Optimization of phased-array transducers for ultrasonic inspection in composite materials using sliding probes

The increasing use in the industries of composite materials implies finding a suitable way for testing and evaluating them. Non-destructive testing by ultrasounds is an appropriate method to detect defects in this type of materials, however, because of their structure it is required to find the most applicable and accurate process for detecting flaws and anomalies in them. For conventional ultrasound testing, single-element probes are used to generate an ultrasonic signal that is transmitted into the material to inspect it. However, when inspections are done on composite materials, phased array probes (PA) are used in order to detect component failures and thereby determine their quality. Such transducers, in contrast with conventional pulse echo ones, use multi-element probes, so that each element can be pulsed independently and therefore transmit and receive signals at different times. In addition, PA probes can be designed in a wide variety of geometries, allowing them to be customized for particular applications. These transducers come in a wide variety of sizes, frequencies, and case styles, but most of them have a common internal structure. Phased Array Ultrasound techniques offer several benefits including better detection, faster scanning, and traceable results. The use of ultrasonic transducers involves the need of using a coupling element that allows the introduction of the ultrasonic beam on the piece to be inspected. Water is the most widely coupling medium used but has many disadvantages in-service inspections. A dry-coupling method is therefore desired for fast and cost efficient inspections. In this way, a few years ago rubber materials appeared with ultrasonic properties similar to water, which were incorporated into the probes for inspection of CFRP in two formats: “Sliding probes” or "Wheel probes” The use of dry coupling for applying ultrasonic testing is an increasingly important practice mainly for the inspection of non-uniform surfaces. The objective of this study is to optimize this type of ultrasonic inspection transducers PA regarding ultrasonic parameters inherent to the probe in relation with the specifications and laws of ultrasonic propagation, the constructive aspects as well as those more general aspects which affect the productivity in the inspections such as coupling material with better signal / noise relation and higher wear resistance than polybutadiene polymers that nowadays exist in the market.