Novel tensile testing apparatus for brittle materials

Applications

• Tensile testing of brittle materials
• Tensile testing of materials with nonlinear stress-strain curves
• Measuring cohesive zone parameters

Key Benefits & Differentiators

• Does not require assuming linear elasticity: results are more reliable
• No twisting or undesired bending ensures reproducible testing
• No asymmetric failure patterns facilitates measurement of post-peak behavior
• Suitable for testing materials exhibiting nonlinear stress-strain curves (such as ceramic matrix composites)
• Able to maintain accurate alignment of grips and fixtures

Problem Addressed

Current methods to measure tensile strength of brittle materials suffer from a few key drawbacks. Direct tensile tests often result in undesired bending and twisting of the specimen, and therefore require carefully designed loading fixtures to reduce eccentricity. On the other hand, indirect tensile testing methods such as three-/four-point bending and Brazilian testing assume linear elastic behavior of the material, which is generally not applicable near peak load. In addition, these testing methods often have poor reproducibility and are not useful for collecting cohesive zone parameters from post-peak behavior.

Invention

Researchers at the New Mexico Tech, Tarbiat Modares University, and University of Minnesota have developed a new apparatus for accurate measurement of tensile strength and post-peak behavior of brittle materials. By ensuring a relatively uniform stress distribution through the specimen thickness, and prevention and minimization of twisting and undesired bending, this apparatus provides more reliable tensile strength data compared to conventional apparatus. In particular, the results from the apparatus are not based on the assumption that the tested material is linearly elastic. This particular benefit makes this apparatus suitable for testing materials exhibiting nonlinear stress-strain response. The apparatus is ideal for testing materials with tensile strength between 1.0 MPa and 20.0 MPa, although the apparatus can be designed and calibrated to measure a wider range of tensile strength values. The novel design of the apparatus helps prevent asymmetric failure patterns. Therefore, when combined with an advanced loading system, this apparatus can be used to study post-peak response to measure cohesive zone parameters for brittle or quasi-brittle materials.

Phase of Development

Prototype developed and tested.