Finite Element Analysis of Mini Baja Frame

Ariana L. Gonzalez

April 29, 2003

MECE

Problem Statement

The Mini Baja Frame needs to withstand any collision that it might be subjected to as part of the testing process or competition.

Four impact scenarios were analyzed to ensure the frame design will not fail. Front Impact Rear Impact Side Impact Roll Over

Material Properties

The frame material is 4130 N Chromoly Steel with an outer diameter of 1.125” and wall thickness of 0.058” but was modeled as solid rods with1.125” diameter.

Elastic Modulus 29 * 10^6 psi Poisson’s Ratio .25 Yield Stress 1.16 * 10^5 psi

Pro/Engineer Model

Actual Frame Design

Calculation of Front Impact Force

Front Impact Analysis

Assumptions:

1. Vmax = 26 mph (maximum car speed)2. Mtotal = 600 lbs (total car mass including driver)3. t = 0.1 s (total time from top speed to full stop)

v = vi + at

v = final velocityvi = initial velocityt = total timea = car decceleration

vi 26mph

v 0mph

Mtotal 600 lb

t 0.1sec

av vi

t

a 381.333ft

s2

F Mtotal a

F 7.111 103 lbf

In this case, F is the total force of impact for a front collision.

Forces and Constraints

The force of 7111 lbf was divided by four and applied to the four front most points of the car (1777.75 lbf).

The rear most points of the car was constrained to prevent movement.

Finite Element Analysis of Front Impact

Close Up

Calculation of Rear Impact Force

Rear Impact Analysis

Assumptions:

1. Vmax = 33 mph (average maximum speed of other cars)2. Mtotal = 600 lbs (total car mass including driver)3. t = 0.1 s (total time from top speed to full braking)

v = vi + at

v = final velocityvi = initial velocityt = total timea = car decceleration

vi 33mph

v 0mph

Mtotal 600 lb

t 0.1sec

av vi

t

a 484ft

s2

F Mtotal a

F 9.026 103 lbf

Forces and Constraints

The force of 9026 lbf was divided by four and applied to the four rear most points of the car (2256.5 lbf).

The front most points of the car was constrained to prevent movement.

Finite Element Analysis of Rear Impact

Close Up

Finite Element Analysis of Rear Impact

Calculation of Side Impact Force

Side Impact Analysis

Assumptions:

1. Vmax = 33 mph (average maximum speed of other cars)2. Mtotal = 600 lbs (total car mass including driver)3. t = 0.1 s (total time from top speed to full braking)

v = vi + at

v = final velocityvi = initial velocityt = total timea = car decceleration

vi 33mph

v 0mph

Mtotal 600 lb

t 0.1sec

av vi

t

a 484ft

s2

F Mtotal a

F 9.026 103 lbf

Forces and Constraints

The force of 9026 lbf was divided by four and applied to the right most points of the car (2256.5 lbf).

The left most points of the car was constrained to prevent movement.

Finite Element Analysis of Side Impact

Close Up

Calculation of Roll Over Force

Roll Over Analysis

Assumptions:

1. Vmax = 26 mph (maximum speed of car)2. Mtotal = 600 lbs (total car mass including driver)3. t = 0.1 s (total time from top speed to full braking)

v = vi + at

v = final velocityvi = initial velocityt = total timea = car decceleration

vi 26mph

v 0mph

Mtotal 600 lb

t 0.1sec

av vi

t

a 381.333ft

s2

F Mtotal a

F 7.111 103 lbf

Forces and Constraints

The force of 7111 lbf was divided by two and applied to the top most points of the car (3555.50 lbf).

The bottom of the car was constrained to prevent movement.

Finite Element Analysis of Roll Over

Close Up

Alternative Design

FEA of Alternative

Close Up

Conclusions

The solid model can only be used to determine places where there is a stress concentration.

The proposed alternative reduces the stress concentration at desired location.