Daniel Cepli’s research while affiliated with German Aerospace Center (DLR) and other places

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Publications (7)


Notch sensitivity of C/C-SiC composite evaluated by flexural tests
  • Article

December 2023

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28 Reads

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4 Citations

Journal of the European Ceramic Society

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Yanlei Xiu

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Peifang Wu

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[...]

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Overview of investigations in this paper
Test configuration for testing of (A) planar and (B) curved 3 PB specimens
Acetylene‐oxygen burner rig; (1): nozzle, (2): infrared thermometer (CTLaser MT), (3): mount with sample, (4): infrared camera Optris PI 450
Oxide ceramic matrix composites (O‐CMC) sample mounted on shaker for high‐cycle‐fatigue (HCF) preload, (1): curved sample, (2): mounting screw with adapter below, (3): mount, (4): shaker table
Boundary conditions of FEM simulation; the orange area was subjected to a heat flux that was then calibrated to match the observed temperatures. The gray areas on the sample edges were fixed to ensure comparable boundary conditions to the practical tests.

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Effect of coupon geometry and preload on flexural properties of oxide ceramic matrix composites
  • Article
  • Full-text available

January 2023

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67 Reads

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.

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Manufacture and thermomechanical characterization of wet filament wound C/C‐SiC composites

May 2021

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138 Reads

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4 Citations

The paper presents manufacture of C/C‐SiC composite materials by wet filament winding of C fibers 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 siliconization, and tensile strength strongly depend on the fiber/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.


Experimental evaluation and theoretical prediction of elastic properties and failure of C/C‐SiC composite

May 2021

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256 Reads

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9 Citations

The paper presents experimental characterization and theoretical predictions of elastic and failure properties of continuous carbon fiber reinforced silicon carbide (C/C‐SiC) composite fabricated by Liquid Silicon Infiltration (LSI). Its mechanical properties were determined under uniaxial tensile, compression, and pure shear loads in two sets of principal coordinate systems, 0°–90° and ±45°, respectively. The properties measured in the 0°–90° coordinate system were employed as the input data to predict their counterparts in the ±45° coordinate system. Through coordinate transformations of stress and strain tensors, the elastic constants and stress‐strain behaviors were predicted and found to be in good agreement with the experimental results. In the same way, three different failure criteria, maximum stress, Tsai‐Wu, and maximum strain, have been selected for the evaluation of the failure of C/C‐SiC as a type of genuinely orthotropic material. Based on the comparisons with experimental results, supported by necessary practical justifications, the Tsai‐Wu criterion was found to offer a reasonable prediction of the strengths, which can be assisted by the maximum stress criterion to obtain an indicative prediction of the respective failure modes.


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

April 2021

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27 Reads

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

February 2021

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103 Reads

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6 Citations

Journal of the European Ceramic Society

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.


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

July 2019

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20 Reads

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.

Citations (3)


... The cost and process complexity for the 3D weaving, knotting, stringing technologies are between the needle punching and the braiding [13], and the obtained composites have their advantages in terms of delamination resistance, impact damage tolerance, and ballistic damage resistance [17]. In general, most studies are now concentrated on the mechanical properties and failure of these C/SiC composites [18][19][20][21][22]. Part of the studies reported the ablation behavior of 2D, 3D needle-punched, 3D braided C/SiC composites [23][24][25]. ...

Reference:

Mechanical and ablation properties of 3D orthogonal woven C/C-SiC composite based on high-solid-loading slurry impregnation
Manufacture and thermomechanical characterization of wet filament wound C/C‐SiC composites

... The main load is carried by the fiber bundles of the vertical screen, leading to the interface debonding and fiber pullout fracture. [39][40][41] With the increase in bulk density of the C/C preform and the HT, the overall fiber pullout length of the C/C-SiC composites increases, improving the fracture strain of the composite, as shown in Figure 9. ...

Experimental evaluation and theoretical prediction of elastic properties and failure of C/C‐SiC composite

... It is the sub-group of wet-laid nonwoven which offer a wide range of shaping possibilities due to its unique manufacturing process and the resulting textile has very few fibers in thickness direction which allows a higher FVF than regular nonwovens. It was found, that depending on the fiber preparation during the fabric manufacturing, short fiber reinforced ceramics as well as monolithic ceramics are obtainable [13]. The manufacturing of the wet-laid nonwoven ceramics is summarized in Fig. 1 and shows their two possible microstructures. ...

Wet-laid nonwoven based Ceramic Matrix Composites: An innovative and highly adaptable short fiber reinforcement for ceramic hybrid and gradient materials
  • Citing Article
  • February 2021

Journal of the European Ceramic Society