ISO 14679:1997

Overview

ISO 14679:1997 specifies a laboratory test method for measuring the adhesion characteristics of cured adhesives (with or without primer) using a three‑point bending method. The method evaluates the adhesive/substrate interfacial performance by molding a rectangular block of adhesive onto a rigid substrate (typically steel or aluminium alloys), bending the specimen, and recording the force‑displacement (force‑deformation) curve to determine initiation of fracture. This standard is intended for quality assurance and is not suitable for film adhesives or substrates that cannot be made sufficiently rigid without stiffening.

Key topics and requirements

• Test principle: A substrate with a central adhesive block is loaded in three‑point bending; the force‑displacement curve yields maximum force (Pmax), maximum deformation (dmax), and compliance (slope) at fracture initiation in the interfacial zone.
• Specimen dimensions: Typical substrate size (50 × 10 × e mm) and adhesive block (25 × 5 × 4 mm); substrate thickness e adjusted to material elasticity or stiffened as required.
• Apparatus: Specimen preparation device (lower plate, silicone mould, securing plate), syringe to dispense 0.5 cm3 adhesive per cell, bending test rack (support bars 6 mm diameter, 33 mm span; load bar 12 mm diameter) and measurement equipment with deformation resolution ~0.001 mm and force accuracy ~1%.
• Test conditions: Specimen preparation and testing at 23 °C ±2 °C and 50 % ±5 % relative humidity; condition specimens at these conditions for a minimum of 24 h before testing. Cure adhesives per supplier instructions.
• Procedure and data: Record full force‑displacement curves, note fracture propagation, extract compliance, Pmax, dmax, and the area between bonded and unbonded substrate curves. Test at least six specimens and include an unbonded substrate control.
• Limitations: Applicable only to rigid substrates or those stiffened to resist bending; not suitable for film adhesives. Fracture originating within the adhesive block indicates cohesive failure and does not directly measure adhesive interfacial strength.

Applications and users

ISO 14679 is used for quality assurance and comparative adhesion testing by:

• Adhesive manufacturers for product verification and batch testing
• Materials and test laboratories validating metal bonding processes
• R&D and formulation teams assessing primer and surface‑preparation effects
• Industries relying on metal bonding (aerospace, automotive, general metal fabrication) where rigid substrates (steel, aluminium) are common

The method helps evaluate the effectiveness of surface preparation, primers and curing regimes in producing robust adhesive bonds to rigid substrates.

Related standards

• ISO 4588 - Surface preparation of metals for adhesives
• ISO 13895 - Surface preparation of plastics
• ISO 9142 - Laboratory ageing conditions for bonded joints
• ISO 10365 - Designation of main failure patterns
• ISO 286‑1 - Limits and fits (tolerances)

Keywords: ISO 14679, three‑point bending method, adhesion testing, adhesives, adhesion characteristics, force‑displacement curve, interfacial zone, quality assurance.