1. By: Noemi Y. Rodriguez Antonio Galloza Levi L Vargas Julio Alvarez

2. 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.

3. Mini-Stepper

4. 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.

5.  What are the most important engineering considerations in our design? Material Safety Costs

6. Design

7. Stress Analysis (Static Load)  Bendings: σx=Mc/I σy=Mc/I  Shears: τx=4V/3A τy=4V/3A  Torsions: Due to the sleeve the: Torsion→0 Sleeve

8. Stress Analysis (Static Load) Bending Stresses

9. Stress Analysis (Static Load) Shear Stresses

10. Stress Analysis (Static Load)  Von Misses Stress

11. Stress Analysis (Static Load)  Safety Factor

12. Deflection Analysis  EIV=F  EIM=EI∫Vdx  EIθ=EI∫Mdx  Eiv=EI∫θdx

13. Deflection Analysis  Force component Fy  Force component Fx

14. Deflection Analysis  Overall

15. Material Selection  Material Indexes M=Cvr/E^(1/2) M=Cvr/σf^(2/3) Has to be minimized

16. Material Selection

18. MaterialModulus E GPa Fracture Strength MPaRelative cost Cvr Al Alloys70190.9 Steel 1040200450.75 Cast Iron150690.65 For Al AlloyFor Steel 1040For Cast Iron

19. Dynamic Load Analysis  For the Stress concentration  Endurance Limit Se=ksize*ksurface*kload*ktemperature* kreliability*Se’

20. Dynamic Load Analysis  Endurance Limit Se=(0.957092)*(0.819629)*(0.7532)*(44.95) =26.5519ksi  Component live: 10^6 Cycles

21. Dynamic Loads Analysis  Stress concentration factor Kt,bend=1.62 Kt,shear=1.35 Kf,bend=1.52 Kf,shear=1.29

22. Dynamic Load Analysis  Fmax,Fmin

23. Dynamic Loads  Fa,Fm

24. Dynamic Load Analysis

25. Point A Point B

26. Dynamic Load Analysis  Safety Factor (Modified Goodman)

27.  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.

28.  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

29.  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.

30.  What we learn from this project? Team work Design is not just stetic, but is a more complex analysis on which men life depends

31. QUESTIONS?