IntroductionFibre reinforced ceramics can be defined as composite materials, which on the one hand demonstrate the typical material characteristics of high temperature ceramics, and on the other open up the technical manufacturing possibilities for the construction of large, thin walled, complex structures feasible with polymer based composites. Ceramic matrix composites (CMC) are very promising materials for use in structural applications when one considers their low mass (~ 2 g/cm 3 ), excellent thermal shock stability and strength at high temperatures. Different processing techniques are currently in use for the manufacture of complex shaped CMC components based on a fibre architecture of continuous carbon or silicon carbide fibres. A novel technology to produce CMC structures with lower costs and shorter manufacturing times has been developed at DLR [1]. The Liquid Silicon Infiltration (LSI) process is based on the infiltration of economically manufactured carbon / carbon with molten silicon and leads to so-called C/C-SiC materials. The LSI process allows the fabrication of thin walled, extremely lightweight C/C-SiC structures. It is a three step process starting with carbon fibre reinforced polymer (CFRP) manufacture followed by carbonization and concluding with liquid silicon infiltration. The advantage of the LSI process is that it is a near net shape process without reinfiltration steps. Moreover, the LSI process enables the joining of substructures in-situ. An homogeneous, and therefore strong, joint can be produced by implementing molten silicon as a joining material which reacts with carbon, either from the joining specimen or introduced as a paste to the joining surfaces, to form silicon carbide so the joint is as strong and thermally stable as the basis C/C-SiC material.The typical field of application for CMC lies where metals, or superalloys, due to their insufficient mechanical strength at elevated temperatures, can no longer be considered and encompasses all areas of lightweight construction. Thus, all projects concerning future space transportation systems and hypersonic aircraft foresee the extensive use of these materials, in particular for engine intake flaps, nozzles, thermal protection systems (TPS) or so-called hot, load bearing structures in the wings and fuselage, in order to fulfill the extreme lightweight construction demands. However, if the application is in an oxidising atmosphere carbon burnout of both the fibres and the matrix will start at temperatures as low as 450 °C. For these applications, carbon based CMCs can only be utilised for a limited lifetime. Even oxidation protective coatings will only reduce material degradation rather than to prevent oxidation completely.This paper discusses the LSI process and presents examples of CMC applications. Successful applications for the high temperature regime are space reentry structures. Commercially attractive applications within the medium temperature regime take advantage of the excellent High Temperature Ceramic Matrix Composites....
The article contains sections titled: 1. Carbon Fiber Reinforced Polymers 1.1. Raw Materials 1.2. Manufacturing Technologies 1.3. Design and Simulation 1.4. Mechanical Properties 1.5. Applications 1.6. Economic Aspects 2. Carbon Fiber Reinforced Carbon 2.1. Introduction 2.1.1. History 2.1.2. Definition, Nomenclature 2.2. Raw Materials 2.2.1. Carbon Fibers and Textile Fiber Precursors 2.2.2. Matrix Resins 2.2.3. Additives 2.2.4. Pitch 2.2.5. Pyrocarbon 2.3. Manufacturing Processes 2.3.1. Pressing, Manual Layup 2.3.2. Winding 2.3.3. Autoclave Technology 2.3.4. Joining 2.3.5. Densification 2.3.5.1. Liquid Impregnation 2.3.5.2. Gas Phase Deposition (CVI, CVD) 2.3.6. Graphitization 2.4. Structure and Properties 2.4.1. Fiber–Matrix Binding, Structure, Crack Structure 2.4.2. Material Properties 2.4.2.1. Mechanical Properties 2.4.2.2. Thermophysical Properties 2.4.2.3. Tribological Properties 2.4.3. Chemical Properties 2.4.3.1. Chemical Corrosion 2.4.3.2. Oxidation and Oxidation Protection 2.5. Component Design and Numerical Methods 2.5.1. Problems Specific to CFC 2.5.2. Characteristic Material Parameters 2.5.3. Design Procedure 2.5.4. Experimental Studies and Component Tests 2.6. Applications 2.7. Outlook 3. Carbon Fiber Reinforced Ceramics 3.1. Introduction 3.2. Manufacture 3.2.1. Chemical Vapor Infiltration (CVI) 3.2.2. Liquid Polymer Infiltration (LPI) 3.2.3. Liquid Silicon Infiltration (LSI) 3.3. Properties 3.4. Applications 3.4.1. Space Applications 3.4.2. Aeronautics 3.4.3. Friction Systems 3.4.4. Low‐Expansion Structures 3.4.5. Lightweight Armor 3.4.6. Other Applications
Ceramic materials offer a high thermal and chemical stability and are therefore potential candidates for high temperature applications in severe environments, where metals can not longer be used. In future energy applications, high process temperatures > 1200 °C are required to increase the efficiency, to lower the fuel consumption, and to decrease the emissions. In order to achieve these goals, novel ceramic materials and manufacturing processes for complex structures are under development.
This paper shows three different joining methods for fibre ceramic materials. The so called in-situ joining method is an integral part of the manufacturing process for CMC structures via the liquid silicon infiltration (LSI) process. Stiffening elements, local patches within attachment areas, inserts etc. are permanently joined to shell structures, thus enabling highly integrated components to be realised with low manufacturing costs. Mechanical joining methods are required for the attachment of CMC thermal protection systems and the assembly of large structures which can not be manufactured as one part due to the limited size of manufacturing devices (e.g. autoclave, furnaces). For these cases, two different principles are available. The first method takes advantage of interlocking effects of hardened castable ceramics for permanent joints and the so called ceramic rivet, which has similar properties to metallic rivets, however using only elastic and frictional properties of the CMC basic material. The last joining method presented within this paper deals with the attachment of hot structures to a cold substructure. To solve the problems associated with thermal mismatch, elastic or kinematic attachment systems, well adapted to the thermal expansion behaviour are suitable candidates.
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