Ceramic matrix composites are composed of ceramic fibers in a ceramic matrix. Ceramics, which have extraordinarily high ultimate strength are also brittle. The brittle nature of ceramics results in fatigue cracking to be a leading failure mechanism. CMC's were derived to improve the fracture toughness of ceramics. Determining the quality of the CMC is done through testing of mechanical properties; typically in bending, compression, or tension. Bend testing the ceramics perpendicular to the ceramic fibers is a valid way to determine how the fibers have improved the fatigue properties of the composite.
The stress intensity factor is a mechanical property that is the result of the fracture mechanics testing, and an indication of fatigue crack resistance. To perform a crack propagation test of this type a dynamic testing machine is used to apply large cyclic loads to the ceramic. The crack tip opening is measured and observed during the test to determine a stress intensity factor. Mechanical properties of the CMC's that result from testing are generally applied to the design process, and for quality control efforts. ASTM C1399 is a test method for determining the crack growth parameters in a cermaic matrix composite. ASTM C1360 is a constant amplitude fatigue test of cermaic matrix composites. TestResources suggests either a servo hydraulic or servo electric t dynamic testing machines for fatigue testing materials. Servo hydraulic test machines, such as the 902 series has high load capabilities up to 22 kip and high cyclic frequency capacity up to 100 Hz. Servo electric test machines, such as the 830 and 810 series, have lower load capacity and lower speed capacity then the servo hydraulic models. TestResources has a wide variety of grips and fixtures for fatigue testing ceramic metal composites.
Applicable Testing Standards
- ASTM C1360 Tension Fatigue Fiber-Reinforced Ceramics Test Machine
- ASTM C1399 Residual Strength Fiber-Reinforced Concrete Test Equipment
- ASTM E466 Load Controlled Constant Amplitude Fatigue Tests of Metals
Recommended Test Machine
Static and fatigue forces up to 50 kN (11,250 lbf)
Frequency ratings up to 75 Hz
Oil-free, all electric actuator for clean test conditions
Lower purchase, operating, and maintenance costs than hydraulic equivalents
Static and fatigue forces up to 25 kN (5,500 lbf)
Frequency ratings up to 100 Hz
Servohydraulic
Small, portable footprint
Recommended Testing Accessories
Load ratings from 50 kN to 300 kN (11,250 lbf to 67,500 lbf)
Hydraulic actuation
Designed to cycle dynamically through zero-load
Temperature ratings up to 1,000°C (1,800°F)