Flex Cracking for 0402 MLCCs
I found a very thorough PhD thesis that measured flex cracking on MLCCs, and 0402s are MUCH less likely to crack than larger parts.
The test was performed by dropping a circular test board such that it was subjected to 5000g for 0.3ms.  It turns out that &quot;fast&quot; strains induce cracking at lower strains than &quot;slow&quot; strains created by bending a board by slowly pressing on it, so this is a worst-case analysis for many board flex environments.
See EVALUATING THE SUSCEPTIBILITY OF ELECTRONIC COMPONENTS ASSEMBLED WITH LEADED SOLDER TO FLEXURAL FAILURES, WITH HIGH RATE CONSIDERATIONS by James Robert Watkins here.
The plot below shows that 0402 failure rate was significantly lower than larger parts.  See the paper for a description of the test setup.