Effect of lattice design on mechanical response of PolyJet additively manufactured cellular structures

Abstract

Additively manufactured complex lattice geometries incorporated in structural materials is a relatively new concept and gaining popularity. In this approach solid bodies are replaced by repeating tailored design cellular structures enabling significantly light-weighted components. However, as a building block of the entire part, these cellular structures' design has crucial role on the overall mechanical properties. The purpose of this work is to reveal how different design parameters (3 different cell types representative of stiff, just stiff and under stiff cases, and cell size) affect the modulus of elasticity and the maximum stress of the compression test samples additively manufactured in cellular fashion. A comprehensive methodology is presented for the design, fabrication, and prediction of mechanical properties of polymer-based lattice structures. A commercial material jetting based 3D printer (i.e., the Objet 30 Prime by Stratasys) was used to manufacture the rigid translucent photosensitive polymer samples with porosity ranging from 54 to 70% and different unit cell structures. Uniquely designed or existing unit cells were used to obtain stretch and bending dominated mechanical behaviors. The failure mechanisms and the performance of the custom design unit cell specimens are investigated via numerical simulation and compression tests. The elastic modulus of cellular structures was calculated and compared using both Gibson-Ashby and Hooke equations. The effect of the unit cell structure and size on mechanical properties is discussed. The results show that while stretch dominated diagonal model shows better strength properties (up to 250%), bending dominated centered model has better elongation (up to 120%). As a general conclusion, it is seen that mechanical properties are enhanced with downsizing of the cell scales. Fine tuning of the unit cells gives a new perspective on tailored lattice structures, enabling structures with stiff or rubber-like behavior to be obtained using the same material.