Replicate the acrylic viewport pressure experiments of J. D. Stachiw with Calculix finite element modelling

J. D. Stachiw performed experiments to measure the deflection of 3 different sizes and thicknesses of acrylic over a flange with a range of pressures until implosion. My goal was to replicate these results using finite element modelling in Calculix and then compare this against the real-world experiments to see if they match.

Repository and Book

The source code for my repository is available at https://github.com/waynepiekarski/openscad2calculix4stachiw and is a fork of the OpenSCAD to Calculix tool https://github.com/timmaxw/os2cx. This repository is designed to replicate the experiments done by J. D. Stachiw in Figure 7.12 from the following book:

Stachiw, J. D., Acrylic plastic viewports for ocean engineering applications (1977)
https://catalog.hathitrust.org/Record/008333526
Main Author:    Stachiw, J. D
Language(s):    English
Published:      San Diego, Calif. : Naval Undersea Center, 1977
Subjects:       Ocean engineering > Ocean engineering / Materials
Oceanographic submersibles > Oceanographic submersibles / Materials
Physical Description:   2 v. : ill. ; 28 cm

Link to Figure 7.12 and the PDF of the book: https://babel.hathitrust.org/cgi/pt?id=uc1.31822009085754&view=1up&seq=337

Real-world measurements

In Figure 7.12, Stachiw measures the deflection of 3 different sizes and thicknesses of acrylic over a flange over a range of pressures until implosion. The figures for 1.5 inch, 3.33 inch, and 4.0 inches are included below.

Compiling and running the simulation

Code tested on Ubuntu 20.04:

./apt-get-deps
qmake
make
cd stachiw
# Perform calculations for different sizes, thickness, and pressure
./all_stachiw_multi.sh
# Generate graphs of experiments
./pandas-plot-stachiw.py
# Run GUI with single example
./gui_stachiw_single.sh

Results

These plots compare the Stachiw results against those calculated from CalculiX, as well as using standard equations for circular plate with uniform load and edges simply supported. Both the CalculiX results and the equations are perfectly linear, while Stachiw's results are curves that stop when the acrylic burst open. So the results are close and useful for approximate calculations, but do not predict the burst pressure or change at the same rate with pressure.

1.5 inch - Stachiw vs Calculix

3.33 inch - Stachiw vs Calculix

4.0 inch - Stachiw vs Calculix

Plot of all Stachiw Figure 7.12 measurements