To investigate the mechanical properties of fibre reinforced resin

matrices

Niall KirwanBachelor Engineering Honors Degree Mechanical Engineering

Introduction

Composites are widely used in the aerospace and sailing industry

and over the past decade it has been used in small consumer goods

like bike frames, fishing rods and tripods.

For a composite to be used as the main material of a product, the

critical question of whether the forces exerted will result in the

failure of the composite must be asked.

It is very important that this question be answered, such that there is

no risk to human life if the product was to catastrophically fail. As a

result an investigation was be carried out on the mechanical

properties and the make-up of the composite presented at the start of

this research project.

Composites

The most basic form of composite material is one that is made up of

two elements that when combined together produce material

properties that are greatly different to the properties of the individual

elements. A composite is made up of matrix and reinforcement. The

reinforcement is added to increase the strength and stiffness

properties of the matrix which consists of a resin that impregnates

the reinforcement or fibre.

Abstract

The purpose of this project was to investigate the various mechanical

properties of fibre reinforced composites. This was done by

conducting a number of experimental tests with reference to the

British Standards and American society testing and materials. The

results from these tests were cross referenced against known values

as well as theoretical values that were ascertained using the

appropriate equations. Any and all discrepancies were noted and

explanations were drawn up by conducting a micrograph analysis of

the test specimens to understand these errors. Recommendations

were outlined for further study in relation to composite failure

modes and FEA analysis.

This project also contained a sub project which was to create an

experimental procedure for the tensile testing of tubular composites

without premature failure within the gripping zones of the tensile

testing machine.

Tensile Test

Each step or reduction in load was the result of CSA being reduced

by the development of fractures seen below.

Overall results

Experimental results line up more closely to CES results than

theoretical .Explanation for discrepancies:-

Manufacturing process : Pultrusion

Turning the specimens down on the lathe

Lumen of composite was not coaxial

Possible failure modes

Compression Test

Large discrepancy due to unidirectional fibres as the fibres do not

resist the compressive force and thus act as voids.

It is believed that the experimental values represents the individual

specimen and not the fibre glass composite as a whole.

Experimental Design

Results

Fibre Volume Fraction testThis test involved placing four composite specimens in a furnace at 560°C for five minutes. The time for the matrix to disintegrate leaving only

the reinforcing fibres. Knowing the weights of the composites prior the test and the fibres after, the density of the fibres, their mass volume and

fibre volume fraction can be calculated. The results from this test can be seen in the table below. Based on the fibre and composite densities as

well as a thermoplastic polymer identification test, the composite specimens were said to be fibre glass composites.

Glass fibres as the reinforcement

Epoxy resin as the matrix

Fibre type and orientation

Micrograph Analysis

Below are micrographs of the specimens after a tensile test was

conducted.

The white fibres on the left and black fibre on the right indicate

delamination. This is where the parrallel fibres separated from each

other leaving the black epoxy on one side of the fibres

Above shows individual fibres with no epoxy coating, this suggests

fibre pull out, where the fibre literally pull out from the epoxy. The