Compozite Cu Matrice Polimerica

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  • Revista Romn de Materiale / Romanian Journal of Materials 2010, 40 (4), 323 - 331 323

    CARACTERISTICILE BARELOR DIN POLIMERI ARMAI CU FIBRE DE STICL SOLICITATE LA TRACIUNE

    TENSILE CHARACTERISTICS OF GLASS FIBRE REINFORCED POLYMERIC BARS

    NICOLAE RANU, CTLIN BANU, GABRIEL OPRIAN, MIHAI BUDESCU,

    VLAD MUNTEANU, OANA IONI

    1 Universitatea Tehnic Gh. Asachi Iai, Facultatea de Construcii, Bdul. Mangeron nr. 43, cod 700050, Iai, Romnia

    Compozitele polimerice armate cu fibre din sticl

    (CPAFS) sunt utilizate la fabricarea barelor pentru armarea elementelor din beton sau a structurilor hibride. Caracterizarea comportrii la traciune a barelor din CPAFS este obligatorie pentru proiectani naintea utilizrii acestora la armarea elementelor portante. n acest sens, s-a realizat un program experimental privind comportarea la traciune a barelor compozite din CPAFS cu matrice vinil-esteric, iar rezultatele obinute sunt prezentate n aceast lucrare. ncercrile experimentale au fost completate de modelri numerice efectuate n scopul determinrii cmpurilor de tensiuni n zonele extremitilor barelor i n zona median de testare.

    Au fost testate la ntindere trei seturi a cte 10 bare din CPAFS avnd diametrele de 8, 12 i 16 mm n vederea determinrii rezistenei ultime la ntindere, modulului de elasticitate longitudinal i a deformaiei specifice ultime la ntindere.

    Rezultatele experimentale se nscriu n limitele valorilor nregistrate la teste silimilare de ctre alte echipe de cercetare. n urma ncercrilor experimentale i a modelrii numerice s-a constatat c aceste metode pot asigura caracterizarea adecvat a barelor compozite solicitate la traciune oferind proprietile mecanice principale necesare n procesul de proiectare.

    Glass fibre reinforced polymer (GFRP) composites

    are currently being used as reinforcing bars in concrete and hybrid structures. An appropriate characterization of GFRP bars for concrete reinforcement is required by the structural designers prior to their use in structural applications. An extensive experimental program has been carried-out and the test results obtained from tensile tests on samples made of glass fibres and vinyl ester resins are presented and analysed in the paper.

    The experimental tests have been accompanied by a numerical modelling performed to characterize the stress field in the bar ends and along the test portion of the specimens.

    Three sets of 10 bars with diameters 8, 12 and 16 mm have been tested in tension, determining the ultimate tensile strength, the elastic longitudinal modulus and the ultimate tensile strain.

    The experimental results are in line with similar work carried out by other research teams. It has been found out that the experimental procedure and the accompanying numerical modelling provide an adequate characterization of the GFRP bars giving the main properties needed for design.

    Keywords: glass fibre, end anchorages, tensile modulus, tensile strength, numerical modelling 1. Introducere

    Barele din compozite polimerice armate cu fibre de sticl au nceput s fie produse la scar industrial cu douzeci de ani n urm i au fost utilizate ca armturi pentru elemente portante i structuri din beton armat datorit rezistenei la coroziune, raportului favorabil rezisten/greutate i a neutralitii elecromagnetice [1]. Aceste bare compozite sunt folosite n mod frecvent ca armturi interioare pentru grinzi i plci din beton [2, 3], precum i ca produse de armare pentru lucrri de reabiliatare i consolidare a pereilor din zidrie de crmid nglobate n sliuri superficiale [4]. Barele din CPAFS pot fi folosite i ca armturi longitudinale pentru stlpii cu seciune inelar [5], circular sau rectangular din beton armat [6], tuneluri [7-8] i grinzi din lemn [9].

    1. Introduction Glass fibre reinforced polymer bars have

    been industrially produced over the last twenty years and utilised as reinforcement for concrete load bearing elements and concrete structures due to their corrosion resistance, high strength to weight ratio and electromagnetic neutrality [1]. These composite bars are frequently used as internal reinforcing bars for concrete beams and plates [2, 3] and as reinforcing products to structurally rehabilitate and strengthen masonry walls using near surface mounting (NSM) solution [4]. They can be also utilised as longitudinal reinforcement for tubular, concrete columns [5], circular or rectangular concrete columns [6], tunnelling projects [7-8] and timber beams [9].

    When loaded in tension, GFRP bars do not

    Autor corespondent/Corresponding author, Tel.: +40 232 23.22.19, e-mail: taranu@ce.tuiasi.ro

  • 324 N. ranu, C. Banu, G. Oprian, M. Budescu, V. Munteanu, O. Ioni / Tensile characteristics of glass fibre reinforced polymeric bars

    Barele din CPAFS solicitate la ntindere nu se plasticizeaz nainte de rupere [10]. Comportarea la ntindere a acestor bare este caracterizat printr-o relaie cvasi-liniar elastic ntre tensiuni i deformaii specifice pn la cedare. Rezistena la ntindere i modulul de elasticitate al barelor din CPAFS depind de o serie de factori care includ: tipul fazelor constituente (fibre i matrice), fraciunea volumetric de fibre (avnd n vedere faptul c fibrele particip n principal n preluarea eforturilor) precum i tehnologia de fabricaie utilizat.

    Determinarea rezistenei la ntindere a barelor din CPAFS nu poate fi realizat n conformitate cu prevederile normelor ASTM [11], redactate pentru epruvete plate subiri, ntruct comportarea epruvetelor este complex datorit concentrrilor de tensiuni n zonele de ancorare. De aceea, pentru a evita cedarea prematur a capetelor probelor i pentru a dirija ruperea n zona median este necesar utilizarea unor dispozitive speciale la fixarea probelor solicitate la traciune. n cadrul normelor AIC [10] s-a propus o metod de testare special, cu tratarea adecvat a capetelor epruvetei care se nscrie n linia metodologiei de testare n cazul altor elemente de armare i care asigur rezultate experimentale compatibile cu alte reglementri referitoare la calculul elementelor din beton armat. La prelucrarea statistic a rezultatelor experimentale se admite o distribuie normal care s reprezinte caracteristicile mecanice determinate pe un set reprezentativ de epruvete [12, 13]. Programul experimental s-a desfurat n condiii normale de temperatur din laborator, dei astfel de teste pot fi efectuate i n condiii severe de temperaturi sczute sau ridicate [14]. Acest program experimental face parte din obiectivele i activitile incluse n proiectul de cercetare cu tema Structuri hibride realizate din materiale compozite i tradiionale, Program PN II-Idei-Cod 369, 2008-2011 [15].

    2. Programul experimental

    2.1 Materiale Epruvetele au fost decupate din bare cilindrice

    produse de ctre Schck Bauteile GmbH din Baden-Baden, Germania [16]. Barele CPAFS au fost produse prin pultrudere, n matrie prenclzite unde procesul de impregnare i saturare a fibrelor cu matrice s-a desfurat n condiii de presiune atent controlate, obinndu-se valori ale fraciunii volumetrice de fibr de peste 70%.

    La fabricarea barelor au fost folosite fibre de sticl rezistente la alcalii, cu rezistena la ntindere Rft=3600 MPa i modulul de elasticitate Ef=80,5 GPa, ca material de armare [17]; matricea utilizat este o rin vinil-esteric de uz general, cu rezistena la ntindere Rmt=85 MPa i modul de elasticitate Em=3.5 GPa [18].

    2.2 Epruvete Pentru realizarea programului experimental

    exhibit plastic behaviour before rupture [10]. The tensile behaviour of these bars is characterised by a quasilinearly elastic stress-strain relationship until failure. The tensile strength and elastic modulus of GFRP bars are dependent on several factors including: the nature of the composite constituents (fibres and matrices), the fibre volume fraction (since the fibres are the main load-caring constituents) and the manufacturing process.

    Determination of GFRP bar strength loaded in tension by testing can not be performed by ASTM norms [11] written for thin plate-like samples, since the sample behaviour is complicated due to stress concentrations in the anchorage regions. Therefore, a suitable testing grip should be utilized to avoid premature failure at the specimen ends and enable failure to occur in the middle of the test specimens. A special ACI test method has been developed [10] to be inline with the test methodology for other types of reinforcing bars and to provide calculated test results that are compatible with other design norms for reinforced concrete. Usually a normal distribution can be assumed to represent the mechanical characteristics of the population of specimens [12, 13]. The experimental program has been carried out at normal laboratory temperature, although the tensile tests can be performed under low or high temperature [14]. The testing program is part of the objectives and activities included in the research project on Hybrid structures made of polymeric composites and traditional building materials, Program PN II-Idei-Cod 369, 2008-2011 [15].

    2. Experimental program 2.1 Materials

    The test specimens have been cut from cylindrical bars produced by Schck Bauteile GmbH from Baden-Baden, Germany [16]. GFRP bars have been manufactured by pultrusion in heated dies where impregnation and saturation of glass fibres by resin has been performed under pressure and tightly controlled conditions enabling fibre volume fractions over 70% to be achieved.

    Glass fibres with a tensile strength Rft=3600 MPa and an elas