Computing the bond strength of 3D printed polylactic acid scaffolds in mode I and II using experimental tests, finite element method and cohesive zone modeling

Nogol Nazemzadeh,Anahita Ahmadi Soufivand,Nabiollah Abolfathi

doi:10.1007/s00170-021-08124-w

Abstract

The advent of the Three-Dimensional (3D) printing technique, as an Additive Manufacturing technology, made the manufacture of complex porous scaffolds plausible in the tissue engineering field. In Fused Deposition Modeling based 3D printing, layer upon layer deposition of filaments produces voids and gaps, leading to a crack generation and loose bonding. Cohesive zone model (CZM), a fracture mechanics concept, is a promising theory to study the layers bond behavior. In this paper, a combination of experimental and computational investigations was proposed to obtain bond parameters and evaluate the effect of porosity and microstructure on these parameters. First, we considered two different designs for scaffolds beside a non-porous Bulk design. Then, we performed Double cantilever beam and Singe Lap Shear tests on the 3D printed samples for Modes I and II, respectively. Afterward, we developed the numerical simulations of these tests using the Finite element method (FEM) to obtain CZM bond parameters. Results demonstrate that the initial stiffness and cohesive strength were pretty similar for all designs in Mode I. However, the cohesive energy for the Bulk sample was approximately four times of porous samples. Furthermore, for Mode II, the initial stiffness and cohesive energy of the Bulk model were five and four times of porous designs while their cohesive strengths were almost the same. Also, using cohesive parameters was significantly enhanced the accuracy of FEM predictions in comparison with fully bonded assumption. It can be concluded that for the numerical analysis of 3D printed parts mechanical behavior, it is necessary to obtain and suppose the cohesive parameters. The present work illustrates the effectiveness of CZM and FEM combination to obtain the layer adhesive parameters of the 3D printed scaffold.

Highlights

The cutting-edge 3D printing technology fabricates objects by deposition of materials in the layer upon layer fashion [1, 2]
It is noticeable that the numerical Finite Element Method (FEM) approach was used repeatedly in the literature to predict the mechanical response of Fused Deposition Modeling (FDM) parts in silico very well [1, 6, 16]
3D printing and characterization: The samples were 3D printed with specified parameters in Figure 7, and scanning electron microscopy (SEM) images were captured from top and side views

Summary

Introduction

The cutting-edge 3D printing technology fabricates objects by deposition of materials in the layer upon layer fashion [1, 2]. Extrusion-based FDM, as a straightforward and cost-effective method [4, 5], provides users to fabricate complex threedimensional parts quickly by deposition of the melted filaments through a nozzle on a building platform. Naghieh et al predicted the mechanical properties of porous PLA bone scaffolds fabricated by FDM [6]. Gremare et al performed tensile tests on the 3D printed PLA bone scaffold to examine the effect of pore dimension on the mechanical properties [15]. In the experimental approach, fabrication of numerous specimens and performing mechanical tests to find an appropriate mechanical property for FDM parts are costly and time-consuming. Crack propagation is susceptible to occur between adjacent layers of the part [18], which leads to ultimate failure This phenomenon can be modeled and analyzed by the fracture mechanics-based CZM

Methods

Results

Conclusion