Concurrently, as the materials are refined, designers must have access to material properties and performance databases in order to integrate the material systems into their advanced engineering concepts.
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Without extensive materials characterization, producers of materials cannot evaluate relative process improvements nor can designers have confidence in the performance of the material for a particular application. Developing and verifying appropriate test methods as well as generating design data and design experience for advanced materials is expensive and time consuming.
High-temperature ceramic composites are more expensive to process than monolithic ceramics, not just because of the extra cost of constituent materials but also because of labor-intensive fabrication steps. Equipment for testing at elevated temperatures is highly specialized and expensive. Unique and novel test methods must be developed to take into account thermal stresses, stress gradients, measurement capabilities, gripping methods, environmental effects, statistical considerations, and limited material quantities.
It is therefore imperative that test methods be carefully developed, standardized, verified, and utilized so that accurate and statistically significant data are generated and duplication of efforts can be minimized in test programs. Similarly, design codes must be written to establish which information on material properties and performance are required for particular applications as well as which standard test methods are recommended to quantify this information.
The papers in this publication provide current results of research and development programs on continuous fiber ceramic composites. The papers are divided into four major categories: 1. The papers in the Environmental Effects and Characterization section address the thermal diffusivity changes due to microstructural damage, oxidation behavior in aggressive environments, time dependent deformation, and the effects of interphase oxidation.
In the section on Damage Accumulation and Material Development, papers address damage accumulation during mechanical loading, effect of loading mode, temperature and environmental degradation of a novel pre-commercial material, degradation under constant load, and process development of a novel material system. With this symposium and the resulting special technical publication, ASTM has made another stride forward in standardization activities by providing a wealth of information on continuous fiber ceramic composites.
This information will assist the research, processing, and design community in better understanding the behavior, characterization and design nuances of these materials. This information is also invaluable for standards and code development background as test methods continue to be introduced and verified for continuous fiber ceramic matrix composites. Gonczy Gateway Materials Technology Mt.
Ojard,2 and Ronald R. Jenkins, E. Lara-Curzio, and S. Gonczy, Eds. Abstract: The evolutionary path of ceramic matrix composites CMCs to viable candidate materials for current engineering designs of today and tomorrow has been littered with appropriate and inappropriate theoretical models, useful and useless test methods, and hopeful and hopeless materials systems.
As continuous fiber ceramic composite CFCC material systems have been introduced, theoretical models and practical test methods have been proposed and adopted to characterize their behavior.
Often these materials are targeted for specific applications intended to exploit the bulk CFCC as well as its constituent properties. The unique position and expertise of the author's employer, a private research laboratory, have enabled an up-close and detailed perspective on not only CFCCs and their characterization but also the targeted engineering applications. In this paper, a case study will be discussed regarding characterization of a CFCC for a particular application; a high temperature combustor liner in a gas turbine engine.
The potential for standardized methods will be reviewed. This position has enabled an up-close and detailed perspective on not only the ceramic matrix composites and their characterization but also the targeted engineering applications. In this paper, a case study will be discussed regarding hoop characterization of a CMC for a high temperature combustor liner in a gas turbine engine. The pursuit of next generation supersonic transports to carry people around the world at twice the speed of sound has fostered the development of technology and materials to make the effort cost effective, reliable, and environmentally compatible.
In order to meet these goals, companies have focused on advanced materials such as ceramic matrix composites [3,4]. CMCs have the potential to enable components to run hotter to improve thermodynamic efficiency and reduce noise and emissions. Innovative design and the judicious use of CMCs in hot section components of gas turbine engines and creative interfacing with metallic components are key to their successful implementation. The ability to run without surface cooling has made CMCs particularly attractive for combustor applications.
A key contributor to the success of fabrication was agreement and utilization of standard test methods that allowed testing to be done at a variety of independent test laboratories with results that were consistent from laboratory to laboratory. Application of a CMC- Combustor Liners A major concern with high-speed air transports is the addition of nitrogen oxides NOx to the upper atmosphere . To reduce NOx emissions, new combustor configurations that improve thermodynamic efficiency are required - CMCs are viable candidate materials for such designs Figure 1.
Application of Test Methodology - Hoop Tensile Evaluation To assess the materials resistance to thermal stress induced by axial temperature gradients in combustor liners, one of the necessary properties is the hoop tensile strength. Data obtained from coupons of flat plates would be a starting point; however, it is generally known that as complexity of parts increase, properties tend to decrease because of the difficulty of replicating ideal processing conditions in curved or transitional regions or in the vicinity of unique out-of-plane features .
Consequently, a test methodology to characterize hoop properties is required. The two cover plates are clamped together with a circle of bolts. The ring specimen is mounted between the upper and lower spacer rings. Spacer blocks, mounted between the spacer rings, maintain approximately 0. Application of pressure by hydraulic oil to a rubber bladder, which mates to the inner diameter ID of the ring, causes expansion of the specimen.
A string wrapped around the outside of the hoop and attached to spring-loaded linear variable differential transformers LVDTs mounted on a rigid frame Figure 3 monitors the circumferential change in displacement with increasing pressure. The change in circumference can be transformed into the outer diameter OD circumferential strain.
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A pressure transducer is used to measure the pressure applied to the ring. The plot consists of internal pressure versus the deformation signal from the string. The data reported are ultimate hoop tensile strength, hoop elastic modulus, and hoop tensile strain-to-failure. Typical hoop stress-strain responses from ceramic matrix composites evaluated in this facility are shown in Figure 4. To obtain these properties, the elevated temperature hoop facility Figure 5 was used . As with the room temperature test, pressure is applied to a rubber bladder by hydraulic oil.
However, in this case, the bladder mates to the ID of water-cooled wedges 18 total , which in turn mate to low thermal conductivity wedges, which then mate to the ID of the test ring. Further analysis is currently being conducted using finite elements to determine the pressure profile applied to the ID of the ring in both polar and axial directions and the true peak hoop stress in the CMC test ring.
The ancillary equipment for the elevated temperature test is essentially as that for the room temperature test. Fiber 1 Ring Size: 9. The test methodology is not limited to just combustor liners, i. Pressure vessels, exit cones, filters for hot gas filtration, and other body-of-revolution components are examples to which the methodology is directly applicable. If warranted, the current test methodology may be transferred to an existing nation, or international, standards writing body for formal normalization.
It is important that test standards development continue because standards: 9 9 9 9 provide guidelines and terms for transfer of consistent information between designers, manufacturers, and end users, provide consistent, meaningful data to users, provide consistent, meaningful data to material databases, permit confidence in data interchange and integration.
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During development of standards, careful consideration should be given to ensure that the standard provides the proper guidelines for the data required and the technique is analogous in terms of applied loading and boundary conditions to the application, etc. Also, there are pitfalls to using only established standards, i.
An example is the tensile hoop strength of CMCs determined with an elastomeric insert. Although it is a viable technique of comparative testing for down-selecting materials, the hydrostatic methodology discussed previously has certain advantages such as better-defined boundary conditions and wider applicability. The hydrostatic approach might be the test of choice when developing and verifying analytical models.
The boundary conditions are not affected by specimen size, diameter or height, or material. It is possible that the "calibrations" of the eiastomeric insert might be affected by the changes in test specimen dimensions and material properties. Thus the choice of test method should be dictated by the information required. Summary In conclusion, test characterization of current and emerging materials should not be performed without challenging the prevailing test procedure and specimen configuration for relevance to the specific design application.
There are many unique attributes such as high temperature, directional stress, anisotropy, or low strain-to-failure in these materials that require more precise understanding of the mechanics of deformable bodies. Though not a replacement for rig or engine tests, judicious use of specialized laboratory test specimens and procedures can economically reduce component risk by highlighting Unanticipated failure modes or damage accumulation mechanisms in a controlled environment. Gonczy, 3 and Larry P. Ten each of flexure, in-plane tension, in-plane Iosipescu shear, and interlaminar double notch compression test specimens were tested by each of seven to ten different laboratories per the applicable ASTM test method for totals of sixty to one hundred replicate tests for each test type.
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Emerson, Mt. Prospect,IL CFCCs exhibit greatly increased "toughness" i. A variety of industrial applications have been targeted for CFCCs, including tubing, nozzles, vanes and supports in heat recovery equipment and heat engines [1, 2]. In the chemical industry, reformers, reactors and heat exchangers are other potential applications.
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In gas turbine power generation CFCC components allow increased temperatures resulting in substantial reductions in nitrous oxide NOx emissions and savings in the cost of power generation . Thermo-mechanicat behavior and its subsequent characterization of CFCCs is currently the subject of extensive investigation worldwide . In particular, determination of the properties and performance mechanical, thermal, thermomechanical, physical, environmental, etc.
As CFCC prototype and trial products begin to reach the marketplace, the paucity of standards i. Standards The term "standards" has many implications. To the researcher and the technical community it may be fundamental test methodologies and units of measure.
To the manufacturer or end-product user it may be materials specifications and tests to meet performance requirements. Commercial standards equate to the rules and terms of information transfer among designers, manufacturers and product users . At present, there are few -- nationally or internationally -- full-consensus standards  for testing not only advanced ceramics and but especially CFCCs. However, of those standards that do exist, American Society for Testing and Materials ASTM standards are arguably considered the most technically rigorous and of the highest quality.
Design Codes and Data Bases The meaning of the term 'design code' is not generally well understood. As used here 'design code' is not a design manual i. Instead, 'design codes' are widely-accepted, but general rules for the construction of components or systems with emphasis on safety .