PI: Shi-Chang Wooh MIT Ultrasonic Phased Arrays for Nondestructive Evaluation of Cementitious Materials and Structures
This is a threeyear research proposal challenging the problems associated with the nation's aging infrastructure. It is aimed to study and develop ultrasonic phased array transducers most effective for assessing concrete structures and cementitious materials.
Deterioration of civil infrastructure systems (CIS) has become a central issue in reference to both safety and socioeconomic concerns. Deterioration itself is inevitable, but nondestructive evaluation (NDE) may offer a solution for preventing more serious consequences by detecting damage in its earlier stage. Development of reliable, expeditious and effective NDE methods facilitates early warnings of deterioration and structural integrity. Consequently, it helps making decision of priorities on repair, retrofitting and replacement, thus making contribution to assurance of public safety. Concrete structures are major building blocks of CIS. As the impact of their degradation is widely recognized, there are growing demands for efficient condition assessment technology. NDE of structural concrete is a relatively undeveloped discipline as compared with that of steel and other metals. The main mode of difficulty is the heterogeneous and attenuating nature of concrete.
Ultrasonic phased array systems, widely employed in the area of medical diagnostics, provide both quantitative measurement and imaging by means of electronic scanning of a target object with an acoustic beam. This feature eliminates the need of mechanical scanning and enhances nondestructive inspection capabilities, which cannot be realized by static methods using single element transducers. The potential advantages of the arrays include (1) increased maneuverability of the ultrasonic beam, (2) greater area of insonification from a fixed position, (3) high signal-to-noise-ratio, (4) reduced inspection time and automated testing procedure, and (5) expeditious imaging capability.
Phased arrays are recently extending their applications to metals and composite materials as well. However, these arrays cannot be utilized for concrete since they are designed without considering relevant aspects of importance. This research program intends to deal with innovative low frequency phased array ultrasonic sensors and their applications to cementitious materials.
It was observed from our previous study that acoustic focusing is more effective in dealing with inhomogeneous materials, and the feasibility tests demonstrated promising results that phased arrays can be utilized for concrete if properly designed. Nevertheless, the analysis raised a potential problem of enlarged "dead" zone that subsequently reduces effective inspectable area. This is a serious deficiency from a practical standpoint, while our previous study suggests an approach to resolve this challenging problem as presented in this proposal. We would like to explore the possibilities of extending the study in the proposed program.
The main objective of the proposed research is to examine the benefits and limitations of using ultrasonic arrays for detecting cracks and other defects within concrete structures. For this, a threephase research plan is proposed: (1) modeling and optimization, (2) system development, and (3) implementation and performance evaluation. It is anticipated that phased arrays will offer extreme flexibility in transforming the data into useful information presentable in either quantitative forms or imaging of defects in concrete.
