Materials and Design 32 (2011) 2091–2099

Contents lists available at ScienceDirect

Materials and Design

journal homepage: www.elsevier .com/locate /matdes

Glass–basalt/epoxy hybrid composites for marine applications

V. Fiore a,⇑, G. Di Bella b, A. Valenza a

a Department of ‘‘Ingegneria Civile, Ambientale e Aerospaziale’’, University of Palermo, Viale delle Scienze, 90128 Palermo, Italyb Advanced Technologies Institute for Energy ‘‘Nicola Giordano’’, National Research Council, Via Salita Santa Lucia sopra Contesse 5, 98126 Messina, Italy

a r t i c l e i n f o

Article history:Received 2 August 2010Accepted 19 November 2010Available online 25 November 2010

Keywords:A. Natural materialsB. LaminatesE. Mechanical

0261-3069/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.matdes.2010.11.043

⇑ Corresponding author. Tel.: +39 091 23863708; faE-mail addresses: vincenzo.fiore@unipa.it (V. Fiore

Di Bella), valenza@unipa.it (A. Valenza).

a b s t r a c t

The aim of this work is to evaluate the influence of uniaxial basalt fabric layers on the mechanical per-formances 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 uni-directional basalt fabric, have been produced by vacuum bagging technique. Three points bending andtensile tests have been carried out in order to evaluate the effect of number and position of basalt layerson the mechanical properties of the investigated structures.

The experimental tests have showed that the presence of two external layers of basalt involves thehighest 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 uni-directional basalt on the specific mechanical properties of the laminates. The correspondence betweenthe predicted numerical results and the experiments proves the accuracy of this model, which has alsobeen applied to a real ship component.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Basalt is an inert, naturally occurring, volcanic rock that can befound worldwide. Basalt-based materials are environmentallyfriendly and non-hazardous. The current production technologyfor continuous basalt fibres is very similar to that used for E-glassmanufacturing. The main difference is that E-glass is made from acomplex batch of materials whereas basalt filament is made frommelting basalt rock with no other additives and, as a consequence,with an advantage in terms of cost. Thanks to the simplicity of themanufacturing process lower energy is needed.

Moreover, basalt fibres have high chemical stability [1,2], theyare non-toxic, non-combustible [3] and resistant to hightemperatures [4]. Moreover, their specific mechanical propertiesare comparable with, or better than, those of E-glass ones (seeTable 1).

Over the last years basalt fibres have begun to be used in severalapplications such as the manufacture of compressed natural gas(CNG) cylinders which have to be strong, lightweight and resistantto impact and temperature. These cylinders are usually built withmetallic materials or lighter fibres reinforced by polymeric materi-als (FRP). By using carbon fibres as reinforcement the cylinder

ll rights reserved.

x: +39 091 7025020.), guido.dibella@itae.cnr.it (G.

maintains its durability and strength but the extremely high priceand current shortage of carbon fibres make basalt fibres (strongerthan E-glass fibres and more available and cheaper than carbonones) 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 signif-icantly improve deformation and energy absorption capacities ofgeopolymeric concrete while there is no notable improvement indynamic compressive strength.

Liu et al. considered the possibility to use basalt fibres in thefield of transportation. In a preliminary work [8] polymer compos-ites reinforced by basalt fabric and glass fabrics were produced fortensile, compressive, flexural and shear tests. A void content below3% was measured for all the composites produced for the testingprogram and no significant differences in Young’s modulus, tensilestrength, flexure strength, shear strength and compressionstrength were found between basalt composites and glasscomposites.

As the use in transportation requires also environmental dura-bility, another research work [9] from the same authors reportedthe tolerance of basalt-fibre-reinforced polymer composites to-wards salt water immersion, moisture absorption, temperatureand moisture cycling. Parallel tests were conducted for the corre-sponding glass-reinforced polymer composites. A 240 days’ agingin salt water or water has displayed a slight but significant de-crease in Young’s modulus and tensile strength of basalt compos-ites. Freeze–thaw cycling up to 199 cycles did not change the

Table 1Glass and basalt fibres properties compared.

Property E-glass Basalt

Density [g/cm3] 2.56 2.8E modulus [GPa] 76 89Tensile strength [GPa] 1.4–2.5 2.8Elongation to fracture [%] 1.8–3.2 3.15Specific E modulus [GPa/g/cm3] 30 31.78Specific tensile strength [GPa/g/cm3] 0.5–1 1

Fig. 1. Unidirectional basalt fabric.

2092 V. Fiore et al. / Materials and Design 32 (2011) 2091–2099

shear strength significantly, but aging in hot (40 �C) salt water orwater made the shear strength of basalt composites decrease.The aging results indicated that the interfacial region in basaltcomposites can be more vulnerable to damage than that in glasscomposites.

Sim et al. [10] studied the applicability of the basalt fibre as astrengthening material for structural concrete members. Throughvarious experimental tests for durability, mechanical properties,and flexural strengthening, the authors demonstrated that, whenmoderate structural strengthening but high resistance for fire issimultaneously sought, e.g. for building structures, the basalt fibrecan be a good alternative methodology among other fibre (i.e. glassor carbon) reinforced polymer (FRP) strengthening systems.

Basalt can replace asbestos in almost all its possible applica-tions (i.e. insulation) since the former has three times the latter’sheat insulating properties. Furthermore, the fibre diameter canbe controlled in order to prevent uptake of harmful ultra-fine fi-bres. Because of its good electrical insulating properties (higherthan E-glass), basalt fibres are also incorporated into printed circuitboards, resulting in superior overall properties compared to thoseof conventional components made of fibreglass. They are also em-ployed in other electro technical applications such as extra fineresistant insulation for electrical cables and underground ducts.Because of its thermal insulating properties it has already beenused as fire protection in the form of fabrics or tapes [11]. In com-bination with its high specific strength, high resistance to aggres-sive media [12], and high electrical insulating properties, thisoccurs in special products such as insulators for high voltage powerlines.

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

The aim of this work is to analyse the feasibility of use of basaltfibres in substitution of glass ones as reinforcement of compositematerials for nautical applications. For this purpose, compositestructures reinforced by randomly oriented E-glass short fibres(in the next ‘‘GFRP’’) and hybrid ones (reinforced by both glassmat and unidirectional basalt fabric) have been produced by vac-uum bagging technique. Three point bending and tensile tests havebeen carried out in order to evaluate the effect of this replacing onthe properties of the GFRP structures.

Finally, a simplified numerical model has been proposed toevaluate the influence of basalt layers on the mechanical proper-ties of hybrid structures, by employing a commercial code (i.e.Ansys). Experimental data have been compared with finite elementanalysis, confirming the good predictive capability of the numeri-cal model.

As a consequence, it is possible to foresee the behaviour of thishybrid laminates by using the physical and mechanical propertiesof the composite constituents as input data, thus optimising thebasalt layer position for the design of complex compositestructures.

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

2. Experimental setup

2.1. Materials and manufacturing

All the composite structures have been made with a single lam-ination using the vacuum bagging technique. This method involvesan initial hand lay-up phase and then the polymerisation of thematrix in a flexible bag in which negative pressure is reached bya vacuum pump. Vacuum bag technology brings some advantagesto the final characteristics of composite laminate if compared tohand lay-up technology. All the laminates have been cured at roomtemperature for 24 h and then post-cured at 60 �C for 8 h.

The glass composite laminates (in the next ‘‘GFRP’’) have beenconstituted by six layers of E-glass mat (randomly oriented fibres,with areal weight of 450 g/m2 in a matrix of epoxy resin (i.e. SP106) mixed with own hardener. The total average thickness ofthe laminates is 2.6 mm.

The hybrid composites have been produced, starting from GFRPstructure, replacing one or two layers of glass mat with one or twoof uniaxial non-woven basalt fabric with areal weight of 400 g/m2

(see Fig. 1). As shown in Table 2, seven hybrid structures have beenproduced.

2.2. Mechanical testing

2.2.1. Flexural testThese tests have been carried out according to ASTM standards

[13], by using an Universal Testing Machine (UTM) mod. 3365 byInstron, equipped with a load cell of 5 kN.

Particularly, flexural tests have been performed on each realisedstructure, using five prismatic samples with dimensions20 � 96 mm. For all tests, the span length is equal to 80 mm andcross-head speed to 4.26 mm/min.

2.2.2. Tensile testTensile tests have been carried out according to ASTM standards

[14], by employing an UTM by Zwick Roell, equipped with a loadcell of 600 kN, with a cross-head speed of 2 mm/min. For eachstructure realised, five prismatic samples with dimensions25 � 250 mm have been tested.

Table 2Hybrid laminates.

Sample B1 B2 B3 B4 B5 B6 B1–6

No. of basalt layers 1 1 1 1 1 1 2Position of basalt Lamina 1 Lamina 2 Lamina 3 Lamina 4 Lamina 5 Lamina 6 Lamina 1–6Orientation of basalt 0�Average thickness [mm] 2.66 2.68 2.68 2.68 2.68 2.66 3.19

Fig. 2. Flexural modulus of the laminates.

Fig. 4. Delamination failure mechanism of B1–B6 structures (flexural test).

V. Fiore et al. / Materials and Design 32 (2011) 2091–2099 2093

3. Results and discussion

3.1. 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 stiff-ness of the hybrid structures increases compared to the GFRPlaminates. Particularly, the B2 and B5 structures show animprovement of about 20% in the modulus while higherincreases of the stiffness are obtained by replacing the externallayers of glass mat (31% and 39% for B1 and B6 structures,respectively);

– the best improvement in the flexural modulus are obtained byreplacing both external layers of glass mat with basalt unidirec-tional ones: the B1–6 structure shows flexural modulus equal to19.5 GPa (about 118% higher than that of the GFRP laminate).

These results can be explained considering both the kind of fab-ric used to substitute the glass mat and the stress rxx trend in abeam loaded in a three point bending mode.

In this work the authors replaced one or two randomly orientedshort glass fibres/epoxy layers with correspondent layers rein-

Fig. 3. Flexural strength of the laminates.

forced by long unidirectional basalt fibres; as a consequence thelaminates are more stiff. In fact, for the typical load configuration,these fibres are subjected to tensile and compressive stresses toguarantee a better resistance.

Moreover it is known that in each section of the beam, the stressrxx increases moving through the thickness from the central zoneto the external sides of the beam. A neutral axis exists in the mid-dle zone of the beam while the layers in top and bottom side aresubjected, respectively, to maximum compression and tensilestress.

Thus, the higher increases of the modulus properties are ob-tained by replacing the external layers of glass mat (with long uni-directional basalt fibres oriented towards x direction) since the

Fig. 5. Failure mechanisms of B1–6 structure (flexural test).

Table 3Tensile properties of the laminates.

GFRP B1 B2 B3 B4 B5 B6 B1–6

E [GPa] 8.28 ± 0.34 9.82 ± 0.28 9.6 ± 0.75 10.2 ± 0.67 10.7 ± 0.96 10.1 ± 0.55 10.4 ± 0.46 14.1 ± 0.81r [MPa] 145.4 ± 11.7 170.5 ± 7.39 167.6 ± 8.5 168.6 ± 11.6 165.7 ± 9.5 169.6 ± 7.8 170.4 ± 12.5 210.3 ± 20.7

Fig. 6. Failure mechanisms of the laminates (tensile test).

2094 V. Fiore et al. / Materials and Design 32 (2011) 2091–2099

maximum values of the stress rxx just occur in these layers of thecomposite structures. Moving from the external side to the middlezone of the beam, the stress rxx decreases and the replacement ofthe glass mat layer with uniaxial basalt influences the specific per-formances of the structure in a slighter way [15].

The highest improvement in the modulus is obtained by replac-ing both external glass mat layers with unidirectional basalt onesbecause of reasons above mentioned (kind of replaced fabric andposition of the basalt unidirectional layers) together with the pres-ence of two layers of basalt UD (rather than one in other struc-tures) that contribute to stiffen the hybrid laminate.

About the flexural strength showed in Fig. 3, it is evident that:

– the replace of a layer of glass mat with unidirectional basalt onecauses significant decreases in this property in terms of positionof basalt layer. Particularly, for B6 structures a decrease of 23%in the flexural strength is observed while for B4 laminate thisproperty is lower of 33% than that of the GFRP laminate. Allother hybrid structures have showed decreases between 23%and 33%;

– by replacing the two external layers of glass mat with unidirec-tional basalt ones (B1–6 structure) it is achieved an increase ofthe flexural strength equal to 44%.

Fig. 7. Tensile curves of the laminates, glass and basalt.

These results can be explained taking into account the failure modeevidenced:– As shown in Fig. 4, the B1–B6 laminates fail for a premature

delamination at the interface between the basalt layer and glassmat one. Delamination is one of the most common and danger-ous failure mechanisms of the composite laminates, caused byinternal failure of the layers interface [16].Due to the relatively low strength of the matrix, defects of thedelamination type frequently occur in the structure made ofcomposite materials. Most of these defects appear during thetechnological process (i.e. the causes including ungluing orshrinkage stresses). The process of defect formation continuesin the stage of utilization of the structures under the effect oftemperature stresses, local loads, impact and vibrations.Failure due to delamination of laminated composite usuallybegins from free edges, surface cuts, surface defects, unrein-forced openings and other structural stresses concentration[17]. The mechanism of failure is determined by the distributionof macro- and micro-stresses which is a function of the struc-ture of each layer and the stack as a whole.In the investigated case, this kind of failure can occur due to theadhesion between two very dissimilar layers (i.e. glass mat –unidirectional basalt) which is lower than that shown betweenidentical ones (i.e. glass mat–glass mat). In fact, regions ofweakened interfacial adhesive contact on the interfaces of thecomponents of the structure have an important effect on thecharacter of local failure of composite materials. Moreover themismatch of elastic properties between different layers of com-posite laminates, promotes the arising of interlaminar stressesin the free-edge region. These interlaminar stresses can leadto delamination failure for in-plane loads significantly lowerthan those typically observed in these structures [18].Further explanation can be due to the stress rxx gap establishedat the interface between two layers adjacent with differentmechanical properties (i.e. isotropic–orthotropic lamina), whichcan be evaluated by lamination theory [19]. For these reasons,delamination failures happen for the hybrid structures unlikeGFRP ones that fail for tensile mechanism of the bottom layers.The flexural stiffness of these hybrid laminates is not reducedby delamination before it reaches free edges of a structure. Infact, as the local thickness increases with the growth of delam-ination area due to separation between adjacent plies withinthe laminate, the global bending stiffness increases [20];

Fig. 8. Comparison experimental/FEA.

V. Fiore et al. / Materials and Design 32 (2011) 2091–2099 2095

– The hybrid laminates with both external layers reinforced byunidirectional basalt (i.e. B1–6) show both compressivemechanism in top layer (Fig. 5a) and tensile one in bottomlayer (Fig. 5b). In this case delamination mechanism doesnot happen as the presence of two unidirectional basalt layers(rather than one in other hybrid structures) leads the stressrxx gap between the basalt layers and glass ones to decre-ment. The evidenced failure mode can explain the higherstrength of these hybrid structures rather than those of thestructures with one basalt layer (i.e. B1–B6) that, as discussedabove, fails for a premature delamination. Despite the evi-dence of the same failure mechanism these hybrid laminatesshow higher strength than that of GFRP laminates and thiscan be attributed to the presence of unidirectional basaltlayers.

3.2. Tensile test

In Table 3 the tensile properties of the structures realised arereported.

It is possible to observe that:

– by replacing a layer of mat glass with uniaxial basalt, the tensilestrength of the hybrid structures increases if compared to thatof GFRP structure: the improvements vary between 14% and17.3%, for B4 and B1 structures, respectively. As in the previouscase, the highest improvement in this mechanical property isobtained by replacing each external layer of glass mat with abasalt unidirectional one: the B1–6 structure shows a tensile

Fig. 9. Maps for the tensile test: (a) B1;

strength equal to 210.3 MPa (about 45% higher than that ofthe GFRP laminate);

– hybrid laminates with a unidirectional basalt layer showincreases in tensile modulus in a range between 16% and29.2% for B2 and B4 structures, respectively. On the other hand,by replacing both external layers of glass mat, the tensile mod-ulus of the B1–6 structures reaches 14.1 GPa, about 70% higherthan that of the GFRP structure.

Considerations similar to those discussed in the previous para-graph can be employed to explain these experimental results. In-creases in the modulus of the hybrid structures are due to thereplace of one (or two for B1–6 structure which, as expected,shows the highest improvement of this property) glass isotropiclayer with unidirectional basalt ones. In fact, the fibres, arrangedalong the load direction, give a higher stiffness to the structure.

Unlike the previous case, the tensile strengths of hybrid struc-tures are higher than that of GFRP one. This can be explained byconsidering the failure mechanism: for this loading configurationall tested structures fail for the fibres’ tensile failure as evidencedin Fig. 6. The failure interests firstly the glass layers and then thebasalt ones. This phenomenon prevails on the delamination failurethat does not occur. The absence of this premature failure mecha-nism make the orientation of fibres the most important parameterinfluencing the mechanical properties of the laminates. Fibres ori-entation directly affects the distribution of load between fibres andmatrix: the contribution of the fibres to the composite properties ismaximum only when they are parallel to the loading direction[21].

(b) B2; (c) B3; (d) B1–6 structures.

Fig. 10. Maps for the flexural test.

2096 V. Fiore et al. / Materials and Design 32 (2011) 2091–2099

4. Finite element analysis

4.1. Setup

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

The sample that has been used to simulate the laminate is con-stituted by a rectangle having the dimensions defined in Section 2.A shell element type (i.e. Shell99) has been used to build the mod-el. The shells are a viable alternative to conventional solid elementsfor the modelling and analysis of laminate structures. These allowto simulate the behaviour not only of plane structures but also ofcomplex curved profiles in several fields; i.e. aeronautical (fuse-lages, wings), marine (hulls) and automotive (chassis) ones. In par-ticular Shell99 is an 8-node, 3-D shell, layered element with sixdegrees of freedom at each node: translation in the nodal x, yand z directions and rotations about the nodal x, y and z axes. Itis designed to model thin to thick moderately plate and shell struc-tures with a side-to-thickness ratio of roughly 10 or greater. TheShell99 element allows a total of 250 uniform-thickness layers.

In the real constants box of this element the following parame-ters have been added: number of layers (i.e. six), material (i.e.glass, basalt), thickness (i.e. 0.4 mm for the glass layer, 1 mm forthe carbon one) and orientation (i.e. 0�).

The mechanical and physical properties of the laminates con-stituents have been obtained through theoretical study [19] andtensile tests on samples constituted by only glass or basalt fabrics.Fig. 7 reports the typical tensile curves of both materials, imple-mented in the finite element model.

The sample has been constrained as in the experimental tests.Moreover, a displacement corresponding to the start of the inelas-tic trend, has been applied.

Actually, the composite structure behaviour has been simulatedby a numerical procedure performed in elastic regime and thepost-elastic behaviour has been intentionally neglected; the aimis to obtain a simple and versatile numerical simulation, conditionsrequired for an effective design methodology and, particularly, tocharacterize the composite structure in the elastic regime, whereit exploits its work [22].

5. Results

To validate the finite element model, a fit between the numer-ical results, obtained from the simulations, and the experimentalones, obtained from the mechanical tests, has to exist.

In particular, it is possible to observe that the elastic trend of theexperimental curve matches well with the straight line, corre-sponding to the stiffness of the simulated structure (see Fig. 8).The experimental curve is processed as output of the UniversalTesting Machine used to test the composites laminates whereasthe stiffness of the structure is evaluated in post-processing, afterthe run phase of the simulation.

As reported in the previous section, our interest has been fo-cused only on the elastic behaviour and, then, this comparison con-firms the good predictability of the model.

Particularly, Fig. 8 reports the comparison experimental/numer-ical for the sample with the external basalt lamina in the tensiletest. Similar results have been obtained for the other simulatedstructures.

Fig. 9 shows the stress trends for the tensile test. To comparethe results for different samples, same displacement (i.e. 1 mm)is considered.

Fig. 9a is related to the laminate with the external basalt lamina(i.e. more thick one identified in the figure with ‘B’). The deformed

Fig. 11. Hull of a 85 ft ship.

Fig. 12. Bulkhead P1.

Table 4Lamination sequence.

Layer Thickness [mm]

BDR 300/BDR 300/Mat 225 1.21BDR 300/BDR 300/Mat 225 1.21BDR 300/BDR 300/Mat 225 1.21PVC 40BDR 300/BDR 300/Mat 225 1.21BDR 300/BDR 300/Mat 225 1.21BDR 300/BDR 300/Mat 225 1.21Total 47.26

Table 5Boundary conditions.

Side x y z

Top – �50 0Bottom – 0 0Left 0 – 0Right 0 – –

V. Fiore et al. / Materials and Design 32 (2011) 2091–2099 2097

sample is characterized by a concavity on the right side, wherethere are the basalt fibres. This behaviour is not observed in otherhybrid samples (i.e. glass–carbon [15]). In fact, basalt is more resis-tant than glass in the load direction, but the difference is not ele-vated and, as a consequence, the stresses maps are influencedalso by the transversal properties that, obviously, are lower forthe unidirectional basalt fibres. Then, the laminates do not presenttensile and compressive regions [15], but they are always sub-jected to a traction with a changeable stress.

It is possible to observe that the basalt fibres present severalstress levels (i.e. 50–80 MPa). The higher stress is reached at thebasalt/glass interface, near the symmetry axis of the sample, where

there is also the highest stress gap that produces the failure in thiszone. Fig. 9b and c are related to the laminate with the basalt lam-ina in position 2 and 3, respectively. The stress is not uniformly dis-tributed, it decreases towards the concavity maintaining a constantvalue in the basalt fibres. The sample B2 is characterized by a high-er stress value concentrated in the external glass lamina placednear the basalt fabric. At the interface between these layers thefailure occurs. On the contrary, in sample B3, the failure intereststhe more solicited glass fibres.

Finally, Fig. 9d deals with the samples with the external basaltlaminas. In this case the concavity is not present because of thesymmetry of the laminate. Moreover the stress is homogeneouslydistributed.

Fig. 10 shows the stress trends for the flexural test. To comparethe results from different samples, same displacement (i.e.1.5 mm) is considered. In a homogeneous sample [15], the stress

Fig. 13. Stress along y direction.

2098 V. Fiore et al. / Materials and Design 32 (2011) 2091–2099

distribution is symmetrical; i.e. compression stress on top side andtensile on the bottom. The neutral axis is the x symmetrical axis. Ina hybrid composite the behaviour is different. Fig. 10 (B1) refers tothe laminate with external carbon lamina on the top (i.e. morethick one identified in the figure with ‘B’). It is possible to observethat the basalt fibres are subjected to compressive stresses,whereas the glass fibres are subjected to tension. So, in this casethe neutral axis is at the glass/basalt interface and it is identifiedwith a dotted line.

It is interesting to observe how the neutral axis (i.e. dotted line)slightly moves in the sample with the variation of the basalt lam-ina position. Particularly, this happens in the basalt layer for theconfigurations B2, B3, B4 and B5. In the configurations B1 and B6it is in the glass layer near to the basalt one. In the sample B1–6the stresses distribution is symmetrical.

Fig. 14. Stress along y directi

5.1. Implementation in ship design

In order to verify directly on a ship component the righteous-ness of both the proposed numerical model, as tool in ship design,and of the substitution of a glass fabric with a basalt one, a bulk-head has been modelled.

Fig. 11 reports the hull of a 85 ft ship. The bulkheads are evi-denced by the capital P.

In particular, the bulkhead, called P1 (Fig. 12), has been studied.Table 4 reports both the lamination sequence and the thickness of

the sandwich structure that constitutes the component. This structureconsists of a common PVC foam core and two identical skins (i.e. withlayers of glass mat and glass bidirectional fabrics with areal density of225 g/m2 and 300 g/m2, respectively). These data have been imple-mented in the real constants of the numerical code.

on within the thickness.

V. Fiore et al. / Materials and Design 32 (2011) 2091–2099 2099

Table 5 reports the boundary conditions for each side of thebulkhead as a function of the kind of the joining (overlaminationor adhesion). Moreover, due to the symmetry, only a half of thesample has been analysed.

Fig. 13 reports the stress along the y direction. The region highersolicited is in the corner between the left side and the bottom one.

The simulations show that the substitution does not produce anevident change in the global properties of the component. Themaximum stress is slightly higher (1.5%) in the sample with basaltfibres.

In order to see how the stress distributes among different lay-ers, Fig. 14 reports it within the thickness of the section corre-sponding to the symmetry axis. Particularly, the core of thesandwich is not solicited, the bidirectional fabrics are characterizedby the higher stress values, whereas the glass or basalt fibres pres-ent a lower value.

In the glass mat the stress changes between �260 MPa and�150 MPa, in the basalt fabric between �150 MPa and �90 MPa.Then, for the basalt the stress level is lower, and this is mainlydue to the different kind of fabric, isotropic versus orthotropic.However, the range is reduced due to the unidirectionality of thefibres for the same reason.

On the other side (i.e. near the hull), in the glass mat the stresschanges between �600 MPa and 50 MPa. The basalt fibres show areduced range, i.e. between �400 MPa and 100 MPa.

Then, there is not only a compressive condition but also a ten-sile one. For the compression, the behaviour is similar to that ob-served previously. For the tension it is different. The basalt fibrescontrast better this kind of stress.

6. Conclusions

In this work composite structures reinforced by randomly ori-ented E-glass short fibres and hybrid ones, reinforced by both glassmat and unidirectional basalt fabric, have been produced by vac-uum bagging technique and tested.

Three point bending and tensile tests show that the presence oftwo external layers of basalt involves the highest increases inmechanical properties of hybrid laminates compared to those ofGFRP laminates. These results highlight both that the basalt fibresmay be considered as a possible alternative of the glass ones innautical application and hybrid structures could be used in themanufacturing of a boat.

Finally, the finite element analysis, validated by the experimen-tal results, shows how the stresses distribute in the layers of thesample. This model is a valid tool in ship design. The results ob-

tained in the simulation of a bulkhead are very useful to under-stand the behaviour of a naval component.

References

[1] Wei B, Cao H, Song S. Environmental resistance and mechanical performance ofbasalt and glass fibres. Mater Sci Eng A – Struct 2010;527:4708–15.

[2] Wei B, Cao H, Song S. Tensile behavior contrast of basalt and glass fibres afterchemical treatment. Mater Des 2010;31:4244–50.

[3] Berozashvili M. Continuous reinforcing fibres are being offered forconstruction, civil engineering and other composites applications. Adv MaterCom News, Compos Worldwide 2001;6:5–6.

[4] Cerny M, Glogar P, Sucharda Z, Chlup Z, Kotek J. Partially pyrolyzed compositeswith basalt fibres – mechanical properties at laboratory and elevatedtemperature. Compos Part A – Appl S 2009;40:1650–9.

[5] Pavlovski D, Mislavsky B, Antonov A. CNG cylinder manufacturers test basaltfibre. Reinf Plast 2007;51:36–9.

[6] Li W, Xu J. Mechanical properties of basalt fibre reinforced geopolymericconcrete under impact loading. Mater Sci Eng A – Struct 2009;505:178–86.

[7] Li W, Xu J. Impact characterization of basalt fibre reinforced geopolymericconcrete using a 100-mm-diameter split Hopkinson pressure bar. Mater SciEng A – Struct 2009;513–514:145–53.

[8] Liu Q, Shaw MT, Parnas RS, McDonnel AM. Investigation of basalt fibrecomposite mechanical properties for applications in transportation. PolymCompos 2006;27:41–8.

[9] Liu Q, Shaw MT, Parnas RS, McDonnel AM. Investigation of basalt fibrecomposite aging behaviour for applications in transportation. Polym Compos2006;27:475–83.

[10] Sim J, Park C, Moon DY. Characteristics of basalt fibre as a strengtheningmaterial for concrete structures. Compos Part B-Eng 2005;36:504–12.

[11] Hao LC, Yu WD. Evaluation of thermal protective performance of basalt fibrenonwoven fabrics. J Therm Anal Calorim 2010;100:551–5.

[12] Shokrieh MM, Memar M. Stress corrosion cracking of basalt/epoxy compositesunder bending loading. Appl Compos Mater 2010;17:121–35.

[13] ASTM D 790-03 (2003). Standard test methods for flexural properties ofunreinforced and reinforced plastics and electrical insulating materials. ASTMInternational, West Conshohocken, PA, 2003; p. 1–11.

[14] ASTM D 3039/D 3039M-00 (2006). Standard test methods for tensileproperties of polymer matrix composite materials. ASTM International, WestConshohocken, PA; 2006. p. 1–13.

[15] Valenza A, Fiore V, Di Bella G. Effect of UD carbon on the specific mechanicalproperties of glass mat composites for marine applications. J Compos Mater2010;44:1351–64.

[16] Marat-Mendes RM, Freitas MM. Failure criteria for mixed mode delaminationin glass fibre epoxy composites. Compos Struct 2010;92:2292–8.

[17] Sihn S, Kim RY, Kawabe K, Tsai SW. Experimental studies of thin-ply laminatedcomposites. Compos Sci Technol 2007;67:996–1008.

[18] Tong JW, Xie MY, Shen M. The interlaminar stresses of symmetric compositelaminates. J Reinf Plast Compos 2004;23:1023–9.

[19] Mallick PK. Fibre reinforced composites: materials, manufacturing and design.2nd ed. New York: Marcel Dekker Inc.; 1993.

[20] Hou JP, Jeronimidis G. Bending stiffness of composite plates withdelamination. Compos Part A – Appl S 2000;31:121–32.

[21] Agarwal BD, Broutman LJ. Analysis and performance of fiber composites. 2nded. New York: John Wiley & Sons Inc.; 1990.

[22] Valenza A, Borsellino C, Calabrese L, Di Bella G. Geometry and stackingsequence effect on composite spinnaker pole’s stiffness: experimental andnumerical analysis. Appl Compos Mater 2006;13:217–35.