Experimental investigation of mechanical properties, formability and forming limit diagrams for tailor-welded blanks produced by friction stir welding

Materials Science and Engineering A 528 (2011) 6083–6085 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Rapid communication Experimental investigation of the mechanical properties of polymer mortars with nanoparticles J.M.L. Reis ∗ , D.C. Moreira, L.C.S. Nunes, L.A. Sphaier Theoretical and Applied Mechanics Laboratory – LMTA, Mechanical Engineering Post Graduate Program – PGMEC, Universidade Federal Fluminense – UFF, Rua Passo da Pátria, 156 Bl. E sala 216, Niterói, Rio de Janeiro, Brazil a r t i c l e i n f o Article history: Received 7 February 2011 Received in revised form 25 March 2011 Accepted 17 April 2011 Available online 22 April 2011 a b s t r a c t The present paper examines the mechanical properties of polymer mortar (PM), with different weight fraction of nano-Al2 O3 and nano-Fe2 O3 . The results showed that flexural and compressive strength measured of PM filled with nanoparticles were lower than plain polymer mortar but a considerably stiffness increase was observed for all formulations tested. © 2011 Elsevier B.V. All rights reserved. Keywords: A. Mechanical characterization B. Composites D. Failure 1. Introduction Polymer composites such as polymer mortars are often used in structures due to their excellent resistance to corrosion, high strength-to-weight ratio, low permeability and low thermal conductivity [1–4]. Further development of such materials can be achieved mainly by their modification. The search for effective modification methods and the analysis of the results give an opportunity to adjust a material’s characteristic to the requirements of a particular application. The main ways to change the properties of resin composites comprise adding admixtures to the resin and using different types of fillers. The final characteristics of such modified composites depend on properties of the components as well as on the synergy effects between them [5] and nanocomposites are a typical example, in which nanoparticles are used (nanostructured materials) as additives in a polymer matrix. Nano-sized metals have different properties from bulk metals originating from nanocrystals size. Nanocrystals measure a few nanometers containing few hundred atoms. In this way, nanocomposites can show unique properties (electronic, magnetic, structural) depending on nano-structure size. The employment of nanoparticles composed of metal-oxides for improving mechanical properties of cement mortars have been recently investigated [6–8]. Results showed that compared to plain cement mortars, nanoparticles can enhance compressive and flexural strengths when added to cement mortars mixture. ∗ Corresponding author. Tel.: +55 2126295588; fax: +55 2126295585. E-mail address: jreis@mec.uff.br (J.M.L. Reis). 0921-5093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2011.04.054 In this paper, polymer mortars mixed with nano-Al2 O3 (alumina) or nano-Fe2 O3 (hematite) particles were proposed and manufactured, and their mechanical properties such as compressive and flexural strength were experimentally studied. Alumina nanoparticles can work on the structure as electrical insulator and flame retardant whereas hematite nanoparticles can act as anticorrosive agents as well as semiconductors. 2. Materials and methods 2.1. Materials Polymer mortar (PM), in essence, is a composite material combining a mixture of two phases: one continuum (polymer resin) and the other disperse (sand). PM formulations were prepared in two stages, first the epoxy resin was blended with 3%, 5%, 7% and 10%, in weight, with nano-Al2 O3 or nano-Fe2 O3 and then the resin/nanoparticles solutions were mixed with a siliceous sand with rather uniform granulometry. The epoxy resin system used was RR515 from SILAEX® based on a diglycidyl ether bisphenol A and an aliphatic amine hardener, being processed with a maximum mix ratio of 4:1 (with low viscosity). The resin systems properties provided by the manufacturers are presented in Table 1. The nanoparticles was obtained from NANOAMOR® ; its properties are shown in Table 2. The aggregate used was a siliceous one, of rather uniform particle size, with an average diameter of 245 ␮m. The sand specific gravity is 2.65 g/cm3 and fineness modulus of 2.5. J.M.L. Reis et al. / Materials Science and Engineering A 528 (2011) 6083–6085 6084 Table 1 Properties of the epoxy resin. 3. Results and discussion Property Epoxy ◦ Viscosity at 25 C  (cP) Density  (g/cm3 ) Heat distortion temperature HDT (◦ C) Modulus of elasticity E (GPa) Flexural strength (MPa) Tensile strength (MPa) Maximum elongation (%) 12,000–13,000 1.16 50 5.0 60 73 4 Table 2 The properties of nano-Al2 O3 and nano-Fe2 O3. Property Nano-Al2 O3 Nano-Fe2 O3 Crystal phase Purity (%) Density (g/cm3 ) Specific surface area (m2 /g) Average size (nm) 99.99 3.7 180 30–40 ˛ 98 5.24 20–60 20–60 The resin/nanoparticles content was 12% by weight and 88% of aggregates complete PM formulations. Previous studies [9], considering an extensive experimental program, allowed an optimization of mortar formulations that are now being used in the present work. The mixture was performed mechanically, in order to achieve a more homogeneous material. With those mix proportions, polymer mortar specimens were cast to prismatic (40 mm × 40 mm × 160 mm) and cylindrical ( 50 × 100 mm) specimens according to RILEM TC113/PC-2 [10], specification. For each formulation five cylinder and five prismatic specimens were cast. All specimens were allowed to cure for 7 days at room temperature and then post-cured at 80 ◦ C for 3 h before being tested for flexural and compression. 2.2. Methods Measurements of nanoparticles polymer mortar under different loading conditions were taken under flexion and compression. Prismatic polymer mortar beams were tested by three-point bending up to failure at a loading rate of 1 mm/min, with a span length of 100 mm, according to the RILEM TC113/PCM-8 [11] specifications. In terms of specimen geometry and span length, the specifications of this standard are similar to those of the ASTM C348-02 standard testing method for flexural strength of hydraulic cement mortars [12]. Despite the very short span compared to the thickness, the shear effect was disregarded. Cylindrical specimens were tested under compression at a loading rate of 1.25 mm/min, according to the ASTM C39-05 standard [13]. Mechanical properties of polymers mortars incorporating different contents of nano-Al2 O3 or nano-Fe2 O3 from flexural and compressive tests performed are presented in Table 3, in which mortars with nano-Al2 O3 are represented by letter A and letter I represents specimens made with nano-Fe2 O3 . The numbers after the representing letters corresponds to the nanoparticles content in weight. It can be seen from Table 3 that incorporating nano-Al2 O3 or nano-Fe2 O3 particles in mortar mixtures decreases overall mechanical strength, both flexural and compressive when compared to plain mortars. However, for lower nanoparticle content, 3%, this decrease is not significant, since less than 10% and is within the standard deviation range. In flexion, the increase of nano-Al2 O3 or nano-Fe2 O3 contributes to diminish strength in the order A-10 > A-7 > A-5 > A-3 and I-10 > I7 > I-5 > I-3. In compression, the same behavior is observed for both nanoparticles mixtures. These results indicate, under the present dispersion conditions, that the optimal content of nano-Al2 O3 for reinforcing polymer mortars purposes should be less than 5%. Also, according to Hui et al. [6,7], nano-Al2 O3 or nano-Fe2 O3 in cement mortars mixtures contributes to both flexural and compressive strength enhancement. In another study by Li et al. [8] a decrease in compressive strength is seen for mortar with 3% and 5%, similarly to polymer mortars. Fig. 1 represents the typical stress–deflection curves obtained from flexural tests performed on nanoparticles polymer mortar specimens. As can be seen, despite the decrease in flexural strength with the incorporation of nano-Al2 O3 or nano-Fe2 O3 , the elastic modulus correspondingly increases. From the presented curves we can observe that the flexural behavior is different from plain polymer mortar, but as nanoparticles are added PMs behave equally, except for the ultimate flexural strength, which decreases with the increase of nanoparticle content. The addition of nano-Al2 O3 and nano-Fe2 O3 in polymer mortars considerably elevate flexural stiffness while compared to plain polymer mortars; hence, a higher resistance to deflection is offered, producing a stiffer material. This observation is expected because the Young’s modulus for nano-Al2 O3 or nano-Fe2 O3 are much greater than that of epoxy; thus, the modulus of the nanocomposite is enhanced by adding rigid nanoparticles into epoxy matrix, as documented previously [14,15]. Fig. 2 presents typical stress–strain curves obtained from compressive tests performed on (a) nano-Al2 O3 mortars and (b) nano-Fe2 O3 mortars. As one can observe, nano-Al2 O3 and nano-Fe2 O3 mortars follow the same path in compression as in flexion. A decrease in compressive strength is reported when nanoparticles are introduced in the mixture. A higher concentration of nano-Al2 O3 and Table 3 Mechanical properties of specimens. Formulations Flexural strength (MPa) Target Plain A-3 A-5 A-7 A-10 I-3 I-5 I-7 I-10 15.9 14.5 14.2 13.9 13.8 15.0 14.6 13.8 13.0 ± ± ± ± ± ± ± ± ± 0.6 0.7 0.2 0.6 0.3 0.4 0.7 0.6 0.5 Compressive strength (MPa) Loss (%) Target 0 8.8 10.7 12.6 13.2 5.7 8.2 13.2 18.2 38.0 38.0 37.8 35.6 35.0 34.1 35.9 35.1 30.6 ± ± ± ± ± ± ± ± ± Loss (%) 1.0 1.9 1.0 1.1 0.5 1.1 0.9 1.3 1.5 0 0 0.5 6.3 7.9 10.3 5.5 7.6 19.5 J.M.L. Reis et al. / Materials Science and Engineering A 528 (2011) 6083–6085 6085 Fig. 1. Typical load–deflection curves obtained from flexural tests performed on nano-Al2 O3 mortars (a) and nano-Fe2 O3 mortars (b). Fig. 2. Typical stress–strain curves obtained from compressive tests performed on nano-Al2 O3 mortars (a) and nano-Fe2 O3 mortars (b). nano-Fe2 O3 produces a lower compressive strength of polymer mortars. Again, the compressive strength–strain curves demonstrate a significant increase in stiffness of mortars containing nanoparticles while compared to plain mortars. dination of Improvement of Higher Level Personnel) are gratefully acknowledged. 4. Conclusions [1] D.W. Fowler, Cement Concrete Compos. 21 (1999) 449–452. [2] D. Van Gemert, L. Czarnecki, M. Maultzsch, H. Schorn, A. Beeldens, P. Łukowski, E. Knapen, Cement Concrete Compos. 27 (2005) 926–933. [3] B. Chmielewska, L. Czarnecki, J. Sustersic, A. Zajc, Cement Concrete Compos. 28 (2006) 803–810. [4] P.J.R.O. Novoa, M.C.S. Ribeiro, A.J.M. Ferreira, A.T. Marques, Compos. Sci. Technol. 64 (2004) 2197–2205. [5] L. Czarnecki, V. Weiss, Proceedings of the Second International Symposium on Brittle Matrix Composites, Bochum, 1991. [6] L. Hui, X. Hui-gang, J. Yuan, O. Jinping, Composites: Part B 35 (2004) 185–189. [7] L. Hui, H. Xiao, O. Jin-ping, Cement Concrete Res. 34 (2004) 435–438. [8] Z. Li, H. Wang, S. He, Y. Lu, M. Wang, Mater. Lett. 60 (2006) 356–359. [9] J.M.L. Reis, Mater. Res. 12 (2009) 63–67. [10] RILEM, PC-2: Method of Making Polymer Concrete and Mortar Specimens Technical Committee TC-113. Test Methods for Concrete–Polymer Composites (CPT), International Union of Testing and Research Laboratories for Materials and Structures, 1995. [11] RILEM, PCM-8: Method of Test for Flexural Strength and Deflection of Polymer-modified Mortar Technical Committee TC-113. Test Methods for Concrete–Polymer Composites (CPT), International Union of Testing and Research Laboratories for Materials and Structures, 1995. [12] ASTM C 348-02 (2002). [13] ASTM C39/C39 M – 05e1 (2005). [14] D.K. Shukla, S.V. Kasisomayajula, V. Parameswaran, Compos. Sci. Technol. 68 (2008) 3055–3063. [15] S. Zhao, L.S. Schadler, R. Duncan, H. Hillborg, T. Auletta, Compos. Sci. Technol. 68 (2008) 2965–2975. Nano-Al2 O3 and nano-Fe2 O3 polymer mortars were prepared by adding nanoparticles to PM epoxy matrices. The mechanical properties (flexural and compressive strength) of well-dispersed nano-Al2 O3 and nano-Fe2 O3 particles with different percentages were measured. No flexural or compressive strength enhancement was observed with the introduction of nanoparticles into the mixture. In fact a slight decrease was observed for lower concentrations. On the other hand, the use of nanoparticles showed a significant increase the flexural and compressive elastic modulus of the tested polymer mortars, making nanocomposite polymer mortars stiffer. This research demonstrates the feasibility of producing nano filled polymer mortars with nano-Al2 O3 , which is an electrical insulator component and nano-Fe2 O3 , which produces a smart structural material that can sense its own stress by electrical resistivity. Acknowledgments The financial support of FAPERJ (Rio de Janeiro State Funding), CNPq (Research and Teaching National Council) and CAPES (Coor- References