Experimental and Finite Element Analysis of Fracture Toughness on Al/SiCp MMCs in Different Conditions

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1 Volume-5, Issue-5, October-2015 International Journal of Engineering and Management Research Page Number: Experimental and Finite Element Analysis of Fracture Toughness on Al/SiCp MMCs in Different Conditions C.Rajaravi 1, P.R.Lakshminarayanan 2 1,2 Department of Manufacturing Engineering, Annamalai University, Annamalai Nagar, INDIA ABSTRACT Aluminum alloy and 6% volume fraction SiC p MMCs have been fabricated by using stir casting at different pouring temperature, cast with permanent. In this present study, mechanical properties (i.e.), Tensile and Hardness properties were studied. The, hardness and tensile strength of the composites are higher than the best processing temperature in this study seems to be 750 C. Finite element (FE) simulations for the proposed 3 point bend (3PB) geometry was carried out using ANSYS software package (v13) to compute K I with quarter-point crack-tip elements was used, which results correlate with experimental values. The predicted results were in good agreement with the experimental values. The observation of SEM micrographs shows homogenous distribution of the reinforcement particles in the cast composite. Keywords---- Aluminum Matrix Composites, Reinforcement, Scanning Electron Microscope, Titanium di-boride. I. INTRODUCTION With increasing demand in vehicle weight reduction for fuel efficiency with cast aluminium components have drawn great attention in automotive industries, due to their excellent cast ability, corrosion resistance and especially high strength to weight ratio [1][2]. Particle reinforced metal matrix composites (PRMMCs) have become very promising materials due to their significant advantages over conventional materials such as high specific modulus improved resistance to high cycle fatigue and fatigue crack threshold high stiffness to weight ratio low co efficient of thermal expansion and high thermal conductivity [3][4]. Stir casting is a liquid state method of fabrication of composite materials in which a dispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal by means of mechanical stirring. Stir casting is the simplest and the most cost effective method of liquid state fabrication. The smooth transfer of the dispersions into the melt, impeller design, mixing and casting conditions are the important steps involved for the uniform distribution of the dispersions [5] [6]. is an indication of the amount of stress required to propagate a preexisting flaw. It is a very important material property since the occurrence of flaws is not completely avoidable in the processing, fabrication, or service of a material/component. Flaws may appear as cracks, voids, metallurgical inclusions, weld defects, design discontinuities, or some combination thereof. Since engineers can never be totally sure that a material is flaw free, it is common practice to assume that a flaw of some chosen size will be present in some number of components and use the LEFM (Linear Elastic Fracture Mechanics) is considered for a brittle material where only elastic analysis is carried out to determine stress and displacement fields near the crack tip with characterizing parameters like Stress Intensity Factor (SIF). The critical crack length when the stress intensity factor is equal to the fracture toughness is to be determined [7] [8]. Failure analysis are mainly based on experimental analysis recently Finite element analysis has become a novel and supplementary approach to failure analysis. This is applied in many of the mechanical engineering problems and results obtained are found to be agreeable with the experimental results. For i.e. Numerical simulations of tubular shell subjected to combined loading were conducted. The analytical solutions showed excellent agreement with the numerical results predicted by FEM [9]. The purpose of this paper is to experimentally evaluate the fracture toughness, hardness and tensile properties. Then finite element analysis is carried out to validate the obtained results [10]. 320 Copyright Vandana Publications. All Rights Reserved. II. EXPERIMENTAL WORK

2 Aluminium (A356) was used as the base metal and SiCp used as reinforcement. Aluminium was melted at different conditions i.e. 730 C, 750 C, 770 C, after which the SiCp are preheated at 250 C maintained about 30 min. After that the powder were added into the molten Aluminium by using the stirring method. The stirring of molten metal was continuously up to 30 min. The Al/ SiCp MMCs were fabricated by sand mould and permanent mould conditions and to analyze mechanical behaviours. The fracture toughness specimens were pre cracked in accordance with ASTM E399 to provide a sharpened crack of adequate size and straightness. The applied load ranges were determined from the geometry of the test specimens and material properties, and remained fixed throughout the tests. The tests were continued until the specimens failed ultimately due to unstable crack growth or fracture. test was carried out in the Instron 8801 testing machine is shown in Fig.1. The fracture toughness test specimens as shown in Fig.2. Figure 2: specimens a) before testing b) after testing conditions Tensile test Tensile specimens were prepared according to ASTM standards E8-03. In each casting two samples were tested. Tensile test was carried out at UTM servo hydraulic testing machine. The average results were obtained for final value. The tensile test specimens as shown in Fig.3. Figure.3.a Figure.1. Instron Testing Machine Figure.3.b Figure 3: Tensile specimens a) before testing b) after testing conditions Figure.2.a Hardness test The hardness tests were carried out by Brinell hardness testing machine and determine the hardness value for each three samples were tested. The average results were obtained for final value. The hardness test specimens as shown in Fig.4. Figure.2.b Figure.4 Figure 4: a) Permanent mould specimens before and after testing 321 Copyright Vandana Publications. All Rights Reserved.

3 III FINITE ELEMENT ANALYSIS This section presents a finite element modeling for the size of 3PB specimen, made as per ASTM (E399) standard. Half specimen was modelled using symmetry boundary conditions as shown in Fig.5 (a-b). These triangular elements are available in ANSYS.13 in two dimensions by modifying the PLANE (8node183) element using the KSCON command. The FE models initially formed with elastic material properties, E = 77.2E3 MPa and γ = 0.35, and a load P of 25 Mpa and Mesh the CT specimen. The nodes at the quarter points adjacent to the crack tip ensure that the displacements in the near-tip region are proportional to r (where r is the distance from the crack tip) the Stress intensity factor K IC is the relevant fracture parameter to characterize the stress and strain fields around the crack tip as shown Fig.5 (c). ANSYS Parametric Design Language, APDL, is employed for creating the fully automatic program to simulate the problem without any user interaction through this process. Figure 5: (a-c) Image of the FE model simulating the 3PB test. IV. RESULTS AND DISCUSSION Microstructure Fig.6 (a-b) shows SEM Micrographs of Al-6 vol % of SiCp composites with different temperature. The SiCp particles were homogenously dispersed and uniform distribution of reinforcement particles in the matrix phase is observed from these SEM micrographs. There is good bonding between the matrix and reinforcement phases present in white and dark colure of SiCp and aluminium respectively. In compared to different levels of temperature particularly the casting were produced at 750 C temperature more number of SiCp particles were dispersed, because the reduced common defects such as porosity, fluidity and agglomeration. Figure.6(a) Figure.5.a) Figure.5.b) Figure.5.c) Figure.6(b) Mechanical Properties of Composites The fracture toughness results were arrived at with Instron Dynamic Testing Machine and Analysis by FEA of the 3PB specimen as shown in Fig.7. Hence the results arrived at experimentally are almost matching the theoretically predicated fracture toughness value for CT specimen. Under mode I (crack-opening) loading K I may be compared with a material's fracture toughness K IC in order to predict the stability of a crack. The fracture toughness was observed different poring conditions 750 C conditions 322 Copyright Vandana Publications. All Rights Reserved.

4 composites has higher toughness value predicted theoretically is Mpa m and that of corresponding experimentally found value is Mpa m. Mpa m Temperature C Exp FEA HARDNESS TEMPARATURE C Figure 8: Hardness of composite versus the processing temperature Figure 7: Effect of processing temperature on fracture toughness of composite on FEA and Experimental results. TABLE I FRACTURE TOUGHNESS, TENSILE STRENGTH AND HARDNESS OF COMPOSITE Temperature C Fracture toughness (Mpa m) Tensile Strength (MPa) Hardness (BHN) 730 C C C b) Tensile strength Fig.7 shows the UTS bar graph values with Al/SiCp samples compared with different Temperature 750 C composites has higher tensile strength UTS TEMPERATURE C Figure 7: Effect of processing temperature on tensile strength of composite on sand mould and permanent mould. b) Hardness The Brinell hardness test results shows the temperature increases hardness also increases certain level and it decreases, because the melt temperature at 750 C the formation of SiCp increased the strength also increases automatically the hardness of Al/SiCp also increases. V. CONCLUSION Aluminium (A356) SiCp were successfully fabricated different temperature. The SiCp was made to achieve a uniform distribution of particles and good bonding with matrix alloy. To compute K I by the finite element method (FE), quarter-point crack-tip elements is used. The results obtained in ANSYS exhibit a good agreement with the experimental finding. The fracture toughness value found experimentally is less as compared to ANSYS results. This may be attributed to the porosity and clustering of SiCp particles in the specimen The composite exhibit significant improvement the hardness and tensile strength, in comparison with different pouring temperature. The Brinell hardness and UTS of the aluminium vol 6% of SiCp are 152 MPa and 69 BHN as show in table I. Hardness and tensile strength were achieved higher value. So finally, it is concluded that the 750 C is certain more suitable for Al/SiCp composite fabrication. REFERENCES [1] KK. Chawla, Composite materials-science and engineering, 2nd ed. New York: Springer; p.102. [2] N. Chawla, KK. Chawla, Metal matrix composites, New York: Springer, [3] DJ. Lloyd, Particle reinforced aluminium and magnesium matrix composites, Int Mater Rev 1994; 39(1):1 21. [4] Rabindra Behera, Nihar Ranjan, Mohanta, G.Sutradhar, Distribution of SiC particulates in stir cast Aluminium alloy Metal matrix composites and its effect on mechanical properties. International Journal of Emerging trends in Engineering and Development Issue 2, Vol.1. [5] G. Durrant, B. Cantor, Characterization of Reinforcement Distribution in Cast Al-Alloy/SiC p Composites. Materials Characterization 1998, Volume 40, Issue 2, Pages [6] Zhang Jun, Zhang Peng, DU Yun-hui, YAO Sha-sha, Dispersion of SiC particles in mechanical stirring of A356- SiCp liquid, J. Cent. South Univ : Copyright Vandana Publications. All Rights Reserved.

5 [7] Alan Liu, Mechanics and Mechanisms of Fracture-An Introduction, ASM International Publications, (2005). [8] Purkar T. Sanjay and Pathak Sunil, Aspect of Finite Element Analysis Methods for Prediction of Fatigue Crack Growth Rate, Research Journal of Recent Sciences, 1(2), (2012). [9] Shariati Mahmoud, Fereidoon Abdolhosein and Akbarpour Amin, Investigation on Buckling Behavior of Tubular Shells with Circular Cutout, Subjected to Combined Loading, Research Journal of Recent Sciences, 1(7), (2012). [10] H.B. Shivaraja, B.S. Praveen Kumar, Expermental Determination and Analysis of Fracture Toughness of MMC, International Journal of Sciences and Research, 2012, Copyright Vandana Publications. All Rights Reserved.