Why two childshapes of compoundshape break apart so easily?

[cxl124]

Im working on a simulation of physics tests.Pre-fracture is not what I want.I think maybe I can do this with the compoundshape.But it seems that every child-pair in the compoundshape break apart so easily ,which is impossible when we drop a cup in the real world(even though the cup may break apart).
So I wanna know how can i adjust the strength between two child shapes to make the simulation better.I believe there may be a threshold or something I dont know..

Thanks in advance,
Chen