Crack deflection by design – Utilizing the material inhomogeneity effect on miniaturized additively manufactured structures

A natural crack exhibits a surrounding stress field, which may overlap considerably with a stress field caused by any material inhomogeneity, influencing the crack driving force and extension direction. To utilize this effect for potentially increasing the apparent toughness, a defined pore is introduced near a potential crack path, whereby upon interaction, the crack tip can be deflected or trapped, depending on the intermediate distance. Since fundamental mechanics is well-known, a miniaturized notched bending specimen geometry incorporating a pore was selected to investigate the application potential for parts manufactured via multi-photon lithography. The size regime is representative of the smallest available objects and requires in situ SEM testing, which was completed with finite element modeling based on crack path prediction through analyzing the local crack driving force. The high dimensional repeatability of the process allowed for testing reliably reproduced specimens with variation of crack to pore distance only. The prediction represented the actual crack paths well, underlining successfully facilitated crack path alteration. The toughness was mainly increased by crack trapping within the pore, where deflection had a quantitatively negligible effect.