Part A: applied scienc and manufacturing ELSEVIER Composites: Part A 30(1999)561-567 Development of test standards for continuous fiber ceramic composites in the United States Edgar Lara-Curzioa, Michael G Jenkins b Metals and Ceramics Division, Oak Ridge National Laboratory, Oak TN37831-6069,LSA Department of Mechanical Engineering. University of Washingte WA98195-2600,USA Abstract Standardization activities in the United States for continuous fiber-reinforced ceramic composites(CFCCs) are reviewed. This brief review focuses on the development of test standards by subcommittee C28.07 of the American Society for Testing and Materials(ASTM)on the drafting of a section of a design code for ceramic and ceramic matrix composite con part of the American Society of Mechanical Engineers(ASME) Boiler and Pressure Vessel Code, and on the development of a set of volumes on ceramic matrix composites for Military Handbook 17 on composites. The participation of the US in the international harmonization of standards for CFCCs is also reviewed Published by Elsevier Science Limited Keywords: CFCCs, Intemational harmonization; Test standards 1. Introduction advanced ceramics [2]. Committee C28 of the ASTM is structured into eight subcommittees, as indicated in Fig. 1 Continuous fiber-reinforced ceramic composites A workshop organized by the National Institute for Star (CFCCs) have been the focus of intensive developmental dards and Technology (NIST) in February 1990 helped set efforts over the last 15 years. These efforts have been driven the stage for the establishment of subcommittee C28.07 on to a large extent by the promise of substantial economic and ceramic matrix composites [3]. Since its establishment in environmental benefits if CFCCs are used in military and 1991, subcommittee C28.07 has been responsible for forma- energy-related technologies, particularly at elevated lizing seven full consensus standard test methods for CFCC. temperatures secause the commercial diffusion and and for drafting several other documents that are currently standardization efforts concurrent with the development of subcommittee C28.07. In addition to its work of developing these materials have focused on methods for the mechanical standards, subcommittee C28.07 has been responsible for evaluation of test specimens, and on the drafting of design informing the composites community of the progress in the standardization process through the organization of workshops and symposia The work of subcommittee C28.07 has been organized 2. Test standards round task groups, which are responsible for the prepara tion of drafts, and for the progress of these documents In the US, the American Society for Testing and Materi- through the balloting and approval process at the subcom- als(astm) has spearheaded the widespread introduction of mittee, committee and society levels. table 2 lists the task standard test methods for advanced ceramics and ceramic groups currently existing in C28.0 composites years since Its inception, ASTM commit Other efforts for standardization of test methods for ee C28 on Advanced Ceramics has been responsible for the creation of over 25 standards. These standards range from clones of prior ASTM standards(with some new provisions Workshop on Thermal and Mechanical Test Methods and Behavior of to complex, innovative documents tailored specifically to CFCCs", Montreal, Canada, June 1994:"Symposium on Thermal and Mechanical Test Methods and Behavior of CFCCs', Cocoa Beach, FL, 8-9 January 1996:"Workshop on Thermomechanical Tests for orresponding author CFCCs", Bozeman, MT, 18 October 1994 . 835X/99/S-see front matter Published by Elsevier Science Limited 1359-835 00150-X
Development of test standards for continuous fiber ceramic composites in the United States Edgar Lara-Curzioa,*, Michael G. Jenkinsb a Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6069, USA b Department of Mechanical Engineering, University of Washington, Seattle, WA 98195-2600, USA Abstract Standardization activities in the United States for continuous fiber-reinforced ceramic composites (CFCCs) are reviewed. This brief review focuses on the development of test standards by subcommittee C28.07 of the American Society for Testing and Materials (ASTM) on the drafting of a section of a design code for ceramic and ceramic matrix composite components as part of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, and on the development of a set of volumes on ceramic matrix composites for Military Handbook 17 on composites. The participation of the US in the international harmonization of standards for CFCCs is also reviewed. Published by Elsevier Science Limited. Keywords: CFCCs; International harmonization; Test standards 1. Introduction Continuous fiber-reinforced ceramic composites (CFCCs) have been the focus of intensive developmental efforts over the last 15 years. These efforts have been driven to a large extent by the promise of substantial economic and environmental benefits if CFCCs are used in military and energy-related technologies, particularly at elevated temperatures [1]. Because the commercial diffusion and industrial acceptance of CFCCs can be hampered by lack of standard test methods, databases or design codes, initial standardization efforts concurrent with the development of these materials have focused on methods for the mechanical evaluation of test specimens, and on the drafting of design codes. 2. Test standards In the US, the American Society for Testing and Materials (ASTM) has spearheaded the widespread introduction of standard test methods for advanced ceramics and ceramic composites. In 10 years since its inception, ASTM committee C28 on Advanced Ceramics has been responsible for the creation of over 25 standards. These standards range from clones of prior ASTM standards (with some new provisions) to complex, innovative documents tailored specifically to advanced ceramics [2]. Committee C28 of the ASTM is structured into eight subcommittees, as indicated in Fig. 1. A workshop organized by the National Institute for Standards and Technology (NIST) in February 1990 helped set the stage for the establishment of subcommittee C28.07 on ceramic matrix composites [3]. Since its establishment in 1991, subcommittee C28.07 has been responsible for formalizing seven full consensus standard test methods for CFCCs and for drafting several other documents that are currently undergoing the ASTM’s internal balloting process. Table 1 lists the existing standards developed for CFCCs by subcommittee C28.07. In addition to its work of developing standards, subcommittee C28.07 has been responsible for informing the composites community of the progress in the standardization process through the organization of workshops and symposia.1 The work of subcommittee C28.07 has been organized around task groups, which are responsible for the preparation of drafts, and for the progress of these documents through the balloting and approval process at the subcommittee, committee and society levels. Table 2 lists the task groups currently existing in C28.07. Other efforts for standardization of test methods for Composites: Part A 30 (1999) 561–567 1359-835X/99/$ - see front matter Published by Elsevier Science Limited. PII: S1359-835X(98)00150-X * Corresponding author. 1 ‘‘Workshop on Thermal and Mechanical Test Methods and Behavior of CFCCs’’, Montreal, Canada, June 1994; ‘‘Symposium on Thermal and Mechanical Test Methods and Behavior of CFCCs’’, Cocoa Beach, FL, 8–9 January 1996; ‘‘Workshop on Thermomechanical Tests for CFCCs’’, Bozeman, MT, 18 October 1994
E. Lara-Curaio, M.G. Jenkins/Composites: Part A 30 (1999)561-567 Table 2 Task groups within ASTM C28.07 Task group Activity c28.07 01 Tension ≈mm Mataio flexure 2807 Cyclic fatigue C28.94 C280707 Fibers Nomenclature C28.07.08 Interface C2807.09 Fig. 1. Structure of AsTm committee C28 on advanced ceramics C28.07.10 C28.07.11 C28.07.12 Structural/components CFCCs in the US include the development of non-consen- sus, industry-accepted standards developed by the NaSa General Electric/Pratt and Whitney Enabling Propulsion Specimens at Ambient Temperatures. Later, this standard Materials(EPM)Program. These documents, which pre- test method became a template for other documents invol date ASTM standards. are listed in Table 3 ving tensile testing, such as C1337( Standard Test Method In the following sections, the more relevant features of for Creep and Creep Rupture of Continuous Fiber-Rein- existing ASTM standard test methods for CFCCs are forced Advanced Ceramics under Tensile Loading), C1359(Standard Test Method for Monotonic Tensile Strength Testing of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Sections at 2.1. Tensile testing Elevated Temperatures)and C1360(Standard Practice for A survey of US CFCC manufacturers, conducted in 1991 Constant-Amplitude, Axial, Tension-Tension Cyclic Fati provided insights into the needs and priorities of this indus- gue of Continuous Fiber-Reinforced Advanced Ceramics at try for test standards [4]. To address those needs and prio- Ambient Temperatures) rities, the first standard developed for CFCCs by ASTM The most important issues addressed by test method system alignment, subcommittee C28. 07 was test method C1275 for Mono- measurements, specimen geometries, specimen preparation, tonic Tensile Strength of Continuous Fiber-Reinforced mode and rate of testing, and data acquisition. Although Advanced Ceramics with Solid Rectangular Cross-Sectio C1275 allows the use of any specimen geometry if it Table 1 meets the gripping, fracture location and fracture Existing standards under the jurisdiction of ASTM subcommittee C28. 07 requirements prescribed in the document, in the case of C1275-95 Standard test method for monotonic tensile strength Industry-accepted, s standards developed by NASA testing of continuous fiber-reinforced advanced Enabling Propulsion ogram ceramics with solid rectangular cross sections at ambient HSR/EPM-TSS-001-93 Measurement of test system alignment C1292-95 Standard test method for shear strength of continuous under tensile loading fiber-reinforced advanced ceramics at ambient HSR/EPM-D-001-93 Consensus standard. monotonic tensil testing of ceramic matrix, intermetallic C1337-96 Standard test method for creep and creep rupture of matrix and metal matrix composites continuous fiber-reinforced advanced ceramics under HSR/EPM-D-002-93 tensile loading load controlled fatigue testing of ceramic C1341-96 Standard test method for flexural properties of matrix, intermetallic matrix and metal continuous fiber reinforced advanced ceramic matrIx compo C1358-9 Standard test method for monotonic HSR/EPM-D-003-93 Consensus standard, four-point flexure strength testing of continuous fiber-reinforced advanced testing of ceramic matrix. intermetallic ramics with solid rectangular cross-sections at matrix and metal matrix composites ambient temperatures HSR/EPM-D-004-93 Consensus standard, creep rupture and C1359-97 Standard test method for monotonic tensile strength stepped-creep rupture of ceramic matrix, testing of continuous fiber-reinforced advanced intermetallic matrix and metal matrix ceramics with solid rectangular cross sections at levated temperatures HSR/EPM-NDE-001-93 Consensus standard, measurement of the C1360-97 Standard practice for constant-amplitude, axial ow and warp of continuous fiber tension-tension cyclic fatigue of continuous fiber- reinforced test specimens reinforced advanced ceramics at ambient temperatures CMC pre-cracking standard
CFCCs in the US include the development of non-consensus, industry-accepted standards developed by the NASA/ General Electric/Pratt and Whitney Enabling Propulsion Materials (EPM) Program. These documents, which predate ASTM standards, are listed in Table 3. In the following sections, the more relevant features of existing ASTM standard test methods for CFCCs are reviewed. 2.1. Tensile testing A survey of US CFCC manufacturers, conducted in 1991, provided insights into the needs and priorities of this industry for test standards [4]. To address those needs and priorities, the first standard developed for CFCCs by ASTM subcommittee C28.07 was test method C1275 for Monotonic Tensile Strength of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Section Specimens at Ambient Temperatures. Later, this standard test method became a template for other documents involving tensile testing, such as C1337 (Standard Test Method for Creep and Creep Rupture of Continuous Fiber-Reinforced Advanced Ceramics under Tensile Loading), C1359 (Standard Test Method for Monotonic Tensile Strength Testing of Continuous Fiber-Reinforced Advanced Ceramics with Solid Rectangular Cross-Sections at Elevated Temperatures) and C1360 (Standard Practice for Constant-Amplitude, Axial, Tension–Tension Cyclic Fatigue of Continuous Fiber-Reinforced Advanced Ceramics at Ambient Temperatures). The most important issues addressed by test method C1275 are gripping devices, test system alignment, strain measurements, specimen geometries, specimen preparation, mode and rate of testing, and data acquisition. Although C1275 allows the use of any specimen geometry if it meets the gripping, fracture location and fracture requirements prescribed in the document, in the case of 562 E. Lara-Curzio, M.G. Jenkins / Composites: Part A 30 (1999) 561–567 Fig. 1. Structure of ASTM committee C28 on advanced ceramics. Table 1 Existing standards under the jurisdiction of ASTM subcommittee C28.07 on ceramic matrix composites C1275-95 Standard test method for monotonic tensile strength testing of continuous fiber-reinforced advanced ceramics with solid rectangular cross sections at ambient temperatures C1292-95 Standard test method for shear strength of continuous fiber-reinforced advanced ceramics at ambient temperatures C1337-96 Standard test method for creep and creep rupture of continuous fiber-reinforced advanced ceramics under tensile loading C1341-96 Standard test method for flexural properties of continuous fiber reinforced advanced ceramics C1358-97 Standard test method for monotonic compressive strength testing of continuous fiber-reinforced advanced ceramics with solid rectangular cross-sections at ambient temperatures C1359-97 Standard test method for monotonic tensile strength testing of continuous fiber-reinforced advanced ceramics with solid rectangular cross-sections at elevated temperatures C1360-97 Standard practice for constant-amplitude, axial, tension–tension cyclic fatigue of continuous fiberreinforced advanced ceramics at ambient temperatures Table 2 Task groups within ASTM C28.07 Task group Activity C28.07.01 Tension C28.07.02 Compression C28.07.03 Creep C28.07.04 Flexure C28.07.05 Shear C28.07.06 Cyclic fatigue C28.07.07 Fibers C28.07.08 Interfacial C28.07.09 Thermal C28.07.10 Environmental C28.07.11 Thermomechanical fatigue C28.07.12 Structural/components Table 3 Industry-accepted, non-consensus standards developed by NASA’s Enabling Propulsion Materials Program HSR/EPM-TSS-001-93 Measurement of test system alignment under tensile loading HSR/EPM-D-001-93 Consensus standard, monotonic tensile testing of ceramic matrix, intermetallic matrix and metal matrix composites HSR/EPM-D-002-93 Consensus standard, tension–tension load controlled fatigue testing of ceramic matrix, intermetallic matrix and metal matrix composites HSR/EPM-D-003-93 Consensus standard, four-point flexure testing of ceramic matrix, intermetallic matrix and metal matrix composites HSR/EPM-D-004-93 Consensus standard, creep rupture and stepped-creep rupture of ceramic matrix, intermetallic matrix and metal matrix composites HSR/EPM-NDE-001-93 Consensus standard, measurement of the bow and warp of continuous fiberreinforced test specimens Proposed CMC pre-cracking standard
M.G. Jenkins/Composites: Part A 30(1999)561-567 two-dimensionally reinforced(2-D)CFCCs it recommends As indicated, test standard C1275 became the template the use of specimens with contoured gauge sections. This for all other ASTM test standards for CFCCs involving document also addresses the need to test specimens having tensile testing. These standards, particularly those addres- dimensions(e.g, volume)that are consistent with the ulti- sing tests at elevated temperatures, have special provisions mate use of the tensile data. Fig. 2 shows examples of in addition to the requirements outlined in C1275. These recommended test specimen geometries in C1275 include, for example, issues such as heating methods and Applied force is transferred to the specimens through temperature measurements, and address the importance of gripping devices. Gripping devices can have either active mechanical testing rates, since many CFCCs may exhibit (e.g, hydraulically-actuated grips)or passive(e.g, edge- time-dependent deformation at elevated temperatures pin-loaded arrangements)interfaces, and the availability of all of the existing tensile-based astm standard test a given type of testing arrangement will dictate the type of methods for CFCCs address conducting tests in ambient pecimen geometry and vice versa. air, but given the importance of environmental effects on Gripping devices are typically attached to the test the mechanical behavior of CFCCs, ongoing work has been system through couplers, which can be classified either focused on the drafting of test methods to conduct tests in as fixed or non-fixed. However, regardless of the type of controlled simulated environments coupler used, C1275 mandates verification of the align- ment of the test system either prior to each test, or before 2. 2. Shear testing and after a series of tests. Analytical and empirical studies have concluded that, for negligible effects on the estimates Except for the torsion testing of thin-walled tubes, there is of the strength distribution parameters for monolithic cera- no singlegood test to measure the shear strength ofCFCCs mics,allowable percentage bending as defined in ASTM [9]. Because the preparation and testing of tubular speci- Practice E1012 should not exceed 5%[5, 6]. Although mens to measure the shear strength of CFCCs would be recent studies have revealed that the ultimate tensile prohibitively expensive, standard test method C1292 for strength of some CFCCs is relatively insensitive to perce Shear Strength of Continuous Fiber-Reinforced Advanced ge bending [51 2 in the absence of more complete studies Ceramics at Ambient Temperatures addresses two popular, but less than perfect, test methods for determining the for CFCCs C1275 adopted the same percentage bending shear strengths of uni-directionally and two-directionally In contrast to the apparent insensitivity of the ultimate specimen to determine interlaminar shear strength, and the tensile strength of CFCCs to percentage bending, the so- losipescu test to determine both in-plane and interlaminar called proportional stress limit, which is associated with shear strength. Schematics of the specimen geometries and the onset of matrix cracking, is very sensitive to percentage test configurations for these two tests are shown in Fig. 3 bending [7]. This is important because, in the absence of Since both of these tests have been widely used for the environmentally stable fibers and fiber coatings, it appears evaluation of polymer matrix composites, much of the that the proportional stress limit will be considered an uppe groundwork for the drafting of C1292 had already been imit for design stresses for many CFCCs. Therefore, to laid down accurately determine the proportional stress limit of Although both the compression of double-notched speci- hens and the losipescu test have the advantage of requiring FCCs, it is essential to meet the allowable bending strain relatively small specimens and being simple to conduct, requirements prescribed in C1275 Test standard C1275 also addresses different techniques their main disadvantage is that both rely on the stress concentration at the root of notches to initiate shear failure for strain measurements, such as optical methods using As a consequence, in the case of the compression of double- lasers and flags, or contact methods such as adhesively notched specimens, for example, the shear stress in the bonded strain gauges and extensometers. However, regard- less of the type of extensometer used, this shall satisfy Class gauge section( the region between notches)is not uniform, I requirements as outlined in Practice E83 [8]. Additional and furthermore the apparent interlaminar shear strength requirements for contact-type extensometers are that the depends on the distance between the notches [10]. Never- extensometer should not damage the specimen, and to be theless, these test methods provide conservative shear externally supported so that its weight does not introduce trength values bending strains greater than those allowed in C1275 2.3. Flexure testing One of the motivations for developing a standard test This apparently results from loading large aspect ratio fibers when these method to evaluate CFCCs in tension was attributed to the bridge matrices crack in the composite. discrepancies between, and the wide range of, strength 3 Actually, matrix microcracking occurs at stresses lower than the values reported when CFCCs were evaluated in flexure proportional stress limit, but environmental sensitivity, which results from ingress of the nment into the composite, is mostly associated The problem is that, when testing CFCCs in flexure, it is with this macroscopic stress. difficult to relate the forces and displacements measured
two-dimensionally reinforced (2-D) CFCCs it recommends the use of specimens with contoured gauge sections. This document also addresses the need to test specimens having dimensions (e.g., volume) that are consistent with the ultimate use of the tensile data. Fig. 2 shows examples of recommended test specimen geometries in C1275. Applied force is transferred to the specimens through gripping devices. Gripping devices can have either active (e.g., hydraulically-actuated grips) or passive (e.g., edge- or pin-loaded arrangements) interfaces, and the availability of a given type of testing arrangement will dictate the type of specimen geometry and vice versa. Gripping devices are typically attached to the test system through couplers, which can be classified either as fixed or non-fixed. However, regardless of the type of coupler used, C1275 mandates verification of the alignment of the test system either prior to each test, or before and after a series of tests. Analytical and empirical studies have concluded that, for negligible effects on the estimates of the strength distribution parameters for monolithic ceramics, allowable percentage bending as defined in ASTM Practice E1012 should not exceed 5% [5,6]. Although recent studies have revealed that the ultimate tensile strength of some CFCCs is relatively insensitive to percentage bending [5],2 in the absence of more complete studies for CFCCs C1275 adopted the same percentage bending requirements as for tensile testing of advanced monolithic ceramics. In contrast to the apparent insensitivity of the ultimate tensile strength of CFCCs to percentage bending, the socalled proportional stress limit, which is associated with the onset of matrix cracking,3 is very sensitive to percentage bending [7]. This is important because, in the absence of environmentally stable fibers and fiber coatings, it appears that the proportional stress limit will be considered an upper limit for design stresses for many CFCCs. Therefore, to accurately determine the proportional stress limit of CFCCs, it is essential to meet the allowable bending strain requirements prescribed in C1275. Test standard C1275 also addresses different techniques for strain measurements, such as optical methods using lasers and flags, or contact methods such as adhesively bonded strain gauges and extensometers. However, regardless of the type of extensometer used, this shall satisfy Class B-1 requirements as outlined in Practice E83 [8]. Additional requirements for contact-type extensometers are that the extensometer should not damage the specimen, and to be externally supported so that its weight does not introduce bending strains greater than those allowed in C1275. As indicated, test standard C1275 became the template for all other ASTM test standards for CFCCs involving tensile testing. These standards, particularly those addressing tests at elevated temperatures, have special provisions in addition to the requirements outlined in C1275. These include, for example, issues such as heating methods and temperature measurements, and address the importance of mechanical testing rates, since many CFCCs may exhibit time-dependent deformation at elevated temperatures. All of the existing tensile-based ASTM standard test methods for CFCCs address conducting tests in ambient air, but given the importance of environmental effects on the mechanical behavior of CFCCs, ongoing work has been focused on the drafting of test methods to conduct tests in controlled simulated environments. 2.2. Shear testing Except for the torsion testing of thin-walled tubes, there is no single ‘good’ test to measure the shear strength of CFCCs [9]. Because the preparation and testing of tubular specimens to measure the shear strength of CFCCs would be prohibitively expensive, standard test method C1292 for Shear Strength of Continuous Fiber-Reinforced Advanced Ceramics at Ambient Temperatures addresses two popular, but less than perfect, test methods for determining the shear strengths of uni-directionally and two-directionally reinforced CFCCs: the compression of a double-notched specimen to determine interlaminar shear strength, and the Iosipescu test to determine both in-plane and interlaminar shear strength. Schematics of the specimen geometries and test configurations for these two tests are shown in Fig. 3. Since both of these tests have been widely used for the evaluation of polymer matrix composites, much of the groundwork for the drafting of C1292 had already been laid down. Although both the compression of double-notched specimens and the Iosipescu test have the advantage of requiring relatively small specimens and being simple to conduct, their main disadvantage is that both rely on the stress concentration at the root of notches to initiate shear failure. As a consequence, in the case of the compression of doublenotched specimens, for example, the shear stress in the gauge section (the region between notches) is not uniform, and furthermore the apparent interlaminar shear strength depends on the distance between the notches [10]. Nevertheless, these test methods provide conservative shear strength values. 2.3. Flexure testing One of the motivations for developing a standard test method to evaluate CFCCs in tension was attributed to the discrepancies between, and the wide range of, ‘strength’ values reported when CFCCs were evaluated in flexure. The problem is that, when testing CFCCs in flexure, it is difficult to relate the forces and displacements measured E. Lara-Curzio, M.G. Jenkins / Composites: Part A 30 (1999) 561–567 563 2 This apparently results from loading large aspect ratio fibers when these bridge matrices crack in the composite. 3 Actually, matrix microcracking occurs at stresses lower than the proportional stress limit, but environmental sensitivity, which results from ingress of the environment into the composite, is mostly associated with this macroscopic stress
E. Lara-Curaio, M.G. Jenkins/Composites: Part A 30 (1999)561-567 120 a (b (c) (d Fig. 2. Examples of tensile specimen geometries recommended in ASTM C1275:(a-c) face-loaded specimens;(d) shoulder-loaded specimen. Typical during the test to key material properties (e.g, tensile Tensile Strength and Youngs Modulus for High-Modulus strength, work of fracture)through a simple analysis. As a Single-Filament Materials) was transferred from ASTM result, equations that were derived for linear elastic, isotro- committee D30 to subcommittee C28.07. This coincided pic, homogeneous materials that exhibit symmetric beha- with ongoing efforts of a task group in C28.07 to develop vior in tension and compression, and that have been a standard test method to determine the tensile properties of customarily used to calculate the so-called flexural ceramic fibers both at room and elevated temperatures strength' of CFCCs, are not applicable for these materials. Although there are still issues pending resolution (e.g In spite of this, flexural testing has been and remains a fiber diameter measurements), it is expected that a revision popular test method in industrial laboratories because of of D3379 will include much of the work developed by task its simplicity and because it requires relatively small group C28.0707. samples. As a result of the interest expressed by industry Other documents deal ing with the thermomechanical to continue using this method, standard test method C1341 havior of CFCCs, the strength of CFCC-CFCC joints (Standard Test Method for Flexural Properties of Continu- the tensile transverse strength of CFCCs, the determination ous Fiber-Reinforced Advanced Ceramics) was developed of CFCC fiber-matrix interfacial properties and the hoop and approved in 1996. The scope of C1341 is limited to the strength of CFCC tubular components are currently in draft of flexural data' for quality control and material devel- form or undergoing the AsTM balloting process, and it is opment and, in contrast to flexural data for monolithic cera- expected that these will become AsTM standards in the near mics, the use of CFCC flexure data for design purposes is future 2.5. Round robin 2.4. Other The ASTM requires that standard test methods include Recently, the jurisdiction of D3379(Test Method for recision and bias statements. because of the lack of
during the test to key material properties (e.g., tensile strength, work of fracture) through a simple analysis. As a result, equations that were derived for linear elastic, isotropic, homogeneous materials that exhibit symmetric behavior in tension and compression, and that have been customarily used to calculate the so-called ‘flexural strength’ of CFCCs, are not applicable for these materials. In spite of this, flexural testing has been and remains a popular test method in industrial laboratories because of its simplicity and because it requires relatively small samples. As a result of the interest expressed by industry to continue using this method, standard test method C1341 (Standard Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramics) was developed and approved in 1996. The scope of C1341 is limited to the use of ‘flexural data’ for quality control and material development and, in contrast to flexural data for monolithic ceramics, the use of CFCC flexure data for design purposes is discouraged. 2.4. Other Recently, the jurisdiction of D3379 (Test Method for Tensile Strength and Young’s Modulus for High-Modulus Single-Filament Materials) was transferred from ASTM committee D30 to subcommittee C28.07. This coincided with ongoing efforts of a task group in C28.07 to develop a standard test method to determine the tensile properties of ceramic fibers both at room and elevated temperatures. Although there are still issues pending resolution (e.g., fiber diameter measurements), it is expected that a revision of D3379 will include much of the work developed by task group C28.07.07. Other documents dealing with the thermomechanical behavior of CFCCs, the strength of CFCC–CFCC joints, the tensile transverse strength of CFCCs, the determination of CFCC fiber–matrix interfacial properties and the hoop strength of CFCC tubular components are currently in draft form or undergoing the ASTM balloting process, and it is expected that these will become ASTM standards in the near future. 2.5. Round robin The ASTM requires that standard test methods include precision and bias statements. Because of the lack of 564 E. Lara-Curzio, M.G. Jenkins / Composites: Part A 30 (1999) 561–567 Fig. 2. Examples of tensile specimen geometries recommended in ASTM C1275: (a–c) face-loaded specimens; (d) shoulder-loaded specimen. Typical dimensions in mm
E. Lara-Cureio, M.G. Jenkins/Composites: Part A 30 (1999)561-567 Fig 3. (a)Schematic of compression of double-notched specimen for the determination of interlaminar shear strength of CFCCs. (b)Schematic of losipescu pecimen for the determination of in-plane shear properties of CFCS extensive databases with mechanical properties of CFCCs, participate in this effort, which is scheduled to be completed existing ASTM standards for CFCCs lack these statements, by the Spring of 1998 but must include them during their next revision. The US Department of Energy sponsored program on Continuous 26 International harmonization Fiber-Reinforced Ceramic Composites recently sponsored a round robin testing program to determine the precision The US is represented at the technical committees(TCs) and bias statements for standard test methods C1275, of the International Organization for Standardization (Iso) C1292 and C1341. In addition to fulfilling this goal, the through technical advisory groups(TAGs)of the American round robin testing will produce an expanded database for National Standards Institute(ANSI). In 1994, ANSI named the material that will be used in the study, along with statis- the ASTM as administrator of TAG-206 to represent the US tical distributions of properties and performance for both at ISO's TC206 on Fine(Advanced, Technical) Ceramics design and production purposes. More than 10 laboratories, In February 1997, a working group(wGg)on tensile beha- including national laboratories, material manufacturers vior of CFCCs was officially established as part of TC206 universities and independent research institutes, will with the US serving as the convenor. At the first official
extensive databases with mechanical properties of CFCCs, existing ASTM standards for CFCCs lack these statements, but must include them during their next revision. The US Department of Energy sponsored program on Continuous Fiber-Reinforced Ceramic Composites recently sponsored a round robin testing program to determine the precision and bias statements for standard test methods C1275, C1292 and C1341. In addition to fulfilling this goal, the round robin testing will produce an expanded database for the material that will be used in the study, along with statistical distributions of properties and performance for both design and production purposes. More than 10 laboratories, including national laboratories, material manufacturers, universities and independent research institutes, will participate in this effort, which is scheduled to be completed by the Spring of 1998. 2.6. International harmonization The US is represented at the technical committees (TCs) of the International Organization for Standardization (ISO) through technical advisory groups (TAGs) of the American National Standards Institute (ANSI). In 1994, ANSI named the ASTM as administrator of TAG-206 to represent the US at ISO’s TC206 on Fine (Advanced, Technical) Ceramics. In February 1997, a working group (WG9) on tensile behavior of CFCCs was officially established as part of TC206, with the US serving as the convenor. At the first official E. Lara-Curzio, M.G. Jenkins / Composites: Part A 30 (1999) 561–567 565 Fig. 3. (a) Schematic of compression of double-notched specimen for the determination of interlaminar shear strength of CFCCs. (b) Schematic of Iosipescu specimen for the determination of in-plane shear properties of CFCCs