Finite Element Analysis Of a Skateboard Truck

Transcription

1 ite Element Analysis Of a Skateboard Truck

2 Executive Summary: Engeerg is and always has been an tegral part of the sportg scene. This can be seen nearly all sports sce their conception. Downhill skis have gotten faster, Lacrosse sticks have gotten lighter, Adidas even has a pair of shoes that adjusts the cushiong accordg to a small microchip. There is no limit to what can be improved upon. This report strives to analyze the forces present on the baseplate of a skateboard, which is an element of the truck, which holds the wheels. ite Element analysis will be conducted on this piece usg a number of calculated forces and contact pressures representative of a skateboard beg ridden normally, on one set of wheels, as well as an impact from 5 ft the air. After viewg the results of the analysis, an impact from 10 ft the air was also calculated. The analysis for this piece was done usg a combation of SolidWorks (for modelg) and ABAQUS (for fite element analysis). It is evident from the results that stress concentrations do not get very tense this structure, which leads to the conclusion that a strategic re-design of this baseplate could save on material as well as expense. This strength could also potentially be sacrificed for weight, which could lead to easier manipulation of the board while use.

3 Table of Contents Cover Page... 1 Executive Summary..... Table of Contents..... Introduction 4 SolidWorks Modelg 5 ite Element Model 6 Model Importation to ABAQUS...6 Calculations.6 Loadg....8 Constrats...9 ite Element Analysis and Results 9 Conclusions Appendix A...1

4 Introduction: This project strives to understand the stress present the baseplate of a skateboard through computer aided fite element analysis. The baseplate is constructed of alumum with a Young s Modulus of 1E7 ( )/ and a Poissons ratio of.. irst, it is relevant to understand exactly where this component fits to the assembly of a skateboard and the types of forces that the piece withstands durg regular use. igure 1 Assembled Truck igure Separate Baseplate The baseplate withstands forces from the hanger, or the axle piece. These forces are transferred through two small pieces of rubber, which allows for slight flexibility the hanger and the ability to steer a skateboard. This results two pressures beg applied to the baseplate different magnitudes. There are a number of variables that should be brought to light considerg the analysis of this piece. It should be noted that this analysis was not done for all the potential forces that could be curred by this piece due to the sheer volume of skateboardg tricks that exist. In addition to this, the baseplate of the trucks modelg this analysis are bottom of the le components. The major difference trucks seems to be the weight, material (some materials are better for grdg tricks because they slide better), and center of gravity (which makes the board easier to flip the air). The only of these issues relevant to this analysis is the material due to Young s Modulus and Poissons Ratio. Lastly, the forces and pressures present on the baseplate are hardly static. The analysis done here was 4

5 done for the most extreme of the considered conditions (assumg the rider of the skateboard was 50, heavy for the typical skateboarder) attempt to get the most accurate results without the use of dynamic loadg. SolidWorks Modelg: SolidWorks 005 was used the modelg of the baseplate due to the ease of use and the ability to import.igs files to ABAQUS. While this later proved to offer some difficulties, such problems will later be discussed with other conclusions. The modelg of this piece turned out takg significantly longer than origally thought. The piece was measured English units usg a set of digital calipers, accurate to.001. Modelg of the baseplate began with the th metal extrusion, followed by two separate lofts to create the basic profile for the plate. Additional loft-cuts, extruded cuts, fillets, as well as some other mor details were added to produce the fal product seen here. igure CAD Model of Baseplate 5

6 ite Element Model: The construction of the fite element model consists of a number of steps. irst, the model must be serted to ABAQUS order to create a mesh and perform the analysis. Calculations must be performed order to determe the forces applied durg analysis. All calculations were done English units, simply because the part was origally modeled English units. orces and applicable pressures for situations have been calculated and modeled cludg data analysis with an creasg number of elements the mesh to display convergence. The issues of loadg and constrats will also be discussed. Model Importation to ABAQUS In order to properly import the model from SolidWorks to ABAQUS, the file must be saved SolidWorks as a.igs file. Problems were experiencad dug the importation due to the part beg valid. This means that some of the edges and tersections were not modeled friendly to the mesh algorithm that ABAQUS uses to analyze the system. With some help from the TA, this problem was eventually overcome usg the Tools Repair function ABAQUS. Calculations Assumptions: Maximum rider weight 50 Elastic Deflection upon landg.1 Relevant conical contact 1/ area of ner cone Mass of Skateboard neglected Circular Area π π ( r solid r hole ) A (. 5. ).6597 Conical Area CircleContact 6

7 A h C r C t ConeContac π π Normal Ridg psi A P psi A P M ConeContact CircleContact Y truck N N

8 One set of Wheels All pressure on circular area A N CircleContact 50 P psi Impact Loadg 1 impactd mv v v0 + a( x x0 ) mah impact d.1 impact Truck Im pact M Y P psi ACircleContact P psi A.91 ConeContact Extreme Impact Loadg (10 feet) P1 and P from the other impact loadg is simply doubled for the difference a 5 to 10 foot drop. Loadg P psi 1 P psi The loadg this element was reasonably straightforward, with the only major assumption beg that pressure the conical area of the baseplate loadg took place on the bottom third of the circumference of the surface. The only other 8

9 loadg area for the element was the circular area (with a hole) at which loadg was assumed to be distributed evenly. Aga, while the loadg of this element reality is far from a static loadg, the potential dynamic loadg for this element will not be discussed this project paper. Constrats The constrat that was applied for this element was simply the bottom face of the baseplate all directions. In reality, the element is screwed to the board; however, the horizontal forces present this piece are negligible to its overall function. ite Element Analysis and Results: After the fite element analysis was completed ABAQUS, it became clear that the only scenario that had any noticeable affect on the baseplate (on the fite element level) was the impact loadg. This, however, still did not have as large as an affect as was anticipated. Therefore, the height from which the impact itiated was doubled order to see a larger loadg. In order to not be repetitive formation, the only analysis that will be covered depth is the impact loadg from 10 feet with a rider of 50. Pictures for the other analysis steps can be seen Appendix A (low element number of 0000 elements). Stress distribution (as seen igure 6 and 7) was reasonably smooth as the piece has few right angles (or close to 90 o ) and a reasonable amount of fillets. Stress was highest the element towards the bottom of the conical region, which was takg a large majority of the force exerted on the piece over a smaller area. However, this is not of concern due to the location of the stress, which is only separated from the constraed region by a th section of alumum. It should also be noted that these stress concentrations do not come close to a dangerous level of stress for alumum. While the conical region of the piece has the highest stress concentration, the area of more terest is the base of the circular loft near 9

10 the rib. Even with the rib there, there is a noticeable concentration of stress this region. This makes sense physically due to the slight angle of the lofted surface itself and the normal forces creatg pressures on that surface. In other words, it seems as if this rib is more crucial to the design than the average person could know. Here are two figures representative of the Von Mises stresses occurrg due to the impact loadg of a 50 lb rider from 10 feet the air. igure 6 50 lb Rider, 10 foot impact loadg, Isometric View igure 7 50 lb Rider, 10 foot impact loadg, Top View 10

11 Analysis was also performed to show that convergence occurred. This helps to show that the fite element analysis is truly a accurate model of elemental stresses. Six mesh sizes, rangg from elements to elements were graphed with their total stra energies below. As one can see, the graph approaches a fite solution logarithmically with an creasg number of elements. Stra Energy Convergence Stra Energy Number of Elements igure 7 Stra Energy Convergence Conclusions: While it is evident that this analysis does not show every possibility for stress concentrations this element, I do believe that it is safe to say that this piece is over-designed. Perhaps novations material choices or even more optimal designs could be done (and have been, compared to this cheap set of trucks) to 11

12 crease the performance, as well as the weight of these trucks. If I were to do this analysis over aga, I would most likely choose not to import from SolidWorks to ABAQUS, as it caused difficulty the validity of the baseplate. In the future, I would prefer to use one program for the entirety of the modelg and analysis. In closg, I d like to admit that this project was origally tended as an assembly, considerg the entire truck as opposed to just the baseplate. Unfortunately, a day and a halfs worth of work was squandered attempt to make model the hanger. In one last valiant attempt to hope that efforts were not completely wasted, I have cluded a picture of the model with the loft that did not want to execute. It makes me shed a tear. igure 8 The hanger that wasn t meant to be 1

13 Appendix A: igure A.1 50 Rider, Normal Ridg, Isometric View igure A. 50 Rider, Normal Ridg, Top View igure A. 50 Rider, Ridg on one Set of Wheels, Isometric View 1

14 igure A.4 50 Rider, Ridg on one Set of Wheels, Top View igure A.5 50 Rider, Impact from 5ft, Isometric View igure A.6 50 Rider, Impact from 5ft, Top View 14