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By: Noemi Y. Rodriguez Antonio Galloza Levi L Vargas Julio Alvarez. Design of a mini-stepper shaft. Objectives. - PowerPoint PPT Presentation
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By: Noemi Y. Rodriguez
Antonio GallozaLevi L VargasJulio Alvarez
Objectives In this project we were told to design the
shaft that joints the two pedals of a mini-stepper that could support a maximum weight of 250 lb. by analyzing combined loads and stress concentrators. We should take in consideration the type of material to be selected, deflections and deformations in the material. We will be also considering finite life, the critical section and safety factors of the components.
Mini-Stepper
Design Details
Why do we design this device, what is its application?
We design this device because it’s something that we have in our daily use.
A mini-stepper helps people maintain a healthy life exercising themselves.
What are the most important engineering considerations in our design?
MaterialSafetyCosts
Design
Stress Analysis (Static Load)
Bendings:σx=Mc/Iσy=Mc/I
Shears:τx=4V/3Aτy=4V/3A
Torsions:Due to the sleeve the:
Torsion→0Sleeve
Stress Analysis (Static Load)
Bending Stresses
X Mc
I
X 340lb. in 1.0in.
2
4
1.0in.
2
4
0.90in
2
4
X 10070.4029Psi.
Y Mc
I
Y 588.92lb. in 1.0in.
2
4
1.0in.
2
4
0.90in
2
4
Y 17442.449Psi.
Stress Analysis (Static Load)
Shear Stresses
X 4V3A
X 4 85lb.
3 0.14922565in.2
X 759.47622Psi.
YZ 4V3A
YZ 4 147.53lb.
3 0.14922565in.2
YZ 1315.4514Psi.
Stress Analysis (Static Load) Von Misses Stress
VM X Y 2 Y Z 2 Z X 2 6 XY
2 YZ2 ZX
2 2
VM 24253.3751Psi.
Stress Analysis (Static Load) Safety Factor
n Y
VM
n 60,200Psi.
24253.3751Psi.
n 2.48
Deflection Analysis
EIV=F EIM=EI∫Vdx EIθ=EI∫Mdx Eiv=EI∫θdx
Deflection Analysis Force component Fy Force component Fx
0.006414in2
22.1476
22.147
00,02
22.1476
22.147
22.1472
22.147
00,0
22.1472
22.147
22.147*22.147
22.1470,
*22.147
22.147
max
23
3
3
23
2
2
2
2
1
1
v
xL
xEIv
Cvx
Cx
Lx
EIv
Lxx
EIangulo
Cangulox
CLxx
EIangulo
LxEIM
LCMLx
CxEIM
lbEIV
0.003703in2
856
85
00,02
856
85
852
85
00,0
852
85
85*85
850,
*85
85
max
23
3
3
23
2
2
2
2
1
1
v
xL
xEIv
Cvx
Cx
Lx
EIv
Lxx
EIangulo
Cangulox
CLxx
EIangulo
LxEIM
LCMLx
CxEIM
lbEIV
Deflection Analysis
Overall
0.007407in2
1706
170
00,02
1706
170
1702
170
00,0
1702
170
170*170
1700,
*170
170
17080250
max
23
3
3
23
2
2
2
2
1
1
v
xL
xEIv
Cvx
Cx
Lx
EIv
Lxx
EIangulo
Cangulox
CLxx
EIangulo
LxEIM
LCMLx
CxEIM
lbEIV
lbFy
Material Selection
Material IndexesM=Cvr/E^(1/2)M=Cvr/σf^(2/3)
Has to be minimized
Material Selection
Material Selection
Material SelectionMaterial Modulus E GPa Fracture Strength MPa Relative cost Cvr
Al Alloys 70 190 .9
Steel 1040 200 450 .75
Cast Iron 150 690 .65
For Al Alloy For Steel 1040 For Cast Iron
Dynamic Load Analysis
For the Stress concentration
Endurance LimitSe=ksize*ksurface*kload*ktemperature*
kreliability*Se’
Dynamic Load Analysis
Endurance LimitSe=(0.957092)*(0.819629)*(0.7532)*(44.95)
=26.5519ksi
Component live: 10^6 Cycles
Dynamic Loads Analysis Stress concentration factor
Kt,bend=1.62
Kt,shear=1.35
Kf,bend=1.52
Kf,shear=1.29
Dynamic Load Analysis
Fmax,Fmin
Dynamic Loads
Fa,Fm
Dynamic Load Analysis
Dynamic Load AnalysisPoint A
Point B
Dynamic Load Analysis
Safety Factor (Modified Goodman)
What is the unique part of our project?
In our project we analyzed a shaft for a mini-stepper, the unique part comes when four minds merge to achieve the goal of a design of a safety shaft.
What is the most challenging part in our project?
Determine the outer and inner diameters of our shaft to obtain an appropriate safety factor without overdesign
What is the weakness of our project?
The weakness of our project is that in a long period of time, the corrosion will affect our shaft due to the selection of an inexpensive material.
What we learn from this project?
Team workDesign is not just stetic, but is a more
complex analysis on which men life depends
QUESTIONS?