ISO 1288-3:2016

Overview

ISO 1288-3:2016 - Glass in building - Determination of the bending strength of glass - Part 3: Test with specimen supported at two points (four point bending) specifies a laboratory method to determine the bending strength of flat glass used in buildings, including the influence of edge condition. The standard defines test geometry, apparatus, environmental conditions and evaluation rules for four‑point bending tests. Limitations and fundamental principles are covered in ISO 1288‑1.

Key topics and technical requirements

• Test method: Four‑point bending with the specimen supported on two rollers and loaded by two bending rollers (see standard figures).
• Specimen dimensions: nominal length 1 100 mm ±5 mm; width 360 mm ±5 mm; thickness per supplied tolerance.
• Apparatus: testing machine with stepless loading, load measurement accuracy ±2.0%, free‑rotating rollers of 50 mm diameter and ≥365 mm length; rubber strips between rollers and specimen.
• Rubber strips: 3 mm thick, hardness (40 ± 10) IRHD (ISO 48).
• Environmental conditions: test at (23 ± 5) °C and 40–70% relative humidity; temperature held constant to 1 °C during test.
• Loading rate: increase bending stress uniformly at (2 ± 0,4) MPa/s until failure; record maximum force Fmax and time to failure.
• Measurements: specimen width (to nearest 1 mm) and thickness (measured at multiple points; instruments specified for high resolution - see clauses 5.2 and 7.1). Adhesive film is applied to the tensile side to retain fragments and locate fracture origin.
• Evaluation: bending strength σb is calculated from Fmax, specimen geometry and a dimensionless factor k (k depends on central deflection y/h - ISO provides the relation and curves). Self‑weight correction σbG is included where relevant. Only fractures originating between bending rollers are used for surface strength; special rules apply for edge strength statistics.
• Reporting: mandatory items include reference to ISO 1288‑3, glass type, edge finish, pre‑treatment, number of specimens, individual thickness/width, bending or edge strength per specimen, time to breakage, and whether break originated at the edge or body.

Applications and users

ISO 1288-3 is used by:

• Glass manufacturers for product development and quality control.
• Independent testing laboratories for type approval and certification.
• Façade and structural engineers, architects to verify design values for flat glass elements and to assess edge workmanship effects.
• Regulatory bodies and product certifiers needing standardized strength data for safety and compliance.

Practical value: provides repeatable, comparable bending strength data (including edge effects) for structural glass design, fracture analysis and quality assurance.

Related standards

• ISO 1288‑1 (Fundamentals of testing glass)
• Other parts of ISO 1288 (Parts 2, 4, 5)
• ISO 48 (Rubber hardness)
• ISO 16293‑1 (Young’s modulus reference for soda‑lime silicate glass)

Keywords: ISO 1288-3:2016, four point bending, bending strength of glass, edge strength, glass testing, flat glass, building glazing standards.