J. P. Nunes

The use of a three-point support flexural test to predict the stiffness of anisotropic composite plates in bending

Abstract Anisotropic polymeric matrix composite discs supported on three points were subjected to a non-destructive bending test to study their behaviour in complex flexural loading situations. The results show that the flexural behaviour of the composites depends on several factors, such as fibre orientation, laminate stacking, surface waviness and moulding temperature. The experimental data were compared with those obtained from the finite element program software Algor . Differences up to 13% were found between the experimental and simulated values of the flexural stiffness. In spite of that, it was concluded that the non-destructive test used is a useful tool to predict the behaviour of anisotropic composites and to validate the results obtained from computer FEM analysis.

A novel technique for the interfacial characterisation of glass fibre–polypropylene systems

Abstract In the present work, a new technique was developed to determine the interfacial properties of two opaque glass fibre/polypropylene (GF/PP) systems via fragmentation tests on single filament model composites. Fragmentation tests usually require the fibre inside the composites to be completely aligned in the loading direction. Since PP matrices are non-transparent, it is not possible to guarantee a priori this condition. Hence, a novel technique was developed to determine the inclination of the filaments embedded in the composites. The fibre–polymer systems were also evaluated by comparing their interfacial properties with the overall mechanical properties determined on pultruded GF/PP composites. The present work shows that the knowledge of the interfacial properties is important, not only to compare alternative fibre/matrix systems, but also to assess whether the level of adhesion in these systems is adequate to fabricate composites with good mechanical properties.

Formation and Characterization of Carbon/Polycarbonate Towpregs and Composites

A powder coating technique was used to produce carbon fiber towpregs with low fiber content. Unidirectional composites obtained from this material were subjected to mechanical testing. The tensile strength of the carbon fibers was determined from experimental data, using the Weibull and log-normal distribution functions. The properties of the composites are comparable with those of a commercial Sheet Molding Compound (SMC), and could be predicted using the Classical Lamination Theory. It is shown that the tensile strength of the composites is more sensitive than the modulus to processing derived defects.

Advances in Thermoplastic Matrix Towpregs Processing

The present work reports the development of new technologies to fabricate long and continuous-fiber-reinforced composite structures from low-cost thermoplastic matrix semiproducts. These semiproducts, thermoplastic matrix towpregs and preconsolidated tapes (PCTs), were produced in a purposely-built prototype machine, by deposition of a thermoplastic polymer in powder form on continuous fibers. The work also presents the advances made in the processing of these materials into composites by conventional techniques, such as pultrusion, filament winding and compression molding. Finally, it describes the investigation of the optimal processing conditions that maximize the mechanical properties of the composites. These properties are good enough for the composites to be used as engineering materials in many structural applications.

Finite Element Modelling of Thermoplastic Matrix Composite Gas Cylinders

Continuous glass/polypropylene (GF/PP) commingled fiber tapes were employed to produce wrapped pressure gas vessels for domestic applications by using filament winding. The vessel structural-wall was built using a hybrid solution consisting in a very thin steel liner over wrapped by the filament wounded GF/PP commingled fiber tape layers. FEM analysis was used to evaluate if the composite gas pressure vessel based on the hybrid solution (steel liner + glass fiber reinforced thermoplastic) is capable to withstand the following pressure requirements: the metallic liner, alone, a minimum burst pressure of 4MPa and whole hybrid composite vessel minima internal test and burst pressures of 3 MPa and 6.75 MPa, respectively. Finally, gas pressure vessel prototypes manufactured in industrial cycle conditions were submitted to burst pressure tests to prove that they accomplish all European standard strength requirements.

New PVC Matrix Towpregs and Composites

A cost efficient powder coating technology developed in previous work [1-3] was modified to produce glass fibre/polyvinyl chloride (GF/PVC) towpregs that were subsequently processed by compression moulding and filament winding. The production of GF/PVC towpregs was optimized and a process window established. The composite structures obtained were submitted to mechanical testing and the results compared with the theoretical predictions made using the classical laminate theory (CLT). The obtained results showed that the GF/PVC composites properties are compatible with all major engineering applications.

Consolidation of Glass Fibre-Polypropylene Towpregs by Compression Moulding

In this work a theoretical model describing the consolidation of glass fibrepolypropylene (GF/PP) towpregs into composites by compression moulding is studied. Such model relates the constant pressure applied by the press to the other processing operational (consolidation time and temperature) and material variables (fibre/polymer content and packing arrangement, matrix viscosity and powder and fibre dimensions). Compression tests were carried at different temperatures and constant press pressures on unidirectional GF/PP towpreg preforms. The experimentally determined displacement/time curves were compared to the model simulations assuming an isothermal consolidation and two different fibre/polymer packing arrangements, one triangular and the other hexagonal. The results obtained showed that the towpreg consolidation could be successfully predicted using the model under study.

Production of Thermoplastic Towpregs

This work establishes process windows for efficient towpreg production on a developed powder coating equipment. Three different thermoplastic towpregs were studied: one for highly demanding markets (carbon fibre/PrimospireTMPR-120) and other two for commercial applications (glass/polypropylene and glass/polyvinyl chloride). Mechanical properties of compression moulded composites obtained from the produced towpregs were also obtained and discussed.

Glass/Polyvinyl Chloride Composites

This paper summarizes the results obtained in the use of plastisols of vinyl chloride homopolymer (PVC), obtained by the process of emulsion polymerization, as thermoplastic matrix in the production of composite pipes and in pipe repairing. Two processing techniques commonly used with thermosetting matrices were studied: filament winding and hand lay up. The produced composite structures of PVC reinforced with glass fibres were subsequently subjected to tests in order to determine their mechanical properties. This paper concludes that it is possible to use the described technique for piping repairing with good results.

Using Thermoplastic (HDPE) Liners and Glass Fiber Reinforced Thermosetting and Thermoplastic Structural Wall Matrices to Produce Filament Wound Pressure Vessels

Polymer composites are an excellent alternative to replace more traditional materials in the fabrication of pressure cylinders for common applications. They minimize the weight and improve the mechanical, impact and corrosion behavior, which are relevant characteristics for almost all current and future large scale pressure cylinder applications, such as liquid filters and accumulators, hydrogen cell storage vessels, oxygen bottles, etc. A new generation of composite pressure vessels has been studied in this work. The vessels consist on a thermoplastic liner wrapped with a filament winding glass fiber reinforced polymer matrix structure. A conventional 6-axis CNC controlled filament winding equipment was used to manufacture the thermosetting matrix composite vessels and adapted for production of thermoplastic matrix based composite vessels. The Abaqus 6.4.2 FEM package was used to predict the mechanical behavior of pressure vessels with capacity of approximately of 0.068 m3 (68 liters) for a 0.6 MPa (6 bar) pressure service condition according to the requirements of the EN 13923 standard, namely, the minimum internal burst pressure. The Tsai-Wu and von-Mises criteria were used to predict composite laminate and thermoplastic liner failures, respectively, considering the elasto-plastic behavior of the HDPE liner and the lamina properties deducted from the micromechanical models for composite laminates. Finally, the results obtained from the simulations were compared with those obtained from the experimental pressure tests made on the thermoplastic liners and final composite vessels.Copyright