ASTM E238 Pin-Type Bearing Testing

Scope

ASTM E238 covers the determination of bearing yield strength and bearing strength of metallic materials using a pin-type test fixture. A flat specimen with a machined hole is loaded through a cylindrical pin until bearing yield or ultimate failure occurs. The test captures the full bearing load-deformation response, from which both yield and ultimate bearing strength values are extracted.

Key aspects of the test scope include:

• Specimen geometry — flat specimens with a hole of defined diameter; the ratio of edge distance (e) to hole diameter (D) is specified, with e/D = 1.5 and e/D = 2.0 being the most commonly tested conditions
• Pin requirements — the pin must be harder than the specimen (typically hardened steel); pin diameter is matched to the specimen hole diameter within specified tolerances
• Loading condition — unrestricted pin bearing, meaning the pin is free to rotate and the specimen is not clamped at the hole, which differs from restricted bearing tests
• Applicable materials — wrought and cast metals including aluminum alloys, titanium alloys, steels, copper alloys, and magnesium alloys
• Reported values — bearing yield strength (F^by) at 2% offset deformation, and ultimate bearing strength (F^bu) at maximum load

Applications

• Aerospace structures — characterization of aluminum, titanium, and high-strength steel alloys used in bolted airframe joints, skin panels, and bracket connections where bearing failure is a primary design concern
• Mechanical fastener design — generating bearing strength data for materials used with bolts, rivets, and pins to size holes and edge distances correctly and prevent bearing failure before fastener shear failure
• Military and defense hardware — bearing property data for metallic components in weapons systems, vehicle structures, and equipment where joint integrity under load is a safety requirement
• Structural engineering — evaluation of steel and aluminum members with bolted connections in bridges, buildings, and industrial structures
• Material qualification and specification — establishing or verifying bearing property minimums for material procurement specifications (e.g., AMS, MIL-HDBK-5/MMPDS)
• R&D and alloy development — comparing bearing performance of new alloy compositions, heat treatment conditions, or surface treatments to existing baseline materials

Benefits

• Captures the failure mode that governs bolted joint design — tensile and shear tests do not capture bearing behaviour; ASTM E238 is the direct way to get the bearing strength values structural engineers actually use
• e/D ratio testing gives design-relevant data — testing at both e/D = 1.5 and 2.0 shows how edge distance affects bearing capacity, directly informing minimum edge distance requirements in joint design
• Bearing yield strength enables design to deformation limits — the 2% offset bearing yield strength lets designers set allowable load levels that keep hole deformation within acceptable limits under service loads
• Required for MMPDS/MIL-HDBK-5 data submissions — material allowable published in MMPDS (the aerospace structural design handbook) require bearing test data generated per ASTM E238
• Straightforward test setup with clear outputs — load-deformation curve, bearing yield strength, and ultimate bearing strength are all obtained from a single test per specimen