Large Area Detection of Microstructural Defects with Multi-Mode Ultrasonic Signals

Taeho Ju,Alp T Findikoglu

doi:10.3390/app12042082

Abstract

Cyclic loading or other stresses can lead to development of cracks and crack growth in mechanical structures, leading to eventual failure. While ultrasound imaging can be used for non-destructive testing of such structures, conventional ultrasound techniques are often limited by crack size, density, and areal coverage. An effective characterization of real-world, large-area structures is required at an early damage stage to prevent catastrophic failure and predict remaining life. In this study, a new nonlinear ultrasonic testing (NUT) method is proposed for large-area monitoring of practical structures with arbitrary complexity by using multiple-mode guided-wave ultrasonic signals. The proposed guided-wave NUT technique requires single-element transducers, simple electronics, and a mixed time-frequency domain signal processing. As a proof-of-concept demonstration, numerical simulations and experiments are performed on an A36 carbon steel beam assembly with previously formed microstructural defects that cause nonlinearities in ultrasonic response. The quadratic dependence of the nonlinear wave excitation on the input ultrasonic signal amplitude is shown by numerical simulations, and such a nonlinear ultrasonic response is experimentally observed in the zone with a high density of microstructural defects.

Highlights

The materia nonlinearity in these experiments is attributed to the presence of microstructural defects this second test,noticeable the actionable output (AO) iscracks investigated at three different locations using pairs
The defects, material nonlinearity in thesewith experiments is attributed to theinpresence of microstructural nonlinearity in these experiments is attributed the presence of microstructural defects, namely micro-cracks
This study utilized and broadband ultrasonic sigThis work has been limited to studying themulti-mode nonlinear ultrasonic response of a beam nals, single-element transducers, and simple electronics

Summary

Introduction

Ultrasonic testing (UT) has played a major role in the structural health monitoring (SHM) of various safety-critical structures. When a material is subjected to cyclic loading, it can lead to crack development, crack growth, and eventually structure failure. While ultrasound has been widely used for non-destructive testing, conventional ultrasound techniques are often limited by crack size and density—by the time the presence of cracks is detectable with such techniques, a structure may already have consumed 80–90% of its fatigue life and can be close to failure. Small cracks, sometimes termed microcracks or microstructural defects, can themselves compromise the mechanical strength and integrity of the structure [1]. Conventional ultrasonic techniques are limited by the areal size and complexity of a structure, which makes comprehensive evaluation of real-world structures time-consuming, cumbersome, and incomplete [2,3]

Objectives

Methods

Results

Conclusion