Inhomogeneous mechanical properties in additively manufactured parts characterized by nondestructive laser ultrasound technique

Additive manufacturing (AM) or Three dimensional (3D) printing has become a promising manufacturing technique in architecture, aerospace, biomedical and automotive industries. However, additively manufactured parts need to demonstrate their stable mechanical properties like elastic modulus and strength. In this study, four various thickness of 3D printing samples were prepared to measure the elastic modulus by tensile testing and laser ultrasound technique (LUT). Besides, an inversion technique is followed to extract the elastic modulus from the 3D printed parts through LUT measured dispersion curve. Results indicate that significant differences in Young's modulus were observed between the various thickness of the tensile specimens. All the elastic modulus inverted values were well agreed with experimental measurements with the controlled error percentage of 0.02–1.35%. Further, individual layer modulus was calculated from the inversed averaged modulus and fitted with parabolic equation. Form the obtained outcomes, to print a sample with 40-layers, the first (top) layer modulus was 3254 MPa while bottom layer shows 4706 MPa which indicates a difference of 45% with inhomogeneous across the printed layers. While printing a new layer, the ultraviolet (UV) light can be exposed to previously printed layers and this more irradiation of UV light could stimulate to additional polymerization of remaining unreacted monomers and increased the modulus in the bottom layer.