M. G elkins NOminal 15 mmgs ≤100 000-4000-20000 00040006000 LONGITUDINAL STRAIN E (HE) Figure 1. Differences in response of a CFCC in tension and compression [81 2 /. Tension Uniaxial tensile testing is the most fundamental means of measuring mechanical response of most engineering materials and interest in it for CFCCs is driven primarily by limitations of the flexure tests widely used to characterize monolithic ceramics. However, because of the difficulty of deconvoluting tensile response from the flexure results, a uniaxial tensile test is the preferred tensile test for the response of CFCCs in the plane of the reinforcement. This preference has led to a wide range of test specimen geometries(straight-sided to contoured) and gripping systems(face, pin or edge 'loaded')as illustrated in Fig. 2. Another issue which must be addressed for CFCCs is the material,s sensitivity to non-uniform stress (i.e bending during the tensile test)(see Fig 3)[9]. The mode(force, displacement, or strain control) and rate(rapid or slow) of testing as well as means of strain measurement(optical, contacting, etc. are important concerns as well, especially at elevated temperature at which creep or other time-dependent mechanisms may be operatIve. Because the uniaxial tension test is the most fundamental test for mechanical characterization, the greatest number of in-plane monotonic tensile test standards (see Tables I and 2)exist for it(two ASTM, three CEN(standards or advanced drafts), one ISO, one EPM, one PEC). Once developed, the monotonic tensile test also becomes the basis for other types of tests, such as cyclic fatigue or creep/creep rupture. Recent efforts in both ASTM and CEN are moving toward developing plane, elevated-temperature tensile tests for various environments other than mbient air. Concerns here are the type of grip(hot, warm, or cold)and the design of the test specimen so as to minimize the imposition of undesirable thermal and imposed stresses(see Fig 4)[8] More recently, demand has increased to determine the tensile response perpen- dicular to the in-plane reinforcements(see Fig. 5). In two-directionally reinforced CFCCs, this direction can be the weakest since only matrix material with some interphase and no reinforcing fibres are present. An AStM document on'trans-
Standards and codes for CMCs LEWE DPONT FACE LOADED GEOME TRIES (mm) 能是re PIN FACE LOADED GEOMETRES tmmi EDGE LOADED GEOME TRES mmi Figure 2. Examples of various tensile test specimen geometries 150 OF5 u苏-=5 58添 PERCENT BENDING PERCENT BENDING, a)Proportional limit stress b)Ultimate tensile strength Figure 3. Strength as a function of percent bending in room temperature monotonic tensile tests (a)Proportional limit stress and (b) Ultimate tensile strength [81
M. G. Jenkins Table 2 Current industry/ government standard test methods for CFCC Title EPM"(USA) Approve HSR/EPM-D-O01-93 Monotonic Tensile Testing of Ceramic Matrix, Intermetallic 1993 Matrix and Metal Matrix Composite Materials HSR/EPM-D-002-93 Tension-tension Load Controlled Fatigue Testing of Ceramic 199 Matrix, Intermetallic Matrix and Metal Matrix Composite Materials HSR/EPM-D-003-93 Four Point Flexure Testing of Ceramic Matrix, Intermetallic 1993 Matrix and Metal Matrix Composite Material HSR/EPM-D-004-93 Creep-Rupture and Stepped Creep Rupture of Ceramic Ma- 1993 Matrix Compo tIs HSR/EPM-TSS-001-93 Measurement of Test System Alignment Under Tensile Load- 1993 HSR/EPM-NDE-001-93 Measurement of the Bow and Warp of Continuous Fiber 1993 Reinforced Test Specimens Task A 54/A.5.5 CMC Pre-Cracking Standard PEC (Japan) A PEC-TS CMCOI uous Fibre Reinforced Ceramic Matrix Composites at Rom +pproved Test Method for Tensile Stress-Strain Behaviour of Contin- 1997 and Elevated Temperatures PEC-TS CMC04 Test Method for Flexural Strength of Continuous Fibre Re- 1997 inforced Ceramic Matrix Composites at Room and Elevated emperatures PEC-TS CMCO6 Test Method for Shear Strength of Continuous Fibre Rein- 1997 forced Ceramic Matrix Composites at Room and Elevated PEC-TS CMCO8 Test Method for Fracture Toughness of Continuous Fibre 1997 reinforced Ceramic Matrix Composites PEC.'TS CMCO9 Test Method for Fracture Energy of Continuous Fibre Rein- 1997 PEC-TS CMCO1O Test Method for Tensile-Tensile Cyclic Fatigue of Continu- 1997 ous Fibre Reinforced Ceramic Matrix Composites at Room and Elevated Temperatures PEC-TS CMCO Test Method for Tensile Creep of Continuous Fibre Rein- 1997 forced Ceramic Matrix Composites at Elevated Temperatures EC-TS CMCO13 Test Method for Elastic Modulus of Ceramic Matrix Com- 1997 posites at Room and Elevated Temperatures PEC-TS CMCO14 Test Method for Oxidation Resistance of Non- Oxide Ceramic 1997 Matrix Composites at Elevated Temperatures EPM Enabling Propolusion Materials program(NASA, GE. Pratt and Whitney consortium) USA). PEC=Petroleum Energy Center (Japan)