[Optical Strain Imaging Analysis of Selected Polymer Composites Developed From Hemp and Basalt]

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ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University.

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ABSTRACT

Basalt reinforced composites are recently developed materials. These mineral amorphous fibres are a valid alternative to carbon fibres for their lower cost, and to glass fibres for their strength. In order to use basalt reinforced composites for structural applications, it is necessary to perform a mechanical characterisation. With this aim in the present work experimental results of several static and fatigue tests are described. Two polymeric matrices are taken into account, vinylester and epoxy, to assess their influence on the evaluated parameters. In parallel to these mechanical tests, also the thermal answer of the specimens to mechanical loads is evaluated by means of thermography. This experimental technique allows defining the composite local heating during the application of mechanical loads and its behaviour in details. Final discussion on obtained results is proposed focussing the attention on basalt fibre composite behaviour, and comparing mechanical properties of BFRP with other composite materials in glass and carbon fibres.

TABLE OF CONTENTS

ACKNOWLEDGEMENT2

DECLARATION3

ABSTRACT4

CHAPTER 1: INTRODUCTION6

Aim of the research8

CHAPTER 2: LITERATURE REVIEW9

The hybrid effect15

a) Fracture propagation16

b) Process-induced shrinkage17

CHAPTER 3: METHODOLOGY AND EXPERIMENT MATERIALS19

Sample manufacturing19

Description of experimental tests19

Static tests20

Fatigue and stepwise tests23

Thermography: static and fatigue application23

Equipment24

Thermography for static tests of homogeneous materials25

Thermography for cyclic tests of homogeneous materials26

CHAPTER 4: RESULTS AND DISCUSSION29

Results29

Delamination characterisation of the composites32

Fatigue tests33

Thermographic data analysis35

Discussion41

CHAPTER 5: CONCLUSION46

REFERENCES49

CHAPTER 1: INTRODUCTION

Traditionally, precise strain measurements during uniaxial tensile testing can be performed by clamping a strain gauge to the sample. However, if the sample is very small, stripe-shaped or very compliant, this may alter the testing geometry and hence influence the measurement significantly. Contactless strain measurement is possible with laser extensometers or by using cameras combined with digital image correlation software. The drawback of such systems is that they are often quite expensive, usually predefined and thus have a limited flexibility. Strain determination by digital image correlation may be challenging if the sample surface is reflective. Additionally, it is nearly impossible if the surface structure changes significantly during the course of experiment, for example due to thin film fragmentation or buckling under externally applied strain. Due to such difficulties this research aims to investigate the combination of the eco-friendly natural fibres of 'Hemp' with the advanced mechanical strength of other reinforcements available like 'Basalt' in order to create a new, innovative material and use a number of Optical Measuring techniques to perform a damage evaluation test on it.

Imaging techniques that utilize low-energy resonant phenomena (electronic, vibrational, or nuclear) to probe the structure and dynamics of molecules, molecular complexes, or higher-order ...