Ceramic Tensile Test Grips

Advanced engineering ceramics have a number of material properties that have made them one of the most important classes of engineering materials. Ceramics have an extremely high elastic modulus, maintain consistent performance at elevated temperatures, and have great resistance to wear and corrosion, which has contributed to their widespread use as bearing surfaces, heat resistance, and insulation applications. The ability for ceramics to perform at high temperatures has made them the go to material for high end automobile brake rotors and pads, space re-entry vehicle heat shields, and ball bearings in high speed and high temperature applications. The use of fiber reinforcement with a ceramic matrix provides an increase in tensile strength and fracture resistance, making ceramics a viable material for structural applications. The strength properties of ceramics can be greatly reduced by the presence of internal and surface imperfections. Specimen breaks near the grip-sample interface are telltale signs of surface damage or internal crack initiation due to poor or improper fixturing. Proper clamping of ceramic test specimens for tensile tests is achieved by close tolerances for specimen and grip dimensions and parallelism of jaw and specimen clamping faces, for flat test specimens. High quality grips, properly prepared test specimens, and good test procedures will ensure uniform loading of the ceramic samples. Since the high modulus characteristic of ceramics is often a key property for ceramics applications, elongation measurements are important. Due to the low strains present in ceramic materials, strain and elongation measurements must be made using an extensometer or strain gage. Care must be taken to prevent contact extensometers from damaging the ceramic specimen surface. To help prevent extensometer slippage, some test procedures allow the machining of grooves for the placement of extensometer contacts. For help with configuring the right test machine and fixturing for tensile testing a ceramic, give one of our applications engineers a call today. ASTM and ISO have developed standard test methods to aid in the proper testing of the wide variety ceramic materials. These tests address the various applications of ceramic materials and environments in which they will be used. Popular standards for tensile testing of ceramic materials at ambient temperature are ASTM C1273 for monolithic ceramics, ASTM C1275 for rectangular shaped continuous fiber reinforced ceramics, ASTM C1360 for tension-tension fatigue of continuous fiber reinforced ceramics, ASTM C1361 for tension-tension fatigue of monolithic, particle, and discontinuous fiber reinforced ceramics, ASTM C1468 for continuous fiber reinforced ceramics, ISO 15490 for monolithic ceramics, and ISO 15733 for ceramic continuous fiber reinforced composites. Test machines for ceramic tensile testing must have a high force capacity. Small displacements correspond to large force increases for ceramic materials, so machine actuators and controls must be able to apply this increasing force without significant oscillation around the desired force caused by crosshead vibration. The machines below are suitable for most ceramic applications and custom machines are available for even higher force requirements. The grips are representative of fixtures made specifically to meet the unique fixtureing needs of ceramics and the requirements of ASTM test standards.

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