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Improve the Quality of Automated Composite Inspection Techniques with Time-Reversal Phased Array

Aerospace and automotive industries are pioneers in the adoption of composites. With lower weight, stiffness, thermal stability, resistance to chemical damage, and ability to create complex, structurally-sound components, composites are replacing metals and other traditional fabrication materials. Adoption of composites is increasing rapidly—a compound annual growth (CAGR) of 7.8% with projected market growth to $130.83 billion by 2024.

Automation plays a critical role in composite manufacturing. Robotics coordinate the layup of resins and reinforcement materials to precisely and consistently create standard shapes—rods, round and shaped tubing, plates, sandwich panels, and stringers and spars with t-joint noodles. Manufacturers are exploiting the unique properties of composites to fabricate components with complex geometries and variable thicknesses.   

Automation is equally important in the inspection of these critical components. High-speed fabrication requires high-speed composite inspection techniques to detect defects. Foreign bodies, porosities, delaminations, surface or sub-surface matrix cracking, or fiber density variations that may have been introduced during the manufacturing process compromise the structural integrity.

With the evolution of composites manufacturing, ultrasonic testing (UT) has become the preferred inspection technique. Advances in ultrasonic technology are replacing standard UT methods and improving the quality and efficiency of composite inspection techniques.

Limitations of Standard Phased Array UT

Phased array ultrasonic technique (PAUT) is the widely-adopted standard for composite inspection. However, to ensure accurate results, standard PAUT inspections require exact alignment between the probe and the composite component being inspected. For automated, high-volume inspection of standard components—tubing, plates, and panels—alignment is rarely a problem.

However, with complex geometries and variable thickness, accurate automated inspection depends on the understanding of component geometry and corresponding alignment of the probe. Even with custom-designed automated inspection mechanisms, probe alignment may be off, resulting in failures to accurately detect locations and characteristics of flaws. A better approach to solving the probe alignment and complex geometry inspection problems is the time reversal technique.

Time Reversal Phased Array Ultrasound Technique

Time Reversal phased array ultrasound (PAUT) combines dedicated probe configurations with a high-performance UT system that uses advanced software algorithms to improve the quality and efficiency of composite inspection techniques. The Time Reversal technique delivers accurate inspections of complex composite geometries and variable thickness while maintaining high inspection speeds.

Time Reversal PAUT eliminates problems of misalignment between the probe and the composite component. Time Reversal PAUT improves the signal quality when a probe is not optimally aligned with the composite surface​ component, using a real-time, two-step process.

Step 1: Create the Surface Profile

Time Reversal PAUT first creates a surface profile using time of flight from individual probe elements fired simultaneously. The wave reflected back to the probe is affected by the shape of the component being inspected, with a different time of flight for each individual element of the probe. Using the different times of flight the software calculates the delay for each element corresponding to the surface profile. These delays not only compensate for surface profiling but also probe misalignment when inspecting complex geometries.

Reverse TOFD

Step 2:  Capture the Data

Time reversal PAUT then uses the surface profile to apply a compensation delay to the individual probe elements. Those delays are used during the scanning and data recording phase to achieve a normal beam incidence on the inspection surface and obtain accurate data despite varying surface geometry.  

Data recorded using surface-adapted delays

The two-step process is performed in a real-time, single pass process to enable inspection speeds equivalent to standard phased array UT techniques. The key benefit of the Time Reversal PAUT composite inspection technique is the ability to immediately compensate for any probe misalignment that may occur during automated inspections.

Implementing Time Reversal PAUT

Time Reversal PAUT is implemented with dedicated 1D linear array PAUT probes, state-of-the-art phased array units controlled by sophisticated software and algorithms that manage surface profiling and UT data acquisition. The unit’s powerful performance also displays real-time images and provides advanced analysis of data as well as reporting capabilities. Via consulting services, Time Reversal PAUT probes and phased array units can easily be integrated with a composite manufacturer’s automated inspection processes.

Composite Inspection Techniques: Time Reversal PAUT Offers Clear Advantages

Time reversal PAUT provides a clear advantage over traditional phased array inspection techniques. It benefits composite manufacturers and industries using composites (particularly the aerospace and automotive industries) in critical areas of their operations by:

  • Improving inspection accuracy of standard as well as complex composite geometries without reducing inspection speeds;
  • Automatically compensating for probe misalignment caused by manual or automated inspection methods; and
  • Eliminating the need for expensive automated inspection systems custom-engineered to accommodate complex composite geometries and variable thicknesses.

Learn more, from a technical perspective, about the capabilities and benefits of Time Reversal phased array ultrasound techniques by downloading the Iterative Time Reversal Technique for Inspection of Composite Structures white paper.

Zetec has been a trusted source for nondestructive testing equipment and services for decades and has become the clear leader in both UT and eddy current technologies. For improved accuracy and efficiency in composite inspection techniques—contact Zetec today.