the time required for the crack to propagate that distance is measured, and the crack velocity is simply v=0c/0t. the major advantage of using this test geometry should now be obvious: Since K1 is not a function of crack length, its follows that v is also not a function of crack length;i.e.,a constant crack velocity should be observed for any given load, which greatly simplifies the measurement and analysis the major disadvantage of the technique,however,is that it requires reasonably large samples that require some machining