Crack Orientation Research Articles

On the crack resistance and damage tolerance of 3D-printed nature-inspired hierarchical composite architecture

Materials scientists have taken a learn-from-nature approach to study the structure-property relationships of natural materials. Here we introduce a nature-inspired composite architecture showing a hierarchical assembly of granular-like building blocks with specific topological textures. The structural complexity of the resulting architecture is advanced by applying the concept of grain orientation internally to each building block to induce a tailored crack resistance. Hexagonal grain-shaped building blocks are filled with parallel-oriented filament bundles, and these function as stiff-blocks with high anisotropy due to the embedded fiber reinforcements. Process-induced interfacial voids, which provide preferential crack paths, are strategically integrated with cracks to improve fracture toughness at the macroscopic scale. This study discusses the structural effects of the local/global orientations, stacking sequences, feature sizes, and gradient assemblies of granular blocks on crack tolerance behavior. Alternating stacking sequences induce cracks propagating in the arrestor direction, which boost the fracture energy up to 2.4 times higher than the same layup stacking sequence. Gradient arrangements of feature sizes from coarse to fine or fine to coarse result in the coexistence of stiffness and toughness. Our approach to applying crystallographic concepts to complex composite architectures inspires for original models of fracture mechanics.

Automatic Method for Detecting Deformation Cracks in Landslides Based on Multidimensional Information Fusion

As cracks are a precursor landslide deformation feature, they can provide forecasting information that is useful for the early identification of landslides and determining motion instability characteristics. However, it is difficult to solve the size effect and noise-filtering problems associated with the currently available automatic crack detection methods under complex conditions using single remote sensing data sources. This article uses multidimensional target scene images obtained by UAV photogrammetry as the data source. Firstly, under the premise of fully considering the multidimensional image characteristics of different crack types, this article accomplishes the initial identification of landslide cracks by using six algorithm models with indicators including the roughness, slope, eigenvalue rate of the point cloud and pixel gradient, gray value, and RGB value of the images. Secondly, the initial extraction results are processed through a morphological repair task using three filtering algorithms (calculating the crack orientation, length, and frequency) to address background noise. Finally, this article proposes a multi-dimensional information fusion method, the Bayesian probability of minimum risk methods, to fuse the identification results derived from different models at the decision level. The results show that the six tested algorithm models can be used to effectively extract landslide cracks, providing Area Under the Curve (AUC) values between 0.6 and 0.85. After the repairing and filtering steps, the proposed method removes complex noise and minimizes the loss of real cracks, thus increasing the accuracy of each model by 7.5–55.3%. Multidimensional data fusion methods solve issues associated with the spatial scale effect during crack identification, and the F-score of the fusion model is 0.901.

Effect of rare earth element Y on the crack propagation behavior of Mg alloys: A molecular dynamics simulation

The effect of the distribution and concentration of rare earth (RE) element Y, crack orientation, temperature, and strain rate on the crack propagation behavior of the Mg alloys is investigated by molecular dynamics/Monte Carlo simulations. The results show that the RE element Y tends to form locally short-range order structures in the Mg alloys, and the introduction of the RE element Y can enhance the fracture toughness of the Mg alloys. The results indicate that with the increase of Y concentration, the crack propagation mode of the Mg alloys shifts from a mode, dominated by the dislocation emissions at the crack tip and the crack cleavage propagation to a mode dominated by the solid-state amorphization and the slip of amorphous bands. In addition, the results show that the faster the strain rate, the slower the crack propagation speed, and the crack propagation resistance increases with increasing temperature.

Martian seismic anisotropy underneath Elysium Planitia revealed by direct S wave splitting

Seismic anisotropy, arising from the crystallographic/lattice-preferred orientation of anisotropic minerals or the shape-preferred orientation of melts or cracks, can establish a critical link between Mars's past evolution and its current state. So far, seismic anisotropy in Mars has been proposed due to different velocities of vertically and horizontally polarized shear waves in the Martian crust, obtained from crustal converted waves, multiples, and surface waves recorded by the InSight seismometer. However, the shear wave splitting, which stands out as a straightforward indicator of seismic anisotropy, has not been reported using marsquake records. In this study, we employ low-frequency marsquakes detected by the InSight seismometer to reveal shear wave splitting in marsquake recordings. We find that the direct S waves of three marsquake recordings (S0173a, S0235b, and S1133c) with high signal-to-noise ratios exhibit the splitting phenomenon. We rule out the possibility of apparent anisotropy through synthetic tests, affirming the presence of seismic anisotropy in Mars. The delay time measured from the direct S wave splitting is too large to be solely attributed to the seismic anisotropy in the upper crust (0 – 10 km) beneath the InSight. Thus, seismic anisotropy in the deeper region of Mars is required. Combined with other geophysical evidence near the InSight landing site, the seismic anisotropy observed in this study implies the aligned cracks in the crust are greater than 10 km beneath the InSight and/or the existence of mantle flow underneath the Elysium Planitia of Mars.

Finite element analysis of macro-crack behavior in the cortical bone of a human tibia

The bone is a biological tissue that possesses a highly complicated hierarchical structure; hence, the tissue components of the bone exhibit variable mechanical proper-ties and a complex bone geometry. This is why the creation of a three-dimensional mod-el through CAD software facilitates the study of the mechanical behavior of bones. Com-bining the concepts of linear elastic fracture mechanics and finite element analysis pro-vides a practical solution to study the fracture behavior of the tibial bone. The objective of this study is to analyze the behavior of cracks in the cortical bone of the human tibia us-ing stress intensity factors in mode I, II, and III as rupture criteria to assess the bone damage response. The tibial bone is one of the most common sites for lower limb stress fractures, which pose problematic injuries. The results investigating the effect of the crack position in the bone demonstrate that the risk of crack propagation is mainly due to mode I opening and is highly favored in the distal zone compared to the middle and proximal regions, regardless of bone density. For the second case study, it is observed that regardless of the crack size, the maximum values of stress intensity factors KI are obtained in the distal zone. Regarding the effect of crack orientation, the results indicate the dominance of mode II for angles α = – 45°, 30°, 45°, leading to high values of stress intensity factors KII.

Stress–strain hysteresis during hydrostatic loading of porous rocks

A micro-mechanical model is proposed to predict the stress–strain hysteresis during the cyclic hydrostatic loading of fluid-saturated rocks under drained or undrained conditions. A spherical pore is surrounded by a multi-cracked shell where local deviatoric stress develops despite the remote hydrostatic loading. The effective properties of the material composing the shell are constructed assuming an isotropic distribution of cracks with no interaction, and the overall properties thanks to the spherical assemblage approach. The fluid pressure in drained and undrained conditions is assumed to be uniform throughout the assemblage. A new analytical solution is proposed, assuming all cracks are closed and slipping either forwardly or reversely. It is shown with numerical simulations for drained conditions that this assumption is indeed respected for sufficiently small values of the crack friction angle. However, for reasonable values, the closed cracks during the unloading phase could slip in either direction: reversely close to the pore and still forwardly away from the pore. Moreover, at critical radii, the slip could occur in either direction depending on the crack orientation. A similar micro-structural response is observed for undrained conditions, although the remote confining stress required to close the cracks is much larger. The model’s predictions compare favourably with recent experimental data on dry sandstones and carbonates, which were presented in a study on the influence of strain amplitude on the transition between static and dynamic properties. The crack density and matrix elasticity modulus are sufficient fitting parameters to accurately predict the hysteresis loops, especially for porosity levels above 10%.

Microstructural Instability and Its Effects on Thermoelectric Properties of SnSe and Na-Doped SnSe.

Effects of thermal cycling on the microstructure and thermoelectric properties are studied for the undoped and Na-doped SnSe samples using X-ray computed tomography and property measurements. It is observed that thermal cycling causes significant cracks to develop, which decrease both the electrical and lattice thermal conductivities but do not affect the thermopower. The zT values are drastically reduced after the repeated heat treatment. It is important to account for density changes during cycling to obtain accurate values of the thermal conductivity. Even before thermal cycling, the spark-plasma sintered (SPS) samples have a significant number of microcracks. The orientation of cracks within the SPS pellets and their effect on the microstructure are influenced by the presence of a Na-rich impurity. The SnSe and Sn0.995Na0.005Se samples without the impurity develop cracks and exhibit grain growth parallel to the pellet surface, which is also the plane of the 2D SnSe layers. The Sn0.97Na0.03Se sample containing the impurity develops cracks that are orthogonal to the pellet surface. Such an orientation of cracks in Sn0.97Na0.03Se inhibits grain growth. All samples appear mechanically unstable after thermal cycling.

A phase‐field framework for stress corrosion cracking prediction in elastoplastic metallic materials

AbstractTo capture the stress corrosion cracking (SCC) in metallic materials, a phase‐field framework considering localized plastic deformation and stress states is established. A new function of critical energy release rate is proposed to describe the degradation of cracking resistance of materials in the SCC process. This proposed framework can reproduce SCC results consistent with experimental observations in C‐ring steel SCC tests, especially capturing the directionally characteristic of the cracks. Furthermore, the influences of localized plastic deformation and stress states on the SCC process are studied. This novel phase‐field framework can capture (1) the influences of coupled electricity, mechanics to the SCC mechanisms; (2) the contribution of plastic strain energy as the driving force for the phase‐field; (3) the potential and preferential crack initiation and propagation morphology within the complex stress and strain domain; and (4) the dependence of SCC rate and propagation direction on stress state and localized plastic deformation.

The influence of the disturbing effect of roadways through faults on the faults' stability and slip characteristics

AbstractIn order to mitigate the risk of geological disasters induced by fault activation when roadways intersect reverse faults in coal mining, this paper uses a combination of mechanical models with PFC2D software. A mechanical model is introduced to represent various fault angles, followed by a series of PFC2D loading and unloading tests to validate the model and investigate fault instability and crack propagation under different excavation rates and angles. The results show that (1) the theoretical fault model, impacted by roadway advancing, shows a linear reduction in horizontal stress at a rate of −2.01 MPa/m, while vertical stress increases linearly at 4.02 MPa/m. (2) At field excavation speeds of 2.4, 4.8, 7.2, and 9.6 m/day, the vertical loading rates for the model are 2.23, 4.47, 6.70, and 8.93 Pa/s, respectively. (3) Roadway advancement primarily causes tensile‐compressive failures in front of the roadway, with a decrease in tensile cracks as the stress rate increases. (4) An increase in the fault angle leads to denser cracking on the fault plane, with negligible cracking near the fault itself. The dominant crack orientation is approximately 90°, aligned with the vertical stress.

Neural network potential for Zr-H

The introduction of Hydrogen (H) into Zirconium (Zr) influences many mechanical properties, especially due to low H solubility and easy formation of Zirconium hydride phases. Understanding the various effects of H requires studies with atomistic resolution but at scales that incorporate defects such as cracks, interfaces, and dislocations. Such studies thus demand accurate interatomic potentials. Here, a neural network potential (NNP) for the Zr-H system is developed within the Behler-Parrinello framework. The Zr-H NNP retains the accuracy of a recent NNP for hcp Zr and exhibits excellent agreement with first-principles density functional theory (DFT) for (i) H interstitials and their diffusion in hcp Zr, (ii) formation energies, elastic constants, and surface energies of relevant Zr hydrides, and (iii) energetics of a common Zr/Zr-H interface. The Zr-H NNP shows physical behavior for many different crack orientations in the most-stable ε-hydride, and structures and reasonable relative energetics for the 〈a〉 screw dislocation in pure Zr. This Zr-H NNP should thus be very powerful for future study of many phenomena driving H degradation in Zr that require atomistic detail at scales far above those accessible by first-principles.

Short fatigue crack growth and retained austenite in steels processed via quenching and partitioning

Previous research has consistently found that introducing metastable retained austenite (RA) as a second phase retards the failure of steel under fatigue. However, the reasons for this benefit are not understood. Accordingly, the properties of RA most advantageous to resist fatigue are not known. Within this context, this paper examines the interaction between second-phase RA and short fatigue crack growth in a steel processed via quenching and partitioning, using quasi in situ electron backscatter diffraction experiments. Results show that most RA transforms into martensite under the plastic strain surrounding the crack. They also reveal various mechanisms whereby RA transformation delays short fatigue crack propagation; transformation-induced crack closure (TICC), crack deflection and branching, and roughness-induced crack closure (RICC). Crack deflection and branching are driven by a tendency of cracks to propagate towards transformed RA, which is against the previous assumptions in the literature. Furthermore, the impact of crack deflection/branching on retardation is more powerful than that of TICC acting alone. Microstructures including second-phase RA should avoid RA-lean areas and promote elongated RA grains, with relatively large size, and major axis normal to the preferential crack growth direction. Untransformed RA within the plastic zone (i.e. overstabilized) does not contribute to crack retardation.

Anisotropic damage evolution in solid fractures: A novel phase field approach with multiple failure criteria and directional-dependent structural tensor

This study proposes a novel phase-field fracture model based on unified phase field theory, aiming to overcome current limitations in simulating material complex fracture behaviors. Through this model, analytical solutions for two-dimensional bars subjected to tensile or compressive stresses are provided, enabling the coupling of multiple failure criteria and further proficient simulation of mode-I, mode-II, and mixed mode-I/II fractures, effectively addressing challenges faced in modelling materials with different or complex failure modes under various loading conditions. Furthermore, to account for the strong anisotropic failure behavior of materials, a novel directional-dependent structural tensor is proposed. The tensor correlates fracture energy with crack surface orientation, facilitating precise characterization of material damage evolution with multiple potential crack orientations. This tensor ensures the consistency of phase-field fracture evolution with predefined fracture patterns. The effectiveness of the proposed model is validated through case studies, emphasizing its robustness and superior predictive capability in capturing fracture behavior under various conditions. This research provides a more accurate and universally applicable approach for simulating material failure, particularly for complex or multiple failure mode material failure simulations.

Wearable flexible eddy current instruments for defect inspection of curved surfaces

ABSTRACT The utilisation of curved structural components is prevalent, despite their proneness to degradation over time. This research introduces a wearable and flexible electromagnetic non-destructive testing instrument that is furnished with an eddy current sensor, multi-channel excitation and acquisition circuits, amplifiers, as well as signal processing circuits. A unique design for the flexible Eddy Current Testing (ECT) sensor is suggested to ensure its suitability for diverse curved surfaces. By combining the sensor with gloves, it facilitates wearable inspection. Leveraging the self-developed instrument system, this sensor can detect defects with a minimum depth of 0.1 mm while also being capable of identifying crack orientation accurately. Furthermore, it quantitatively determines the depth of defects on curved surfaces with high signal-to-noise ratios. The instrument system exhibits high portability, flexibility, and efficiency, rendering it readily adaptable for various applications.

Dynamic response and sound radiation of cracked asphalt pavements under moving loads and variable thermal profiles

ABSTRACT This study investigates the acoustic performance and dynamic response of cracked, viscoelastic porous asphalt pavements under moving loads and variable thermal conditions. Realistic pavement cracks are modelled using an advanced line spring model with fracture compliance coefficients. The novelty lies in the synergistic integration of a heterogeneous triple-porosity media model, a non-uniform depth-dependent temperature profile, and an advanced fracture mechanics-based line spring model with arbitrary crack orientation. Variations in temperature that are uniform, linear, and nonlinear with respect to the thickness layer axis are taken into account. The governing equations are derived by Hamilton’s principle and solved analytically via Fourier-Laplace transforms. The acoustic pressure is first-time predicted through Rayleigh integral analysis. Durbin’s numerical inversion validates the model’s accuracy versus sophisticated finite element simulations. Parametric analysis offers new insights into the effects of crack length, pore size distribution, loading frequency, and thermal gradients on noise pollution and fatigue cracking. The integrated chemo-thermo-mechanical modelling enables optimal structural design and accelerated pavement testing to limit acoustic radiation and premature failure in porous asphalt pavements. It allows for the development of noise-reducing porous asphalt mixtures by modifying aggregate gradation, binder content, and air void distribution.

Crystallographic Orientations of Cracks Formed in SiGe/Ge/Si(111)

Crystallographic Orientations of Cracks Formed in SiGe/Ge/Si(111)

Modeling of defects in ultrasonic flaw detection. Status and prospects

In the introduction to the article four factors, which are most important for ensuring the accuracy of defect parameters measurements at ultrasonic inspection, are mentioned: parameters of artificial reflectors in samples, compliance of acoustic properties of material of tuning samples and controlled products, transient characteristics of electroacoustic paths, methodological features of measurements. The present article is devoted to the analysis of the first and partly fourth of listed factors. The review of reflectors, the use of which is regulated in various standards, is carried out. Advantages and disadvantages of flat-bottomed holes, segmental and angular reflectors (“notches”), lateral (BCO) and vertical cylindrical drills, grooves are noted. Taking into account the peculiarities of ultrasonic wave scattering, it is noted that artificial “reflectors” such as “grooves” and BCOs are used to adjust the parameters of modern diffraction control methods. It is recommended to expand the use of grooves, BCO and vertical drilling in the revision of standards governing the use of classical echo-methods. The estimation of accuracy of measurement of defects parameters, first of all — coordinates of crack tip, with application of modern digital methods of information processing at ultrasonic control is given. It is indicated that to increase the accuracy of measurements, to determine the position and orientation of cracks in welds, it is necessary to create a database of digital doubles of samples with artificial reflectors and products with real defects. The general scheme of quality control work execution is given, taking into account the use of standards (measures), digital models of artificial reflectors and digital twins of the control process to ensure the necessary detectability of defects and reliability of manual, automated and, potentially, automatic control.

Effects of Heat Treatment and Processing Conditions on the Microstructure and Mechanical Properties of a Novel Ti–6.3Cu–2.2Fe–2.1Al Alloy

Adding transition alloying elements to achieve a columnar to equiaxed transition (CET) in Ti alloys gains attention in additive manufacturing (AM). AM, which may be categorized as an advanced solidification process, is commonly a near‐net‐shaped process. This thus does not allow traditional thermomechanical processing to reduce grain size, which drives research toward novel alloys able to establish a primary grain structure with equiaxed grains upon solidification. The Ti–Cu alloy system catches attention through inducing the CET, but so far, no focus is placed on its secondary, solid‐state, and phase transformations during the heat treatment, therefore, requiring modified heat‐treatment strategies to accommodate for the inability of mechanical preforming prior to heat treating and thus achieving desired mechanical properties. In this work, insights are provided on microstructural evolution and tensile properties of a novel Ti–6.3Cu–2.2Fe–2.1Al alloy gained in an extensive heat‐treatment study. In the results, a lamellar α+β Widmannstätten microstructure with Ti2Cu precipitation and other features including grain boundary α, precipitate‐free zones, and very fine secondary α precipitates are shown. Utilizing micrographs and fractographic imaging, the fracture mode is identified as quasi‐cleavage mode with preferential crack initiation at grain boundary α layers. Tensile tests on heat‐treated samples show high strengths with simultaneously limited ductility.

Electrical conductivity model for transversely isotropic rocks with interconnected cracks

The electrical conductivity of subsurface rocks is generally anisotropic. The anisotropy of the subsurface electrical conductivity provides important information on the stress-strain state and geodynamics. To quantitatively interpret anisotropic conductivity structures revealed by electromagnetic surveys, it is essential to use a mixing model considering the anisotropy. Although there exists a mixing model for transversely isotropic rocks with crack-shaped pores, the previous model seems inappropriate in interpreting conductive anomalies revealed by electromagnetic exploration because cracks are assumed to be isolated in the model. Therefore, this study develops a theoretical mixing model for transversely isotropic rocks with mutually interconnected cracks by a statistical approach. The derived mixing model considers the macroscopic tortuosity of a collection of cracks as well as the tortuosity of each crack. The derived model can represent general transverse isotropy and includes the isotropic and parallel models as special cases. I compare the developed model to previously proposed mixing models, showing that the developed model can reproduce a much wider range of anisotropy than the already-existing anisotropic mixing model. By applying the developed model to an example of the anisotropic conductivity in the oceanic upper crust inferred by electromagnetic exploration, I demonstrate that the developed mixing model enables us to quantitatively infer the crack orientation and fluid volume fraction that reproduce significant anisotropic conductivity found by field observations. Furthermore, I compare the developed model to the anisotropic seismic velocity model for fluid-filled cracks.

Experimental study on direct shear properties and shear surface morphologies of hydrate-bearing sediments

The safe production of methane gas requires a comprehensive understanding of the geomechanical behavior for hydrate-bearing sediments (HBS). Currently, there is a lack of detailed exploration of the shear surface failure characteristics of specimens. To address this, direct shear tests were performed to observe shear surfaces at the microscopic level. This study mainly focuses on the mechanical parameters of HBS and the morphological characteristics of shear surfaces, aiming to elucidate the deformation modes and failure mechanisms. Results reveal that shear load-displacement curves illustrate three stages: elastic deformation, strain softening, and stability stage. The shear strength increases from 12.65 KPa to 153.86 KPa with hydrate saturation rising from 12% to 72%, while decreases versus shear rate. Shear surfaces exhibit concave, convex, and S-shape patterns with remarkable differences in crack number and orientation. The shear load-displacement curves and shear surface morphology are closely correlated with shear rates, especially shear strength and shear surface roughness. Furthermore, the shear surface roughness varies between 2.02 mm and 3.61 mm with hydrate saturation increasing from 12% to 72%, which are also influenced by the shear rate. Empirical formulas were established based on test data to predict the shear strength and surface roughness. The failure mechanism of the specimens mainly depended on the movement modes of the sediment particles, hydrate strength, and hydrate-sediment cementation strength. Findings of this study provide a theoretical reference for evaluating geo-mechanical stability and predicting the destabilization of natural gas hydrate reservoirs.

Solid solution of zirconium on the M-site in Ti2AlC MAX phase coatings: Synthesis, structure and mechanical properties

Ti2AlC MAX phase is considered an ideal candidate for surface protective coatings in harsh environments due to its excellent resistance to oxidation and corrosion, yet poor mechanical properties are a key bottleneck for practical applications. In this work, taking the conception of solid solution, high-purity and high-hardness (Ti, Zr)2AlC coatings were synthesized on Ti-6Al-4V substrates using a multiple-target magnetron sputtering technique combined with subsequent annealing. The as-deposited Ti-Zr-Al-C coating was partially crystalline containing TiAlx phase, and MAX phases formed after annealing at 750 °C for 90 min. Comprehensive X-ray diffraction and high-resolution TEM analysis identified the formation of solid solution (Ti0.9Zr0.1)2AlC. The incorporation of Zr reduced the surface roughness and grain size of the coatings due to the increased nucleation sites and the suppressed atomic diffusion. Comparing with pristine Ti2AlC coating, the hardness of the (Ti0.9Zr0.1)2AlC coating was enhanced by 30 % from 12.8 GPa to 16.6 GPa. This enhancement can be ascribed to the synergistic strengthening from solid solution and grain refinement. However, fracture toughness slightly deteriorated in the (Ti0.9Zr0.1)2AlC coating due to the preferential crack path along the refined-grain boundaries.