Overview
EN ISO 9664:1995 (ISO 9664:1993) specifies a laboratory method to evaluate the fatigue properties of structural adhesives in tensile‑shear (lap shear) loading. The procedure cyclically stresses standardized bonded specimens with a sinusoidal load that can be regarded as an alternating stress superimposed on a static mean stress. Results are used to establish S–N (Wöhler) curves and to estimate the confidence zone for joint fatigue resistance. The standard cautions that fatigue results are specimen‑geometry dependent and do not represent intrinsic adhesive properties nor are they directly suitable for structural design.
Key Topics and Requirements
- Test principle: Sinusoidal cyclic tensile‑shear loading with defined mean stress (Zm) and stress amplitude (Ta) to determine cycles to failure.
- S–N curves: Plot stress (Ta or Tmax) vs. lifetime (N) to identify fatigue and endurance zones; endurance limit often referenced at 10^6 cycles.
- Specimen dependence: Geometry, substrate and joint thickness affect results-tests characterize a bonded joint configuration, not the adhesive alone.
- Specimen preparation & conditioning:
- Surface preparation per ISO 4588.
- Static shear strength determined by ISO 4587 (minimum six specimens recommended).
- Standard atmosphere: 23 °C ± 2 °C and 50 % ± 5 % RH (ISO 291).
- Test machine & parameters:
- Sinusoidal fatigue test machine with self‑centring fixture; ensure specimen alignment.
- Typical frequency: 30 Hz; maximum recommended: 60 Hz (to avoid overheating).
- Mean stress selection: between 0.25·ZR and 0.5·ZR (ZR = static shear strength); a common choice is 0.35·ZR.
- Choose at least three amplitude levels producing failures between 10^4 and 10^6 cycles; test at least four specimens per amplitude (minimum 12 specimens).
- Data analysis:
- Use the staircase (Dixon–Mood) method (Annex A) for estimating endurance limit when testing individual specimens.
- For simultaneous group testing, use data reclassification (Annex B).
- Reporting: Include reference to the standard, adhesive and substrate IDs, surface prep, bonding/curing, specimen geometry, number of specimens, test frequency, static strength and S–N data.
Applications - Who Uses It
- Adhesive manufacturers and R&D labs for material screening and comparative fatigue performance.
- Test laboratories and quality teams for batch qualification and process control of bonded joints.
- Materials and structural engineers in aerospace, automotive, rail and marine industries for joint characterization and life‑estimation studies (with caution: not a design code).
- Bonding specialists validating surface preparation and fabrication procedures.
Related Standards
- ISO 4587 - Determination of tensile lap‑shear strength of high‑strength adhesive bonds
- ISO 4588 - Preparation of metal surfaces for adhesive bonding
- ISO 291 - Standard atmospheres for conditioning and testing
Keywords: EN ISO 9664, ISO 9664:1993, fatigue properties, structural adhesives, tensile shear, S–N curve, fatigue testing, staircase method, lap shear specimen.
