Double‑Ring Bending Test on Glass According to ISO 1288‑5

The double‑ring bending test determines the flexural strength of flat glass specimens by applying a concentric ring load. Under a centered compressive force between the support ring and load ring, the specimen bends so that a defined bending stress develops in the outer ring. From the force–displacement curve and the ring dimensions, the maximum flexural strength is calculated in accordance with ISO 1288‑5.

Test Procedure

1. Specimen Preparation
   • Square plates: side length L = 66 ± 1 mm
   • Round plates: radius r₃ = 33 ± 0.5 mm
   • Planar, parallel glass specimens
2. Setup
   • Support ring with radius r₂ = 30 mm defines the bearing area
   • Load ring with radius r₁ = 6 mm applies the compressive load concentrically
3. Loading
   • Upper load platen is pivot-mounted to minimize transverse forces
   • Protective guard mounted on the upper platen for operator safety
4. Evaluation
   • Capture of force and displacement via LabMaster testing software
   • Calculation of flexural strength using the standard’s formula

Test Fixture & Integration

• Type R30 fixture for inspekt table 20 kN or inspekt blue 20 kN (connection R20/8‑H)

With this 20 kN test fixture, you achieve rapid, safe, and fully compliant double‑ring bending tests on glass—delivering reproducible, precise results with minimal setup.

Further information on the test fixture on request