Modelling the mechanical response of piezoelectric force transducers

Pneumatic conveying systems are used to transport particulate materials, for example cereal grains or plastic pellets, in an enclosed pipeline; therefore, a well-designed system is safe and reliable. However, if systems are not designed correctly, damage to the conveyed material and/or the pneumatic conveying pipeline can result. This paper discusses the investigations undertaken to understand better the resonant response of a piezoelectric force transducer during single particle-surface impacts. The impacts in question are typical of those found in pneumatic conveying systems.
The commercial software ANSYS LS-DYNA was used to model Silica Glass and Nylon 6,6 particles impacting a measurement system which incorporated a piezoelectric force sensor and a steel impact surface. The piezoelectric force transducer was modelled based on supplier literature and knowledge of basic transducer construction, where the piezoelectric material was modelled as a mechanical item only with no consideration of the changes in properties due to the piezoelectric effect. The impact was also modelled without the piezoelectric sensor in order to predict the effect of the transducer on the impact characteristics such as contact time, deflection of the particle and the surface (maximum approach), and the force of contact.
The numerical investigation found that the size of the particle and its material properties were important in determining the response of the measurement system to the impact, as was observed in previous experiments. This was demonstrated through comparing the deflection response of the piezoelectric material to that observed in experiments for the particles mentioned previously and to a particle with the properties of a ‘golf ball’. The effect of refining the mesh and by consequence changing the length of the time-step was also investigated to show convergence within the resolution of the model. Furthermore, the number of elements in the contact area was dependent on both the particle material properties and the refinement of the mesh, resulting in an effect on the uncertainty in the determination of the maximum contact force which is calculated from the maximum pressure and a determination of the maximum contact radius. It is anticipated that these results could be used in the future to evaluate measurements of resonant response from a force transducer in impact situations.