Since concrete members with fiber-reinforced polymer (FRP) reinforcement are not as ductile as conventional structures, and since concrete in retrofitted members is often covered and not readily available for visual inspection, development of nonintrusive and nondestructive damage assessment tools is essential. Ultra- sonic pulse velocity (UPV) can provide such an assessment tool, and help quantify the extent and progression of damage in concrete. Continuous UPV monitoring of a number of concrete cylinders and concrete-filled FRP tubes showed the concrete-filled tubes to have higher sensitivity at lower stress ratios as compared to plain concrete. When compared with the axial strain energy, the UPV damage index has a much better resolution for stress ratios up to about 50% of ultimate strength. This ratio depends on the thickness of the jacket. It was also shown that the UPV has a strong correlation with volumetric strains after confinement is activated. Therefore, at high levels of axial loads when the confining pressure of the jacket results in volumetric compaction, the UPV increases by about 6% of the initial pulse velocity. Repeated loading generally induces the same rate of change of UPV damage index as that of the initial loading on the virgin specimen. This phenomenon occurs irrespective of the stress ratio at which the specimen is unloaded or reloaded. A comparison of the UPV damage index with the normalized acoustic emission counts reveals that the two methods have different sensitivities at different stages of loading and could potentially complement each other as a hybrid damage assessment tool.

Damage assessment of frp-encased concrete using ultrasonic pulse velocity

Ultrasonic velocity is widely used in the investigation of material properties. Physical dimensions such as sample thickness and surface profile can also be the information sought after in nondestructive testing. In a conventional ultrasonic measurement, however, the measured quantity is usually the time-of-flight, not velocity or thickness. When either velocity or thickness is precisely known, the other can be easily deduced. Unfortunately in many cases, neither the velocity nor the thickness is known to the required precision, or they can both vary spatially. A method is therefore needed to map out the spatial distribution of the velocity and thickness simultaneously. The ability to image the surface profiles that give rise to the thickness variation is also desirable. Simultaneous velocity and thickness scan can be implemented in a number of configurations and have been reported by a number of authors in the literature. This paper focuses on the ability of this technique to image very small changes in velocity and thickness simultaneously. This technique is also extended to map out the surface elevation contours and cross-sectional profiles of a sample. Special considerations for achieving accurate and reliable velocity, thickness and profile images are discussed in detail. This technique for nondestructive evaluation and material characterization is then demonstrated using three industrially relevant materials: (1) plasma sprayed thermal barrier coating, (2) composite laminates containing foreign objects and anomalies, and (3) creep/rupture tested superalloy samples.

Simultaneous Velocity, Thickness and Profile Imaging by Ultrasonic Scan

Directing ultrasound at the cemento-enamel junction (CEJ) of human teeth: I. Asymmetry of ultrasonic path lengths.

This article describes a single transducer ultrasonic imaging method based on ultrasonic velocity measurement that eliminates the effect of thickness variation in the images of ceramic and composite plate samples. The method is based on using a reflector located behind the sample and acquiring echoes off the sample and reflector surfaces in two scans. As a result of being thickness-independent, the method isolates ultrasonic variations due to material microstructure. Its use can result in significant cost savings because the ultrasonic image can be interpreted correctly without the need for precision thickness machining during nondestructive evaluation stages of material development. Velocity images obtained using the thickness-independent methodology are compared with apparent velocity maps and c-scan echo peak amplitude images for monolithic ceramic (silicon nitride), metal matrix composite and polymer matrix composite materials having thickness and microstructural variations. It was found that the thickness-independent ultrasonic images reveal and quantify correctly areas of global microstructural (pore and fiber volume fraction) variation due to the elimination of thickness effects. A major goal achieved in this study was to move the thickness-independent imaging technology out of the lab prototype environment and into the commercial arena so that it would be available to users worldwide.

Using a single transducer ultrasonic imaging method to eliminate the effect of thickness variation in the images of ceramic and composite plates

The speed of ultrasound at 20MHz differs inside human teeth depending on which tissues are involved. At least two out of four dental tissues exhibit variations in the longitudinal velocity (cL). The aim of this in vitro study is to describe the laterally varying propagation velocity of tangentially propagating longitudinal waves. At a distance of 5mm from the crown reference, the cL is determined using longitudinal sections and a pulse-echo technique. Several graphs are combined to account for the corono-apical decrease in cL and the laterally varying cL distribution along horizontally adjacent relative tooth width portions. The laterally increasing cL of 21 specimens at radial locations rises from 2900to4000m∕s. A mathematical evaluation reveals an optimal horizontal formula of the form cL(5mm)=a+bX2ln(X), where X is the standardized lateral parameter relative to individual tooth width w, which is compensated for offsets. Individual residuals and a,b coefficients of the corresponding approximations are p...

M.S. Hughes

Papers

An automated algorithm for simultaneously producing velocity and thickness images