# The role of defects in dictating the strength of brittle honeycombs made by rapid prototyping

## TL;DR

This study investigates how manufacturing and design defects affect the tensile strength of 3D-printed PMMA honeycomb structures using experiments and finite element analysis, highlighting defect sensitivity and transition flaw size.

## Contribution

It provides a comprehensive analysis of defect impacts on honeycomb strength, combining experimental data with finite element modeling to quantify defect sensitivity.

## Key findings

- Manufacturing defects reduce tensile strength significantly.
- Design defects like missing cells and inclusions also weaken the lattice.
- A transition flaw size concept quantifies defect sensitivity.

## Abstract

Rapid prototyping is an emerging technology for the fast make of engineering components. A common technique is to laser cut a two-dimensional (2D) part from polymethyl methacrylate (PMMA) sheet. However, both manufacturing defects and design defects (such as stress raisers) exist in the part, and these degrade its strength. In the present study, a combination of experiment and finite element analysis is used to determine the sensitivity of the tensile strength of PMMA hexagonal lattices to both as-manufactured and as-designed defects. The as-manufactured defects include variations in strut thickness and in Plateau border radius. The knockdown in lattice tensile strength is measured for lattice relative density in the range of 0.07 to 0.19. A systematic finite element (FE) study is performed to assess the explicit role of each type of as-manufactured defect on the lattice strength. As-designed defects such as randomly perturbed joints, missing cells, and solid inclusions are introduced within a regular hexagonal lattice. The notion of a transition flaw size is used to quantify the sensitivity of lattice strength to defect size.