Overview
ISO 9664:1993 - Adhesives - Test methods for fatigue properties of structural adhesives in tensile shear - defines a laboratory method to evaluate the fatigue behavior of structural adhesives under tensile‑shear loading. The procedure cyclically superposes an alternating stress on a static mean stress, records the number of cycles to failure for given mean stress and stress amplitude, and uses those data to build SN curves (Wöhler curves) and estimate the confidence zone for joint fatigue resistance. Results are specimen‑geometry dependent and do not represent intrinsic adhesive properties nor are they intended for direct design use.
Key topics and requirements
- Test principle: sinusoidal fatigue cycles considered as alternating stress plus mean stress; measure cycles to failure at specified mean stress (Zm) and stress amplitude (Ta).
- SN curve construction: test multiple amplitudes to generate stress versus life data and identify endurance and fatigue zones.
- Statistical methods: normative Annex A - the staircase (Dixon & Mood) method for estimating endurance limit; Annex B - data reclassification method for grouped testing.
- Specimen and substrates: standard specimen geometries for steel and aluminium double‑overlap configurations; recommended substrates include aluminium 2024‑T3 and steels XC 18 or E24 (grade 1 or 2).
- Preparation & references: surface preparation per ISO 4588; static lap‑shear strength per ISO 4587; conditioning per ISO 291 (23 ± 2 °C, 50 ± 5 % RH).
- Test conditions: typical frequency 30 Hz (max 60 Hz to avoid overheating); self‑centering fixtures to ensure alignment; account for adhesive creep under non‑zero mean stress.
- Sample counts: minimum recommendations - at least six specimens for static shear strength and at least four specimens at three different amplitudes (minimum 12 specimens) to establish an SN curve in the 10^4–10^6 cycle range.
Applications and users
ISO 9664:1993 is used for:
- Comparative fatigue performance testing of structural adhesives in R&D and product development.
- Quality control and material screening by adhesive manufacturers and testing laboratories.
- Bonding engineers in aerospace, automotive, marine and industrial sectors who need laboratory‑based fatigue ranking of adhesive systems and joint configurations.
Note: because results depend on specimen geometry and test conditions, the standard is suited for comparative assessment and confidence estimation rather than direct structural design.
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: ISO 9664:1993, fatigue properties, structural adhesives, tensile shear, SN curve, endurance limit, staircase method, adhesive fatigue testing.