Crack Detection in Engineering Materials: A Systematic Review Based on Physical Principles

English (OpenAlex)

Crack detection in engineering materials has become a prominent research area due to the severe consequences of potential failures in safety-critical systems such as pipelines, railway systems, welded joints, rotating machinery elements, and load-bearing structures. Although significant advancements have been made in nondestructive testing (NDT) methods, there is currently no single method capable of simultaneously meeting the requirements of high detection sensitivity, quantitative crack characterization capability, and applicability under real service conditions. In this study, literature published from 2000 to the present is reviewed using a systematic and method-oriented approach. Unlike conventional reviews, this study classifies existing methods based on the fundamental physical principles underlying the crack detection mechanism rather than the types of sensors used. The investigated approaches are discussed under the categories of Magnetic Flux Leakage (MFL), direct current electromagnetic and motion-induced eddy current techniques, Eddy Current Testing (ECT) and ACFM methods, thermography-assisted electromagnetic approaches, weak magnetic field and Metal Magnetic Memory (MMM) techniques, magneto-optical and visual methods, hybrid EMAT-ultrasonic systems, and optical/data-driven approaches. Each method is comparatively analyzed in terms of material compatibility, sensitivity to crack type, quantitative evaluation capacity, static/dynamic or real field/load/structure applicability, and system complexity. The cross-evaluation demonstrates that high quantitative accuracy, applicability under real field conditions, and low system complexity cannot be simultaneously achieved in most methods. Consequently, crack detection is evolving as a multidisciplinary research area at the intersection of materials science, sensor physics, and data-driven modeling, necessitating the development of holistic and application-specific sensing strategies in the future.