Bracket Deflection Design

Overview

The goal of Phase II of this project was to design, manufacture, and validate a compliant aluminum structure that deflects in a predictable and linear elastic manner under load with no yielding. The structure was required to achieve a target deflection of 0.4 inches under a 100 lbf vertical load, corresponding to an overall spring constant of 250 lbf/in, while minimizing material usage to improve structural efficiency. 

Design Approach

Using SolidWorks, my team designed a custom geometry constrained by fixed support and load locations, mandatory mounting holes, and protected manufacturing zones. The design process was iterative and simulation-driven, with Finite Element Analysis used to evaluate deflection, stress distribution, and potential yielding under load. Particular attention was paid to stress concentrations created by geometry transitions and cut features, leveraging fillets and material redistribution to maintain linear elastic behavior.

Fabrication and Experimental Validation

The finalized design was exported as a DXF file and manufactured from 0.25-inch-thick 6061-T6 aluminum using a waterjet cutter. The part was then tested on an Instron universal testing machine, where a vertical load was applied incrementally up to 100 lbf. Load-deflection data from the physical test was used to evaluate the accuracy of the FEA predictions and to assess how closely the structure met the target spring constant.

Results and Discussion

Results

Discussion

The final bracket met the design objectives with strong agreement between simulation and experimental testing. Under a 100 lbf load, the bracket exhibited a measured deflection of 0.415 in, within 3.75% of the 0.4 in target, corresponding to an effective spring constant of 242.8 lbf/in, just 3% below the design goal. Instron testing showed a linear force–displacement response with no observable yielding, validating the FEA predictions. Minor discrepancies between predicted and measured deflection were attributed to material tolerances and fixturing differences, but did not significantly impact overall performance.

Future iterations of this analysis could improve the accuracy of spring constant predictions by refining both the modeling assumptions and boundary conditions used in FEA. In particular, revisiting the fixture constraints to more closely replicate the Instron test setup, such as accurately modeling pin contacts and degrees of freedom, would reduce differences between simulated and experimental stiffness. Additionally, updating the model to use the measured bracket thickness rather than the assumed nominal 0.25 in would further improve prediction accuracy. Together, these refinements would help align the simulated force–displacement response more closely with test results.