Application of impact hammers without inbuilt force transducer towards isolator dynamic stiffness and blocked force measurements

In-situ characterisation of structure borne sources and resilient elements (e.g. isolators/elastomeric mounts, springs) are important steps in diagnosis of noise and vibration issues. Such characterisation techniques involve measurement of Frequency Response Functions (FRF's) using an impact hammer or shaker excitation. While both excitation techniques are well developed, the impact hammer is widely in use for its ease of application. The impact hammer comes with an inbuilt force sensor to measure the contact force during excitation. The current paper presents an alternative way of using a standard tool hammer (without any inbuilt force sensor) to measure the same FRF's. The method employs measurement of transmissibility functions which only requires accelerometers. A case study is presented where the blocked forces of the source and the dynamic transfer stiffness of isolators is measured in-situ using the alternative hammer technique. The results are then compared to results obtained from a standard impact hammer (with force sensing). The new hammer technique provides excellent agreement in FRF measurement and source and isolator characterisation. The technique validates as a potential alternative for impact testing especially when standard impact testing tools are not available.