Influence of Fiber Type on the Properties of Short-Fiber Based C/C-SiC

Originally developed for heat shields and hot structures of space vehicles, C/C-SiC materials were adapted to be applied as lightweight, high performance brake discs for automotive use. Thereby, costly fiber preforms based on woven fabrics, typically used for thin walled aerospace structures, were replaced by cut fiber rovings, leading to economic as well as technical advantages. Press masses with randomly oriented short fibers and powdery phenolic resin offer a high flowability and even thick-walled parts with complex shaped geometries, like internally ventilated brake discs in single piece design, can be manufactured economically in near net shape technique. In a new approach, short-fiber based C/C-SiC materials have been further developed for the use in space propulsion systems, where high mechanical and thermal loads are a challenge. In order to meet these requirements, the commonly used high tenacity (HT) fibers were replaced by intermediate modulus (IM) and pitch based ultrahigh modulus (UHM) carbon fibers with a fiber length of 10 mm. The resulting C/C-SiC materials showed different microstructures with significantly different phase composition. Compared to HT based C/C-SiC, strength an elastic modulus were increased by UHM fibers, whereas the use of IM fibers lead to higher fracture strain. The manufacture of the sample plates as well as the influence of the fiber type on the mechanical properties is presented in detail

Manufacture and Thermomechanical Characterization of Wet Filament Wound C/C‐SiC Composites

The paper presents manufacture of C/C‐SiC composite materials by wet filament winding of C‐fibres with a water based phenolic resin with subsequent curing via autoclave as well as pyrolysis and liquid silicon infiltration (LSI). Almost dense C/C‐SiC composite materials with different winding angles ranging from ±15° to ±75° could be obtained with porosities lower than 3% and densities in the range of 2 g/cm3. Thermomechanical characterization via tensile testing at room temperature and at 1300 °C revealed higher tensile strength at elevated temperature than at room temperature. Thus, C/C‐SiC material obtained by wet filament winding and LSI‐processing has excellent high temperature strength for high temperature applications. Crack patterns during pyrolysis, microstructure after siliconisation and tensile strength strongly depend on the fibre/matrix interface strength and winding angle. Moreover, calculation tools for composites, such as classical laminate and inverse laminate theory can be applied for structural evaluation and prediction of mechanical performance of C/C‐SiC structures

Effect of coupon geometry and preload on flexural properties of oxide ceramic matrix composites

Oxide ceramic matrix composites (O-CMCs) have a high potential for usage in thermal protection systems or combustion chambers because of their low weight, temperature- and corrosion stability as well as non-brittle failure behavior. Mechanical property changes over their lifetime due to operational loads are not well understood. Moreover, mechanical properties from planar samples under laboratory conditions often differ substantially from upscaled components with complex geometries. In this work, the influences of curvature and preloading conditions were investigated experimentally using modeling to determine boundary conditions. Effects of curvature and trends among preload conditions were determined, with high-cycle-fatigue-preload (HCF) reducing strength and Young’s Modulus by 15% compared to their original values where low-cycle-fatigue-preload (LCF) had smaller effect. The low impacts of high temperatures and small-to-medium loads on the properties of O-CMCs makes them an interesting choice for high-temperature combustive environments

Manufacture and Thermomechanical Characterisation of Wet Filament Wound C/C-SiC Composites

Ceramic matrix composites based on wet filament winding and LSI-processing are attractive candidates (C/C-SiC) for many applications in aerospace. Therefore, commercial C-fibres and a water-based phenolic resin were used for wet filament winding on a mandrel and subsequent curing in an autoclave, followed by pyrolysis to a C-matrix and liquid silicon infiltration (LSI) to form a C-SiC-matrix. By applying wet filament winding the mechanical properties can be tailor-designed according to the chosen fibre orientation since C/C-SiC is a fibre dominant and damage tolerant CMC material. Wet filament winding was performed on a mandrel with winding angles of +/-15°, +/-30° and +/-45°, +/-60° and +/-75° were made possible by cutting samples in perpendicular direction. Tubes in wet state were cut in axial direction, flattened and cured on a flat plate without applying additional pressure, such as warm pressing, in order to obtain similar curing conditions to tubes. Mechanical and thermomechanical characterisation of flat specimen of C/C-SiC composites was performed by using an Indutherm universal testing machine using inductive heating of samples and a laser extensometer for measuring of displacement under inert conditions. Testing of tensile specimens was performed at room temperature as well as high temperatures up to 1600°C. In addition, microstructural characterization was performed by SEM

A new automotive application for ceramic matrix composites (CMC): C/C-SiC based piston rings for internal combustion engines (IC-engine)

Alternative energy and the transition away from fossil fuels is one of the core subjects of current politics. In the automotive industry the internal combustion engine, however, remains the most commonly used power unit. In terms of improving its environmental compatibility, the current research goal is to increase its efficiency and service life while maintaining or even reducing the fuel consumption. The DLR develops a ceramic fiber-reinforced piston ring, which should contribute to fuel savings and reduced piston wear. In order to investigate fundamental questions of feasibility and functionality, piston ring prototypes made of C/C-SiC (carbon fiber reinforced silicon carbide) were developed in cooperation with the DLR Institute of Structures and Design and DLR Institute of Vehicle Concepts. For a ceramic piston ring the mounting is one of the most restricting requirements, as the material is usually not flexible and fiber reinforcement has to be carefully adjusted in order to provide elastic behavior. Within the project, variants of C/C-SiC with different preforming technology were developed. Weaving-, winding- and tailored fiber placement-technologies were used for preform manufacturing. The mechanical examination of the samples was carried out according to ASTM C1323 - 16 for ceramic C-rings and the results were promising. In addition, the work provides further insights into the expected running behavior of the ceramic piston rings and how economic production can be achieved. Further research now aims at examining the effects on the energy consumption and service life when utilized in IC-engines

Wet-laid nonwoven based ceramic matrix composites: An innovative and highly adaptable short fiber reinforcement for ceramic hybrid and gradient materials

The wet-laid nonwoven as a preform manufacturing technique for C/C-SiCs has been pioneered in this study and holds great promises for the field, especially for hybrid materials. The wet-laid nonwovens are compatible with liquid silicon infiltration (LSI), and standalone samples of the wet-laid nonwoven ceramics, as well as a hybrid material, were produced. Through variations in the manufacturing process of the wet-laid nonwoven, the formation of short fiber C/C-SiC (69 % Carbon) and SiSiC (68 % SiC) was possible. Intense characterization (porosity, phase composition, flexural strength, Young's modulus, coefficient of thermal expansion, specific heat capacity, and thermal conductivity) exhibited similar material properties compared to well-established materials (SGL, Schunk). Wet-laid nonwoven usage allowed an in situ formed hybrid, which eliminates several high-temperature steps of traditional hybrid manufacturing and cuts down costs. It was demonstrated on a real scale component (ceramic brake disc) with a final material paring of C/C-SiC and SiSiC