Foot Stretcher Finite Element Analysis
Evaluate and strengthen foot stretcher subassembly, a key structural component, to reduce maximum stress and improve fatigue life.
Role
Mechanical Engineering Co-Op
Team
Hydrow Hardware Engineering
Company
Hydrow, Inc.
Date
May 2020
Requirements
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Must interface with existing components such as injection molds
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Must be able to be installed during service visits if necessary
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Must withstand worst-case scenario loading conditions over the lifecycle of a Hydrow
Hydrow with foot stretchers called out
Simulations
Static FEA simulations were utilized to compare maximum stresses applied to each design iteration including the original design. Design changes to reduce stress concentrations were increasing bend radii, incorporating a supporting part to direct load paths, and increasing material thickness especially in locations that interfaced with fasteners. The maximum stress endured by the foot stretcher, under the same load conditions, reduced by a factor of 2.74 by the final design.
Original Design: Stress Concentrations at Bracket Bend
Final Design: Stress Concentrations Distributed within subassembly
TESTING
Due to the use of static FEA analysis, my team and I devised static test fixtures to confirm analysis results. The following images are brainstorms for this fixture which were eventually narrowed down to a modified hydraulic press.
The hydraulic press was outfitted with a cross plate mounted on square tubing. This mounting plate interfaced with the foot stretcher samples to simulate the interface between a foot stretcher and a Hydrow.
Hydraulic Press Fixture with Arduino Driven Load Cell
From these tests, it was determined that the stress concentrations would not cause a static failure but a fatigue failure. The testing was thereon outsourced to a cyclic testing laboratory where the final design was proven to endure worst-case scenario loading conditions over the equivalent cycles to the Hydrow lifecycle.
Final Design
Through design iterations and self-taught SolidWorks FEA, I reduced the maximum stresses applied to the foot stretcher assembly by a factor of 2.74. I worked with Hydrow's manufacturer to produce the new foot stretcher design documentation. This design is now in production.
