A comparative study of piezoelectric unimorph and multilayer actuators as stiffness sensors via contact resonance

Piezoelectric bar-shaped resonators were proposed to act as hardness sensors in the 1960 s and stiffness sensors in the 1990 s based on the contact impedance method.In this work, we point out that both multilayer and unimorph（or bimorph） piezoelectric actuators could act as stiffness/modulus sensors based on the principle of mechanical contact resonance. First, the practical design and the performance of a piezoelectric unimorph actuator–based stiffness sensor were presented. Then the working principle of piezoelectric multilayer actuator–based stiffness sensors was given and verified by numerical investigation. It was found that for these two types of resonance-based sensors, the shift of the resonance frequency due to contact is always positive, which is different from that of the contact impedance method. Further comparative sensitivity study indicated that the unimorph actuator–based stiffness sensor is very suitable for measurement on soft materials, whereas the multilayer actuator–based sensor is more suitable for hard materials.

Mechanical Property Evaluation on the Bending and Compressing Behaviour of Nano-beam

Based on quasicontinuum（QC） multiscale simulation method,a series of simulation models were set up for bending and compressing rod-shaped microstructure of single crystal Cu.The effects of structural parameters on typical mechanical properties were analyzed,such as elastic modulus,elastic limit,yield strength,and Poisson’s ratio.According to the analysis of displacement,inner stress and strain energy,the mechanisms of deformation and failure were also revealed.The experimental result shows that the mechanical properties exhibit obvious size effect during the bending and compression process.In the bending simulation,when the span-thickness ratio is more than 10,the elastic modulus rises slightly with the increase of strain.And the smaller the beam is,the faster the elastic modulus grows.Meanwhile,when the spanthickness ratio keeps constant the elastic modulus will decrease with the growth of the beam sizes.However,in the compression model,the size effect on Poisson’s ratio is not remarkable.The dimensional change in one direction cannot influence the mechanical parameters greatly.Mechanical twins and dislocation contribute to the compression behaviour greatly.Meanwhile,the stress concentration can also be found in the inner partial area and the strain energy decreases abruptly after the crush of beam microstructure.