By: Noemi Y. Rodriguez Antonio Galloza Levi L Vargas Julio 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? Material Safety Costs

Design

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

Stress Analysis (Static Load) Bending Stresses

Stress Analysis (Static Load) Shear Stresses

Stress Analysis (Static Load)  Von Misses Stress

Stress Analysis (Static Load)  Safety Factor

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

Deflection Analysis  Force component Fy  Force component Fx

Deflection Analysis  Overall

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

Material Selection

MaterialModulus E GPa Fracture Strength MPaRelative cost Cvr Al Alloys Steel Cast Iron For Al AlloyFor Steel 1040For Cast Iron

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

Dynamic Load Analysis  Endurance Limit Se=( )*( )*(0.7532)*(44.95) = ksi  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

Point 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 work Design is not just stetic, but is a more complex analysis on which men life depends

QUESTIONS?