The aim of the present work was to estimate non-linear thermoelastic behavior of three-phase AA5454/silicon nitride nanoparticle metal matrix composites. The thermal loading was varied from subzero temperature to under recrystallization temperature. The RVE models were used to analyze thermo-elastic behavior. The AA5454/silicon nitride nanoparticle metal matrix composites have gained the elastic modulus below 0oC and lost at high temperatures.

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- 1. Chennakesava R Alavala Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 3) January 2016, pp.104-109 www.ijera.com 104|P a g e Nanomodeling of Nonlinear Thermoelastic Behavior of AA5454/ Silicon Nitride Nanoparticulate Metal Matrix Composites Chennakesava R Alavala Department of Mechanical Engineering, JNT University, Hyderabad-85 ABSTRACT The aim of the present work was to estimate non-linear thermoelastic behavior of three-phase AA5454/silicon nitride nanoparticle metal matrix composites. The thermal loading was varied from subzero temperature to under recrystallization temperature. The RVE models were used to analyze thermo-elastic behavior. The AA5454/silicon nitride nanoparticle metal matrix composites have gained the elastic modulus below 0o C and lost at high temperatures. Keywords - AA5454, finite element analysis, RVE model, silicon nitride, thermoelastic. I. INTRODUCTION Metal matrix composites offer enhanced properties such as higher strength, stiffness, damping capacity and weight savings. The use of silicon carbide [1-5] and alumina [6-11] were dealt as a reinforcement particulate in most of the metal matrix composites. Al-alloys [12] and Mg-alloys [13] were employed as matrix materials in the metal matrix composites intended for automotive applications. Silicon nitride has the best combination of mechanical, thermal and electrical properties of any advanced technical ceramic material. Its high strength and toughness make it the material of choice for automotive and bearing applications. AA5454 aluminum alloy is commonly used in welded structures such as pressure vessels and ships. The dimensional stability is very important at high operating temperatures [14, 15]. Because the constituents usually have very different stiffness and coefficients of thermal expansion (CTE), the internal stress inhomogenity can rapidly increase even under a low level of external applied loads or changes in the environmental temperature [16]. Therefore, it is necessary to understand the thermo-elastic behavior of AA5454/Si3N4 nanoparticulate metal matrix composites. Finite element method (FEM) is applied to estimate the local response of the material using unit cell reinforced by a single particle subjected to periodic and symmetric boundary conditions [17-19]. The aim of the present work was to assess the nonlinear thermoelastic behavior of AA5454/Si3N4 nanoparticulate metal matrix composites. The RVE models were used to analyze the AA5454/Si3N4 nanoparticulate metal matrix composites with interphase between them using finite element analysis. II. MATERIALS AND METHODS The matrix material was AA5454 aluminum alloy. The reinforcement material was Si3N4 nanoparticles of average size 100nm. The mechanical properties of materials used in the present work are given in table 1. The composites were prepared by the stir casting technology and pressure die casting process [4, 8]. The volume fractions of Si3N4 nanoparticles were 10% and 30%. The as-cast samples were heat treated under H34 conditions. The tensile properties were established as per ASTM D3039 standard test procedure. Table 1. Mechanical properties of AA5454 matrix and Si3N4 nanoparticles Property AA5454 Si3N4 Density, g/cc 2.69 3.31 Elastic modulus, GPa 70.3 317 Ultimate tensile strength, MPa 303 397 Poisson’s ratio 0.33 0.23 CTE, µm/m-o C 21.9 3.4 Thermal Conductivity, W/m-K 134.0 27.0 Specific heat, J/kg-K 900 170 In this research, a square RVE (Fig.1) was implemented to analyze the thermo-elastic (compressive) behavior AA5454/ Si3N4 nanocomposites. The large strain PLANE183 element was used in the matrix and the interphase regions in all the models. In order to model the interphase between nanoparticle and matrix, a CONTACT172 element was used. The maximum contact friction stress of 𝜎𝑦 / 3 (where, 𝜎𝑦 is the yield stress of the material being deformed) was applied at the contact surface. The basic Coulomb friction model was considered between two contacting surfaces. Both uniform thermal and RESEARCH ARTICLE OPEN ACCESS
- 2. Chennakesava R Alavala Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 3) January 2016, pp.104-109 www.ijera.com 105|P a g e hydrostatic pressure loads were applied simultaneously on the RVE model. Fig.1. Square RVE containing a nanoparticle. III. RESULTS AND DISCUSSION The finite element analysis (FEA) was carried out at sub-zero and high temperature conditions. The hydrostatic pressure load was applied RVE model to investigate thermo-elastic tensile behavior of AA5454/Si3N4 nanoparticulate composites. The volume fractions of Si3N4 nanoparticles in the AA5454 matrix were 10% and 30%. 3.1 Thermoelastic Behavior Elastic and thermo-elastic strains as a function of temperature are shown in Fig.2. The thermo-elastic strain increased with increase of temperature (Fig.2b). The thermo-elastic strain was very high at 300o C for the composites having 10% Si3N4. For composites with low volume fraction (10%) of Si3N4, the elastic strain decreased from -300o C to 0o C and again it increased from 0o C to 300o C (Fig.2a). For composites with high volume fraction (30%) of Si3N4, the elastic strain increased from -200o C to 300o C. The basic reason could be the CTE mismatch of 18.5 µm/m-o C between AA5454 alloy and Si3N4. Fig. 2. Influence of temperature on elastic and thermo-elastic strains. Fig. 3. Elastic (a) and thermo-elastic (b) strains developed in composites with 10%Vp nanoparticles. Fig.3 demonstrates the state of elastic and thermo-elastic strains developed in the AA5454/ 10%Si3N4 composites. Fig. 4 demonstrates the state of elastic and thermo-elastic strains developed in the AA5454/ 30%Si3N4 composites. In all the cases, Si3N4 nanoparticles had experienced the compressive stains below 0o C in the counter direction of tensile loading and above 0o C in the normal direction of the loading [14]. For Si3N4 nanoparticles the CTE is lower than that of AA5454 matrix. The tensile strength decreased with increase of temperature from -300 o C to 0o C for both the volume fractions of 10% and 30% Si3N4 (Fig. 5). However, the tensile strength increased with the increase of temperature for the composites having volume fraction of 10% Si3N4 0 o C to 300o C. This might be due to the dominant role of AA5454 matrix extending the yield point and elongation. But, the influence of temperature (from 0 o C to 300o C) was
- 3. Chennakesava R Alavala Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 3) January 2016, pp.104-109 www.ijera.com 106|P a g e continued for the composites having volume fraction of 30% Si3N4 as that prevailed from -300 o C to 0o C. The tensile strength increased with increase of volume fraction of Si3N4. The raster images of tensile strength are shown in Fig. 6 for clear understanding the penalty of temperature on the tensile strength. Fig. 4. Elastic (a) and thermo-elastic (b) strains developed in composites with 30%Vp nanoparticles. Fig. 5. Effect of temperature and volume fraction of Si3N4 on tensile strength. Fig. 6. Tensile strength induced in composites with (a) 10% and (b) with 30%Vp nanoparticles. Fig. 7. Effect of temperature and volume fraction of Si3N4 nanoparticles on the elastic modulus. The effect of temperature and volume fraction of Si3N4 nanoparticles on elastic modulus is shown in Fig. 7. It was observed that the effective elastic modulus of the composite increased with higher particle volume fraction and decreased with increase of temperature. The gain in the elastic modulus was observed below 0o C on account of increase in the stiffness of the composites (Fig. 8). The loss in the
- 4. Chennakesava R Alavala Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 3) January 2016, pp.104-109 www.ijera.com 107|P a g e elastic modulus was observed below 0o C on account of decrease in the stiffness of the composites. Fig. 8. Effect of temperature and volume fraction of Si3N4 nanoparticles on loss and gain of the elastic modulus. 3.2 Fracture Behavior The von Mises stress decreased with the increase of temperature increased from -300o C to 300o C (Fig. 9) for the composites having 30% Si3N4. This phenomenon was appeared from -300o C to 0o C for the composites having 10% Si3N4. This trend was inverse from -300o C to 0o C for the composites having 10% Si3N4. Within the nanoparticle various contours were also observed due to CTE mismatch between Si3N4 nanoparticle and AA5454 matrix. It was also noted that the maximum stress field in the vicinity of interphase was up to three to four times higher than that far away from the nanoparticle–matrix interfaces (Fig. 10). This implies a potential early debonding [20, 21]. At the subzero temperatures, the maximum stress field was in the normal direction of tensile loading. As the temperature increased ductile mode of failure was witnessed in the composites. Some structural changes were also locally occurred in the Si3N4 nanoparticle. Below 0o C, the Si3N4 nanoparticle was elongated in the normal direction of tensile loading while it was elongated in the direction of loading. At subzero temperature the failure mode was brittle in nature. The room temperature fracture in the AA5454/Si3N4 can be seen in Fig. 11. Fig.9. Effect of temperature and volume fraction of Si3N4 nanoparticles the von Mises stress. Fig. 10. Von Mises stress induced in the composites. Fig. 11. Fracture mode in AA5454/ Si3N4 composites. IV. CONCLUSION The thermo-elastic strain increased with increase in the temperature of AA5454/ Si3N4 metal matrix composites except for low volume fraction of Si3N4. As the temperature increased, the maximum stress occurred in the interphase region between the matrix AA5454 and Si3N4. The effective elastic modulus of the composite increased with higher particle volume fraction and decreased with increase of temperature.
- 5. Chennakesava R Alavala Int. Journal of Engineering Research and Applications www.ijera.com ISSN: 2248-9622, Vol. 6, Issue 1, (Part - 3) January 2016, pp.104-109 www.ijera.com 108|P a g e There was gain in the elastic modulus below 0o C and loss of it above 0o C. Acknowledgements The author is thankful to University Grants Commission (UGC), New Delhi for sponsoring this project. REFERENCES [1] A. C. Reddy and B. Kotiveerachari, Effect of Matrix Microstructure and Reinforcement Fracture on the Properties of Tempered SiC/Al-Alloy Composites, National conference on advances in materials and their processing, Bagalkot, 28-29th November, 2003, 78-81. [2] S. Sujatha and A. C. Reddy, Assessment of strength improvement in heat treated AA2024/SiC metal matrix composites using finite element analysis: experimental validation, National Conference on Advances in Design Approaches and Production Technologies (ADAPT-2005), Hyderabad, 22-23rd August 2005, 341-343. [3] M. Chamundeswari and A. C. Reddy, Evaluation of strength improvement in tempered AA5050/SiC metal matrix composites using finite element analysis: experimental validation, National Conference on Advances in Design Approaches and Production Technologies (ADAPT-2005), Hyderabad, 22-23rd August 2005, 338-340. [4] A. C. Reddy, Mechanical properties and fracture behavior of 6061/SiCp Metal Matrix Composites Fabricated by Low Pressure Die Casting Process, Journal of Manufacturing Technology Research, 1(3&4), 2009, 273-286. [5] A. C. Reddy, Tensile fracture behavior of 7072/SiCp metal matrix composites fabricated by gravity die casting process, Materials Technology: Advanced Performance Materials, 26(5), 2011, 257- 262. [6] K. Swapna Sudha and A. C. Reddy, Tensile performance of heat treated AA2024/Al2O3 metal matrix composites using RVE models: experimental validation, National Conference on Advances in Design Approaches and Production Technologies (ADAPT-2005), Hyderabad, 22-23rd August 2005, 332-334. [7] V. K. Prasad and A. C. Reddy, Tensile behavior of tempered AA5050/Al2O3 metal matrix composites using RVE models: experimental validation, National Conference on Advances in Design Approaches and Production Technologies (ADAPT-2005), Hyderabad, 22-23rd August 2005, pp. 335-337. [8] A. C. Reddy and Essa Zitoun, Tensile properties and fracture behavior of 6061/Al2O3 metal matrix composites fabricated by low pressure die casting process, International Journal of Materials Sciences, 6(2), 2011, 147-157. [9] A. C. Reddy and Essa Zitoun, Tensile behavior 0f 6063/Al2O3 particulate metal matrix composites fabricated by investment casting process, International Journal of Applied Engineering Research, 1(3), 2010, 542-552. [10] A. C. Reddy, Studies on fracture behavior of brittle matrix and alumina trihydrate particulate composites, Indian Journal of Engineering & Materials Sciences, 9(5), 2003, 365-368. [11] E. Carreno, S.E. Urreta and R. Schaller, Mechanical spectroscopy of thermal stress relaxation at metal-ceramic interfaces in Aluminum-based composites, Acta Materialia, 48, (2000), 4725-4733. [12] A. C. Reddy and Essa Zitoun, Matrix al- alloys for alumina particle reinforced metal matrix composites, Indian Foundry Journal, 55(1), 2009, 12-16. [13] B. Ramana A. C. Reddy, and S. S. Reddy, Fracture analysis of mg-alloy metal matrix composites, National Conference on Computer Applications in mechanical Engineering, Anantapur, 21st December 2005, 57-61. [14] A. C. Reddy, Experimental Evaluation of Elastic Lattice Strains in the Discontinuously SiC Reinforced Al-alloy Composites, National Conference on Emerging Trends in Mechanical Engineering, Nagpur, 5-6th February, 2004, 81 [15] A. C. Reddy and B. Kotiveerachari, Effect of aging condition on structure and the properties of Al-alloy / SiC composite, International Journal of Engineering and Technology, 2(6), 2010, 462-465. [16] M. Taya and R.J. Arseanult, Metal Matrix Composites, ( Pergamon Press, Oxford, 1989). [17] B. Balu Naik, A. C. Reddy and T. K. K. Reddy, Finite element analysis of some fracture mechanisms, International Conference on Recent Advances in Material Processing Technology, Kovilpatti, 23-25th February 2005, 265-270. [18] D. Duschlbauer, H.J. Bohm and H.E. Pettermann, “Computational simulation of
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