Single-fibre transverse debonding: tensile test of a necked specimen

The aim of the paper is the development of a test to measure the adhesion strength between a fibre and a matrix material. The basis is the necked sample with a single fibre under compressive load proposed by Broutman (Broutman LJ. Measurement of the fiber-polymer matrix interfacial strength. Interfaces in composites 1969; ASTM STP 452:27–41. American Society for Testing and Materials). The essential innovation is to load the specimen in tension and to generate the interfacial load by an optimized specimen geometry. Starting from a stress analysis of a specimen without a fibre a stress ratio is introduced to describe the level of optimization. Optimized geometric dimensions and the corresponding interfacial transverse stress are derived. The paper provides tools for developing new micromechanical tests and the appropriate data reduction schemes. The tensile loading removes several problems of the original Broutman test, especially fibre buckling and breaking. The attainable interfacial stress is higher. If an axisymmetrically necked specimen is used, the stress state will be really axisymmetrical.