Transcript Slide 1

The Trapezoidal Solution
ME 104Q Final Design Project
Steven Ivancic • Liz Kaminsky • Brendan Tracey • Jason Miller
“A
big
part
of
any
engineering
project
is
Maximum Structural Stress : 26.1 ksi
the ability to take advantage of the
Projected Supported Load: 300lbs.
available technology.”
Executive Summary
This project embodies a culmination of all aspects of design and
drawing
learned throughout the semester. The challenge is to span an 8 1/2” inch
chasm with a bridge and allow for a 3x5” index card to pass underneath, while
supporting the entire weight of two students. The design must be made of
aluminum in two alloys, the T6 temper and a more ductile untempered TO
specification. The bridge can only be fastened with 1/8” rivets.
A key element was the need to create a rigid structure while keeping the
material weight to a minimum. The load supported divided by the weight of the
structure itself would constitute a “figure of merit” which would be used to
determine efficient design.
The design was fabricated in a machine shop, so the design also had to
be made producible. This meant drafting up drawings of each part, as well as
an assembled view of the structure.
Ideas
Sketches
Finite Element Analysis
Revisioning
Weight of Structure : .33lbs
Anticipated Figure of Merit : 910
To cut down on the need for physical tests, we used Ansys
8.1 and Ansys workbench. This allowed us to test the
stresses electronically without needing to build a physical
model for each prototype.
Prototyping
Deck Part Drawing
These drawings were put together in powerpoint
using a standard drafting template. There is one
assembly drawing and three part (detail) drawings.
We did some initial tests in Ansys 8.1, including testing the effect of
rivets on stress distribution. These tests simulated three different
sized rivets, and took advantage of the symmetry effect to minimize
effort. We found that the smaller the rivet, the higher the stress
concentration (but as to be expected, for the bigger rivets, there was
a higher stress over a greater area).
Assembly Drawing
The maximum stress is 26.1 ksi and occurs
directly under the loading bar.
Final Build Pictures
After modeling our design in Ansys
Workbench we used its finite element
analyzer to tests the stresses on our
bridge. We found that our minimum
theoretical safety factor was around 1.3,
about the minimum allowable without
knowing the exact properties of the
material in use.
Leg Part Drawing
As expected, the total deformation of the
bridge was largest in the center where
the load would be applied. This design allows
the legs to flex to a degree, taking some of the
stress off the main beam.
Team Super Awesome