Crack Length Research Articles

A deep learning informed-mesoscale cohesive numerical model for investigating the mechanical behavior of shield tunnels with crack damage

The present deep learning (DL)-based detection of crack damage of shield tunnels through images can only provide part of geometric information of the crack damage, which prevents the comprehensive understanding of the mechanical behavior of the cracked tunnel linings. This study bridges the gap between the geometric information identified by DL models and the transformation law of mechanical behavior of tunnel linings revealed by numerical methods. A mask-region-based hybrid attention convolutional neural network (Mask R-HACNN) and mesoscale cohesive numerical model are developed to obtain the geometric information of crack damage and investigate the structural response of segments and joints with crack damage, respectively. The numerical simulation results demonstrate that the relationship between in-depth crack length and crack opening displacement and the relationship between the degradation stiffness and in-depth crack length are independent of the loading path. Based on these findings, prediction formulas are established to interpret the relationships between the stiffness degradation coefficients, flexural stiffness, in-depth crack length, joint openings, and crack opening displacement. Then, the geometric information of crack damage obtained by the Mask R-HACNN is provided to the mesoscale cohesive numerical model to estimate the in-depth crack length, flexural stiffness, and stiffness degradation coefficient of cracked segments. Results show that the deep learning informed-mesoscale cohesive numerical model is satisfying in understanding the mechanical behavior of segments and joints during crack damage evolution.

Experimental Study of Needle Insertion into Gerbil Tympanic Membrane.

The perforation characteristics and fracture-related mechanical properties of the tympanic membrane (TM) greatly affect surgical procedures like myringotomy and tympanostomy performed on the middle ear. We analyzed the most important features of the gerbil TM perforation using an experimental approach that was based on force measurement during a 2-cycle needle insertion/extraction process. Fracture energy, friction energy, strain energy, and hysteresis loss were taken into consideration for the analysis of the different stages of needle insertion and extraction. The results demonstrated that (1) although the TM shows viscoelastic behavior, the contribution of hysteresis loss was negligible compared to other irreversible dissipated energy components (i.e., fracture energy and friction energy). (2) The TM puncture force did not substantially change during the first hours after animal death, but interestingly, it increased after 1week due to the drying effects of soft tissue. (3) The needle geometry affected the crack length and the most important features of the force-displacement plot for the needle insertion process (puncture force, puncture displacement, and jump-in force) increased with increasing needle diameter, whereas the insertion velocity only changed the puncture and jump-in forces (both increased with increasing insertion velocity) and did not have a noticeable effect on the puncture displacement. (4) The fracture toughness of the gerbil TM was almost independent of the needle geometry and was found to be around 0.33 0.10kJ/m2.

Assessing correlations between two linear amplitude sweep (LAS) standards for evaluating the fatigue properties of aged bitumen

ABSTRACT Linear amplitude sweep (LAS) is an accelerated and well-established testing method to evaluate bitumen fatigue. However, there are different versions of LAS procedures employed. Significant differences in loading modes, damage failure criteria and calculations exist between existing standards, leading to the inconsistency in the performance characterisation of bitumen. This study investigated the fatigue performance of six different bitumen at various ageing levels using two versions of the LAS standards (TP101-14 and T391-20). The stress–strain curves, damage characteristic curves, prediction of fatigue life and cracking length were analysed and compared. It was seen that conclusions drawn from the old version of LAS standard (TP101-14) were unclear as no distinct trends related to change in fatigue life could be observed for binders with progressively increased ageing levels, regardless of the strain levels used for analysis. The new version of LAS (T391-20), however, showed acceptable consistency. The trends indicate that at low strain levels, the fatigue life increases with ageing levels, while opposite trend was observed at higher strain levels. Moreover, the cracking length as defined in the T391-20 standard increases with progressively increased ageing. The new version of LAS standard (T391-20) is recommended for characterising the fatigue performance of aged bitumen.

Structure and property evolution of LaYbZr2O7/YSZ heterogeneous interface in double‐layer thermal barrier coatings after thermal exposure

AbstractDouble‐layer thermal barrier coatings are one of the development directions of thermal barrier coatings technology. LaYbZr2O7 (LYZO) has high toughness and low thermal conductivity, making it promising for use as a high‐temperature thermal barrier coating. However, its relatively poor mechanical properties, especially low fracture toughness, limit its further application. Therefore, we prepared a double‐layer coating of LYZO and Y2O3 partially stabilized ZrO2 (YSZ) using atmospheric plasma spraying, with the inner layer being YSZ and the outer layer being LYZO. The results showed that after spraying, LYZO was in the metastable fluorite phase, while YSZ was in the tetragonal phase. LYZO and YSZ had good chemical compatibility, and an interaction layer formed at the interface between them, with its thickness increasing with the sintering time. Eventually, after 100 h of heat treatment, the thickness reached 12 µm. The hardness of the LYZO/YSZ interface increased with the sintering time, reaching a maximum value after sintering at 1300°C for 10 h. When evaluating the interfacial bonding strength using indentation method, the length of cracks caused by indentation significantly decreased with the increase of sintering time. The increase in bonding strength can be attributed to the formation of a reaction layer and the reduction of thermal residual stresses. Raman spectroscopy was used to measure the thermal residual strain at the LYZO/YSZ interface. Unbalanced distribution of thermal residual stress and M phase was observed near the interface. As the sintering time increased, both thermal residual stress and M phase content decreased. In summary, the double‐layer thermal barrier coating of LYZO/YSZ has good potential for development.

Thickness-dependent micro-fracture behaviors of pre-cracked aluminum plates by crystal plasticity finite element method and damage criteria

Despite the fact that fracture behaviors of pre-cracked metal plates were investigated by the crystal plasticity finite element method (CPFEM), the thickness effect on their micro-fracture behaviors is still not clear because of the different out-of-plane constraints. Here, mechanical properties and micro-fracture patterns of pre-cracked aluminum plates with different thicknesses are obtained by experiments, as well as by CPFEM combining with two damage criteria. First, finite element models are constructed based on grain morphologies of specimens achieved by electron back scattered diffraction experiments. Next, some key parameters required in CPFEM and two damage criteria are determined by fitting experimental stress–strain relationships. In particular, the factors affecting accuracy of FE predictions are clarified by CPFEM. Finally, thickness-dependent micro-fracture mechanisms of two different damage criteria in pre-cracked aluminum plates with various thicknesses and crack lengths are revealed by comparison with the experimental results and CPFEM. This investigation should be of great help for understanding thickness-dependent micro-fracture mechanisms of metal and other material plates.

Comparative analysis of microdamage-affected chloride transport in concrete under static and dynamic hydraulic pressure

Concrete structures in marine environments frequently encounter the adverse impacts of hydraulic pressure, leading to a decrease in their durability. This study aims to conduct a comparative analysis of the internal microdamage in concrete when subjected to static and dynamic hydraulic pressure of equal intensity, and to examine the influence of such damage on chloride transport. By employing potentiometric titration, MIP, N2 adsorption, and AFM tests, the chloride concentration, pore structure parameters, and microscale elastic modulus of concrete under static and dynamic hydraulic pressure were analyzed. The results indicate that dynamic hydraulic pressure accelerates chloride transport in concrete. Compared with static hydraulic pressure, dynamic hydraulic pressure — sustained at the same intensity—results in an elevated threshold pore size along with an increased most probable pore size of the concrete. Furthermore, dynamic hydraulic pressure induces the expansion of microcracks, consequently decreasing the microscale elastic modulus of concrete. The use of mineral admixtures can effectively mitigate the damage evolution of concrete microstructure subjected to dynamic hydraulic pressure. Besides, a model is developed for relative chloride diffusion based on the principle of energy conservation and from the evolution law of the microscale elastic modulus gleaned from AFM tests. Through calculations, it can be found that the crack propagation rate and the decline rate of the relative chloride diffusion coefficient Df1Df2 increase markedly when dynamic hydraulic pressure intensity surpasses 40,000 Pa. The propagation of the crack length is moderated by a larger initial crack width.

Laboratory testing of desiccation crack growth in terrestrial Martian analog environments using digital image correlation

The unique geologic features of raised ridges and polygonal cracks filled with multiple layers of cement observed in Gale and Jezero craters on Mars have origins that remain uncertain due to limited knowledge and measurement techniques. This study hypothesizes that these cracks result from the volumetric shrinkage of clay fabric due to dehydration and salinity fluctuations in ancient Martian lakes. The research aims to quantify the shrinkage of terrestrial simulants with varying mineral compositions analogous to those found at Gale Crater and Jezero Crater under diverse desiccation conditions. By simulating Martian regolith using the Rocknest soil simulant and examining historical aqueous conditions through sedimentary rock analogs, this study provides new insights into Martian geological structures. The extent and rate of shrinkage in simulant samples were quantified using ImageJ, while strain localization and propagation were measured using the Digital Image Correlation (DIC) technique until full desiccation crack patterns developed. Laboratory testing revealed that desiccation cracks tend to form polygonal patterns, which are patently similar to the polygonal patterns observed in some regions of Mars. However, not all simulants produced visible cracks, with some producing linear rather than polygonal patterns. Key findings indicate that higher temperatures result in wider and deeper cracks, while lower temperatures decrease crack density and length. Increased initial water content leads to more extensive cracking, with higher crack density and length per unit area. Sodium chloride and sodium sulfate significantly impact desiccation cracking, with low concentrations stabilizing the soil and high concentrations promoting extensive cracking. Smectite-rich samples exhibit extensive cracking, and tensile strain distribution during evaporation is non-uniform, influencing crack development based on sample properties and drying conditions. These insights enhance our understanding of polygonal crack formation on Mars, improving Mars sample return missions and informing the design of robust exploration equipment.

The effects of three-dimensional bedding on shale fracture behavior: Insights from experimental and numerical investigations

The three-dimensional (3D) structural characteristics of the bedding planes exhibit strong anisotropy in the fracture behavior of shale. Previous studies on the anisotropy of shale fracture characteristics focused on 2D bedding effects, while 3D bedding effects that comprehensively consider bedding angles α and β have been rarely investigated. Therefore, the fracture behavior of shale with 3D bedding planes was studied based on laboratory experiments and numerical simulation. The results indicated that the apparent fracture toughness (AFT) of shale decreased with increasing bedding angle α. The fracture toughness of shale with a bedding angle of α = 0° was 2.26 MPa·m0.5 (β = 0°). However, when the loading angle α increased to 90°, the AFT decreased by 67.70 %. The increase in bedding angle β could improve the AFT significantly, and the higher the loading angle α, the more significant the improvement. The improvement amplitude at α = 90° reached 156.65 %. Due to the enhanced ability of shale to resist crack propagation by the bedding angle β, the trend of dissipation energy under the influence of 3D bedding effects was consistent with the AFT, and the two were positively correlated. Affected by the 3D bedding effect, three typical failure modes of shale have been observed: bedding failure, matrix failure, and mixed failure mode. Based on the calculation of the fractal dimension of the fracture surface, the roughness of the fracture surface under different failure modes was mixed failure > matrix failure > bedding failure. In addition, a 3D numerical model was established based on the DEM method, and the influence of new cracks on fracture toughness was considered after verifying the effectiveness of the numerical model. The length of newly formed cracks at the tip of shale prefabricated cracks exceeded 4.0 mm under critical load. Ignoring the length of new cracks will underestimate the fracture toughness of shale by about 30 %. Finally, the influence of 3D bedding planes on the crack propagation path was discussed.

Novel cell-based smoothed extended finite element method for simulating the interactions of ultrasonic waves with randomly distributed cracks in solid structures

The conventional extended finite element method (XFEM) is a powerful tool for simulating crack-related problems in materials; however, several limitations exist, such as numerical instabilities and convergence issues. These problems arise because enriched elements have higher stiffness than standard elements, and this difference can cause computational difficulties. To overcome these limitations, we developed the cell-based smoothed extended finite element method (CS-XFEM), an advanced computational technique designed to simulate the intricate interactions between ultrasonic waves and randomly distributed cracks within solid materials. This innovative approach integrates a cell-based smoothing technique into the XFEM, effectively softening the stiffness of the enriched elements around crack tips. Therefore, the CS-XFEM eliminates numerical instability, providing a more stable and reliable computational framework. In this study, numerical experiments were conducted in which plasticity properties were assigned to both the crack bodies and tips to reflect crack yielding. Further, frictional contact in the crack body elements was formulated using the Heaviside function, and deformation around the crack tips was approximated using a singular function. Through comprehensive numerical investigations, we demonstrated that the conventional XFEM fails to converge and, instead, diverges when ultrasonic waves interact with randomly distributed cracks. By contrast, our proposed CS-XFEM method demonstrates strong convergence capabilities, rendering it well-suited for exploring the interactions between ultrasonic waves and randomly distributed cracks under varying crack quantities, lengths, and friction coefficients. Overall, the proposed CS-XFEM is an efficient, accurate, and robust method for investigating the acoustic nonlinearity induced by randomly distributed cracks with frictional contact in solid structures.

Understanding the interface fracture mechanism by composite BFPMPC mortar and cement concrete bending beam

This study aims to utilize basalt fiber-reinforced polymer-modified magnesium phosphate cement (BFPMPC) mortar as an overlay for rapidly repairing surface defects such as raveling and delamination on Portland cement concrete (PCC) pavements, thereby swiftly restoring traffic flow and enhancing pavement service durability. Initially, double layered three-point bending fracture (DLTPB) tests were conducted on composite BFPMPC and PCC specimen with different predetermined crack lengths. The flexural strength was measured, fracture parameters were obtained based on the double-K fracture criterion, and crack propagation paths were determined using digital image correlation (DIC) methods. Subsequently, the fracture behavior of the composite beam was predicted by boundary effect model, and the interface microstructure between BFPMPC and PCC was characterized using nanoindentation, nano-scratch, and SEM/EDS techniques. Finally, by analyzing the fracture characteristics of the composite specimens, the crack propagation model was established and validated by finite element analysis (FEA). The results indicated that BFPMPC mortar overlay can enhance the flexural strength of composite structure. The unstable fracture toughness, cohesive fracture toughness, and fracture energy decreased with increase of crack length-to-height ratio (a0/D), while the initiation fracture toughness increased with increase of a0/D. DIC measurements provided insights into the morphology of the crack tip and the length of the fracture process zone (FPZ). The boundary effect model predictions aligned with the fracture characteristics of the specimens, which were controlled by nonlinear fracture criteria. Nanoindentation tests revealed that the mechanical properties of the interface are influenced by multiple sub-interfaces, with the elastic modulus relationship being ITZ-4 > ITZ-2 > ITZ-3 > ITZ-1. Further analysis of scratch hardness and scratch fracture toughness confirmed that the BFPMPC-PCC interface exhibited high fracture toughness, which was crucial for improving structural resistance to fracture. SEM/EDS observations revealed significant cracks at the interface between BFPMPC and ordinary Portland cement (OPC), while cracks between BFPMPC and coarse aggregates were smaller. Subsequently, the fracture analysis model for composite specimens was proposed to finely reveal interface fracture failure, and the FEA results exhibited a high degree of consistency with experimental results.

Decoding nonlinear ultrasonic time-frequency characteristics for fatigue crack quantification and localisation via CNN

ABSTRACT Early detection of fatigue cracks is crucial to guarantee the safe operation of engineering structures. Nonlinear ultrasonic technique (NUT) is widely used for closed crack characterisation as it breaks through the detection sensitivity limit upon closed defects that are usually invisible to linear ultrasonic techniques. The nonlinearity parameter is generally defined as the damage index (DI) to qualitatively detect these cracks. However, DI-based methods are underdetermined for quantifying and localising cracks in most circumstances. In this study, a deep learning method for intelligently decoding nonlinear ultrasonic time-frequency characteristics is developed to quantify and localise fatigue cracks. The nonlinear ultrasonic time-frequency spectrogram, which includes features characterising crack severity and location, is obtained by cleverly selecting the excitation frequency. The convolutional neural networks (CNNs) establish a mapping relationship between the nonlinear ultrasonic time-frequency characteristics and the crack length and location. It is worth mentioning that frequency-dependent convolutional kernels are proposed to more competitively decode nonlinear ultrasonic time-frequency characteristics. The results indicate that the CNNs with the frequency-correlation kernels are particularly robust and effective in both noiseless and noisy environments. The study demonstrated the potential of the proposed nonlinear ultrasonic time-frequency characteristic decoding method for accurate and efficient characterisation of damage.

Experimental and virtual testing of mode II and mixed mode crack propagation under dynamic loading

Under static loading, measuring experimentally the mode II and mixed mode fracture toughness of composite materials and adhesive joints is well standardised. However, under dynamic loading, no standard procedure has been defined yet. Therefore, this paper proposes an experimental methodology to measure the mode II and mixed mode interlaminar fracture toughness of composite materials and adhesive joints. The methodology is based on a modified split Hopkinson compression bar. Two different data reduction schemes are explored and compared, one based on measuring the crack length, and another based on measuring the force from the strains in the transmitted bar. The two data reduction methods provided considerably different results. By using the method based on measuring the force, the mode II and mixed mode fracture toughness for both interlaminar and adhesive joints decreased for higher strain rates, while the opposite was found with the other approach. The method based on the crack length measurement was deemed to be unreliable due to the difficulties in measuring it.

Fracture behaviour of reaction-bonded silicon carbide-boron carbide using digital image correlation

The current research uses the Digital Image Correlation (DIC) approach to study the fracture behaviour of Reaction-Bonded Silicon Carbide-Boron Carbide (SiC–B4C) ceramic (RBSBC). A Photron camera with 137,500 fps was used to capture the crack propagation at an interframe time frame of 2.6 ms before final fracture. The purpose was to capture the rapid brittle behaviour of the ceramic during the onset of crack propagation. The RBSBC failed in a transgranular manner like most monolithic SiC-based materials as Hexoloy-SA. The presence of randomly dispersed coarse B4C grains helps in deflecting the crack path which increases the overall crack length. The material’s resistance to crack propagation (R-curve) was measured using the crack tip opening displacement, the stress intensity at the crack tip KI, and the J-integral against crack extension. Two methods were used to determine the KI: experimentally based on the displacement values at the crack tip as obtained from the DIC images, and quasistatic based on the fracture load and the geometrical dimension of the crack. The experimentally-determined KI and J resulted in higher values compared to the quasistatic ones. However, they reflect the actual conditions at the crack tip, while the quasistatic conditions underestimate the resistance-plot. The RBSBC has higher R-curve compared to commercially available SiC-only materials as Hexoloy-SA and ABC-SiC. To improve the crack-resistance of RBSBC, the Si amount should decrease to a nm level, while the percentage of B4C grains should increase and be evenly dispersed across the material.

Longitudinal Shear of a Composite Material in Which the Binder and Inclusions are Weakened by Cohesive Cracks

Background: An elastic medium is considered that is weakened by a doubly periodic system of round holes filled with washers made of a homogeneous elastic material and has cohesive cracks, the surface of which is uniformly covered with a cylindrical non-metallic film. The binder (medium) is weakened by two doubly periodic systems of rectilinear cohesive cracks, directed parallel to the abscissa and ordinate axes, and the length of the crack and their dimensions are not the same (different). General concepts are constructed that describe a class of problems with doubly periodic stress distribution outside circular holes and cohesive cracks under longitudinal shear. The analysis of the limit equilibrium of cracks within the framework of the end zone model is performed on the basis of a nonlocal failure criterion with a force condition for the advancement of the crack tip and a deformation condition for determining the advance of the edge of the end zone of the crack. In solving the problem, the main resolving equations are obtained in the form of infinite algebraic systems and three nonlinear singular integro-differential equations. The equations obtained in each approximation were solved by the Gaussian method with the choice of the main element for different order values depending on the radius of the holes. Calculations were carried out to determine the forces in the connections of the end zones and the ultimate loads causing crack growth. Objective: In the considered problem, the problem of longitudinal slip weakened by cracks parallel to the x axis in the filling medium with two pairs of two periodic cracks weakened by 2 periodic circular holes is considered. In the problem, the boundary problem along the contour of the circular holes is determined, and at the same time, the surface problem is established for the cracks parallel to the x and y axes. The solution of the problem is sought analytically, and taking into account the boundary condition, a system of linear algebraic equations for circular holes and 3 singular integral equations for cracks is obtained. Theoretical Framework: The problem is solved analytically, as the system of linear algebraic equations obtained for circular holes and the system of linear integral equations are jointly solved, and the stress intensity factor at the end of the cracks is determined. Method: The problem was solved using "Kolosova Muskhalashvili" functions and "Collondia's method of solving singular integral equations". Results and Discussion: The main essence of the considered issue is that the stress intensity factor at the end of the cracks is determined according to Fig. 1. Research Implications: For the first time, the stress intensity factor was calculated in composite materials with two pairs of biperiodic cracks of different lengths weakened by biperiodic round holes. Originality/Value: For the first time, the stress intensity coefficient was determined in composite materials with two periodic two pairs of cohesive cracks.

Heterogeneity induced fracture characterization of concrete under fatigue loading using digital image correlation and acoustic emission techniques

Understanding the fatigue failure mechanisms in concrete is complex and remains an area of ongoing investigation. Material heterogeneity, along with the size effect, plays a significant role in specifying the crack propagation behaviour and fatigue life in case of repetitive loading conditions. In this study, the influence of material heterogeneity on the fatigue behaviour of concrete has been examined. Three different-size beam specimens with varying heterogeneity (aggregate sizes) have been considered to investigate various fracture characteristics under repetitive load conditions. Acoustic emission and digital image correlation techniques have been employed to analyse crack growth behaviour. The results revealed that stiffness degradation and crack propagation rates are faster for the specimens with smaller aggregate sizes compared to the larger aggregate size specimens of the same depth. Moreover, the fatigue life and effective crack length at failure are also higher in the case of larger aggregate sizes compared to smaller ones. Therefore, a heterogeneity-adjusted, analytical model of fatigue crack growth has been proposed. Further, the AE parameters have been utilized to characterize the tensile and shear crack dominance in different stages of fatigue crack propagation. The outcome of this study can be utilized to anticipate the crack propagation behaviour and residual fatigue life for any combination of specimen size and aggregate size.

Ultrasonic-Assisted Tungsten Inert Gas Welding of Inconel 625 Joints to Reduce Hot Cracking and Improve Microhardness: Optimization and Prediction Methods

Abstract This research article investigated the optimized process parameters for decreasing the hot cracking phenomenon and improving the microhardness of ultrasonic vibratory-assisted tungsten inert gas (U-TIG) welding of Inconel 625 alloy. The study employed two approaches: response surface methodology (RSM) and RSM coupled with a genetic algorithm (RSM-GA). The objective was to analyze the impact of welding process parameters, including welding current, gas flow rate, presence or absence of ultrasonic vibration, and filler material, on the crack length and microhardness of the welded joints. Experimental tests were conducted using RSM with a full factorial central composite design matrix, enabling comprehensive parameter space exploration. Parametric mathematical models were developed based on the obtained experimental data. These models were then utilized as fitness functions within the GA to determine the global optimal solution, aiming to minimize crack length and maximize microhardness. Additionally, artificial neural network (ANN) models were developed to predict the responses and optimize the welding process. The comparison between the experimental and predicted data demonstrated the reliability of the ANN model in accurately estimating the crack length and microhardness of U-TIG welded Inconel 625 alloy joints. The developed models achieved a prediction accuracy of less than 5 % error.

High-pressure corrosion fatigue experiments employing diverse methodologies for assessing rates of crack propagation

The new extreme faces strain gauges (XFS) technique, when compared to the direct current potential drop (DCPD) and back face strain gauge (BFS) methods, has shown superior accuracy and reliability in studying corrosion fatigue in high pressure. The XFS method serves a dual purpose by accurately measuring the crack length and acting as a mechanical load transducer. The results indicate that all three techniques can predict the final crack length effectively. However, BFS is unsuitable for high-pressure environments, and the current DCPD method can affect the crack propagation rate. The developed XFS methodology shows excellent performance in accurately evaluating corrosion fatigue studies.

Tectonic, Topographic, Geologic, and Hydroclimatic Influence on Crack Formation During the 2021 Haiti Earthquake

AbstractThe 14 August 2021 Haiti earthquake mainly portrayed reverse motion to the east near L’Asile town and left‐lateral strike‐slip motion to the west near Camp‐Perrin town. To map the rupture and infer its segmentation, we conducted the first post‐seismic field reconnaissance along the left‐lateral strike‐slip Enriquillo fault from L’Asile to Macaya mountain. We identified 98 linear, minor cracks that are not representative of primary fault surface rupture. Analyzing the topographic slope distribution, we detected that the cracks were often located in areas that are prone to topographic instability. About 60% of the cracks are located in Quaternary alluvium and Middle‐Miocene continental marls, indicating a preference for soft sediments. The rivers also have an impact, as crack lengths and openings negatively correlate with their distance to neighboring rivers. In addition, the earthquake occurred in a rainy region with up to 2,479.34 mm of rainfall in 2021, increasing soil instability. Above all, we found a contrast and asymmetry between the eastern and the western parts of the rupture. By dividing the 60‐km long rupture into two equal parts, we observed 57 cracks to the west against 41 to the east. The longest and the widest cracks are to the west. Analyzing their orientation, the cracks mainly oriented as left‐lateral strike‐slip faults to the west and mainly thrusts to the east. This configuration appears to be influenced by the slip pattern of the 2021 Haiti earthquake and consistent with the regional stress field.

Crack growth and fracture mechanics of CuCrFeNiCo high-entropy alloy during tension testing

In this work, the crack growth and fracture mechanics of CuCrFeNiCo high-entropy alloy (HEA) during tension process are studied through molecular dynamics simulation method. The single-crystalline, nanocrystalline, and twinned-nanocrystalline CuCrFeNiCo HEA samples with an initial crack are prepared. The influences of boundary conditions, crack length and crystallographic orientation are considered in detail. The results indicate that the phase transition from face-centered cubic (FCC) structure into hexagonal close-packed (HCP) structure and the appearance of Shockley dislocations are the majority in all samples. The dislocations appear most densely in the twinned-nanocrstalline sample and most sparsely in the single-crystalline sample. The growth of the initial crack combined with the formation and expansion of new cracks along the grain boundaries (GBs) is the determining factor in the fracture mechanics of the CuCrFeNiCo HEA samples. The deformation capacity of the samples with free boundary conditions along the y-axis is better and the plastic deformation process is longer than the samples with periodic boundary conditions along the y-axis. The tensile strength values of the CuCrFeNiCo HEA samples change significantly in the range from 2.61 GPa to 7.75 GPa when changing the simulation conditions. The von Mises stress in the grains is markedly lower than that in the GBs.

Guided-wave Dynamic Probability Model-based Crack Quantification Method for Metal Structures

In the process of applying guided-wave-based aircraft online structural health monitoring, the characteristics of guided wave signals used to represent structural status exhibit random uncertainty due to the interference of loads on guided wave propagation. The trend of signal feature changes caused by damage is often obscured, making the quantification of cracks under loads one of the challenges in online structural health monitoring for aircraft. To address this challenge, this paper proposes a crack quantification method using an adaptive Gaussian mixture model (GMM) and optimized probability migration distance measurement. This method effectively mitigates the uncertainty caused by loads by constructing an adaptive Gaussian mixture model to track the probability distribution changes of guided wave signal features under different structural health conditions. Subsequently, an optimized probability migration distance measurement method is employed to characterize the structural state, further enhancing the correlation between features and the extent of structural damage. Finally, an optimized probability migration distance relationship with crack length is established to estimate the crack length of new structural specimens. The effectiveness of this method is validated using load-induced crack propagation experiments on metal structures.