Novel in-situ residual strain measurements in additive manufacturing specimens by using the Optical Backscatter Reflectometry

Shaoquan Wang,Kaspar Lasn,Christer Westum Elverum,Di Wan,Andreas Echtermeyer

doi:10.1016/j.addma.2020.101040

Shaoquan Wang, Kaspar Lasn + Show 3 more

Open Access

https://doi.org/10.1016/j.addma.2020.101040

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Abstract

Material extrusion (MEX) is a well established production method in additive manufacturing. However, internal residual strains are accumulated during the layer-by-layer fabrication process. They bring about shape distortions and a degradation of mechanical properties. In this paper, an in-situ distributed measurement of residual strains in MEX fabricated thermoplastic specimens is achieved for the first time. This innovative measuring system consists of an Optical Backscatter Reflectometry (OBR) interrogation unit connected to a distributed fiber optic strain sensor which is embedded during the MEX process. The characteristic residual strain distribution inside 3D printed components is revealed and numerically validated. The main mechanisms of residual strain creation and the sensing principles of in-situ OBR are described. A minimum measuring range of 4 mm and a spatial resolution of 0.15 mm were experimentally demonstrated. The potential of in-situ OBR technology for detecting invisible manufacturing defects was shown by a trial experiment.

Highlights

Material extrusion (MEX) is the most conventional additive manufacturing technology for plastics, known as 3D printing
The in-situ Optical Backscatter Reflectometry (OBR) has never before been adopted for MEX fabricated thermoplastic components according to the best of this author's knowledge
A novel approach for in-situ measurements of the solidification induced residual strain distribution in MEX fabricated specimens was demonstrated for the first time

Summary

Introduction

Material extrusion (MEX) is the most conventional additive manufacturing technology for plastics, known as 3D printing. MEX technology shows good potential in the automotive, aerospace, design and biomedical industries, due to its low cost, simplicity and environmental friendliness. It has already captured half of the 3D printing market [2]. Residual stresses can significantly affect the dimensional accuracy, cause warping, interlayer delamination, cracking, decrease of mechanical properties and even interrupt the printing procedure when the specimen detaches from the printing bed. This kind of disadvantage, innate to layer-by-layer build-up hinders the application of the MEX

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