Finite Element Method Final Project “ Rear Suspension- Double A- Arms”

Finite Element Finite Element MethodMethod

Final ProjectFinal Project“ Rear “ Rear

Suspension-Suspension-Double A- Arms”Double A- Arms”

Jaime Taha T.Jaime Taha T. April 29April 29thth 20032003

Mini Baja Mini Baja Competition takes place on a motor cross Competition takes place on a motor cross

track.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 trackBe strong enough to survive the track

More pictures.More pictures.

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

Problem StatementProblem Statement The Rear Suspension of the Mini Baja car The Rear Suspension of the Mini Baja car

must be able to withstand the rough must be able to withstand the rough terrains associated with the competition’s terrains associated with the competition’s motor cross track. motor cross track.

Problem StatementProblem Statement The Rear Arm Suspension consist of 3 parts: Top The Rear Arm Suspension consist of 3 parts: Top

Arm, Bottom Arm, and a Hub. Arm, Bottom Arm, and a Hub. Using the material properties for 4130 Chromoly Using the material properties for 4130 Chromoly

Steel.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 AnalysisFEA Analysis 3 Scenarios were analyzed (Worst Case 3 Scenarios were analyzed (Worst Case

scenarios)scenarios) Arm MovingArm Moving Tire hits a rock, wood, bump, etc.Tire hits a rock, wood, bump, etc. Tire hit from the sideTire hit from the side

F=820 lbf2 & 3 Scenarios

Impact ForceImpact Force This force is applied in the second and This force is applied in the second and

third scenarios where:third scenarios where: Another car traveling at 30 MPH hits our car Another car traveling at 30 MPH hits our car

and comes to rest at one second and comes to rest at one second The car hits an object traveling at 30 MPHThe car hits an object traveling at 30 MPH

VVii=30 MPH, V=30 MPH, Vff=0 MPH, Time (t) = 1 =0 MPH, Time (t) = 1 second, Mass (m) = 600 lb second, Mass (m) = 600 lb

lbfF

impactamFt

VVimpacta

taVV

if

if

820

)(

)(

Forces acting in the Forces acting in the systemsystem

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 forceonly on the Top Arm

Car Frame

Pro E ModelPro E Model

Top Arm

Spherical JointsSpring/Damper

Spring Force = 175 lb/inDamper Force (C) = 10.2 Lbf

Impact Force

= 820 lbf

AssumptionsAssumptions Welded zones where neglectedWelded zones where neglected The actuator in the tire simulates the displacement of The actuator in the tire simulates the displacement of

the tire-arm when the car is driven.the tire-arm when the car is driven. The spring-dash is acting in the as a distributed load The spring-dash is acting in the as a distributed load

(Pro E model image.)(Pro E model image.) Spherical joints were used where the arm is attached Spherical joints were used where the arm is attached

to the car’s structure, also the car frame was to the car’s structure, also the car frame was assumed that doesn’t move (Car’s frame doesn’t take assumed that doesn’t move (Car’s frame doesn’t take any load.)any load.)

To simulate the impacts in the car, a ramp function To simulate the impacts in the car, a ramp function was used.was used.

The reaction force of the tire is calculated as a worse The reaction force of the tire is calculated as a worse case scenario where all the weight of the car is case scenario where all the weight of the car is applied only in one tire applied only in one tire 600 lb, as a distributed 600 lb, as a distributed force.force.

Finite Element ModelingFinite Element Modeling Scenario 1 – Arm moving.Scenario 1 – Arm moving.

Stress Analysis 0.03ftMax. Value = 7.46e8

Value in a specific point = 6.03e8 Pa

Stress Analysis 0.02ftMax. Value = 8.6 e8


Stress AnalysisStress Analysis


Factor of SafetyFactor of Safety

FS-0.03 - Front (above) and Back (below) views of Factor of Safety (Mesh size of 0.03 ft)FS-0.02 - Front (above) and Back (below) views of Factor of Safety (Mesh size of 0.02 ft)

FS-0.03 FS-0.02

Finite Element ModelingFinite Element Modeling Scenario 2 – Tire hits a rock, wood, Scenario 2 – Tire hits a rock, wood,

bump, etc.bump, etc. Using 0.02 ft. MeshUsing 0.02 ft. Mesh

Max. Value = 8.62e8 Pa Value in a specific point = 6.71e8 Pa


bump, etc.bump, etc. Using 0.03 ft. MeshUsing 0.03 ft. Mesh



bump, etc.bump, etc. Using 0.04 ft. Using 0.04 ft.

MeshMesh


Factor of SafetyFactor of Safety


bump, etc.bump, etc.

FS – 0.02ft FS – 0.03ft

Simulation of stress analysis in the Simulation of stress analysis in the tire-arm with movement tire-arm with movement


bump, etc.bump, etc.

Change in stresses when object moves Movement and stresses

Finite Element ModelingFinite Element Modeling Scenario 3 – Tire hit from the side.Scenario 3 – Tire hit from the side.

Using 0.03 ft. MeshUsing 0.03 ft. Mesh



Using 0.02 ft. MeshUsing 0.02 ft. Mesh



Change in stresses when object moves Movement and stresses

Simulation of stress analysis in the Simulation of stress analysis in the tire-arm with movement tire-arm with movement

Improvement - Pro E Improvement - Pro E Drawings.Drawings.

Previous

Adding the pipe showed, the stresses Adding the pipe showed, the stresses concentration could be distributed.concentration could be distributed.

Possible Alternative

……Cont’Cont’ Comparing the 1Comparing the 1stst case scenario: case scenario:

The addition of the pipe decreases the stresses The addition of the pipe decreases the stresses and also distribute the stress concentrationand also distribute the stress concentration

Stress Analysis 0.03ftMax. Value = 7.46e8 Pa


Stress Analysis 0.03ftMax. Value = 1.4e8 Pa

Value in a specific point1 = 2.9e7 PaValue in a specific point2 = 1.1e8 Pa

Point2


As explained before, with the addition of the pipe, the stress As explained before, with the addition of the pipe, the stress concentration decrease and also was distributed (Mesh size concentration decrease and also was distributed (Mesh size 0.03 ft). An increase is notable in the new model (right image) 0.03 ft). An increase is notable in the new model (right image) in the Factor of Safety from 0.54 to 3.46.in the Factor of Safety from 0.54 to 3.46.

Actual part Modify part (addition of a pipe)


In this scenario, the addition of the pipe also affect the factor In this scenario, the addition of the pipe also affect the factor of safety, as we can see the red zones from the figures.of safety, as we can see the red zones from the figures.

Actual part Modify part (addition of a pipe)

Problems/Comments Problems/Comments while doing my project.while doing my project.

Pro EPro E DrawingsDrawings Cut the inside of the pipesCut the inside of the pipes Verify unitsVerify units Geometry settings/connection to Visual Geometry settings/connection to Visual

Nastran (Why doesn’t work???)Nastran (Why doesn’t work???)

Problems/Comments Problems/Comments while doing my project.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 The use of H-Adaptivity is hard to run it

because thin structure and other elements because thin structure and other elements (such as spring, actuator, etc)(such as spring, actuator, etc)

Verify the restraints, forces, springs, actuators, Verify the restraints, forces, springs, actuators, motor, etc.motor, etc.

Verify Joints (also is very important to verify the Verify Joints (also is very important to verify the dynamic loadings)dynamic loadings)

While running the FEA with motion there’s no While running the FEA with motion there’s no way to stop it.way to stop it.

CommentsComments 3 scenarios were analyzed 3 scenarios were analyzed H-Adaptivity was not used because of the H-Adaptivity was not used because of the

complexity of the part and the thickness.complexity of the part and the thickness. A possible alternative of adding a pipe between A possible alternative of adding a pipe between

the arms with the purpose of decrease stress the arms with the purpose of decrease stress concentration and also distribute the load. In concentration and also distribute the load. In fact the results showed that by adding the fact the results showed that by adding the pipe, the stresses slightly reducepipe, the stresses slightly reduce

FEA is a time consuming process, it can be FEA is a time consuming process, it can be improve if the analysis is run on a more improve if the analysis is run on a more capable computers.capable computers.

Further work: Further work: Verify the pipes diameter/thickness and do FEAVerify the pipes diameter/thickness and do FEA

Dr. Arturo Fuentes Dr. Arturo Fuentes

Mini Baja TeamMini Baja Team

ClassmatesClassmates

AcknowledgemAcknowledgementsents

Finite Element Method Final Project “ Rear Suspension- Double A- Arms”

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