Overview
ISO 14324:2003 - "Resistance spot welding - Destructive tests of welds - Method for the fatigue testing of spot welded joints" defines standardized fatigue test specimens and procedures for evaluating the fatigue performance of resistance spot welded joints. The standard covers ambient-condition, repeated tensile loading that produces either shear or cross-tension stresses in spot welds made in steel sheet thicknesses from 0.5 mm to 6 mm. It notes that laboratory test results are not generally directly applicable to the fatigue behaviour of an assembled component or structure, and that the method can be adapted for other materials if appropriate test conditions (e.g., heating) are determined.
Key topics and technical requirements
- Test specimen designs: Defined geometries for shear and cross-tension fatigue specimens, with specified overlaps, widths and free lengths (dimensions depend on sheet thickness).
- Test sheets and fabrication: Requirements for edge condition (deburring), flatness, welding jig alignment and spot-weld position tolerances.
- Testing machine capabilities:
- Secure clamping and alignment of specimen/jig with loading axis
- Load or displacement control with recording of mean load and load range (or max/min)
- No automatic restart after interruption
- Maximum permissible load error: 3% of indicated load or 0.5% of machine capacity
- Clamping and jig details: Use of shim plates or offset clamps to avoid bending; cross-tension clamping jig geometry; guidance to avoid damaging the weld during clamping.
- Test procedure controls:
- Rapid attainment of specified load range without exceeding maximum load
- Constant maximum and minimum loads during a test
- Control of transverse oscillations for thin-sheet lap specimens (acceptable S-type oscillation only)
- Monitoring and recording of interruptions
- Termination criteria: Failure defined by development of surface cracks of a specified length (commonly at least one spot-weld diameter) or complete separation; or reaching a specified endurance without failure.
- Data and analysis:
- Determination of the L–N curve (load range vs. number of cycles) and endurance/fatigue limit
- Minimum recommended sample sizes (at least 10 specimens to establish an L–N curve; multiple load levels, at least three load levels spanning 10^2 to 10^7 cycles; replication recommended)
Practical applications and users
ISO 14324:2003 is used by:
- Welding engineers and metallurgists assessing fatigue performance of spot welds
- Automotive and sheet-metal fabricators validating joint designs and weld parameters
- R&D labs performing comparative fatigue testing of materials, electrodes or welding processes
- Quality and test laboratories producing L–N curves and endurance limits for specification or design guidance
Note: Test outcomes are primarily comparative and for material/weld-process evaluation; direct extrapolation to in-service component life requires additional analysis and real-world validation.
Related standards
- ISO 669 (resistance welding equipment)
- ISO 14271 (Vickers hardness testing of spot welds)
- ISO 14272 (cross-tension test specimen/procedure)
- ISO 14273 (shear test specimen/procedure)
- ISO 14329 (failure types and geometric measurements for resistance welds)
Keywords: ISO 14324:2003, resistance spot welding, fatigue testing, L–N curve, shear fatigue, cross-tension fatigue, spot welded joints, endurance limit.