Finite Element Method Final Project “ Rear Suspension- Double A- Arms” Jaime Taha T.April 29 th 2003

Mini Baja Competition takes place on a motor cross track. Competition takes place on a motor cross track. Suspension must Suspension must React and perform well. React and perform well. Protect the driver from impacts from the rough terrain. Protect the driver from impacts from the rough terrain. Be strong enough to survive the track Be strong enough to survive the track

More pictures. As we can see, is very feasible that the cars could be hit by another one, or that the tires could hit a rock, bumps, etc. As we can see, is very feasible that the cars could be hit by another one, or that the tires could hit a rock, bumps, etc.

Problem Statement The Rear Suspension of the Mini Baja car must be able to withstand the rough terrains associated with the competition’s motor cross track. The Rear Suspension of the Mini Baja car must be able to withstand the rough terrains associated with the competition’s motor cross track.

Problem Statement The Rear Arm Suspension consist of 3 parts: Top Arm, Bottom Arm, and a Hub. The Rear Arm Suspension consist of 3 parts: Top Arm, Bottom Arm, and a Hub. Using the material properties for 4130 Chromoly Steel. Using the material properties for 4130 Chromoly Steel. The tubing is a 1” diameter and 0.058” thickness. The tubing is a 1” diameter and 0.058” thickness. In this project the Top arm was analyzed. In this project the Top arm was analyzed.

FEA Analysis 3 Scenarios were analyzed (Worst Case scenarios) 3 Scenarios were analyzed (Worst Case scenarios) Arm Moving Arm Moving Tire hits a rock, wood, bump, etc. Tire hits a rock, wood, bump, etc. Tire hit from the side Tire hit from the side F=820 lbf2 & 3 Scenarios

Impact Force This force is applied in the second and third scenarios where: This force is applied in the second and third scenarios where: Another car traveling at 30 MPH hits our car and comes to rest at one second Another car traveling at 30 MPH hits our car and comes to rest at one second The car hits an object traveling at 30 MPH The car hits an object traveling at 30 MPH V i =30 MPH, V f =0 MPH, Time (t) = 1 second, Mass (m) = 600 lb V i =30 MPH, V f =0 MPH, Time (t) = 1 second, Mass (m) = 600 lb

Forces acting in the system Reaction force of the weight of the structure acting on both arms Weight of the car, acting on both arms Stress of the Spring/Damper force only on the Top Arm Car Frame

Pro E Model Top Arm Spherical Joints Spring/Damper Spring Force = 175 lb/in Damper Force (C) = 10.2 Lbf Impact Force = 820 lbf

Assumptions Welded zones where neglected Welded zones where neglected The actuator in the tire simulates the displacement of the tire-arm when the car is driven. The actuator in the tire simulates the displacement of the tire-arm when the car is driven. The spring-dash is acting in the as a distributed load (Pro E model image.) The spring-dash is acting in the as a distributed load (Pro E model image.) Spherical joints were used where the arm is attached to the car’s structure, also the car frame was assumed that doesn’t move (Car’s frame doesn’t take any load.) Spherical joints were used where the arm is attached to the car’s structure, also the car frame was assumed that doesn’t move (Car’s frame doesn’t take any load.) To simulate the impacts in the car, a ramp function was used. To simulate the impacts in the car, a ramp function was used. The reaction force of the tire is calculated as a worse case scenario where all the weight of the car is applied only in one tire  600 lb, as a distributed force. The reaction force of the tire is calculated as a worse case scenario where all the weight of the car is applied only in one tire  600 lb, as a distributed force.

Finite Element Modeling Scenario 1 – Arm moving. Stress Analysis 0.03ft Max. Value = 7.46e8 Value in a specific point = 6.03e8 Pa Stress Analysis 0.02ft Max. Value = 8.6 e8 Value in a specific point = 7.03e8 Pa Stress Analysis Stress Analysis

Finite Element Modeling Scenario 1 – Arm moving. Factor of Safety Factor of Safety FS Front (above) and Back (below) views of Factor of Safety (Mesh size of 0.03 ft) FS Front (above) and Back (below) views of Factor of Safety (Mesh size of 0.02 ft) FS-0.03 FS-0.02

Finite Element Modeling Scenario 2 – Tire hits a rock, wood, bump, etc. Using 0.02 ft. Mesh Using 0.02 ft. Mesh Max. Value = 8.62e8 Pa Value in a specific point = 6.71e8 Pa

Finite Element Modeling Scenario 2 – Tire hits a rock, wood, bump, etc. Using 0.03 ft. Mesh Using 0.03 ft. Mesh Max. Value = 7.68e8 Pa Value in a specific point = 4.66e8 Pa

Finite Element Modeling Scenario 2 – Tire hits a rock, wood, bump, etc. Using 0.04 ft. Mesh Using 0.04 ft. Mesh Max. Value = 1.42e9 Pa Value in a specific point = 1.12e9 Pa

Factor of Safety Factor of Safety Finite Element Modeling Scenario 2 – Tire hits a rock, wood, bump, etc. FS – 0.02ft FS – 0.03ft

Simulation of stress analysis in the tire-arm with movement Simulation of stress analysis in the tire-arm with movement Finite Element Modeling Scenario 2 – Tire hits a rock, wood, bump, etc. Change in stresses when object movesMovement and stresses

Finite Element Modeling Scenario 3 – Tire hit from the side. Using 0.03 ft. Mesh Using 0.03 ft. Mesh Max. Value = 6.7e8 Pa Value in a specific point = 5.06e8 Pa

Finite Element Modeling Scenario 3 – Tire hit from the side. Using 0.02 ft. Mesh Using 0.02 ft. Mesh Max. Value = 1.27e9 Pa Value in a specific point = 8.25e8 Pa

Finite Element Modeling Scenario 3 – Tire hit from the side. Change in stresses when object moves Movement and stresses Simulation of stress analysis in the tire-arm with movement Simulation of stress analysis in the tire-arm with movement

Improvement - Pro E Drawings. Previous Adding the pipe showed, the stresses concentration could be distributed. Adding the pipe showed, the stresses concentration could be distributed. Possible Alternative

…Cont’ Comparing the 1 st case scenario: Comparing the 1 st case scenario: The addition of the pipe decreases the stresses and also distribute the stress concentration The addition of the pipe decreases the stresses and also distribute the stress concentration Stress Analysis 0.03ft Max. Value = 7.46e8 Pa Value in a specific point = 6.03e8 Pa Stress Analysis 0.03ft Max. Value = 1.4e8 Pa Value in a specific point1 = 2.9e7 Pa Value in a specific point2 = 1.1e8 Pa Point2

Finite Element Modeling Scenario 1 – Arm moving. As explained before, with the addition of the pipe, the stress concentration decrease and also was distributed (Mesh size 0.03 ft). An increase is notable in the new model (right image) in the Factor of Safety from 0.54 to As explained before, with the addition of the pipe, the stress concentration decrease and also was distributed (Mesh size 0.03 ft). An increase is notable in the new model (right image) in the Factor of Safety from 0.54 to Actual part Modify part (addition of a pipe)

Finite Element Modeling Scenario 3 – Tire hit from the side. In this scenario, the addition of the pipe also affect the factor of safety, as we can see the red zones from the figures. In this scenario, the addition of the pipe also affect the factor of safety, as we can see the red zones from the figures. Actual part Modify part (addition of a pipe)

Problems/Comments while doing my project. Pro E Pro E Drawings Drawings Cut the inside of the pipes Cut the inside of the pipes Verify units Verify units Geometry settings/connection to Visual Nastran (Why doesn’t work???) Geometry settings/connection to Visual Nastran (Why doesn’t work???)

Problems/Comments while doing my project. Visual Nastran Visual Nastran Meshing the part – “play” with the mesh size. Meshing the part – “play” with the mesh size. The use of H-Adaptivity is hard to run it because thin structure and other elements (such as spring, actuator, etc) The use of H-Adaptivity is hard to run it because thin structure and other elements (such as spring, actuator, etc) Verify the restraints, forces, springs, actuators, motor, etc. Verify the restraints, forces, springs, actuators, motor, etc. Verify Joints (also is very important to verify the dynamic loadings) Verify Joints (also is very important to verify the dynamic loadings) While running the FEA with motion there’s no way to stop it. While running the FEA with motion there’s no way to stop it.

Comments 3 scenarios were analyzed 3 scenarios were analyzed H-Adaptivity was not used because of the complexity of the part and the thickness. H-Adaptivity was not used because of the complexity of the part and the thickness. A possible alternative of adding a pipe between the arms with the purpose of decrease stress concentration and also distribute the load. In fact the results showed that by adding the pipe, the stresses slightly reduce A possible alternative of adding a pipe between the arms with the purpose of decrease stress concentration and also distribute the load. In fact the results showed that by adding the pipe, the stresses slightly reduce FEA is a time consuming process, it can be improve if the analysis is run on a more capable computers. FEA is a time consuming process, it can be improve if the analysis is run on a more capable computers. Further work: Further work: Verify the pipes diameter/thickness and do FEA Verify the pipes diameter/thickness and do FEA

Dr. Arturo Fuentes Mini Baja Team Classmates Acknowledgements