A 3-balls-on-3-balls strength test for ceramic disks

In the usual tests to determine strength or lifetime under tension, bending or compression loading, the uniaxial stress state is present. However, in components very often multiaxial stresses occur. But also under uniaxial external loading, multiaxial stresses are possible, for instance, in notched components. Common tests are bending tests on thin circular disks.Following the description of conventional tests, a recently developed test using three loading and three supporting balls shall be addressed. For this test, the maximum principal stresses and the biaxiality are determined for a wide range of geometries by using the finite element method. First experimental results carried out on glass and alumina are reported.It was found that in all cases the results of the 3-balls-on-3-balls (3B3B) tests are slightly lower than the strengths obtained from the ball-on-3-balls (1B3B) tests. The main reason for this tendency is assumed to be the influence of the different effective surfaces involved in the two types of tests. The Weibull exponents m for these tests overlap within the 90% confidence intervals.