Ultrasonic Lamb wave tomography

TLDR

Nondestructive evaluation of aerospace structures is complex and time‑consuming, and conventional techniques struggle to detect hidden corrosion; ultrasonic Lamb waves offer rapid, large‑area inspection by converting travel times into thickness maps. The study presents ultrasonic Lamb wave tomography to generate quantitative structural maps that technicians can interpret or integrate into integrity and lifetime prediction models. The authors employ algebraic reconstruction tomography with a square perimeter transducer array to produce fast, portable quantitative maps, reducing reliance on expert waveguide physics. Laboratory tests confirm that square‑perimeter transducer arrays with algebraic reconstruction tomography can detect aircraft material flaws, and the algorithms are fast and suitable for portable systems.

Abstract

Nondestructive evaluation (NDE) of aerospace structures using traditional methods is a complex, time-consuming process critical to maintaining mission readiness and flight safety. Limited access to corrosion-prone structure and the restricted applicability of available NDE techniques for the detection of hidden corrosion or other damage often compound the challenge. In this paper we discuss our recent work using ultrasonic Lamb wave tomography to address this pressing NDE technology need. Lamb waves are ultrasonic guided waves, which allow large sections of aircraft structures to be rapidly inspected for structural flaws such as disbonds, corrosion and delaminations. Because the velocity of Lamb waves depends on thickness, for example, the travel times of the fundamental Lamb modes can be converted into a thickness map of the inspection region. However, extracting quantitative information from Lamb wave data has always involved highly trained personnel with a detailed knowledge of mechanical waveguide physics. Our work focuses on tomographic reconstruction to produce quantitative maps that can be easily interpreted by technicians or fed directly into structural integrity and lifetime prediction codes. Laboratory measurements discussed here demonstrate that Lamb wave tomography using a square perimeter array of transducers with algebraic reconstruction tomography is appropriate for detecting flaws in aircraft materials. The speed and fidelity of the reconstruction algorithms as well as practical considerations for person-portable array-based systems are discussed in this paper.