G. Ojard

Ceramic Matrix Composite Combustor Liner Rig Test

The NASA High Speed Research (HSR)/Enabling Propulsion Materials (EPM) program was charged with the responsibility for developing the materials and technologies necessary to meet the High Speed Civil Transport (HSCT) engine requirements. The combustor liner was identified as a critical component for meeting the efficiency and environmental acceptability goals of the HSCT engine. The EPM Ceramic Matrix Composite (CMC) Combustor liner program was tasked with developing and demonstrating a material system and design concept that meets the HSCT environmental, thermal, structural, economic, and durability requirements. Melt Infiltration (MI) SiC/SiC composites were ultimately selected for the combustor liner application. The culmination of this development effort was the delivery and testing of a CMC combustor liner. Testing was performed at NASA Glenn Research Center in the Sector Rig under HSCT operating conditions. The initial results of the rig testing are presented.Copyright

Modeling of crack density in ceramic matrix composites

The feasibility of utilizing the shear lag theory to estimate crack density in fabric reinforced composites was investigated. A geometric model was constructed for the fabric and meshed using a hybrid finite element approach. The small segment of the yarn and the surrounding matrix enclosed within each element were treated as a unidirectional composite and the shear lag theory was used to estimate the crack density. Model results were compared to experimental data for a 5-harness satin melt-infiltrated SiC/SiC composite under tension and showed a pattern similar to experimental data with the model starting to accumulate cracks at a stress corresponding to the point of departure from linearity in the stress–strain curve while cracks were experimentally observed around 60u2009MPa higher. The model and experimental data had a similar value for the crack density at the saturation level. Sensitivity analysis showed that the crack density was highly sensitive to the fiber volume fraction in the load direction followed by the weave angle of the crimped segments of the yarns and the interfacial shear strength between the fibers and the matrix.

Engine Test and Post Engine Test Characterization of Self-Sealing Ceramic Matrix Composites for Nozzle Applications in Gas Turbine Engines

The advancement of self-sealing ceramic matrix composites offers durability improvements in hot section components of gas turbine engines. These durability improvements come with no need for internal cooling and with reduced weight. Building on past material efforts, ceramic matrix composites based on either a carbon fiber or a SiC fiber with a sequenced self-sealing matrix have been developed for gas turbine applications. The specific application being pursued on this effort is an F100-PW-229 nozzle seal. Full design life ground engine testing has been accomplished with both material systems. The ground testing has demonstrated a significant durability improvement from the baseline metal design. Residual properties are being determined for both systems by extracting tensile and microstructural coupons from the ceramic matrix composite seal. Nondestructive interrogation showed no material degradation and was used as a guide in setting cutting diagrams. The results from this effort will be presented along with documentation from flight test efforts.Copyright

Characterization and Nozzle Test Experience of a Self Sealing Ceramic Matrix Composite for Gas Turbine Applications

Advanced materials have the potential to improve gas turbine engine durability. One general area of concern for durability is in the hot section components of the engine. Ceramic matrix composites offer improvements in durability at elevated temperatures with a corresponding reduction in weight for nozzles of gas turbine engines. Building on past material efforts, a next generation SiC/SiC composite with a self-sealing matrix has been developed for gas turbine applications. An extensive baseline test characterization has been done that shows the overall material suitability. Prior to ground engine testing, a reduced test matrix was undertaken to aggressively test the material in a long-term hold cycle at elevated temperatures and environments. This tensile low cycle fatigue testing was done in air and a 90% steam environment. While the steam environment aggressively attacked the material, no appreciable debit in material life was noted. Nondestructive testing and post test characterization of this testing were performed. After completion of the aggressive testing effort, two nozzle seals of constant thickness were fabricated and installed in an F100-PW-229 engine for accelerated mission testing. The self sealing CMC seals were tested for over 250 hours in accelerated conditions without damage. The results of the engine testing will be shown and overall conclusions drawn.Copyright

Engine Test Experience and Characterization of Self Sealing Ceramic Matrix Composites for Nozzle Applications in Gas Turbine Engines

Advanced materials are targeting durability improvement in gas turbine engines. One general area of concern for durability is in the hot section components of the engine. Ceramic matrix composites offer improvements in durability at elevated temperatures with a corresponding reduction in weight for nozzles of gas turbine engines. Building on past material efforts, ceramic matrix composites using a carbon and a SiC fiber with a self-sealing matrix have been developed for gas turbine applications. Prior to ground engine testing, a reduced test matrix was undertaken to aggressively test the material in a long-term hold cycle at elevated temperatures and environments. This tensile low cycle fatigue testing was done in air and a 90% steam environment. After completion of the aggressive testing effort, six nozzle seals were fabricated and installed in an F100-PW-229 engine for accelerated mission testing. The C fiber CMC and the SiC Fiber CMC were respectively tested to 600 and 1000 hours in accelerated conditions without damage. Engine testing is continuing to gain additional time and insight with the objective of pursuing the next phase of field service evaluation. Mechanical testing and post-test characterization results of this testing will be presented. The results of the engine testing will be shown and overall conclusions drawn.Copyright

Post Engine Test Characterization and Flight Test Experience of Self Sealing Ceramic Matrix Composites for Nozzle Seals in Gas Turbine Engines

The advancement of self-sealing ceramic matrix composites offers durability improvements in hot section components of gas turbine engines. These durability improvements come with no need for internal cooling and with reduced weight. Building on past material efforts, ceramic matrix composites based upon a silicon carbide or carbon fiber with a novel self-sealing matrix have been developed for gas turbine applications. The specific application being pursued on this effort is an F100-PW-229 nozzle seal. Ground engine testing has been completed that exceeds the full design life. The ground testing has demonstrated a significant durability improvement from the baseline metal design. Residual properties have been determined by extracting tensile and microstructural coupons from the ceramic matrix composite seal. This was done as a function of design life. Nondestructive interrogation was used as a guide in setting cutting diagrams. The results from this effort will be presented.© 2005 ASME

Thermographic investigation of damage in ceramic matrix composites

As the engineering application of ceramic matrix composites progresses, a key part of the insertion effort is the non-destructive characterization. While most non-destructive evaluation is focused on the initial state based on the presence of defective conditions, the evolution of damage or change with exposure is more relevant. Thermography offers the benefit of fast inspection times with the option of finding defects or material changes based on the diffusivity of the material. A series of samples made out of ceramic matrix composite were inspected by thermography. Samples consisted of asfabricated and ones exposed to different conditions of temperature, stress and time. The results of this testing along with mechanical testing and analysis are presented and trends discussed.

An Approach for Mechanistic Modeling of Ceramic Matrix Composites

A mechanistic modeling approach for material characterization and for life prediction of CMC components is described. The approach includes consideration of environment-induced degradation of CMC properties, progressive microcracking of the matrix material and interfacial damage. The mechanistic model has been embedded in a finite element analysis (FEA) framework to enable structural analyses of components and to analyze macro damage, such as cracks and delaminations. This paper describes the modeling approach and its application in the study of substructures. Examples include analyses of simple test specimen coupons, stress concentration at holes and a structural element configuration of a 2D woven SiC/SiC composite. The results include predicted and measured strain field near circular holes and global load-displacement behavior of structural elements. In each case, the model predictions are compared with the experimental measurements.Copyright

Acoustic emission as a screening tool for ceramic matrix composites

Ceramic matrix composites are composite materials with ceramic fibers in a high temperature matrix of ceramic or glass-ceramic. This emerging class of materials is viewed as enabling for efficiency improvements in many energy conversion systems. The key controlling property of ceramic matrix composites is a relatively weak interface between the matrix and the fiber that aids crack deflection and fiber pullout resulting in greatly increased toughness over monolithic ceramics. United Technologies Research Center has been investigating glass-ceramic composite systems as a tool to understand processing effects on material performance related to the performance of the weak interface. Changes in the interface have been shown to affect the mechanical performance observed in flexural testing and subsequent microstructural investigations have confirmed the performance (or lack thereof) of the interface coating. Recently, the addition of acoustic emission testing during flexural testing has aided the understanding ...

Thermal and destructive interrogation of ceramic matrix composites

Ceramic matrix composites are intended for elevated temperature use and their performance at temperature must be clearly understood as insertion efforts are to be realized. Most efforts to understand ceramic matrix composites at temperature are based on their lifetime at temperature under stress based on fatigue or creep testing or residual testing after some combination of temperature, stress and time. While these efforts can be insightful especially based on their mechanical performance, there is no insight into how other properties are changing with thermal exposure. To gain additional insight into oxidation behavior of CMC samples, a series of fatigue and creep samples tested at two different temperatures were non-destructively interrogated after achieving run-out conditions by multiple thermal methods and limited X-ray CT. After non-destructive analysis, residual tensile tests were undertaken at room temperature. The resulting residual properties will be compared against the non-destructive data. Ana...