Real-Time and Quantitative Measurement of Crack-Tip Stress Intensity Factors Using Digital Holographic Interferometry

Haiting Xia,Feng Yan,Rongxin Guo,Heming Cheng

doi:10.1155/2018/1954573

Abstract

Detection of the crack in an object is a critical problem for the health monitoring of a transparent object. The real-time and quantitative measurement of the crack-tip stress intensity factor (SIF) remains an open issue. In this paper, an approach for real-time and quantitative measurement for the SIFs of a Mode I crack is presented based on digital holographic interferometry (DHI). A transmission digital holographic system is established to measure the phase difference of an object wave during loading. The expression to achieve the SIF from the phase difference is formulated. To enhance the accuracy of measurement, calibrated phase unwrapping based on least-squares and iteration and median filtering is applied to retrieve the actual phase from the noisy wrapped one. The SIFs of the Mode I crack in a transparent polymethyl methacrylate (PMMA) specimen are measured by this approach. The results are compared with the theoretical ones to demonstrate the feasibility of the proposed approach.

Highlights

Transparent materials are widely used in many engineering applications such as conductive materials [1,2,3], electrode materials [4,5,6,7], thermoelectric materials [8], encapsulation materials [9], and bulletproof materials [10, 11]. e fracture and fatigue problems are critical for many applications of the transparent materials. e crack is the key reason of materials failure
digital holographic interferometry (DHI) can detect the damage and cracks in transparent materials which means it can be used in the health monitoring of a transparent structure and experimental study on the fracture and damage mechanics [33]
From these wrapped phase maps, it can be seen that there exists high speckle noise, the fringes near the crack tip are very close, and the phase data inside the crack region is invalid

Summary

Introduction

Transparent materials are widely used in many engineering applications such as conductive materials [1,2,3], electrode materials [4,5,6,7], thermoelectric materials [8], encapsulation materials [9], and bulletproof materials [10, 11]. e fracture and fatigue problems are critical for many applications of the transparent materials. e crack is the key reason of materials failure. Many measurement approaches were used to detect the SIF near the crack in transparent materials including photoelasticity [12, 13], coherent gradient sensing (CGS) [14,15,16], and digital coherent sensing (DGS) [17,18,19]. These approaches need birefringent materials, identification of the fringes, phase shifting, or fabrication of speckles which affect the application and accuracy of the measurement of the SIF. Detection of the crack by DHI remains a qualitative analysis and does not realize the quantitative measurement

Objectives

Results

Conclusion