At International Syalons Ltd, each of our silicon nitride-based ceramic grades are manufactured onsite from high purity raw materials, and every batch is rigorously analysed using various testing methods, ensuring we continue to produce high quality engineering components.
Physical testing and statistical analysis is at the forefront of materials engineering, ensuring safety, quality, and compliance to international standards and customer expectations. Some examples of in-house testing we employ are: X-Ray diffraction (phase analysis), particle size measurements, powder morphology and rheological testing, density measurements, and thermomechanical testing.
Mechanical testing of advanced ceramics at International Syalons. Image Credit: International Syalons (Newcastle) Ltd.
Mechanical testing of high strength ceramics such as Si3N4 is challenging due to the brittle and abrupt fracture observed when stressed. Tensile testing, used commonly on metals and polymers, is highly susceptible to varied results caused by the stress propagation of defects as well as misalignment of the test specimen, which is further heightened by the limited plastic deformation advanced ceramics undergo when loaded (R. Danzer, 2014). Alongside this, tensile specimens are challenging and time consuming to manufacture, making flexural testing more favourable and suited to the industry.
Flexural testing can be done in a number of ways, such as: 3-point bending, 4-point bending, and biaxial testing, which are proposed by the International Organisation for Standardisation (ISO) and American Society for Testing and Materials (ASTM) (ISO, 2015; ASTM, 2019; ASTM, 2023). Although, similar to flexural testing, 3- and 4-point bend testing involves lengthy specimen fabrication due to the requirements of chamfered edges and polished surface finishes which reduce the edge effect on strength, but making this route extremely costly.
Biaxial testing can be performed via a range of methods, including, ball-on-three-ball (B3B), ring-on-ring (RoR), torsion test and Brazilian disk test to name a few. Biaxial loading presents some benefits compared to uniaxial tensile testing as commonly used for metals:
- Easier test specimen preparation compared to uniaxial testing.
- The biaxial strength is independent of the quality of the edge.
- Strength data is more practical due to the stresses subjected onto the specimen, mimicking real world engineering applications.
- Use of small thin test specimens.
- Biaxial flexure tests produce more reliable and consistent values since the maximum stress is located at the centre of the test specimen.
Sialon test discs, before (left) and after (right) biaxial strength testing. Image Credit: International Syalons (Newcastle) Ltd.
However, biaxial testing lends itself to some drawbacks which include:
- Uncertainty on optimal test specimen dimensions.
- Calculations which rely on other material parameters to be known.
- Biaxial strength data cannot be directly related to uniaxial strength.
(R. Morrell, 1999, p234)
In the pursuit of more accurate test data to represent our materials, International Syalons is investigating novel and standardised biaxial testing methods to supply customers with data supported by the latest ASTM and ISO guidelines. We are also investigating and developing numerical conversions between experimental data and 3-point, 4-point or uniaxial strength. This is done in parallel with our current test method and, with support from third party organisations to independently validate emerging techniques, we aim to develop a more accurate well defined strength test. Utilising the latest Instron testing machines and software, alongside expertly trained engineers, we ensure cohesion between industry practise, international standards, and customer expectations.
Luke Forster
Apprentice Ceramic Development Technologist
22nd November 2024
References
ISO 14704 Fine ceramics (advanced ceramics, advanced technical ceramics). Test method for flexural strength of monolithic ceramics at room temperature (2015). British Standards Institute.
C1161 standard test method for flexural strength of advanced ceramics at ambient temperature (2023).
C1499 standard test method for monotonic equibiaxial flexural strength of advanced ceramics at ambient temperature (2019).
Danzer, R. (2014). On the relationship between ceramic strength and the requirements for mechanical design. Journal of the European Ceramic Society, 34(15), 3435–3460.
Morrell, R. (1999). Biaxial disc flexure – modulus and strength testing. British Ceramic Transactions, 98(5), 234–240.