Early-stage Crack Research Articles

Modeling and analysis of internal excitation and vibration characteristics of gears with early-stage crack and 3D tooth surface error

Affected by the tooth surface errors, the vibration characteristics of early crack failures are usually various under different tooth surface precision level. Therefore, to reveal the influence of three-dimensional (3D) tooth surface error (TSE) on the internal excitation and vibration characteristics of gears with early-stage crack (ESC), a coupling internal excitation model of gears with ESC and 3D errors is proposed based on a double-layer iterative method. In this model, the influence of meshing phase between tooth pair and along tooth width direction (TWD) on the time-varying mesh stiffness (TVMS) are simultaneously considered, which overcomes the limitations of traditional models that are only suitable for characterizing the coupled excitation of the two-dimensional tooth profile errors and TVMS. Based on verifying the proposed model, the effects of TSE type, parameters, and load on the TVMS, loaded static transmission error (LSTE), load distributions, and torsional deformation of the cracked gear teeth are investigated, and the vibration characteristics of ESC failures under the effects of 3D TSE are also explored. The research results show that the distribution parameters of 3D TSE have a significant effect on the internal excitation and vibration characteristics of gears with ESC, and thus measuring and evaluating the distribution parameters of TSE can help improve the accuracy of gear fault identification and diagnosis methods.

How many critical planes? A perspective insight into structural integrity

The topic of material fatigue is a subject extensively investigated within both scientific and industrial worlds. Fatigue-induced damage remains a critical concern for a variety of components, encompassing both metallic and non-metallic materials, often leading to unexpected failures during their operational lifecycle. In cases necessitating the assessment of multiaxial fatigue, critical plane methodologies have emerged as a valuable approach. These methodologies offer the means to pinpoint the component's critical regions and anticipate early-stage crack propagation. Nevertheless, the conventional technique (i.e., plane scanning method) for computing critical plane factors is a time-intensive process, reliant on nested iterations, predominantly suited for research purposes. In numerous cases, where the critical area within a component is unknown in advance (i.e., primarily due to complex geometries and loading conditions) the method proves impractical. Furthermore, the plane scanning method does not provide a deep comprehension of the critical plane concept; indeed, it is just a numerical artifice for calculating stress and strain quantities on different planes. Recently, the authors introduced an efficient algorithm for evaluating critical plane factors. This algorithm is based on a closed form solution and is applicable to all instances where the maximization of a specific parameter, based on stress or strain components, is required. The methodology relies on tensor invariants and coordinates transformation principles thus enhancing the investigation of various critical plane methods. The paper addresses two formulations of the Fatemi-Socie critical plane factor and discusses how the number of critical planes depend on the loading conditions the component is subjected to. By the use of a closed form solution a deep insight of critical planes orientation can be achieved.

Synergistic Effects of SAP, Limestone Powder and White Cement on the Aesthetic and Mechanical Properties of Fair-Faced Concrete

In this investigation, a comprehensive assessment was conducted on the cooperative effects of Super Absorbent Polymers (SAP), limestone powder, and white cement within the realm of fair-faced concrete. We discerned that while white cement augments the color vibrancy of the concrete, its accelerated hydration rate potentially induced early-stage cracks and compromised performance. To mitigate these challenges, SAP was incorporated to regulate early hydration, and limestone powder was introduced as a fortifying agent to bolster the mechanical robustness of the concrete. Our findings highlighted not only the capability of SAP to enhance concrete workability and longevity but also the pivotal role of limestone powder in amplifying its mechanical attributes. Microscopic evaluations, undertaken via Scanning Electron Microscopy (SEM), unveiled the potential of both SAP and limestone powder in refining the microstructure of the concrete, thereby elevating its performance metrics. Synthesizing the research outcomes, we pinpointed an optimal amalgamation of SAP, limestone powder, and white cement in fair-faced concrete, offering a valuable reference for prospective architectural applications.

Damage analysis in composite materials using a hybrid artificial immune system

Structural health diagnosis and condition monitoring of structures and components meant for aerospace industries is a challenging task for researchers and aerospace scientists. Presence of a minute crack in a structural element causes variation in local stiffness. The variations of local stiffness depend on crack location and crack depth. Change in stiffness in consequence affects the vibration behaviour of whole structural member. These abnormities in the structures if sustain over a long period cause catastrophic failure. Unexpected failure of any components of space vehicles results huge loss of life, more casualty and affect the economy of a country. To stay away from such situations, regular monitoring on safe operation of structures is extremely essential. Development of efficient damage detection methods is vital for early stage crack detection and its severity. In this work a novel online crack detection method based on artificial immune system has proposed. This article presents analytical and numerical (Finite element method) analysis for crack detection in a hybrid carbon fiber/ kevlar reinforced epoxy composite cantilever beam under free vibration. From the analysis, by varying crack sites and crack depth, alteration in natural frequencies and corresponding mode shapes curvature are recorded. Data (first three natural frequencies) from FEA has trained in negative selection algorithm (NSA). The result of FEA and NSA has compared. Then total average percentage of error is calculated. One statistical method has been used to make NSA more adaptive for the online damage detection. For this purpose a data mining technique named as “Regression Analysis” (RA) is used to reduce residual errors during the data acquisition method. The results are compared with standalone NSA and flexible NSA. Total average percentage of error has calculated.

A double-layer iterative analytical model for mesh stiffness and load distribution of early-stage cracked gear based on the slicing method

To reveal the coupling relationship between the time-varying mesh stiffness (TVMS) and the load distribution along the tooth width direction (TWD) of gears with early-stage crack (ESC), a double-layer iterative analytical model for the TVMS and load distributions of gears is proposed considering the effects of the non-uniformly distributed load (NDL) along TWD caused by the ESC. In the proposed model, an analytical model of tooth torsional deformation and a parallel slice stiffness model of the tooth pair with ESC are separately developed based on the slicing method. On this basis, a double-layer iterative calculation method for the TVMS and load distributions is proposed, in which the coupling relationships between the slice stiffness and load distribution along TWD as well as the TVMS and load distribution between the meshing tooth pairs are respectively presented with the inner- and outer- layer iterations. Finite element (FE) models are established to verify the proposed double-layer iterative model. The effects of crack parameters and applied torque on the tooth torsional deformation, TVMS, and load distributions of the gear with ESC are finally investigated based on the proposed model. The results show that the proposed model can realize the accurate and fast decoupling calculation of the TVMS and load distributions of gears with ESC. This study can provide a basis for the establishment of the refined ESC fault diagnosis method and the rapid evaluation of the load distributions of gears with asymmetric errors or faults along TWD.

The role of microstructural evolution on the fatigue behavior of additively manufactured Ti–6Al–4V alloy

The fatigue behaviour of additively manufactured Ti–6Al–4V via Laser Powder Bed Fusion (L-PBF) was evaluated in three different conditions, as-built, heat-treated and hot isostatically pressed (HIP'ed). Fractography analysis interpreted together with the S–N curves indicates that fatigue failure in as-built and heat-treated conditions where <0.2% porosity was present, was mainly driven by early-stage crack growth. However, crack initiation was determined to be the main controlling factor for fatigue deformation of HIP'ed samples. Moreover, a strong correlation between the impact energy and fatigue limit was found. The findings were based on detailed microstructural and crystallographic characterization, as well as mechanical testing. The as-built and heat-treated conditions exhibited poor fatigue response in comparison to HIP'ed which is largely attributed to the lower levels of porosity identified. Even though similar levels of porosity are present in as-built and heat-treated samples, improvement in fatigue limit was determined in the heat-treated condition due to phase transformation and microstructural coarsening leading to reduction in micro-strain.

Improvement in repeatability of ultrasonic array imaging in materials with high structural noise

Developments of automated systems in recent years have improved fast non-destructive evaluation (NDE) of complex structures. This opens up the possibility of looking for small changes between repeat measurements, either to increase the detectability of small defects, or to more accurately characterise the growth of known defects. In this paper, we study the effect of positioning inaccuracy, array element variability, and couplant wave velocity variability on inspection repeatability performance. We propose a post-processing approach to compensate for the degradation in repeatability due to changes in these parameters between inspections. A two-medium, ray-based, forward model is used to quantitatively study the effect of these parameters on inspection repeatability, and the results show a good agreement with experiments. The study indicates positioning inaccuracy and couplant wave velocity variability are the dominant factors affecting inspection repeatability and that the effect of element variability is negligible. We find the repeatability is profoundly sensitive to positioning inaccuracy, which requires a method to measure and correct for the difference between nominally identical inspection positions. Modest differences in wave velocity in the couplant can be tolerated, provided that the relative difference in true couplant wave velocity and that assumed in imaging calculations is preserved. The proposed compensation approach is shown to offer significant performance advantages for baseline subtraction and early-stage crack detection.

Finite elements analyses of early-stage crack propagation in aluminum wire bonds due to power cycling

This paper focuses on the thermomechanical behaviour and the consecutive damage of the bond-wire contacts in power semiconductors. Electro-thermal-mechanical finite element analysis of power cycle loads was used to model realistic transient temperature loadings as well as mechanical stresses. Mechanical damage modelling using the cohesive zone approach was used in conjunction with coupled finite element analysis. Parallel to the theoretical research, a pulse width modulation power cycling test bench was realized, and thermal cycles tests were carried out on power modules with temperature swing ∆Tj = 30°C and minimal temperature Tj, min = 55°C. Electron Back Scatter Diffraction was used to investigate crack early-stage crack propagation and crack propagation of the samples. Fatigue cracks were found to be always initiated from the interface wire –metallization and propagate exactly at the contact.

Overview of Stage 1b Stress Corrosion Crack Initiation and Growth of Pipeline Steels

Stress corrosion cracking (SCC) can cause catastrophic failure of buried pipelines for oil and gas transmission. The life cycle of pipeline steels experiencing SCC consists of five stages: incubation stage, stage 1a (crack initiation), stage 1b (early-stage crack growth), stage 2 (sustainable crack growth caused by mechanical driving force), and stage 3 (rapid crack propagation to rupture). Stage 1b encompasses a large portion of the pipeline’s lifespan, which is of great significance to pipeline integrity management aimed at service life extension. However, this stage is less studied so far. This invited paper provides a brief review of the recent progress on stage 1b stress corrosion crack initiation and growth for buried pipeline steels. Emphasis is placed on the effects of loading conditions and their interactions on stage 1b growth of high pH SCC, while some progress of near-neutral pH SCC is included for the purpose of comparison. It first introduces SCC in pipeline steels which is followed by a definition of stage 1b and its significance in terms of the service life of pipeline steels. Then the most recent advancements in understanding early-stage crack growth in stage 1b are reviewed and discussed. In summary, stage 1b growth can be self-induced by existing cracks (the so-called mother-daughter analogy), involving crack initiation in the plastic zone ahead of the surface tip of a surface crack, which is quite different from the stochastic process of coalescence of randomly formed individual cracks. Stage 1b growth extends crack length and increases the stress intensity factor at the depth tip without a physical increase in crack depth, serving as a bridge to stage 2. Further, the need for future research on stage 1b SCC initiation and growth of pipeline steels is discussed.

Surface integrity of hybrid CM247LC/Inconel 718 components produced by laser-directed energy deposition

High-temperature alloys pose significant challenges in additive manufacturing. These materials have unique properties, such as high resistance to mechanical and chemical degradation when exposed to high temperatures. Furthermore, when these alloys are used to produce hybrid components with other similar alloys, investigating their surface integrity is critical because any residual stress can lead to early stage cracks and poor fatigue performance. In this research, a hybrid manufacturing approach is employed to produce components from difficult to weld alloys, i.e. CM247LC deposited on IN718 through a laser based direct energy deposition (L-DED) process. The surface integrity, mechanical properties and microstructure of such hybrid components is investigated, especially their welding/joint areas. Crack-free processing regimes were established to deposit CM247LC while mitigating the negative effects onto the microstructure of the Inconel substrate. Especially, the thermal gradients were managed to deliver crack free sections of CM247LC with good interface bonding, strength and fine microstructure. It is important to note that this is achieved without any significant preheating that contrasts with what is reported in other investigations so far. Furthermore, end-use hybrid blisks with deposited CM247LC blades onto Inconel 718 disks (HUB) were manufactured and then machined within a single processing set-up. The results show that the substrate thickness, the machining between the deposited layers and the final machining and heat-treatment play a role in reducing residual stresses. Ultimately, such hybrid manufacturing approach can be considered a new solution for producing such components and also for their subsequent repair.

Dam Gate Control System using IOT

Abstract: Dams are in the main used for producing hydroelectricity and for irrigation purposes. This utilization has resulted within the construction of a variety of dams in potential areas over the years. As there are plenty of risk factors related to the existence of those dams, it’s became the necessity to develop a correct automatic monitoring system regarding the opening of the dam gates thereby managing a system for maintaining a secure water level in dams. Mismanagement of dams can also bring about manmade disasters. The dams that are present now are monitored and controlled manually. This ends up in pause in deciding. The proposed system involves real-time monitoring of water levels of the dam. Water levels may also range because of drastic adjustments in water levels of linked rivers of lakes, or because of the immoderate rainfall withinside the catchment area. The proposed system is an IoT system which is able to monitor and send real time parameters associated with Dam. The system also includes features like SMS alerts to the people of the locality and higher authorities, live display of water level and also the early-stage crack identification so as to scale back the risks of cracks which can lead to dam failure.

In-situ observation of microstructurally small fatigue crack initiation and growth behaviors of additively-manufactured alloy 718

To reveal the effects of microstructural features on fatigue property, microscopic fatigue crack initiation and growth behavior were successively observed for rolled plate and additively-manufactured nickel base 718 alloy. Three types of additive manufacturing (AM) methods: powder bed Electron Beam Melting (EBM), Selective Laser Melting (SLM), and wire-fed Electron Beam Additive Manufacturing (EBAM) were adopted for specimen preparation to create various microstructures for comparison. The results showed that the fatigue lives of the EBM and EBAM specimens, which have a robust (001) texture, were shorter than those of the rolled plate and SLM specimens. This fatigue life difference could not be explained by the defects, because the fatigue cracks in the part of EBAM specimen were initiated along a slip plane. On the other hand, acceleration of the early stage fatigue crack growth rate (FCGR) was found in the EBM and EBAM specimens. Cross-sectional electron back scatter diffraction (EBSD) observations also showed that early stage cracks initiated and grew along the {111} slip plane; but in the EBAM specimens, the cracks continuously propagated straight to an adjacent grain due to their (001) texture. It thus appears that the low-angle grain boundaries which tend to be generated as a result of the (001) texture do not act as barriers to the penetration of dislocations; instead, they accelerate the shear mode fatigue crack growth rate in the early stages and decrease fatigue life.

Strain-shock-induced early stage high pH stress corrosion crack initiation and growth of pipeline steels

This investigation demonstrated the occurrence of strain-shock associated with steels having discontinuous yielding and its effect on high pH stress corrosion cracking (SCC) under load-control (e.g., internally pressurized pipeline), instead of displacement-control, for the first time. Results showed that microcrack initiation in the plastic zone and microcrack coalescence to the main crack tip were the main growth mechanism in the early stage of crack growth, distinct from the generally believed stochastic initiation and coalescence mechanisms. Discontinuous yielding associated with strain-aging would create a strain-shock effect under load-control and substantially enhance the early stage crack initiation and growth.

Early stage crack detection in mechanically joined steel/aluminum joints by condition monitoring

Abstract Monitoring systems for machines, plants, materials and equipment are increasingly used in production processes. These online condition monitoring systems can detect damage or excessive loads at an early stage and can drastically reduce or prevent long downtimes of plants and machines as well as high repair and maintenance costs. This paper depicts a method for online crack detection with pattern recognition methods for specimens joined by self-pierce riveting under cyclic load in fatigue tests (laboratory application). A software specially conceived for this application was developed. This software, AnrissMF, uses active acoustic testing with a structure-borne sensor to detect cracks in the joints at a very early stage. It is shown in this paper that this software can detect cracks much earlier than classical failure criteria for joints (i. e. before any drop in stiffness or frequency is observed). Furthermore, the successful application of software AnrissMF for online crack detection during the fatigue strength test is presented.

Early stage crack detection in mechanically joined steel/aluminum joints by condition monitoring

Abstract Monitoring systems for machines, plants, materials and equipment are increasingly used in production processes. These online condition monitoring systems can detect damage or excessive loads at an early stage and can drastically reduce or prevent long downtimes of plants and machines as well as high repair and maintenance costs. This paper depicts a method for online crack detection with pattern recognition methods for specimens joined by self-pierce riveting under cyclic load in fatigue tests (laboratory application). A software specially conceived for this application was developed. This software, AnrissMF, uses active acoustic testing with a structure-borne sensor to detect cracks in the joints at a very early stage. It is shown in this paper that this software can detect cracks much earlier than classical failure criteria for joints (i. e. before any drop in stiffness or frequency is observed). Furthermore, the successful application of software AnrissMF for online crack detection during the fatigue strength test is presented.

Effect of steel fiber content on structural and electrical properties of ultra high performance concrete (UHPC) sleepers

This experimental research investigates the structural and electrical responses of ultra-high performance concrete (UHPC) railway sleepers with three different levels of steel fiber content. The UHPC sleepers used in this research were fabricated using a conventional concrete sleeper manufacturing process including the post-tensioning method. They were then evaluated via static bending tests at the rail-seat section and via electrical insulation performance tests. Test results indicate that UHPC sleepers with all three levels of steel fiber content sufficiently meet international requirements. The results from the first cracking load and the load when a crack width becomes 0.05 mm indicate that an amount of steel fiber greater than 1% is required to effectively control early-stage crack development in UHPC sleepers. In addition, the relationship between fiber volume fraction and normalized strength highlights that the material characteristics of UHPC, especially its tensile capacities, correlate strongly with the structural behavior of UHPC sleepers.

Performance Degradation Assessment of Concrete Beams Based on Acoustic Emission Burst Features and Mahalanobis-Taguchi System.

Acoustic emission (AE) has been used extensively for structural health monitoring based on the stress waves generated due to evolution of cracks in concrete structures. A major concern while using AE features is that each of them responds differently to the fractures in concrete structures. To tackle this problem, Mahalanobis—Taguchi system (MTS) is utilized, which fuses the AE feature space to provide comprehensive and reliable degradation indicator with a feature selection method to determine useful features. Further, majority of the existing investigations gave little attention to naturally occurring cracks, which are actually more difficult to detect. In this study, a novel degradation indicator (DI) based on AE features and MTS is proposed to indicate the performance degradation in reinforced concrete beams. The experimental results confirm that the MTS can successfully distinguish between healthy and faulty conditions. To alleviate the noise from the DI obtained through MTS, a noise-removal strategy based on Chebyshev inequality is suggested. The results show that the proposed DI based on AE features and MTS is capable of detecting early stage cracks as well as development of damage in concrete beams.

Initiation and Early-Stage Growth of Internal Fatigue Cracking Under Very-High-Cycle Fatigue Regime at High Temperature

The initiation and early-stage crack growth under very-high-cycle fatigue (VHCF) at room temperature, 750 °C, and 850 °C on directionally solidified Ni-base superalloy have been investigated. There was little frequency effect of 20 kHz on fatigue lives when compared with 100 Hz, nor did the deformation and fracture mechanisms. Dislocation tangles re-arranged themselves to form well-defined networks at interface of γ/γ′, accounting for the enhanced fatigue strength at 850 °C in VHCF regime when compared to that at 750 °C. In most cases, internal casting pore was the crack initiation site. Crack initiation and early-stage growth occurred on one of the {111} planes or their intersecting planes, a characteristic of Stage I cracking. With the use of optimized intermittent loading conditions, both the initiation and early-stage crack growth processes were successfully tracked on the basis of fine but visible beach marks within the Stage I cracking region. The first registered fatigue beach mark can be as close as only 86 μm to the crack initiation site and the crack length increased steadily over the whole early-stage crack growth stage. The enhanced fatigue strength at 850 °C can be rationalized with the higher threshold for propagating the early-stage crack. The fraction of fatigue life consumed for early-stage crack growth reduces with the decreasing stress, eventually leading to the initiation-controlling VHCF fatigue failure. The implications of these results are discussed with respect to the model prediction of fatigue life and fatigue strength.

High Spatial Resolution Crack Monitoring in Concrete Structures Using a Distributed Fiber Optic Sensor

Abstract A method to monitor the mechanical behavior and identify crack location and growth in a concrete structure element using a distributed fiber optic sensor (FOS) system is demonstrated experimentally by testing concrete specimens in four-point bending. The sensor system consisted of an optical frequency domain reflectometry (OFDR) interrogator unit paired with an all-grating sensing fiber that was bonded to the surface of the concrete test specimen. Strain measurements with high spatial resolution of &lt;10 mm were obtained at various points along a single fiber cable. Large strain values at the crack locations indicated strain concentrations that could be used to assess the crack growth. The distributed sensing system demonstrated the capability to detect localized, early stage cracks, with crack width smaller than 0.1 mm, well before they become observable by visual inspection.

Ductile fracture of dual-phase steel sheets under bending

Ductile fracture involving nucleation, growth and coalescence of microscale voids limits the performance, safety, reliability and manufacturability of a variety of metallic components and structures. This phenomenon is affected by length-scales induced by the geometry of deformation, loading conditions and microstructure of the material. For example, under uniaxial tension, dual-phase (DP) advanced high strength steel sheets exhibit similar flow response along rolling (RD) and transverse directions (TD) with ductility along RD being either equal to or greater than TD. However, the bendability of sheet specimens with bend axis parallel to RD is less than the bendability of sheet specimens with bend axis parallel to TD. The objective of this work is to model the interplay of length-scales induced by bending and microstructure on ductile fracture of DP steel sheets. To this end, microstructure-based finite element calculations of ductile fracture in DP steel sheets under bending have been carried out. In the calculations, DP microstructures in a bend specimen are discretely modeled. Our results show that the microscopic state of stress/strain, and hence, damage evolution in DP steel sheets under bending are highly heterogeneous. The extent to which length-scales induced by bending and DP microstructure affects crack nucleation and early stage crack growth is discussed. Parametric studies to quantify the effect of initial porosity, susceptibility to secondary void nucleation and energy dissipated in damage evolution prior to crack nucleation on the bendability of DP steel sheets have also been carried out.