Conception and Structural Analysis of a Frame

Pedro Fonseca Serrador [email protected] Mechanical Engineering, Instituto Superior Técnico, Lisboa, Portugal October 2016

Abstract In the present Master’s Thesis, it’s intended to create a new frame on the basis of the Famel z3 motorcycle and to validate the proposed structure using analytic models and finite element models (Siemens NX). It starts by analyzing the market of electric motorcycle, showing its medium-term growth perspective. From the study performed are selected the most suitable motor and number of batteries required for a stipulated range of 100 Km in city, obtaining an estimate for the weight of the structure in order of 6,5 Kg. Based on a table built of Needs vs Metrics, were created three concepts of different structure and modeled in SolidWorks. To select the winning concept, these were subjected to multiple comparison tests, supplemented with finite element analysis using Siemens NX. Finally, two materials were tested for the winning concept, steel S235J2H and aluminum 6061. Using static failure and fatigue test methods (Mechanical Design) at critical points found with the critical loads calculated, there were made the necessary changes so that the structure verified security for the calculated safety factor. To select the winning material, their structures were subjected to multiple comparison tests. These analyses were supplemented with finite element analysis using Siemens NX and an analysis of production costs, using the tables of Formula SAE. As final result it was obtained a validated structure of concept 3 in aluminum, with a unit cost of production of 69,35 €, for a total production of 1000 frames.

Keywords: Electric Motor, Famel z3, Finit Elements, Formula SAE, Needs vs Metrics, Mechanical Design

1. Introduction Famel, Fábrica de Produtos Metálicos, was EEC in 1986 Famel found itself confronted founded in 1949 in Águeda. In the 50s with some problems, forced to declare began to produce with engines from bankruptcy in 2002. However, Joel Sousa, Pachancho, Victoria and JLO and in the 80s 28, car engineer, recently bought the right to launched the Famel z3 model, known for its the brand and intends to bring it back into Zündapp engine with only 3 speeds. Despite focus. In an interview to Marketeer [1], he its small 50cc engine, this motorcycle could reveals that in 2017, if all goes as planned, reach high speeds as it was lightweight and the first new model, based on the XF-17, of a 2-troke engine, making it quite amusing. the reborn brand Famel will be released. “A With the bankruptcy of Zündapp in 1984 and motorização elétrica é o futuro. (…) Estamos the opening of the market to Europe by the convictos que podemos revolucionar a

1 maneira como se encara o veículo elétrico characterized by its single section beam with em Portugal…”. Famel z3 is part of the high dimensions, used mostly in low-cylinder product development portfolio of the , or motorcycles where the company and will be the subject of this weight must be rationalized and when it is document. desired to lower production costs, due to ease of manufacture. Dual Sport Motorcycles A very important factor is the material to be Dual Sport bikes, where the bike under study used in the structure because, for a given fits, are, according to Motor Sport Rider [2], shape and specific load, the thickness can characterized by having dual purpose, as change as well as the geometry of the they are not only able to be ridden in structure, depending on the resistance of the highways with safety and comfort, but also material. because of their agility, lightweight and high In order to study the frame resistance and maneuverability, making them suitable for whether it supports the critical loads applied, off-road riding. is necessary to take into account criteria Motorcycle Frame Modeling such as stress, strength and fatigue. The To model the frame of a bike it is necessary methods to do so are shown and explained to take several factors into account. by Richard G. Budynas and J. Keith Nisbett According to Tony Foale [3], the frame has [4], and Carlos Moura Branco [5], such as two main functions: static and dynamic. Von Mises method and modified Goodman In static terms this should support the weight method. of the driver and the passenger as well as Electric Motor the engine, fuel tank and oil and accessories Nowadays, people seem to be more that the bike may have, such as bags of concerned and aware of environmental luggage. pollution and its effect on our planet, and On the other hand, in dynamic terms, it transports are one of the major contributors should have stable and precise direction, to this degradation. According to EPA [6], in have good adhesion to the ground, good United States motor vehicles are handling and must be comfortable. Each responsible for about 70% of air pollution. bike has a purpose of use and typical efforts Despite the electric motors not showing any that is submitted to, so there are several type kind of emissions, the truth is that electricity of frame formats, each modeled in order to has to come from somewhere and often, or better support a particular type of loads. mostly, it is produced with polluting Therefore, to build a motorcycle and know resources such as coal, fossils, low-carbon the best format to use on your frame, it is or mixtures [7]. Though, Portugal is a country necessary to know the type of use intended. where renewable energies are one of the There are 5 main type of frames: major power suppliers, making it possible for triangulated frames, , structural the energy that reaches electric motors to be engine, tubular backbone and twin-spar [3]. clean of pollutants. This is the only way it can This project is based on a motorcycle, which be said that electric motors do not show any uses a tubular backbone type of frame,

2 kind of emissions, making Portugal a good 120 with 12,3 Kg. As for the batteries the country to use them. most suitable ones are the Shenzen WS- According to Navigant Research [8], it is NCM20AH-3.7V20C. expected that the two-wheel electric vehicle Table 2.1 - Electric Motorcycles Market industry reaches a stable and continuous weight Power Price (thousands of Brand Model economic growth over the coming years. It is (Kg) (KW) euros) Brammo / Victory 213 40 20 expected that annual sales of electric Polaris Impusle S 171-205 40 11-16,7 motorcycles will grow from 1,2 million SR 188-208 50 16-18,7 DS 173-207 40 11-16,7 DSR 190-210 50 16-18,7 vehicles in 2015 to 1,5 million in 2024, while Zero FX/FXS 112-114 20 8,5 for electric scooters is expected that there is 3.3 FX/FXS 131 33 11 a sales increase of 4,1 million to 4,4, making 6.5 MX 115 19-30 15 Alta a total of 5,3 million in 2015 and 5,9 million SM 124 19-30 15,5 Freeride 106 11-16 11 in 2024. Therefore, this matter will be taken E-SX Freeride KTM 110 11-16 11,3 in account. E-XC Freeride 110 11-16 11,6 E-SM C 2. Problem Statement BMW 265 11-35 15,5 Evolution Motor and Batteries To get an idea of the loads involved in the Based on its properties and taking in account structure caused by the motor and batteries, the performance of the FXS model from is necessary to know specifically what will be Zero, it was calculated the number of used, being also useful to, in terms of batteries needed for a range of 100km in city geometry, know if it fits in the frame. So, to was around 55 with a total weight of choose the most suitable engine it was 24,75Kg. Hence if 55 batteries can provide a performed a study of electric motorcycle range of 100km to a model with 112Kg it can, market, in order to realize the weight/power for sure, provide the same range or more for ratio practiced in the industry, Table 2.1. a less heavy motorcycle. So taking in As is intended to model a frame of a bike, it account the model on which this project is is understandable not to know the final based on, Famel z3, weights about 63,6Kg weight of the bike, so to choose the engine and have a frame with 6,5Kg, the new frame was decided to set a desired value for the being modeled should weight about the power of the bike. According to the same or less, if possible. Portuguese Institute of Mobility and Geometry Modeling transport [9], holders of category B driving According to Karl T. Ulrich and Steven D. license are also qualified to drive Eppinger [10], the best way to develop a new motorcycles with power up to 11KW, if they product is to follow a specific procedure are over 25 years old, or so, or are holders consisting of several well-defined steps. This of mopeds driving license. way it was produced a Table of needs vs This way, and based on projects of the metrics, in which the main parameters are students from DEM in IST, FST and TL shown in Table 2.2, based on final moto, the most suitable motor to choose is a consumer’s opinions, to help create a variety Double-sided Synchronous Motor – PMS of concepts.

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Table 2.2 - Needs vs Metrics

Center Max. Metrics Nº of Yield Allowable of Mass Volume weight Displacement Production Material Stress stress Location (mm3) (Kg) for Max. Cost (€) Needs points (MPa) (MPa) (mm) Load (mm) Easy to x x x maneuver Comfortable x x Stable x x Resistant x x x x Price x

Given that the base model is the frame of between the two main beams, reduces the Famel z3, it was decided this should be one overall weight and improves the frame’s of the concept evaluated, Concept 1, in order resistance when subjected to torsional to compare with the new ones, Fig.2.1. loads.

Fig. 2.3 - Concept 3

Fig 2.1 - Concept 1, Famel z3 Frame Boundary Conditions Beside the first concept were created two As the frame is yet being projected its more. One that only difference is the external loads are still uncertain. However, direction of the curvature of the main beam, since this project is based on the Famel z3, in order to change the type of tension applied it is possible to estimate the normal reactions to the structure, Concept 2 Fig 2.2. As a on the wheels using a balance and result, instead of traction, the beam will be measuring the weight supported by each under compression, which is always a better wheel. In addition to its own weight, the choice when it comes to structures stresses. structure must also withstand the weight of two passengers and cargo. According to [11] the friction coefficient, µ, can reach a maximum value of 1,3. Hence Table 2.3 shows the set of critical loads calculated. When a simulation in Siemens NX is started,

the structure studied is presented without Fig. 2.2 - Concept 2 any constrains. As a consequence, the On other hand, it was created a third structure appears as a free body, in a way concept, Concept 3 Fig 2.3, in which instead that when a load is applied to it no of two beams there was only one, as this is deformation is seen. Therefore, it will be one of the advantages of the tubular necessary to block some movements, so backbone frames. Thus, it prevents the that, alongside with the loads calculate, appearance of cracks in the bonding zone

4 exemplify, the best way possible, the real study it was used the aluminum 6061 for all case. The best approach is to consider the concepts, in order to inshore that the connection between the frame and the differences observed in the same test where as a cylindrical joint. Thus, to do it only due to the geometry of the structure. so, the inner cylindrical surface is blocked With the models made in SolidWorks it was both in translational and rotational possible to obtain some useful information, movements. Fig. 3.1 for the analysis intended to do. So it

Table 2.3 - Critical Load started by comparing the weight/volume, the center of mass and the number of welding Wheel Reaction Force (N) Friction Force (N) Front 900 1200 points. Back 1900 2500 Table 3.1 – Needs and Metrics Score

% of the importance of each metric in each need Safety Factor Max. Nº of C.M. Weight/ Needs Score % Displacement welding ! / ! Position Volume " #$% To calculate the safety factor, it was used the for Max. Load points Easy to 3 21% 50% 50% - - - Pugsley method, where using several data, maneuver Comfortable 2 14% - 100% - - - such as material quality, accuracy of stress Stable 4 29% - - 100% - - Resistant 5 36% - - - 55% 45% analysis, dander to personnel, etc. two factors are calculated nsx=1,3 and nsy=1,5 , resulting in a safety factor of nproj=1,95. In Table 2.4 are shown the properties of the Steel S235J2H and Aluminum 6061 taking in account the safety factor calculated. Table 2.4 - Material Properties (a) (b)

E S S S Material n y ut adm (GPa) (MPa) (MPa) (MPa) Steel 470 to 210 0,3 355 182 S235J2H 630 Aluminum 69 0,3 276 310 154 6061

3. Concept Selection (c) In order to choose the winning concept, it will Fig. 3.1 - Solidworks Information of Concept 1 (a); 2 (b); 3 (c) be used the table of needs, weighted values Observing the data presented in Fig 3.1, it will be assigned to each need and metric and follows that concept 1 and 2 are the each concept will have a certain score in heaviest, and being the first heavier than the every metric and need, so that the winner will second. Thus, the concept presenting a high be the one which has the higher score. Thus, score is the third being the lightest. When it based on the opinion of current users of comes to volume the concepts have the motorbikes and potential buyers of bike same relation as in weight, since the material being projected was created Table 3.1. used is the same, so both parameters were There will be 5 metrics evaluated on each joined to form only one parameter. concept in order to compare them and decide which one is the winner. For this

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In terms of the center of mass it is important tension felt in the connection between the to know that the lowest the better and the two beams and compare it with the more centered the better, on other hand it is simulation obtained in NX. also important to know that the center of the bike is -144mm far from the models origin. Observing “z” values it comes that all of them are zero, this is because all frames are symmetric by the plane “xy”, so this will not be a differentiating factor. On the contrary, analyzing “y” values, it’s concluded that concept 1 wins, having the lowest C.M. of them all, followed by concept 2, leaving Fig. 3.2 – Suspension’s Free Body concept 3 in last. At last observing “x” values it’s determined that concept 3 wins, having the C.M. nearest to the center of the bike then the others, followed by concept 2, leaving concept 1 in last. As a result, concept 1 wins, followed by concept 3, leaving concept 2 in last. When it comes to the number of the welding points, it can be seen in Fig. 2.1 and 2.2, Fig. 3.3 – Swingarm Free Body corresponding to concept 1 and 2, that both Table 3.2 – Forces Applied to the Frame have the same number, though in Fig. 2.3, Force F1 F2 F3 F4 F5 corresponding to concept 3, it is possible to (N) 900 1200 1779 979 208 notice that having only one beam this models wins in this parameter being possible F3 to have one less welding point then the other two concepts. F1 F2 F5 In order to perform Siemens NX tests, first F4 it’s important to know if the simulations are valid. So first it was necessary to know the loads applied to the frame, and to do so it Fig. 3.4 - Siemens NX sim. Whit Loads Applied. was created two free bodies diagrams The approximation was made comparing the exemplifying the suspension, Fig 3.2, and connection to a fixed tube where the the swingarm, Fig 3.3. Calculating the sum tensions was calculated and obtained a of forces in “x”, as well as in “y” and the sum value of � = 110MPa. The results of NX of moments it was obtained Table 3.2, whit simulation is shown in Fig. 3.5, with a value the directions shown in Fig 3.4. of � = 134MPa, around the same as Once calculated the forces involved it was calculated before. As a result, the simulation time to calculate an approximation of the is validated.

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the main beam with a different direction reducing the stress applied, it still has the connection between the two beams, making concept 2 and 1 equally scored.

Fig. 3.5 - NX Simulation Now it’s possible to evaluate the stress involved in each concept. In Fig 3.6, it’s shown a simulation for concept 1, Fig. 3.7, for concept 2 and Fig 3.8 for concept 3. Fig. 3.8 – Stress Simulation for Concept 3 When it comes to displacements concept 3 is the winner with a maximum of 7,2mm, followed by concept 2 with 8,54mm, leaving concept 1 in last with 8,58mm. The final scores are presented in Table 3.3.

Table 3.3 – Concepts Evaluation

Easy to maneuver Fig. 3.6 – Stress Simulation for Concept 1 Comfortable Stable Resistant Center Max. Nº Of Weight/ Sy / Concept of Mass Displacement Welding Volume Location for Max. Load Points Sadm Concept 3 1 1 2 2 1 Concept 1 2 2 2 2 2 Concept 2 3 3 3 3 3

Calculated the scores with the information of Table 3.1 and 3.3, concept 3 was the winner with a score of 2,895, followed by concept 2 Fig. 3.7 – Stress Simulation for Concept 2 with 1,895 and concept 1 with 1,570. Observing Fig 3.6 and 3.7, it’s possible to 4. Material Selection see that there is a zone in common much To choose between aluminum 6061 and demanded, showing high stresses applied. Steel S235J2H it was used the same method This zone corresponds to the connection as in chapter 3., though this time the between the two beams. Thusly in Fig. 3.8 parameters evaluated where different as it’s possible to see that the stresses are well shown in Table 4.1. distributed throughout the structure. This is Before starting evaluating these parameters because there its structure comprises only it is needed to study the critical points of the one beam instead of two, making possible to structure, in order to know if it is necessary reduce stress. So in this parameter concept to make any change so that in both cases 3 is the winner and, although concept 2 has

7 verify security in static failure and fatigue The results obtained show that for both steel tests. The critical points in this structure are and aluminum the value of “Se” is greater the cylinder that supports the rear than “Sf”, thereby both cases have infinite suspension, and the connection between the life. beam and subframe. To test the connection between the beam

Table 4.1 – Needs and Metrics Score and the subframe it is important to note that

% of the importance of each metric in each need the forces used do not correspond to the Max. C.M ! / Needs Score % Weight Displacement for " Cost Position ! total of the forces applied to the front wheel, Max. Load #$% Easy to 3 17% 50% 50% - - - maneuver because there is a distribution along several Comfortable 2 11% - 100% - - - Stable 4 22% - - 100% - - parts of the structure. Using NX analysis it Resistant 5 28% - - - 100% - Price 4 22% - - - - 100% was noticed that only 30% of the forces were

supported by that section. Consequently, the Starting with the cylinder it was made an forces used in this test were 30% of the approximation, considering a cylinder fixed forces applied on the front wheel, Table 2.3. in one side and two loads applied in the So first it was calculated the stress with the middle of the length representing the forces section of a annulus with r1=10mm and r =8mm as in the original frame, though it F4 and F5. At first it was calculated the stress 2 with the section of a circle with r=5mm as it was calculated a value of �=185MPa that was in the original frame though, it was is too close to the “Sadm” of steel of 182MPa, hence it can be said that steel passes static calculated a value of � = 256MPa that is test with security for the safety factor higher than 154MPa, “Sadm” of aluminum, projected. On other hand the aluminum fails and 182MPa, “Sadm” of steel. As with this value both materials would not pass in this this test, so a change was made, the interior test a change was made, the ray was ray was changed to r2=7mm. Hence it was changed to r=6mm. It was calculates a new calculates a new stress of �=144MPa, consequently the structure in aluminum stress of � = 148MPa and both materials pass the static test. passes the static test. For the fatigue test it was considered a For the fatigue test it was considered a sinusoidal load with R=0, meaning that the sinusoidal load with R=0, just like before, meaning again that F =F and both are minimum load is equal to zero and Fa=Fm a m and both are equal to half of the loads from equal to half of the loads from static test. So static test. So for Steel and aluminum were for Steel and aluminum were obtained the obtained the values from Table 4.2. values from Table 4.3. The results obtained show that for both steel Table 4.2 - Fatigue Results for Steel and Aluminum

and aluminum the value of “Se” is greater Results Steel Aluminum Unit than “S ”, therefore both cases have infinite Se 209,0 137,1 MPa f Sf 101,13 112,86 MPa life. �a 85,42 81,76 MPa With all necessary changes made, is now �m 85,42 81,76 MPa possible to study the parameters necessary to compare both materials.

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Table 4.3 - Fatigue results for Steel this parameter aluminum is the winner, Results Steel Aluminum Unit leaving steel in last. Se 209,0 137,1 MPa In terms of displacements it was concluded �a 110,20 82,25 MPa �m 110,17 82,24 MPa that the winner in this parameter is steel, with Sf 137,80 113,39 MPa a max. displacement of 2mm, against

aluminum, with 6mm. Firstly, in Fig. 4.1 is shown the simulation for On other hand when it comes to weight the stress in the aluminum structure, and in aluminum wins with 2,27Kg, against 5,85Kg Fig. 4.2 is shown the same simulation for the of the steel structure. steel structure. As for the cost of production, even with more expensive welding costs aluminum is still cheaper than steel, because according to [12] machining steel is 3 times more expensive than aluminum. So in this parameter aluminum wins with a productions cost of 69,35€, leaving steel as loser with a

cost of 88,57€ Now analyzing the center of mass, as well as Fig. 4.1 - Stress Analysis for Aluminum in concepts evaluation “z” values are the same because of symmetry. Observing “y” values, it’s concluded that steel wins over aluminum, with a value of 311,3 mm over a higher value of 315,65mm. At last observing “x” values it’s determined that steel wins again with a value of -40,51mm over -

15,93mm, having the C.M. nearest to the

Fig. 4.2 - Stress Analysis for Steel center of the bike then the structure of aluminum, leaving concept 1 in last. As a The maximum stress observed in aluminum consequence steel is the winner of this is lower, with a value of 435MPa, than the parameter. steel, with a value of 445MPa. Observing the The final scores are presented in Table 4.4. stress distribution along both structures it is noticed that higher stress values are Table 4.4 – Materials Evaluation presented in the subframe as well as in the Easy to maneuver Comfortable Stable Resistant Price seat supporter. Though blue colors Max. C.M. S / Material Weight Displacement y Cost Position S displayed in steel structure are lighter than in for Max. Load adm Steel 1 2 2 1 1 the aluminum’s. This fact is aggravated by Aluminum 2 1 1 2 2 the fact that steel scale displays a higher Calculated the scores with the information of maximum value, meaning that for the same Table 4.1 and 4.4, aluminum was the winner color the stress is higher in steel. Hence in with a score of 2,89 and steel lost with 1,46.

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5. Motor and Batteries Location the development of the product, particularly The location of the batteries and the motor to perform real tests in a prototype. It was have a great influence on the center of mass, estimated a unit cost of production of 69,35€, aerodynamics, as well as the visual for a total production of 1000 frames. aspect/design. In Fig. 5.1 are represented 3 As future developments there should be different solutions. made a study of geometry and length of the frame welds, frame impact tests and a detailed study of the motor and batteries location as well as the connections. Making these suggested studies, it has every

interest that a prototype is built, in order to (a) (b) validate all the performed tests.

7. Bibliography [1] Markteer, edição de Abril, (2015). “Famel quer regressar à estrada”. goo.gl/E33gcP

[2] Rider, M. S. (2013). “Introduction to Dual Sport (c) Motorcycle”; goo.gl/AoWH5k Fig. 5.1 - Solution 1 (a); 2 (b); 3 (c) [3] Foale, T. (2002); “Motorcycle Handling and Of the 3 solutions presented, the one that Design the art and science”. Spain shows to be more advantageous. All of them [4] Budynas, R. G. and J. K. Nisbett, (2011). have the motor in the same position, so the “Elementos de Máquinas de Shigley”. New York. differentiation factor shall be the location of [5] Branco, C. A. G. M. (2011). “Mecânica dos Materiais”. Fundação Calouste Gulbenkian the batteries. As it can be seen in the 3 [6] EPA (Environmental Protection Agency), (2016); figures of the different solutions, the third goo.gl/fMIJH3 one shows a better way to distribute the [6] Shrink That Footprint, (2013); “Shades of Green, batteries along the whole structure, Electric cars’ carbon emissions arround the globe”. providing a better weight distribution, that is [7] Shrink That Footprint, (2013); “Shades of Green, Electric cars’ carbon emissions arround the globe”. better for de C.M., and less air resistance, [8] Navigant Research, (2015); “Electric Motorcycles making this the better solution of the three. and Scooters, Market Drivers and Barriers, However, this study should have further Technology Issues, Key Industry Players, and developments in partnership with Famel Global Demand Forecasts”. designers. [9] Intituto da Mobilidade e dos Transportes, 2009; “Diário da República, 1.ª série – N.º156 – 13 de 6. Conclusion and Future Agosto de 2009”. Developments [10] Ulrich K. T and Eppinger S. D. (2012); “Product As final result it was obtained a validated Design and Development”. New York. structure of concept 3 in aluminum, solution [11] Foale, T. (2002); “Motorcycle Handling and Chassis Design the art and science”. Spain that best satisfy the final consumer and, [12] Formula SAE, (2016); “Downloads for 2017 having passed at static failure and fatigue Competition Season”; goo.gl/L0V tests, this frame would be able to continue

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