ASTM C1684
Rod Flexure Fixture for Advanced Ceramics
ASTM C1684 Rod Flexure Fixture – Universal Grip Data Sheet (PDF)
ASTM C1684 measures the flexural strength of advanced ceramics in the form of cylindrical rods at room temperature. It is used by ceramic producers, component makers and researchers who need strength data for pins, rods and rollers without first machining them into rectangular bars. Universal Grip supplies a grooved, articulating four-point rod flexure fixture built to this standard.
What ASTM C1684 Measures
The test reports the flexural strength of a round ceramic specimen, calculated from the fracture load, span and rod diameter using simple beam theory. Because ceramic strength depends on flaws, results are usually treated statistically, and the standard includes Weibull effective volume and effective surface expressions so rod data can be compared with other specimen sizes. It applies to monolithic and particulate- or whisker-reinforced ceramics and glasses, but not to continuous fiber-reinforced ceramic composites.
How the ASTM C1684 Test Works
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Measure the rod diameter at the test section and confirm it is within the recommended size range.
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Set the support and loading spans to suit the rod size and chosen configuration.
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Seat the rod in the grooved support members so it rests without rolling or twisting.
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Load in four-point (preferred) or three-point flexure at a controlled rate until fracture.
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Calculate flexural strength from fracture load, span and diameter.
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Examine fracture surfaces to identify the strength-limiting flaw where design data are needed.
Specimens and Setup
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Recommended rod diameters are about 1.5 to 8 mm (0.06 to 0.31 in); other sizes are permitted.
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Recommended lengths are about 25 to 85 mm (1 to 3.3 in).
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Machined, drawn or as-fired rods can be tested, with some allowance for size and cross-section variation.
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Average grain size should be small relative to rod diameter (no more than about 1/50 of it).
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Tell us your rod diameter and length so groove size and spans can be matched to your specimens.
Universal Grip ASTM C1684 Fixture
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Grooved support and loading members locate round specimens
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Articulating design prevents twisting of rods during loading
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Hardened tool steel with corrosion-resistant finish and hardened bearing surfaces
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5 kN (about 1,100 lbf) standard capacity; higher capacities on request
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Spans configured to the specimen size used, four- or three-point
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Clevis pin or threaded adapter for electromechanical and servo-hydraulic test machines
Applications
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Ceramic pins, rods and rollers
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Bearing and wear components
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Dental and bio-ceramic rods
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Glass rods and drawn ceramic forms
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Materials qualification and R&D
Related Standards and Products
Tell us your rod diameter, length and load frame on our contact page and we will quote an ASTM C1684 rod flexure fixture configured for your specimens. Request a quote
ASTM C1684 FAQ
Why test rods instead of rectangular bars?
Many ceramic parts, such as pins, rollers and drawn rods, are round. Testing them directly avoids machining them into bars, which can change the surface and the flaws that control strength. C1684 lets you measure strength on the actual product form or on rods cut from components.
Should I use four-point or three-point loading?
Four-point loading is preferred for most characterization because it stresses a larger region of the rod. Three-point loading is permitted but tends to give higher strength values since only a small region sees peak stress, so results from the two setups are not directly interchangeable.
Why does the fixture need grooved, articulating members?
A round rod on flat rollers can roll or twist, adding torsion and uneven contact. Grooves locate the rod, and articulation lets the members follow small variations in straightness and diameter, so the specimen fails under the intended flexural stress.
How are results reported?
Each rod gives a flexural strength calculated from fracture load, span and diameter. Because ceramic strength scatters, labs typically test a set of specimens and report mean, standard deviation and often Weibull parameters, with fractography used to identify strength-limiting flaws.
What machine capacity do I need?
Small ceramic rods usually break at modest loads, which is why the standard fixture is rated at 5 kN (about 1,100 lbf). A benchtop universal testing machine with an appropriately sized load cell is often sufficient. Larger, stronger rods may need a higher-capacity fixture, available on request.