These days, piezoelectric energy harvesting (PEH) is introduced as one of the clean and renewable energy sources for powering the self-powered sensors utilized for wireless condition monitoring of structures. However, low efficiency is the biggest drawback of PEHs. This paper introduces an innovative embedded metamaterial subframe (MetaSub) patch as a practical solution to address the low throughput limitation of conventional PEHs whose host structure has already been constructed or installed. To evaluate the performance of the embedded MetaSub patch (EMSP), a cantilever beam is considered as the host structure in this study. The EMSP transfers the auxetic behavior to the piezoelectric element (PZT) wherever substituting a regular beam with an auxetic beam is either impracticable or suboptimal. The concept of the EMSP is numerically validated, and the comsol multiphysics software was employed to investigate its performance when a cantilever beam is subjected to different amplitude and frequency. The finite element model results demonstrate that the harvesting power in cases that use the EMSP can be amplified up to 5.5 times compared to a piezoelectric cantilever energy harvester without patch. This paper opens up a great potential of using EMSP for different types of energy harvesting systems in biomedical, acoustics, civil, electrical, aerospace, and mechanical engineering applications.

The low stretchability of plain membranes restricts the sensitivity of conventional diaphragm-based pressure and inflatable piezoelectric sensors. Using theoretical and computational tools, we characterized current limitations and explored metamaterial-inspired membranes (MetaMems) to resolve these issues. This paper develops two MetaMem pressure sensors (MPSs) to enrich the sensitivity and stretchability of the conventional sensors. Two auxetic hexagonal and kirigami honeycombs are proposed to create a negative Poisson’s ratio (NPR) in the MetaMems which enables them to expand the piezo-element of sensors in both longitudinal and transverse directions much better, and consequently provides the MPSs’ diaphragm a higher capability for flexural deformation. Polyvinylidene fluoride (PVDF) and polycarbonate (PC) are considered as the preferable materials for the piezo-element and MetaMem, respectively. A finite element analysis was conducted to investigate the stretchability behavior of the MetaMems and study its effect on the PVDF’s polarization and sensor sensitivity. The results obtained from theoretical analysis and numerical simulations demonstrate that the proposed MetaMems enhance the sensitivity of pressure sensors up to 3.8 times more than an equivalent conventional sensor with a plain membrane. This paper introduces a new class of flexible MetaMems to advance wearable piezoelectric metasensor technologies.

There is a higher necessity for a safe and intelligent railway transportation system as an important foundation for the smart city concept. The need to develop real-time condition monitoring technology for limited access parts of high-speed trains, such as wheels, is an important challenge. This paper develops an Internet of Things (IoT) based nondestructive evaluation (NDE 4.0) platform for autonomous inspection of in-service train wheels. The proposed NDE 4.0 platform consists of a wireless transmission module (WTM) which is used to remotely transfer power from the bogie to its surrounded wheels and also to receive back the data from sensors installed on the axle box of the wheels. The WTM’s circuits were designed and simulated in LTSpice software. This paper reveals the great potential of using cyber-physical systems to intelligently manage big data and autonomously control National Railway Networks (NRN).

Interest in blue energy harvesting systems is rapidly growing and becoming widespread given its promise as a renewable and clean energy source. Blue energy harvesting from raindrop impact would allow low-power systems to operate in remote areas without the need for battery replacement and related maintenance. Insufficient power output is the most critical limitation that makes the conventional types of rain energy harvester (REH) typically unusable or/and infeasible. To overcome this limitation, a bio-inspired metasurface skin is proposed in this paper to serve as the membrane for a piezoelectric type of REHs. The proposed metasurface membrane is comprised of a system of biaxial-cuts inspired by snake scale. The power enhancement of the bio-inspired harvester with a metamembrane was studied and compared to its equivalent conventional harvester with a plain membrane when the substrate was under raindrop pressure. The Finite Element Model (FEM) results showed that the metamembrane could transfer more stress deformation to the piezo-element layer, thus enhancing power output. This is attributable to the metasurface membrane polarizing the PVDF better than a conventional plain membrane because of its higher ability to stretch the PVDF. The proposed bio-inspired harvester could be used for different public facilities such as tents, umbrellas, awnings, temporary roofs, coverings, and tarps to provide power for sensing, lighting, signage, digital displays, etc., especially in heavy-rain regions.

This Special Issue of the ASME Journal of Nondestructive Evaluation, Diagnostics and Prognostics of Engineering Systems (JNDE) has selected papers from the 47th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE 2020), which was held virtually on August 25 and 26, 2020. Papers selected for this special issue have gone through a rigorous selection and review process. First, conference session chairs recommended two papers with the potential to be journal papers. The authors of these papers were invited to further develop their conference papers into journal quality papers. All received manuscripts were reviewed following the journal's rigorous review process.The final selected papers represent the classical and contemporary disciplines of importance to NDE, diagnosis, and prognosis of engineering systems covered in the conference.We are grateful to the JNDE editorial board, conference track organizers, session chairs, authors, reviewers, and ASME journal publication staff for making this publication possible.

Structural health monitoring (SHM) using direct-write transducers is an emerging technology wherein the piezoelectric ultrasonic transducers are directly produced on the structures using scalable in situ processing method. In contrast to implementation of discrete piezoelectric transducers by manual installation as in existing SHM technologies, the direct-write transducer technology is promising for achieving the long-envisioned smart structures with self-diagnostic function, with the advantages of improved reliability, lowered cost, minimized weight and lowered profile. In this work, direct-write piezoelectric ultrasonic transducers were designed and fabricated near fastener holes in aluminum structures for evaluating the feasibility of monitoring the structural integrity around the holes. Notches and fatigue crack were produced from the holes, and the ability of detecting the notches and crack using the direct-write transducers was investigated by comparing the ultrasonic signals and evaluating appropriate damage indexes related to ultrasonic energy. The results and analyses show the potential of applying direct-write ultrasonic transducers for SHM around fastener holes.

Nondestructive Testing (NDT), Nondestructive Inspection (NDI), and Nondestructive Evaluation (NDE) are concerned with the techniques and measurements that provide data on the condition of the materials and structures at the time of manufacturing and during in-service experience. The NDT/I/E techniques for polymer-based composite fiber reinforced structures draw on a variety of physics principles for material measurements such as ultrasound, x-ray, infrared (thermography), shearography and electromagnetics. The precise method used for a given application will depend on the economic cost, subject to a sufficient probability of detection of any flaw or damage. This chapter discusses the modes of damage which can occur with polymer composites that are not obvious to the naked eye. The methodologies currently employed for NDT/I/E of aircraft structures are detailed and examples shown.

Ultrasonic sensors are one of the important technologies for structural monitoring and assessing the structural integrity for aircraft diagnostics and health management. Discrete ultrasonic sensors based on piezoelectric ceramics manually installed on structures have been evaluated for aircraft diagnostics and health management. However, it is challenging and time-consuming to install a large number of bulky and heavy discrete ultrasonic sensors in aircraft. In addition, positioning inaccuracy and bonding quality from the manual sensor installation may result in inconsistency. Direct-write ultrasonic sensors are batch fabricated on the structures using scalable processing method. The sensors have low profile and light weight as they are made of thin layer of coatings (typical total thickness <; 100 μm), By eliminating the adhesive layers required for installing discrete sensors, the direct-write sensors offer excellent acoustic coupling with the structure, and thus enable improved reliability and consistency. In this work, two case studies of using direct-write sensors made of piezoelectric polymer coating to detect cracks near fastener holes in aluminum structures are reported. Notches cut from the holes simulated fatigue cracks in Case Study I, and fatigue cracks extended from the notches were involved in Case Study II. The presence of these defects around the fastener holes resulted in reduced signal amplitude of different modes of ultrasonic waves. A computer-controlled testing system was developed to collect time-domain signals at various frequencies and to plot the data into 2D graphs, which can be potentially used as an “ultrasonic signature” of the structure. In addition, damage indexes based on the residual ultrasonic energy were calculated, and could be used as an indicator of severity of damage of the structure.

Kirigami and auxetic topologies are combined to design an innovative metamaterial-based substrate (MetaSub) for piezoelectric energy harvesters. The proposed MetaSub piezoelectric energy harvester (MPEH) contains both advantageous metamaterial properties of negative Poisson’s ratio capability and enhanced planar stretchability. A computational parametric analysis is conducted to develop the optimum design for the MPEH to trap the maximum elastic energy. A finite element analysis (FEA) is employed to analytically and numerically validate the simulation model of the MPEH. Accordingly, two experimental results of conventional and auxetic strain energy harvesters are used to evaluate the power enhancement of the MPEH. The FEA results demonstrate the average power gained by the MPEH at a low level of frequency and strain excitation (10 Hz and 150 με peak-to-peak) is 165 μ W which easily satisfies the minimum electric power amount required as a sensor node for self-powered wireless sensor networks. The harvested power output of the MPEH is 19.2 times more than power output produced by an equivalent conventional harvester with a plain substrate (8.6 μ W). The performance of the MPEH is investigated at different combinations of both low and high excitation frequencies. The creative design of the MetaSub can significantly improve the productivity of strain-induced devices whose efficiency is dependent on their deformation performance such as vibration energy harvesters, wearable sensors, flexible actuators, and micro electromechanical applications.

This paper introduces a creative metamaterial-based substrate (MetaSub) for piezoelectric energy harvesters. The MetaSub is a platform with a high flexibility in both longitudinal and transverse directions. The novel design of the MetaSub remarkably improves the productivity of strain-induced devices in structural health monitoring (SHM) applications, internet of thing (IoT) networks, micro electromechanical (MEMS) systems, vibration energy harvesters, sensor and actuators, and hundreds applications that its performance is related to their deformation capability. In this paper, a piezoelectric type of energy harvester is selected to be studied numerically as the first application of the MetaSub. The finite element results predict the average power output gained by the MetaSub piezoelectric energy harvester to be up to 19.2 times more than power generated by an equivalent conventional piezoelectric energy harvester.

Composite materials are widely used in a number of industrial sectors from aviation, space, to boat building, automotive, and sports goods. In recent years composite structures have seen a substantial increase of their use in the new generation of airplanes. The nondestructive testing and inspection of composite structures, both for manufacturing quality assurance and for in-service damage detection, has prompted the development and adaptation of a number of methods and techniques over the years. In this paper we review the various NDT methods for inspecting composites including water- and air-coupled ultrasound, bond testing, manual and automated tap testing, radiography, thermography, and shearography with emphasis given to techniques that demonstrated benefits to the practice of composite inspection.

A method, apparatus, and system for scanning an elongate structure. A scanner (112) in a scanning system (106) is moved axially along the elongate structure (102) using a translating structure (110) in the scanning system (106). The elongate structure (102) is scanned axially using an x-ray beam emitted by the scanner (112) as the scanner moves axially along the elongate structure (102) to perform an axial scan. The x-ray beam has a first orientation. A location on the elongate structure having an inconsistency is detected while scanning the elongate structure axially. The elongate structure (102) is scanned at the location with the x-ray beam in a second orientation.

A new class of rationally designed mechanophores is developed for highly sensitive built-in strain sensors in polymer composites. These mechanophores are designed to regenerate the π-conjugation pathway between the electron donor and electron acceptor by force-induced cleavage of the covalent bond to form a fluorescent dipolar dye.