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

• Must interface with existing components such as injection molds

• Must be able to be installed during service visits if necessary

• 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.