Acousto-Ultrasonic Structural Health Monitoring of Aerospace Composite Materials

Piezoelectric transducers have a long history of applications in nondestructive evaluation (NDE) of material and structure integrity owing to their ability of transforming mechanical energy to electrical energy and vice versa. From an acoustic point of view, there is no difference between structural health monitoring (SHM) and conventional NDE since both rely on the same physics in the sense that in either case acoustic waves are generated and then detected. SHM was ‘born’ from the conjunction of several techniques and has a common basis with NDE. In fact, several NDE techniques can be converted into SHM techniques, by integrating sensors and actuators inside the monitored structure. For instance, traditional ultrasonic testing can be easily converted into an acousto-ultrasonic SHM system, using embedded or surface-mounted piezoelectric wafer active sensors (PWAS). These sensors should be affordable, lightweight, and unobtrusive such as to not impose cost and weight penalty on the structure and to not interfere with the structural strength and airworthiness. Other damage measuring methods based on large area measurements have been used in SHM development for verification and validation of damage and/or for understating the proposed SHM approach; however, they do not seem appropriate for permanent installation onto the monitored structure and will not be discussed under the heading of ‘SHM sensors’. This paper presents and discusses an overview of ultrasonic SHM techniques for composite materials. After a brief introduction, it presents the PWAS-based SHM principle, which is followed by a discussion of the passive and active ultrasonic SHM techniques. The paper identifies advantages and disadvantages of these in-situ NDE methods and guidelines for future work on heterogeneous, anisotropic materials, like aerospace composite polymer

Roll Maneuver Control of UCAV Wing Using Anisotropic Piezoelectric Actuators

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76333/1/AIAA-2002-1720-656.pd

Effect of central and non-central frequency components on the quality of damage imaging

Accurate image reconstruction of damage through Lamb wave diffraction tomography (LWDT) requires substantial information of scatter field. This can be achieved using transducer network to collect the scatter field data. However, this requires a large number of transducers that creates logistical constraints for the practical applications of the technique. Various methods have been developed to improve the practicability of LWDT. One of the main approaches is to employ data at multiple frequencies within the bandwidth of the excitation signal. The objective of this study is to investigate the performance of using the data at non-central frequencies to reconstruct the damage image using LWDT. This provides an understanding on the influence of data at each individual frequency in the damage image reconstruction.In this paper, a series of numerical case studies with consideration of different damage sizes and shapes are carried out. Different non-central frequencies data is used to reconstruct the damage image. The results show that using the data at different non-central frequencies leads to different qualities of the reconstructed damage images. The quality of these reconstructed damage images are then compared to investigate the information contained of the data at each individual frequency. The study shows that the non-central frequencies data can provide additional information in the damage image reconstruction. Overall, the results of this study provide insights into the influences of the data at different frequencies, which is essential to advance the developments of the LWDT.Gnana Teja Pudipeddi, Ching-Tai Ng, Andrei Kotouso

A review of zoonotic infection risks associated with the wild meat trade in Malaysia.

The overhunting of wildlife for food and commercial gain presents a major threat to biodiversity in tropical forests and poses health risks to humans from contact with wild animals. Using a recent survey of wildlife offered at wild meat markets in Malaysia as a basis, we review the literature to determine the potential zoonotic infection risks from hunting, butchering and consuming the species offered. We also determine which taxa potentially host the highest number of pathogens and discuss the significant disease risks from traded wildlife, considering how cultural practices influence zoonotic transmission. We identify 51 zoonotic pathogens (16 viruses, 19 bacteria and 16 parasites) potentially hosted by wildlife and describe the human health risks. The Suidae and the Cervidae families potentially host the highest number of pathogens. We conclude that there are substantial gaps in our knowledge of zoonotic pathogens and recommend performing microbial food safety risk assessments to assess the hazards of wild meat consumption. Overall, there may be considerable zoonotic risks to people involved in the hunting, butchering or consumption of wild meat in Southeast Asia, and these should be considered in public health strategies