The blowup mechanism for 3-D quasilinear wave equations with small data

For a class of special three-dimensional quasilinear wave equations, we stu dy the blowup mechanism of classical solutions. More precisely, under the n ondegenerate conditions, any radially symmetric solution with small initial data is shown to develop singularities in the second order derivatives whi le the first order derivatives and itself remain continuous, moreover the b lowup of solution is of "cusp type".