Mounting of accelerometers with structural adhesives: experimental characterization of the dynamic response

The use of accelerometers to monitor the vibrations of either complex machinery or simple component involves some considerations about the mounting of the sensor to the structure. Different types of mounting solutions are commonly used but in all cases they can be classified in one of these categories: stud mounting, screw mounting, adhesive mounting, magnetic mounting and probe sensing. Indeed each of them has a specific field of application depending on e.g. the mounting surface conditions, the temperature, the accessibility to the specific mounting point, etc. The choice of the mounting solution has a important effect on the accuracy of the usable frequency response of the accelerometer, since the higher the stiffness of the fixing, the higher the low-pass frequency limit of the mounting. This paper specifically focuses on adhesive mounting of accelerometers, which includes a great number of different products from the temporary adhesives like the beeswax to the permanent ones like cyanoacrylate polymers. Among the variety of commercial adhesives, three specific glues have been experimentally compared to assess their transmissivity and the results are reported in this paper. A two component methylmethacrylate (HBM X60), a modified silane (Terostat 737) and a cyanoacrylate (Loctite 401) adhesives have been used to joint two aluminium bases, one connected to an accelerometer and the other to the head of electromagnetic shaker. A design of experiments (DOE) approach was used to test the system at several levels of amplitude and frequency of the external sinusoidal excitation supplied by the shaker.