Progressive Cracking Research Articles

A coupled thermomechanical nonordinary state‐based peridynamics for thermally induced cracking of rocks

AbstractA novel coupled thermo‐mechanical nonordinary state‐based peridynamics is proposed to study thermally induced damage in rocks. The thermal expansion characteristics of solid material are introduced into the coupled thermomechanical model to consider the influence of temperature. The deformation gradient tensor is obtained by the temperature fields, which is solved by peridynamic heat conduction theory. By introducing the deformation gradient tensor into the force state function of the nonordinary state‐based peridynamics, the coupling of thermal and mechanical is realized. A failure criterion is developed to investigate the thermally induced cracking of rocks. Then, the validity of the coupled thermo‐mechanical model is demonstrated by a numerical simulation. The correctness of the coupled model is validated by a benchmark example with analytic solution. Moreover, the thermal cracking progress in rocks is simulated using the proposed coupled nonordinary state‐based peridynamic model, and it is found that the numerical results are in good agreement with the previous experimental observations.

Understanding and treatment of squat defects in a railway network

A comprehensive investigation of the Sydney Trains railway network has been carried out to control and minimize rail degradation, especially squat defects. Squat occurrence was analysed with respect to the parameters of traffic operation and track geometry. Detailed metallurgical examination of the ex-service rails revealed a possible connection between brittle White Etching Layers (WELs) and the occurrence of squats in the running band of the rail. Initiation of squats was found to be associated with the progression of surface cracks in the WELs. Furthermore, two distinguishable types of WELs were found, based on different track operational conditions. These are described as Thermally Produced WEL (TP-WEL) which was found in heavy braking regions, and Severe Deformation WEL (SD-WEL) which was found in track regions under steady traffic speeds. In addition to the explanations based on thermal phase transformation and severe plastic deformation, the arcing phenomenon associated with electrical leakage at the wheel/rail interface was considered an alternative formation mechanism of WELs observed on rails. A revised rail grinding strategy was proposed by considering the formation of WELs and addressing it through more regular, relatively shallow grinding to effectively control squat defects.

Rising R-curves in particulate/fiber-reinforced resin composite layered systems

BackgroundAn anisotropic fracture behavior has already been successfully induced in a condensable resin composite by reinforcement with discontinuous glass fibers, developing a steep rise in the fracture resistance curve. There is still the need for developing such concepts further, by evaluating the behavior of layered structures that attempt to replicate the natural gradient structure of enamel and dentin. MethodsMonolithic and bilayer specimens of a flowable short-fiber particulate-reinforced composite (SFPRC) material (GC Corp.) and a commercial flowable particulate-reinforced composite (PRC) (Essentia HiFlo, GC Corp.) were produced with the fibers aligned perpendicular or randomly oriented to the plane of crack propagation. Pre-cracked specimens were tested in 3-point bending using the single-edge-V-notch-beam method with accurate displacement tracking recordrecord. Controlled crack growth experiments were conducted at progressive crack extension intervals to build R-curves using linear-elastic and elastic-plastic fracture mechanics. ResultsWe demonstrate firsthand the development of R-curves in resin composite bilayers, with crack arrest at the interface and a steep rise in crack resistance with subsequent drop within the SFPRC layer. Crack deflection and fiber bridging were found to contribute to a higher rise in the R-curves for specimens with aligned fibers; still, randomly oriented fibers showed significant R-curve development, especially at short range intervals. An increase in the vol% of fibers and a decrease in the Young's modulus contributed to a higher overall performance of the flowable vs. the condensable SFPRF materials. ConclusionsSFPRC materials show an up to 5-fold improvement in the fracture resistance over conventional PRCs, and show the potential to be used to build gradient structures by varying the fiber alignment and fibers parameters (length and packing).

Chlorine Dioxide Degradation Issues on Metal and Plastic Water Pipes Tested in Parallel in a Semi-Closed System.

Chlorine dioxide (ClO2) has been widely used as a disinfectant in drinking water in the past but its effects on water pipes have not been investigated deeply, mainly due to the difficult experimental set-up required to simulate real-life water pipe conditions. In the present paper, four different kinds of water pipes, two based on plastics, namely random polypropylene (PPR) and polyethylene of raised temperature (PERT/aluminum multilayer), and two made of metals, i.e., copper and galvanized steel, were put in a semi-closed system where ClO2 was dosed continuously. The semi-closed system allowed for the simulation of real ClO2 concentrations in common water distribution systems and to simulate the presence of pipes made with different materials from the source of water to the tap. Results show that ClO2 has a deep effect on all the materials tested (plastics and metals) and that severe damage occurs due to its strong oxidizing power in terms of surface chemical modification of metals and progressive cracking of plastics. These phenomena could in turn become an issue for the health and safety of drinking water due to progressive leakage of degraded products in the water.

Damage Tomography as a State Estimation Problem: Crack Detection Using Conductive Area Sensors

Typically, structural damage tomography (SDT) approaches aim to reconstruct a parameter field containing damage information from distributed data by solving an iterative inverse problem. Often, there are two shortcomings in adopting such an approach: First, the high computational expense and second temporal information is inadequately used. In principle, both issues may be alleviated by approaching SDT as a state-estimation problem-i.e., treating the reconstruction problem as a temporally evolving stochastic process. In this letter, we study the feasibility of state estimates in SDT. For this, we use an extended Kalman filter (EKF) for electrical resistance tomography (ERT) imaging of progressive cracking on an experimentally tested reinforced concrete beam with an applied surface area sensing skin. In the investigation, we quantitatively analyze the effect of including multiple temporal datasets and corroborate EKF-ERT reconstructions with standard and advanced ERT approaches. It is shown that increasing the amount of temporal data significantly improves the quality of EKF-ERT reconstructions, which compare favorably with the standard and advanced ERT approaches. In addition, for the data-sets used herein, the EKF-ERT regime computed seven reconstructions approximately 50-100 times faster than the standard and stacked approaches required to reconstruct one image, respectively.

Characterisation of White Etching Layers formed on rails subjected to different traffic conditions

Brittle White Etching Layers on rail initiate surface cracking and further progress to cause squats. The nature of WELs and their formation mechanism are not fully understood. In current study, ex-service damaged rails containing both WELs and squats, obtained from distinct rail track regions associated with different traffic contact conditions, were investigated in details. The particular interested sites of WELs, including topmost, middle and transition regions, were characterised by advanced material characterisation technologies, such as high resolution Synchrotron diffraction, Focus Ion Beam milling, transmission electron microscopy and selected area electron diffraction. In heavy braking rail regions, WEL containing martensite and retained austenite was observed, alongside undeformed pearlite at the interface between the WEL and the parent rail matrix. It was concluded that this type of WEL, referred as TP-WEL, is induced by temperature and pressure changes. In contrast, in low braking utilisation regions where the traffic speed is steady, WEL caused by rolling contact fatigue deformation contained nanocrystalline martensite and a region of severe plastic deformation immediately below the WEL. This type of WEL is termed as SD-WEL. Microstructural observations suggest that both WELs types play significant roles in crack initiation and squat formation.

Crack Progression from Inside to Outside of Intermediate Shaft Flange Mating Surface

Crack Progression from Inside to Outside of Intermediate Shaft Flange Mating Surface

Total Recycled Asphalt Mixes: Characteristics and Field Performance

The use of recycled materials in asphalt concrete (AC) pavement has increased significantly because of their economic and environmental benefits. The use of recycled materials can pose risks to the performance of asphalt pavements, however. The Illinois Department of Transportation developed five total recycled asphalt (TRA) mixes in the pursuit of environmentally sustainable pavements. These mixes contain up to 60% asphalt binder replacement (ABR) obtained from reclaimed asphalt pavement (RAP) and recycled asphalt shingles. Virgin aggregates were replaced by 100% recycled aggregates including RAP, steel slag, and recycled concrete aggregate (RCA). Based on laboratory testing, all the mixes offered excellent rutting resistance because of their high ABR content. The TRA mixes were relatively less compliant and not very sensitive to field aging, whereas indirect tensile strength tests showed indistinguishable results. All mixes had comparable complex modulus |E*| and phase angle ([Formula: see text]) values at low temperatures. Laboratory-compacted specimens had relatively low flexibility index (FI) compared with field cores taken after construction. The FI values of the field cores decreased with aging, higher recycled materials content, or both. An exponential increase in transverse cracking was observed in the field cores because of their relatively high ABR, RCA/steel slag content, or both. The progression of field transverse cracking over time and FI values are well correlated. A three-dimensionally balanced mix design was introduced and used successfully to distinguish between AC mixes; it is proposed as a tool for better control mix designs and optimum field performance.

Interferência da adição de fibras de polipropileno e finos de basalto na resistência mecânica de micro-concreto

Este estudo propõe adicionar resíduos de basalto e fibras de polipropileno ao micro-concreto observando sua resistência à tração e à compressão, bem como sua trabalhabilidade. Foi estabelecido inicialmente o traço de referência de concreto convencional 1:2:3 em massa, a relação água/cimento 0.47 e desenvolvidos traços com diferentes teores de adições. Foi fixada uma consistência padrão a partir do traço de referência, a qual foi mantida com o uso de aditivo plastificante. Verificou-se que os concretos com as adiçoes apresentaram-se mais untuosos e fáceis de manusear que o concreto de referência, mesmo com o mesmo abatimento. Ocorreu um aumento de 30% na resistência mecânica à compressão comparado ao concreto convencional, que se considera ser pelo efeito filer do pó de basalto e um pouco pela interferência das fibras na progressão das fissuras térmicas. Não se verificou alteração considerável na resistência à tração. O estudo revelou que os materiais ensaiados são compatíveis em função do desempenho apresentado pelas misturas, tanto no estado fresco, quanto no estado endurecido. Pelos resultados mecânicos apresentados de resistência à tração e compressão concluiu-se que o uso desse material é viável para a produção de micro-concreto.

Damage assessment of concrete using a non-contact nonlinear wave modulation technique

This paper presents the development of a nonlinear vibro-acoustic modulation technique based on non-contact piezoelectric sensors to detect the crack progression of concrete subjected to both mechanical and thermal load. Two types of crack are investigated in the work including the isolated single crack induced by the three point bending test and distributed mapping cracks caused by heating treatment. Experimental results show that the damage index defined in the air-coupled wave modulation method – ultrasonic nonlinear parameter presents a positive correlation with the growth of single crack in bending test and the accumulation of mapping crack in thermal test. The sensitivity of developed method is validated through a comparison between the ultrasonic nonlinear parameter and two traditional linear parameters namely the phase velocity of Rayleigh wave and resonance frequency of vibrations. X-ray Computed Tomography (CT) technique and three-dimensional (3D) image reconstruction method are used to visualize microstructure of thermal damage. The CT images show that proposed nonlinear parameter is reliable and well correlated with the microstructural defects of concrete specimen. The repeatability of the air-coupled method is better than the contact method because the coefficient of variation of non-contact measurements is averagely about 43.2% of the contact measurements. Due to the advantage of removable characteristic of non-contact ultrasonic measurements, the developed air-coupled nonlinear wave modulation method could be promising for fast damage assessment of concrete structures in engineering practice.

Influence of micro arc oxidation coating thickness and prior shot peening on the fatigue behavior of 6061-T6 Al alloy

Micro arc oxidation (MAO) coatings of 5-different thicknesses were formed on 6061-T6 Al alloy with and without prior shot peening. The surface and cross-sectional morphologies, the surface roughness (Ra, Rz), relative phase composition, depth of peening were investigated as a function of MAO coating thickness. The high cycle fatigue performance of Plain MAO and prior shot peened MAO (SP + MAO) coatings were evaluated as a function of coating thickness and maximum alternating stress levels in comparison with that of bare substrate. Independent of the coating thickness, the Plain MAO coatings offer substantial degradation in fatigue life wherein the extent of fatigue debit increases with increasing coating thickness. Increasing surface roughness of Plain MAO coatings with increasing coating thickness resulted in multiple crack nucleation leading to consistent debit in fatigue life. However, irrespective of coating thickness, SP + MAO samples exhibit consistently improved fatigue life over the entire alternating stress range investigated wherein the net effect of increased surface roughness with increasing coating thickness was well-compensated by the compressive residual stresses present beneath the substrate-coating interface. The fractured surface and progressive crack morphologies clearly highlight the mechanisms responsible for the overall fatigue life are distinctly different for the Plain MAO and SP + MAO coatings as a function of coating thickness.

FATIGUE LIFE ANALYSIS OF RAIL-WELDS USING LINEAR ELASTIC FRACTURE MECHANICS

The initiation and growth of fatigue cracking is mainly due to high stress concentration, heterogeneity and poor quality of weld. The detection and rectification of such weld defects are major concerns of rail network managers to reduce potential risk of rail breaks and derailments. To estimate the fatigue life of welded joints and to analyze the progress of fatigue cracks, a fracture mechanics-based analysis and fatigue models were developed using Finite Element Analysis. The initial flaw is obtained from a sample weld using ultrasonic flaw detecting machine test. Linear Elastic Fracture Mechanics (LEFM) approach based on the Paris law was applied to determine critical crack size and the number of cycles to failure using FRANC3D software. The inspection interval of rail welds before fracture (failure) was suggested based on reliability and life cycle analysis that correspond with minimum overall cost and frequency interval. It is recommended that fracture-based models in combination with reliability analyses can be a sustainable infrastructure decision-making algorithm.

Fatigue crack propagation at aeronautic engine vane guides using the extended finite element method (XFEM)

This work presents the numerical modeling and validation of two different fatigue propagation tests that attempt to simulate the crack growth situation that takes place at aeronautic engine vane guides. These vanes, which are cylindrical skins of very thin thickness (few millimeters), are responsible for holding the static blades of both the compressor and the turbine. The union of discs and blades is a very conflictive zone due to high stresses and possible manufacturing defects. The first test designed for this work tries to reproduce crack growth at geometric discontinuities and sharp edges, such as the union between the disc and the blades. The second test tries to reproduce the crack growth situation that takes place in skins of very thin thickness, such as vane guides. First, the experimental set-ups as well as the experimental results are presented. Then, the numerical FE models and simulations -corresponding to the experimental tests that have been performed- are explained. Finally, the comparison between the experimental and numerical results is presented. Crack growth was controlled by optical microscopy and by progressive crack surface heat-tinting. For the numerical simulations, the Extended Finite Element Method (XFEM) implemented in Abaqus® 2017 software has been used. The comparison between the experimental and numerical results shows very good correlation regarding crack shape and number of cycles until failure. The capabilities of the XFEM-based LEFM approach to simulate fatigue crack growth in complex crack fronts are validated.

Fracture mechanisms and microstructure in a medium Mn quenching and partitioning steel exhibiting macrosegregation

A medium-Mn steel, exhibiting manganese macrosegregation, was investigated. In order to study how the microstructure development influences the fracture mechanisms, the steel was quenching and partitioning processed using two different partitioning temperatures. At 400 °C partitioning temperature, the microstructure exhibits intergranular fracture at low plastic strain, following Mn-rich regions in which fresh martensite predominates. Elongated thin precipitates at prior austenite grain boundaries facilitate the initiation and progress of cracks at these locations. After partitioning at 500 °C, the redistribution of carbon triggers the formation of pearlite, the precipitation of carbides in the carbon-enriched austenite and the formation of spheroidal carbides at prior austenite grain boundaries. All these microstructural features result in an interlath fracture with more ductile character than after partitioning at 400 °C. In both cases, manganese macrosegregation triggers brittle fracture mechanisms by creating large hardness gradients.

Temperature Independent Defect Monitoring Using Passive Wireless RFID Sensing System

A significant requirement of low-cost sensing systems for defect detection is essential to bridge the gap in non-destructive testing and evaluation and structural health monitoring. In practical situation, the temperature variation will be unknown in a priori and hence will give rise to uncertainty and unreliability in the defect detection. This paper demonstrates the potential use of low-frequency radio frequency identification tag antenna-based wireless sensors to characterize corrosion and crack progression in high-temperature conditions for potential structural monitoring. Consideration of the parasitic parameters which depend on the temperature variation is presented. The key factors that influence the sensing accuracy with regards to different materials due to inhomogeneity are presented. A cost-effective self-compensation method is proposed by means of a self-swept frequency measurement through selection and fusion of temperature dependent feature near the tag’s resonance region. The experimental work validates the effectiveness of the method in temperature compensation and some initial results demonstrate the efficiency of the technique to overcome the inhomogeneity.

Leveraging Point Cloud Data for Detecting Building Façade Deteriorations Caused by Neighboring Construction

Building facade deterioration due to aging and nearby construction sites is a continuous public safety concern. Within the past half-decade, there have been more than twelve-thousand complaints regarding falling debris from building facades in NYC, where it has around 1 million aging buildings. Thus, an effective method for facade inspection is essential for property owners and inspection agencies. Nowadays, 3D laser scanners are widely utilized for their ability to capture as-is conditions. However, an appropriate scanning setting when facing distinct types of tasks, such as crack detection and progression of damages on building façades is essential to expedite the data collection process. The overarching goal of this research is to compare the datasets captured through different settings of laser scanners (i.e., resolution and scanning distance) for crack detection and to evaluate the measurement accuracy of the detected/progressed cracks. In this study, we report back on the analysis performed on point clouds obtained with terrestrial laser scanners for crack detection. The results provide a performance analysis of terrestrial scanning systems and corresponding settings for crack detection. Findings can provide an alternative way to comply with the laws (e.g., Local Law 11/98 in NYC) that require periodical evaluations of buildings in cities.

Investigations on acoustic emission parameters during damage progression in shear deficient and GFRP strengthened reinforced concrete components

Shear deficiency in reinforced concrete (RC) structures brings the vulnerability of brittle and abrupt failure to those structures, and thus, provides very little time for taking any precautionary actions. The present study focuses on the investigations on damage progression in shear deficient RC components using acoustic wave propagation technique. Three levels of shear deficiency with respect to the control beam are considered. Various acoustic parameters are considered to determine their efficacy in identifying the initiation and propagation of crack in concrete structures. Few of the acoustic parameters are identified to be very effective and able to clearly differentiate the tensile and shear cracking in concrete. Intensity characteristics, as identified in the present study, can be used to classify the type of damage (progression of shear and tensile cracks) under different stages of loading. Further, the acoustic emission monitoring technique is employed for detecting the crack initiation in strengthened beams where the critical shear deficient beam was strengthened using two layers of GFRP fabric in the shear zone. It is found that, unlike the original deficient beams, AE signals obtained from the strengthened beam clearly indicate the clear shift from shear failure to flexural failure. The present study underlines that the acoustic wave propagation technique can be effectively used to monitor the health of the reinforced concrete structures and to uniquely assess the appropriateness of any scheme(s) for strengthening of the deficient concrete structures.

Relationship between laboratory and full-scale fatigue performance of asphalt mixtures containing recycled materials

Use of recycled materials in asphalt mixtures is an important sustainability practice, and yet the oxidized asphalts introduced may compromise the cracking performance of pavement. This study evaluated the fatigue crack resistance of ten asphalt mixtures containing reclaimed asphalt pavement or recycled asphalt shingles. The materials were acquired from the full-scale test lanes constructed at the Federal Highway Administration Accelerated Loading Facility in McLean, Virginia. Three simple performance tests were employed given their simple testing procedures and analysis approaches: semi-circular bend, indirect tension, and Texas overlay tests. The test data were analyzed to obtain the corresponding fatigue parameters following the latest test standards and relevant literature. A new parameter named corrected crack progression rate (CCPR) was proposed for the Texas overlay test considering the viscoelastic nature of asphalt mixtures. Statistical comparison was performed on the laboratory results to assess the potential of each parameter in discriminating mixtures. This study further investigated the relationship between the laboratory results and fatigue performance of the full-scale lanes. It was found that the proposed CCPR parameter for the Texas overlay test provided the strongest correlation with field performance. Additionally, the fatigue life parameter determined from the same laboratory test, although relatively more variable, demonstrated the highest potential in detecting differences in mixture compositions.

Stochastic Modelling and Prediction of Fatigue Crack Propagation Based on Experimental Research

Numerical analysis of the propagation of an edge crack in a plate was performed in this study. The theoretical model of fatigue crack progression is based on linear fracture mechanics. Calibration functions for short edge cracks are applied in stochastic models and the stochastic dependencies between input random variables and the fatigue resistance are described. Attention is focused on the domain of the relative crack length. Results are obtained using the Latin Hypercube Sampling method. Sensitivity analysis is evaluated using methods ranging from the screening method to quantitative techniques based on correlation measurements. Pearson correlation coefficient, Spearman rank-correlation coefficient and Kendall rank correlation coefficient are used for the evaluation of sensitivity analysis. The study demonstrates the application of several numerical simulation procedures covering both qualitative and quantitative sensitivity analysis using a one-sample base. The effects of non-linear stochastic dependencies and outliers on the results of sensitivity analysis are discussed.

PWSCC growth rate model of alloy 690 for head penetration nozzles of Korean PWRs

Abstract This work aims to establish a model of a primary water stress corrosion crack growth rate of Alloy 690 material for the head penetration nozzles of Korean pressurized water reactors. The test material had an inhomogeneous microstructure with bands of fine-grains and intragranular carbides in the matrix of coarse-grains, which was similar to the archive materials of the head penetration nozzles. The crack growth rate was measured from the strain-hardened materials as a function of the stress intensity factor in simulated primary water at various temperatures and dissolved hydrogen contents. The effects of strain-hardening, temperature, and dissolved hydrogen on the crack growth rate were analyzed independently, and were then introduced as normalizing factors in the crack growth rate model. The crack growth rate model proposed in this work provides a key element of the tools needed to assess the progress of a stress corrosion crack when detected in thick-wall Alloy 690 components in Korean reactors.