Crack Orientation Research Articles

Quantitative evaluation of crack based on the sparse decomposition of array Lamb wave propagation

Crack damage is one of the significant factors that may accumulate at the stress concentration area of engineering structures and cause catastrophic accidents. In this paper, we proposed a novel approach to identify the crack location and size by exploiting the reflections and diffractions of Lamb waves. The interaction mechanism between the crack and Lamb wave has been analyzed thoroughly, our analysis of the interaction between the crack and Lamb wave revealed that both reflections and diffractions carry valuable damage information that reflects the size and orientation of the crack. As the interaction coefficients between these two components and the crack are different, there are supposed to exist differences between them in the amplitude value. We implemented a threshold to classify the signals received from all paths into two groups: reflections and diffractions. Then we constructed an overcomplete dictionary of waveforms corresponding to different propagation distances to extract the damage information. Using sparse decomposition, the received signals were mapped to their corresponding propagation distances without the use of baseline signals. The diffractions allow us to determine the crack's tip points, while the reflections provide information about the edge points. The kinked crack's size and orientation were visualized based on the time-domain signals acquired in our experiment. We provided a comprehensive description of our algorithm and verified it through numerical simulation and experimental data. Our results show high agreement with actual cracks, demonstrating the efficacy of our proposed method.

Design of a novel dual-polarized microwave sensor for human bone fracture detection using reactive impedance surfaces

This paper presents a novel miniaturized dual-polarized transceiver sensor system for detecting fractures in human bone tissues. The system features a patch antenna and a Reactive Impedance Surface (RIS) layer that reduces its size by 30% compared to conventional designs, resulting in enhanced fracture detection accuracy. Additionally, the system includes a dielectric plano-concave lens that adapts to the human body and improves impedance matching for optimal performance. The lens contains via holes filled with a lossy dielectric material similar to human fat tissue, which concentrates electromagnetic (EM) power and increases penetration depth for more effective crack detection. To detect fractures, two identical sensors are placed opposite each other on the tissue and moved simultaneously. The amount of EM power collected by the receiver sensor is measured using S-parameters; the transmission coefficient (S21) phases and contrast between the crack and surrounding tissue are used to construct images of fractured bones. Full-wave simulations and experimental measurements on a semi-solid human arm mimicking phantom demonstrate the proposed dual-polarized sensor's ability to detect the location and orientation of narrow cracks in the millimeter range. The system exhibits reliable performance across different human bodies.

Determination of the Predominant Orientation of Cracks in Ice Cover of the Laptev Sea from the Ice Drift Data

Received April 10, 2023; revised May 25, 2023; accepted June 27, 2023The paper shows that in order to solve the problem of predicting the predominant orientation of cracks in ice covering the Laptev Sea, when the satellite information is absent, the orientation of cracks in ice cover can be calculated using data on the ice drift in the Sea. We have selected 200 satellite images made in both visible and infrared spectral bands allowing to obtain actual data on ice cracks in the Laptev Sea for seasons 2016–2021, and then calculated the predominant orientation of them using data on the OSI SAF ice drift for the date of each image as well as for several previous days. Results obtained were compared with actual modal orientations of the cracks and with characteristics of the atmospheric pressure fields in these days. It was found that selecting of initial ice drift data should be done with regard for the intensity of air flows, the invariability or constancy of the direction of air flows over the sea aquatory during several days, and the presence of a cyclone centered over the sea area. An algorithm has been developed for automatic selection of a date when the ice drift can be most likely accompanied by formation of cracks on the day under consideration, and calculation of predominant orientation of cracks should be made exactly on that day. The selected data on ice drift serve as a basis for calculating. It was revealed also that with the difference in the types of intensity of air flows in the northern and southern parts of the Laptev Sea, the developed algorithm for determining the date of ice drift should be applied to each part of the sea separately. The number of squares of the Laptev Sea grid in which the calculated orientation of cracks corresponded to its actual meaning with an established permissible error of 30° has been determined. The ratio of this number to the total quantity of grid squares (skill score) was equal to 69% on the average. The skill score exceeded 70% in 46 percent of the cases. The skill score falls below 60% in only 16 percent of the cases, with minimum value of 50%.

Detection of crack on a mild steel plate by using a magnetic probe incorporating an array of fluxgate sensors

Magnetic flux leakage (MFL) and eddy current testing (ECT) are two of the most commonly used techniques to detect cracks in ferromagnetic materials. The MFL technique excels in determining the locality of a crack, while the ECT technique can provide useful information regarding the dimension and orientation of cracks. The objective of this research is to propose a simultaneous application of both MFL and ECT techniques in a single probe and to improve the visual resolution of the defect by superimposing signals from a sensor array. A magnetic probe was developed with an array of fluxgate sensors and two excitation coils. Line scan measurements and 2D mapping of artificial slits with different depths were conducted on a mild steel SS400 plate with a thickness of 12 mm to evaluate the performance of the developed probe. The line scan measurement results demonstrated the ability of the probe to detect the presence of artificial slits on the sample and to predict the depth of the slits, especially at the 110-Hz excitation frequency. Then, from the 2D mapping results, the location of the slit was determined. Furthermore, by obtaining a superimposed 2D map generated by each sensor, an improved 2D map resolution with lower background noise was obtained.

A peridynamic model based on generalized thermoelastic theory in a plate with oblique cracks

In this paper, a peridynamic model based on generalized thermoelastic theory is derived by irreversible thermodynamics. This model avoids the spatial derivative and can be easily applied to generalized thermoelastic problems with discontinuities. The transient temperature response is captured using the non-Fourier CattaneoVernotte (C-V) model. The interaction integral is employed to calculate the transient thermal stress intensity factors (TSIFs). Numerical examples are presented for analyzing the effects of crack orientation angle and multi-crack distribution on transient thermoelastic response. And the crack propagation behavior under non-Fourier thermal shock is further discussed in detail. It is found that with the increase of the angle between inner crack and heating boundary, the sensitivity of mode-I TSIFs to the non-Fourier effect increases, while the sensitivity of mode-II TSIFs to the non-Fourier effect decreases. This peridynamic model may be useful for understanding the crack behaviors of thermal protection materials under thermal shock.

Fracture Resistance and Crack Growth Mechanisms in Functionally Graded Ti–TiB

This paper presents the results of fracture tests and crack path observations for a layered functionally graded material (FGM) consisting of Ti and TiB phases. The composition varied in a nearly linear manner from a TiB-rich layer at the bottom to commercially pure (CP) Ti at the top. Elastic properties of the mixed phase interlayers were measured using nanoindentation testing, demonstrating a linear variation with composition. These results differ significantly from approximations calculated in previous studies using a non-linear rule-of-mixtures approach. Fracture tests were conducted on single edge notch bend [SEN(B)] specimens with the notch aligned orthogonal to the direction of the composition gradient. For this crack orientation, "average" R-curve behavior based on the J-integral was investigated to understand the mechanics of crack growth. The value of J was found to be minimal (less than 1 N/mm) below 47 pct volume fraction of TiB compared to a reported value of approximately 150 N/mm for pure Ti. These results indicate that a steeper transition to high concentrations of the metallic phase is necessary to achieve adequate fracture resistance in this metal/ceramic FGM. Observations on the specimen surface indicate crack path toughening mechanisms of this functionally graded material include crack bridging, branching, and deflection.

On the initiation of hydraulic fractures in anisotropic rocks

This paper addresses hydraulic fracture initiation from an initially notch-free wellbore situated in an anisotropic host rock, where the rock mass is subjected to an in-situ stress state that is also anisotropic in nature. In such conditions, hydraulic fracture initiation is fully characterized by three parameters, namely initiation pressure, initiation orientation, and initiation length. While a strength-based criterion captures only two of these parameters, break-down pressure and orientation, the evaluation of initiation length requires a mixed criterion approach in which both stress and energy conditions are met. We extend the existing mixed criterion formulation for isotropic rocks to also include anisotropic material behavior. We then investigate how material anisotropy interacts with stress anisotropy to determine the break-down pressure as well as the size and orientation of the starter crack. The results show that material anisotropy can overshadow the stress anisotropy, in the sense that it can drive the crack towards the weakest plane. It is demonstrated from a fracture energy perspective that the initiation length cannot extend as large as the fracture process zone length even when the wellbore size is unrealistically large. The difference between initiation pressures predicted by the mixed criterion and strength-based theory rises as the wellbore size decreases. Based on these observations, applying the mixed criterion is essential especially in relatively small wellbores.

On predicting crack length and orientation in twill-woven CFRP based on limited data availability using a physics-based, high fidelity machine learning approach

Predicting crack length and orientation in twill woven CFRP plates is notoriously non-trivial due to the interplay of complex physics over multiple length scales. Furthermore, on an industrial scale, a timely yet accurate non-destructive prediction based on a limited amount of data is critical for successful industrial adoption. This paper proposes a physics-assisted surrogate approach, by first measuring electrical conductivities using the Electrical Resistance Charge (ERC) and then developing high-fidelity through-thickness crack models resulting in 42 datasets, and processing the resulting data with a polynomial regression coupled with the leave one out cross validation using physics-based engineered features. The proposed method achieved averaged error of 0.09% and 0.48% for crack length and orientation, respectively, exhibits advantages over the Artificial Neural Network (ANN) in terms of both accuracy and tendency to overfit. This proposed approach paves the way for the maturing of the sought-after real-time Structural Health Monitoring (SHM) of crack length and orientation.

Multiscale characterization of the fracture mechanics of additively manufactured short fiber-reinforced composites

We present a multiscale characterization approach to experimentally investigate the influence of architectural features, namely pores, weakly bonded filaments’ interfaces, and layer stacking, on the failure of composites manufactured by fused filament fabrication. Combining standard approaches, such as tensile and flexural tests, with contactless techniques, we identified the local phenomena driving the damage of 3D-printed short carbon fiber-reinforced polyetheretherketone specimens. The elastic and fracture tests highlighted the process-induced anisotropy and the incomplete interface adhesion resulting in the transverse tensile modulus drop to around 20% of the longitudinal value. Equivalent fracture toughness was measured for a crack propagation along filaments’ and layers’ interfaces, while the stress intensity factors doubled for a crack propagation involving the filaments’ breakage, when compared to the interface failure. The displacement and strain contours obtained by digital image correlation emphasize the influence of the stacking (i.e., 0°–90°, ±45°) on the preferential crack propagation at the layers’ and filaments’ interfaces. The specimen inspection by scanning electron microscopy and by X-ray tomography further highlighted the influence of the printed composites’ meso and microscale architecture on the fracture mechanisms, such as the simultaneous damage of parallel ±45° oriented layers’ interfaces or the zig-zag crack propagation for specimens with ±45° stacking undergoing intralayer delamination. The elastic and fracture properties, together with the full-field measurements, provide the tools to guide the design of complex and reliable components for high-performance applications (e.g., aerospace, automotive) and benchmark for damage prediction models.

Seismic anisotropy and geodynamics of the East Japan subduction zone

Seismic anisotropy in the East Japan arc has been extensively investigated by conducting shear-wave splitting measurements, receiver-function analyses, and tomographic inversions of body-wave travel times and surface-wave dispersion data, which have provided a wealth of information on dynamic processes associated with active subduction of the Pacific plate. Measuring shear-wave splitting is popular and effective to detect seismic anisotropy, but it has poor depth resolution. This problem has been overcome by conducting 3-D anisotropic tomography, which has high-resolution in both lateral and vertical directions. Both P and S wave anisotropies are revealed in the crust, which are caused by alignment or preferred orientation of crustal minerals and stress-induced microcracks related to active faults. Trench-normal fast-velocity directions (FVDs) of azimuthal anisotropy are revealed in the back-arc mantle wedge, reflecting subduction-driven convection there. Trench-parallel FVDs appear in the forearc mantle wedge under the land area, which may reflect deformation that results in B-type olivine fabric. The forearc mantle wedge offshore may lack anisotropy, suggesting that it is stagnant and decoupled from the subducting slab and does not participate in the viscous flow, in sharp contrast with the rest of the mantle wedge. The most significant findings of the body-wave anisotropic tomography are its constraints on the slab anisotropy. The subducting Pacific slab exhibits mainly trench-parallel FVDs, which reflect shape-preferred orientation of crystals and cracks related to normal faults produced in the outer-rise area before the plate subduction, overprinting the fossil anisotropy that the Pacific plate gained when it was produced at the mid-ocean ridge. Trench-parallel intraslab fast velocity planes of anisotropy intersect the slab upper surface at high angles (∼45–90°), reflecting aligned hydrated faults in the slab. Ruptures of the hydrated faults in the upper part of the slab may cause large intraslab earthquakes (M ≥7.0) that take place frequently beneath the forearc area. Trench-normal FVDs also appear in the subslab mantle, which may reflect asthenospheric shear deformation associated with the overlying slab subduction.

Fretting fatigue crack growth simulation and residual life assessment of railway press-fitted axle

To evaluate the inspection interval and safety margin of a railway press-fitted axle with fretting cracks, we conducted a fretting fatigue crack growth simulation and residual life assessment of a railway press-fitted axle by employing an actual load spectrum. The predicted results were compared with the measured crack to examine the effectiveness of various crack orientation criteria for assessing crack growth. Based on the validated crack orientation criteria, a finite element model was built to perform incremental fretting fatigue crack growth analysis. Then, the fretting fatigue crack growth life of the railway axle was predicted using two conventional crack growth rate models and compared with the experimental results. The results indicate that the max(ΔkI*) criterion provides a better approximation of the fretting fatigue crack growth path. The Paris equation can yield excessively conservative prediction life due to the strong load dependence of the effective stress ratio of fretting cracks, which can vary with the crack length and is influenced by press fitting. In contrast, the NASGRO equation yielded prediction results that were closer to the test results and can be utilised to determine the inspection interval. This study can serve as a vital reference for the operation and maintenance strategies for damaged axles with fretting cracks.

Overall assessment of CFRP-wrapped concrete affected by alkali-silica reaction

The multi-level approach coupling of mechanical (i.e., Stiffness Damage Test -SDT) and microscopic (i.e., Damage Rating Index -DRI) testing procedures, was found to be promising for evaluating the condition of ASR-affected concrete elements under unconfined and internally confined conditions. Yet, only a few studies investigated the effect of external confinement (i.e., CFRP wrap) on ASR-induced damage. Thus, this study aims to study the impact of various external confinement conditions (i.e., none, 1 ply CFRP and 2 plies CFRP) on ASR-induced damage. One hundred and seventy concrete specimens incorporating distinct reactive aggregates (coarse and fine aggregate) and confinement conditions were fabricated, stored in an environmental chamber, and monitored over time. Upon reaching the given expansion levels, a multi-level assessment was conducted. The results show the mitigation nature of confinement against ASR-induced expansion as well as yielding damage transfer according to the confinement condition. Moreover, different crack features and orientations, as well as mechanical degradation, are observed in restrained specimens, which confirms that ASR exhibits different damage developments under “free expansion” and externally restrained conditions.

Residual life prediction of compressor impeller with microcrack damage

Taking compressor impeller with pressure ratio less than 3 as research object, a prediction method of residual life of compressor impeller was proposed. Considering the action of “inertial” load centrifugal force, finite element method (FEM) technology and sub-model technology were used to comprehensively analyze the mechanical quantities, such as blade stress, and the hot spot stress location of compressor impeller was determined. Crack orientation was determined according to maximum principal stress criterion. The linear elastic fracture mechanics (LEFM) based on FEM and Forman-Newman-de Koning (FNK) model were used to investigate the whole process of crack growth, including stable growth and instability growth stages. The crack growth law and residual life of impeller at different rotate speeds were given. The results show that with the increase of rotate speed, the stress intensity factor (SIF) of initial crack front increases in a quadratic power law, the critical length decreases linearly, and the residual life decreases nonlinearly. The crack grows along the height of blade and then fractures after a deflection of about 90 degrees to the outer edge of blade. The obvious deflection of crack is the sign of crack transition from stable growth stage to instability growth stage. The life of crack in the instability growth stage can be neglected compared with that in the stable growth stage. The analysis method proposed in this article can provide a basis for the damage tolerance evaluation of compressor impeller, and can also provide a reference for maintenance work.

Effective elastic properties and S-wave anisotropy for rocks containing any oriented penny-shaped cracks in transversely isotropic background

Fractures have a significant influence on rock elastic properties. The existing elastic models for cracked medium mainly consider the crack dip angle. In this work, based on the previous transversely isotropic (TI) background and arbitrary dip crack model, a theoretical model is derived using the Bond transform matrix to quantify the effects of any oriented penny-shaped cracks on the elastic properties of rocks with a TI background. Based on this model, the effects of crack orientation on rock elastic properties are studied. Particularly, a special case with random crack orientation is investigated by using the spherical averaging of the crack compliance matrix with any orientations. Furthermore, the S-wave anisotropy for rocks containing multiple crack sets also is analyzed. The results indicate that the crack orientation has a great influence on rock elastic properties. Especially, the rock elastic properties indicate nonlinear changes with crack azimuth angles when cracks are inclined with respect to the TI background isotropic plane. The randomly oriented cracks decrease the overall rock elastic moduli but have little effect on rock anisotropy. For rocks containing multiple crack sets, parallel crack sets have great effects on the S-wave anisotropy, whereas the effects of orthogonal crack sets are negligible. Using this model, a complete workflow for the inversion of fracture properties using field data measured by acoustic logging is introduced. To explain the effect of crack azimuth angle, the crack density is inverted without considering crack orientation, only considering crack dip angle, and considering both crack dip and azimuth angles. The results indicate that the inversion results considering the crack dip and azimuth angles are in good agreement with the resistivity imaging results. This work provides the theoretical basis for fracture properties inversion for rocks with a TI background.

A generalized machine learning framework for brittle crack problems using transfer learning and graph neural networks

Despite their recent success, machine learning (ML) models such as graph neural networks (GNNs), suffer from drawbacks such as the need for large training datasets and poor performance for unseen cases. In this work, we use transfer learning (TL) approaches to circumvent the need for retraining with large datasets. We apply TL to an existing ML framework, trained to predict multiple crack propagation and stress evolution in brittle materials under Mode I loading. The new framework, ACCelerated Universal fRAcTure Emulator (ACCURATE), is generalized to a variety of crack problems by using a sequence of TL update steps including (i) arbitrary crack lengths, (ii) arbitrary crack orientations, (iii) square domains, (iv) horizontal domains, and (v) shear loadings. We show that using small training datasets of 20 simulations for each TL update step, ACCURATE achieved high prediction accuracy in Mode-I and Mode-II stress intensity factors, and crack paths for these problems. We demonstrate ACCURATE’s ability to predict crack growth and stress evolution with high accuracy for unseen cases involving the combination of new boundary dimensions with arbitrary crack lengths and crack orientations in both tensile and shear loading. We also demonstrate significantly accelerated simulation times of up to 2 orders of magnitude faster (200x) compared to an XFEM-based fracture model. The ACCURATE framework provides a universal computational fracture mechanics model that can be easily modified or extended in future work.

Surface cracks growth for superalloy in a round bar under different loading

The main objective of this paper is to experimentally and numerically detect the surface cracks in the round bar for Ni-Al- 315 steel superalloy and calculate the crack depth which induces the sintering of these alloys. Several factors have contributed to surface defects, such as metallurgical defects and notches. The surface crack orientation can be estimated at the observed crack increase by using displacement. Various crack aspect ratios, a/b, ranging from 0.0 to 1.0, and relative crack depth, a/D, ranging from 0.2 to 0.4, are considered. The superalloy (Ni, Al and 315 steel) has been successfully modified utilizing the powder metallurgical process. The specimens are typically made up of Six layers, starting with (Al, Ni) across one side and ending with (Ni-Al- 315 steel) on another. Transmission electron microscopy (SEM) Instrument analysis has been used to detect the surface cracks and analyze the microstructure of superalloy used in detail using the X-pert analytical program.

Passive atomic-scale optical sensors for mapping light flux in ultra-small cavities

Understanding light propagation and attenuation in cavities is limited by lack of applicable light sensing technologies. Here we demonstrate the use of light-sensitive metastable states in wide bandgap aluminosilicates (feldspar) as passive optical sensors for high-resolution mapping of light flux. We develop non-destructive, infrared photoluminescence (IRPL) imaging of trapped electrons in cracks as thin as 50 µm width to determine the spatio-temporal evolution of light sensitive metastable states in response to light exposure. Modelling of these data yields estimates of relative light flux at different depths along the crack surfaces. Contrary to expectation, the measured light flux does not scale with the crack width, and it is independent of crack orientation suggesting the dominance of diffused light propagation within the cracks. This work paves way for understanding of how light attenuates in the minutest of cavities for applications in areas as diverse as geomorphology, biology/ecology and civil engineering.

Effects of Crack Formation on the Mechanical Properties of Bilayer Graphene: A Comparative Analysis

We present a molecular dynamics simulation study on the effects of crack formation on the mechanical properties of bilayer graphene. Bilayer graphene possesses unique electronic properties that can be modified by applying a voltage, making it an attractive material for various applications. We examined how the mechanical properties of bilayer graphene vary under various crack configurations and temperatures, measuring Young’s modulus, fracture toughness, fracture strain, and fracture stress. We compared the effect of crack presence on single and both layers and found the appearance of double peaks in the stress–strain curves in the case of a monolayer crack, indicating a subsequent fracture of the cracked layer and the uncracked layer. We also examined the effect of crack shape, size, and orientation on mechanical properties, including circular, hexagonal, and rectangular cracks along two axes. We found that both circular and hexagonal cracks had a smaller Young’s modulus and toughness than rectangular cracks, and the orientation of the crack had a significant impact on the mechanical properties, with a 2.5-times higher toughness for cracks with a length of 15Å. Additionally, we found that Young’s modulus decreases with increasing temperature in bilayer graphene with cracks on both layers. Our findings provide valuable insights into the potential applications of bilayer graphene in the design of advanced nanoscale electronic devices.

Theoretical investigation of reactive burn in a highly cracked energetic material

While energetic material reactive burn processes such as the buildup to detonation are well understood for energetic materials like PBX 9501 that contain small amounts of porosity, the same is not true for highly cracked energetic materials. This work addresses this shortcoming by performing theoretical reactive burn calculations where thin submillimeter thick cracks permeating a PBX 9501 system are explicitly modeled. We use the Scaled Uniform Reactive Flow (SURF) model for the reactive burn calculations. Before considering highly cracked structures, we first show that SURF closely reproduces reactive burn experiments done on pristine and single air gap PBX 9501. For all cases of this investigation, a high-pressure shock is introduced by way of a high velocity impact to initiate a detonation in our cracked PBX 9501 structures. Using fully three-dimensional simulations and the physics code PAGOSA, we investigate the reactive burn process in cracked structures that have a propensity to have cracks either aligned with or orthogonal to the direction of wave propagation. While each crack structure has the same net crack porosity, we demonstrate that the reactive burn produced differs for the two cases. We also provide crack structure metrics, beyond porosity, that characterize the average crack orientation relative to the direction of wave propagation. Simulation results are provided for several variants of cracked structures. At the highest crack porosity studied here we observed the breakdown of stable detonation propagation. This high porosity case was achieved by doubling the average crack width, leaving all other features of the crack network unchanged. We conclude with a synthesis of our simulation observations to make general comments regarding how crack networks can affect points on the PBX 9501 detonation pop plot.

Atomistic study on crystal orientation-dependent crack propagation and resultant microstructure anisotropy in NiTi alloys

The primary objective of this study was to explore the crystal orientation-dependent fracture mechanism of nickel–titanium (NiTi) alloys by using molecular dynamics simulations. We discovered that the stress concentration ahead of the crack tip induced the formation of martensite with a herringbone twin or mixed HCP/OTHER atom morphology, while reverse martensite transformation occurred behind the crack tip due to stress relaxation. Interestingly, typical brittle fracture by cleaving along the high-energy domain boundary, quasi-brittle fracture as a result of the transformation-induced plasticity, as well as ductile fracture caused by a combination of phase transition, stacking fault, and atomic slip were observed in the samples with (1¯00) [010], (110) [11¯0], and (1¯1¯2) [111] crack orientations, respectively. The findings demonstrated that the crack growth behavior in each orientation was closely correlated to the microstructure evolution around the crack tip. Moreover, the relationship between the traction force and separation was achieved from the fracture process zone near the crack surface. The reported orientation dependency of the traction–separation curves was decisively driven by the anisotropy of cracking characteristics and microstructure morphologies. The results of this work offer comprehensive insights into the importance of crystal orientations on the atomic-scale fracture performance of NiTi alloys.