In this paper, we examine the long-standing problem of cracking during constrained sintering of a powder aggregate. Using binder jet 3D printing, we prepare ceramic green bodies in the form of center-notched panels, then use in situ imaging to observe how cracks nucleate and grow from the notch as the material sinters under restraint. Quantitative image analysis allows us to identify important characteristics of the sinter-cracking process, indicating a framework for analyzing the problem and developing methods for avoiding it, including representation of sinter-cracking as a creep crack growth process, use of fracture mechanics parameters to design specimen geometries that do not exceed critical stress intensities, and the possibility of exploiting the inherently ductile nature of sinter-cracking to mitigate damage.
K E Y W O R D Sfracture, in situ imaging, sinter/sintering, solid freeform fabrication
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Binder jet three-dimensional (3D) printing is a scalable, potentially low-cost additive manufacturing route able to process materials not attainable to other techniques, especially nonweldable materials. It relies on postprocess sintering to achieve final properties but encounters problems with distortion and cracking during sintering. The present work seeks to understand how part design geometry and 3D printing build orientation influence cracking during sintering, with the goal of mitigating the problem. In situ monitoring experiments reveal how sinter-cracks initiate and grow in 3D-printed notched panel specimens during densification. Different design geometries and build directions are tested to identify sinter-crack-resistant regimes.
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