further reacted with dissociated oxygen which
is very excess in this case, forming CO2 as following:
COþO-CO2þ520.9 kJ/mol (5)
N2 also begins to undergo heterogeneous reactions directly
with the surface to form CN as following:
1/2N2 þC(s)-CN–460.5 kJ/mol (6)
which is further reacted with dissociated oxygen atoms as
following:
CNþ2O-CO2þ1/2N2þ1364 kJ/mol (7)
The resulting energy change due to combustion is therefore
exothermic, giving a positive contribution to the heat trans-
ferred to the surface. Above 3000 K, carbon also started
sublimation in addition to the oxidation [31]. In the specimen
1, the plasma stream temperature was the highest (4750 K)
with a minimum air mass flow (15.89þ16.0 g/s). At such a
high temperature, the oxidation reaction of carbon was
governed by the restricted diffusion rate because of the limited
amount of oxygen [32]. The surface of the specimen 1 was
roughly smooth with a few oxidation pits. It is to be noted that
the plasma stream temperature was 4750 K based on the
testing parameters, the temperature of the ablated surface
was a little lower due to the heat transfer and dynamic thermal
balance existing among the plasma, the specimen and the
environment [33]. We can define the sublimation regime as the
range of conditions where the mass loss due to vaporization
exceeds the diffusion controlled oxidation mass loss rate. It is
noted that at the high surface temperatures, not only do
chemical reactions occur between carbon and oxygen, but also
nitrogen reacts with carbon to form cyanogen (CN) and the
cyano radical CNn
[34]. As the surface temperature rises, the
vaporization rate of atomic and molecular carbon species, such
as C, C2, C3, C4 and C5, all increase exponentially. Note that,
the sublimation process yields appreciably greater amounts of
triatomic carbon gas than monatomic carbon [35].
The major sublimation reactions can be summarized as
following:
3C(s)-C3–753.5 kJ/mol (8)
3C3 þ3N2-6CN–1297 kJ/mol (9)
which is further reacted with limited supply of dissociated
oxygen as following:
CNþO-COþ1/2N2 þ849.5 kJ/mol (10)
The overall energy change in this zone is endothermic. The
effect of these exothermic and endothermic regimes was
further noted in the back-face temperature of the specimens
during ablation testing. The back-face temperature of the
specimen 1 and 6 was 1094 K and 1075 K, respectively. The
difference was not very large as compared with the very large
difference between the hot-face plasma stream temperatures.
The temperature profile is plotted in Fig. 5. The experimental
conditions in the specimen 1 corresponded to the sublimation
regime and in this case, chemical heat flux was negative, while
in the specimen 6, it was positive into the solid which gave
nearly the same back face temperature as that in case of
sublimation regime. In the specimen 1, the effect of ultra-high
temperature on the back-face temperature was lowered by the
dominant sublimation reaction (cooling) whereas in the speci-
men 6, oxidation reaction (heating) reheated the high tempera-
ture conditions. The back-face temperature rose exponentially
at the beginning of the experiment and attained the maximum
growth rate at 4À5 s when a small wiggle in the rising curve
3000 4000 5000 6000
2.0
2.2
2.4
2.6
Ablation rate
Temperature
Enthalphy (KJ/Kg)
Ablationrate(Kg/m2-s)
2400
3200
4000
4800
Temperature(K)
Fig. 4. Effect of stagnation enthalpy on ablation rate of 4D C/C composites
and exposure temperature of plasma arc heater.
Table 2
Summary of arc-heater parameters and resulting recession rates of 4D C/C composites.
Sr.
no
Recession rate (kg/
m2
-s)
Temperature
(K)
Back face
temperature (K)
Enthalpy
(kJ/kg)
Primary air flow
rate (g/s)
Secondary air flow
rate (g/s)
Flow
ratio
Plasma velocity
(m/s)
1 2.17 4750 1094 5750 15.89 16.00 1.01 570
2 2.25 4127 – 4936 15.83 22.50 1.42 587
3 2.31 3531 – 4198 15.80 27.28 1.73 600
4 2.40 3389 – 4033 15.79 29.69 1.88 607
5 2.50 2967 – 3480 15.80 34.86 2.21 617
6 2.62 2467 1075 2819 15.80 41.42 2.62 630
S. Farhan et al. / Ceramics International 41 (2015) 13751–13758 13755
6. occurred. After that, it started rising with a decreasing growth
rate for the 15 s of test duration and continued 5À7 s after the
completion of the tests. The cooling profiles were different in
the two cases: slow in oxidation leading ablation and fast in
sublimation leading ablation. The small wiggle in the growth
curve occurred at about 373 K due to the moist air superheated
and trapped in the specimens. The melting and sublimation of
the specimen 1 were considered because these phenomena are
significant at a surface temperature greater than 4000 K [36].
At this higher surface temperature, the vaporizing species of C
react with nitrogen into the boundary layer and some of CN
evolved diffuses back to the condensed phase. Also, as before,
CO diffuse back to the surface. All these endothermic reactions
near the surface will reduce the back face temperature [37].
Temperature overshoot from the exothermic reaction occurs
further out in the gas phase.
3.2. Thermal diffusivity
The thermal diffusivity represents the ability of a material to
conduct thermal energy relative to its ability to store thermal
energy and make the temperature uniform in the materials [38].
The thermal diffusivity value of the 4D C/C composite
decreased with the rise in temperature till 1173 K and later
on became fairly flat till 1523 K and onwards as shown in
Fig. 6. It may be noted that the thermal diffusivity of all the
constituents of C/C composites decreases with the rise in
temperature [16]. In this case, the thermal diffusivity decreased
by 44 mm2
/s when the temperature from room temperature
was increased to 1100 K which is almost the back-face
temperature of the specimens in arc heater testing. In C/C
composites, carbon fibers are the main channels of heat
transmission and hence their direction and distribution has a
major impact on thermal diffusivity. Their thermal diffusivity
varies from 60 to 19 mm2
/s in the temperature range of
500À1500 K. In all the specimens, the Z-axis fibers are along
the test direction and their volume percentage is 13.5, which
provides more continuous channels for the phonon transmis-
sion. After final densification with coal tar pitch, the residual
open porosity of the pre-densification step was further reduced
to 3.25% and the composite became more compact. These
entire factors contributed in higher thermal diffusivity at room
temperature. However, as the test temperature went up, the
phonon vibration frequency also increased resulting in scatter-
ing or decrease in the mean free path of the phonon leading to
a rapid decrease in thermal diffusivity. It also has an influence
on the decreasing trend of back-face temperature during
ablation testing.
3.3. Compression after ablation (CAA)
Fig. 7 shows the load–displacement curves of the specimen
1 and 6 after the ablation test. The linear region, representing
the true elastic response of the material was used to calculate
0 12 24 36 48 60
300
600
900
1200
Temperature(K)
Time (s)
Specimen 6
Specimen 1
Back-face absolute temperature
Distance from hot face = 15 mm
Fig. 5. Back-face temperature profile of sublimation (specimen 1) and
oxidation (specimen 6) regime ablation testing.
Fig. 6. Effect of temperature on thermal diffusivity and heat capacity of 4D C/C
composites along Z-axis.
0.0 0.2 0.4 0.6
0
7
14
21
28
Load(kN)
Dispalcement (mm)
Specimen 6Specimen 1
Fig. 7. Residual load–displacement curves of specimen 1 (sublimation regime)
and 6 (oxidation regime) after plasma arc heater testing.
S. Farhan et al. / Ceramics International 41 (2015) 13751–1375813756
7. the compressive modulus. The specimen 1 showed a residual
compressive strength of 75.63 MPa with a Young’s modulus
of 6.04 GPa. The specimen 6 showed a bilinear response in the
linear portion. The peak portion between 0.2 to 0.45 mm
displacements was the ultimate compressive load. The result-
ing strength and modulus were 69.15 MPa and 4.02 GPa,
respectively. These lower values were due to the deep
penetration of the oxidative plasma into the interfacial areas
of the composite. The load displacement curves represented a
typical brittle behavior without a catastrophic failure. The
specimen 1 failed on the non heat-effected side with both the
ends crushed and shear-failure in the central portion. The end
crushing is typical in this configuration of compression testing
and it is due to the buckling of carbon rods and matrix failure
(Fig. 8). When the load was applied on the specimen, shear
stress was induced along the interface between the specimen
end and the loading platen [39]. From the macro images
(Fig. 2) of the ablated specimens, a sequential difference in the
surface morphology can be observed. The surface of the
specimen 1 is smooth and flat with a few pinholes while deep
mesh like pits with surface undulation are visible on the whole
surface of the specimen 6. From the specimen 1 to 6, there is a
transition from smooth to rough surface. The material became
tougher at the heat-affected zone because of more gasification
and failed on the opposite side in the compression testing. The
specimen 6 sowed end brushing at the plasma heat-effected
zone. This behavior along with macro image (Fig. 2) con-
firmed the deep penetration of plasma into the intra rod spaces
with oxidation of matrix carbon. The 4D C/C composites show
extremely low interfacial strength between the fiber and the
matrix [40]. The strong oxidizing conditions and high-
temperature further reduced the strength and the carbon rods
failed due to macro-buckling.
4. Conclusions
4D C/C composite was fabricated using an intermediate
modulus carbon fiber and a hybrid processing method using a
TCVI and HiPIC processes resulting in a final density of
1.86 g/cm3
and a fiber volume fraction of 13.5% in Z-axis.
Plasma arc-heater testing was conducted to see the ablation
behavior. Arc-heater parameters like temperature, enthalpy,
velocity and flow rate were adjusted to create the ultra high-
temperature (4750 K) sublimation and high-temperature
(2467 K) oxidation regimes. The ablation rate increased with
the transition from oxygen-lean sublimation to oxygen-rich
oxidation environment. The back-face temperature showed a
similar but not so rapid rise in temperature as compared with
the large variation in the plasma stream temperatures at the hot
face. The endothermic sublimation reaction lowered the back-
face temperature while the exothermic oxidation reaction
reheated the specimen so that the net effect on the back-face
in both the cases was similar. In the compression test after
ablation, the ultra-high temperature exposed specimen showed
toughening at the plasma-affected zone, failed in end crushing
and shear mode from the opposite side while the high
temperature exposed specimen showed end brushing in plasma
heat affected zone with a lower residual strength and modulus.
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