PSI - Issue 68

Zili Huang et al. / Procedia Structural Integrity 68 (2025) 266–271

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Z. Huang et al. / Structural Integrity Procedia 00 (2025) 000–000

3. Result and discussion Fig. 3 shows the AUSBIT application and results on two 3D printed cement-based specimens with the diameter of 100 mm. The use of this technique to control snap-back has been reported in our recent work (Huang et al., 2024) and this study focuses on fracture energy evaluation. The load is applied diametrically from the top of the disc specimen which is perpendicular to the printing layers. The load increases from zero to the load set point of 1 kN. After reaching this load set point, the test switches control from vertical to lateral displacement, and proceeds with a set value of lateral displacement rate. As expected in Brazilian disc testing, the load increases almost linearly to the peak values of 17.2 kN and 17.4 kN respectively. Snap-back behaviour can be clearly seen in two successful tests in Fig. 3. As can be seen, the load-vertical displacement curve in both figures show the snap-back behaviour with reversals of displacement in the post-peak stage.

Fig. 3. Load-vertical displacement curves with snap-back.

The tensile strength of the specimen can be obtained using the peak load as per Equation 1 (Verma et al. 2021b): ! = $ " % # ! (1) where P is peak load (kN), D is the diameter (mm), and t is the thickness (mm) of the disc specimen. The obtained tensile strength of 2.88 MPa and 2.62 MPa are very close as shown in Table 2.

Table 2. Dimensions and tensile strength of test specimens. Specimen No. Diameter ( mm )

Thickness (mm )

Tensile strength ( MPa )

1 2

98.5 98.1

38.5 43.1

2.88 2.62

In this study, AUSBIT presents the potential of obtaining class-II (snap-back) response from the indirect tensile testing approach of 3D printed cement-based materials. In class-II response the strain energy stored in the specimen at peak load is enough to drive the failure process and cause the specimen to break. Therefore, to maintain stability during the failure process, the excess energy needs to be systematically reduced. Hypothetically, the specimen will be fully fractured at the end of snapback stage at point “e” in Fig. 4a and 4b, and that can be assessed using image-based instrumentation. The red region (area of “abef”) in Fig. 4a and 4b indicates the dissipated energy due to cracking. Once the specimen is fully fractured diametrically (e.g. at the end of snap-back stage), the unloading slope can be assumed to be the same as the loading slope of the specimen. The blue region (area of “bce”) indicates the elastic strain energy in the two broken halves, and the dotted pattern region (area of “adf”) indicates the total energy stored in the specimen at peak load. The averaged fracture energy describes the energy release per unit area of newly created fracture surface when the specimen is fully fractured. Therefore, the averaged intrinsic fracture energy can be determined by the area under the load-vertical displacement curve with snap-back response which is signified as the total energy release to break the