PSI - Issue 51

Mohammad Reza Khosravani et al. / Procedia Structural Integrity 51 (2023) 81–87 Mohammad Reza Khosravani et al. / Procedia Structural Integrity 00 (2022) 000–000

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as construction (Marchment and Sanjayan, 2020), electronics (Khosravani and Reinicke, 2020a), automotive (Leal et al., 2017), aerospace (Joshi and Sheikh, 2015), medicine (Marinopoulos et al., 2022), food industry (Mantihal et al., 2020), and healthcare monitoring (Nasiri and Khosravani, 2020). The review of previous research works confirmed that advances in 3D printing has led to improvements in dental care and provided a significant changes in industry (Jindal et al., 2020). A review of the literature reveals that di ff erent engineering aspects such as fatigue behavior (Ezeh and Susmel, 2018), structural integrity (Khosravani et al., 2020), failure analysis (Tezel et al., 2020), printing accuracy (Herpel et al., 2021), creep behavior (Reis et al., 2020), tensile properties (Gljuscic et al., 2021), environmental impacts (Khos ravani and Reinicke, 2020b) have been investigated in this field. However, further research seems to be necessary according to increasing applications of this rapid manufacturing process. Based on the American Society for Test ing and Materials (ASTM), 3D printing techniques have been classified into seven fundamental processing methods (ASTM F2792, 2012) of which vat photopolymerization is considered in the current study. Stereolithography (SLA) is a common form of vat photopolymerization technology used for creating models and prototypes in a layer-by-layer fashion using photo polymer resins. Among seven 3D printing methods, vat photopolymerization has announced a promising digital technique to produce dental restorations (Whitley et al., 2017). Advances in digital technologies (e.g., desktop and intra-oral scanners) and 3D printing provided significant increases in orthodontic treatments. In fact, Computer Aided Design (CAD), Computer Aided Manufacturing (CAM) software and 3D printing paving the way for transition from analogue to digital dentistry as a common practice in reality. Since 3D-printed parts are currently used as end-use products, fracture behavior and structural integrity of addi tively manufactured components have become of significant importance. In this respect, utilizing theory of fracture mechanics plays a crucial role in study of structural integrity. Indeed, the fracture mechanics approach is beneficial for characterization of materials. In this context, various techniques and methods have been developed to test metal lic and polymeric materials which can be used in fracture analysis of 3D-printed parts. Data obtained from fracture mechanics-based tests can be used to evaluate critical loads and determine remaining lifetimes of components. Liter ature investigation confirmed that study mechanical properties and fracture behavior of 3D-printed resins are ongoing research topics. For instance, e ff ects of curing time on the strength behavior of 3D-printed resin is investigated in (Miedzinska et al., 2020). In this respect, researchers printed the specimens using photocurable resin based on SLA technique. Based on a series of experiments under static and dynamic loading conditions, the stress-strain relationships are determined. According to the results, it is concluded that the examined material strengthened with an increase in the strain rate, which is a well-known phenomenon for polymers. Printing parameters such as printing direction and layer thickness have influence on the printing accuracy and mechanical properties of 3D-printed resins (Lowery et al., 2021). Moreover, printing process parameters can change the surface roughness and surface energy of the resin (Shin et al., 2020). Recently, in (Lee et al., 2022) e ff ects of layer thickness and printing orientation on the color stability of 3D-printed resin material have been investigated. To this aim, tooth-colored resin specimens are printed with three di ff erent printing directions and two layer thicknesses. The surface roughness of test coupons was measured at di ff erent time points. The obtained results conformed that the layer thickness, printing orientation, and storage time have significant e ff ects on the color stability of the 3D-printed resin samples. In this study, we investigated the mechanical behavior of 3D-printed dental resin. To this end, photocurable resin has been used to print the specimens using SLA method. Later, cylindrical 3D-printed specimens were subjected to static and dynamic compression tests. Based on the experimental finding, mechanical behavior of examined parts under di ff erent strain rate is determined. This work is structured as follows: in Section 2 an overview of AM is presented. Section 3 describes details of specimen preparation and experimental tests. Building on these experimental observations, the obtained results are presented. Finally, a short summary in Section 4 concludes the paper.

2. An overview of SLA 3D printing

The term SLA was first disclosed within Chuck Hull’s patent application, but the roots of the technique can be traced back to experiments carried out by Hideo Kodama in 1981 at the Nagoya Municipal Research Institute. While the first commercial SLA printers were developed in the 1980s by 3D systems, currently large industrial photocuring 3D printing machine is mainly based on SLA technique.