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The geographical separation between various supply chain participants creates challenges in ensuring the integrity of the parts under circulation. These supply chains have to regularly deal with counterfeiting, a significant problem with an estimated value equivalent to at least the tenth-largest global economy. Industries are constantly upgrading their anti-counterfeiting methods to tackle this ever-increasing issue. Traditionally, a physical or cyber-physical part identifier is used to assert the integrity and identity of parts moving through the supply chain. For this work, we propose the use of electromechanical impedance measurements to generate a robust, unique part identifier linked to physical attributes. Electromechanical impedance measurements have been employed as a basis for non-destructive evaluation techniques in damage detection and health monitoring. We propose using these high-frequency measurements recorded through bonded piezoceramic transducers to help uniquely identify parts.

For this study, identical piezoceramic transducers (cut from the same wafer to minimize variations) were mounted on identically manufactured specimens. The only distinction between these specimens was the physical variation introduced during manufacturing and instrumentation. Multiple measurements for each specimen were recorded. A unique part identification methodology based on linear projection was created using these measurements. Lastly, a leave-one-out-study was performed to uniquely identify the left-out specimen. This was used to validate the part identification methodology. This paper introduces the use of electromechanical impedance measurements (widely adopted for damage detection) as a unique part identifier, with a basic experimental implementation of the proposed mechanism on identically manufactured parts. The paper also highlights some challenges and future work needed to make this methodology robust and adaptable.

 

Impedance-based structural health monitoring (SHM) is recognized as a non-intrusive, highly sensitive, and model-independent SHM solution that is readily applicable to complex structures. This SHM method relies on analyzing the electromechanical impedance (EMI) signature of the structure under test over the time span of its operation. Changes in the EMI signature, compared to a baseline measured at the healthy state of the structure, often indicate damage. This method has successfully been applied to assess the integrity of numerous civil, aerospace, and mechanical components and structures. However, EMI sensitivity to environmental conditions, the temperature, in particular, has been an ongoing challenge facing the wide adoption of this method. Temperature-induced variation in EMI signatures can be misinterpreted as damage, leading to false positives, or may overshadow the effects of incipient damage in the structure.

In this paper, a new method for temperature compensation of EMI signature is presented. Data-driven dynamic models are first developed by fitting EMI signatures measured at various temperatures using the Vector Fitting algorithm. Once these models are developed, the dependence of model parameters on temperature is established. A parametric data-driven model is then derived with temperature as a parameter. This allows for EMI signatures to be calculated at any desired temperature. The capabilities of this new temperature compensation method are demonstrated on aluminum samples, where EMI signatures are measured at various temperatures. The developed method is found to be capable of temperature compensation of EMI signatures at a broad frequency range.

 

Printed low-density materials form microrobots capable of high-speed motion, force output, and self-sensing feedback. 

Steady-state traveling waves in structures have been previously investigated for a variety of purposes including propulsion of objects and agitation of a surrounding medium. In the field of additive manufacturing, powder bed fusion (PBF) is a commonly used process that uses heat to fuse regions of metallic or polymer powders within a loose bed. PBF processes require post-process removal of loose powder, which can be difficult when blind holes or complex internal geometry are present in the fabricated part. Here, a preliminary investigation of a simple part is conducted examining the use of traveling waves for post-process de-powdering of additively manufactured specimens. The generation of steady-state traveling waves in a structure is accomplished through excitation at a frequency between two adjacent resonant frequencies of the structure, resulting in two-mode excitation. This excitation can be generated by bonded piezoceramic elements actuated by a sinusoidal voltage signal. The response of the structure is affected by the parameters of the excitation, such as the particular frequency of the voltage signal, the placement of the piezoceramic actuators, and the phase difference in the signals applied to different actuators. Careful selection of these parameters allows adjustment of the quality, wavelength, and wave speed of the resulting traveling waves. In this work, open-top rectangular box specimens composed of sintered nylon powder and coated with fine sand are used to represent freshly fabricated parts yet-to-be cleaned of un-sintered powder. Steady-state traveling waves are excited in the specimens while variations in the frequency content and phase differences between actuation points of the excitation are used to affect the characteristics of the dynamic response. The effectiveness of several response types for the purpose of moving un-sintered nylon powder within the specimens is investigated. 

The flexibility offered by additive manufacturing (AM) technologies to fabricate complex geometries poses several challenges to non-destructive evaluation (NDE) and quality control (QC) techniques. Existing NDE and QC techniques are not optimized for AM processes, materials, or parts. Such lack of reliable means to verify and qualify AM parts is a significant barrier to further industrial adoption of AM technologies. Electromechanical impedance measurements have been recently introduced as an alternative solution to detect anomalies in AM parts. With this approach, piezoelectric wafers bonded to the part under test are utilized as collocated sensors and actuators. Due to the coupled electromechanical characteristics of piezoelectric materials, the measured electrical impedance of the piezoelectric wafer depends on the mechanical impedance of the part under test, allowing build defects to be detected. This paper investigates the effectiveness of impedance-based NDE approach to detect internal porosity in AM parts. This type of build defects is uniquely challenging as voids are normally embedded within the structure and filled with unhardened model or supporting material. The impact of internal voids on the electromechanical impedance of AM parts is studied at several frequency ranges.