Variably Dense Objects

2024

Experimental analysis to determine the effects of infill pattern and density on part strength using uni-axial tension tests.

Context

Course: Mechanics of Solids and Structures (ENGR2320)
Project Prompt: “Design and conduct an analytical experiment that enhances your understanding of the content covered in the course”
Timeframe: 2 weeks‍
Year: Spring 2024

Process

I’ve always wondered whether the infill pattern I choose when preparing a 3D print has any effect on the strength of my final part. So, for my final Mechanics of Solids and Structures (MechSolids) project, I wanted to conduct an experiment that would tell me just that.

Along with two teammates, I conducted a series of 24 uni-axial tension tests with 3D printed ‘dog bone’ samples. We tested for two different variables: infill density and infill pattern. The density tests were performed at 15% (control), 30%, 45%, and 60%, using the grid infill pattern. The pattern tests were performed with the cubic, gyroid, and 3D honeycomb patterns. For each variable, we tested 3 identical samples and averaged the collected data between them to get 7 sets of data.

*Diagram showcasing the infill densities and patterns tested*

*Photo of a fractured 3D printed dog bone sample in the jaws of the Instron machine used for tension testing*

After conducting tests on all 24 samples and condensing the results into 7 sets of load and extension data, we analyzed the results based on the ultimate tensile strength, fracture stress, extension at fracture, and modulus of toughness.

Through this analysis, we produced a number of plots:

*Plot comparing the resulting stress-strain curves from all 7 data sets*

*Plot comparing the ultimate tensile strength between each data set*

*Plot comparing the stress at fracture between each data set*

*Plot comparing extension at fracture between each data set*

*Plot comparing modulus of toughness between each data set*

Based on these comparisons, we determined that increasing infill density is a way to increase part strength under uni-axial load. However, there appears to be no difference in overall part strength between different infill patterns. When infill density is increased, more material is being added to the inside of the object, and therefore distributes force over a greater area over a given cross-section. Infill pattern, however, only arranges the same amount of material in different ways and not increasing the area over which a force is distributed.

After our analysis was complete, we used Adobe Illustrator to create a final poster to showcase our work to our peers:

*Final Project Poster* *created in Adobe Illustrator*

Reflection

This project offered a valuable opportunity to bridge theoretical knowledge of material mechanics with practical application. Designing and conducting uni-axial tension tests allowed me to gain a deeper, intuitive understanding of how forces act on complex objects. Observing the physical effects of tension and analyzing the corresponding data provided meaningful insights into the process of determining material properties, reinforcing the connection between experimental results and theoretical principles.