An improved fan blade impact test

Abstract

Impact testing may be performed on an axial fan blade using a strain gage as a reference and a dead blow hammer instead of an instrumented impact hammer. The strain gage is mounted between the blade base and airfoil and is sensitive to all bending modes. This method is useful when the mass of a hammer or exciter armature would affect the blade response adversely. A small accelerometer is moved around a grid in the normal fashion. Some of the improvements are a better defined response in both bending and twisting modes and higher coherence frequency response functions.