PSI - Issue 51

Maja Dundović et al. / Procedia Structural Integrity 51 (2023) 192 – 198 M. Dundovi ć et al. / Structural Integrity Procedia 00 (2019) 000–000

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displacement with vertical component being -4 mm for Sample A and -5 mm for Sample B, while the horizontal component has been measured using digital microscope. Maximal calculated stresses are 62.7 MPa for Sample A, and 72.4 MPa for Sample B, while the stress distributions are shown in Fig. 4c and Fig. 4d, for Samples A and B, respectively. The Sample A have failed approximately after 2500 cycles, while the Sample B after 300 cycles. The maximal force curve per cycle is shown at Fig. 4a and Fig. 4b, for Samples A and B, respectively. 3.3. Photoelastic observations Photoelastic observations on DLP printed corner-filleted flexure hinges subjected to dynamic loading have been performed by means of a circular polariscope in order to assess the photoelastic methods in dynamic tests on relatively small compliant mechanisms, which will serve as preliminary data for further research. In our previous work static pure bending tests on printed samples (using the same material) have been performed and photoelastic constant has been determined. Dynamic photoelastic experiments performed in this paper showed that the sample wide to depth ratio has been too high, resulting in a very bright fringes on compliant parts of flexure hinges. Despite this fact, the performed qualitative photoelastic observations have shown that the photoelasticity is applicable in dynamic experiments and useful for stress concentration and residual stress determination. In Fig. 5 the last cycle snapshots of Sample B under the dynamic loading are shown, clearly showing the fringes around the stress concentration locations. The last snapshot shows the plastic deformations immediately after fracture. Very similar fringe pattern caused by the residual stress has been noticed; this can surly be used for modeling and verifying the anisotropic material behavior, which can be expanded for similar nontransparent materials. The residual stress fringe pattern is shown in Fig. 6. The samples, 14 mm thick, used in previously discussed experiments are shown on Fig.6a, while the thickness of the samples shown in Fig.6b is 7 mm. Aforementioned difference in fringes brightness can be observed.

Fig. 4. Corner-filleted hinges flexural tests result (a) Sample A maximal force per cycle; (b) Sample B maximal force per cycle; (c) Sample A maximal stress; (d) Sample B maximal stress.