ASTM C1211
High-Temperature Flexure Fixture for Advanced Ceramics
ASTM C1211 High-Temperature Flexure Fixture – Universal Grip Data Sheet (PDF)
ASTM C1211 measures the flexural strength of advanced ceramics at elevated temperatures using rectangular bars in three- or four-point bending. Developers of hot-section, refractory and structural ceramics use it to see how strength holds up near service temperature. Universal Grip supplies a refractory ceramic flexure fixture and push-rod load train for use inside a furnace on a universal testing machine.
What ASTM C1211 Measures
The test gives the flexural strength of a ceramic bar at a set elevated temperature, calculated from fracture load, spans and specimen cross-section using simple beam theory. At temperature, slow crack growth and creep can lower measured strength, so the standard controls heating, temperature measurement, atmosphere and loading rate. It covers monolithic and particulate- or whisker-reinforced ceramics and glasses; continuous fiber ceramic composites are tested under ASTM C1341 instead.
How the ASTM C1211 Test Works
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Install the ceramic fixture and push rods in the furnace on the test machine.
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Place the bar on the support bearings with the loading bearings centered over it.
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Heat to the test temperature and hold until the specimen and fixture are stable.
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Load in four-point (preferred) or three-point flexure at the specified rate until fracture.
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Calculate flexural strength from fracture load, spans and specimen dimensions.
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Recover fragments for fractography to identify the failure origin.
Specimens and Setup
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Typical bars are about 3 x 4 x 45–50 mm (0.12 x 0.16 x 1.8–2.0 in); half- and double-size specimens are also allowed.
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Standard spans are matched to the specimen size, for example a 40 mm (1.57 in) outer span for the common bar.
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Specimens may be machined or as-fired, using a machining procedure suited to the application.
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Inert atmospheres such as dry nitrogen or vacuum can be used to limit humidity-driven slow crack growth.
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Specify maximum temperature and furnace dimensions so fixture material and push-rod length can be chosen.
Universal Grip ASTM C1211 Fixture
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Silicon carbide or alumina fixture components, selected for the temperature range
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Ceramic bearing cylinders with articulating design for correct load distribution
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Push-rod load train designed to pass through the furnace
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5 kN (about 1,100 lbf) standard capacity; higher capacities on request
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Spans configured to standard specimen sizes, three- or four-point
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Adapters to suit the customer frame and furnace; split-tube or box furnaces on request
Applications
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Silicon nitride and silicon carbide
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Oxide ceramics and particulate-reinforced ceramics
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Hot-section and refractory components
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High-temperature materials R&D
Related Standards and Products
Share your maximum test temperature, specimen size and furnace dimensions on our contact page and we will quote an ASTM C1211 high-temperature flexure fixture. Request a quote
ASTM C1211 FAQ
How is C1211 different from ASTM C1161?
C1161 covers ceramic flexural strength at ambient temperature, and C1211 covers the same type of bar test at elevated temperature. Specimen configurations are similar, but C1211 adds requirements for furnace heating, temperature measurement, fixture materials and atmosphere.
Why are the fixtures made of ceramic instead of steel?
Steel softens, oxidizes and creeps at the temperatures used for advanced ceramics. Silicon carbide or alumina keeps its stiffness and shape in the furnace, so spans stay accurate and the bearings do not deform or react with the specimen.
What maximum temperature can the fixture reach?
It depends on the fixture material, the furnace and the atmosphere. Alumina and silicon carbide suit different ranges. Tell us your highest test temperature and environment and we will recommend the material for the fixture and push rods.
Why does loading rate matter at high temperature?
At elevated temperature many ceramics show slow crack growth or creep, so a slower test can give lower strength. C1211 uses a moderately fast rate to limit these effects, and results may still differ from inert strength. Report the rate with your data.
Should I use four-point or three-point loading?
Four-point loading is preferred for most characterization because a larger region sees peak stress. Three-point results tend to be higher and are not directly interchangeable with four-point values, so stay consistent within a data set.