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Piezoelectric Vibration Absorber for Machining Applications

Periodic Reporting for period 1 - PIEZOMACH (Piezoelectric Vibration Absorber for Machining Applications)

Reporting period: 2016-10-01 to 2018-09-30

Undesired vibrations affect many engineering system, limiting their performance. This phenomenon is experienced in everyday life, for example driving a car on a rough road: the faster we go, the more we are affected by even small irregularities of the terrain, which cause dangerous vibrations.
Although smart engineering solutions enable us to reach unprecedented performance, such as for high speed trains and hypersonic airplanes, in some engineering fields, undesired vibrations are still a major concern.
In machining, oscillations generated by the so-called regenerative effect, significantly limit the speed of operation and the material removing rate.

The objective of the project is to suppress undesired vibrations in turning and milling machining operations by the development of a passive vibration absorber.
This vibration absorber exploits a modal interaction between the primary system (either the cutting tool or the workpiece) and the absorber itself. In other words, the absorber is designed such that it resonates at the same frequency of the primary system. This enables an exchange of energy between the two, allowing the absorber to dissipate vibration energy of the machine.
Furthermore, the implementation of an electrical circuit in the absorber, coupled to the mechanical system via piezoelectric elements, allows the transformation of mechanical energy into electrical one and to dissipate it through simple resistors.
The project also focuses on the exploitation of nonlinear components of the absorber, in order to enhance its performance and avoid detrimental dynamical phenomena.

The successful accomplishment of the project might have impact on the society at different level. Its direct outcome is a device able to improve performance of machining, enabling faster production and reduction of costs of many machined components.
From a scientific/engineering point of view, the exploitation of nonlinearity for vibration absorption might establish a benchmark, motivating the exploitation of the same working principle for other engineering field.
On the long term, the development of sophisticated and efficient vibration absorbers will give benefit to the society providing more reliable and safe engineering systems.
"At the beginning of the project, a thorough analysis of the performance of a mechanical absorber for vibration mitigation of a turning machine was performed. In particular, the dynamics of the so-called unsafe zone was investigated. This is a particularly troublesome parameter region, since it involves nonlinear phenomena only partially understood and it is characterized by unexpected instability of the machining operation. Results are explained in the journal paper ""Chatter Mitigation using the Nonlinear Tuned Vibration Absorber"" (Int. J. Non-Linear Mechanics), realized through a collaboration with the University of Liege (Belgium).

Then, the actual danger of the unsafe zone was experimentally studied. This investigation was performed at IK4-IDEKO (Spain), a research center specialized in machine tool vibrations. The results were twofold. On the one side, they clearly illustrated that the unsafe region exists (this is still a matter of debate in the community), on the other side, the experimental analysis illustrated the unpredictability of the system behavior in this region and its limited extent in the parameter domain, which, considering also the general uncertainty of system parameters in machining, reduces its relevance from a practical point of view. Results will be soon published in the journal ""Phil. Trans. Royal Society A"".

The third step of the project consisted in an experimental investigation of the performance of a vibration absorber based on a piezoelectric transducer for vibration mitigation in a milling machine. The analysis took more time than expected and it is still ongoing. Preliminary results illustrate the good matching between analytical predictions and experiments, however, they also highlight that the coupling factor between the mechanical and the electrical subsystems is a critical parameter.

Additionally, the performance of a passive vibration absorber based on a chaotic (but deterministic) behavior was investigated. The analysis illustrates the potential benefit of the proposed design for vibration mitigation in a general mechanical system. Results are published in the journal paper ""The Tuned Bistable Nonlinear Energy Sink"" (Nonlinear Dynamics), realized in collaboration with the Sapienza University of Rome (Italy).

The analysis of involved nonlinear systems illustrated the appearance of unusual dynamical phenomena; in particular, isolated resonance curves were experiences. These can be hardly identified with standard numerical and experimental techniques. A thorough analysis of the phenomenon was performed during this project. Results are published in the journal paper "" Isolated Resonances and Nonlinear Damping"" (Nonlinear Dynamics), realized in collaboration with the University of Cambridge (UK) and the University of Liege.

The possibility of addressing detrimental nonlinear behavior of a system by linearizing it was addressed in another study, currently under review at the J. Sound Vibration.

The application of the vibration absorber designed for machining was studied also for human induced vibration, for example in haptics devices. A paper presenting the obtained results is currently under preparation.

All results obtained in this project were presented in several conferences and seminar, as detailed below:

IMAC XXXV, Garden Grove (USA) January 2017
ENOC 2017, Budapest (Hungary) June 2017
EURODYN 2017, Rome (Italy) September 2017
CSNDD, Tangier (Morocco) June 2018
IFAC TDS 2018, Budapest (Hungary) June 2018
IUTAM Symposium ENOLIDES, Novi Sad (Serbia) July 2018
ICDVC-2018, Shijiazhuang (China) 28-30 June 2018

Department seminars:
University of Liege (Belgium), Host: Prof. Gaetan Kerschen
Technical University of Wien (Austria), Host: Prof. Alois Steindl
Nanjing University of Aeronautics and Astronautics (China), Host: Prof. Li Zhang

The work performed enabled us to shed some light on one of the most obscure aspects of instability in machining, that is the unsafe zone.
First, an analytical study illustrated a possible way to eliminate it, then a thorough experimental investigation clearly showed its practical relevance and extent.
The clear characterization obtained enables other researchers to better address their studies in the topic, towards critical aspects for machining performance.

The technological solutions proposed will be further exploited for other applications, sharing similar mathematical model. This process already started applying the developed vibration absorber to haptics devices.

The research stimulated various basics researches on nonlinear dynamics, such as isolated resonances generated by nonlinear damping and passive linearization of nonlinear structures. These works contribute to expand the global knowledge of nonlinear dynamical system behavior, necessary to face future engineering challenges.
Performance improvement in machining