What you're taling about is the field of fracture mechanics. Engineers have spent countless hours trying to figure out how cracks propagate in different materials. It turns out different types of cracks behave differently (shocker). It's a field applied not only to ceramics, but also to metals other materials.
But defects are also a big part of how metals deform. If you calculate the theoretical strength of a perfect crystal of, say, aluminum you get a strength of several times what it's actual strength is. This is because real crystals have defects at the atomic level - misalignments in the crystal structure that allow for the metal to deform more easily. These are called "dislocations" and are similar to cracks, except they're not - as I said these are atomic-level "shifts" in crystal structure. The misalignment allows groups of atoms to slide more easily by other groups.
Interestingly, adding dislocations to a metal will decrease it's strength- to a point. But when you add too many dislocations, they interfere with each other and actually increase the strength of the metal. This is how materials like copper work harden (When you deform them, you create dislocations. It's also why when you heat them up, they soften again - the heat allows the crystal structure to resettle in a more organized structure, decreasing dislocations.
But defects are also a big part of how metals deform. If you calculate the theoretical strength of a perfect crystal of, say, aluminum you get a strength of several times what it's actual strength is. This is because real crystals have defects at the atomic level - misalignments in the crystal structure that allow for the metal to deform more easily. These are called "dislocations" and are similar to cracks, except they're not - as I said these are atomic-level "shifts" in crystal structure. The misalignment allows groups of atoms to slide more easily by other groups.
Interestingly, adding dislocations to a metal will decrease it's strength- to a point. But when you add too many dislocations, they interfere with each other and actually increase the strength of the metal. This is how materials like copper work harden (When you deform them, you create dislocations. It's also why when you heat them up, they soften again - the heat allows the crystal structure to resettle in a more organized structure, decreasing dislocations.