Session: 06-03-01: Advances in Aerospace Structures and Materials-1

Paper Number: 172748

Tensile Fracture Behavior of Octahedral Lattice Structures Containing a Large-Scale Crack 

Over the past decade, significant progress in additive manufacturing technologies has facilitated the creation of complex geometries, particularly for lightweight structural components. Among the most promising applications of these advancements is the development of lattice structures, which have received considerable attention from industries such as aerospace engineering and civil engineering. Traditionally, lattice structures have predominantly been studied under compression loading conditions, due to their remarkable energy absorption characteristics. However, their fracture behavior, defined as the response of a lattice structure containing one or more macroscopic flaws, remains relatively underexplored especially under different loading scenarios. Moreover, much of the existing research has concentrated on far-field mechanical characterization, with limited emphasis on the localized phenomena occurring within the lattice itself.

The present study is dedicated to investigating the “fracture” behavior exhibited by octahedral lattice structures that contain what we define as a macroscopic “crack”–a series of broken or disconnected joints over several cells in the structure. These structures are fabricated using polylactic acid (PLA) through the fused deposition modeling (FDM) technique, a widely accessible additive manufacturing method. In order to assess the influence of defects introduced by limitations of the fabrication process and how these might interact with the macroscale crack, a comparison between the designed geometry and the actual manufactured specimens is conducted using X-ray computed tomography (CT). This non-destructive technique allows for the identification of internal voids and manufacturing inconsistencies that may influence mechanical performance.

Several different sample configurations are loaded experimentally under tensile loading conditions, both in the pristine (i.e., uncracked) case and in specimens that include pre-existing macroscale cracks. The experimental setup of the cracked lattice structures enables a focused examination of their fracture behavior under mode I loading (i.e., symmetric opening), which is then compared to the uncracked structure response. All experiments are performed using a displacement-controlled ramp loading until complete failure occurs. The mechanical response during these experiments is monitored using optical methods, specifically by applying particle tracking techniques to a series of marked points at the joints on the specimen surface. This allows for detailed tracking of joint displacements in relation to the advancing crack tip.

The results reveal distinct and insightful behaviors regarding how cracks initiate and propagate through the lattice, leading up to eventual failure of the specimen. The analysis further explores potential explanations for the observed fracture mechanisms. Key parameters such as the strain field distribution, the presence and distribution of internal voids, and the influence of the specimen’s geometric features are examined. Both far-field and local (within the lattice) measurements are considered to provide a comprehensive fracture characterization. Finally, a finite element model is developed, showing good agreement with the experimental data in the linear elastic range. This model is then used to investigate various parameters affecting fracture, such as strain energy release rate or near-tip stress concentrations, which may be difficult or impossible to measure experimentally. Through this multifaceted experimental-numerical approach, a deeper understanding of lattice structure failure under tensile loading can be achieved.

Presenting Author: Polyvios Romanidis University of Illinois, Urbana-Champaign

Presenting Author Biography: Polyvios Romanidis is a graduate student at the University of Illinois at Urbana-Champaign. His interests lie in the field of Structural Mechanics and Materials for aerospace applications, with a specific focus on lattice structures.

Authors:

Polyvios Romanidis University of Illinois, Urbana-Champaign
John Lambros University of Illinois, Urbana-Champaign