PSI - Issue 14

Puneeth N et al. / Procedia Structural Integrity 14 (2019) 53–59 Structural Integrity Procedia 00 (2018) 000 – 000

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Toughness. Stress-intensity factor (K) is the important parameter to determine the fracture toughness of most materials. Determination of the fracture related problems for design applications are very much essential as fracture related issues and can be pre determined during machining and testing as it inhibits for future loss and excess revenue accomplishments. Completing the production helps in identifying to know the spam device. Areas relating to more complex/sensitive become very important to know the fracture property as in to exclude major damage and loss of the device (machine).Complex areas include aerospace, thermal, nuclear engineering, space ships, rockets, piping and offshore structures [6].Crack tip opening displacement (CTOD) and J -Integral are two important fracture evaluation parameters in Elastic Plastic Fracture Mechanics (EPFM) and are being extensively followed for many industrial and structural applications. The objective of this method is reaching the best result with minimum experiments [7]. Orthogonal arrays (OAs) are the most important tools used by this method. It allows studying many process control factors simultaneously and can be used to evaluate the effect of each factor independent of the other factors [8]. The main effects indicate the general trend of influence of each parameter. Also, a statistical analysis of variance (ANOVA) is performed to see suitable parameter is statistically significant. Finally, a confirmation test is conducted to verify the optimal process parameters obtained from the process parameter design. 2. Materials and Methods Al6082 alloy with the chemical composition given in Table 1 below was used as the matrix material. Alumina (Al 2 O 3 ) and Aluminium silicate (Al 2 SiO 5 ) particulates were used as reinforcement with particle size of around 25μ and 30μ respectively. The hybrid composites were developed using stir cast method [9]. Table 1 Element Si Mg Mn Fe Cr Zn Cu Al % 1.3 1.2 1 0.5 0.25 0.2 0.1 Balance Al 2 SiO 5 was kept constant at 4wt% and Al 2 O 3 was varied from 3wt% to 9wt% in steps of 3viz. 3, 6 and 9. Tensile tests were performed on rectangular sectioned specimens of thickness 6 mm and gauge length 25 mm. The tests were conducted by the ASTM E8 standard. All tests were carried out with the help of a 100kN servo-hydraulic Universal Testing Machine. The software had facility for controlling the test control parameters, like strain rate, cross head speed and data acquisition system on load, displacement and extensometer in the channels. Charpy impact toughness test were conducted on Indian standard specimen with dimension 10mmX10mm square cross section with 55mm length, provided 2 mm deep V-notch notched at one side at mid-point of its length according to ASTM E23.The elastic plastic fracture toughness parameter J-integral were done on SENB specimen with width 25 mm and the thickness 12.5 mm. Each SENB specimen was fatigue pre-cracked by machine to generate a sharp initial crack and made ready according to ASTM E813.Taguchi technique was used for design of experiments (DOE) to improve the performance of products, process design and system. This method determines the most influential process parameter on result response for extensive improvement in overall performance. Three level L9 3 3 orthogonal array was selected and in total nine specimens were subjected for tests. 3. Results and Discussion Fabrication of hybrid MMC’s with Al 2 O 3 and Al 2 SiO 5 particles by stir casting processes is usually difficult due to low wettability of Al 2 O 3 and Al 2 SiO 5 particles. Agglomeration phenomena which leads to uneven distribution and exhibits poor mechanical properties. In this study, an attempt has been made to prepare hybrid MMC’s by incorporating Taguchi’s design model by using three process parameters i.e. wt. % of Al 2 O 3 (3, 6, 9), stirring speed (150, 200, 250 rpm) and stirring time (5, 10, 15 min), where each parameter has three levels. Al6082 matrix composites with Al 2 O 3 and Al 2 SiO 5 particles of 30 microns 3 stage mixing combined with reinforcing preheating. Here 4 wt. % of Al 2 SiO 5 particles used in each level with varying Al 2 O 3 particles with 3, 6, 9 wt. %. The optical micrographs of all nine types of composites are shown in Fig 1.Composites with 6 and 9% wt.%, 200 and 252 rpm stir speed and 10 and 5 min have uniform distribution of reinforcement particles and the dendritic structure are seen clearly . Al 2 O 3 particles have good bonding with base so that it gives improved properties. B3, B4, B5, B6, B7 have good result in terms of strength, hardness and uniform distribution.