Effect of thickness on Fatigue Crack Growth of Aluminium alloys

IOP Conference Series: Materials Science and Engineering You may also like PAPER • OPEN ACCESS Effect of thickness on Fatigue Crack Growth of Aluminium alloys To cite this article: Haftirman et al 2018 IOP Conf. Ser.: Mater. Sci. Eng. 343 012034 View the article online for updates and enhancements. - Inhibition of AA2024-T351 Corrosion Using Permanganate Samuel B. Madden and John R. Scully - Empirical Propagation Laws of Intergranular Corrosion Defects Affecting 2024 T351 Alloy in Chloride Solutions Christel Augustin, Eric Andrieu, Christine Baret-Blanc et al. - Formation of a Trivalent Chromium Conversion Coating on AA2024-T351 Alloy J. Qi, T. Hashimoto, J. Walton et al. This content was downloaded from IP address 3.237.24.134 on 24/01/2023 at 00:14 ICEAMM 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 343 (2018) 012034 doi:10.1088/1757-899X/343/1/012034 1234567890‘’“” Effect of thickness on Fatigue Crack Growth of Aluminium alloys Haftirman1, Haris Wahyudi1, Julpri Andika2, and Noor Afifah Yahadi3 1 Department of Mechanical Engineering, Faculty of Engineering, Universitas Mercu Buana, 11650 Jakarta, Indonesia. 2 Department of Electrical Engineering, Faculty of Engineering, Universitas Mercu Buana, 11650 Jakarta, Indonesia. 3 Universiti Malaysia Perlis, Malaysia hatirman@gmail.com Abstract. The effect of thickness on fatigue crack growth has been investigated for aluminium alloys such as a high-strength aluminium alloy (A7075-T6), a medium strength alloy (A6063T6), and A2024-T351. The fatigue tests were conducted using Instron 8801 fatigue testing machine on all those materials with thicknesses of 12.7, 15.8, and 20 mm. All specimens were undergoing finishing process on the surface. These tests were run under constant amplitude load for each different thickness and materials. Fatigue crack growth specimen made of A2024-T351 and A6063-T6 aluminum alloys with thickness of 12.7 mm were higher than specimen made of A7075-T6 aluminum alloy with thickness of 20 and 12.7 mm and A6063-T6 aluminum alloy with thickness of 15.88 mm. It is concluded that fatigue crack growth decreases significantly with increasing thickness, and the crack initiates very fast on surface material. 1. Introduction In a previously paper, the fatigue crack initiation and growth of aluminium alloy A7075-T6, A6063T6 and A2024-T351 with various stress ratios were investigated using the compact test specimens having thickness of 12.7 mm [1]. The result found that the gradients of crack growth rate increase while the stress ratio, R increase. Higher R ratio result in higher value range of minimum applied load. Using the sheet specimens having an edge notch 3 mm deep and 0.1 mm root radius at stress ratios R raging from -0.5 to 0.5, the result shows that the fatigue crack propagation rate was dependent on the stress ratio that was the higher the stress ratio, the higher the rate of fatigue crack growth for a given ΔK value [2]. The present paper is concerned with an effect of thickness on fatigue crack growth of aluminium alloy. Effect of thickness in fracture of 2219-T851, 6061-T651,7075-T6, 7075–T651, and 7079-T651aluminum alloy [3,4], the result show that value of KIc generally increase with increasing specimen thickness. Then, the amount of fatigue crack growth of 2024-T3 aluminum alloy delay increases with decreasing sheet thickness. This behavior is attributed to greater plastic strains associated with the larger plastic zone size formed under plane stress conditions [5]. With finite element analysis and experimental of critical crack-tip-opening angle (CTOA) in 2024-T351 aluminum alloy, the result shows both computationally and experimentally that the critical surface CTOA value continues to decrease for increasing specimen thickness [5,6]. The present thickness of specimens is used 20, 15.7, and 12.7 mm will investigate the fatigue crack growth of aluminum alloy. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 ICEAMM 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 343 (2018) 012034 doi:10.1088/1757-899X/343/1/012034 1234567890‘’“” 2. Materials and Experimental Procedure The fatigue tests were conducted using Instron 8801 fatigue testing machine on aluminium alloys such as a high-strength aluminium alloy (A7075-T6), a medium strength alloy (A6063-T6), and A2024T351 with thickness of 12.7, 15.8, and 20 mm. All the specimen designs were referred to the ASTM E647-11 standard for compact test for fatigue crack growth rate testing. One of the specimens is shown in Figure 1. Recommended thickness and suggested minimum dimensions are provided to ensure the results or data obtained are valid and full in the ranged of predominantly elastic condition with the force applied. All specimens were undergoing finishing process on the surface. These tests were run under constant amplitude load for each different thickness and materials. The standard test method consists of determining the fatigue crack growth rate near threshold to maximum stress intensity controlled instability. The dimensions stated were provided with the tolerance. Design is done by AutoCAD software. Since the EDM wire cut machine is only support with the AutoCAD software drawing. Table 1 and Table 2 show the mechanical properties and chemical compositions of all types of aluminium alloy. Instron console software is the software that collaborates with the Instron 8800 to transfer the setting on the software successfully to the Instron 8801 Hydraulic Server Machine. The fatigue crack growth experiment was conducted using Instron 8801 Hydraulic Server Machine. After the data acquisition system, the specimens were further analysing using the Scanning Electron Microscope (TM3000 Table top Microscope). SEM was used to analyze on specimen surface and the crack propagation area to identify the crack initiation and the fatigue behaviour on the particular locations. Paris law is used to describe the long crack behavior under constant amplitude loading with the small range of yielding. Further modification on Paris law are needed for describe the overall crack growth, the effect of stress ratio and the effect of high amplitude loading [12]. Paris= fatigue crack growth rate, = Stress Erdogan equation can be shown as in Eq. (1) where intensity factor range, C and m are the coefficients of material constants. Figure 1. Standard Compact Specimen for fatigue Crack Growth Rate Testing [11], dimension is in mm and degree. Table 1. Mechanical Properties of Aluminum Alloy Aluminum alloy Yield Strength (MPa) Tensile Strength (MPa) A2024-T351 290 444 A6063-t6 172 207 A7075-T6 535 585 2 ICEAMM 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 343 (2018) 012034 doi:10.1088/1757-899X/343/1/012034 1234567890‘’“” Table 2. Chemical Composition of Aluminum Alloy (%wt) Materials Si Fe Cu Mn Mg Cr Zn Ti A2024-T351 0.11 0.15 4.58 0.66 1.54 0.02 0.04 0.032 A6063-T6 0.42 0.22 0.04 0.05 0.48 0.02 0.03 0.03 A7075-T6 0.10 0.38 1.52 0.10 2.6 0.21 5.55 0.03 3. Results and Discussion 3.1. Fatigue crack growth of A2024-T351, A6063-T6, and A7075-T6 aluminum alloy. Fatigue crack growth experiments under constant stress amplitude have been carried out in order to investigate the effect of thickness on fatigue crack growth aluminium alloys. The fatigue crack growth curves da/dN vs ΔK is shown in Fig. 2 for all sizes of specimen. This figure shows as prediction of fatigue crack growth on A2024-T351, A6060-T6, and A7075-T6 aluminum alloys. Fatigue crack growth specimen made of A2024-T351 and A6063-T6 aluminum alloys with thickness of 12.7 mm were higher than specimen made of A7075-T6 aluminum alloy with thickness of 20 and 12.7 mm, and specimen made of A6063-T6 aluminum alloy with thickness of 15.88 mm. It can be seen that aluminum alloy with thicker size has lower fatigue crack growth rate in stress intensity, ΔK region (10-20 MPa m1/2) significantly than that thinner size of specimen, which according to [8] are evidence of ΔK region the same as result for A2024-T351 aluminum alloy. Specimen with thickness of 20 mm for A7075-T6 aluminum alloy material, fatigue crack initiation and crack propagation were faster than others of aluminum alloy. da/dN (m/cycle) 1.00E-05 1.00E-08 2024-12.7 7075-12.7 1.00E-06 7075-20 6063-12.7 6063-15.88 1.00E-07 ΔK (MPa m^1/2) Figure 2. Fatigue crack growth rate for all types of aluminum alloy with difference specimen size 3 ICEAMM 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 343 (2018) 012034 doi:10.1088/1757-899X/343/1/012034 1234567890‘’“” 0.1 0 20.64 21.14 21.71 22.29 22.91 23.44 23.92 24.41 25.06 25.71 26.24 26.76 27.35 27.99 28.77 29.59 30.58 32.00 3.2. Effect of thickness on A2024-T351, A6063-T6, and A7075-T6 aluminum alloy As mentioned earlier, fatigue crack growth of aluminium alloy specimen with thickness of 20 mm is higher than that of aluminum alloy specimen with thickness of 12.7 and 15.8 mm. However, fatigue crack growth based on crack length, the result show that specimen with thickness of 12.7 mm for A7075-T6 aluminum alloy is faster than of specimen with thickness of 20, and 15.8 mm for A7075T6, A6063-T6, and A2024-T351 aluminum alloy. The effect of thickness on the fatigue crack growth for A7075-T6, A6063-T6, and A2024-T351 with thickness of 12.7, 15.8, and 20 mm is shown in Figure 3. Figure 3 shows that the crack length for A7075-T6 aluminum alloy materials specimen with thickness of 12.7 mm initiates at crack length of 20 mm and then crack propagate up to failure with crack length of 23.92mm. For A6063-T6 specimen with thickness of 15.88, and 12.7 mm and A2024T351specimen with thickness of 12.7 mm, crack initiates at crack length of 20 mm and propagate up to failure at similar crack length around 27.99 mm. Fatigue crack growth of A7075-T6 specimen with thickness of 20 mm initiates slower than that of other aluminum alloy. It can be seen that retardation occurrence of this crack due to the A7075-T6 specimen was thicker than that of other specimen. Figure 4 shows crack length versus number of cycles curve. This figure indicates that at lower number of cycles, A7075-T6 specimen with thickness of 12.7 mm crack occurs faster than that of A6063-T6, A7075-T6, A2024-T351 and A7075-T6 specimen with thickness of 12.7, 15.88, 12.7, and 20 mm, respectively. Similarity the result from Figure 3 that fatigue crack growth based on crack length, A7075-T6 specimen with thickness of 12.7 mm initiates faster than that of other specimen. da/dN (m/cycles) 0.01 0.001 7075-T6, 12.7 7075-T6, 20 6063-T6, 15.8 6063-T6, 12.7 0.0001 2014-T351,12.7 1E-05 Crack Length a (mm) Figure 3. Effect of thickness on fatigue crack growth for all types aluminum alloy with difference specimen size 4 ICEAMM 2017 IOP Publishing IOP Conf. Series: Materials Science and Engineering 343 (2018) 012034 doi:10.1088/1757-899X/343/1/012034 1234567890‘’“” 37 7075-20mm 35 Crack length (mm) 33 7075-12.7mm 31 29 6063-15.88 27 6063-12.7mm 25 2024-12.7mm 23 21 19 0 10000 20000 30000 Number of cycles Figure 4: Crack length versus Number of cycles curve. 4. Conclusion The effect of thickness on fatigue crack growth of aluminum alloys such as A2014-T351, A7075-T6, and A6063-T6 specimen with thickness of 12.7, 15.8, and 20 mm was investigated. Fatigue crack growths of A2024-T351 and A6063-T6 aluminum alloy specimen with thickness of 12.7 mm were higher than A7075-T aluminum alloy specimen with thickness of 20 and 12.7 mm, and A6063-T6 aluminum alloy specimen with thickness of 15.88 mm. It is concluded that fatigue crack growth of aluminum alloy decreases significantly with increasing thickness, and the crack initiates very fast on aluminum alloy material. Based on the number of cycles was found similar result that the crack size of 12.7 mm was faster than size of 20 and 15.8 mm. This conclusion should assist the designer in optimizing aluminum alloy selection for fracture resistant aluminum engineering structures. 5. References [1] [2] [3] [4] [5] [6] [7] [8] Haftirman Idrus, M. Afendi, Wong Chun Hoe,”Fatigue crack initiation and growth of aluminum alloy with aatio effects,” Key Engineering Materials, vol 594-595,pp. 1105-1111, 2013. Omer G. Bilir and Metin Harun,”Effect of stress ratio on the rate of growth of fatigue cracks in 1100 Al-alloy,” Engineering Fracture Mechanics, vol 37, 6, pp. 1203-1206, 1990. Robert E. Zinkham,”Anistropy and thickness effects in fracture of 7075-T6 and–T651 aluminum alloy,” Engineering Fracture Mechanics, vol 1, pp. 275-289, 1968. Nelson. F. G, Schilling, P. E and Kaufman. J. G,”The effect of specimen size on th results of plane-strain fracture –toughness tests,” Engineering Fracture Mechanics, vol 4, pp. 33-50, 1972. Mills. W. J, and Hertzberg. R. W,”The effect of sheet thickness on fatigue crack retardation in 2014-T3 aluminum alloy,” Engineering Fracture Mechanics, vol. 7, pp. 705-711, 1975. Samer Mahmoud and Kaven Lease,”The effect of specimen thickness on the experimental characterization of critical critical crack-tip-opening angle in 2024-T351 aluminum alloy,” Engineering Fracture Mechanics, vol. 70, pp. 443-456, 2003. Samer Mahmoud and Kaven Lease,”Two-dimensional and three-dimensional finite element analysis of critical crack-tip-opening angle in 2024-T351 aluminum alloy at four thicknesses,” Engineering Fracture Mechanics, vol. 71, pp. 1379-1391, 2004. Kermanidis, A.T and Pantelakis, Sp. G,” Prediction of crack growth following a single overload in aluminum alloy with sheet and plate microstructure”, vol.78,pp. 2325-2337, 2011. 5