Evaluation of the fatigue damage development using ESPI method

Abstract

Fatigue damage process developing in structural materials under long-term cyclic loading is still an unsolved problem of modern engineering. Attempts to assess a degree of materials degradation under fatigue conditions on the basis of changes in the areas of local strain concentration determined by optical methods can be treated as the promising contemporary research direction of majority of scientific centers in the world. In most cases, fatigue damage has a local character and it is based on damage development leading to generation of cracks appearing around structural defects or geometrical notches. An identification of these areas and their subsequent monitoring requires a full-field displacement measurements performed on the objects surfaces. It seems that modern contemporary optical methods for displacement components measuring on the surfaces of structural elements or tested specimens are suitable for such purpose. Digital Image Correlation (DIC) and Electronic Speckle Pattern Interferometry (ESPI) are nowadays the most widely used testing methods in this area. Both of them enable capturing of displacement and strain components distributions. This paper presents an attempt to use the ESPI method for fatigue damage evaluation and its monitoring on specimens made of the aluminide coated nickel super-alloys. Flat specimens were subjected to cyclic loading. The fatigue tests were interrupted several times in order to perform a static loading during which the optical measurements were carried out. An analysis of the results captured by the ESPI system allowed indication of places of the greatest stress concentration and demonstration of the damage development process as a function of the increasing number of cycles.

Fatigue-Crack Detection in a Multi-Riveted Strap-Joint Aluminium Aircraft Panel Using Amplitude Characteristics of Diffuse Lamb Wave Field

“…The methods used for damage detection in lap joints include well established Non-Destructive Testing (NDT) approaches, such as: ultrasonic testing [ 18 ], eddy current [ 19 , 20 ], acoustic emission [ 21 , 22 ] and thermography [ 23 , 24 ]. They also include more novel techniques, such as: electronic scanning-laser Doppler vibrometry [ 25 ], speckle-pattern interferometry [ 26 ], electromechanical impedance [ 27 ], the Comparative Vacuum Monitoring (CVM) technique [ 28 ], vibro-acoustic monitoring [ 29 ] or a combination of some of these techniques [ 30 ].…”

Bulletin of the Polish Academy of Sciences: Technical Sciences

“…ESPI technique is based on holographic interferometry in which the laser beam is distracted from the optically rough surface. Because it is capable to detect cracks in actual and residual stress fields [9], this technique has been widely used to monitor deformation on metallic specimens including steel [8] and aluminum [9] as well as AA2124/SiC metal matrix composites [10] or nickel based superalloys [11]. Hence, it has been found to be a promising tool in stress distribution maps determination for P91 steel specimens tested under different states and in their elastic range.…”

Suitability of DIC and ESPI optical methods for monitoring fatigue damage development in X10CrMoVNb9-1 power engineering steel

“…It was found that application of correcting asymmetries or parallel illumination beams could successfully eliminate such measuring issue. ESPI was successfully used to detect the crack initiation in coatings and the delamination occurrence at the coating/substrate interface during the fatigue [20,21]. It should be mentioned, however, that the differences between hard coating and substrate material enable to localise the stress concentrators (hard phases or particles) much easier, than on homogenous material; therefore, the ESPI measurements are relatively easy to perform.…”