Approaches to Determine Material Model of Fibre Reinforced Concrete

The paper deals with possible ways of defining the material model of fibre reinforced concrete as a material for structural design. The material model is a tool that can be used to describe response of material to the applied load. It usually includes several different parameters: strengths, ultimate deflections, deformation modules, fracture energy, etc. The paper deals with the problematic phases of tests that are necessary to create a material model, but which may not always provide relevant data. Due to the nature of the material (a fibre reinforced composite with a relatively brittle matrix), it is necessary to analyse separately the behaviour of the material before and after cracks when creating the material model.

Impact Improvement of Tape Carbon Fiber Composite Modified by Submicron Glass Fiber

It is well known that thermoplastic composite is vulnerable to impact fracture. Submicron glass fiber (sGF) was used to modify the matrix of chopped tape carbon fiber reinforced polypropylene composite. The impact resistance improved 20% and 7.4% coressponding to the dimeter sGF of 0.28 and 0.69 µm used in modified-composite. To shed light upon the mechanism of this improvement, the internal damage statement of post-impact specimens was observed by the CT scanner. The results pointed out that the increase of the impact resistance was due to the enlargement of delamination area under impact load. The micro droplet test and end notch flexure test suggest that the decrease of Mode II fracture toughness in modified-composite comes from narrowing the difference between the interfacial shear strength (IFSS) and the bending strength of matrix thanks to significant improving of IFSS with the addition of sGF while the flexural strength remains the unchanged. Consequently, the failure mode changed from debonding fiber/matrix in unmodified composite into brittle matrix failure in modified composite, resulting in the decrease of the Mode II interlaminar fracture toughness and the enlargement of delamination area. The stress transfer test also indicates that the modified composites is prone to the brittle matrix failure.