Ultrasonic technology is causing a shift in the nondestructive evaluation (NDE) and testing (NDT) industry. Many companies are moving toward ultrasonic testing (UT) as an alternative to radiographic testing (RT). UT uses ultrasonic waves to perform weld inspection, while RT uses x-rays to perform weld inspection. In my career, I have used more RT than UT for oil and gas weld inspection. This is not to say that RT is better than UT, but there are more UT solutions finding their way into the NDE market. One major push for UT is the decreased safety risk (to radiation exposure) when compared to RT.

I want to discuss a paper that was written in 1999 about angle beam ultrasonic spectroscopy (ABUS) that was used to assess the bond quality in adhesive joining. ABUS is an advance UT technology and two questions come to mind: 1) what is adhesive joining and 2) why would anyone want to inspect adhesives bond quality using ultrasonic waves? First, adhesive joining is any process that joins two or more materials using epoxy, glue or any other plastic substance that aid bonding via curing or evaporation of a particular solvent [1]. Second, it is important to inspect these special joints because adhesive joints are expanding from typical household items to heavy equipment in structural applications.

Now let’s get into the ABUS technology. ABUS takes advantage of angled incident ultrasonic beam on the adhesive bond line [2]. As the ultrasonic beam interacts with the bond line, it sends magnitude and phase data of the reflected ultrasonic signal. Good versus bad bonding are qualitatively defined by the shear stress introduced into the joint. UT has the ability to measure component thicknesses by recording the time it takes for an ultrasonic pulse to travel round trip through the component’s thickness. ABUS can also determine bond line thickness via the longitudinal (or normal) ultrasonic wave. On the surface the ABUS system, which was developed in 1999, appears to perform similar tasks as many state-of-the-art UT systems today.

The theoretical background of the ABUS system describes the use of the spring model to relate the ultrasonic signal to the adhesive joint quality [2]. The spring model is a representation of a complex system where springs are used to serve as the individual members/components of the overall system. The springs mimic the physical interface of the bond and the magnitude of the spring constant can resemble a good or poor adhesive joint. Couple this simple model with the angle ultrasonic beam and the ABUS system is able to accurately determine adhesive joint quality and integrity.

The ABUS system is a fascinating technology that still is relevant today. Many of the concepts such as using computer code to control the ultrasonic transducer movement and the signal acquisition rate are currently in use for advance ultrasonic imaging systems. In addition, the ABUS is able to produce gray scale maps of good bond regions versus poor bond regions. These maps show good correlation to the fracture surfaces of tensile test performed. Gray scale maps are a staple in the NDE for showing complex ultrasonic signal data as a pass/fail illustrated criteria.

Thank you for your time!

— DB PhD

References:

  1. TWI. (2022). What is adhesive bonding? Retrieved May 21, 2022, from https://www.twi-global.com/technical-knowledge/faqs/adhesive-bonding
  2. Adler, L., Rokhlin, S., Mattei, C., Blaho, G., & Xie, Q. (1999). Angle beam ultrasonic spectroscopy system for quantitative inspection of adhesive bonds. In Review of Progress in Quantitative Nondestructive Evaluation (pp. 1553-1559). Springer, Boston, MA.