PSI - Issue 61

Zili Huang et al. / Procedia Structural Integrity 61 (2024) 252–259 Huang et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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2.2. Specimen preparation In this study, a simple wall structure containing nine layers was printed using the Delta WASP 3D clay/mortar printer at the University of Adelaide (UoA). Each layer is about 17mm in height and 400mm in length, printed using a circular plastic nozzle with a diameter of 30mm. The printer parameters were kept the same in all printings to maintain the consistency and repeatability of 3D-printed specimens. All the printed samples were cured for 28 days in the fog room at UoA under the same storage environment conditions to maintain consistency. For each printed wall, three cylindrical specimens of 100mm in diameter were prepared by waterjet cutting equipment as shown in Fig. 1a. The originally textured surfaces of all specimens were then smoothed using a saw, followed by the grinding technique to obtain cylindrical samples with two smooth surfaces for Brazilian disc testing. All disc specimens were air-dried before the application of speckle pattern for instrumentation using Digital Image Correlation (DIC).

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Fig. 1. (a) Three cylindrical specimens from the printed wall; (b) A cylindrical sample with smooth surface after grinding.

2.3. Test setup using AUSBIT The cylindrical specimens, after 28 days of curing period, were used in indirect tensile tests to examine the interlayer bond between layers. MTS loading frame is used in conjunction with the DIC technique to obtain the full field strain distribution and its evolution during loading. DIC is a non-contact and non-destructive method to measure the strain and deformation on the surface of specimens (Chu et al. 1985). It has been widely used in testing engineering materials, including 3D-printed disc specimens under impact loading (Sharafisafa & Shen 2020). In this study, the disc specimens after surface grinding were painted with black speckles in random patterns on a white background. The camera location and lighting conditions should be suitable for clear image capture and correlation throughout the whole testing procedure. This study applied the VIC-snap 2D Correlation Solutions commercial package (Correlation Solutions 2009). The load and displacement from the MTS loading machine were recorded at a rate of five samples per second, while images captured using the camera were at one frame per two seconds, given a huge amount of image data and the expected long duration of the testing, thanks to the use of AUSBIT (Verma et al. 2021b). The readings obtained from the two systems (MTS and DIC camera) were correlated and synchronized in time during post processing. Fig. 2a presents the overall testing setup.