Concentric Ring (Equibiaxial) Flexure Compression

Equibiaxial flexure compression testing is a materials testing method used to evaluate a specimen’s resistance to bending under multi-directional loading. Unlike uniaxial flexure tests, which apply force along a single axis, this method distributes stress evenly in two perpendicular directions, providing a more realistic measure of a material’s performance in service.

It is particularly valuable for brittle materials such as ceramics, glass, and advanced composites that can fail suddenly without significant plastic deformation. By replicating the combined stresses found in real-world applications, the test offers a more accurate assessment of strength, defect sensitivity, and product durability.

The most widely used approach to equibiaxial flexure compression testing is the concentric ring method. A circular specimen is supported on an outer ring and loaded through a smaller, concentric inner ring. This configuration generates a uniform bending moment across the specimen, allowing engineers to measure isotropic flexural strength.

Step-by-step procedure

• Specimen preparation - Cut the material into a circular disc, typically 25 mm to 100 mm in diameter, with a controlled thickness. Ensure edges are smooth and free from defects.
• Conditioning - Store and prepare specimens in a controlled environment, usually at 23°C ± 1°C and 50% ± 2% relative humidity, in line with relevant standards.
• Equipment setup - Centre the specimen on the support ring, ensuring it is stable and accurately aligned.
• Load application - Apply force through the inner loading ring at a constant rate, typically in the range defined by the relevant standard (for ceramics, BS EN 843-1 specifies around 1 mm/min).
• Data collection - Record the maximum force sustained before failure. Calculate equibiaxial flexural strength using specimen dimensions and applied load.
• Analysis - Compare results with specification requirements or baseline values to assess material performance.

The concentric ring method is particularly suited for testing isotropic strength, making it an important quality control tool for high-specification materials.

Internationally recognised standards ensure accuracy, repeatability, and comparability of results. Common references include:

• BS EN 843-1 - Mechanical testing of advanced ceramics, including equibiaxial flexure methods.
• ASTM D790 - Flexural properties of plastics.
• ISO 178 - Determination of flexural properties of plastics under a defined load.

These standards define specimen dimensions, environmental conditioning, load application rates, and calculation methods.

Equibiaxial flexure compression testing is used wherever material reliability under multi-directional stress is critical.

• Automotive - Testing ceramic brake discs, composite body panels, and advanced polymer parts to ensure performance under variable loads.
• Aerospace - Evaluating turbine blade ceramics, composite fuselage panels, and thermal protection materials.
• Ceramics industry - Assessing tableware, insulators, and technical ceramics for defect sensitivity and durability.
• Construction - Testing architectural glass, tiles, and stone products for safety and structural performance.

Example: In ceramic road marker production, equibiaxial flexure testing revealed a manufacturing defect that caused premature cracking under load. Adjusting the firing process improved flexural strength by around 20 percent, reducing in-service failures.

Mecmesin designs and manufactures precision equipment for standards-compliant equibiaxial flexure compression testing, including the concentric ring method. Our systems combine robust mechanical design with advanced control and analysis software.

OmniTest and MultiTest-dV motorised test stands, together with VectorPro software, provide:

• High-accuracy load measurement to 0.1 N resolution
• Displacement measurement to 0.01 mm
• Programmable speed control for full compliance with BS EN 843-1 and other standards
• Customisable concentric ring fixtures for precise specimen alignment
• Automatic data capture, analysis, and reporting for quality audits and traceability

These systems offer versatility for testing across a range of materials, from advanced ceramics to composite laminates.

Equibiaxial flexure compression testing via the concentric ring method is a powerful tool for evaluating material strength under realistic, multi-directional stresses. It is especially important for brittle and high-performance materials where safety margins and defect detection are critical.

To discuss your testing requirements, select the right Mecmesin equipment, or integrate equibiaxial flexure testing into your quality control process, speak to our technical team. We will help you configure a precise, reliable, and standards-compliant solution for your application.