Dietmar Koch

• Professor (Full) at University of Augsburg

The material behavior of Polymer Infiltration and Pyrolysis based SiC/SiCN composites is studied and the characteristic thermal and mechanical properties in on- (0/90 °) and off-axis (±45 °) direction are summarized. The tensile properties are determined at room temperature and 1300 °C. Based on the ratio of Young’s modulus and strength between on-...

The material behavior of Polymer Infiltration and Pyrolysis based SiC/SiCN composites is studied and the characteristic thermal and mechanical properties in on- (0/90 ◦) and off-axis (±45 ◦) direction are summarized. The tensile properties are determined at room temperature and 1300 ◦C. Based on the ratio of Young’s modulus and strength between on-...

Silicon carbide fiber-reinforced silicon carbide matrix composites (SiC/SiC CMCs) are promising candidates for hot gas components in jet engines. Three common manufacturing routes are chemical vapor infiltration, reactive melt infiltration (RMI) and polymer infiltration and pyrolysis (PIP). A combination of the processes seems attractive: the remai...

This paper presents a damage-based failure criterion and its implementation in order to predict failure in ceramic matrix composites (CMC) manufactured via filament winding. The material behavior of CMCs is anisotropic and strongly depends on the angle between fiber orientation and loading direction. The inelastic behavior of laminates with differe...

The microstructure and mechanical properties of carbon fibre reinforced ZrB2 composites produced by slurry infiltration and consolidated by reactive melt infiltration were investigated. Fibres were preliminary infiltrated with ZrB2/B slurries with varying ZrB2/B ratios. Then the composites were infiltrated with Zr2Cu melt at 1200 °C under vacuum. B...

Thanks to their high energy density and thermal conductivity, metallic Phase Change Materials (mPCM) have shown great potential to improve the performance of thermal energy storage systems. However, the commercial application of mPCM is still limited due to their corrosion behavior with conventional container materials. This work first addresses on...

In this study, burner rig testing of Si/Yb2Si2O7 environmental barrier coating protected SiC-based ceramic matrix composites was conducted. Tests were performed at standard conditions as well as with liquid water injection to the flame. Furthermore, the influence of the impingement angle of the flame (45° vs. 90°) on water vapor corrosion was explo...

The microstructure and mechanical properties of carbon fibre reinforced ZrB2 composites produced by slurry infiltration and consolidated by reactive melt infiltration were investigated. Fibres were preliminary infiltrated with ZrB2/B slurries with varying ZrB2/B ratios. Then the composites were infiltrated with Zr2Cu melt at 1200°C under vacuum. Bo...

SiC/SiCN ceramic matrix composites (CMCs) are promising candidates for components of aero‐engines. To evaluate the properties of these CMCs under realistic conditions, a quasi‐flat panel with effusion cooling holes was investigated in a high pressure combustor rig. A Tyranno SA3 fabric‐based SiC/SiCN composite with high strength and strain to failu...

The significant increase of world energy consumption raises the demand for imperatively clean energy resources. Since energy production methods have been greatly improved, one of the biggest challenges remains the development of high-performance energy storage systems. In this work, two newly developed thermal storage concepts with different storag...

Continuous fiber reinforced ceramics (Ceramic matrix composites CMC) are well known for their damage tolerance. Even when critical stresses occur and matrix cracks are induced the fibers are still able to bridge these cracks and prevent catastrophic failure of structural parts. This behavior makes CMC very attractive for application in severe envir...

Silicon carbide fiber-reinforced silicon carbide matrix composites (SiC/SiC CMCs) are promising candidates for components in the hot gas section of jet engines, as they exhibit high temperature resistance and low density compared to their metal alloy counterparts. Three common manufacturing routes are chemical vapor infiltration, reactive melt infi...

Due to their high thermal stability and low cost, molten chlorides are promising high-temperature fluids for example for thermal energy storage (TES) and heat transfer fluid (HTF) materials in concentrated solar power (CSP) plants and other applications. However, the commercial application of molten chlorides is strongly limited due to their strong...

C/C-SiC sandwich structures have been developed using liquid silicon infiltration (LSI) process and in situ joining method. They offer high specific stiffness and strength, low thermal expansion, high environmental stability and temperature resistance. Potential application areas are geometrically stable satellite structures like optical benches or...

Ceramic matrix composites usually utilize carbon or ceramic fbers as reinforcements. However, such fbers often expose a low ductility during failure. In this work, we follow the idea of a reinforcement concept of a ceramic matrix reinforced by refractory metal fbers to reach pseudo ductile behavior during failure. Tungsten and molybdenum fbers were...

Damage-tolerant ceramic matrix composites (CMC) are prone to high temperature applications under severe environmental conditions and usually utilize carbon or ceramic fibres (e.g. SiC) as reinforcements of ceramic matrices with inherent low elongation to break compared to common metals. However, CMC reveal an elongation to break and stiffness simil...

SiC/SiCN ceramic matrix composites (CMCs) are promising candidates for components of aero-engines. To evaluate the properties of these CMCs under realistic conditions, a quasiflat panel with effusion cooling holes was investigated in a high pressure combustor rig. A Tyranno SA3 fabric based SiC/SiCN composite with high strength and fracture strain...

Alloxide fiber reinforced composites are well known for their damage tolerant behavior up to temperatures of 1000°C. These properties make them attractive for various industrial applications, not only under extreme conditions but also at moderate temperatures when the overall properties are beneficial. One example is a hot gas rotor which will be u...

Carbon fiber reinforced ceramics manufactured via liquid silicon infiltration (LSI) have been developed at DLR since the late 1980s. Carbon fibers are infiltrated with a polymer based matrix which will be converted to carbon during the pyrolysis process and then reacted to SiC by LSI. The resulting C/C-SiC composites show high abrasion resistance,...

The Liquid Silicon Infiltration (LSI) process is used to manufacture carbon fiber based C/C-SiC composites. A CFRP-preform (carbon fibre reinforced polymer) is manufactured by infiltrating C fibre rovings with a phenolic resin, wet filament winding and warm pressing. After curing, the polymer matrix is converted to carbon by a high temperature trea...

Mo- and W-fiber reinforced CMCs can be easily manufactured via polymer infiltration and pyrolysis at 1300 °C (PIP) Mo/SiCN and W/SiCN composites are light-weight in comparison to Mo/Mo and W/W composites Mo/SiCN and W/SiCN show increased fracture strain compared to CMCs Mo/SiCN and W/SiCN can be considered as WMCs and thus need no weak interphase M...

Sandwich structures based on C/C–SiC composites (carbon fibre-reinforced carbon with silicon carbide matrix), manufactured using the liquid silicon infiltration (LSI) process and an in situ joining method, offer high specific stiffness and strength, low thermal expansion, high environmental stability, and temperature resistance. Potential applicati...

Because of the excellent fracture toughness and oxidation resistance, carbon fiber reinforced silicon carbide (C/C-SiC or C/SiC) exhibits a sound potential in various application areas such as aerospace technology and high-performance braking systems. For the composite’s reliable design, production, examination, quality assurance and verification,...

The paper presents characterization and modeling of generation of cracks during pyrolysis process of manufacturing of C/C–SiC material. Crack patterns during pyrolysis strongly depend on the fiber/matrix interface strength and temperature. In order to model the exact crack pattern as in the material, fiber/matrix interface strength was taken as a v...

The determination of elastic properties at application temperature is fundamental for the design of fibre reinforced ceramic composite components. An attractive method to characterize the flexural modulus at room and high temperature under specific atmosphere is the nondestructive Resonant Frequency Damping Analysis (RFDA). The objective of this pa...

The surface of a commercial PAN-based carbon fiber (CF) was modified to optimize fiber–matrix adhesion (FMA) in a CF-reinforced polymer (CFRP) preform used for the manufacture of CF-reinforced silicon carbide (C/C-SiC) composites. For these purposes, CFs were thermally desized and then electrochemically oxidized. The surface of the fibers was inves...

The article introduces a test method that allows the measurement of the indentation hardness of ceramic composites (CMC). CMCs are anisotropic materials consisting of high-strength ceramic fibres in a ceramic matrix. Knowledge of the hardness of CMCs is relevant in practice in order to be able to classify their machinability and wear resistance. Th...

For the continuous development of ultra high temperature ceramic matrix composites manufactured using reactive melt infiltration (RMI), the influence of three different melt alloys and two preform routes on mechanical behaviour and melt infiltration is investigated. Contact angle and viscosity measurement are performed to describe the melt infiltra...

Ceramic matrix composites usually utilize carbon or ceramic fibers as reinforcements. However, such fibers often expose a low ductility during failure. In this work, we follow the idea of a reinforcement concept of a ceramic matrix by refractory metal fibers to reach pseudo ductile behavior during failure. Tungsten and molybdenum fibers were chosen...

The determination of the hardness allows useful qualitative conclusions regarding the mechanical properties of materials. It is one of the most economical characterization methods, since this can be carried out with little effort on small specimens. However, due to the heterogeneous structure containing hard and brittle ceramic phases, the determin...

Four unidirectional fiber reinforced SiCN ceramic matrix composites were manufactured by means of polymer infiltration and pyrolysis. Two carbon fibers (T800H and Granoc XN90) as well as two silicon carbide fibers (Tyranno ZMI and SA3) without fiber coating were chosen. As matrix precursor, a poly(methylvinyl)silazane was investigated and utilized....

The paper presents enhanced studies of investigation and modeling of failure properties for wound ceramic matrix composites with varied fiber orientations under tensile loading. Based on mechanical tests and microstructure analysis, the characteristics of a virtual equivalent unidirectional layer (UD-layer) were examined and treated as input for mo...

The sandwich structures based on continuous fiber reinforced grid cores and skin panels have been developed via Liquid Silicon Infiltration (LSI) and in situ joining methods. Because of its excellent specific stiffness and temperature resistance, these lightweight structures have a sound potential for various application areas such as aerospace and...

Ceramic matrix composites offer remarkable strength and toughness and are usually designed based on the stacking of fiber plies. These composites are susceptible to debonding of these plies, as their interlaminar strength is significantly lower than in direction of the fibers. In this study, the application of torsion tests for the measurement of t...

This chapter examines how silicon carbide fiber reinforced SiC composites offer performance advantages such as higher temperature capability and significant lower density over the currently used metallic superalloys. The fiber coating is aimed for the creation of a weak fiber‐matrix interface in order to promote energy dissipating effects such as f...

In this work, a recent production technique of oxide ceramic matrix composites with a porous matrix based on commercial prepregs from Axiom, USA, was developed and investigated. The main objectives were to study the influences of the different prepreg types and the manufacturing process on the material properties. Two commercially available prepreg...

The understanding of the directional dependence of electrical properties in composite materials is essential to develop an accurate electromechanical model for these materials. However, determining the out-of-plane electrical resistivity in composite materials is a challenging task due to the architectural complexity of these materials and the diff...

The microstructures of MiCaSiC ® ceramics (Metal Infiltrated Carbon based Silicon Carbide) depend among others on the pore space properties of the carbon preforms before the liquid silicon infiltration (LSI). The aim of this work was to obtain three-dimensional information of the complex and non-homogeneous pore network in the carbon preform using...

Hypersonics, materials, structures, concepts, re-entry, C/C-SiC

This chapter examines the hot gas stability of oxide and non-oxide CMC, fabricated in different institutions of the CCeV in the burner rig of Fraunhofer IKTS Dresden. The tests were performed at 1250 °C and 1400 °C, a gas speed of 100 m/s and a water vapor pressure between 0.2 and 0.25 bar. The chapter also examines microstructure of surface and bu...

In a new design approach, C/C–SiC sandwich structures have been realized via liquid silicon infiltration and in situ joining methods. In the first process step, the carbon fiber reinforced polymer preforms for the planar skin plates as well as for the core structures were manufactured via warm pressing and autoclave technique, using C fiber fabrics...

At the Institute of Structures and Design of German Aerospace Center (DLR) in Stuttgart, C/C-SiC sandwich structures based on continuous fiber reinforced folded cores and skin panels have been developed via Liquid Silicon Infiltration (LSI) and in situ joining method. The resulting lightweight structures offer a high potential in various applicatio...

Liquid Silicon Infiltration (LSI) is a technique to manufacture non-oxide ceramic matrix composites such as C/C-SiC or SiC/SiC. In the beginning of this three-step process, fiber preforms are shaped and impregnated with phenolic resins. After curing, the preforms are pyrolyzed to convert the polymer matrix to a porous carbon matrix. This porosity i...

At the Institute of Structures and Design of German Aerospace Center (DLR) in Stuttgart, C/C-SiC sandwich structures based on continuous fiber reinforced folded cores and skin panels have been developed via Liquid Silicon Infiltration (LSI) and in situ joining method. The resulting lightweight structures offer a high potential in various applicatio...

From the literature, it is known that due to their glass formation tendency, it is not possible to deposit fully-crystalline silicate coatings when the conventional atmospheric plasma spraying (APS) process is employed. In APS, rapid quenching of the sprayed material on the substrate facilitates the amorphous deposit formation, which shrinks when e...

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. Durin...

Silicon-carbide-fiber-reinforced silicon carbide matrix composites (SiC/SiC) exhibit good thermal shock resistance, a low coefficient of thermal expansion and excellent physical properties as well as chemical stability at elevated temperatures and are therefore regarded as promising candidates for various applications in heavily loaded turbine sect...

Yttria-stabilized zirconia (YSZ) is the state-of-the-art material for the top coat of thermal barrier coatings. To increase the efficiency and lifetime of gas turbines, the integration of MoSi2 as a healing material was proposed. A new method of manufacture was explored in order to enable the spraying of a homogeneous mixed layer of YSZ and MoSi2....

For use of short fiber reinforced ceramics the knowledge of the influence of coupon geometry on the failure mode and the determined resistance in bending tests is necessary. In contrast to the continuous fiber reinforced ceramic matrix composites (CMC), for short fiber reinforced CMC there are only few studies and no standard on consideration of si...

A damage tolerant weak matrix SiC fiber reinforced composite was developed by utilising a polyvinylsilazane in the polymer infiltration and pyrolysis (PIP) process. The polysilazane was infiltrated via resin transfer moulding in a layup of SA3 fabrics, thermally cured and pyrolyzed. This process was repeated until a residual open porosity of below...

The present work includes a constitutive damage meso-model which is based on the investigations of mechanical properties under room and high temperature of a plain-woven oxide/oxide Ceramic Matrix Composite (CMC) material. The models developed for unidirectional plies have been adapted to a plain-woven ply. The damage is defined as the degradation...

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. Durin...

Ceramic matrix composites (CMC) offer the potential of increased service temperatures and are thus an interesting alternative to conventional combustor alloys. Tubular combustor liner demonstrators made of an oxide/oxide CMC were developed for a lean combustor in a future aero-engine in the medium thrust range and tested at engine conditions. Durin...

Fiber reinforced composites containing a ZrB2 matrix are prepared by reactive melt infiltration, using a Zr based intermetallic compound. The reactive melt infiltration process is further characterized by determining the contact angle of the different melt and preform elements. Two different methods for boron powder impregnation of the preforms, wh...

In the present study, the feasibility of the production of silicon carbide based ceramics via liquid silicon infiltration process (LSI-process) was demonstrated. The manufactured MiCaSiC ceramics (metal infiltrated carbon based silicon carbide) were based on novel raw material compositions. For these material compositions, activated carbon, carbon...

In order to develop SiC/SiC ceramic matrix composites with a low porosity, liquid silicon infiltration (LSI) was chosen as a technique, characterized by short processing times. To create the matrix, a tailored phenolic resin containing ß-naphthol units was synthesized and infiltrated in wound fiber preforms, thermally cured, pyrolysed and siliconiz...

Herstellung und Test von C/C-SiC Sandwichstrukturen mit Faltkernen.

Übersucht zur Herstellung von C/C-SiC und dessen Werkstoffeigenschaften. Entwicklung von Reibbelägen für Airbus A 400M. Neue Preformtechniken und Sandwichsrukturen für Bremsscheiben.

Herstellung und Test von C/C-SiC Sandwichstrukturen mit Faltkernen.

Herstellung und Test von C/C-SiC Sandwichstrukturen mit Faltkernen.

This study presents enhanced studies of inverse approach of the classical laminate theory for prediction of the elastic properties of a wound oxide ceramic matrix composites material (CMC). Based on mechanical tests and microstructure analysis, elastic properties of virtual equivalent unidirectional layers were calculated. To adapt the analytical m...

Fiber reinforced composites containing a ZrB2 matrix is prepared by reactive melt infiltration, using a Zr based intermetallic compound. Different precursors are evaluated in order to manufacture fiber reinforced preforms and enable a melt infiltration process. In order to infiltrate the porous preform, capillary forces must be high enough to pull...

During atmospheric re-entry high thermal loads are generated on the surface of the entry vehicle with peak loads in the stagnation area. Typical entry vehicles have a blunt shape avoiding sharp tips or leading edges because the heat load increases with a decreasing curvature radius of the surface structure. Recent developments for vehicles in the h...

The main objective of this work is the evaluation of the mechanical shear properties of a short-carbon-fiber-reinforced ceramic, which shows strong non-homogeneity in its microstructure and anisotropy through different fiber orientations. In this work, the shear modulus (G-modulus) and shear strength of this material were determined with the Iosipe...

For continuous fiber-reinforced ceramic matrix composites, there is an extensive knowledge of the influence of specimen geometry on the failure mode and the determined strength in bending tests. In contrast, there are almost no studies on this topic for short-fiber-reinforced CMC, and as a consequence no testing standard for bending tests for such...

SiC/SiC ceramics consist of silicon carbide fibres embedded in a silicon carbide matrix. As an alternative to classic CVI and PIP routes, Liquid Silicon Infiltration (LSI) was chosen as a technique with short process times to obtain composites with low porosity. Silicon carbide composites show good thermal shock resistance, a low coefficient of the...

Uncoated SiC fibres in SiC/SiC composites manufactured by the liquid-silicon infiltration (LSI) process show a strong degradation as a result of silicon attack. The goal of this research is the development of a SiNx-based fibre coating, which acts as a barrier against the liquid silicon. The coating is applied by means of low-pressure chemical vapo...

The key step in the manufacture of C-fibre reinforced SiC composites (C/C-SiC) via liquid silicon infiltration of porous C/C structures is the manufacture of CFRP composites. In this step fibre matrix bonding (FMB) is determining the microstructure in C/C state: strong FMB leads to a block structure of dense C/C segments which are hardly accessible...

Specific phenolic resin samples have been developed as the carbon precursor for SiC/C composites. Liquid phenolic resins suitable for fiber-infiltration in the resin transfer moulding (RTM) process are synthesized by using versatile combination of the aromatic component (phenol, naphthalen-2-ol) with various formaldehyde equivalents such as methana...