Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Projectnatalieferrari.weebly.com/uploads/6/1/3/9/6139829/... · Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project case

Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project

Analysis 1—Change in Beam Section/ Frame Structure

Assume that all members are tubular with an outside diameter of 1 inch and an inside diameter of 0.87 inch. Determine if

any yield failure is likely when the material is aluminum (E = 10 Mpsi, = 0.33, and yield = 50 kpsi).

If yielding occurs, redesign the frame by replacement of highly stressed members with more substantial sections of

standard sized tubing and/or alter the design layout. (Cite references for any tables of standard tubing sizes used.) If the

frame is unnecessarily over-designed in certain members (i.e., significantly lower stresses compared to others), refine the

design to reduce weight. Make certain that resulting deflections seem reasonable. You should have evidence of trying at

least three design changes, and state which would result in the lowest increase in weight (You can use an Excel

spreadsheet to show this).

1 2 3

4

5

6

Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project Analysis 2—Change in Loading or Boundary Conditions

Using your results from Analysis 1 as a starting point, consider the loading and boundary conditions assumed for the

model. Do these seem reasonable? Make changes to your model, considering the way the elements are connected or the

loads that are applied (i.e. should we have a load at the pedal, etc.) Justify any changes made in your loading or boundary

conditions and cite any references used. With these new loading conditions, does yielding occur?

Analysis 3—Change in Material

Using the starting frame design or the design from Analysis 1, change the material properties of the bike frame. Cite any

references used when researching typical bike frame materials. Based on this material change, will your frame structure

still work or do the tube sizes or design need to be modified? If yielding occurs, try a redesign of the frame by

replacement of highly stressed members with more substantial sections of standard sized tubing and/or alter the design

layout. Again, you should have evidence of trying at least three design changes, and state which would result in the lowest

increase in weight (You can use an Excel spreadsheet to show this).

Submission

Following the lab report format given on mycourses, each group (2 students) should turn in one report. Your report

should include a description of your ANSYS model or models (Boundary conditions, Loading Conditions, etc.) In

addition, include in your discussion any problems you encountered with ANSYS or information about ANSYS you

wished had been covered in class. (This information will be used to modify the labs for next year.) Your report can be

submitted to the Final Project Assignment dropbox in mycourses or printed out and left in the bucket outside my office.

Your ANSYS .db file(s) must also be submitted to the Final Project Assignment dropbox in mycourses.

Assumptions:

1. Original material is aluminum

2. Neglect node welds

3. All material properties are uniform throughout all members

4. Analysis is static

5. Neglect any potential tire effects

6. The Bicycle Frame is 2 dimensional where the front tire is only supported by one tube

Abstract:

In this lab, the goal was to practice the basics of iterative design in ANSYS Classic via the set up and analysis of a two

dimensional bicycle frame. With the preliminary bicycle design shown in Figure 1, the iterative process began by

modeling and determining the initial stresses and deflection values of the bicycle to be further optimized for weight via

ANSYS. The mesh length of the frame was 0.5 inches. The design process began by minimizing weight under the original

design parameters. Next, the original load case was modified for more accurate redistributive loads on the frame and

rechecking to avoid frame yielding due to stress in the tubes. Lastly, the material was changed from aluminum to titanium

to be reanalyzed and designed for structural stability and weight.


Analysis 1:

Figure 2. Bicycle Design with Associated Tube Numbers Figure 3. Bicycle Design with Body Forces and Mesh Size of 0.5 in

Two body forces were applied to the bicycle frame with a load factor of 3, shown in Figure 2. The total body forces

applied at node 5 and 6 are 75 lbs. and 450 lbs., respectively, shown in Table 1.

Ori

gin

al

Lo

ad

Ca

se Node

Force in

X

Force in

Y

Force in

Z

1 0 0 0

2 0 0 0

3 0 0 0

4 0 0 0

5 0 -75 0

6 0 -450 0

Table 1. Original Load Case

For Analysis 1, Iteration 1:

Figure 4. Original Load Case - Displacement Vector Sum Plot Figure 5. Original Load Case - Von Mises Stress Plot

Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project The maximum stress and displacement in the frame under the given load conditions and frame design is 24978 psi and

0.345 in, respectively. As the yield stress of material, aluminum, is 50000 psi, the design can be refined with a smaller

outer diameter tube and same wall thickness to reduced overall system weight and maintain strength.



The maximum stress and displacement in the frame under the given load conditions and frame design is 47146 psi and

0.865 in, respectively. As shown in Figure 7, tubes 1, 2, 3 and 7 see very little stress and can therefore be replaced with

thinner walled tubes in order to reduce system weight. Most importantly, by only changing the volume of the low stress

tubes, the load capacity of the high stress tubes will not be compromised.




0.881 in, respectively. Again, as shown in Figure 7, tubes 1, 2, 3 and 7 see very little stress and can therefore be replaced

with even thinner walled tubes in order to reduce system weight. Most importantly, by only changing the volume of the

low stress tubes, the load capacity of the high stress tubes will not be compromised.





0.902 in, respectively. Compared to the previous designs, this iteration proves to be the lightest while maintaining

structural stability under the given load conditions.

Analysis I Iteration Results

Material Aluminum

Density 0.097504

Elastic Modulus (psi) 10000000

Poisson's Ratio 0.33

Yield Stress (psi) 50000

Iter

ati

on

1

Tube Number 1 2 3 4 5 6 7

Tube OD (in) 1.000 1.000 1.000 1.000 1.000 1.000 1.000

Tube ID (in) 0.870 0.870 0.870 0.870 0.870 0.870 0.870

Tube Thickness (in) 0.065 0.065 0.065 0.065 0.065 0.065 0.065

Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000

Element Length (in) 0.5 0.5 0.5 0.5 0.5 0.5 0.5

Total Volume (in3) 13.770 13.770 15.274 12.563 9.737 3.246 15.274

Total Weight (lb) 8.155

Maximum Displacement (in) 0.345

Maximum Stress (psi) 24978

Iter

ati

on

2


Tube OD (in) 0.750 0.750 0.750 0.750 0.750 0.750 0.750

Tube ID (in) 0.620 0.620 0.620 0.620 0.620 0.620 0.620


Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000


Total Volume (in3) 10.088 10.088 11.190 9.204 7.134 2.378 11.190





Iter

ati

on

3


Tube OD (in) 0.750 0.750 0.750 0.750 0.750 0.750 0.750

Tube ID (in) 0.652 0.652 0.652 0.620 0.620 0.620 0.652


Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000


Total Volume (in3) 7.783 7.783 8.633 9.204 7.134 2.378 8.633




Iter

ati

on

4


Tube OD (in) 0.750 0.750 0.750 0.750 0.750 0.750 0.750

Tube ID (in) 0.680 0.680 0.680 0.620 0.620 0.620 0.680


Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000


Total Volume (in3) 5.670 5.670 6.289 9.204 7.134 2.378 6.289




Table 2. Summary of All Iterations for Analysis 1

Analysis 2:

Lo

ad

Ca

se 1

Node Force in X Force in Y Force in Z

1 0 0 0

2 0 -180 0

3 0 0 0

4 0 0 0

5 0 -75 0

6 0 -270 0

Lo

ad

Ca

se 2

Node Force in X Force in Y Force in Z

1 0 0 0

2 0 -450 0

3 0 0 0

4 0 0 0

5 0 -75 0

6 0 0 0

Table 3: Load Case 1 and 2

For Analysis 2, the boundary conditions remain constant where node 1 is constrained in all directions and node 3 is only

constrained in the z direction while nodes 2, 4, 5 and 6 remain unconstrained. The boundary conditions remain constant

because it best modeled real world constraints.

Upon comparing the original load case to a real world scenario, it was believed that the original loading did not best

represent the true distribution of weight across the frame. The original weight of the rider was placed on the seat.

Therefore, the load case was changed to mimic an actual bicycle rider. This was modified to account for the leg weight on

the pedals as well as input force. This modification is Load Case 1, shown in Table 2. Load Case 2 accounts for the worst

Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project case scenario where the bicycle rider is fully standing on the pedals while riding, shown in Table 2. The model used to test

the new load cases was Iteration 4 from Analysis 1.


Figure 12. Load Case 1- Displacement Vector Sum Plot Figure 13. Load Case 1- Von Mises Stress Plot


0.055 in, respectively. As a result of the implementing load case 1, the stress was more evenly and accurately distributed

across the frame. This is exemplified in Figure 13, where the maximum stress decreased 56%.



To ensure that the current design is adequate for hill climbing, Load Case 2 was implemented where all body weight is

positioned on the pedals. The maximum stress and displacement in the frame under the given load conditions and frame

design is 30956 psi and 0.082 in, respectively. As shown in Figure 15, the maximum stress remains under the yield stress

limit for aluminum.


Analysis 3:

The bicycle frame material was changed from aluminum to titanium. This material change was performed for the

increased material strength properties of titanium. While titanium is a heavier material, the strength properties enabled

further reductions in weight in particular tube members. The model used to test the material change was Iteration 4 from

Analysis 1 under Load Case 1.




0.033 in, respectively. Shown in Figure 17, the maximum stress at node 4 exceeds the allowable yield strength of titanium

of 20.3 kpsi1. Therefore, tubes 5 and 6 were modified by increasing the outer diameter while maintaining the same wall

thickness, shown in Iteration 2.



Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project The maximum stress and displacement in the frame under the given load conditions and frame design is 13230 psi and

0.023 in, respectively. As shown in Figure 19, the stress at node 4 decreased to an acceptable level below the yield stress

for titanium. In addition, it was noticed that tubes 2 and 3undergo small amount of stress. Therefore, the tube dimensions

can be reduced to optimize weight.




0.022 in, respectively. Therefore, out of the 3 design iterations for titanium, the optimal design is iteration 4 due to the

lowest stress in the frame as well as deflection and weight. The final weight of the design was 8.242 lbs.

Analysis III Iteration Results

Material Titanium

Density 0.163

Elastic Modulus (psi) 16800000

Poisson's Ratio 0.34

Yield Stress (psi) 20300

Iter

ati

on

1


Tube OD (in) 0.750 0.750 0.750 0.750 0.750 0.750 0.750

Tube ID (in) 0.680 0.680 0.680 0.620 0.620 0.620 0.680


Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000


Total Volume (in3) 5.670 5.670 6.289 9.204 7.134 2.378 6.289




Iter

ati

on

2


Tube OD (in) 0.750 0.750 0.750 0.750 1.000 1.000 0.750

Tube ID (in) 0.620 0.620 0.620 0.620 0.870 0.870 0.620



Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000


Total Volume (in3) 10.088 10.088 11.190 9.204 9.737 3.246 11.190




Iter

ati

on

3


Tube OD (in) 0.750 0.750 0.750 0.750 1.000 1.000 0.750

Tube ID (in) 0.652 0.620 0.620 0.620 0.870 0.870 0.652


Tube Length (in) 18.030 18.030 20.000 16.450 12.750 4.250 20.000


Total Volume (in3) 7.783 10.088 11.190 9.204 9.737 3.246 8.633




Table 4. Summary of All Iterations for Analysis 3

Discussion:

It was observed that after redistributing the load at the seat to both the seat and pedal to mimic that of an actual rider, the

maximum stress in the frame decreased by a factor of 56%. With this change, the deflection increased at node 2 while

decreasing the stress at node 4. The load redistribution, in Load Case 1, was then maintained throughout the lab. Using a

variety of different tube geometries allowed for customization of the frame in order to reduce weight and stress.

For example, Iterations 2 and 3 from Analysis 3 exemplified this benefit. By increasing the outer diameter of front tubes 5

and 6, a reduction in stress was observed. Also, because tubes 2 and 3 experienced minimal stress, the wall thickness was

reduced in order to cut weight from the frame. Lastly, changing the material to titanium yielded lower deflections in the

tubes due to its high elastic modulus and intrinsic strength properties. While this material would provide more stiffness,

the high cost and additional weight would not be advantageous for the average bicycle rider. Therefore, it was concluded

that aluminum is a better suited material for a light weight bicycle frame under the loading conditions for this analysis.

Overall, the results make sense given the loading scenario proposed and the constraints applied to the model.

Sources:

For Titanium material properties:

1MatWeb - The Online Materials Information Resource. (n.d.). Online Materials Information Resource -

MatWeb. Retrieved February 16, 2011, from

http://www.matweb.com/search/DataSheet.aspx?MatGUID=66a15d609a3f4c829cb6ad08f0dafc01

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Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Projectnatalieferrari.weebly.com/uploads/6/1/3/9/6139829/... · Kursten O’Neill & Natalie Ferrari 2/17/2011 Final Project case