ME 370 · Machine Design
Beam Deflection: Model and Measurement
I compared beam-deflection calculations and SolidWorks FEA with measurements from a clamped PVC tube. The study also shows how fitting a material property to the measurements affects the interpretation of model agreement.
ME 370 · Machine Design · BYU–Idaho
Experiment overview
I loaded a hollow PVC tube with both ends clamped and measured its deflection. The fixed-end constraints make the model statically indeterminate, so the calculation must include compatibility conditions as well as equilibrium.
Question
How closely do beam-theory calculations and FEA reproduce the measured deflection, and how sensitive is that agreement to the assumed material stiffness?
Measurements and model fitting
The tube was 32.25 inches long, with a 0.397-inch outer diameter and 0.272-inch inner diameter. I applied three loads—0.298, 0.553, and 0.861 lb—at 20.125 inches from one end and measured deflection with a dial indicator. I compared Euler–Bernoulli hand calculations, singularity functions, and SolidWorks FEA. The elastic modulus began at an assumed 400,000 psi and was then fitted to the measurements at 668,000 psi.
Results and limitations
At the highest load, the recorded deflection was 0.201 inches. The hand calculation gave 0.2004 inches and FEA gave 0.201 inches at the reported precision. Because the modulus was fitted using the experimental data, this agreement is a consistency check on the fitted model rather than independent validation. The study taught me to distinguish measured inputs, assumed properties, and calibrated parameters.
Machine DesignBeam DeflectionFEAStructural Analysis