Dynamic fracture effects such as fracture delay and dependence of the material strength on the loading rate are known from multiple experiments on crack initiation and spallation. Classic linear oscillator (mass-spring system) is considered and critical spring stretch fracture condition is added. Due to relative simplicity of the model and availability of analytical solutions, the dynamic fracture effects can be studied analytically for the case of dynamic loading. Moreover, the mass-spring model can be calibrated to simulate some known experimental results on dynamic crack initiation due to pulse loading.