Thickness effect on 3D material properties 

The main objective of this chapter is to study the influence of the thickness on the threedimensional (3D) mechanical elastic properties (E1, E2, E3, ν12, ν13, ν23, G12, G13 and G23) of unidirectional (UD) laminates. The chosen material is a UD E-glass/epoxy laminated composite manufactured using a vacuum infusion process. In order to achieve this objective, a total of eighty-eight specimens of three different thicknesses are tested in tension and shear using mechanical tests based on the American Society for Testing and Materials’ methods  (ASTM, 2005; 2006). In addition, tensile and shear strengths and strain, at failure, are measured, when possible, and discussed. A detailed description of experimental procedures, specimens manufacturing and testing, is given. Test results are presented and commented, and some suggestions for future works are also proposed.

Design of Experiments 

The material used in this experimentation is an E-glass/epoxy composite. The UD dried glass fibres constituting the laminates are UT-E300-500 provided by Gurit and the epoxy resin holding the fibres together is EPR/EPH 04908 from Hexion. Glass fibres have been chosen opposed to carbon fibres principally due to a lower cost. The properties of both individual constituents are provided by the suppliers . In order to observe the influence of the thickness on mechanical properties, different thicknesses are evaluated. In fact,  The number of plies in each laminate is based on a factor of 8 plies due to future comparisons with symmetric cross-ply and quasi-isotropic lay-ups. In addition, the thickness of each laminate is computed using an average thickness of a single cured ply of 0.185 mm multiplied by the number of layers of its respective lay-up. Then, as a thin laminate, below 6 mm thick, 8 plies of UD dried glass fibres are stacked to form laminate of 1.48 mm thick,hereafter named 1.5 mm. As a moderately thick laminate, between 6 and 16 mm thick, 56 plies of glass fibres are stacked to form a laminate of about 10 mm thick (10.36 mm). As a thick laminate, 112 plies are stacked to form a laminate of about 20 mm thick (20.72 mm).

Specimens Manufacturing

This section includes a description of all steps of the vacuum infusion manufacturing process. Those steps are the mould preparation, the cutting of the fibres, the bagging setup for thin and thick laminates, the matrix preparation, the injection and the curing.

Mould Plate Preparation 

The first step is to prepare the mould plate. The best material for a mould plate is aluminium. The geometry of the mould plate is a function of laminate dimensions. The plate needs to be 10 cm longer and wider than the laminate to provide enough space for the injection setup. It is 15 cm longer for a thick laminate due to the vacuum chamber under the laminate. The thickness of the plate will influence the flatness tolerances; a plate of 10 to 15 mm thick should respect those tolerances.

The mould plate is cleaned with a ScotchBrite and acetone. Any remaining dirt is removed with water and ethanol. Pieces of transparent adhesive tape are applied on all edges where the sealant tape will, in a later stage, be applied. The transparent tape prevents release agent from being applied where the sealant tape needs to stick to the mould. In addition, in manufacturing a thick laminate, transparent tape’s bands are applied where the vacuum room under the laminate will be positioned. For the same reason, sealant tape needs to stick to the mould to seal the vacuum room under the laminate with the VAP material. Vacuum room dimensions are in order to fit the laminate inside sealant tape’s limits plus a 5-10 cm in the injection direction for the vacuum tube installation .

Products from WaterWorks are used to prepare the mould plate adequately. FRESH START is recommended to thoroughly clean the mould surface. It is applied directly to the surface from a handy squeeze pouch and worked in with a piece of ScotchBrite; after the plate is well rinsed with water and wipe off. To condition the mould prior to the application of a release coating, the PREFLIGTH is applied with a piece of cloth. It is repeated for four coats separated by a cure of 15 minutes and the last cure is done in an oven at 83°C for 15 minutes or at room temperature for at least 30 minutes. Then a non-hazardous release agent, DEPARTURE, is lightly sprayed on the plate. After 2 minutes, the plate is wiped and 15 minutes later another coating is applied and wiped after 2 minutes, and then left for at least 30 minutes. After that, the transparent tape is removed and replaced by the sealant tape from AeroVac, LTS9OB, The backing paper of the sealant tape should be left on until the vacuum bag is positioned.

Cutting the fibres

During each drying step of the WaterWorks release agent, the fibres may be cut. The fibres are cut with the desired dimensions, laminate’s length (Ll) and width (Wl). All around the laminate, about 50 mm should not be used in specimen’s geometry; and the cut width is around 3 mm. So, those dimensions have to be taken into account in the laminated plate design. The laminate’s thickness (tl) is determined by the number of plies (n), and the average thickness of one cured ply (tp). In this study, 8, 56 and 112 plies correspond to laminate thicknesses of about 1.5, 10 and 20 mm respectively. On a cleaned cutting table, the material is unrolled and cut to correct dimensions with a roller cutter . A metal ruler or a rigid template is used to get the desired fibres’ shape. A particular attention should be given to the fibres, because they provide the strength and the stiffness of the laminate; a paper envelop can be used to protect them. Also during cutting, a special care should be given to an accurate fibres’ alignment.

Vacuum Bagging Setup 

The bagging setup step consists of arranging, in a particular order, different layers of materials. There is the difference between thin and thick laminates, expect for the vacuum pump settings.

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Table des matières

1.1 Presentation of Composite Materials
1.2 Manufacturing Processes
1.2.1 Wet Lay-up
1.2.2 Vacuum Infusion
1.2.3 Autoclave Curing
1.2.4 Compression Moulding
1.2.5 Filament Winding
1.2.6 Resin Transfer Moulding (RTM)
1.2.7 Structural Reaction Injection Moulding (SRIM)
1.3 Analysis Methods
1.3.1 Lamination Theories
1.3.2 Finite Element Analysis (FEA)
1.4 Thick Laminates Opposed to Thin Laminates
1.4.1 Manufacturing: Thin vs Thick Laminates
1.4.2 Characterization and Testing: Thin vs Thick Laminates
1.4.3 Thickness Effect Summary
1.5 Originality
2.1 Comparison Statement
2.2 Evaluation of Beam Deflection
2.2.1 Classical Lamination Theory (CLT)
2.2.2 Timoshenko First-order Beam Theory (TFBT)
2.2.3 Refined Higher-order Beam Theory (RHBT)
2.2.4 Beam Model Characteristic
2.3 Comparison of Results
2.3.1 Deflection vs Span-to-Depth Ratio
2.3.2 Deflection vs Thickness
2.3.3 Relative Difference with ANSYS®
2.4 Comparison Summary
3.1 Design of Experiments
3.2 Specimens Manufacturing
3.2.1 Mould Plate Preparation
3.2.2 Cutting the fibres
3.2.3 Vacuum Bagging Setup
3.2.4 Matrix Preparation
3.2.5 Injection and Curing
3.2.6 Specimens Preparation
3.3 Quality of the Manufacturing Process
3.4 Theoretical Estimation of Elastic Properties
3.5 Specimens Testing
3.5.1 Tension
3.5.2 Shear
3.6 Results Analysis
3.6.1 Tensile Elastic Properties Presentation
3.6.2 Tensile Elastic Properties Analysis
3.6.3 Elastic Shear Properties Presentation and Analyses
3.6.4 Failure Properties Analyses
3.7 Conclusion and Future Works
4.1 Design of Experiments
4.2 Experimental Results
4.2.1 Laminates Quality
4.2.2 Elastic Tensile Properties
4.2.3 Stress and Strain at Failure
4.3 Evaluation with the Classical Lamination Theory
4.4 Evaluation with Finite Element Modeling
4.5 Results Comparison
4.6 Conclusion
5.1 Experimental Strain using a Digital Extensometer
5.2 Torsion of Rectangular Bar
5.2.1 Test Specifications
5.2.2 Geometric Parameters

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