FBG Based In Situ Characterization of Residual Strains in FDM Process

Abstract

Additive Layered Manufacturing has emerged as a popular manufacturing direction to accelerate product creation. Layered manufacturing can build parts that have traditionally been impossible to build because of their complex shapes or variety of materials. Layered manufacturing processes accumulate residual stresses and strains during material build up. Theses stresses may cause layer delamination and part distortion. This paper presents the work done on investigating residual strain accumulation in one of the most used additive processes, namely the Fused Deposition Modeling (FDM) and as a function of two typically selected process parameters. The developed residual strains at the end of the fabrication process were recorded using an optical sensor with a short fiber Bragg grating (FBG), embedded at the midplane of FDM built prismatic specimens. To assess the strain development without constraining effects from any adhesion to the building platform surface, measurements were taken at free-standing state at the end of the fabrication process. It is demonstrated that the magnitude of the solidification induced residual strains is significant and depends significantly on the selected material deposition direction (bead orientation) as a result of the formation of poor interbead interfaces and void (air gap) regions.