Elsevier

Materials & Design

Volume 32, Issue 4, April 2011, Pages 2091-2099
Materials & Design

Glass–basalt/epoxy hybrid composites for marine applications

https://doi.org/10.1016/j.matdes.2010.11.043Get rights and content

Abstract

The aim of this work is to evaluate the influence of uniaxial basalt fabric layers on the mechanical performances of a glass mat/epoxy composite used for marine applications.

Polymer composites, reinforced by glass mat (GFRP), and hybrid ones, reinforced by glass mat and unidirectional basalt fabric, have been produced by vacuum bagging technique. Three points bending and tensile tests have been carried out in order to evaluate the effect of number and position of basalt layers on the mechanical properties of the investigated structures.

The experimental tests have showed that the presence of two external layers of basalt involves the highest increase in mechanical properties of hybrid laminates compared to those of GFRP laminates.

In addition, a simplified numerical model has been proposed to better understand the influence of unidirectional basalt on the specific mechanical properties of the laminates. The correspondence between the predicted numerical results and the experiments proves the accuracy of this model, which has also been applied to a real ship component.

Research highlights

GFRP composite structures and glass/basalt ones are produced and tested. ► The external layers of basalt involves the highest mechanical increases. ► Basalt fibres can be considered as a possible alternative in nautical application. ► A simplified numerical model is proposed to understand the influence of basalt. ► This valid model is also applied to a real ship component.

Introduction

Basalt is an inert, naturally occurring, volcanic rock that can be found worldwide. Basalt-based materials are environmentally friendly and non-hazardous. The current production technology for continuous basalt fibres is very similar to that used for E-glass manufacturing. The main difference is that E-glass is made from a complex batch of materials whereas basalt filament is made from melting basalt rock with no other additives and, as a consequence, with an advantage in terms of cost. Thanks to the simplicity of the manufacturing process lower energy is needed.

Moreover, basalt fibres have high chemical stability [1], [2], they are non-toxic, non-combustible [3] and resistant to high temperatures [4]. Moreover, their specific mechanical properties are comparable with, or better than, those of E-glass ones (see Table 1).

Over the last years basalt fibres have begun to be used in several applications such as the manufacture of compressed natural gas (CNG) cylinders which have to be strong, lightweight and resistant to impact and temperature. These cylinders are usually built with metallic materials or lighter fibres reinforced by polymeric materials (FRP). By using carbon fibres as reinforcement the cylinder maintains its durability and strength but the extremely high price and current shortage of carbon fibres make basalt fibres (stronger than E-glass fibres and more available and cheaper than carbon ones) a good alternative [5].

Thanks to their excellent physical and mechanical properties, basalt fibres can also be used as reinforcing material for concrete. Li and Xu [6], [7] showed that the addition of basalt fibre can significantly improve deformation and energy absorption capacities of geopolymeric concrete while there is no notable improvement in dynamic compressive strength.

Liu et al. considered the possibility to use basalt fibres in the field of transportation. In a preliminary work [8] polymer composites reinforced by basalt fabric and glass fabrics were produced for tensile, compressive, flexural and shear tests. A void content below 3% was measured for all the composites produced for the testing program and no significant differences in Young’s modulus, tensile strength, flexure strength, shear strength and compression strength were found between basalt composites and glass composites.

As the use in transportation requires also environmental durability, another research work [9] from the same authors reported the tolerance of basalt-fibre-reinforced polymer composites towards salt water immersion, moisture absorption, temperature and moisture cycling. Parallel tests were conducted for the corresponding glass-reinforced polymer composites. A 240 days’ aging in salt water or water has displayed a slight but significant decrease in Young’s modulus and tensile strength of basalt composites. Freeze–thaw cycling up to 199 cycles did not change the shear strength significantly, but aging in hot (40 °C) salt water or water made the shear strength of basalt composites decrease. The aging results indicated that the interfacial region in basalt composites can be more vulnerable to damage than that in glass composites.

Sim et al. [10] studied the applicability of the basalt fibre as a strengthening material for structural concrete members. Through various experimental tests for durability, mechanical properties, and flexural strengthening, the authors demonstrated that, when moderate structural strengthening but high resistance for fire is simultaneously sought, e.g. for building structures, the basalt fibre can be a good alternative methodology among other fibre (i.e. glass or carbon) reinforced polymer (FRP) strengthening systems.

Basalt can replace asbestos in almost all its possible applications (i.e. insulation) since the former has three times the latter’s heat insulating properties. Furthermore, the fibre diameter can be controlled in order to prevent uptake of harmful ultra-fine fibres. Because of its good electrical insulating properties (higher than E-glass), basalt fibres are also incorporated into printed circuit boards, resulting in superior overall properties compared to those of conventional components made of fibreglass. They are also employed in other electro technical applications such as extra fine resistant insulation for electrical cables and underground ducts. Because of its thermal insulating properties it has already been used as fire protection in the form of fabrics or tapes [11]. In combination with its high specific strength, high resistance to aggressive media [12], and high electrical insulating properties, this occurs in special products such as insulators for high voltage power lines.

In the marine field, basalt fibres are not applied and no research work can be found in the literature. Nevertheless, shipyards are now looking at basalt fibres as a possible alternative to glass fibres in the manufacturing of boats as they are economic and natural and, mainly, safe for the workers (i.e. their sizes are such that they cannot be inhaled).

The aim of this work is to analyse the feasibility of use of basalt fibres in substitution of glass ones as reinforcement of composite materials for nautical applications. For this purpose, composite structures reinforced by randomly oriented E-glass short fibres (in the next “GFRP”) and hybrid ones (reinforced by both glass mat and unidirectional basalt fabric) have been produced by vacuum bagging technique. Three point bending and tensile tests have been carried out in order to evaluate the effect of this replacing on the properties of the GFRP structures.

Finally, a simplified numerical model has been proposed to evaluate the influence of basalt layers on the mechanical properties of hybrid structures, by employing a commercial code (i.e. Ansys). Experimental data have been compared with finite element analysis, confirming the good predictive capability of the numerical model.

As a consequence, it is possible to foresee the behaviour of this hybrid laminates by using the physical and mechanical properties of the composite constituents as input data, thus optimising the basalt layer position for the design of complex composite structures.

The numerical model has been used also to simulate the behaviour of a ship component (i.e. a hull bulkhead).

Section snippets

Materials and manufacturing

All the composite structures have been made with a single lamination using the vacuum bagging technique. This method involves an initial hand lay-up phase and then the polymerisation of the matrix in a flexible bag in which negative pressure is reached by a vacuum pump. Vacuum bag technology brings some advantages to the final characteristics of composite laminate if compared to hand lay-up technology. All the laminates have been cured at room temperature for 24 h and then post-cured at 60 °C for

Flexural test

In Fig. 2 the flexural modulus of the composites is reported.

It is possible to observe that:

  • by replacing a layer of mat glass with uniaxial basalt, the stiffness of the hybrid structures increases compared to the GFRP laminates. Particularly, the B2 and B5 structures show an improvement of about 20% in the modulus while higher increases of the stiffness are obtained by replacing the external layers of glass mat (31% and 39% for B1 and B6 structures, respectively);

  • the best improvement in the

Setup

A 3-D numerical analysis has been conducted in order to simulate both the experimental tests, using a commercial finite element software (i.e. Ansys).

The sample that has been used to simulate the laminate is constituted by a rectangle having the dimensions defined in Section 2. A shell element type (i.e. Shell99) has been used to build the model. The shells are a viable alternative to conventional solid elements for the modelling and analysis of laminate structures. These allow to simulate the

Results

To validate the finite element model, a fit between the numerical results, obtained from the simulations, and the experimental ones, obtained from the mechanical tests, has to exist.

In particular, it is possible to observe that the elastic trend of the experimental curve matches well with the straight line, corresponding to the stiffness of the simulated structure (see Fig. 8). The experimental curve is processed as output of the Universal Testing Machine used to test the composites laminates

Conclusions

In this work composite structures reinforced by randomly oriented E-glass short fibres and hybrid ones, reinforced by both glass mat and unidirectional basalt fabric, have been produced by vacuum bagging technique and tested.

Three point bending and tensile tests show that the presence of two external layers of basalt involves the highest increases in mechanical properties of hybrid laminates compared to those of GFRP laminates. These results highlight both that the basalt fibres may be

References (22)

  • M. Berozashvili

    Continuous reinforcing fibres are being offered for construction, civil engineering and other composites applications

    Adv Mater Com News, Compos Worldwide

    (2001)
  • Cited by (0)

    View full text