Page 1 of 26 EVOLUTION OF 52CRMOV4 FROM 51CRV4 MATERIAL TO WITH STAND FIELD SEVERITY OF PARABOLIC LEAF SPRING SUSPENSION IN HEAVY DUTY COMMERCIAL VEHICLE Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. P.Thangapazham1), L. A.Kumaraswamidhas1) *, D.Muruganandam2) T. Dharanivendhan3) 1) Dept of Mining Machinery Engg, Indian Institute of Technology (ISM), Dhanbad, 826004, India. 2) Dept of Mechanical Engg, Jeppiaar Institute of Technology, Chennai-631604, India. 3) Dept of Mechanical Engg, Indian Institute of Technology, New Delhi-110016, India. E-mail : [email protected] Received July 2018, Accepted December 2018 No. 00-CSME-00, E.I.C. Accession Number 0000 Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 1 Page 2 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. ABSTRACT The investigative study is mainly focused on improving the fatigue life of leaf spring through the following protocols. Protocol-1: The parabolic leaf spring is manufactured with 51CrV4 material through the normal production process, which results in low residual compressive stress and high decarburization. The proto sample does not support severe field application. This issue is resolved by optimizing heat treatment and shot peening process. The proto part is prepared and tested in the Rough Road conditions and the vehicle withstands the field severity up to 10% higher than the design load. However, in highly severe field operation, the severity goes up to 30% higher than design load. Hence, the above process improvements could not sort out the failures of 51CrV4 material. An alternate material is identified 52CrMoV4 and investigated in the protocol 2: In this investigation, the spring proto part is manufactured directly through optimized process. The residual compressive stress, decarburization and mechanical properties are obtained at the desired levels. The proto part is tested in Rough Road conditions; the suspension system can now withstand 30% of field severity. The vehicle was tested in the test track and covered 335 thousand Kilometers in off road distance, with met durability requirements. Keywords: Fatigue life, Residual compressive stress, Hardness, Microstructure and Tensile strength. TITRE FRANÇAIS DE L’ARTICLE (MAXIMUM DEUX LIGNES) RÉSUMÉ Le résumé français est obligatoire. Évidement, si l’article est rédigé en français, le titre principal et le résumé principal sont en français. Par contre, il ne faut pas traduire le texte « Received…Accession Number 0000 ». Mots-clés : premier mot-clé; deuxième mot-clé; troisième mot-clé. Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 2 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 3 of 26 1. INTRODUCTION In mining applications, parabolic leaf spring suspension system is mainly used with high strength materials. The vehicle under consideration has two front axles, which are fitted to the chassis with parabolic leaf spring suspension system. The axle supports the steering components. The main function of the suspension system absorbs the impact forces and vibrations and reduces its impact to chassis frame. A double acting shock absorber is attached with a U-bolt clamping in order to dampen the vibration. The other components include the anti-roll bar is mounted between the front axle and the vehicle frame to protect it from the vehicle rollover behavior. The individual leaf of the multi leaf suspension system is in the shape of a parabolic with variable thickness from center to both ends to achieve optimum spring rate and stress distribution. The rear side of vehicle, it is fitted with an anti-roll bar for better control, stability and reduce roll angle. The general overview of the parabolic leaf spring is shown in Fig.1. Fig.1. Parabolic leaf spring suspension overview The microstructure of a leaf spring greatly determines the fatigue life of leaf spring, which can be attained by appropriate surface treatment (Fragoudakis et al. 2017). Normally, the surface treatment by shot peening as well as heat treatment improves the mechanical properties and fatigue life of the components. The first evaluation of parabolic leaf spring made of 51CrV4 is chosen in this investigation and it is one of the conventionally used spring steel for heavy-duty commercial vehicle suspension system. The main merits of parabolic leaf spring used in suspension system are high fatigue strength and lightweight (Soner et al. 2011). The processes like quenching, tempering and shot peening are important to sustain the amount of residual compressive stresses in the component (Todinv 2000). The leaf spring is manufactured using 51CrV4 material by normal shot peening and heat treatment process, the residual compressive stress increases only up to 310 MPa and decarburization level is found to be 0.30mm. The achieved values of mechanical properties are not sufficient to withstand the field severity and hence the surface treatment by shot peening and heat treatment process were optimized. Specifically, the tensile strength of material increased up to 1535 MPa in 51CrV4 and 1720 MPs in 52CrMoV4. Higher Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 3 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 4 of 26 intermolecular attraction is achieved over the entire component through tempering process. In this process unwanted gases come out of the component, which enables finer grain size. Therein, the component changes from tempered maternsite to fine martensite with good intermolecular attraction. The proto model is prepared with material of 51CrV4 and tested in Rough Road conditions; no premature failure occurred and withstood field severity of 10%. However, in mining application, the filed severity goes up to 30% extra of the design load. The failure in a leaf spring normally occurs based on the following factors-low quality of material, poor design, and poor manufacturing techniques (Fuentes et al. 2008). The leaf spring ensured higher level of safety during dynamic and static conditions (Soner et al. 2013). The first material of 51CrV4 did not support the required field severity conditions. To sort out this issue, an alternate material of 52CrMoV4 was identified. The new material was used to manufacture the parabolic leaf spring in the optimized process. The results shows that the induced residual stress reaches max of 744 MPa, decarburization level reduces to 0.0781 mm, desired levels of micro structure and hardness are also obtained and the tensile strength of material increases to 1720MPa with percentage of elongation of 6.5%. Using the material of 52CrMoV4, the proto model is prepared and tested on Rough Road conditions. Metallographic Microscope measures the decarburization level, Brinell hardness testing machine measures hardness, residual compressive stress is measured by X-Ray Diffractometer and Universal Testing Machine measures the tensile strength. To ensure durability, the components were tested for success until particular expected life cycles. The damage calculation results were used to evaluate the durability of the component. The durability limit set in terms of kilometers run on Rough Road conditions of the test track, has an established co-relation to actual field operation life expected. No premature failure occurs in normal load and system withstands the field severity of 30% of more than the design load and the vehicle does not fails after completing 335 thousands kilometers equivalent operation in normal off road conditions. 2. FAILURE LOCATION The failure of leaf spring is mainly due to field severity. The field severity is nothing but the vehicle’s ability to withstand load more than the design load. The following are various types of field severity that affect the failure of leaf spring-loading material on the scoop area, overloading in the load body, vehicle moving in downward gradient transfer of rear load to front axle pot holes or hair pin bend in which the left side load transfer to right side and vice versa. In rough road conditions, the vehicle is usually operated in controlled speed and load. In actual mining sites, the operation of the vehicle is done under poor terrain conditions and they are overloaded with heavy rocks. 30% withstand field severity 52CrMoV4 Spring Optimized 10% withstand field severity 51CrV4 Spring Optimized Sample tested -100 Nos Mining Truck- 93 Nos Failures in normal shot peening-%1CrV4 spring 51CrV4 Fig.2a. Field severity withstand 51CrV4 &52CrMoV4 Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 4 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 5 of 26 From the Fig.2a, it can be inferred that the same vehicle part, which achieved target durability life in most of operational, sites but failed in few. In these sites, the vehicle is operated with varying acceleration and deceleration. Also during loading in mining operation, the canopy above the truck’s cabin that is meant to protect the cabin from rock falling is also abused by loading with material inadvertently. This additional load on front of vehicles is transferred to first front axle Fig.2b. Fig.2b. Overloading in Scoop and normal area In addition to above, the parabolic suspension system also withstands the vertical, horizontal forces and lateral forces acting on the body. The major load on the axle is the vertical load due to the weight. An additional vertical load also acts on the components during braking, since the entire load tends to shift to the front axle due to the inertia. According to the field data, the suspension system fails at two locations; at the eye end and at the main leaf behind U-bolt area, indicated as 1 and 2 respectively. From the Fig.3, Fig.3. Field severity -51CrV4 Spring Failure Location Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 5 Page 6 of 26 it is observed that 93 nos of vehicles failed among a batch of 100 mining truck at the front axle of leaf spring, failure U-bolt area - 68 nos and eye end failures is 25nos. Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Table 1. Stress limit eye end of leaf spring- 51CrV4 Thickness mm Stress Spec 20 min 27 Measured 22 23 Stress limit < 30 Kg/mm2 The eye end stress values were measured and found that the values are within limit, failure occurred mainly due to field severity. The measured values are tabulated in the Table.1. Thus by changing the material from 51CrV4 to 52CrMoV4 withstands 30% field severity. 3. MANUFACTURING PROCESS - 51CRV4 The raw material 51CrV4 is used for manufacturing parabolic leaf spring as per the flow diagram shown in Fig.4. Each leaf is manufactured separately as main leaf, 2/leaf, 3/leaf, and H1/leaf. The spring metal is heated to 1020C to form an eye on both ends of spring by mechanical operation. Fig.4. Parabolic leaf spring manufacturing process flow diagram From the center section to outer end, the spring is tapered. A special parabolic rolling process is used for manufacturing leaf spring in which the thickness of leaf spring decreases related to the square function of its length. The parabolic profile is needed to ensure uniform stress distribution. A parabolic leaf spring design is lighter than other type of leaf spring and has improved resistance and durability with the desired level of spring stiffness. The eye end of the spring is formed by curling process by maintaining the temperature between 840C and 900C then subsequently, the spring is hardened and cambered into required level as per the structured manufacturing processes. Finally, in the heat treatment process, spring steels is heated to temperature of 865C and held for 20 minutes until the phase transformation from ferrite into austenite is formed. It is followed by next process, which is soaking, in which the temperature of the leaf spring is maintained at 850C to obtain desired mechanical properties. The final process in parabolic leaf spring is tempering, in which process, the spring material is heated to desired temperature of 470C to remove hot spots and unwanted hardness of the steel converts into tempered Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 6 Page 7 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. martensite form. Finally, the surface integrity is improved by shot peening. In this process, balls with varied sizes impinge on the spring surface with higher velocity to induced desired level of residual compressive stresses. After shot peening process, machining operations like boring, reaming bushing operation are carried out and then component is painted for dispatch. The main dimension of parabolic spring is shown in the Fig.5. Fig.5. Parabolic spring drawing with dimension 4. POST PROCESS: HEAT TREATMENT AND SHOT PEENING 4.1.1 Optimized heat treatment process The heat treatment process needs to be optimized to reduce the decarburization level in the spring. Higher level of decarburization layer damage the strength of the component. (Zhao et al. 2016). In normal heat treatment process the decarburization level is seem to be greater,0.30mm in both materials due to uncontrollable entry of atmospheric air. In the optimized heat treatment process, the entry of atmospheric air is controlled. Due to this decarburization, level has reduced in both spring materials of 51CrV4 as 0.0906mm and in 52CrMoV4 is 0.0781mm. The spring is kept for 20 minutes at the temperature of 860C. Here, the spring material is converted from austenite into martensite. The spring enters into soaking zone at 850C and is held for max of 15minutes. The next stage of the manufacturing is tempering. Again, the component is heated to 550C, soaked at a temperature of 470C, and then cooled in oil at temperature of 70C bath. The material is converted from martensite into tempered martensite. Fig.6.Optimized heat treatment process Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 7 Page 8 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. During tempering, unwanted gases come out of the component, which improves strength and ductility. The optimized heat treatment process flow is shown in Fig.6. The hardness is measured in Brinell hardness testing machine as shown in the Fig.7. The decarburization is measured using Metallographic microscope and as shown in the Fig. 8. Fig.7. Brinell Hardness Testing Machine Fig.8. Metallographic Microscope 4.1.2 Optimized shot peening process In normal shot peening process, uniform ball sizes of 1.2 mm is used to impinge on the component for two minutes at room temperature with a velocity controlled by current of 33-35A on the spring top surfaces with single stage of peening. The induced residual compressive stress was found to be 310 MPa. This is shown in Fig.9a. In the optimized process, different sizes of hardened shot balls of 1.2 mm diameter-7%, 0.08 mm diameter-69% and 0.6 mm diameter-24% respectively are mixed and impinged with a higher velocity controlled by current of 35-40A. This high velocity of ball is impinged on the spring for the period of two minutes in two stages of peening which induces compressive stress of 738 MPa in 51CrV4 spring material and 744 MPa in 52CrMoV4 spring material surface. This is shown in Fig.9b. Fig.9a. Normal shot peening - same size of balls Fig.9b. Optimized shot peening -Different size of balls Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 8 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 9 of 26 Balls of higher radius impact the surface and leave gaps in between them, which is proportional to the radius of curvature. The smaller balls hit the surface left out by the bigger balls and create a uniform surface. Shot peening the surfaces induces plastic deformation, increasing the compressive stress on top layers, which in turn improves the fatigue life of the spring and results in prevents of cracks growth when the material tends to develop tensile load. By achieving, the desired level of residual compressive stress subsequently the fatigue strength of component is increased and prevents cracks in the component (Karaagac et al. 2012). Fig.9c. Shot Peening Machine The shot-peening machine is shown in the Fig.9c. The XRD method is used to measure the induced compressive stress on the spring surface. For measuring the above stresses, a specimen of 170 mm length is prepared. Fig.9d. X-Ray-Diffractometer-XRD The testing method of X-Stress 300 G2R was adopted and machine having Crα radiation tube was used for measurement. For residual stress calculation, 2ϴ-156.4 and young modulus of 200500 MPa was used. The XRD machine is shown in the Fig.9d. 5. Manufacturing process of 52CrMoV4 The manufacturing process of 52CrMoV4 leaf spring is similar to 51CrV4 material mentioned in the section.3. The normal manufacturing process does not give required mechanical properties and fatigue strength. Hence, 52CrMoV4 material is manufactured directly through optimized process. The tensile strength of material is increased by adding molybdenum to the leaf spring composition (Andoko and Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 9 Page 10 of 26 Poppy 2016). The material 52CrMoV4 has the composition of molybdenum with added chromium and vanadium to improve the hardenability of the alloy. They favour formation of BCC structure and increase the hardness of the material by forming substitutional alloy in the cold state. The proto part is manufactured and all the mechanical properties are measured. Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. 6. RESULT AND DISCUSSION 6.1.1 Results of heat treatment process In the normal process, there was leakage of atmospheric air entering into the heating zone, due to which decarburization level was 0.30 mm. The decarburization is controlled by arresting the air entry into furnace. During heat treatment the materials changes in two stages. In stage-1: The spring material transforms from austenite into martensite during cooling. Stage-2: In the tempering, the unwanted hardness is fully removed and the tensile property and ductility is increased, during which stage changes from martensite into tempered martensite. Fig.10. Decarburization in one location-51CrV4 and 52CrMoV4 While using the optimized heat treatment process, the spring material finally changed into fine tempered martensite. The low level of decarburization also subjected the material composition like SiliconManganese-Vanadium (Bang-Jun et al.1987). The desired level decarburization obtained in the optimized heat treatment process (Tekal 2002). The decarburization level of 0.0906 mm value was obtained in 51CrV4 and in 52CrMoV4 obtained 0.0781 mm, the metallographic microscope is used to measure the decarburization of both materials and results are shown in the Fig.10. Comparing the two materials decarburization level, the 52CrMoV4 material is very low compared with 51CrV4 material. This is shown in the Fig.11. Fig.11.Decarburization in four location-51CrV4 and 52CrMoV4 Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 10 Page 11 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. 6.1.2 Surface and core hardness test. Both of the spring materials 51CrV4 and 52CrMoV4 are manufactured through optimized heat treatment process. The surface and core hardness of both materials are measured in Brinell hardness testing machine and the values are shown in the Fig.12 and Fig.13. The tensile strength of the component of desired level can be obtained through right manufacturing process like quenching and tempering (Laroiya et al., 2007). Figure 12. Surface Hardness - 51CrV4 & 52CrMoV4 Fig.13. Core Hardness - 51CrV4 and 52CrMoV4 Comparison of the surface and core hardness values of both spring components is done. The material 52CrMoV4 possess higher values in both surface and core hardness. This is due to the addition of Molybdenum in the 52CrMoV4 material. Molybdenum has the natural mechanical properties of high hardenability & wear resistance and hence the surface and core hardness value are higher compared with 51CrV4. Due to the higher hardenability higher tensile strength material 1720 MPa is achieved. 6.1.3 Results of shot peening process The normal shot peening process could not achieve required results. For this reason, both materials of 51CrV4 and 52CrMoV4 are manufactured in the optimized process mentioned in the section 4.1.2. Comparing compressive of stress of both materials, the 52CrMoV4 achieved max compressive stress of 744 MPa and 51CrV4 material obtained only 738 MPa. Both the materials are manufactured using the Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 11 Page 12 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. same optimized process. Both materials induced good compressive stress and 52CrMoV4 obtained higher values. Hence, 52CrMoV4 material possesses superior quality than 51CrV4. Fig.14. Residual compressive stress 51CrV4 &52CrMoV4 The desired level of residual compressive stress is obtained using different ball sizes, higher velocities, double stage shot peening, for a period of two mins at room temperature. The induced compressive stresses are measured using XRD and values are plotted in the Fig.14. The X-Ray Diffractometer is used to measure the induced compressive stress in the components (Karaagac et al. 2012). Pre-stressing and shot peening is the origin to improve compress stress of the component and increase the fatigue life. (Bojan sen et al. 2011). 6.1.4 Microstructure The microstructures of 51CrV4 and 52CrMoV4 spring material are fully analyzed in this section using metallographic microscope. Table 2&Table3 show the chemical composition 51CrV4 and 52CrMoV4. After analyzing chemical composition of two materials. Table 2. Chemical Composition of 51CrV4 Element C Si Mn P S Cr Mo AL V Cu Actual 0.54 0.37 .05 0.015 0.003 1.20 0.014 0.012 0.16 0.014 Specification 0.470.55 <=0.40 0.70-1.10 Max.0.03 Max.0.03 0.90-1.20 - - 0.10-0.20 - Table 3.Chemical Composition of 52CrMoV4 Element Actual Specification C 0.49 0.48-0.56 Si 0.25 0.40 Mn 0.99 0.70-1.10 P 0.019 Max.0.025 S 0.006 Max.0.025 Cr 0.1 0.90-1.20 Mo 0.17 0.15-0.30 V 0.16 0.10-0.20 Cu - The sample was prepared using cutting machine, mounting machine and polishing machine. The samples were checked for any burn or heat marks. spacers were used for moulding two samples at a time. Sample preparation is shown in Fig.15a. Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 12 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 13 of 26 Fig.15a. Sample preparation machine The spring 51CrV4 manufactured with normal process produced decarburization of 0.30 mm and was found with higher level of partial decarburization. In the optimized, process with 51 CrV4 the decarburization was reduced to 0.0906mm and formed tempered martensite therein formed fine tempered martensite. This structure support 10% field severity. The new material of 52CrMoV4 structure had lower decarburization level of 0.0781mm and with higher-level fine tempered martensite. Fig.15b. Microstructure 51CrV4 and 52CrMoV4 The strength of compressive residual stress field near the surface decides the level of decarburization. The intensity of elastic deformation surface to form low decarburization and intensity of plastic deformation surface to form high decarburization. The shot peening process to control both elastic and plastic deformation to obtain required level of decarburization (De la Rosa et al. 2016). This material withstands higher level of field severity. The microstructure analyses of both materials are shown in the Fig.15b. 6.1.5 Tensile Test Materials 51CrV4 and 52CrMoV4. Both materials tensile test were conducted in Universal Testing Machine-UTM with test sample as shown in the Fig16a. and Fig.16b. Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 13 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 14 of 26 Fig.16a. UTM-Tensile Testing Machine Fig.16b. Tensile strength testing sample The first material test sample flat size of 90X27mm and length of 300mm of 51CrV4 material tested in the UTM as per the systematic test procedures, ASTMA 370-17 with Sec 6-14. In 51CrV4 tensile strength is observed to be 1535MPa, and percentage of elongation to be 6%. The second material of 52CrMoV4 prepared three test samples of same flat size of 90X27mm were tested in same machine and the values are tabulated in the Table 4. Table 4. Tensile strength test report of 52CrMoV4 Sample Tensile Strength(MPa) 0.2% Yield strength (MPa) 1 1716 1482 2 1720 1485 3 1720 1493 % Elongation on 50mm GL % of Reduction area 8.1 20.6 6.5 21.2 7.6 20.3 The material obtained the tensile strength is observed to be 1720MPa, and 0.2% offset yield strength of 1485MPa, and percentage of elongation, in 50mm GL, is 6.5% and percentage reduction area is 21.2. Comparing the above two, the 52CrMoV4 possesses higher value of tensile strength than 51CrV4. Hence, the material 52CrMoV4 is of superior quality to withstand field severity. 6.1.6 Field Test on RR 52CrMoV4 The final leaf spring sample is tested in Rough Road conditions. Rough road test was conducted with a load of GVW65T Vehicle. Nature of the normal road condition is unpredictable. Road condition is the prime cause for the limited life of the vehicle. Rough road makes the vehicle to vibrate under both no load condition and load condition. The vehicle runs on the following track articulated test track has zigzag profile with ups and downs. Pot hole test track was made on pots in hemispherical shape. Cobble stone test was set with blue metal cobbles. Gradient test track has radial slope. This is shown in Fig.17a,Fig17b.and Fig.c. The vehicle passed the targeted kilometers of 8334 in RR conditions, one RR Kilometer is equal to 40.19 normal off road kilometer; 8334 RR kilometer is equal to 335 thousand kilometers vehicle passed in normal off road and equivalent off road life of the vehicle passed 335 thousands kilometers. No premature failure occurred in the proto sample and the vehicle withstands the maximum field severity. These test were conducted to ensure the durability of the suspension system and stability of the vehicle. The total fatigue life of the component depend on manufacturing, microstructure, mechanical and surface properties (Giannakis et al. 2016). The proto model is shown in the Fig.18. Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 14 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 15 of 26 Fig.17.a. Gradient Track Fig.17b. Articulation & Pothole Track Fig.17c. Cobble stone track Fig.18. No Premature Failure Model 7. CONCLUSION The parabolic leaf spring material 51CrV4 and alternate new material 52CrMoV4, both are manufactured through optimized process and the tested results are compared. The induced residual compressive stress, decarburization level, microstructure, and mechanical properties are measured and discussed in results and discussion, section 6. The 52CrMoV4 is found to be more suitable than 51CrV4, based on the following conclusions. 1. In field application of 51CrV4 parabolic leaf spring, 93% of failures are observed due to severe field severity, this is due to lesser compressive residual stress induced in the component through normal shot peening with same size of ball. In optimized shot peening operation, different sizes of balls are used with higher velocity induced and high compressive stress 738 MPa obtained. This spring withstands only 10% of field severity. 2. The second material 52CrMoV4 is manufactured by same optimized shot peening process. The material obtained 744 MPa of residual compressive stress. The leaf spring’s fatigue life is increased and crack formation is prevented withstanding high impact load to meet field severity due to overloading. This material withstand 30% of field severity. 3. Surface and core hardness of 52CrMoV4 are found to be higher than of 51CrV4, which enhances the tensile strength of material to 1720MPa with 6.5% of elongation. 4. Microstructure of 51CrV4 material obtained fine martensite with decarburization level of 0.0906mm. The Material 52CrMoV4, obtained 0.0781 mm decarburization with fine tempered martensite. The less Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 15 Page 16 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. decarburization of 52CrMOV4 and finer uniform fine tempered maternsite support maximum field severity. 5. Proto part of 52CrMoV4 spring material is tested in test track the Rough Road conditions like pothole, articulation, gradient, and acceleration. The vehicle has passed the targeted values of 81334 kilometres in Rough Road conditions, withstanding 30% of field severity and no premature failure. This is equivalent to off road life of 335 thousands kilometres. 8. FUTURE SCOPE This investigation work will make the researchers to investigate further improvement performance of parabolic leaf spring through new techniques of heat treatment and shot peening. REFERENCES Andoko, and Poppy, P. 2016. Characteristics of leaf spring strength of material 65si7 and material C17000 using finite element method. Proceedings of the International Mechanical Engineering and Engineering Education Conferences (IMEEEC 2016). doi: 10.1063/1.4965799. Bang-Jun, S., Chuan-Pu, BI., and Ming-Liang,T. 1987.Application of double grooved spring steel 55SiMnVB in Aeolus truck EQ-140. SAE International. doi. 10.4271/871253. De la Rosa, Claudia E. Flores; Trejo, López, Eddy Alfaro. 2016. Effect of Decarburization on the Residual Stresses Produced by Shot Peening in Automotive Leaf Springs. Journal of Materials Engineering and Performance. doi.10.1007/s11665-016-2132-2. Fragoudakis, R., Michailidis, N., and Savaidis,G. 2017. Optimizing the development and manufacturing of 56SiCr7 leaf spring. Journal of Fatigue. doi.org/10.1016/j.ijfatique.2017.05.016. Fuentes, J.J., Aguilar, H.J., Rodriguez.J.A., and Herrera.E.J. 2008. Premature fracture in automobile leaf springs. Engineering Failure Analysis. doi. 10.1016/j.engfailanal.2008.02.008. Giannakis, E., M Malikoutsakis, M., and Savaidis, G. 2016. Fatigue Design of Leaf Springs for New Generation Truck. IOP Conf. Series, Materials Science and Engineering 161 (2016) 012065. doi:10.1088/1757899X/161/1/012065. Karaagac, M., Soner, M., and Togay, A. 2012. Material micro crack failure effects based on residual stress evaluations. SAE International. doi :10.4271/2012- 01-0187. Karaagac, M., Soner, M., and Togay, A. 2012. Material micro crack failure effects based on residual stress evaluations. SAE International. doi:10.4271/2012- 01-0187. Laroiya, S., Sharma, A., de Salis, R., and Holly, M Laroiya, S., Sharma, A., de Salis, R., and Holly, MLaroiya, S., Sharma,A., De Salis, R., and Holly,M. 2007. Hydrogen embrittlement failure in suspension leaf Springs. SAE International. doi. 2007-01-4257. Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 16 Page 17 of 26 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Nenad Gubeljaka, Mirco D., Chapettib, Jožef Predana, Bojan Sen., 2011.Variation of fatigue threshold of spring steel with pre stressing. Proceedia Engineering. doi: Procedia Engineering 10 (2011) 3339– 3344. Soner, M., Guven, N., Kanbolat, A., Erdogus, T. et al., Soner, M., Guven, N., Kanbolat, A., Erdogus, T. et al.,Soner.M., Guven,N., Kanbolt,A., Erdogus,T. et al., .2011. Parabolic leaf spring design optimization considering FEA & Rig Test correlation. SAE International. doi:10.4271/2011-01- 2167. Soner,M., Senocak,C., Erdogus,T., and Karragac, M. 2013. Leaf spring safety and ride comfort circumstances against fatigue behavior. SAE International. doi. 10.4271/2013-01-1383. Soner, M., Senocak, C., Erdogus, T., Karaagac, M. et al., "Leaf Spring Safety and Ride Comfort Circumstances Against Fatigue Behaviour," SAE Technical Paper 2013-01-1383, 2013, https://doi.org/10.4271/201301-1383. Tekal.S. 2002. Enhancement of fatigue strength of SAE 9245 steel by shot peening. Journal on Material Letters. doi. org/10.1016/S0167-577X(02)00838-8 Todinv, M.T. 2000. Residual stresses at the surface of automotive suspension springs. Journal of materials science. doi. 10.1023/A:1004887708822. Zhao, X.J., Guo,S steels subject to contact fatigue. Wear Volumes 364–365,. doi.org/10.1016/j.wear.2016.07.013. Transactions of the Canadian Society for Mechanical Engineering, Vol. 00, No. 0, 0000 17 Page 18 of 26 TABLES Table 1. Stress limit eye of leaf spring-51CrV4 Spec Thickness mm Stress 20 min 27 Stress limit Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. < 30 Kg/mm2 Measured 22 23 Table 2. Chemical Composition of 51CrV4 Element C Si Mn P S Cr Mo AL V Cu Actual 0.54 0.37 .05 0.015 0.003 1.20 0.014 0.012 0.16 0.014 Specification 0.470.55 <=0.4 0 0.701.10 Max.0.03 Max.0 .03 0.901.20 - - 0.10-0.20 - Table 3. Chemical Composition of 52CrMoV4 Element Actual Specification C Si Mn P S Cr Mo V Cu 0.49 0.25 0.99 0.019 0.006 0.1 0.17 0.16 - 0.48-0.56 0.40 0.70-1.10 Max.0.025 Max.0.025 0.90-1.20 0.15-0.30 0.10-0.20 - Table 4. Tensile strength test report of 52CrMoV4 Sample Tensile Strength(MPa) 0.2% Yield strength (MPa) 1 1716 1482 2 1720 3 1720 % Elongation on 50mm GL 8.1 1485eye end of leaf spring-6.5 Table 3. Stress limit 51CrV4 1493 7.6 % of Reduction area 20.6 21.2 20.3 Page 19 of 26 List of Tables Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Table No 1 2 3 4 Caption Stress limit eye end of leaf spring- 51CrV4 Chemical Composition of 51CrV4 Chemical Composition of 52CrMoV4 Tensile strength test report of 52CrMoV4 List of Figures Figure No 1 Caption Parabolic leaf spring suspension overview 2-a Field severity withstand 51CrV4 &52CrMoV4 2-b Overloading in Scoop and normal area 3 Field severity -51CrV4 Spring Failure Location 4 Parabolic leaf spring manufacturing process flow diagram 5 Parabolic spring drawing with dimension 6 Optimized heat treatment process 7 Brinell Hardness Testing Machine 8 9-a 9-b 9-c 9-d 10 11 Metallographic Microscope Normal shot peening - same size of balls Optimized shot peening –Different size of balls Shot Peening Machine XRD-X-Ray-Diffractometer Decarburization in one location-51CrV4 and 52CrMoV4 Decarburization in four location-51CrV4 and 52CrMoV4 12 Surface Hardness - 51CrV4 & 52CrMoV4 13 Core Hardness - 51CrV4 and 52CrMoV4 14 Residual compressive stress 51CrV4 &52CrMoV4 15-a Sample preparation machine 15-b 16-a Microstructure 51CrV4 and 52CrMoV4 UTM-Tensile Testing Machine 16-b 17-a Tensile strength testing sample 17-b 17-c 18 Radial Gradient Test Articulation & Pot Hole Test Track Cobble Stone Test Track No Premature failure- Proto model 18 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 20 of 26 Figure 1. Parabolic leaf spring suspension overview 30% withstand field severity 52CrMoV4 Spring Optimized 10% withstand field severity 51CrV4 Spring Optimized Sample tested -100 Nos Mining Truck- 93 Nos Failures in normal shot peening-%1CrV4 spring 51CrV4 Figure 2a. Field severity withstand 51CrV4 &52CrMoV4 Figure 2a. 2b. Overloading in Scoop and normal area Location Field severity withstand 51CrV4 &52CrMoV4 Figure 3. Field severity -51CrV4 Spring Failure Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 21 of 26 Figure 4. Parabolic leaf spring manufacturing process flow diagram Figure 5. Parabolic spring drawing with dimension Figure 6. Optimized heat treatment process Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 22 of 26 Figure 7. Brinell Hardness Testing Machine Figure 8. Metallographic Microscope Figure 9a – Normal shot peening same size of balls Figure 9b – Optimized shot peening –Three different size of balls same size of balls Figure 9c Shot Peening Machine Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 23 of 26 Figure 9d. XRD-X-Ray-Diffractometer Figure 10. Decarburization one location– 51CrV4 and 52CrMoV4 Figure. 11. Decarburization in four locations – 51CrV4 and 52CrMoV4 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 24 of 26 Figure . 12. Surface Hardness – 51CrV4 & 52CrMoV4 Figure . 13 Core Hardness : 51CrV4 and 52CrMoV4 Figure 14. Residual compressive stress 51CrV4 &52CrMoV4 Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 25 of 26 15a. Sample preparation machine Figure.22 Microstructure analysis -51CrV4 normal process and optimized process of - 51CrV4& 52CrMoV4 Figure 15b. Microstructure 51CrV4 and 52CrMoV4 Figure 16a. UTM- Tensile Testing Machine Figure.16b Tensile strength testing sample Transactions of the Canadian Society for Mechanical Engineering Downloaded from www.nrcresearchpress.com by MACQUARIE UNIVERSITY on 02/23/19. For personal use only. Page 26 of 26 Figure 17a Radial Gradient Test Track Figure 17b Articulation & Pot Hole Test Track Figure 18. No Premature failure- Proto model Figure 17C Cobble Stone Test Track
