Evaluation and prediction of the tensile properties of continuous fiber-reinforced 3D printed structures

doi:10.1016/j.compstruct.2016.07.018

Composite Structures

Volume 153, 1 October 2016, Pages 866-875

https://doi.org/10.1016/j.compstruct.2016.07.018 Get rights and content

Abstract

Three dimensional (3D) printing is a technique conventionally used to manufacture prototypes. Commercial desktop 3D printers have become available which produce functional 3D printed parts. The MarkOne by Mark Forged manufactures printed structures reinforced with continuous Carbon, Fiberglass or Kevlar fibers. The aim of this study is to evaluate the elastic properties of the fiber reinforced 3D printed structures and predict elastic properties using an Average Stiffness (VAS) method. Samples evaluated in this study were produced by varying the volume fraction of fibers within the 3D printed structures (4.04, 8.08 and 10.1% respectively). The experimentally determined elastic modulus was found to be 1767.2, 6920.0 and 9001.2 MPa for fiber volume fractions of 4.04, 8.08 and 10.1% respectively. The predicted elastic moduli were found to be 4155.7, 7380.0 and 8992.1 MPa. The model results differed from experiments by 57.5, 6.2 and 0.1% for the 4.04, 8.08 and 10.1% fiber volume fractions. The predictive model allows for the elastic properties of fiber reinforced 3D printed parts. The model presented will allow for designers to predict the elastic properties of fiber reinforced 3D printed parts to be used for functional components which require specific mechanical properties.

Introduction

Three dimensional (3D) printing or Rapid Prototyping (RP) is a manufacturing process that produces components from computer-aided design (CAD) software. Three dimensional printing is not an entirely new technology but the advent of open source, low cost 3D printers has led to drastic proliferation of this technology. This process has become highly popular with researchers and hobbyists for the design and manufacture of 3D parts as it allows for the rapid design and manufacture of complex component.

3D printing can be divided into several categories: Fused Deposition Modeling (FDM), Selective Laser Melting (SLM), Stereolithography (STL) or Laminated Object Manufacturing (LOM) [1]. Most low-cost desktop 3D printers utilize FDM as the manufacturing process. FDM forms a 3D geometry by assembling individual layers of extruded thermoplastic filament. The FDM manufacturing process is useful for rapidly producing prototypes and in some cases can be used to produce functional components. However, there are disadvantages to utilizing FDM printed parts for functional components. FDM components are formed by an additive manufacturing process combining successive layers of molten thermoplastic. Due to this process delamination of the component layers can occur resulting in premature failure. Additionally, FDM printed parts typically have lower elastic properties than injection molded components of the same thermoplastics [2].

Several authors have evaluated the mechanical properties of FDM 3D printed parts [3], [4]. The primary focus of these studies has been on conventional FDM printed components [3], [4], [5]. These studies have evaluated both commercial FDM 3D printers [3], [4], [5] as well as low-cost desktop 3D printers [2]. Currently, new thermoplastic materials are becoming available; these include thermoplastic filaments with embedded metallic particles or reinforced with short carbon fibers [6], [7]. Additionally, a new 3D printer has become commercially available that reinforces 3D printed parts with continuous Glass Fiber, Kevlar Fiber or Carbon Fiber filaments (the MarkOne by MarkForged). This new 3D printer, MarkOne by MarkForged, is designed to produce functional 3D printed parts which are stronger than conventional FDM printed components. The MarkOne 3D printer reinforces FDM printed parts by embedding concentric rings of fibers that follow the components geometry. Specifically, the objective of these new FDM printing methods is to increase the strength of 3D printed parts so that these components can be used for functional products rather than producing non-functional scale models. Currently, continuous fiber reinforced 3D printed parts have not been extensively investigated in literature. The use of continuous carbon fiber reinforcement was performed by Mori et al. using a RepRap based 3D printer; however, this study did not evaluate or determine the elastic properties of the carbon fiber reinforced 3D printed components [8]. Understanding the tensile properties of fiber reinforced 3D printed components is necessary to ensure these components meet their required design specifications.

To determine if continuous fiber reinforced FDM printed components can be used for functional components, the mechanical properties need to be determined. As a fundamental first step, the first objective of this study is to evaluate the tensile properties of continuous fiber reinforced 3D printed components produced using the MarkOne 3D printer by performing conventional tensile tests. The second objective of this study is to develop a methodology that allows designers to predict the elastic constants of continuous fiber FDM printed components. Conventional composite material modeling techniques, such as classical laminate plate theory (CLPT) or volume averaging methods [3], [5], [9], [10], [11], [12], can be applied to these materials in order to predict its mechanical properties.

Based on the aforementioned composite material modeling framework a mathematical model for predicting the tensile elastic properties of fiber reinforced 3D printed components will be presented. The results of this study aims to provide designers with a methodology for determining the mechanical properties of fiber reinforced 3D printed components. The presented mathematical model will reduce the need for multiple design iterations in order to produce functional 3D printed components.

Section snippets

Mechanical testing

Samples for mechanical testing were fabricated using a MarkOne desktop 3D printer (MarkOne, MarkForged, Somerville, MA). The sample geometry was created according to ASTM D638-14 (ASTM D638-14 Standard Test Method for Tensile Properties of Plastics) using a Type I geometry [13]. The geometry used in this study and critical dimensions are shown in Fig. 1. The test specimen geometry was created using a computer aided design (CAD) software package (SolidWorks 2015 SP4.0, Dassault Systems, Waltham,

Dimensional measurement

Geometric measurements of the test samples were performed to evaluate the consistency of the MarkOne 3D printer. Measurements were also required in order to determine the cross-sectional area of the test samples. The geometric measurements of the test samples were compared with the nominal dimensions for the ASTM D638 Type I dogbone sample shown in Fig. 1. The width of the narrow section (WN), width at both end tabs (W1 and W2) and sample thickness (T) was compared for all samples. A t-test was

Dimensional measurement

The dimensional accuracy of the MarkOne 3D printer was evaluated. The dimensions of the 3D printed test specimen were compared with nominal CAD dimensions for the 3D printed geometry. Table 6, Table 7, Table 8, Table 9 demonstrate that the printed sample geometries differed from the nominal CAD part dimensions. The results in Table 6, Table 7, Table 8, Table 9 are consistent with other studies that have evaluated the dimensional accuracy of desktop 3D printed parts [2]. Table 6, Table 7, Table 8

Conclusions

The tensile properties of fiber reinforced 3D printed components were evaluated in this study. Tensile tests were performed on four combinations of samples that were produced using the MarkOne 3D printer. The testing results demonstrated that an increase in the volume of fiber reinforcement results in an increase in stiffness and ultimate strength of the test samples.

In addition, a volume averaging stiffness method has been developed in order to predict the tensile properties of the fiber

Acknowledgements

The authors would like to thank Bernie Falkner for his assistance with the mechanical testing of the test specimen. We would also like to thank Patrick Pilarski for allowing for us to use his 3D printer for this study.

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Evaluation and prediction of the tensile properties of continuous fiber-reinforced 3D printed structures

Abstract

Introduction

Section snippets

Mechanical testing

Dimensional measurement

Dimensional measurement

Conclusions

Acknowledgements

Procedia Eng

Compos B Eng

Compos Struct

Compos Sci Technol

Additive manufacturing technologies : 3D printing, rapid prototyping, and direct digital manufacturing

Evaluation of dimensional accuracy and material properties of the MakerBot 3D desktop printer

Rapid Prototyping J

Characterization of the mesostructure of fused-deposition acrylonitrile-butadiene-styrene materials

Rapid Prototyping J

Anisotropic material properties of fused deposition modeling ABS

Rapid Prototyping J

Mechanical behavior of acrylonitrile butadiene styrene fused deposition materials modeling

Rapid Prototyping J