Sung R. Choi

University of Toledo, Toledo, Ohio

Anthony M. Calomino, Narottam P. Bansal, and Michael J. Verrilli

Glenn Research Center, Cleveland, Ohio

Life Limiting Behavior in Interlaminar Shear

of Continuous Fiber-Reinforced Ceramic Matrix

Composites at Elevated Temperatures

NASA/TM—2006-214088

January 2006
The NASA STI Program Office . . . in Profile

Since its founding, NASA has been dedicated to

the advancement of aeronautics and space

science. The NASA Scientific and Technical

Information (STI) Program Office plays a key part

in helping NASA maintain this important role.

The NASA STI Program Office is operated by

Langley Research Center, the Lead Center for

NASA’s scientific and technical information. The

NASA STI Program Office provides access to the

NASA STI Database, the largest collection of

aeronautical and space science STI in the world.

The Program Office is also NASA’s institutional

mechanism for disseminating the results of its

research and development activities. These results

are published by NASA in the NASA STI Report

Series, which includes the following report types:

• TECHNICAL PUBLICATION. Reports of

completed research or a major significant

phase of research that present the results of

NASA programs and include extensive data

or theoretical analysis. Includes compilations

of significant scientific and technical data and

information deemed to be of continuing

reference value. NASA’s counterpart of peerreviewed formal professional papers but

has less stringent limitations on manuscript

length and extent of graphic presentations.

• TECHNICAL MEMORANDUM. Scientific

and technical findings that are preliminary or

of specialized interest, e.g., quick release

reports, working papers, and bibliographies

that contain minimal annotation. Does not

contain extensive analysis.

• CONTRACTOR REPORT. Scientific and

technical findings by NASA-sponsored

contractors and grantees.

• CONFERENCE PUBLICATION. Collected

papers from scientific and technical

conferences, symposia, seminars, or other

meetings sponsored or cosponsored by

NASA.

• SPECIAL PUBLICATION. Scientific,

technical, or historical information from

NASA programs, projects, and missions,

often concerned with subjects having

substantial public interest.

• TECHNICAL TRANSLATION. Englishlanguage translations of foreign scientific

and technical material pertinent to NASA’s

mission.

Specialized services that complement the STI

Program Office’s diverse offerings include

creating custom thesauri, building customized

databases, organizing and publishing research

results . . . even providing videos.

For more information about the NASA STI

Program Office, see the following:

• Access the NASA STI Program Home Page

at http://www.sti.nasa.gov

• E-mail your question via the Internet to

help@sti.nasa.gov

• Fax your question to the NASA Access

Help Desk at 301–621–0134

• Telephone the NASA Access Help Desk at

301–621–0390

• Write to:

 NASA Access Help Desk

 NASA Center for AeroSpace Information

 7121 Standard Drive

 Hanover, MD 21076
Sung R. Choi

University of Toledo, Toledo, Ohio

Anthony M. Calomino, Narottam P. Bansal, and Michael J. Verrilli

Glenn Research Center, Cleveland, Ohio

Life Limiting Behavior in Interlaminar Shear

of Continuous Fiber-Reinforced Ceramic Matrix

Composites at Elevated Temperatures

NASA/TM—2006-214088

January 2006

National Aeronautics and

Space Administration

Glenn Research Center
Acknowledgments

This work was supported by the Ultra-Efficient Engine Technology (UEET) Project, NASA Glenn Research Center,

Cleveland, Ohio. The authors are grateful to R. Pawlik for experimental work during the course of this work.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

This report is a formal draft or working

paper, intended to solicit comments and

ideas from a technical peer group.

Trade names or manufacturers’ names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.

Available electronically at http://gltrs.grc.nasa.gov
NASA/TM—2006-214088 1

Life Limiting Behavior in Interlaminar Shear of Continuous 

Fiber-Reinforced Ceramic Matrix Composites at 

Elevated Temperatures 

Sung R. Choi 

University of Toledo 

Toledo, Ohio 43606 

Anthony M. Calomino, Narottam P. Bansal, and Michael J. Verrilli 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Interlaminar shear strength of four different fiber-reinforced ceramic matrix composites was 

determined with double-notch shear test specimens as a function of test rate at elevated temperatures 

ranging from 1100 to 1316 °C in air. Life limiting behavior, represented as interlaminar shear strength 

degradation with decreasing test rate, was significant for 2-D crossplied SiC/MAS-5 and 2-D plain-woven 

C/SiC composites, but insignificant for 2-D plain-woven SiC/SiC and 2-D woven Sylramic SiC/SiC 

composites. A phenomenological, power-law delayed failure model was proposed to account for and to 

quantify the rate dependency of interlaminar shear strength of the composites. Additional stress rupture 

testing in interlaminar shear was conducted at elevated temperatures to validate the proposed model. The 

model was in good agreement with SiC/MAS-5 and C/SiC composites, but in poor to reasonable 

agreement with Sylramic SiC/SiC. Constant shear stress-rate testing was proposed as a possible means of 

life prediction testing methodology for ceramic matrix composites subjected to interlaminar shear at 

elevated temperatures when short lifetimes are expected. 

1. Introduction 

Successful development and design of continuous fiber-reinforced ceramic matrix composites 

(CMCs) are dependent on understanding their properties such as deformation, fracture, delayed failure 

(fatigue, slow crack growth, or damage accumulation), and environmental durability. Particularly, 

accurate evaluation of delayed failure behavior under specified loading/environment conditions is 

prerequisite to ensure accurate life prediction of structural CMC components at elevated temperatures. 

Although fiber-reinforced CMCs have shown improved resistance to fracture and increased damage 

tolerance compared with monolithic ceramics, inherent material/processing defects or cracks in the 

matrix-rich interlaminar regions can still cause delamination under interlaminar normal or shear stress, 

resulting in loss of stiffness or in some cases structural failure. Strength behavior of CMCs in shear has 

been characterized in view of their unique interfacial architectures and its importance in structural 

applications (refs. 1 to 4). Because of the inherent nature of CMCs, it would be highly feasible that 

interlaminar defects or cracks are susceptible to delayed failure particularly at elevated temperatures, 

resulting in strength degradation or shortened time to failure. Although delayed failure is one of the 

important life-limiting phenomena, few studies have been done on this subject for CMCs under shear at 

elevated temperatures. 

In a previous study (ref. 5), both interlaminar and in-plane shear strengths of a unidirectional 

Hi-NicalonTM SiC fiber-reinforced barium strontium aluminosilicate (SiC/BSAS) composite were 

determined at 1100 °C in air as a function of test rate using double-notch shear test specimens. The 

composite exhibited a significant effect of test rate on shear strength, regardless of orientation. The shear 

strength degraded by about 50 percent as test rate decreased from the highest (102

 MPa/s) to the lowest 
NASA/TM—2006-214088 2

(10–2 MPa/s). A phenomenological, life-prediction model has been proposed and formulated to account 

for the shear strength degradation of the composite. 

This paper, as an extension of the previous study, describes life limiting behavior in interlaminar 

shear of four different fiber-reinforced CMCs at elevated temperatures, including three SiC fiberreinforced CMCs and one carbon-fiber reinforced CMC. Interlaminar shear strength of each composite 

was determined in double notch shear as a function of test rate using constant stress-rate testing. The 

interlaminar shear strength was analyzed using the power-law type of crack growth model proposed 

previously in order to quantify the rate dependency/delayed failure of the composites under interlaminar 

shear. Stress rupture testing in interlaminar shear was also conducted at elevated temperatures with three 

selected CMCs in order to validate the proposed model. Some of the data in this paper have been reported 

previously (ref. 6). 

2. Experimental Procedures 

Four different CMCs—three SiC fiber-reinforced and one carbon fiber-reinforced—were used in this 

study, including NicalonTM SiC 2-D crossplied fiber-reinforced magnesium aluminosilicate (designated 

SiC/MAS-5), NicalonTM SiC 2-D plain-woven silicon carbide (designated SiC/SiC), Sylramic SiC 2-D 

woven silicon carbide (designated Sylramic SiC/SiC), and T300TM carbon-fiber 2-D plain-woven silicon 

carbide (designated C/SiC). 

The SiC/MAS-5 composites were fabricated through hot pressing followed by ceraming of the 

composites by a thermal process. The matrix was doped with 5 vol% of borosilicate glass to increase 

oxidation resistance and interfacial shear strength at the fiber/matrix interfaces. The silicon carbide matrix 

in the SiC/SiC composite was processed through chemical vapor infiltration (CVI) into the fiber 

preforms. Silicon carbide was also chemically vapor deposited onto the composite panels to cover the 

residual porosity. More detailed information regarding the processing of these SiC/MAS-5 and SiC/SiC 

composites can be found elsewhere (ref. 7). The Sylramic cloth preforms in the Sylramic SiC/SiC 

composite were stacked and chemically vapor infiltrated with a thin BN-based interface coating followed 

by SiC matrix over-coating. Remaining matrix porosity was filled with SiC particulates and then with 

molten silicon at 1400 °C, a process termed slurry casting and melt infiltration (ref. 8). Mechanical 

properties and fabrication and testing of vane subelements using the Sylramic SiC/SiC composites have 

been evaluated and addressed extensively in recent studies (refs. 9 to 11). The carbon fiber performs in 

the C/SiC composite were coated with pyrolytic carbon as an interface prior to CVI SiC infiltration 

(ref. 12). Stress/life behavior of the C/SiC composites has been characterized in a low partial pressure of 

oxygen at elevated temperatures (refs. 12 and 13). Fiber volume fraction, laminate architecture, nominal 

dimensions of shear test specimens, and other information of the CMCs used in this work are summarized 

in table 1. Weaving patterns of the CMCs are also shown in figure 1. 

The double-notch-shear (DNS) test specimens were machined from panels of each CMC. Typically, 

test specimens were 13 to 15 mm wide (W) and 30 mm long (L). The thickness of test specimens was the 

same as a nominal thickness of panels of each composite (see table 1). Two notches, 0.3 mm wide (h) and 

6 mm (Ln) away from each other, were made into each test specimen such that the two notches were 

extended to the middle of each specimen within ±0.05 mm so that shear failure occurred on the plane 

between the notch tips. Schematics of DNS test specimen showing a notch configuration is shown in 

figure 2. Monotonic shear testing for DNS test specimens was conducted at elevated temperatures with 

different test rates in ambient air (relative humidity of about 45 percent), using an electromechanical test 

frame (Model 8562, Instron, Canton, Massachusetts) under load control. This type of testing, employing 

with different test rates, is called constant stress-rate or “dynamic fatigue” testing that is used for 

advanced monolithic ceramics and other brittle materials such as glasses and glass ceramics in order to 

evaluate their slow crack growth behavior in flexure or in tension (refs. 14 and 15). Test temperatures 

were 1100, 1200, 1316, and 1200 °C, respectively, for SiC/MAS-5, SiC/SiC, Sylramic SiC/SiC, and 

C/SiC composites. 
NASA/TM—2006-214088 3

TABLE 1.—FIBER-REINFORCED CERAMIC MATRIX COMPOSITES USED IN THIS WORK 

Composites Weaving Fiber Fiber 

volume 

fraction 

Panels/notches Manufacturer 

SiC/MAS-5 

(’93) 

SiC/SiC (’92) 

Sylramic 

SiC/SiC (’99) 

C/SiC (’97) 

2-D crossplied (0/90°) 

2-D plain 

woven 

2-D woven 

2-D plain 

woven 

Nicalon#

SiC 

Nicalon 

SiC 

Sylramic* 

SiC 

T300$

carbon 

0.39 

0.39 

0.36 

0.46 

16 plies; t = 3.2 mm; W = 12.7 

mm; Ln = 6 mm 

6.7 epc§; 12 plies; t = 3.5 mm; 

W = 13.0; Ln = 6 mm 

7.9 epc; 5 HS; 8 plies; t = 2 mm; 

W = 12.7/6mm; Ln = 6 mm 

7.5 epc; 26 plies; t = 3.3 mm; 

W = 15.4 mm; Ln = 6 mm 

Corning, Inc. 

(Corning, NY) 

DuPont Lanxide Composites (now GE Power 

Systems Composites, GE PSC) (Newark, DE) 

Honeywell Advanced Composites, Inc. 

(now GE PSC) (Newark, DE) 

Honeywell Advanced Composites, Inc. 

(now GE PSC) (Newark, DE) 

#

 Nippon Carbon Co. (Japan) 

*Dow Corning (Midland, MI) 

$ Toray Industries, Inc. (Japan) 

§

 epc = end per centimeter. 

 

 (a) (b) 

 (c) (d) 

Figure 1.—Weaving patterns of continuous fiber-reinforced ceramic 

matrix composites used in this work: (a) SiC/MAS-5 (2-D crossplied); (b) SiC/SiC (2-D plain-woven); (c) Sylramic SiC/SiC (2-D 

woven); (4) C/SiC (2-D plain-woven). 

 

4 mm
NASA/TM—2006-214088 4

(a) 

 (b) 

Figure 2.—(a) Configurations of double notch shear (DNS) test specimen; (b) A schematic showing test 

fixture and test specimen used in this work. 

 

A total of three to four applied interlaminar shear stress rates ranging from 10–4 to 101

 MPa/s were 

used for a given composite, depending on the type of composite. Typically, three to ten test specimens 

were tested at each test rate, again depending on type and availability of materials. A simple test-fixture 

configuration consisting of SiC upper and lower fixtures, as shown in figure 2, was used for test 

specimens whose thickness was ≥3 mm. With this specimen thickness and the tight machining tolerances, 

the test specimens could stand alone and be subjected to negligible bending (≤4 percent) due to 

misalignment, geometrical inaccuracies, and/or buckling. By contrast, for thin test specimens whose 

thickness was about 2 mm (e.g., Sylramic SiC/SiC composite), anti-buckling guides were used with 

specially designed ring-shaped fixtures. Each test specimen was kept for about 20 min at test temperature 

for thermal equilibration prior to testing. Basically, test specimen configurations and testing procedures 

were followed in accordance with ASTM test method C 1425 (ref. 16). The interlaminar shear fracture 

stress—the average interlaminar shear stress at failure—was calculated using the following relation 

n

f

f WL

P

τ = (1) 

Upper fixture

Test specimen

Lower fixture

Thermocouple

Guides (optional)

P

Notch detail

0.15mmR

 0.30mm 

W

L Ln

t

h
NASA/TM—2006-214088 5

where τf is the interlaminar shear strength, Pf is the fracture force, and W and Ln are the specimen width 

and the distance between the two notches, respectively (see fig. 2). The applied interlaminar shear stress 

rate τ was given as follows: 

WLn

P τ = (2) 

where P is applied shear (or compressive) force rate employed via a test frame in load control. 

Additionally, stress rupture testing in interlaminar shear was conducted with DNS test specimens for 

SiC/MAS-5 at 1100 °C, Sylramic SiC/SiC at 1316 °C, and C/SiC at 1200 °C in air. The test frame, test 

specimen configuration, and test fixture used in stress rupture were the same as those used in constant 

stress-rate testing. For each composite, the number of applied shear stresses was typically three, and the 

minimum number of test specimens used was six. This stress rupture testing was performed to determine 

life limiting behavior of the chosen composites under constant applied shear stress and to relate their 

stress rupture data to the respective constant stress-rate data in order to validate the phenomenological life 

prediction model proposed. 

3. Experimental Results 

3.1. Constant Stress-Rate Testing 

Without exception, all specimens tested failed in interlaminar shear mode along their prospective 

shear planes. A typical example of a tested specimen showing such interlaminar shear mode failure is 

presented in figure 3, together with a test specimen prior to testing for comparison. 

τ

τ

Prospective

shear plane

P

 (a) After test (b) Before test 

Figure 3.—(a) A typical example showing interlaminar shear failure 

of a Sylramic SiC/SiC composite double-notch-shear (DNS) 

specimen tested at 1316 °C in air at 5 MPa/s. The corresponding 

specimen configuration prior to test is shown in (b) for 

comparison. Note a slight change of specimen surface appearance 

due to high temperature exposure/oxidation. 
NASA/TM—2006-214088 6

3.1.1. SiC/MAS-5 Composite 

The results of monotonic interlaminar shear strength testing for the 2-D crossplied SiC/MAS-5 

composite tested at 1100 °C are presented in figure 4, where interlaminar shear strength is plotted as a 

function of applied shear test rate. The solid line in the figure represents a best-fit regression based on the 

log (interlaminar shear strength) versus log (applied shear test rate) relation. The reason for using the 

log-log relation will be described in the “Discussion” section. The decrease in interlaminar shear strength 

with decreasing test rate, indicating a susceptibility to delayed failure or slow crack growth, was 

significant for this composite. The interlaminar shear strength degradation was about 50 percent when test 

rate decreased from the highest (5 MPa/s) to the lowest (0.005 MPa/s) value. A similar trend in shear 

strength degradation with decreasing test rate was also found from a previous study in an 1-D, 

Hi-NicalonTM fiber-reinforced barium strontium aluminosilicate (SiC/BSAS) composite at 1100 °C in air 

(ref. 5). This trend in shear strength with respect to test rate was also analogous to that in ultimate tensile 

strength of various continuous fiber-reinforced CMCs including SiC/MAS-5, SiC/CAS (calcium 

aluminosilicate), SiC/BSAS, C/SiC, and SiC/SiC composites (refs. 17 and 18). These CMCs have 

exhibited significant degradation of ultimate tensile strength with decreasing test rates, with their degree 

of degradation being dependent on material and test temperature. 

Fracture surfaces of the SiC/MAS-5 composite showed that the mode of interlaminar shear failure 

was typified as delamination of fibers from matrix-rich regions, implying that the fiber-matrix interfacial 

architecture is the most influencing characteristic in controlling shear properties of the composite. More 

violent and rough fracture surfaces were seen from the specimens at higher test rate, sometimes exposing 

two more layers (0/90°) therein, while smoother surfaces were noted for the specimens at lower test rate 

with only one layer associated with delamination, as shown in figure 5. The presence of viscous 

flow/phases was obvious from fracture surfaces, particularly at low test rates in which more enhanced 

delayed failure occurred. The residual glassy phase might have been a major cause of delayed failure in 

the SiC/MAS-5 silicate composite, as observed previously in the SiC/BSAS silicate composite (ref. 5). 

Applied shear stress rate, [MPa/s]

10-4 10-3 10-2 10-1 100 101 10

Interlaminar shear strength, 

2

τf [MPa]

20

30

40

50

60

70

80

10

SiC/MAS-5 (DNS/1100 oC)

τ

Figure 4.—Results of interlaminar shear strength as a 

function of applied shear stress rate for 2-D crossplied 

SiC/MAS-5 composite tested at 1100 °C in air. The solid 

line represents the best-fit. 
NASA/TM—2006-214088 7

 

 (a) (b) 

Figure 5.—Fracture surfaces of 2-D crossplied SiC/MAS-5 composite 

specimens subjected to interlaminar shear, tested at 1100 °C in air at: 

(a) 5 MPa/s and (b) 0.005 MPa/s. 

Figure 6.—Results of interlaminar shear strength as a 

function of applied shear stress rate for 2-D plain-woven 

SiC/SiC composite tested at 1200 °C in air. The solid line 

represents the best-fit. 

3.1.2. SiC/SiC Composite 

Figure 6 shows the results for the 2-D plain-woven SiC/SiC composite tested at 1200 °C, in which 

interlaminar shear strength was plotted in the same way as in figure 4, with the line representing the bestfit. Unlike the SiC/MAS-5 composite, the SiC/SiC composite did not exhibit any significant interlaminar 

strength degradation with decreasing test rate. The strength degradation from the highest ( = 5 MPa/s) to 

the lowest (0.0005 MPa/s) test rate was only 5 percent, indicating a greater resistance to delayed failure or 

slow crack growth, compared with the SiC/MAS-5 composite. The corresponding two-parameter Weibull 

interlaminar shear strength distribution with the all the data in figure 6 combined is depicted in figure 7. 

Applied shear stress rate, [MPa/s]

10-4 10-3 10-2 10-1 100 101 102

Interlaminar shear strength, τf [MPa]

20

30

40

50

60

70

80

90

10

100

SiC/SiC (DNS/1200 oC)

τ

2 mm
NASA/TM—2006-214088 8

Interlaminar shear strength, ln [τf] ln [MPa]

3.0 3.5 4.0 4.5

ln ln [1/(1-F)]

-5

-4

-3

-2

-1

0

1

2

m=7.0

τθ=47.3 MPa

SiC/SiC (DNS/1200 oC)

30 40 50 60 70 [MPa]

Figure 7.—Two-parameter Weibull interlaminar shear 

strength distribution of 2-D plain-woven SiC/SiC composite 

tested at 1200 °C in air, with all the data combined in 

figure 6. m: Weibull modulus; τθ : characteristic 

interlaminar shear strength; F: failure probability. 

 

 

 (a) (b) 

Figure 8.—Fracture surfaces of 2-D plain-woven SiC/SiC composite 

specimens subjected to interlaminar shear, tested at 1316 °C in air at: 

(a) 5 MPa/s and (b) 0.005 MPa/s. 

Weibull modulus of interlaminar shear strength was m = 7, somewhat lower than the typical range of 

10 to 20 for flexure or tensile strength of many monolithic ceramics. The characteristic (τθ ) and mean 

shear strengths were 47.3 and 44.3±7.5 MPa, respectively. Fracture surfaces showed that some oxidation 

occurred therein with a bluish discoloration, (see fig. 8). Of course, more discoloration at lower test rates, 

and vice versa. Fracture surfaces also exhibited that well developed interlaminar shear occurred in matrixrich regions between two adjacent laminates by delamination. Except for discoloration, the difference in 

fracture surface of test specimens between high and low test rates appeared to be unnoticeable. 

2 mm
NASA/TM—2006-214088 9

Figure 9.—Results of interlaminar shear strength as a 

function of applied shear stress rate for 2-D woven 

Sylramic SiC/SiC composite tested at 1316 °C in air. 

The data determined with test specimen’s width of 

W = 6 mm are also included for comparison. The solid 

line represents the best-fit. 

3.1.3. Sylramic SiC/SiC Composite 

The results of interlaminar shear strength testing for the 2-D woven Sylramic SiC/SiC composite at 

1316 °C are depicted in figure 9. The composite exhibited no apparent shear strength degradation down to 

0.0005 MPa/s; however, it exhibited strength degradation at the lowest test rate of 0.00005 MPa/s, 

resulting in an about 40 percent reduction in average shear strength. The test time corresponding to the 

lowest test rate was around 85 hr so that this long duration of test would have caused such significant 

strength degradation through a possible environmental degradation. Invariably, a severe discoloration was 

observed from the surfaces of specimens tested at this test rate, as shown in figure 10. The pattern of 

shear fracture was such that an apparent shear delamination with little damage in fiber tows was evident 

from the fracture surfaces of specimens tested at lower test rates, while rough fracture surfaces with a 

somewhat plucking mode in fiber tows were typified at higher test rates, as seen from figure 10. In terms 

of duration of test time, a question arises as to whether strength degradation would take place if an 

extremely low test rate of 0.00005 MPa/s, which was applied for the Sylramic SiC/SiC composite, is 

employed to the 2-D plain-woven SiC/SiC composite. A further investigation is needed. 

It is important to note that the size effect on interlaminar shear strength was negligible for the 

Sylramic SiC/SiC composite, as seen in figure 9, where interlaminar shear strength of additional test 

specimens with W = 6 mm, determined at the same test rate of 5 MPa/s, was compared with that of the 

regular test specimens with W = 13 mm. The average interlaminar shear strength of 10 test specimens was 

27±4 and 25±3 MPa, respectively, for W = 13 and 6 mm. Also, considering that overall intrelaminar shear 

strength was not changed significantly regardless of test rate >0.00005 MPa/s, it could be possible to take 

all strength values at different test rates as single representing data. With this approach, two-parameter 

Weibull interlaminar strength distributions were obtained and the results are shown in figure 11. Weibull 

modulus (m = 10.7 vs. 10.4) as well as characteristic shear strength (τθ = 28 vs. 26 MPa) is about the same 

for both specimen sizes. It is noted that the value of Weibull modulus for the Sylramic SiC/SiC, m≈10, 

compares reasonably well with m = 7 for the 2-D plain-woven SiC/SiC (see fig. 7). 

Applied shear stress rate, [MPa/s]

10-5 10-4 10-3 10-2 10-1 100 101 102

Interlaminar shear strength, τf [MPa]

6

7

8

20

30

40

50

60

10 W=13mm

W= 6mm

Sylramic SiC/SiC (DNS/1316 oC)

τ
NASA/TM—2006-214088 10

 

 (a) (b) 

Figure 10.—Fracture surfaces of 2-D woven Sylramic SiC/SiC composite 

specimens subjected to interlaminar shear, tested at 1316 °C in air at: 

(a) 5 MPa/s and (b) 0.00005 MPa/s. 

Figure 11.—Weibull interlaminar shear strength distributions 

of two different sizes (W = 13 and 6 mm) of double-notch 

shear test specimens of 2-D woven Sylramic SiC/SiC 

composite tested at 5 MPa/s at 1316 °C in air. 

Interlaminar shear strength, ln [τf] ln [MPa]

2.0 2.5 3.0 3.5 4.0

ln ln [1/(1-F)]

-4

-3

-2

-1

0

1

2

W=13 mm

W= 6 mm

10 20 30 40 [MPa]

m=10.4

τθ=26.3 MPa

m=10.7

τθ=28.1 MPa

Sylramic SiC/SiC (DNS/1316 oC)

2 mm
NASA/TM—2006-214088 11

Figure 12.—Results of interlaminar shear strength as a 

function of applied shear stress rate for 2-D plain-woven 

C/SiC composite tested at 1200 °C in air. The solid line 

represents the best-fit. 

 (a) (b) 

Figure 13.—Fracture surfaces of 2-D plain-woven C/SiC composite 

specimens subjected to interlaminar shear, tested at 1200 °C in air at: 

(a) 0.16 MPa/s and (b) 0.00016 MPa/s. 

3.1.4. C/SiC Composite 

Figure 12 shows the results of interlaminar shear strength testing for the 2-D plain-woven C/SiC 

composite at 1200 °C in air. Interlaminar shear strength degradation between test rates of 5 and 

0.16 MPa/s was negligible. However, below 0.16 MPa/s, shear strength degradation with decreasing test 

rate was very significant with a resulting degradation of about 90 percent when test rate decreased from 

0.16 to 0.00016 MPa/s. The C/SiC composite, in fact, did lose almost its shear-load bearing capability at 

that lowest test rate with a corresponding value of interlaminar shear strength of only τf = 2.9±0.6 MPa, 

compared with τf = 22 to 24 MPa at higher test rates. 

Severe oxidation was observed to have occurred throughout the material body particularly at lower 

test rates with a change to more yellowish/golden color, as shown in figure 13. Powdered residues were 

Applied shear stress rate, [MPa/s]

10-5 10-4 10-3 10-2 10-1 100 101 102

Interlaminar shear strength, τf [MPa]

2

3

4

5

6

8

20

30

40

50

1

10

C/SiC (DNS/1200 oC)

τ

2 mm
NASA/TM—2006-214088 12

Figure 14.—Weight loss as a function of test time in 

constant stress-rate and stress rupture testing in 

interlaminar shear for 2-D plain-woven C/SiC composite 

tested at 1200 °C in air. 

often found from the fracture surfaces of these test specimens, an evidence of oxidation products. Also, 

weight loss of test specimens after tests was evident: the more weight loss at the lower test rate and vice 

versa. Figure 14 shows weight loss as a function of test time. The figure also included the weight loss data 

obtained from stress rupture tests. Regardless of the type of testing, weight loss increased exponentially 

with test time and reached a plateau around a test time of about 4 hr. The corresponding weight loss at 

this time was about 40 percent, which is about 80 percent of the original fiber weight fraction. Hence, 

shear strength degradation of the C/SiC composite was due to oxidation of carbon fibers so that effective 

number of carbon fibers decreased with time, resulting in a decrease in shear load carrying capability. 

Evidence of oxidation during testing was also viewed from the nonlinearity of load versus displacement 

curves. The other composites did not exhibit any measurable weight loss by oxidation and showed little 

nonlinearity in load versus displacement curves. 

4. Discussion 

4.1. Model 

Strength degradation in tension at elevated temperatures with decreasing test rate occurred in 

advanced monolithic ceramics including silicon nitrides, silicon carbides, and aluminas (ref. 19). The 

strength degradation is known as a delayed failure (or fatigue or slow crack growth, SCG) phenomenon, 

commonly formulated by the empirical power-law relation (ref. 20) 

n v A KI KIc = ( / ) (3) 

where v, KI, and KIc are crack velocity, stress intensity factor, and fracture toughness under Mode I 

loading, respectively. A and n are SCG parameters. Based on this power-law relation, the tensile strength 

(σf) can be derived as a function of applied tensile stress rate ( σ ) with some mathematical manipulations 

(refs. 14, 15, and 21) 

Test time, x103 [s]

0 5 10 15 20 25

% weight loss

0

10

20

30

40

50

Constant stress-rate tests

Stress rupture tests

C/SiC (DNS/1200 oC)

1h 5h
NASA/TM—2006-214088 13

D

n f log log 1

1 log σ +

+

σ =  (4) 

where D is another SCG parameter dependent on inert strength, n, and crack geometry. 

A test method based on equation (4) is called constant stress-rate (or “dynamic fatigue”) testing and 

has been established as ASTM test methods C 1368 (ref. 14) and C 1465 (ref. 15) to determine SCG 

parameters of advanced monolithic ceramics at ambient and elevated temperatures. It has been shown that 

equation (3) was applicable even to CMCs including SiC/CAS (1-D), SiC/MAS-5 (2-D), SiC/SiC (2-D), 

C/SiC (2-D), and SiC/BSAS (2-D) tested in tension at 1100 to 1200 °C in air, indicating that delayed 

failure of those composites would be adequately described by the power-law formulation, equation (3). 

Examples of some of those CMCs exhibiting an invariably significant strength degradation and showing a 

good data fit to equation (4) are presented in figure 15 (refs. 17 and 18). 

It has been also observed that 1-D SiC/BSAS composite exhibited significant strength degradation in 

shear at 1100 °C in air (ref. 5). A phenomenological model in shear has been proposed and was found to 

describe well the shear strength dependency of the composite on test rate. The proposed model, similar in 

expression to the power-law relation of equation (2), takes a following fundamental delayed failure 

formulation (ref. 5): 

ns s s KII KIIc dt

da

v = = α ( / ) (5) 

where vs, a, t, KII, and KIIc are the crack growth rate in shear, crack size, time, Mode II stress intensity 

factor, and Mode II fracture toughness, respectively. αs and ns are delayed failure parameters in shear. In 

monotonic shear testing, a constant displacement rate or constant force rate is applied to a test specimen 

until the test specimen fails, so that the shear stress applied to the test specimen is a linear function of test 

time: 

APPLIED STRESS RATE, [MPa/s]

10-4 10-3 10-2 10-1 100 101 102 10

ULTIMATE STRENGTH, 

3

f [MPa]

50

60

70

80

90

200

300

400

500

100

σ

SiCf/CAS

SiCf

/MAS

SiCf

/BSAS

SiCf

/SiC

(n=9)

(n=6)

(n=7)

(n=18)

TENSION

Figure 15.—Examples of ultimate tensile strength as a function 

of applied stress rate at elevated temperatures in air for various 

CMCs (refs. 17 and 18) including SiC/MAS (2-D crossplied; 

1100 °C), SiC/CAS (1-D; 1100 °C), SiC/SiC (2-D woven; 

1200 °C), and SiC/BSAS (2-D crossplied; 1100 °C). The error 

bars represent ±1.0 standard deviation. 
NASA/TM—2006-214088 14

t dt t

t

τ = τ = τ ∫  

0

( (6) )

where τ is applied shear stress and τ is applied shear stress rate. The applied shear stress rate τ in 

displacement control can be determined from the slope (ΔP/Δt) of each recorded force-versus-time curve 

including the portion at or near the point of fracture but excluding the initial nonlinear portion, if any, 

using a relation τ = (ΔP/Δt)[1/(WLn)]. In case of load control, the applied shear stress rate can be easily 

obtained from a relation in equation (2). The generalized expression of stress intensity factor (KII) along 

the crack front of a penny-shaped crack subjected to shear loading either on crack planes or on remote 

material body (see fig. 16) can take the following form (ref. 21): 

 ) ( , KII = Ysτa1/ 2 f α φ (7) 

where Ys is a crack geometry factor also related to a function of f (α,φ) with the angles α and φ being 

defined in figure 16. The KII expression can be significantly simplified when shear stress is aligned with 

either x1 or x2 axis, where the KIII component also vanishes, which is the case of the interlaminar shear 

testing employed in this work. Using equations (5) to (7) and following a similar procedure as used to 

derive equation (4) in Mode I, one can obtain interlaminar shear strength (τf) as a function of applied 

shear stress rate as follows (ref. 5): 

s

s

f D

n

log log 1

1 log τ +

+

τ =  (8) 

where Ds is a parameter associated with several constants and other parameters (ref. 5). Equation (8) is 

analogous to equation (4) for Mode I loading. Delayed failure parameters ns and Ds in interlaminar shear 

can be determined from the slope and intercept of a linear regression analysis of the log (individual 

interlaminar shear strength with units of MPa) versus log (individual applied shear stress rate with units 

of MPa/s) data, based on equation (8). 

Figure 16.—An assumed penny-shaped 

crack arbitrarily located at interface 

between matrix and fibers in ceramic 

matrix composites, subjected to equal 

and opposite interlaminar shear stresses 

τ acting on both surfaces of a crack. 

α

x1 φ

x2

x3

τ

a
NASA/TM—2006-214088 15

Applied shear stress rate, [MPa/s]

10-5 10-4 10-3 10-2 10-1 100 101 102 10

Interlaminar shear strength, 

3

τf [MPa]

2

3

4

5

6

8

20

30

40

5060

80

10

Interlaminar DNS

ns=90

τ

ns>90

ns

=2

Syl.

SiC/SiC

C/SiC

SiC/SiC

SiC/BSAS [5]

SiC/MAS ns

=11

ns

=8

Figure 17.—Summary of interlaminar shear strength as a 

function of applied shear stress rate for 2-D crossplied 

SiC/MAS-5 at 1100 °C, 2-D plain-woven SiC/SiC at 1200 °C, 

2-D woven Sylramic SiC/SiC at 1316 °C, and 2-D plainwoven C/SiC at 1200 °C in air. The interlaminar shear data on 

1-D SiC/BSAS at 1100 °C (ref. 5) is also included. The error 

bars represent ±1.0 standard deviation. 

A summary of interlaminar shear strength as a function of test rate, based on equation (8), for the 

CMCs used in this study is shown in figure 17. The average interlaminar shear strength values, instead of 

individual data points, were used for clarity of illustrations. The level of interlaminar shear strength and 

the degree of shear strength degradation with respect to test rate are clearly quantified. The figure also 

includes delayed failure parameters ns for each composite and the previous result for the SiC/BSAS 

composite (ref. 5). The reasonable data fit to equation (8) shown in the figure indicates that the 

fundamental power-law formulation of equation (5) can describe very reasonably the delayed failure 

behavior under interlaminar shear for the current composite materials. Table 2 is a summary of the 

parameters ns and Ds and the coefficients of correlation (rcoef) in regression analysis for all the composites. 

TABLE 2.—DELAYED FAILURE PARAMETERS OF nS AND DS, AND COEFFICIENTS OF 

CORRELATION (rcoef) FOR VARIOUS CMCS DETERMINED IN CONSTANT 

STRESS-RATE TESTING IN INTERLAMINAR SHEAR 

AT ELEVATED TEMPERATURES 

Parameters 

Composites 

Test temperature 

(°C) 

ns Ds rcoef

SiC/MAS-5 

SiC/SiC 

Sylramic SiC/SiC 

C/SiC 

SiC/BSAS (1-D) (ref. 5) 

1100 

1200 

1316 

1200 

1100 

8.2 (1.5) 

88.5 

>90, and 3* 

2.3 (0.3) 

11.2 (2.2) 

31.8 (2.0) 

44.8 (2.0) 

27 

44.7 (7.5) 

19.2 (0.9) 

0.9281 

0.2122 

-------- 

0.9721 

0.8442 

*The value of ns for Sylramic SiC/SiC composite was estimated based on the two lowest test rates of 0.00005 

and 0.0005 MPa/s (see also fig. 9). 

The numbers in parentheses represent ±1.0 standard deviation. 
NASA/TM—2006-214088 16

4.2. Verification of model with stress-rupture data 

Constant stress-rate testing in tension has been shown to be a possible alternative to life prediction 

testing, as verified with stress rupture testing for various CMCs at elevated temperatures of 1100 to 

1200 °C (refs. 17 and 18). The underlying reasoning is that the same failure mechanism might have been 

operative, independent of loading configuration that was either in monotonic ramp (constant stress-rate) 

loading or in static (stress rupture) loading. In the same way, it would be feasible that life prediction in 

interlaminar shear from one loading configuration to another could be made as far as a single delayedfailure mechanism would be dominant in shear, regardless of loading configuration. A phenomenological 

life prediction approach was previously proposed based on the data of ns and Ds using the following 

relation that accounts for shear loading, which was modified from a relation primarily used for brittle 

materials in tension (ref. 5): 

] ( ) 1 [

1

f F

n

D

t s

s

n

s

n

s f −

+

τ

+ = (9) 

where tf is time to failure, τ is applied interlaminar shear stress, and f (F) is a functional expression of 

failure probability and other parameters. Equation (9) determines life as a function of applied interlaminar 

shear stress, based on ns and Ds parameters determined from constant shear stress-rate testing for a given 

probability of failure. 

In order to verify the life prediction relation in equation (9), stress rupture testing, aforementioned in 

the Experimental Procedures section, was conducted for the SiC/MAS-5, Sylramic SiC/SiC, and C/SiC 

composites. The results of stress rupture testing are presented in figure 18. Significant delayed failure in 

interlaminar shear occurred in the SiC/MAS-5 and C/SiC composites. Life prediction was made based on 

equation (9) using the constant stress-rate data ns and Ds for each composite, and the resulting prediction 

is presented as a solid line in the corresponding figure with an approximate failure probability of 

F = 50 percent. Despite a limited number of test specimens used, the prediction for the SiC/MAS-5 and 

C/SiC composites was in good agreement with the stress rupture data, thereby validating equation (9). 

The prediction for the Sylramic SiC/SiC composite, however, was in poor to reasonable agreement. Note 

that scatter of time to failure in stress rupture is considerably greater than that of strength in monotonic 

(constant stress-rate) testing for many brittle materials. Therefore, use of more test specimens is needed 

for the Sylramic SiC/SiC composite to better verify the proposed model. 

Unlike the other CMCs, the C/SiC composite was subjected to significant oxidation of carbon fibers, 

resulting in material loss. Therefore, strength degradation was increased, attributed to decreasing fiber 

volume fraction and subsequently increasing porosity. The stress-oxidation model proposed previously 

(ref. 23) could give a better physical explanation regarding the strength degradation/time dependency 

phenomenon. However, the phenomenological power-law formulation used in this study still provides a 

simple, convenient way to quantify the degree of strength degradation with respect to test rate. The 

oxidation-induced damage would be considered to be equivalent to crack-like flaws growing at matrixfiber interfaces from a fracture-mechanics point of view. The equivalent crack would propagate under a 

driving force (KII) based on equation (5) so that the resulting interlaminar shear strength follows 

equation (8). The fact that there was good agreement between the prediction and the stress rupture data 

implies that equation (4) would have been operative in delayed failure of the C/SiC composite in 

interlaminar shear, irrespective of loading configurations. Stress/life behavior and modeling of C/SiC 

composites in a low partial pressure of oxygen at elevated temperatures in tension can be found elsewhere 

(refs. 12 and 13). 

The results of interlaminar shear strength behavior at elevated temperatures for the four different 

CMCs showed that constant stress-rate testing could be applicable to determine phenomenological life 

prediction parameters of the composites even in interlaminar shear. This was evidenced in this work by 

the results of constant stress-rate testing combined with the results of additional stress rupture testing for 
NASA/TM—2006-214088 17

Time to failure, tf [s]

10-1 100 101 102 103 104 105 106 107 108

Applied shear stress, τ [MPa]

5

6

7

8

9

20

30

40

50

10

SiC/MAS-5 (DNS/1100 oC)

Prediction

Best fit

(a)

Time to failure, tf [s]

101 102 103 104 105 106 107 108

Applied shear stress, τ [MPa]

5

6

7

8

9

20

30

40

50

10

S-SiC/SiC (DNS/1316 oC)

Best fit

Prediction

(b)

Time to failure, tf [s]

100 101 102 103 104 105 106 107

Applied shear stress, τ [MPa]

2

3

4

5

6

8

20

30

40

1

10

 C/SiC (DNS/1200 oC)

Prediction

Best fit

(c)

Figure 18.—Results of stress rupture testing in 

interlaminar shear for: (a) 2-D crossplied SiC/MAS-5 at 

1100 °C; (b) 2-D woven Sylramic SiC/SiC at 1316 °C; 

(c) 2-D plain-woven C/SiC at 1200 °C. Life prediction 

based on equation (8) is shown as a solid line for each 

composite. Best-fit line (log τ versus log tf ) is also 

included for each composite. 
NASA/TM—2006-214088 18

the three chosen CMCs, indicating that the overall delayed failure mechanism in interlaminar shear could 

be the one governed by the power-law type of slow crack/damage growth. The merit of constant stress 

rate testing along with the power-law formulation is enormous in terms of simplicity, test economy (short 

test times), and less data scatter over other stress rupture or cyclic fatigue testing. Although the 

experimental results and phenomenological model were presented in this work, a more detailed study of 

the shear failure mechanism regarding the microscopic influences, which include matrix/fiber interaction, 

matrix cracking, and environmental effects (refs. 24 to 26), is still needed. It should be kept in mind that 

the phenomenological model proposed here may incorporate other operative models such as viscous 

sliding, void nucleation, and coalescence, etc., which can be all covered under a generic term of delayed 

failure, slow crack growth, fatigue, or damage initiation/accumulation. 

Finally, the results of this work also suggest that care must be exercised when characterizing 

elevated-temperature, interlaminar shear strength of composite materials. This is due to the fact that if a 

material exhibits a delayed failure phenomenon, elevated-temperature interlaminar shear strength has a 

relative meaning simply because interlaminar shear strength would depend on which test rate one 

chooses. Therefore, at least two or three test rates including high and low are recommended to better 

characterize interlaminar shear strength behavior of a composite material, as suggested previously for the 

determination of ultimate tensile strength of CMCs at elevated temperatures (refs. 17 and 18). 

5. Conclusions 

Interlaminar shear strength of four different CMCs including 2-D crossplied SiC/MAS-5, 2-D plainwoven SiC/SiC, 2-D woven Sylramic SiC/SiC, and 2-D plain-woven C/SiC was determined using 

different test rates at temperatures ranging from 1100 to 1316 °C in air. Interlaminar shear strength 

degradation in terms of decreasing test rate was significant for SiC/MAS-5 and C/SiC composites and 

was insignificant for SiC/SiC and Sylramic SiC/SiC composites. The Sylramic SiC/SiC composite, 

however, exhibited some degree of strength degradation at a very low test rate of 0.00005 MPa/s. A 

phenomenological, power-law delayed failure model was used to account for interlaminar shear strength 

degradation and showed good agreement with SiC/MAS-5 and C/SiC composites but in poor to 

reasonable agreement with Sylramic SiC/SiC composite, as compared with the additional stress rupture 

results. Constant-shear stress-rate testing could be a possible means of life prediction test methodology 

for composites in interlaminar shear in case that short lifetimes of components are anticipated. 

References 

1. P. Brondsted, F.E. Heredia, and A.G. Evans, “In-Plane Shear Properties of 2-D Ceramic 

Composites,” J. Am. Ceram. Soc., 77[10] 2569–2574 (1994). 

2. E. Lara-Curzio and M.K. Ferber, “Shear Strength of Continuous Fiber Ceramic Composites,” ASTM 

STP 1309, p. 31, American Society for Testing and Material, West Conshohocken, PA (1997). 

3. N.J.J. Fang and T.W. Chou, “Characterization of Interlaminar Shear Strength of Ceramic Matrix 

Composites,” J. Am. Ceram. Soc., 76[10] 2539–2548 (1993). 

4. Ö. Ünal and N.P. Bansal, “In-Plane and Interlaminar Shear Strength of a Unidirectional Hi-Nicalon 

Fiber-Reinforced Celsian Matrix Composite,” Ceramics International, 28 527–540 (2002). 

5. S.R. Choi, N.P. Bansal, A.M. Calomino, and M.J. Verilli, “Shear Strength Behaviors of Ceramic 

Matrix Composites at Elevated Temperatures,” Advanced in Ceramic Matrix Composites, Edited by 

J.P. Singh, N.P. Bansal, and W.M. Kriven, Ceramic Transactions Vol. 165, 131–145 (2005). 

6. S.R. Choi and N.P. Bansal, “Shear Strength as a Function of Test Rate for SiCf/BSAS Ceramic 

Matrix Composite at Elevated Temperature,” J. Am. Ceram. Soc., 87[10] 1912–1918 (2004). 

7. D.W. Worthem, “Thermomechanical Fatigue Behavior of Three CFCCs,” NASA CR–195441, 

National Aeronautics and Space Administration, Glenn Research Center, Cleveland, OH (1995). 
NASA/TM—2006-214088 19

8. D. Brewer, “HSR/EPM Combustor Materials Development Program,” Mat. Sci. Eng., A261 284–291 

(1999). 

9. A. Calomino, “Mechanical Behavior and Characterization 1316 °C In-situ BN Coated MI/SiC/SiC,” 

Technology Forum October 2002, Ultra-Efficient Engine Technology Program, NASA Glenn 

Research Center, Cleveland, Ohio (2002). 

10. A. Calomino and M. Verrilli, “Ceramic Matrix Composite Vane Subelement Fabrication,” 

Proceedings of ASME Turbo Expo 2004, June 14–17, Vienna, Austria, ASME Paper No. GT2004–

53974. 

11. M. Verrilli, A. Calomino, R.C. Robinson, and D.J. Thomas, “Ceramic Matrix Composites Vane 

Subelement Testing in a Gas Turbine Environment,” ibid., ASME Paper No. GT2004–53970. 

12. M.J. Verrilli, A. Calomino, and D.J. Thomas, “Stress/Life Behavior of a C/SiC Composite in a Low 

Partial Pressure of Oxygen Environment: I- Static Strength and Stress Rupture Database,” Ceram. 

Eng. Sci. Proc., 23[3] 435–442 (2002). 

13. A. Calomino, M.J. Verrilli, and D.J. Thomas, “Stress/Life Behavior of a C/SiC Composite in a Low 

Partial Pressure of Oxygen Environment: II- Stress Rupture Life and Residual Strength Relationship,” 

ibid., 23[3] 443–451 (2002). 

14. ASTM C 1368, “Standard Test Method for Determination of Slow Crack Growth Parameters of 

Advanced Ceramics by Constant Stress-Rate Flexural Testing at Ambient Temperature,” Annual 

Book of ASTM Standards, Vol. 15.01, American Society for Testing and Materials, West 

Conshohocken, PA (2003). 

15. ASTM C 1465, “Standard Test Method for Determination of Slow Crack Growth Parameters of 

Advanced Ceramics by Constant Stress-Rate Flexural Testing at Elevated Temperatures,” Annual 

Book of ASTM Standards, Vol. 15.01, American Society for Testing and Materials, West 

Conshohocken, PA (2003). 

16. ASTM C 1425, “Test Method for Interlaminar Shear Strength of 1-D and 2-D Continuous Fiberreinforced Advanced Ceramics at Elevated Temperatures,” Annual Book of ASTM Standards, 

Vol. 15.01, American Society for Testing and Materials, West Conshohocken, PA (2002). 

17. S.R. Choi and J.P. Gyekenyesi, “Load-Rate Dependency of Ultimate Tensile Strength in Ceramic 

Matrix Composites at Elevated Temperatures,” Int. J. Fatigue, 27 503–510 (2005). 

18. S.R. Choi, N.P. Bansal, and M.J. Verrilli, “Delayed Failure of Ceramic Matrix Composites in Tension 

at Elevated Temperatures,” J. Euro. Ceram. Soc., 25 1629–1636 (2005). 

19. S.R. Choi and J.P. Gyekenyesi, “’Ultra’-Fast Fracture Strength of Advanced Structural Ceramics at 

Elevated Temperatures: An Approach to High-Temperature ‘Inert’ Strength,” pp. 27–46 in Fracture 

Mechanics of Ceramics, Vol. 13, Edited by R.C. Bradt, D. Munz, M. Sakai, V. Ya. Shevchenko, and 

K.W. White, Kluwer Academic/Plenum Publishers, New York (2002). 

20. S.M. Wiederhorn, “Subcritical Crack Growth in Ceramics,” pp. 613–646 in Fracture Mechanics of 

Ceramics, Vol. 2, Edited by R.C. Bradt, D.P.H. Hasselman, and F.F. Lange, Plenum Press, New York 

(1974). 

21. A.G. Evans, Slow Crack Growth in Brittle Materials under Dynamic Loading Condition,” Int. J. 

Fracture, 10 251–259 (1974). 

22. H. Tada, P.C. Paris, and G.R. Irwin, The Stress Analysis of Cracks Handbook, Part IV. The American 

Society of Mechanical Engineers, New York, 2000. 

23. M.C. Halbig, “Modeling the Oxidation of Carbon Fibers in a C/SiC Composite under Stressed 

Oxidation,” Ceram. Eng. Sci. Proc., 23[3] 427–434 (2002). 

24. C.A. Lewinsohn, C.H. Henager, and R.H. Jones, “Environmentally Induced Time-Dependent Failure 

Mechanism in CFCCs at Elevated Temperatures,” Ceram. Eng. Sic. Proc., 19[4] 11–18 (1998). 

25. C.H. Henager and R.H. Jones, “Subcritical Crack Growth in CVI Silicon Carbide Reinforced with 

Nicalon Fibers: Experiment and Model,” J. Am. Ceram. Soc., 77[9] 2381–94 (1994). 

26. S.M. Spearing, F.W. Zok, and A.G. Evans, “Stress Corrosion Cracking in a Unidirectional CeramicMatrix Composite, J. Am. Ceram. Soc., 77[2] 562–70 (1994). 
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

REPORT DOCUMENTATION PAGE

2. REPORT DATE

19. SECURITY CLASSIFICATION

 OF ABSTRACT

18. SECURITY CLASSIFICATION

 OF THIS PAGE

Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources,

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this

collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson

Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503.

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102

Form Approved

OMB No. 0704-0188

12b. DISTRIBUTION CODE

8. PERFORMING ORGANIZATION

 REPORT NUMBER

5. FUNDING NUMBERS

3. REPORT TYPE AND DATES COVERED

4. TITLE AND SUBTITLE

6. AUTHOR(S)

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

11. SUPPLEMENTARY NOTES

12a. DISTRIBUTION/AVAILABILITY STATEMENT

13. ABSTRACT (Maximum 200 words)

14. SUBJECT TERMS

17. SECURITY CLASSIFICATION

 OF REPORT

16. PRICE CODE

15. NUMBER OF PAGES

20. LIMITATION OF ABSTRACT

Unclassified Unclassified

Technical Memorandum

Unclassified

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135–3191

1. AGENCY USE ONLY (Leave blank)

10. SPONSORING/MONITORING

 AGENCY REPORT NUMBER

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546–0001

Available electronically at http://gltrs.grc.nasa.gov

January 2006

NASA TM—2006-214088

E–15425

WBS–22–714–30–19

25

Life Limiting Behavior in Interlaminar Shear of Continuous Fiber-Reinforced

Ceramic Matrix Composites at Elevated Temperatures

Sung R. Choi, Anthony M. Calomino, Narottam P. Bansal, and Michael J. Verrilli

Continuous fiber-reinforced ceramic matrix composites; Mechanical testing; Double notch

shear testing; Constant stress-rate testing in shear; Stress rupture in shear; Life prediction;

Life prediction methodology

Unclassified -Unlimited

Subject Category: 07

Sung R. Choi, University of Toledo, 2801 W. Bancroft St., Toledo, Ohio 43606; and Anthony M. Calomino,

Narottam P. Bansal, and Michael J. Verrilli (now with G.E. Aircraft Engines), NASA Glenn Research Center.

Responsible person, Sung R. Choi, organization code RXL, 216–433–8366.

Interlaminar shear strength of four different fiber-reinforced ceramic matrix composites was determined with doublenotch shear test specimens as a function of test rate at elevated temperatures ranging from 1100 to 1316 °C in air. Life

limiting behavior, represented as interlaminar shear strength degradation with decreasing test rate, was significant for

2-D crossplied SiC/MAS-5 and 2-D plain-woven C/SiC composites, but insignificant for 2-D plain-woven SiC/SiC and

2-D woven Sylramic (Dow Corning, Midland, Michigan) SiC/SiC composites. A phenomenological, power-law

delayed failure model was proposed to account for and to quantify the rate dependency of interlaminar shear strength

of the composites. Additional stress rupture testing in interlaminar shear was conducted at elevated temperatures to

validate the proposed model. The model was in good agreement with SiC/MAS-5 and C/SiC composites, but in poor to

reasonable agreement with Sylramic SiC/SiC. Constant shear stress-rate testing was proposed as a possible means of

life prediction testing methodology for ceramic matrix composites subjected to interlaminar shear at elevated temperatures when short lifetimes are expected.