ASTM D5961
Bearing Test Fixture for Composite Laminates
ASTM D5961 Bearing Test Fixture – Universal Grip Data Sheet (PDF)
ASTM D5961 measures the bearing response of polymer matrix composite laminates loaded through a pin or fastener in a hole. Aerospace and composite structures engineers use it to generate bearing strength data for bolted and riveted joint design. Universal Grip supplies bearing fixtures with hardened pins and double-shear clevis or single-shear configurations.
What ASTM D5961 Measures
The test records bearing stress against bearing strain as a pin or fastener is pushed or pulled against the edge of a hole in the laminate. Bearing stress is the load divided by hole diameter and specimen thickness, and bearing strain comes from hole deformation measured with an extensometer. From the curve, labs report bearing chord stiffness, offset bearing strength and ultimate bearing strength, along with the failure mode, to support joint design and material qualification.
How the ASTM D5961 Test Works
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Choose the procedure: double shear or single shear, in tension or compression.
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Drill the fastener hole to the required diameter and tolerance in the laminate.
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Install the specimen with the hardened pin or fastener in the clevis or joint configuration.
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Mount an extensometer to measure deformation across the hole.
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Load at a constant rate while recording force and hole deformation.
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Calculate bearing stress and strain, then report stiffness, offset and ultimate bearing strength and failure mode.
Specimens and Setup
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Laminates should be balanced and symmetric with respect to the test direction.
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Procedure A uses a single-piece specimen in double-shear tension; Procedure D uses double-shear compression.
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Procedures B and C use single-shear specimens (two-piece and one-piece) loaded through a fastener.
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Hole quality, width-to-diameter and edge-distance-to-diameter ratios all affect results; follow the standard's geometry.
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Specify procedure, fastener diameter and laminate thickness so pins and clevis gaps can be matched.
Universal Grip ASTM D5961 Fixture
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Double-shear clevis and pin configurations, with single-shear fastened joint specimens supported
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Hardened, precision-ground pins sized to customer fastener diameter
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Extensometer mounting provisions across the hole
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Anti-buckling support option for compression loading
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Hardened tool steel, corrosion-resistant finish, 50 kN (about 11,200 lbf) standard capacity, higher on request
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Clevis pin or threaded adapter for electromechanical and servo-hydraulic test machines
Applications
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Carbon and glass fiber laminates
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Bolted and riveted composite joints
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Aerospace structural qualification
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Fastener and hole-quality studies
Related Standards and Products
Tell us your procedure, fastener diameter and laminate thickness on our contact page and we will quote an ASTM D5961 bearing fixture for your program. Request a quote
ASTM D5961 FAQ
Which D5961 procedure should I use?
Procedure A, double-shear tension, is the most common for basic material bearing strength. Single-shear Procedures B and C better represent real joints where fastener rotation matters. Procedure D is double-shear compression. Results from different procedures are not directly comparable, so match the procedure to your design need.
How is bearing strain measured?
An extensometer is mounted to measure how much the hole elongates as the pin bears against it. That deformation, divided by the hole diameter, gives bearing strain. The fixture includes extensometer mounting provisions across the hole.
What is offset bearing strength?
It is the bearing stress at which the stress-strain curve departs from its initial linear slope by a set offset, marking the onset of significant hole deformation. Designers often use it alongside ultimate bearing strength because joints are usually limited by hole elongation before final failure.
Why do single-shear and double-shear results differ?
In single shear the fastener tilts under load, concentrating bearing stress at one edge of the hole, which changes the measured strength. Double shear keeps the pin more uniformly loaded. Because of this, data from different procedures should not be mixed.
What machine capacity do I need?
Required force depends on laminate thickness, hole diameter and material. The standard fixture is rated at 50 kN (about 11,200 lbf), which covers many typical coupons, and higher capacities are available. Tell us your laminate and fastener size and we will confirm the fixture and frame.