Fatigue Life Extension of Riveted Joints Using Fiber Metal Laminate Reinforcement

Transcription

1 Fatigue Life Extension of Riveted Joints Using Fiber Metal Laminate Reinforcement Fatigue Life Extension of Riveted Joints Using Fiber Metal Laminate Reinforcement Kiran Babu K.M. 1* and Sendhil Kumar S. 2 1 Assistant Professor, Department of Aeronautical Engineering, Annasaheb Dange College of Engineering and Technology, Ashta, Maharashtra, India 2 Associate Professor, Department of Aeronautical Engineering, Karpagam Institute of Technology, Coimbatore, India SUMMARY The components and parts made of sheet metals are commonly used in the automotive industry. Most of the sheet metal joints are bonded together using riveted joints. Stresses induced into these joints during usage may lead to assembly failure. In this paper, the mechanical and fatigue characterization of the riveted joints reinforced using fiber metal laminate (FML) is carried out. The tensile testing and fatigue testing of the specimens are carried out subsequently and the results illustrate that due to the presence of reinforcement between the riveted joints the overall mechanical strength and fatigue life of the riveted joints is improved by 19% and 21% respectively. Keywords: Riveted joints, Fiber metal laminate (FML), Fatigue failure, FML reinforcement 1. INTRODUCTION Figure 1. Factors responsible for failure of a joint Riveting is a well-known method of joining two components in real world using the friction between them for specific application. Present-day, the rivet joints are commonly used in all automotive sectors and industrial applications due to the efficient clam-up, less weight and resistance to corrosion. Riveting is a process of joining two or more plates with the help of a rivet. The rivet in the rivet joint fills the hole completely arresting the relative motion between the plates. A high amount of mechanical force is necessary to ensure the strong and leak proof joint. The factors that are responsible for the failure of the riveted joints 1,2 are discussed and represented in Figure 1. In riveted joints, fatigue damage occurs due to the crack growth which usually starts on the surface at a point of high stress concentration such as a hole, a *Corresponding author s kiranbabu.aerospec@gmail.com Smithers Information Ltd., 2016 notch, a sharp fillet thereby decreasing the fatigue strength. The fatigue strength of the riveted joint represents its response to the cyclic loading which occurs in many applications. It is well known that strength of the material or joint is significantly reduced under repeated loads. The factors that affect fatigue failure 3,4 are shown in Figure 2. Among the factors that determine the fatigue life, the stress level is one of the predominant factors. This paper analyses the fatigue life of the aluminum riveted joints reinforced with the fiber metal laminate (FML). The purpose of reinforcing FML is to reduce the stress level, by absorbing some amount of the strain energy. FML is a kind of hybrid material and it can be fabricated from an alternating laminate of thin metal sheets and thin composite layers. Glass laminate aluminum reinforced epoxy (GLARE) is one of the known composite of the fiber metal laminate Polymers & Polymer Composites, Vol. 24, No. 7,

2 Kiran Babu K.M. and Sendhilkumar S. Figure 2. Factors affecting fatigue failure Figure 3. Failures in component life cycle family. GLARE is made of aluminum layers with thickness varying from mm, and thickness of glass fiber reinforced composite layers in the range of mm. One of the wide usages of GLARE composite is in the aircraft applications. In this research work aluminum sheet in the GLARE material is replaced with the aluminum wire mesh which provides very good bonding with glass fiber and reduces the delamination effect 5,6. 2. LITERATURE REVIEW The failure of a component in its lifetime can be attributed to various reasons as shown in Figure 3. Out of the cited attributes of the failure, design, technological and assembly flaws are generally hidden and based on their magnitude, character and position these attributes cause serious catastrophic failure and its reason is discussed 7. The susceptibility of ductile and brittle materials subjected to varying loads due to the usage of riveted joints is explained and summarized. The mechanical properties of a riveted joint, which can be improved by composite sandwiching between the aluminum plates 8. The tensile properties of different composites materials are determined and using these results the strain energy absorbed can be calculated. These values are used for comparing normal aluminum riveted joints with composite sandwiched aluminum riveted joints 9. applications of the fiber metal laminates (FLM s), with detailed account of adhesive bonding, surface treatments for adhesive bonding, types of FMLs and their testing methods is investigated. It was concluded that the mechanical properties of FML are enhanced by strong interface bond between fiber and metal plies. The metal ply is replaced with metal mesh ply which reduces the delamination effect 10. The mechanical characterization of the glass laminate aluminum reinforced epoxy (GLARE) belonging to the family of the FMLs, with the aluminum wire mesh of varying sizes as the reinforcement and inferred that the wire mesh reinforcement reduces the delamination effect between the glass fiber and aluminum 6. The crack path and fatigue behavior of riveted lap joints in aircraft fuselage is investigated and its effects of variables related to design and production is detailed 11. The basics of damage tolerant design and the fatigue life Figure 4. Riveted lap joint specimen dimensions of aluminum infinite plates with hole theoretically and numerically investigated emphasizing on the stress concentration factor 12. According to the Griffith criterion the important parameter responsible for the crack propagation is the strain energy generated in the material due to the applied load. This research paper aims to improve the strength of the riveted joints by absorbing the strain energy using fiber metal laminate (FML) as the reinforcing material between the riveted joints. 3. EXPERIMENTAL PROCEDURE The dimensions and position of the riveted joint specimen of 1 mm thickness used for the testing are shown in the Figure 4. The sliced The historical developments, merits and demerits, processes and 518 Polymers & Polymer Composites, Vol. 24, No. 7, 2016

3 Fatigue Life Extension of Riveted Joints Using Fiber Metal Laminate Reinforcement aluminum plates are drilled at the accurate position and the riveted joint specimens for the tensile and fatigue testing are prepared and it is shown in Figure 5. The fiber metal laminate GLARE composite is prepared using the compression molding method with two layers of glass fibers first layer at 00 orientation and the second layer is at 900 orientation and The aluminium wire mesh is used instead of the aluminum plate to reduce the delamination effect 6. The thickness of the GLARE FML composite is 2 mm. The mould is allowed to cure for 48 hours under pressure of 5 bar to get better bonding between the fibres and epoxy matrix. Figure 6 shows the mould used for composite preparation and the pieces of GLARE composite cut with 40 x 40 mm dimensions and these are placed as the reinforcement between the aluminium plates. The prepared GLARE composite is placed as the reinforcement material between the aluminium plates and the riveted joint is merged using a rivet gun. Figure 5. Riveted joint specimens for testing Figure 6. GLARE composite preparation Figure 7. Universal testing machine used for tensile testing 4. RESULTS AND DISCUSSION The effect of the reinforcement in the riveted joints subjected to the tensile testing in 400 KN Universal Testing Machine (UTM) as shown in Figure 7 is investigated. Table 1 represents the obtained ultimate load and it is observed that for all the three specimens there is a variation in the ultimate load due to the craftsmanship of the riveted joints. Thus the average ultimate load for the riveted joints without any reinforcement is 3401 N, and for the riveted joints with GLARE reinforcement is 4060 N, with the percentage improvement of Table 2 illustrate the obtained ultimate tensile stress from the universal testing machine for the 3 specimens without the GLARE reinforcement and 3 specimens with the GLARE reinforcement. The average ultimate tensile stress for the riveted joints without any reinforcement is 84 N/ Table 1. Ultimate load from tensile testing Sl. No Specimen No Ultimate Load (N) Average Ultimate Load (N) 1 TA TA TA TF TF TF Table 2. Ultimate tensile stress Sl. No Specimen No Ultimate Tensile Stress (N/mm 2 ) Average Ultimate Tensile Stress (N/mm 2 ) 1 TA TA TA TF TF TF3 97 TA Tensile test specimens without reinforcement TF Tensile test specimens with reinforcement Polymers & Polymer Composites, Vol. 24, No. 7,

4 Kiran Babu K.M. and Sendhilkumar S. Table 3. Specifications of fatigue testing machine Parameters Specifications Axial Load Capacity 1 Tonne Torque +/-100 Nm Angle +/- 10 Deg C Control Servo Hydraulics Feedback controls Load, Torque and Angle Mechanical wedge gripper Hydraulic Power Pack Table 4. Fatigue test results Sl. No Figure 8. Multi axial fatigue test facility Flat Specimen 2 mm to 6 mm, Round Specimen- 4 mm to 8 mm Capacity to drive 2T parallel 2 Pumps for 2 Actuators Specimen No Load (N) Number of Cycles to Fail Average Number of Cycles to Fail 1 FA FA FA FF FF FF FA Fatigue test specimens without reinforcement FF Fatigue test specimens with reinforcement mm 2, and for the riveted joints with GLARE reinforcement is 100 N/mm 2, with the percentage improvement of The fatigue behaviour of the riveted joints under the cyclic loading is studied, the specimens are subjected to the accelerated fatigue testing in the 1 Ton Servo Hydraulic Multi Axial Fatigue Testing facility as shown in Figure 8, with the load of 80% of the ultimate load to determine the number of cycles to fail. Table 3 shows the specifications of the fatigue testing machine. The failure of a riveted joint could occur in any of the following modes of failure, (a) Tearing of a plate at the section weekend by holes, (b) Shearing of rivets, (c) Crushing of plate and rivet, and (d) Shearing of the plate near the rivet hole. During the fatigue test, tearing of a plate at the section weekend by holes is shown in the Figure 9, which is due to the crack initiation and propagation in the plate and shearing of rivets is shown in Figure 10. Table 4 shows the fatigue test results obtained from the multi axial testing machine with and without the reinforcement. The average number of cycles to fail for the riveted joints without any reinforcement is 4804 cycles, and for the riveted joints with GLARE reinforcement is 5802, with the percentage improvement of Figure 9. Plate failure in fatigue testing machine Figure 10. Rivet failure in fatigue testing machine 5. CONCLUSIONS The tensile testing and fatigue testing of the riveted joints with and without the GLARE reinforced riveted joints, were carried out for six specimens using Universal Testing Machine and Multi Axial Fatigue Testing Machine. From the results obtained from the Universal Testing Machine it is observed that when the GLARE material is reinforced in between the plates of the riveted joints the ultimate load of the riveted joints is improved by 19.37% and the ultimate tensile 520 Polymers & Polymer Composites, Vol. 24, No. 7, 2016

5 Fatigue Life Extension of Riveted Joints Using Fiber Metal Laminate Reinforcement stress is improved by 19.04%. From the results obtained from the Multi Axial Fatigue Testing Machine it is observed that when the GLARE material is reinforced in between the plates of the riveted joints the fatigue life of the riveted joints is improved by 20.77%. The results show that reinforcing between the riveted joints improves the mechanical strength and fatigue life of the riveted joints. REFERENCES 1. Suyogkumar W. Balbudhe, and Prof. S.R. Zaveri, Int. J. Engineering Research & Technology 2(3), (2013), Arumulla. Suresh and Tippa Bhimasankara Rao, Int. J. Computational Engineering Research, 3(4), (2013), P.K. Mallick, Fiber-Reinforced Composites, 3rd Edition, CRC Press, Taylor & Francis Group, (2012). 4. Geoffrey L. Kulak, et.al., Guide to Design Criteria for Bolted and Riveted Joints, AISC Inc, Chicago (2001). 5. AdVlot, Kluwer Academic Publishers, ASTM (05), (2001). 6. P. Kaleeswaran et. al., Int. J. Applied Engineering Research, 9(26),(2014), Gordana M. Bakic et. al. FME Transactions, 35, (2007), Ritchie, R.O., Int. J. Fracture, 100, (1999), Kesavamurthy, Y.C., et. al., Int. J. Emerging Technology and Advanced Engineering, 2(4), (2012), Tamer Sinmazcelik, et. al, Materials and Design, 32, (2011), Skorupa M., and Skorupa A., Institute of Aviation Scientific Publications, Warsaw, (2010). 12. K. Madhan Muthu Ganesh, Proceed. Emerging Trends in Mechanical Engineering, SNS College of Technology, Coimbatore, Polymers & Polymer Composites, Vol. 24, No. 7,

6 Kiran Babu K.M. and Sendhilkumar S. 522 Polymers & Polymer Composites, Vol. 24, No. 7, 2016