Through-transmission ultrasonic

Figure 13 Schematic of the through-transmission ultrasonic mode and associated A-scan.

W. E. Woodmansee, Through-transmission ultrasonic attenuation measurements on adhesively-bonded structures, in Ultrasonic Materials Characterization, NBS SP 596, pp. 425-432, Proc. 1st International Symposium, Gaitherburg, MD (June 7-9, 1978). 

Figure 6.31 General scheme for through-transmission ultrasonic non-destructive testing. An ultrasonic signal is sent from the transmitter to the receiver through the bonded component. If the received signal, 4r, is very small compared to the transmitted signal, 4t, then it may be concluded that most of the energy has been reflected by an area of low acoustic impedance, i.e. a void may be present [138].

Fig. 3.9. Through transmission ultrasonics in a bonded joint (a) ray paths of a single pulse (b) amplitude-time relationship.

Since attenuation and porosity are related, traditional porosity determination in composites is performed as attenuation measurements using ultrasonic tone burst through-transmission. 

The common civil engineering seismic testing techniques work on the principles of ultrasonic through transmission (UPV), transient stress wave propagation and reflection (Impact Echo), Ultrasonic Pulse Echo (UPE) and Spectral Analysis of Surface Waves (SASW). 

The ultrasonic C-scan technique is the most widely used nondestructive method of locating defects in the composite microstructure. The through transmission C-scan is easy to implement and a large composite panel can be scanned in a matter of minutes. The problem with this technique is that a C-scan cannot reveal the type of defect present. Hence, there is no way to determine if a flaw detected by the C-scan is due to incomplete contact of an interply interface or some other type of defect in the composite microstructure. 

Fig. 2. Ultrasonic NDT methods (a) pulse-echo (b) through-transmission (c) reflector-plate (double-through transmission) and (d) angle-beam...

Recent developments have extended the ultrasonic techniques to the characterisation of thin layers of metals and polymers deposited on substances to obtain measurements of the thickness/density product. Using techniques where the film are immersed in a fluid, such as water, measurements have been made, by the low frequency normal incidence double through-transmission method, with film thickness ranging from 20 to 200 pm [112] a range which is of particular relevance to membrane systems. 

Attenuation i.s due to scattering of ultrasonic waves by the fibers and by absorption into isothermal resin. However, attenuation is reduced with the through-transmission method and by the use of low frequencies. Defects such as voids, resin rich or resin starved... 

The two major techniques in ultrasonic testing arc the pulse-echo mode and the through-transmission mode. In pulse-echo mode, the same transducer is used to emit and receive ultrasonic waves and requires access to only one side of the structure inspected (Fig. 12). The pulse-echo technique is effective on the near side skin laminate only, and the sensitivity decreases as a function of depth [29]. With the through-transmission mode, access to both sides of a structure is required as an emitter probe is placed on one side and a receiver on the other (Fig. 13). This technique measures the signal amplitude of ultrasonic waves transmitted through the material tested and is more sensitive to small defects than the pulse-echo mode. The detection of flaws throughout the whole depth of a... 

Rose, J.L. and J.J. Ditri, Pulse-echo and through transmission Lamb wave techniques for adhesive bond inspection. British Journal of NOT, 34(12), 1992. GogUo, L. and M. Rossetto, Ultrasonic testing of adhesive bonds of thin metal sheets. NDT E International, 32 323-331,1999. 

Figure U.l Ultrasonic inspection techniques, (a) Contact pulse echo with a search unit combining a transmitter and receivers, (b) Contact through transmission. Transmitting search unit on top and receiving search unit on the bottom, (c) Immersion pulse echo with search unit (transmitter and receiver) and part inspected under water, (d) Immersion through transmission with both search units (transmitter and receiver) and part under water, (e) Immersion reflector plate. Same as (c) but each unit requires a reflector plate below the part being inspected. (Ref Hagemaier, D.J., End Product Nondestructive Evaluation of Adhesive Bonded Metal Joints , Adhesives and Sealants, vol. 3, Engineered Materials Handbook, ASM International, Materials Park, OH, 1990)...

Through transmission technique-. An examination technique where the material is characterized based on the intensity of mechanical energy of the ultrasonic pulse after it has passed through the examined object. 

ULTRASONIC THROUGH TRANSMISSION 0.063 INCH ALUMINUM SHEETS... 

However, it appears that none of the non-destructive tests currently employed directly correlate with any critical failure property. Most industrial test techniques such as through-transmission and pulse-echo ultrasonics, sonic vibration techniques. X-ray radiography, thermal inspection methods, holography, liquid penetrants, etc. basically attempt to find defects in the joint. Such defects may arise from several sources. Some defects arise from porosity, cracks or voids in the adhesive layer or at the interface and are typically filled with air they will simply be referred to as voids in the present discussions. However, during the service life of the joint such voids may fill with water which makes them far more difficult to detect since, for example, water has a much higher acoustic, impedance than air. Also, zero-volume voids, or debonds, may occur when the adhesive and substrate are in contact but no... 

---