PSI - Issue 31

M. Dundović et al. / Procedia Structural Integrity 31 (2021) 111 – 115

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M. Dundovi ć et al. / Structural Integrity Procedia 00 (2019) 000–000

1. Introduction Photoelasticity is an optical technique for experimental stress/strain analysis, which uses the temporary birefringence or double refraction exhibited by most transparent materials when subjected to strain. This method can be used to determine the state of stress in actual, transparent component or for assessing stress in prototype designs, a good review is given by Ramesh and Sasikumar (2020). It was the most commonly used stress analysis technique until the late twentieth century, when this role was taken over by numerical methods, such as finite element method (FEM) analysis. However, numerical methods require experimental validation in stress and strain analysis especially for complex geometries and loads, it is used in studies of fatigue and fracture as shown by Gupta et al. (2015), Shukla (2001), Baragetti et al. (2019a), Baragetti et al. (2019b), Baragetti et al. (2020) and Papadopoulou et al. (2019); in contact problems as shown by Marković and Franulović (2011) and Cazin et al. (2020); stress concentration as shown by Franulović et al. (2017), Monka et al. (2019) and Matvienko (2020); and composite and granular materials as shown by Hurley et al. (2014); Pertuz et al. (2020) and Kožar et al. (2020). Until now, photoelasticity has had a major drawback in the time and effort required for model preparation and fringe analysis. Nowadays, advances in digital photoelasticity have made stress analysis reliable and easier and advances in additive technologies have enabled the manufacture of test specimens from different materials and complex geometries according to Ajovalasit et al. (2015), Ramesh et al. (2011) and Patterson (2016). The aim of this research is to assess the use of photoelastic measurements for material behavior modeling of AM parts. A review of available sources has shown that stereolithography, Karalekas and Agelopoulos (2006) and Vieira et al. (2019); and polyjet technology Ju et al. (2017); have been used to print photoelastic specimens. The authors have concluded that the manufacturing of photoelastic models has become simpler and faster, and that experimental studies carried out have shown that the investigated methods are suitable for the manufacture of high quality models for use in photoelastic testing, however no reports for use of Digital light processing (DLP) technology in models production were found. DLP has recently emerged as a faster alternative to both stereolitography and polyjet technology, according to Wang and Wang (2017) its main advantage being the production speed and accuracy. It is used for fabrication of lattice metamaterials, shape memory polymers, and pneumatically actuated soft robots as shown by Patel et al. (2017) and Choong et al. (2017), for example. This paper deals with the evaluation of the usage of DLP models, built from an acrylic based photopolymer resin for material behavior modeling. For green and partially cured parts anisotropy is expected due to pixilation of each layer with shadow, poorly polymerized areas between pixels, according to Monzón et al. (2017). High-quality photoelastic models were produced and characterized optically under externally applied mechanical loading. Photoelastic measurements were carried out, and compared to analytical results. 2. Experimental method 2.1. Preparation of test specimens Rectangular beam specimens, 70 mm long, 5 mm thick and 10 mm high, were manufactured using commercially available DentaCLEAR photoreactive resin. The specimens were printed on ASIGA ® MAX UV 3D printer using the default settings and layer thickness of 50 μm. 16 specimens were printed on the building tray in four different layer placement orientations, respectively 0°, 30°, 60° and 90° to the horizontal, as shown in Fig. 1. The specimens were

Fig. 1. Batch of printed specimens.