Cad modelling on Creo Use of ansys workbench for following analysis. Structural static Modal- for natural frequency Transient Analysis/dynamic

1. ME 511 FINITE ELEMENT ANALYSIS
Fall 2015
Design optimization of Roll cage of formula type SAE vehicle
Project report
Instructor Name: Dr. K. Nematollahi
Students:
Satyajeet Udavant
Abhishek Khoje
Surendra Patil
PURDUE SCHOOL OF ENGINEERING

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Objective
The objective of the project is to optimize the roll cage of a formula-style
vehicle by considering weight as a parameter. The roll cage is tubular frame which
has a circular cross section. The project consists of modeling the roll cage in CAD
software considering the rules mentioned in the rulebook for FSAE 2015. The solid
model is then analyzed by modal, static and frontal impact at certain speed. Two
different materials will be used during the analyses and the results will be
compared.
The analysis results from this project will help in optimizing other systems which
require high mechanical properties with low weight.
Introduction
The purpose of the roll cage is to provide a minimal three‐dimensional space
surrounding the driver ensuring his safety under all circumstances. The main
objective of the design process was to design a compact, sporty robust and
manufacturing friendly roll cage taking into consideration the FSAE Rule Book. The
cage is required to be designed and fabricated to prevent any failure of the cages’
integrity.
An optimized roll cage design is one which helps in achieving the best performance
parameters. Weight of a race car plays an important role in achieving the latter.
Finding a balance between the strength and weight of the roll cage is the
underlying reason of the optimization process.
Finite element analysis helps in the optimization process by discretization of the
entire model into smaller elements and then analyzing their behavior under
different loading conditions.

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The finite element method for optimization includes the modeling of the roll cage
structure in a CAD software considering standard parameters. This model is then
imported into the FEA environment by using the ANSYS Workbench software. The
ANSYS software virtually assigns different material with different thickness to the
tubular frame structure. The structure was further meshed and then subjected to
different loading conditions and results were obtained. The results thus obtained
were compared and the best material with an optimum thickness for the tubes
was determined.
Background
Transient dynamic analysis (sometimes called time-history analysis) is a
technique used to determine the dynamic response of a structure under the action
of any general time-dependent loads. You can use this type of analysis to
determine the time-varying displacements, strains, stresses, and forces in a
structure as it responds to any combination of static, transient, and harmonic
loads. The time scale of the loading is such that the inertia is considered to be
important.
Model Details
The roll cage is a tubular frame of a uniform cross section. The roll cage has been
designed around a 95 percentile male sitting in an optimized and comfortable
driving position. The chassis consists of the front bulkhead for the pedal box and
front suspension components, a cockpit for the driver and the driving controls, and
an engine bay for the engine, powertrain and rear suspension components.
For impact analysis, velocity of the vehicle was assumed to be 60 km/hr and the
impact time was considered to be 0.4 sec. The force was calculated from the mass

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and the deceleration after impact. The force was calculated to be 18,348 N. The
mass of the vehicle is considered to be 244 kg (Roll cage: 64 kg Driver: 80 kg
Engine/powertrain: 75 kg and Mountings: 15 kg)
Materials used
Properties AISI 1018 Mild Carbon
Steel
AISI 4130 Chromoly
Outer Diameter (mm) 25.4 25.4
Thickness (mm) 3 2.3
Density (kg/m3) 7870 7870
Ultimate tensile
strength (MPa)
440 670
Yield tensile strength
(MPa)
370 435
Poisson’s Ratio 0.29 0.29

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Procedure
The roll cage was modeled on a CAD software. This model was imported into
ANSYS workbench. The geometry was discretized with a medium size mesh. The
material properties for the roll cage were uploaded and were assigned to the
geometry. The following analyses were done:
 Static Analysis:
Static analysis was an initial step for the later transient analysis done for the
impact study. Static analysis was done by fixing the rear end or the rear
frame of the rollcage and by applying the driver weight, engine/powertrain
weight and the mounting weights at their respective positions in the rollcage.
The calculated force was applied to the front faces of the front bulkhead.
Gravity was applied to the whole frame structure. The static analysis was run
and results were obtained.
 Modal Analysis:
Modal analysis was performed as a prerequisite for the transient analysis.
The analysis was performed by fixing the rear end of the rollcage frame
structure and six modes were obtained.
 Transient analysis:
Transient analysis was done for the impact study of the rollcage. The
conditions used for the transient analysis were similar to the static analysis
done earlier and deceleration factor which was computed from the velocity
and impact time factor was included for the analysis. Hence the inertia effect
was considered for this analysis. The transient analysis was run and the
deformation and the stresses were obtained.

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Results and Discussions
1. Static Analysis
AISI 1018 (Mild Carbon Steel)
Equivalent Stress
Total Deformation

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Factor of Safety
Material second
AISI 4130 (Chromoly)
Equivalent Stress

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Total Deformation
Factor of Safety

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Modal Analysis
AISI 1018 (Mild Carbon Steel)
Mode Frequency
(Hz)
1 22.438
2 29.95
3 44.977
4 56.75
5 70.138
6 93.252

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AISI 4130 (Chromoly)
Mode Frequency (Hz)
1 22.036
2 29.893
3 44.261
4 55.9
5 68.638
6 92.76

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Transient Analysis
AISI 1018
Equivalent Stress
Total Deformation

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12
Factor of Safety
Material second
AISI 4130 (Chromoly)
Equivalent Stress

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Total Deformation
Factor of Safety

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Discussions
Material Properties:
Properties AISI 1018 Mild Carbon
Steel
AISI 4130 Chromoly
Outer Diameter (mm) 25.4 25.4
Thickness (mm) 3 2.3
Density (kg/m3) 7870 7870
Ultimate tensile
strength (MPa)
440 670
Yield tensile strength
(MPa)
370 435
Poisson’s Ratio 0.29 0.29
Comparison:
AISI 1018 Mild Carbon
Steel
AISI 4130 Chromoly
Equivalent Stress (MPa) 144.58 215.79
Total Deformation (mm) 1.0381 1.918
FOS 1.6599 2.0158
Wall thickness (mm) 3 2.3
Conclusion
Increased crash worthiness of the roll cage model. As shown in above table of comparison I
was successful in reducing the diameter thereby reducing the overall weight of the roll cage
and increasing the stress handling capacity.