Crack Size Measurement Research Articles

Exploring Probability of Detection (POD) Analysis in Nondestructive Testing: A Comprehensive Review and Potential Applications in Phased Array Ultrasonic Corrosion Mapping

In nondestructive testing (NDT), ensuring defect detection, measurement accuracy, and reliability guarantees various components’ structural integrity and safety. The Probability of Detection (POD) concept has emerged as a fundamental measure of the effectiveness of an inspection technique in identifying defects. Since NDT plays a crucial role in aerospace, manufacturing, and infrastructure industries, enhancing POD has become critical. POD refers to the likelihood that a flaw or defect of a certain size will be detected using the NDT technique. The “â versus a” and the “hit/miss” methods are particularly notable among the commonly employed POD estimation methods. The POD curve is determined based on crack size measurements in the “â versus a” approach, typically used in ultrasonic testing. On the other hand, the “hit/miss” method establishes the POD curve by analysing binary outcomes, where a “hit” signifies successful detection and a “miss” denotes detection failure. This review focuses on POD in the context of NDT, specifically in phased array ultrasonic corrosion mapping (PAUCM), to uncover current uncertainty parameters and explore an innovative avenue for enhancing POD assessment by incorporating the material surface temperature as an additional parameter.

Deep learning based initial crack size measurements utilizing macroscale fracture surface segmentation

To this date the safety assessment of materials, used for example in the nuclear power sector, commonly relies on a fracture mechanical analysis utilizing macroscopic concepts, where a global load quantity K or J is compared to the materials fracture toughness curve. Part of the experimental effort involved in these concepts is dedicated to the quantitative analysis of fracture surfaces, which is a cumbersome and time-consuming process. In addition, however, it is affected by subjective bias. Within the scope of our study, we have introduced a methodology that employs deep learning models for macroscopic fracture surface segmentation. To fight subjective bias and enable improved reproducibility, we set up three distinct and unique datasets labeled by different experts that correspond to typical isolated laboratory conditions and complex real-world (multi-laboratory) scenarios. To demonstrate the benefit of our approach for the fracture mechanics assessment, we employed the models for initial crack size measurements utilizing the area average method. Furthermore, the influence of structural similarity on the segmentation capability, differing due to the miscellaneous materials, specimen types, as well as imaging-induced variance has been analyzed. For semi-supervised learning a weak-to-strong consistency regularization was implemented. We were able to train robust and well-generalizing models that learned feature representations from images across different domains without observing a significant drop in prediction quality. Our approach reduced the number of labeled images required for training by a factor of 6. The deep learning assisted measurements proved to be as precise as manual measurements. For the multi-laboratory data, mean measurement deviations smaller 1 % could be achieved, showcasing the enormous potential of our approach.

Image-based Concrete Cracks Identification under Complex Background with Lightweight Convolutional Neural Network

Cracks are important indexes to evaluate the health status of concrete structures. To accurately and automatically identify the cracks of concrete structures, and solve the time-consuming and labor-intensive limits of manual detection methods, this paper proposed an image-based concrete cracks identification method based on a lightweight Convolutional Neural Network, which includes three modules: crack classification, semantic segmentation and quantitative calculation of crack geometric size. Firstly, the S_MobileNet was used to classify cracks, exclude irrelevant regions, and reduce the interference of non-crack images; Secondly, the optimized method SM-UNet based on the U-Net network was employed to segment the detected crack image at the pixel level; Finally, based on the results of crack semantic segmentation, image post-processing technology was used to realize the quantitative calculation of crack geometric size parameters, which provides a basis for crack damage assessment of concrete structures. The experimental results show that this study provides a solution for the automatic detection of crack images and high-precision measurement of crack size, which has an important value in scientific research and engineering application.

Measurement of Cracks in Concrete Bridges by Using Unmanned Aerial Vehicles and Image Registration

Crack development is a clear indicator of the durability of concrete bridges. Traditional bridge inspections that rely inspectors to climb on bridges with lift cars are unsafe for inspectors and also time- and labor-consuming. Therefore, this research proposes a solution that applies unmanned aerial vehicles (UAV) and high-resolution digital cameras to measure concrete bridge cracks. An experiment was conducted on an Ai-He concrete bridge located in Yangmei District, Taoyuan City, Taiwan. Two types of images were taken. Close-up images observed cracks more clearly, and long-range images covered the ground control points. We registered these two types of images to establish the absolute coordinate system with ground control points and tie points through block triangulation. This research examines three approaches of generating tie points: (1) manually select tie points with features on the bridge such as nails and dots, (2) randomly input tie points generated from Scale-Invariant Feature Transform (SIFT), and (3) randomly input tie points generated from SIFT as the initial tie points and perform automatic tie generation with the ERDAS Leica Photogrammetry Suite (LPS) image matching module (automatic tie generation). Afterwards, close-up images were processed into orthorectified images with 0.1 mm pixel size for crack size measurements. Crack sizes were determined by a manual measurement approach and an inflection point approach for comparison. This research established a workflow for UAV bridge inspection that locates and measures cracks in concrete bridges, which consequently provides a safe and cost-efficient concrete bridge crack monitoring solution with acceptable accuracies.

Interlaboratory comparison study of crack size measurements performed with two different methods

An interlaboratory study (ILS) involving 15 laboratories from North America, Europe, and Japan, was conducted to validate crack size measurements on various types of fracture toughness specimens by means of two commonly used methodologies: the 9-Point Average (9PA) method and the Area Average (AA) method. The results of this ILS confirm the findings of previous investigation published by the author in 2021, which showed that crack sizes measured by the two methods are in close agreement, and therefore we recommend the AA method be included as an alternative to the other approach in all fatigue and fracture test methods that require crack sizes to be measured.

Proposal of inspection and evaluation rules of the Rules on Fitness-for-Service to eliminate the circumferential crack angle limitation of class 1 piping

The Rules on Fitness-For-Service (the Rules on FFS) of the Japan Society of Mechanical Engineers (JSME) limits the circumferential crack angle to 60 degrees or less for Class-1 piping. This limitation was based on a deterministic evaluation because of the concern about fracture that would occur if the measurement error of the crack size was taken into consideration. However, ASME Section XI, which is a standard similar to the Rules on FFS, has no limitation on the circumferential crack angle, and the crack angle limitation is unique to the Rules on FFS. After the first edition of the Rules on FFS was published in 2000, some research on crack size measurement were performed. The number of inspections according to the measurement error that satisfy the target fracture frequency regardless of the crack angle can be evaluated by using probabilistic evaluation. In this study, the number of measurements of the crack size required to satisfy the target fracture frequency is determined based on the thickness of pipes, crack size measurement error, the fracture frequency according to the number of crack size measurements, and the conditional core damage probability due to pipe fracture. Based on this result, the requirement for inspection and evaluation of the Rules on FFS was proposed.

Stochastic filter-based fatigue crack growth prediction for pipelines considering unknown model parameters and measurement uncertainty

In this study a methodology is developed and implemented in Python for fatigue crack growth prediction in pipelines, by leveraging measurement data and fatigue growth model predictions. Specifically, Particle Filter (PF) algorithm, Paris law, and the stress intensity factor (SIF) model in API 579 are integrated into a tool to use noisy crack size measurements for estimating the current crack size and fatigue model parameters, also known as joint state-parameter estimation. For illustration purpose, pseudo-data set for crack size measurements is generated considering additive Gaussian white noise of two different noise levels, aiming to mimic crack size data obtained from In-line Inspection (ILI) tools. It is found that the crack state can be reliably estimated compared to noisy measurements and initial model predictions, and the true model parameters can be updated with good accuracy. As such, the current crack size estimated and model parameters updated can be used in the fatigue growth model (i.e., Paris law) to predict the future trajectory of the fatigue crack growth. As more measurement data becomes available, the developed tool more reliably estimates the future crack growth trajectory.

PTZ Camera-Based Image Processing for Automatic Crack Size Measurement in Expressways

Cracks in road surfaces are among the most critical problems in the management of expressways. Their sizes, which not only have severe consequences in relation to expressway safety, decide maintenance timing, which if accurately estimated, can prevent the rapid development of crack disease. Currently, the main techniques used for crack size measurement makes use of either human inspection or sophisticated mobile equipment, which are respectively, very time consuming, labour-intensive, and difficult to implement in civil engineering. Thus, there is great interest in practical and highly efficacious automated crack identification systems coupled with low-cost data-processing sensors. A PTZ (pan/tilt/zoom) camera-based image processing idea is investigated in this paper for crack size measurement in expressways in China. The proposed method consists of four steps: 1) image acquisition, 2) corner-based line size calculation, 3) pixel size calculation, and 4) crack size estimation. A case study of roadway lane images and crack images, collected from China G4/Jingshi, is conducted to demonstrate the feasibility of the proposed method. The results demonstrate that PTZ camera-based image processing is capable of efficiently quantifying cracks, obtaining high accuracy crack size results at range of 0 m to 40 m. The method shows promise for crack size measurement in a cost-effective manner and can provide an objective and timely means for transportation agencies to conduct maintenance plans.

An assessment of different approaches for measuring crack sizes in fatigue and fracture mechanics specimens

Several fatigue and fracture mechanics test standards prescribe the use of fatigue precracked specimens, and measured initial and final crack sizes are required for the analyses. All these test methods utilize the X-Point Average Method, with X = 2 ÷ 9, for measuring crack sizes, but another approach, the Area Average Method, is also often used for the same purpose. This investigation compared the two measurement approaches on 140 fracture toughness tests performed on various materials and specimen types, both in the ductile-to-brittle transition (Master Curve) and upper shelf (J-R tests) fracture regimes. Results obtained fully support the inclusion of the Area Average Method in all test standards requiring crack size measurements.

Different Bayesian Methods for Updating the Fatigue Crack Size Distribution in a Tubular Joint

Abstract Offshore platforms are prone to fatigue damage. To evaluate the fatigue damage, these platforms are periodically inspected during the in-service lifetime. Inspection activities provide additional information, which includes detection and measurement of crack size. A Bayesian framework can be used to update the probability distribution of the uncertain parameters such as crack size. After updating the distribution of the crack size, it is possible to improve the estimation of joint reliability. The main purpose of this study is to present different methods of Bayesian inference to update the probability distribution of the crack size using the inspection results and to demonstrate how the results are different. Two different methods are presented: analytical (conjugate) and numerical methods. The advantages and shortcomings of each method are discussed. To compare the results of the analytical and numerical methods, two different situations are considered; updating the crack size distribution for a particular joint and updating the crack size distribution for several joints that have almost the same conditions. Although the proposed methodology can be applied to different kinds of structures, an example of tubular joints in a specific jacket platform is presented to demonstrate the proposed approach and to compare the results of two methods.

Main Approaches to Cable Aging Management at Nuclear Power Plants in Ukraine

The mechanisms of cable ageing at nuclear power plants (NPPs) mainly depending on the insulation material, as well as the damaging factors affecting cables that are determined by the operating conditions are considered in the paper. The main and additional mechanisms of aging resulting from the effects of damaging factors are provided. The paper presents the main methods of cable aging management: determining the actual service life and testing using field methods and other means. The basic principles for the arrangement of cable aging management at Ukrainian NPPs, as well as the methods used to investigate the technical condition of cables, are presented. A list of mandatory lists has been defined when performing activities on cable aging management. A methodology is described for lifetime extension of cables, and conditions for extending the service life of cables that are in service are provided. A number of methods of testing cables for aging management are considered: visual inspection of insulation and measurement of crack size, discoloration, etc.; insulation hardness test; insulation chemical analysis; electrical insulation tests; tensile strength measurement; measurement of elongation at break; measurements of dielectric loss at low frequency or sweep frequency; testing by dynamic reflectometry method; AC and DC current impedance measurements. The paper presents results of separate laboratory studies for selected 1 kV representative power cables with PVC insulation of SUNPP-1, ZNPP-1 and KhNPP-2 conducted within Ukrainian NPP long-term operation, which included a stage of laboratory examination and examination of cable samples in operating conditions. The following results were obtained: dependence of VVGng 4x6 cable lifetime on operating temperature; dependence of AVVG cable lifetime on operating temperature; dependence of AVVG (a) cable lifetime on operating temperature. There are possibilities and conditions under which the use of cables within long-term operation is permissible.

Statistical Inference of the Equivalent Initial Flaw Size Distribution Using the Boundary Element Method under Multiple Sources of Uncertainty

In this work, a method for determining the Equivalent Initial Flaw Size (EIFS) distribution using the Boundary Element Method (BEM) is proposed. Maximum Likelihood Estimation (MLE) is used to infer the EIFS distribution of a cracked stiffened panel under multiple sources of uncertainty, including uncertainty in the loading conditions, fatigue crack growth model parameters, and in the measurement of crack size found from routine inspections. Results suggest that MLE is an effective tool for estimating the parameters of an EIFS distribution when no prior knowledge is available regarding the EIFS distribution or its parameters.

ASTM E08.07.09 Analytical Round-Robin on the Use of DC Electrical Potential Difference for the Measurement of Crack Size in Ductile Fracture Testing.

The Direct Current Electrical Potential Difference (DCEPD) technique has been used for many years in fatigue and fracture testing for monitoring crack propagation in metallic materials. The principle of DCEPD methods is that when a constant current flows through a cracked specimen, the voltage change measured across the crack plane can be analytically related, empirically related, or both, to the change in crack size. In fatigue testing, performed within the limits of Linear Elastic Fracture Mechanics, crack propagation is the sole source of potential change. In ductile fracture testing, additional contributions from specimen dimension changes and crack-tip plastic deformation (blunting) have to be accounted for and distinguished from the DCEPD increase caused by crack growth. The ASTM E08.07.09 Task Group, formed in 2013 and chaired by the author, has been developing an annex for ASTM E1820, Standard Test Method for Measurement of Fracture Toughness, which focuses on the use of DCEPD measurements for the prediction of crack size and crack extension in ductile fracture toughness tests. This article presents the analysis of an analytical round-robin, in which 8 participants analyzed 24 existing fracture toughness data sets using two different approaches, based on the analysis of the displacement versus DCEPD and force versus DCEPD, respectively. The comparison between these two approaches and the implications for the ASTM E1820 annex being developed are the focus of this article.

A recursive Bayesian approach to small fatigue crack propagation and detection modeling

Engineers have witnessed much advancement in the study of fatigue crack detection and propagation modeling. More recently, the use of certain damage precursors such as acoustic emission signals to assess the integrity of structures has been proposed for application to prognosis and health management of structures. However, due to uncertainties associated with small crack detection of damage precursors and crack size measurement errors of the detection technology used, applications of prognosis and health management assessments have been limited. In this article, a methodology is developed for the purpose of assessment of crack detection and propagation parameters and the minimization of uncertainties including detection and sizing errors associated with a series of known crack detection and propagation models that use acoustic emission as the precursor to fatigue cracking. The methodology is facilitated by the Bayesian inference of a joint-likelihood model which includes sizing and detection models. Examples where several dog-bone Al 7075T6 specimens are tested to produce fatigue crack initiation and propagation data and estimates based on remaining useful life support the effectiveness and usefulness of the proposed methodology.

Progress in development of fracture toughness test methods for SENT specimens

Fracture toughness testing using clamped single edge notched tension (SENT) specimens has been receiving broad attention in the oil and gas industry for direct measurement of low-constraint fracture toughness of pipeline steels. In order to develop robust SENT fracture toughness test methods, this paper reviews and summarizes existing SENT test methods, including the DNV practice, CANMET procedure, ExxonMobil method and BS 8571 standard, and their recent progress. Typical results are analyzed and compared with regard to the stress intensity factor solution, J-integral estimation, CTOD calculation and crack size measurement. On this basis, recommendations are made. Further studies and applications of SENT testing are also discussed.

Grinding damage assessment for CAD-CAM restorative materials

ObjectivesTo assess surface/subsurface damage after grinding with diamond discs on five CAD-CAM restorative materials and to estimate potential losses in strength based on crack size measurements of the generated damage. MethodsThe materials tested were: Lithium disilicate (LIT) glass-ceramic (e.max CAD), leucite glass-ceramic (LEU) (Empress CAD), feldspar ceramic (VM2) (Vita Mark II), feldspar ceramic-resin infiltrated (EN) (Enamic) and a composite reinforced with nano ceramics (LU) (Lava Ultimate). Specimens were cut from CAD-CAM blocs and pair-wise mirror polished for the bonded interface technique. Top surfaces were ground with diamond discs of respectively 75, 54 and 18μm. Chip damage was measured on the bonded interface using SEM. Fracture mechanics relationships were used to estimate fracture stresses based on average and maximum chip depths assuming these to represent strength limiting flaws subjected to tension and to calculate potential losses in strength compared to manufacturer’s data. ResultsGrinding with a 75μm diamond disc induced on a bonded interface critical chips averaging 100μm with a potential strength loss estimated between 33% and 54% for all three glass-ceramics (LIT, LEU, VM2). The softer materials EN and LU were little damage susceptible with chips averaging respectively 26μm and 17μm with no loss in strength. Grinding with 18μm diamond discs was still quite detrimental for LIT with average chip sizes of 43μm and a potential strength loss of 42%. SignificanceIt is essential to understand that when grinding glass-ceramics or feldspar ceramics with diamond discs surface and subsurface damage are induced which have the potential of lowering the strength of the ceramic. Careful polishing steps should be carried out after grinding especially when dealing with glass-ceramics.

Real-Time Fatigue Crack Monitoring Based on Fiber Bragg Grating Sensors

In this paper, an real-time fatigue crack monitoring method is investigated based on the fiber Bragg grating (FBG) sensors. Three FBGs are applied along the direction of crack propagation to monitor a fatigue crack with size of 10mm. Experimental results demonstrate that the reflection spectrum changes observably with the propagation of crack when the crack is within 3-4mm long of each FBG. Characteristic parameters are constructed to detect the variation degree of reflection spectrum. A crack quantification model based on characteristic parameters is proposed to describe the correlation between the crack size and damage sensitive features extracted form FBG measurements. It makes possible to monitor the propagation of crack quantitatively within 3-4 mm long for each FBG. Finally, a certain size crack can be monitored using several FBGs.

Estimation of J-resistance Curves for CT Specimen Based on Unloading Compliance Method and CMOD Data

Abstract The unloading compliance method is one of the most widely used methods in laboratory testing for J-resistance estimation. A specimen configuration including compact tension (CT) is recommended by almost all the standard test procedures for evaluating fracture toughness, such as ASTM E1820-11, ISO 12135-2002, and GB/T 21143-2007. In the unloading compliance method, key techniques including instantaneous crack size measurement, correction of specimen rotation, and J-integral computation can be used for a CT specimen when using load line displacement (LLD) but not when using crack mouth opening displacement (CMOD) from those standard test procedures. However, a CT specimen with CMOD measurement is also used for J-resistance estimation under certain severe environments because of the convenience of measuring displacement. This study proposes a simplified linear formula for crack size calculation for a CT specimen with CMOD data, discusses the rotation correction in detail based on the equivalence of work, and develops reasonable incremental expressions for J-integral computation and a CMOD-to-LLD conversion equation. By measuring the LLD and CMOD data of a CT specimen simultaneously, we carried out experiments on J-resistance curve estimation for four different types of materials. According to the developed procedure of the unloading compliance method in this study, J-resistance curves for all materials determined from LLD and CMOD data of the CT specimen are clearly exhibited.

Investigation of the Cracking Behaviors by Indentation Based on an <i>In Situ</i> Observation

In this paper, an in-situ measurement of crack size as a function of applied indentation load during indentation test was conducted. To perform the in-situ measurement, an instrumented indentation test machine with the in-situ observation system was developed and used. The joints of transparent ceramics by diffusion bonding were prepared as the specimen used in this study. The indentations were performed at the interface of the joints, and in the monolithic transparent ceramics by means of the instrumented indenter with the in-situ observation system. The relationship between crack shape and indentation load, as well as, the effect of the indenter shape on it were discussed.

An Alternative Method to Evaluate Endurance Limit in Plain Steel Specimens (JIS, S15C, S45C and A286)

Crack size measurement is necessary in order to calculate stress intensity factor (SIF), K. Definition of the initial crack size in plain specimens is more complex than notched specimens because artificial defects are not introduced. In this study, the effect of difference between initial crack size calculated with both average grain size and maximum shear mode crack size on K, and fatigue limit value, σw were examined. A new alternative method to predict endurance limit of plain specimen, σw with a combination of threshold stress in shear mode and in Mode I was proposed.