Impact testing lightweight structures

Impact testing has always been an attractive method when exciting all types of structures to estimate frequency response functions (FRFs). For most structures, the option of using single or multiple input excitation with shakers is also a reasonable possibility. Lightweight structures made of carbon fiber construction, thin metal panels or plastics pose problems for both excitation methodologies. For these lightweight structures, the use of shaker excitation, even with very small shakers, is often undesirable since the attachment of the shaker(s) may result in constraining or altering the structure. While impact testing does not have these constraints, using very small excitation hammers create practical problems as well. Some of these are well known (like multiple impacts) and some are less well known (high energy signal distortion in the delta-sigma ADCs). This paper reviews some of these problems, shows examples of data collected demonstrating these problems and suggests ways that these problems can be minimized once the problems are understood.