Adrian Cuc

Embedded non-destructive evaluation for structural health monitoring, damage detection, and failure prevention

In this paper we review the state of the art in an emerging new technology: embedded ultrasonic non-destructive evaluation (NDE). Embedded ultrasonic NDE permits active structural health monitoring, i.e. the on-demand interrogation of the structure to determine its current state of structural health. The enabling element of embedded ultrasonic NDE is the piezoelectric wafer active sensor (PWAS). We begin by reviewing the guided wave theory in plate, tube, and shell structures, with special attention to Lamb waves. The mechanisms of Lamb wave excitation and detection with embeddable PWAS transducers is presented. It is shown analytically and verified experimentally that Lamb wave mode tuning can be achieved by the judicious combination of PWAS dimensions, frequency value, and Lamb mode characteristics. Subsequently, we address in turn the use of pitch-catch, pulse-echo, and phased array ultrasonic methods for Lambwave damage detection. In each case, the conventional ultrasonic NDE results are contrasted with embedded NDE results. Detection of cracks, disbonds, delaminations, and diffuse damage in metallic and composite structures are exemplified. Other techniques, such as the time reversal method and the migration technique, are also presented. The paper ends with conclusions and suggestions for further work.

Structural Health Monitoring with Piezoelectric Wafer Active Sensors for Space Applications

Ultrasonic guided waves inspection using Lamb waves is suitable for damage detection in metallic structures. This paper will present experimental results obtained using guided Lamb waves to detect flaws in aluminum specimens with design features applicable to space applications. Two aluminum panels were fabricated from a variable-thickness aluminum top plate, with two bolted I-beams edge stiffeners and four bonded angle stiffeners. Artificial damages were introduced in the two panels: cracks, corrosions, and disbonds. The proposed investigation methods used bonded piezoelectric wafer active sensors to excite and receive Lamb waves. Three wave propagation methods were used: pitch-catch, pulse-echo, and the embedded ultrasonic structural radar. In addition, we also used a standing-wave damage detection technique, the electromechanical impedance method. The paper will present in detail the salient results from using these methods for damage detection and structural health monitoring. Where appropriate, comparison between different methods in detecting the same damage will be performed. The results have demonstrated the ability of piezoelectric wafer active sensors working in conjunction with guided Lamb waves to detect various types of damages present in complex geometry structures typical of space applications.

Space Application of Piezoelectric Wafer Active Sensors for Structural Health Monitoring

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive enablers for a large class of structural health monitoring (SHM) applications. This paper presents and discusses the challenges and opportunities related to the use of PWAS in the structures specific to space applications. The challenges posed by space structures are often different from those encountered in conventional structures. After a review of PWAS principles, the paper discusses the multi-physics power and energy transduction between structurally guided waves and PWAS; predictive modeling results using a simplified analytical approach are presented. Experimental results on space-like specimen structures are presented. Survivability of PWAS transducers under cryogenic space-like conditions is experimentally verified. The paper ends with conclusions and suggestions for further work.

Disbond detection in adhesively bonded structures using piezoelectric wafer active sensors

Adhesively bonded joints between metallic and composite plates are gaining increasing acceptance in safety critical applications such as automotive and aerospace structures. Lamb wave methods have considerable potential for the inspection of adhesive joints and assemblies for two reasons: they do not require direct access to the bond region, and they are much more amenable to rapid scanning than are compression wave techniques. Lamb waves can be excited in one plate of a bonded assembly, propagated across the joint region, and received in the second plate of the assembly. The paper will present a study of the use of guided Lamb waves for disbond detection in adhesively bonded layered media using piezoelectric wafer active sensors (PWAS). The focus is on developing and compare methods for damage and disbond detection in adhesively bonded structures. For far-field detection, propagating Lamb waves will be used in pitch-catch and pulse-echo modes. The pitch-catch method will send Lamb waves across the adhesive joint, while the pulse-echo method will send Lamb waves along the joint line. For near-field detection, high-frequency standing Lamb waves will be used to evaluate the presence of disbond from the changes in the mechanical impedance of the bonded joint. The standing wave approach is achieved with the self-sensing electromechanical impedance method. Both, the propagating and the standing Lamb waves are generated with the same PWAS installation. The combination of far-field and near-field damage detection in the same sensor installation is a unique feature of our work.

NON-DESTRUCTIVE EVALUATION (NDE) OF SPACE APPLICATION PANELS USING PIEZOELECTRIC WAFER ACTIVE SENSORS

Ultrasonic guided waves inspection using Lamb waves is suitable for damage detection in metallic structures. This paper will present experimental results obtained using guided Lamb waves to detect flaws in aluminum specimens with design features applicable to space applications. Two aluminum panels were fabricated from a variable-thickness aluminum top plate, with two bolted I-beams edge stiffeners and four bonded angle stiffeners. Artificial damages were introduced in the two panels: cracks, corrosions, and disbonds. The proposed investigation methods used embedded piezoelectric wafer active sensors (PWAS) to excite and receive Lamb waves. Three wave propagation methods were used: pitch-catch, pulse-echo, and the embedded ultrasonic structural radar (EUSR). In addition, we also used a standing-wave damage detection technique, the electro-mechanical impedance method. The paper will present in detail the salient results from using these methods for damage detection and structural health monitoring. Where appropriate, comparison between different methods in detecting the same damage will be performed. The results have demonstrated the ability of piezoelectric wafer active sensors working in conjunction with guided Lamb waves to detect various types of damages present in complex geometry structures typical of space applications.Copyright

Propagation of guided Lamb waves in bonded specimens using piezoelectric wafer active sensors

The nondestructive evaluation (NDE) of adhesively bonded structures is a complex process. Earlier work has confirmed that ultrasonic waves are influenced by the properties of the material in which they travel. Acousto-ultrasonic methods have been widely used by previous researchers to generate ultrasonic waves in plates and bonded structures for flaw detection, visualization, and measurements of the local properties of the jointed materials. This paper will present the methods and principles used for generation and propagation of ultrasonic guided waves (Lamb waves) using piezoelectric wafer active sensors (PWAS).

Predictive Modeling of Piezoelectric Wafer Active Sensors for Structural Health Monitoring

Piezoelectric wafer active sensors (PWAS) are lightweight and inexpensive transducers made from ferroelectric piezoceramic wafers attached to safety-critical structure. PWAS transducers enable a large class of structural health monitoring (SHM) applications. The focus of this paper is on the predictive modeling of structurally-attached PWAS. After a brief introduction, the paper reviews the PWAS-based SHM principles. Then, it follows with a discussion of shear-lag analysis, the transfer matrix method approach and the investigation of power and energy transduction between PWAS and structure. Finally, the paper presents a multi-physics finite element (MP-FEM) simulation. The paper ends with summary and conclusion.

Acoustical crack detection of the structure: Wigner–Ville distribution versus short time Fourier transform

The innovative acoustical forced oscillation method with nonstationary excitation for fatigue crack diagnostics of the structure is considered. Because of the nonstationarity of the acoustical structure response, the modern time‐frequency technique is used for diagnostics. The numerical simulation is carried out to investigate the diagnostic capabilities of the time‐frequency signal processing technique based on Wigner–Ville distribution. Results from the Wigner–Ville procedure are compared to results from the short time Fourier transform. [Financial support of the U.S. National Research Council Twinning Program with Ukraine (Senior Program Officer Kelly Robbins) is thankfully acknowledged.]