We analyze the dynamics of stress waves interacting with the right-angled and/or the semicircular free surface in the PMMA (polymethyl-methacrylate) specimen using the smoothed particle hydrodynamics (SPH) method. The stress waves emanate from the charge hole and interact with the free surface. The results obtained from the numerical calculation are compared with experimental results of the model blasting using the electric detonator as a charge. The stress waves in PMMA and shock waves in air are observed by means of the laser-shadowgraph method. Propagation of stress waves, reflection and transmittance at the interface between PMMA and air are visualized both experimentally and numerically.