NASA Technical Memorandum 103171 

Thermomechanical Testing Techniques for 

High-Temperature Composites: TMF 

Behavior of SiC(SCS-6)/Ti-15-3 

Michael G. Castelli 

Sverdrup Technology, Inc. 

Lewis Research Center Group 

Brook Park, Ohio 

and 

J. Rodney Ellis and Paul A. Bartolotta 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 

Prepared for the 

10th Symposium on Composite Materials: Testing and Design 

sponsored by the American Society for Testing and Materials 

San Francisco, California, April 24-25, 1990 

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THERMOMECHANICAL TESTING TECHNIQUES FOR HIGH TEMPERATURE 

COMPOSITES: TMF BEHAVIOR OF SiC(SCS-6)/Ti-15-3 

Michael G. Castelli 

Sverdrup Technology, Inc. 

Lewis Research Center Group 

Brook Park, Ohio 44142 

and 

J. Rodney Ellis and Paul A. Bartolotta 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135 

ABSTRACT 

Thermomechanical testing techniques recently developed for monolithic structural alloys were 

successfully extended to continuous fiber reinforced composite materials in plate form. The success 

of this adaptation was verified on a model metal matrix composite (MMC) material, namely 

SiC(SCS-6)/Ti-15V-3Cr-3AI-3Sn. Effects of heating system type and specimen preparation are also 

addressed. Cyclic lives determined under full thermomechanical conditions were shown to be 

significantly reduced from those obtained under comparable isothermal and in-phase bi-thermal 

conditions. Fractography and metallography from specimens subjected to isothermal, out-of-phase 

and in-phase conditions reveal distinct differences in damage/failure modes. Isothermal metallography 

revealed extensive matrix cracking associated with fiber damage throughout the entire cross-section of 

the specimen. Out-of-phase metallography revealed extensive matrix damage associated with minimal 

(if any) fiber cracking. However, the damage was located exclusively at surface and near-surface 

locations. In-phase conditions produced extensive fiber cracking throughout the entire cross-section, 

associated with minimal (if any) matrix damage. 

INTRODUCTION 

Metal Matrix and Intermetallic Matrix Composites (MMC and IMC) are being developed for a 

number of high-temperature aerospace applications. The advantage of these composite materials is 

that they offer superior strength/ density ratios compared to monolithic materials, particularly at 

elevated temperatures. This level of performance typically is achieved by using high strength 

ceramic fibers and low density matrix materials. One obvious problem with this approach is that it 

combines materials with widely differing physical properties. This mismatch raises questions 

regarding the performance of MMC and IMC materials under the complex thermomechanical loading 

conditions typical of aerospace service. 

The development of reliable thermomechanical testing techniques for this class of materials was 

viewed as being a logical first step in addressing this concern. The approach adopted was to 

extend advanced testing techniques recently developed for monolithic structural alloys (ref. 1) such as 

Hastelloy Alloy-X and Haynes 188 to composite materials in thin plate form. This effort included 

the development of computer test control software, an advanced heating fixture, a proper specimen 

design and innovative experimental techniques. To verify the success of this adaptation, the full 

thermomechanical fatigue (TMF) behavior of a high-temperature composite was investigated. 

Specialized real-time control software was developed to perform thermomechanical tests under 

load, strain and combined load-strain control. One difficulty encountered with thermomechanical 

testing involves the task of ensuring precise phasing between the controlled variable, load or 

mechanical strain, and specimen temperature. This problem arises because of the response-time 

difference which typically exists between the temperature and the mechanical component of loading. 

Tests performed under conditions of improper phasing will often produce distorted hysteresis loops, 

making subsequent data reduction and analysis difficult, if not impossible. The approach taken here 

was to incorporate subtle shifts in the temperature-command waveform at appropriate points in the 

cycle (i.e. , reversals). For example, the temperature-command is reversed prematurely such that the 

actual temperature response will reverse simultaneously with the mechanical load. Through this 
"shifting" of the temperature-command waveform, the temperature-response can be tailored and 

phased correctly with the mechanical component of loadng. 

Another difficulty encountered with uniaxial thermomechanical testing arises under strain control 

conditions. Under this control mode, thermal strains have a first order effect on the mechanical 

loading component, namely, the axial strains. In order to properly control the mechanical strains, 

an accurate assessment of the thermal strains must be made at all times. This task is further 

complicated if phasing problems exist. The computer code extended for this study incorporates a 

function to calculate the real-time thermal strains based on a continuous analog-to-digital reading of 

the specimen's temperature. These calculated thermal strains are then appropriately added to the 

desired mechanical strains to obtain a total command strain. By this means, a nonlinear thermal 

expansion can be accurately compensated for to maintain the desired mechanical strain waveform. 

Other important issues and problems which must be addressed include minimizing dynamic 

thermal gradients, temperature monitoring and heating/cooling rates. Procedures were developed to 

optimize these interrelated variables with respect to specific equipment and test material. Adopting 

this approach, techniques originally developed for testing monolithic alloys have been successfully 

extended to composite materials. 

OBJECTIVE AND APPROACH 

The main objective of this work was to evaluate the extended thermomechanical testing 

techniques on a model MMC. A silicon carbide continuous fiber reinforced titanium MMC 

designated SiC(SCS-6)/Ti-15V-3Cr-3AI-3Sn (Ti-15-3) was chosen as the material to be investigated. 

This particular system was selected because of availability, established processing parameters and well 

defined mechanical properties. Although the system is not typically thought of as a high temperature material, it is useful as a n characteristic" material for developing and refining high temperature 

testing techniques. 

A second objective was to characterize the TMF behavior of SiC(SCS-6)/ Ti-15-3. Recently, the 

room temperature (refs. 2 and 3), isothermal (ref. 4) and bi-thermal (ref. 5) behavior of this 

composite system has been investigated. Also, work was performed by Majumdar et al., (ref. 6) to 

characterize the full TMF behavior of angle-ply laminates. However, very little (if any) information 

is available addressing the full TMF behavior of the unidirectional system. Lastly, there is some 

concern in the testing community about the effects of induction heating, and method of specimen 

preparation on the fatigue life of the test specimens. These issues will be briefly addressed through 

the comparison of several isothermal fatigue tests. 

All material tested here is 9 ply laminate with 0° (longitudinal) fiber orientation. All test 

specimens had a nominal fiber volume ratio of 34 percent and a nominal thickness of 2 mm. The 

test specimens were cut from one 30.5 by 30.5 cm plate using wire electric discharge machining 

(EDM), followed by a light diamond grinding. Although the Ti-15-3 matrix material is a stabilized 

beta (bcc) phase, long term exposures at elevated temperatures can lead to the precipitation of a 

a-Ti phase (refs. 7 to 9). This primary hardening phase has been shown by several investigators to 

affect the mechanical properties. Therefore, to stabilize the material, the specimens were heat 

treated in a vacuum at 700°C for a 24 hr period .

l 

The specimen geometry used for this investigation is shown in figure 1. The "dogbone" design 

features a 25.4 mm parallel section to facilitate close control of the temperature profile. Tabs were 

attached to the specimen with adhesive for assembly purposes, and held in position by high 

clamping forces during the test. 

All TMF experiments were conducted on a computer controlled, servo-hydraulic test system; a 

close-up of the load train is shown in figure 2. Specimen heating was accomplished through direct 

induction work coils powered by a 5 kW radio-frequency heater. The induction coil fixture used 

here consists of three independently adjustable coil segments. This fixture, developed at NASA 

Lewis Research Center (ref. 10), provided the flexibility necessary to obtain closely controlled 

dynamic temperature profiles. Specimen cooling was accomplished through the combination of water1 Although the heat treatment improved the microstructural stability, it IS believed that the 

material was still slightly metastable. 

2 
cooled griPS and forced all'. Although forced air creates difficulties when attempting to attain very 

precise temperature profiles, it was necessary here to obtain a target cycle period of 3 min. 

Intrinsic (spot-welded) K-type thermocouples were used for temperature monitoring and closed-loop 

control. The thermocouple locations did not exhibit premature cracking, and hence had no influence 

on the fatigue life of the specimen. Axial strains were measured over a 12.7 mm gauge section on 

the edge of the specimen by a high temperature water-cooled extensometer. A selected number of 

baseline isothermal experiments were also conducted to investigate the effects of heating system type 

and method of specimen preparation. For these tests, a small two-zone direct resistance furnace was 

used to heat the specimens. 

The test matrix performed for this study is given in figure 3. All tests were run under load 

control. The isothermal tests were conducted at 427 0 C, where a triangular load control function 

was cycled with a frequency of 10 cycles/min. As a result of the specimen's geometry, compressive 

loads would induce buckling, therefore, all tests (including thermo mechanical) were run to failure 

under cyclic tension-tension conditions with a minimum/maximum stress ratio, (Ru), of 0.05. The 

TMF tests were conducted with both sinusoidal load and temperature control waveforms. Both 

in-phase and out-of-phase (180 0 phase shift between maximum load and maximum temperature) 

conditions were run with a cycle period of 3 min, and a temperature range of 93 to 538 0 C. 

As mentioned above, thermomechanical conditions introduce several new concerns associated with 

high temperature testing. Previous testing performed on monolithic alloys (ref. 1) revealed that the 

dynamic thermal gradients were significantly greater than the static gradients existing before 

temperature cycling was initiated. Further, the dynamic gradient at anyone location did not 

remain constant throughout the cycle, rather, it was found to cyclically fluctuate with the 

temperature magnitude. The degree of these effects were found to depend upon variables such as 

temperature range, temperature magnitude and cycle period. The approach taken to minimize 

dynamic thermal gradients involves establishing an appropriately imposed isothermal/static 

gradient at some midcycle temperature. This technique is given in detail in (ref. 1). Shown in 

figure 4 is a typical dynamic temperature profile (longitudinal) taken from a TMF experiment. 

Note the variable dynamic gradient, illustrated by the changing distances between the respective 

curves. The three most closely grouped curves represent the gradients within the gauge section, 

which experienced a maximum U~15 °C) at the "hot" end of the cycle. This value was typical for 

all of the TMF tests. 

The TMF test specimens were thermally cycled under zero load prior to mechanical loading in 

order to quantify the thermal strains and ensure that a stable strain response existed. This cycling 

did not exceed 10 cycles because the temperature-strain response was found to be initially stable. 

RESULTS AND DISCUSSION 

Isothermal fatigue results are plotted as life curves on a stress basis in figure 5. Also shown in 

this plot are duplicate tests generated by Ervin et al., (Pratt and Whitney) and similar tests 

generated by Gayda et al., (NASA Lewis) (unpublished data obtained through personal communication). The same material and specimen geometry was used for all the tests. In each case, failure 

is defined as complete fracture of the specimen into two pieces. The three sets of data compared 

were generated employing a combination of specimen preparation and specimen heating methods. 

For specimen preparation, Gayda et al., utilized wire EDM cutting followed by light diamond 

grinding, whereas Ervin et aI., employed water jet cutting followed by hand polishing. For 

specimen heating, Gayda et al., utilized direct induction and Ervin et al., employed radiant heating. 

As shown in figure 5, the various cyclic fatigue lives are in very good agreement. This result was 

particularly surprising, given that the data were generated by three independent experimental groups. 

An initial interpretation may be that the isothermal cyclic fatigue lives of this unidirectional 

composite material are not sensitive to the method of specimen preparation or method of heating. 

However, it is important to note that there are several issues of concern which need to be 

addressed, particularly in regard to specimen design . The test specimens are cut from a large, 

continuously reinforced plate, and as a result, contain cut fibers along the edges. These locations 

are potential stress concentration/crack initiation points. Also, the specimens are tested with 

"as-received" surface conditions which, from the traditional fatigue viewpoint, were less than ideal. 

Further, the majority of as-manufactured specimens exhibited curvature along their length, introduced 

into the original 30.5 by 30.5 cm plate during processing. Clearly, this curvature leads to nonuniform stress-strain states being developed in the specimens upon gripping and loading. Another area 

of concern is that the majority of the specimens failed at the blend between the parallel section and 

the beginning of the radius. Given these uncertainties, another interpretation of figure 5 may be 

3 
that one or all of these effects play an important role in dictating the fatigue life of the test 

specimen. If this were the case, the plot would suggest that the effects promoted by method of 

specimen preparation and method of heating are secondary issues of concern, at least for the 

unidirectional material under investigation. 

The stress-strain response for two of the isothermal tests is given in figure 6. Shown are the 

first and second cycle, and a cycle close to failure for tests performed with maximum stresses of 896 

and 1034 MPa. The strain offset between these cycles is that which naturally accumulated 

throughout the test. The cyclic strain ranges were found to change very little throughout the tests, 

suggesting minimal modulus degradation. However, as shown in figure 7, the cyclic mean strains 

significantly increased over the first several thousand cycles and continued to increase gradually 

throughout the life of the specimens. This ratchetting effect was amplified as stress range was 

increased. 

Typical Scanning Electron Microscope (SEM) fractographs taken from the a max = 896 MPa 

isothermal specimen are shown in figure 8. In general, the fracture surfaces from all of the 

isothermal specimens were very similar, revealing flat regions of fatigue cracking accompanied by 

r andomly distributed areas of fiber pull-out and ductile matrix failure. The higher stressed 

specimens displayed a slightly increased amount of fiber pull-out and ductile matrix failure. 

Oxidation patterns and SEM backscatter imagery strongly suggest that matrix cracking was initiated 

at both surface and internal fiber/matrix interface locations. Matrix "river" patterns suggest that 

there were numerous crack initiation points, and that the cracks have propagated only short 

distances (:::l1 to 2 fiber rows) before coalescing. This relatively short crack growth may be a result 

of the fibers hindering fatigue crack growth. 

Results from the TMF tests are plotted in figure 9 as life curves on a stress basis. For 

reference purposes, the isothermal fatigue line displayed in figure 5 is also shown in this figure. In 

general, cyclic lives determined under full TMF conditions were greatly reduced from those obtained 

under comparable isothermal conditions. Also, for the case of high stress in-phase loadings, lives 

were reduced by several orders of magnitude from those obtained under comparable isothermal and 

bi-thermal (nonisothermal) conditions. This magnitude of degradation is best illustrated in 

figure 9 by a line drawn through amax = 1034 MPa. The 538°C isothermal datum point was 

obtained from a specimen subjected to fatigue cycling with a 3 min cycle period. This condition 

was imposed to address the effects (i.e., increased ratchetting, environmental) of the relatively slow 

cycle period. The isothermal specimen experienced a fatigue life of approximately 4000 cycles, 

whereas the specimens subjected to true in-phase loading conditions from 93° to 538°C consistently 

failed upon the second load-up. 

The large magnitude of life degradation resulting from true in-phase conditions was not seen 

under in-phase bi-thermal (nonisothermal) conditions (ref. 6) where a 3 to 4X decrease from 

isothermal life was obtained. The decreased life displayed under full TMF conditions may be 

attributed to factors (not present under bi-thermal conditions) promoting minimized reversed inelastic 

strains in the matrix and thus increased ratchetting (discussed later). One obvious condition 

promoting damage is that attributed to the coefficient of thermal expansion (CTE) mismatch. 

Work performed by Gabb et aI., (ref. 6) on this MMC system revealed that specimens subjected to 

10 000 thermal cycles (from 300 0 to 550 0 C) under zero load did not exhibit degraded mechanical 

responses during subsequent tests. However, the CTE mismatch did promote highly localized cracks 

in the reaction zone and carbon-rich coating of the fibers. True thermomechanical conditions 

introduce this damaging effect from the CTE mismatch as a dynamic component compounded with 

the transverse Poisson's effects associated with mechanical loading. 

The stress-mechanical strain response for an out-of-phase and in-phase test with a max 

896 MPa is shown in figure 10. Note that the hysteresis loops do not exhibit irregular 

distortions. This is an essential check in verifying that the thermomechanical test is well controlled. 

Again, the first two cycles, and a cycle just before failure is plotted, where the mechanical strain 

offset is that which naturally occurred throughout the test. 

In general, the out-of-phase hysteresis loops (fig. 10( a)) were ORen, displaying evidence of 

inelastic deformation in any given cycle. Of the three conditions lisothermal, out-of-phase and inphase), only the specimens subjected to out-of-phase loadings displayed a noticeable change in 

compliance. This change in compliance is evidenced by an overall change in slope of the TMF 

loop. Out-of-phase TMF involves "cold" temperatures at high stress and "hot" temperatures at low 

stress. This condition is not conducive to creep-ratchetting effects, and thus, as shown in figure 11, 

the behavior reveals gradual increases in mean strain at the onset of the test. This increase is 

4 
followed by a subtle decrease in mean strain, as a possible result of matrix work hardening and/or 

the precipitation of t he a-Ti phase. Also, specimens subjected to out-of-phase conditions displayed 

substantial increases in mean strain late in life (N > O.7Nf)' suggesting failure was approaching. 

In-phase thermomechanical cycling involves "hot" temperatures at high stress and "cold" 

temperatures at low stress. This, combined with the specific test parameters selected for the TMF 

experiments, results in conditions which are highly conducive to creep-ratchetting. Specifically, 

several parameters can be identified; (1) high stress coinciding with high temperatures, (2) a load 

control environment where strain limitations are not imposed, (3) a sinusoidal control waveform 

which lingers at the function 's extremes, (4) a relatively slow cycle period of :I min and, (5) a 

tension-tension cycle where reversed inelastic strains are minimal. The ratchetting attributed to 

minimized reversed inelastic strains is further amplified by an increasing elastic modulus (due to a 

temperature decrease) during unload. This" cold", "nearly-elastic" unload is absent under in-phase 

bi-thermal conditions (ref. 6), and hence may contribute to the differences in cyclic fatigue lives 

discussed earlier. 

As shown in figures 10(b) and 12, the in-phase loading response exhibits an extensive increase 

in mean strain (creep-ratchetting) during the initial cycles. This" unrestrained" ratchetting is 

believed to be the primary cause of the dramatic decrease in fatigue life when compared with 

out-of-phase TMF conditions. At 538°C, the titanium-based matrix will tend to creep readily 

(ref. 11). At these high temperatures, the matrix is unable to carry its share (on a rule of 

mixtures basis) of the load, therefore, it will tend to relax as if in a strain controlled environment. 

The load shed by the matrix is distributed to the fibers, thus causing an increased fiber stress and 

composite mean strain. This process gradually continues at a decreasing rate (due to hardening of 

the matrix) until eventual fiber overload occurs. This process occurs under isothermal (ref. 5) and 

bi-thermal (ref. 6) conditions, but is greatly accelerated under in-phase TMF conditions as a result 

of the factors leading to minimal reversed inelastic strains. The mean strain response tended to 

stabilize early in life and did not experience an increase late in life as seen under out-of-phase 

conditions (compare with fig. 11); thus there was no phenomenological indication that failure was 

approaching. Also, as evidenced in figure 10(b), there was no detectable change in compliance for 

specimens subjected to in-phase loadings. 

Typical SEM fractographs taken from a specimen subjected to out-of-phase loading conditions, 

O"max = 896 MPa, are shown in figure 13. The fracture surface reveals a fair amount of fatigue 

cracking, but in general, the area associated with tensile overload appears to be larger than that 

found in comparable isothermal specimens. True thermomechanical conditions appear to have 

introduced crack initiation and propagation mechanisms different from those found under isothermal 

conditions. Oxidation patterns and SEM imagery clearly suggest that crack initiation sites occurred 

almost exclusively at surface and near-surface fiber-matrix interface locations. Out-of-phase 

conditions consistently produce fracture surfaces displaying an outer "ring" of oxidized cracking 

(approximately 2 to 3 fibers into the cross-section) surrounding an internal region exhibiting ductile 

matrix failure and fiber pull-out. This suggests that the surface plays a decisive role in the damage 

processes. Also, matrix "river" patterns reveal that individual cracks are less numerous (compared 

to isothermal fracture surfaces) and appear to have propagated greater distances, as illustrated upon 

comparing figures 8 and 13. Under out-of phase conditions, the fibers appear less effective at 

arresting the crack growth. 

Typical longitudinal and transverse sections taken from an out-of-phase specimen 

(O"max = 896 MPa) are shown in figure 14. The sections reveal that the primary cyclic fatigue 

damage consists of transverse matrix cracking. This cracking was clearly found to initiate at surface 

locations and near-surface fiber-matrix interfaces. Very little fiber damage was visible. A matrix 

dominated failure, initiated by matrix microcracking at these locations, is compatible with the fact 

that the out-of-phase conditions maximize the longitudinal stresses in the matrix; matrix stresses 

produced by the mechanical loading and thermal expansion mismatch are additive. 

In contrast, metallography from specimens subjected to in-phase TMF conditions exhibits trends 

which are quite different from those seen in isothermal and out-of-phase TMF specimens. Typical 

SEM fractographs taken from an in-phase specimen, a max = 896 MPa, are shown in figure 15. 

This figure reveals extensive fiber pull-out and ductile matrix failure across the entire fracture 

surface. In fact, the features illustrated here (and from all other in-phase tests performed) most 

closely resemble those displayed by specimens subjected to tensile tests (ref. 12). This pattern of 

5 
pure tensile overload and lack of matrix cracking was a somewhat surprising result, given that 

several of the lower stress tests experienced well over 1000 cycles. 

Longitudinal, shown in figure 16, and transverse sections taken from the gauge section (away 

from the fracture surface) clearly reveal extensive fiber damage in the absence of matrix cracking (A 

scenario which is completely opposite to that displayed by the out-of-phase metallography) . Fiber 

cracking was found in both the transverse (more predominant) and longitudinal directions. The 

fiber dominated failure found under in-phase conditions is also compatible with the fact that inphase conditions maximize the longitudinal stresses in the fiber, where fiber stresses produced by 

mechanical loading and thermal expansion mismatch are additive. 

Because the results presented here are influenced by the particular test parameters, it is 

important to note that dramatically different material behavior and resulting fatigue lives can be 

produced by changing these test parameters. By changing the control mode from load to strain, 

several of the prime factors leading to extreme creep-ratchetting during in-phase TMF can be 

eliminated. A similar argument can be used when considering the use of a triangular control 

function, rather than the sinusoidal employed here, since the sinusoidal function lingers at the 

extremes. Further, the advent of computer controlled testing has enabled any combination of 

mixed-mode and mixed-function control. For example, a load controlled test exhibiting a fixed 

stress rate can be performed with limiting strain boundaries. The ongoing debate addressing the 

appropriateness of "load control" or "strain control" will most likely never be resolved. However, 

"test induced" effects, such as creep-ratchetting, should be an issue of concern, both before the tests 

are performed and during subsequent data interpretation and analysis. 

CONCLUSIONS 

Improved thermomechanical testing techniques developed for monolithic materials were successfully extended to SiC/Ti-15-S in plate form. As a result, closely controlled TMF tests were performed 

with minimal experimental uncertainties. Isothermal fatigue life data did not reveal any sensitivity 

to heating method (direct induction versus radiant) or specimen preparation method (water cutting/ 

hand polishing versus wire EDM/light diamond grmding) . This was evidenced by the close 

agreement existing among tests generated by three independent experimental groups. However, 

several key concerns were identified as potentially having a degrading effect on the cyclic fatigue life 

of the test specimen. These issues are currently being addressed through the investigation of new 

specimen geometries which minimize stress concentrations, as well as through techniques which lead 

to test specimens containing completely encapsulated, uncut fibers. 

The isothermal data exhibited an essentially linear response after the first cycle with no 

evidence of modulus degradation throughout the test, however, significant increases in mean strain 

developed with the majority of this occurring early in the cyclic life. Metallography revealed a 

large amount of flat fatigue cracking throughout the cross-section of the specimen. 

Cyclic fatigue lives were greatly reduced under TMF conditions when compared to isothermal 

and in-phase bi-thermal data. This was particularly the case for in-phase loadings at high stresses 

where lives were decreased by several orders of magnitude. 

Failure modes displayed under TMF conditions were significantly different from those displayed 

under comparable isothermal conditions. Out-of-phase loadings clearly displayed a matrix dominated 

failure, where cracking and crack initiation points were found exclusively at surface locations and 

near-surface interface locations. In-phase TMF loadings displayed fiber dominated failures, where 

extensive fiber damage was found in the absence of matrix cracking. 

ACKNOWLEDGMENTS 

The authors wish to acknowledge Tim Gabb and Ralph Corner for their work on the SEM and 

optical microscope, and Ron Shinn for his technical assistance with the servo-hydraulic load frames. 

REFERENCES 

1. Castelli, M.G., "Thermomechanical Deformation Testing and Modeling in the Presence of 

Metallurgical Instabilities, " NASA Report CR-185188, National Aeronautics and Space 

Administration, Lewis Research Center, Cleveland, OH, Jan. 1990. 

6 
--- ---~-- .. - _._

;......,. iN 

2. Johnson, W.S., Lubowinski, S.J., Highsmith, A.L., Brewer, W.D., and Hoogstraten, C.A., 

"Mechanical Characterization of SCS6 / Ti-15-3 Metal Matrix Composites at Room Temperature," 

NASA Report NASP TM-1014, National Aeronautics and Space Administration, Langley 

Research Center, Hampton, Va, Apr. 1988. 

3. Johnson, W.S., "Fatigue Testing and Damage Development in Continuous Fiber Reinforced 

Metal Matrix Composites," NASA Report TM-100628, National Aeronautics and Space 

Administration, Langley Research Center, Hampton, VA, June, 1988. 

4. Gayda, J.G., Gabb, T.P., and Freed, A.D., "The Isothermal Fatigue Behavior of a Unidirectional SiC/Ti Composite and the Ti Alloy Matrix," NASA Report TM-101984, National Aeronautics 

and Space Administration, Lewis Research Center, Cleveland, OH, Apr. 1989. 

5. Gabb, T.P., Gayda, J.G., and MacKay, R.A., "Isothermal and Nonisothermal Fatigue Behavior 

of a Metal Matrix Composite," Submitted to Journal of Composite Materials. 

6. Majumdar, B.S., and Newaz, G.M., "Thermo-Mechanical Fatigue of an Angle-Ply Metal Matrix 

Composite," Presented at ASTM Third Symposium on Composite Materials: Fatigue and 

Fracture, Orlando, FL, Nov. 1989. 

7. Bania, P.J., Lenning, G.A., and Hall, J.A., in Beta Titanium Alloys in the 80's, R.R Boyer 

and H.W. Rosenberg, Eds., TMS-AIME, Warrendale, PA, 1984, pp. 209-230. 

8. Duerig, T.W., and Williams, J.C., in Beta Titanium Alloys in the 80's, R.R Boyer and H.W. 

Rosenberg, Eds., TMS-AIME, Warrendale, PA, 1984, pp. 19-67. 

9. Lerch, B.A., Gabb, T.P., and MacKay, R.A., "Heat Treatment Study of the SiC/Ti-15-3 

Composite System, " NASA Report TP-2970, National Aeronautics and Space Administration, 

Lewis Research Center, Cleveland, OH, Jan. 1990. 

10. Ellis, J.R., and Bartolotta, P.A., "A Fixture Facilitating the Use of Induction Heating in 

Mechanical Testing," NASA Report TM-102416, National Aeronautics and Space Administration, 

Lewis Research Center, Cleveland, OH, June 1990. 

11. Rosenberg, H.W., in Beta Titanium Alloys in the 80's, R.R Boyer and H.W. Rosenberg, Eds., 

TMS-AIME, Warrendale, P A, 1984, pp. 409-432. 

12. Castelli, M.G., Bartolotta, P.A., Ellis, R. , Ervin, D.R., and Heine, J.E., in HITEMP Review 

1989: Advanced High Temperature Engine Materials Technology Program, NASA Report CP10039, National Aeronautics and Space Administration, Lewis Research Center, Cleveland, OH, 

Oct. 1989, pp. 43:1-43:14. 

7 

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UNITS = mm 

FIGURE 1. - TEST SPEC IMEN GEOMETRY AND TAB DETA ILS. 

FIGURE 2. - SERVO-HYDRAULIC LOAD TRAIN. 

8 
600 

500 

qOO u 

0 

W 

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Ic( 300 

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"-:EO 

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I200 

100 

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MAXIMUM STRESS. MPa 

12q1 103q 965 896 827 

ISOTHERMAL 

q27 °c 1 1 1 

(FURNACE HEATING) 

TMF OUT -OF-PHASE 

93°C - 538°C 2 2 2 2 (DIRECT INDUCTION 

HEATI NG) 

TMF IN-PHASE 

93°C - 538°C 

<DIRECT INDUCTION 2 2 2 2 

HEATING) 

ALL TESTS WERE PERFORMED UNDER TENSION-TENSION CONDITIONS WITH A 

STRESS RATIO RO = 0.05. 

FIGURE 3. - TEST MATRIX. 

TOP SHOULDER 

UPPER GAUGE 

MIDDLE GAUGE 

LOWER GAUGE 

BOTTOM SHOULDER 

/, 

}; 

~=~ 

q.O Q.5 5.0 

TIME. MIN 

FIGURE Q. - DYNAMIC LONGITUDINAL TEMPERATURE PROFILE. 

9 

5.5 6.0 
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w 

"'" >-

V) 

:IE 

=> 

E: 

x 

« E: 

1200 

1000 

800 

600 

o DIRECT INDUCTION HEATI NG, 

FREQUENCY z 7 CPM (GAYDA ET AL .) 

() RADIANT HEATING, FREQUENCY = 10 CPM 

(ERVIN ET AL .) 

<> RADIANT HEAT ING, FREQUENCY = 10 CPM 

103 104 

FATIGUE LIFE Nf' CYCLE 

FIGURE 5. - COMPARISON OF ISOTHERMAL FATIGUE LIFE OF 

SiC/Ti-15-3, [0]9' AT 427 DC. 

'" 

"-E: 

'" V) 

w 

"'" >-

V) 

lOS 

10 

1000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 

1100 

1000 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 

_. .

0MAX = 896 MPa 

CYCLE 1 AND 2 

CYCLE 29 000 

Nf = 29 845 

(a) 0MAX = 896 MPa . 

0MAX = 1034 MPa 

CYCLE 1 AN D 2 

CYCLE 12 000 

Nf = 12 352 

.4 .9 1.0 

MECHANICAL STRA IN, PERCENT 

(b) 0MAX = 1034 MPa . 

FIGURE 6. - STRESS-STRAI N RESPONSE FOR TWO ISOTHERMAL 

FATIGUE TESTS AT 427 QC. 
--I 

.9 

1034 MPa 

.8 965 MPa MAXIMUM STRAIN 

~ .7 z 

w 

u 

'" w .6 c.. 

Z 896 MPa 

:;;: .5 

'" ~ 

'" ...J .4 ct 

U 

Z 

ct .3 1034 Mpa 965 MPa :J: 

U 

W 

£ .2 

.1 

a 4000 8000 12 000 16 000 20 000 24 000 28 000 32 000 

CYCLE 

FIGURE 7. - CHANGE IN MAXIMUM AND MINIMUM STRAI N DURING ISOTHERMAL FATIGUE TESTS PERFORMED AT 

427 °e. 

11 
(a) 30X. 

(b) 100X. 

FIGURE 8. - TYPICIIL SEM BIICKSCIITTER rRIlCTORGRIlPIiS TIIKEN FROM THE 0MIIX = 896 MPa ISOTlIERMIlL TEST pERrORMEO AT q77 °c. 

12 
CL '"

:E: 

en 

V) 

w 

'" lV) 

:E: 

:::> 

~ x 

~ 

1400 

1200 

1000 

800 

600 

o ISOTHERMAL, 538 DC 

l> B I-THERMAL I N-PHASL 

100 DC - 427 DC 

'V TMF OUT -OF-PHASE, 

93 DC - 538 DC 

o TMF IN-PHASE, 

93 DC - 538 DC 

o 0 

, ISOTHERMAL FATIGUE 

\ LINE - 427 DC 

\ 

100 101 102 103 104 105 

FATIGUE LIFE N f' CYCLE 

FIGURE 9. - THERMOMECHANICAL FATIGUE LIFE RESULTS FOR 

SiC/Ti-15-3, [OJ9. 

"-'" 

:E: 

en 

V) 

w 

l-'" V) 

13 

900 

800 

700 

600 

500 

400 

300 

200 

100 

0 

900 

800 

700 

600 

500 

400 

300 

200 

100 

o 

TMF OUT-OF-PHASE 

93 DC - 538 DC 

CYCLE 3500 

(a) OUT -OF-PHASE. 

TMF IN-PHASE 

93 DC - 538 DC 

CYCLE 1 AND 2 

CYCLE 1060 

.2 .4 .6 

MECHANICAL STRAIN, PERCENT 

(b) IN-PHASE. 

FIGURE 10. - STRESS-MECHANICAL STRAI N RESPONSE FOR TWO 

THERMOMECHANICAL TESTS PERFORMED AT 0MAX = 896 MPa. 

.8 
.30 

.25 

I- .20 z: 

LJ.J 

U 

"" UJ 

Cl. 

Z .15 

;:c 

"" I- .15 (f) 

-' 

<C 

le 

I-

.10 

.05 

0 

1.0 

.9 

I- .8 z 

UJ 

u 

"" LJ.J 

Cl. 

Z .7 <C 

"" I-

(f) .3 -' 

<C 

le 

I-

.2 

.1 

o 

L-. _____ _ _ 

(a) MAXIMUM STRAIN. 

CYCLE 

(b) MINIMUM STRAIN. 

fIGURE 11. - CHANGE IN MAXIMUM AND MINIMUM STRAIN fOR AN OUT-Of-PHASE TEST WITH 0MAX = 

896 MPa. 

50 100 150 

(a) MAXIMUM STRAI N. 

200 250 

CYCLE 

300 

(b) MINIMUM STRAIN. 

350 ~OO ~50 

fIGURE 12. - CHANGE IN MAXIMUM AND MINIMUM STRAI N fOR AN IN-PHASE TEST WITH 0MAX = 

896 MPa. 

14 

500 
INTERNAL 

REGION 

DOMINATED 

BY TENSILE 

OVERLOAD ""'\ 

\ 

(bl 100X. 

FIGURE 13 . - TYPICAL SEM BACKSCATTER FRACTORGRAPIIS TIIKEN FROM A SPECI MEN SUBJECTED TO OUT-OF -PHASE LOAD ING WITH 

0MAX = 896 MPa . 

15 
FIBER HOLE 

• 

1 

SPECIMEN EDGE ....... 

(a) LONGITUDINAL . 100 IJM 

ROW 2 ....... 

ROW 1 ~ 

SPECIMEN EDGE ~ 

(b) TRIINSVERSE. 100 IJM 

FIGURE lQ . - TYPICAL SECTIONS TIIKEN FROM II SPECIMEN SUBJECTED TO OUT-OF-PHASE LOIIDING WITH 0MX = 896 MPa . 

16 
- - - 

- -- 

~ --,.. ~  _._ --' '~' ~- --- -_. 

(a) 30X. 

(b) 100X. 

FIGURE 15. - TYPICAL SEM FRACTOGRAPHS TAKEN FROM A SPECIMEN SUBJECTED TO IN-PHASE LOADING 

WITH 0MAX = 896 MPa . 

17 

1 
1_ -

I 

100 11m 

(a) THROUGH THE WIDTH. 

100 11m 

(b) THROUGH THE THICKNESS. 

FIGURE 16. - TYPICAL LONGITUDINAL SECTIONS TAKEN FROM A SPECIMEN SUBJECTED TO IN-PHASE 

LOAD I NG W!TH crMAX = 896 MPa. 

18 

~~--~~---.. ~-
NJ\SI\ 

Nallonal Aeronautics and Report Documentation Page Space Admlnlstrauon 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

NASA TM-103171 

4. Tille and Subtille 5. Report Date 

Thermomechanical Testing Techniques for High-Temperature 

Composites: TMF Behavior of SiC(SCS-6)/Ti-15-3 6. Performing Organization Code 

7. Author(s) 8. Performing Organization Report No. 

Michael G. Castelli, 1. Rodney Ellis, and Paul A. Bartolotta E-5543 

10. Work Unit No. 

505-63-1B 

9. Performing Organization Name and Address 

11. Contract or Grant No. 

National Aeronautics and Space Administration 

Lewis Research Center 

Cleveland, Ohio 44135-3191 13. Type of Report and Period Covered 

12. Sponsoring Agency Name and Address Technical Memorandum 

National Aeronautics and Space Administration 14. Sponsoring Agency Code 

Washington, D.C. 20546-0001 

15. Supplementary Notes 

Prepared for the 10th Symposium on Composite Materials: Testing and Design sponsored by the American 

Society for Testing and Materials, San Francisco, California, August 24-25, 1990. Michael G . Castelli, 

Sverdrup Technology, Inc., Lewis Research Center Group, 2001 Aerospace Parkway, Brook Park, Ohio 44142. 

J. Rodney Ellis and Paul A. Bartolotta, NASA Lewis Research Center. 

16. Abstract 

Thermomechanical testing techniques recently developed for monolithic structural alloys were successfully 

extended to continuous fiber reinforced composite materials in plate form. The success of this adaptation was 

verified on a model metal matrix composite (MMC) material , namely SiC(SCS-6)/Ti-15V-3Cr-3AI-3Sn. Effects 

of heating system type and specimen preparation are also adressed. Cyclic lives determined under full thermomechanical conditions were shown to be significantly reduced from those obta ined under comparable isothermal 

and in-phase bi-thermal conditions. Fractography and metallography from specimens subjected to isothermal, outof-phase and in-phase conditions reveal distinct differences in damage/failure modes. Isothermal metallography 

revealed extensive matrix cracking associated with fiber damage throughout the entire cross-section of the 

specimen. Out-of-phase metallography revealed extensive matrix damage associated with minimal (if any) fiber 

cracking. However, the damage was located exculsively at surface and near-surface locations. In-phase conditions 

produced extensive fiber cracking throughout the entire cross-section, associated with minimal (if any) matrix 

damage. 

17. Key Words (Suggested by Author(s)) 18. Distribution Statement 

Thermomechanical fatigue Unclassified - Unlimited 

Metal matrix composites Subject Category 39 

SiC/Ti-15-3 

Damage/failure mode 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21 . No. of pages 22. Price' 

U nclassi fied Unclassified 20 A03 

NASA FORM 1626 OCT 86 'For sale by the National Technical Information Service, Springfield, Virginia 22161