Crack Length Research Articles

A quantitative description of the influence of plastic dissipation on crack growth behaviors

This paper has transferred the influence of plastic dissipation on the crack driving force into the crack growth resistance curve based on a displacement quantity defined at the current crack tip. Such a displacement is the crack-tip-opening displacement of the corresponding stationary crack for an elastic–plastic growing crack and represents the plastic wake height. Then, this displacement-based resistance curve provides a quantitative description of the plastic deformation influences during crack growth. This paper has three novel points: 1) the crack-tip-opening displacement for an imaginary stationary crack is divided into the separation displacement and the plastic wake height, in which the separation displacement is related to the crack driving force and the plastic wake height is correlated with the plastic influence term. 2) A unified constraint of the traction-separation law (TSL) for the cohesive zone is provided by the relation between separation displacement and the crack driving force, which can shed further light on how to choose a proper TSL. 3) According to the relation between the plastic wake height and the plastic dissipation term, the influence of plastic deformation on the crack driving force is found to be independent of initial crack length, specimen width and geometrical type as long as the crack tip plastic zone does not reach the outer boundary or merge with the plastic zone of the outer boundary.

The chemo-mechanics of initiation of crack advance in Niobium Tungsten Oxide single crystals due to delithiation

Niobium tungsten oxide (NWO) micron-sized single crystals show promise as the active particles in the anodes of lithium ion batteries due to their fast charge/discharge and high storage capabilities. Within the “block” phases such as Nb16W5O55, Nb14W3O44 and the HNb2O5 polymorph, Li ion diffusion occurs in a unidirectional manner along a single axis of the crystal and lithiation/delithiation results in significant length changes in this direction. A chemo-mechanics analysis is developed for delithiation of an NWO “block” phase single crystal that contains a pre-existing flaw in the form of a through-thickness edge crack. Galvanostatic delithiation occurs by the flux of Li ions through the free ends of the crystal and also through the faces of the crack, with concomitant shrinkage of the surface layer over a depth equal to that of the crack. The induced tensile stress in the surface layer can be of sufficient magnitude to advance the crack in the NWO crystal, consistent with recent experimental observations for Nb14W3O44. A 2D full-field finite element version of the chemo-mechanics model is used to explore the sensitivity of cracking to crack length, delithiation rate of the anode, diffusivity of Li ions within the NWO single crystal storage particle and to the kinetics of Li ion transfer across the particle surface-electrolyte interface. Additionally, a simplified, lumped parameter model is developed by assuming that the Li ion occupancy is spatially uniform in a surface layer that extends to a depth of the pre-existing crack, and has a spatially uniform but different value than that of the underlying core of the particle. This simplified model can be expressed as a set of first order differential equations in time and gives the main features of delithiation and the associated transient stress state in the single crystal. Both the full model and the lumped parameter version predict that crack advance from a pre-existing defect is triggered by a high delithiation rate, consistent with the experimental literature.

The effect of crack orientation on the mode I fracture resistance of pinewood

AbstractThe fracture resistance of pinewood under mode I loading is investigated experimentally for different crack plane orientations and the crack propagation direction parallel to longitudinal cells. Experiments are conducted on double cantilever beams using a digital image correlation system to evaluate the crack tip opening displacement. The compliance based beam method is used to determine the energy release rate at various crack lengths. The decomposition of crack propagation into the pre-peak and post-peak propagations is proposed to find the fracture energy contributions from individual toughening mechanisms in pinewood. The cohesive strengths measured in the experiments are confirmed by comparison with the tensile strengths obtained from separate tests performed on pinewood. An analytical model for evaluating the fracture process zone is used to validate the experimental results. The difference between the fracture energy values in different crack propagation systems is explained by using X-ray microtomography images of the fracture surfaces.

Real-time structural health monitoring of carbon fiber-reinforced plastic sandwich structures with carbon nanotube-dispersed core using electromechanical behavior data

Sandwich composite structures have been widely used in many industrial fields because of their high bending strength, especially in large structures. As such, the need for structural health monitoring of sandwich structures to reduce maintenance costs during their lifetime is highly sought after. Here, the structural health status of sandwich composite structures comprising carbon nanotube (CNT)-dispersed cores and carbon fiber-reinforced polymers (CFRPs) was monitored in real time using self-sensing data. Previous studies using self-sensing methods have only monitored the occurrence of damage and deformation in the elastic region. Here, we conjointly investigated various failure mechanisms in real time to propose a self-sensing health index system to determine the damage severity in sandwich structures. The self-sensing technique allows for the analysis of various damage types in both the skin and core of sandwich structures. Furthermore, the actual propagation of damage (i.e., the length of the core crack) in composite sandwich structures can be investigated. The results demonstrate that self-sensing structural health monitoring is an effective and reliable method for analyzing sandwich structures, with promising applications in aircraft components, wind turbines, and personal aerial vehicles.

Designing the geometry of compact tension specimens for easy fracture toughness measurement using reinforcement learning

Abstract For composite laminates, a rising R-curve is observed for their fracture toughness under Mode I stress, which is important for a comprehensive failure analysis of the materials. Since it is laborious to measure the R-curve due to its dependence on both the load and the crack extension, we put forward a novel compact tension specimen by modifying its geometry to eliminate the relation between fracture toughness and crack extension, so as to simplify the experimental process of the R-curve measurement by only recording the load history. Two machine learning models were developed for the optimum sample design based on the finite element analysis of the effect of sample geometries on the R-curve. A simple neural network model was built for designing tapered specimen and a reinforcement learning model was created for further finding the best design from a broader design space. The results showed that, in contrast to the specimens with a tapered shape, which only ensure the independence between the R-curve and crack extension in the case of a small extension, the design provided by the reinforcement learning provides such independence across a wider range of crack length and an improved accuracy.

Effect of glazing and thermocycling on the fracture toughness and hardness of a New fully crystallized aluminosilicate CAD/CAM ceramic material

BackgroundThe mechanical properties of fully crystallized lithium aluminosilicate ceramics may be influenced by intraoral temperature variations and postmilling surface treatment. The purpose of this study is to explore the interplay among glazing, thermocycling, and the mechanical characteristics (namely, fracture toughness and hardness) of fully crystallized lithium aluminosilicate ceramics.MethodsBending bars (n = 40) cut from LisiCAD blocks (GC, Japan) were randomly assigned to glazed or unglazed groups (n = 20) and subjected to the single edge v-notch beam method to create notches. A glazing firing cycle was applied to the glazed group, while the unglazed group was not subjected to glazing. Half of the specimens (n = 10) from both groups underwent thermocycling before fracture toughness testing. The fracture toughness (KIC) was evaluated at 23 ± 1 °C using a universal testing machine configured for three-point bending, and the crack length was measured via light microscopy. Seven specimens per group were selected for the hardness test. Hardness was assessed using a Vickers microhardness tester with a 1 kg load for 20 s, and each specimen underwent five indentations following ISO 14705:2016. The Shapiro–Wilk and Kolmogorov-Smirnov tests were used to evaluate the normality of the data and a two-way ANOVA was utilized for statistical analysis. The significance level was set at (α = 0.05).ResultsRegardless of the thermocycling conditions, the glazed specimens exhibited significantly greater fracture toughness than did their unglazed counterparts (P < 0.001). Thermocycling had no significant impact on the fracture toughness of either the glazed or unglazed specimens. Furthermore, statistical analysis revealed no significant effects on hardness with thermocycling in either group, and glazing alone did not substantially affect hardness.ConclusionsThe impact of glazing on the fracture toughness of LiSiCAD restorations is noteworthy, but it has no significant influence on their hardness. Furthermore, within the parameters of this study, thermocycling was found to exert negligible effects on both fracture toughness and hardness.

Reinforcement induced microcracking during the conversion of polymer-derived ceramics

This study investigates the role of discontinuous reinforcement on the microcracking of a preceramic polymer matrix during polymer to ceramic conversion. The material system comprised a carbosilane-based, preceramic polymer reinforced with mullite particles. The preceramic resin slurry was formulated for photopolymerization on a digital light projection 3D printer. Micro X-ray computed tomography, using a synchrotron light source, monitored a printed composite part during pyrolysis. The conversion of the carbosilane matrix into Si(O)C generated microcracks in the matrix that radially extended from particles. The likelihood of microcrack formation positively correlated with particle size. The largest particles (>104 µm3 volume or >60 µm side length) always abutted microcracks, while the matrix surrounding smaller particles (<5 µm) was free of microcracks. Numerical calculations showed the particles resist the shrinking matrix during its conversion. This created tensile stresses within the matrix. The driving force for microcrack growth was also analyzed with regard to the influence of matrix material parameters, particle form-factor and crack length. These results reveal the need to consider the form factor of discontinuous reinforcements, with regard to the material properties of the polymer-derived ceramic, in order to reduce or eliminate defects in the final part.

Exploring an eco-friendly approach to improve soil tensile behavior and cracking resistance

Soil tensile strength is a critical parameter governing the initiation and propagation of tensile cracking. This study proposes an eco-friendly approach to improve the tensile behavior and crack resistance of clayey soils. To validate the feasibility and efficacy of the proposed approach, direct tensile tests were employed to determine the tensile strength of the compacted soil with different W-OH treatment concentrations and water contents. Desiccation tests were also performed to evaluate the effectiveness of W-OH treatment in enhancing soil tensile cracking resistance. During this period, the effects of W-OH treatment concentration and water content on tensile properties, soil suction and microstructure were investigated. The tensile tests reveal that W-OH treatment has a significant impact on the tensile strength and failure mode of the soil, which not only effectively enhances the tensile strength and failure displacement, but also changes the brittle failure behavior into a more ductile quasi-brittle failure behavior. The suction measurements and mercury intrusion porosimetry (MIP) tests show that W-OH treatment can slightly reduce soil suction by affecting skeleton structure and increasing macropores. Combined with the microstructural analysis, it becomes evident that the significant improvement in soil tensile behavior through W-OH treatment is mainly attributed to the W-OH gel's ability to provide additional binding force for bridging and encapsulating the soil particles. Moreover, desiccation tests demonstrate that W-OH treatment can significantly reduce or even inhibit the formation of soil tensile cracking. With the increase of W-OH treatment concentration, the surface crack ratio and total crack length are significantly reduced. This study enhances a fundamental understanding of eco-polymer impacts on soil mechanical properties and provides valuable insight into their potential application for improving soil crack resistance.

Assessment of slope stability with study parametric of faults (shear joints) using the lower and upper limit analysis method

Slope instability is widespread throughout the world, has become well known to geotechnical engineers, and poses a major challenge. The causes of slope slippage vary, which is why it is considered important and dangerous. Until now, researchers are trying to understand this phenomenon and the extent to which it is affected by surrounding elements, such as the slope ratio, slope height, water level, soil properties, and other physical and chemical properties. In this research, we will discuss one of the characteristics, which is the presence of cracks on slopes. The presence of combined shear on slopes poses a challenge to geotechnical engineers to determine field mechanical parameters, analyze, and study these slopes. In this research, we studied the effect of faulting on slopes. We changed the crack in the slope in five cases, and in each case we changed the length of the crack (21.5 m, 16.2 m, 11.2 m, 7.5 m, 3.5 m) and its location (five places) in order to understand a fracture. Slope behavior as a result of the effect of crack length and location on the safety factor, failure of the slope surface, and deformations of this slope using the top and bottom analysis method. This study provides valuable insights into the effects of fault zones on slope stability using OptumG2 software. It is helpful for us to use these results to better understand slope sliding, and from this, we can reduce the risk of sliding in areas where cracked soil is present.

Compact-tension-shear specimen for orthotropic materials in fracture toughness testing

Conducting Compact-Tension-Shear (CTS) tests emerges as a promising research methodology to determine the fracture toughness of orthotropic materials in mixed-mode I&II. However, the absence of pertinent fracture parameter solutions incorporating material orthotropy impedes the further application and standardization of CTS testing. Therefore, this study performed a systematic two-dimensional finite element analysis (FEA) on orthotropic CTS specimens to evaluate critical fracture parameters, including the normalized stress intensity factors (YI, YII) and compliance (u). First, the impacts of three commonly cited boundary conditions (BCs) of CTS models were investigated, revealing that the simplified or equivalent methods developed for isotropic CTS models are no longer applicable. Subsequently, the suitable CTS models were used to analysis the coupling effects of material orthotropy (λ, ρ), crack length ratios (a/W), and loading angles (β). Findings indicated that YI or u no longer exhibit a monotonic relationship with respect to a/W or β under strong orthotropy. The impact of λ and ρ on fracture parameters is equally significant across different geometries and loading conditions. Further, the impact of orthotropy on YII is relatively small, while the more affected YI may have a difference compared to isotropic results of over 80%. Finally, CTS tests were carried out on the unidirectional carbon fiber-reinforced epoxy resin composite measuring the fracture toughness in mixed-modes I&II. The obtained fracture parameter solutions were applied and validated during the process. The acquired results are poised to contribute to the advancement of fracture toughness testing standardization for orthotropic materials under mixed-mode loading.

Prediction of asphalt concrete energy release rate from Texas Overlay Test using machine learning

This study aimed to apply machine learning (ML) models to predict the energy release rate (ERR) in the Texas Overlay Test (TXOT) for the reflective cracking of asphalt concrete (AC) overlay. The Generalised Finite Element Method model was developed with TXOT experimental results. Subsequently, a TXOT Finite Element database was constructed. Four different cases were formulated, each utilising distinct input variables and the same output variable (i.e. ERR). Five ML models were trained and evaluated for ERR prediction. The model performances were compared across four cases to determine the optimal set of input variables. Shapley Additive exPlanations methods were employed to interpret ML models. The results demonstrated that ML models performed differently across different cases. Artificial Neural Network achieved the highest accuracy in the case which included crack length, crack opening, AC modulus, and sigmoidal function parameters. Therefore, ML models prove to be accurate and reliable for predicting ERR.

Automatic and time-resolved determination of fracture characteristics from in situ experiments

The characterization of materials in ever smaller dimensions is crucial for the growing demand for miniaturized devices. Hence, in situ fracture experiments are frequently performed at the micron to sub-micron scale. To evaluate fracture process of these experiments, knowledge of the crack length or the crack tip opening displacement is required. Acquired in situ frames provide a direct measurement of the crack length, crack tip opening displacement and -angle. An algorithm was developed to extract these parameters from the in situ frame sequences automatically. To verify the performance of the algorithm, fracture characteristics were measured manually for several frames of the available in situ experiments. The fracture behavior of these samples ranged from brittle over semi-brittle to ductile. The comparison between algorithmic results and manual measurements demonstrated the applicability of the algorithm to different fracture behaviors. Additionally, the fracture characteristics determined by the algorithm are in accordance with the fracture toughness data reported in literature. The crack tip opening displacement measurement gives thorough insight into the plastic deformation during fracture. The automatic extraction of the fracture characteristics allows a more detailed analysis of small-scale fracture processes and enables a reproducible, continuous evaluation of the fracture characteristics of all frames.

Experimental study on decoupled charge blasting-induced crack propagation with parabolic shaped charge

In this study, a new parabolic shaped charge structure is proposed to realize bidirectional blasting in coal mines. To examine the fracture characteristics of rock mass induced by shaped charge structure under explosion load, a dynamic caustic experimental system is adopted. Further, the blasting-induced damage distribution characteristics of rock mass caused by different decoupling coefficients are investigated. Using polymethyl methacrylate (PMMA) as the experimental material, a two-dimensional model is established. AUTODYN, an explicit dynamics simulation program, is used to examine the initial crack generation process under shaped charge blasting. The stress wave propagation rule and the relationship between blasting damage and decoupling coefficient are explored. The results show that the parabolic shaped charge structure can control the explosion energy distribution and reduce the surrounding rock damage. When the decoupling coefficient is 2, the main crack length is optimum. During the crack propagation process, the growth rate and stress intensity factor of the main crack of the specimen show an oscillatory downward trend. Two stress concentration points are generated on either side near the main crack, forming the initial crack. When the decoupling coefficient is less than 2, long cracks exist in both the shaped and non-shaped charged directions, and the energy gathering effect is poor. When the decoupling coefficient is greater than 2, the energy gathering effect is obvious, but the main crack length is shorter.

Bridge crack segmentation and measurement based on SOLOv2 segmentation model

With the continuous increase of vehicular traffic, the safety caused by bridge crack damage is becoming increasingly prominent. Bridge crack analysis and measurement are of great significance for promoting road traffic safety. However, existing bridge crack image segmentation methods have shortcomings in processing image detail features, resulting in the inability to better measure the actual size of bridge cracks. Therefore, to further optimize the calculation method, a bridge crack image segmentation method based on improved SOLOv2 is designed to achieve more accurate bridge image segmentation. Based on the image segmentation results and combined with the skeleton data extraction method, a bridge crack calculation method is designed. From the results, the segmentation accuracy for crack images was 92.05 % and 93.57 %, respectively. The average mIoU of AM-SOLOv2 method was 0.75, significantly lower than commonly used crack image segmentation methods. In addition, the mIoU value variation amplitude of the AM-SOLOv2 method was relatively smaller. The crack length and width errors were within 0.05 mm and 0.06 mm, significantly lower than the comparison method. It indicates that this method can achieve more accurate crack image segmentation and calculation. This is beneficial for a deeper understanding of the performance degradation and crack damage evolution of bridge structures, thereby improving bridge design and construction technology.

A novel semi-analytical method for fillet foundation deflection calculation in presence of a tooth crack propagating into the rim of a spur gear

Existing analytical approaches for calculating fillet foundation deflections in spur gear struggle to adequately address the complexities introduced by tooth cracks, particularly as cracks propagate into the gear body. The finite element methods are accurate but computationally expensive. In response to these challenges, the paper introduces a novel semi-analytical method based on elastic circular ring theory that is capable of calculating the fillet foundation deflection for both healthy and cracked conditions. To establish the usefulness of the method, the fillet foundation deflections obtained are further used to obtain the time-varying mesh stiffness. A methodology centered on compatibility conditions is employed to achieve load distribution during double tooth engagement. The results are verified using two three-dimensional finite element models. In addition, the effect of different hub hole radii, crack lengths and orientations on the fillet foundation deflections and TVMS are investigated. The outcomes suggest that the proposed semi-analytical approach demonstrates superior accuracy in the calculation of spur gear mesh stiffness compared to alternative methods.

Impact Performance of 3D Orthogonal Woven Composites: A Finite Element Study on Structural Parameters

This study uses the finite element method (FEM) to investigate the effect of key structural parameters on the impact resistance of E-glass 3D orthogonal woven (3DOW) composites subjected to low-velocity impact. These structural parameters include the number of y-yarn layers, the path of the binder yarn (z-yarn), and the density of the x-yarn. Using ABAQUS, yarn-level finite element (FE) models are created based on the measured geometrical parameters and validated for energy absorption and damage behavior from experimental data gathered from the previous study. The results from finite element analysis (FEA) indicate that the x-yarn density and the binder path substantially influenced the composites’ damage behavior and impact performance. Increasing x-yarn density in 3DOW leads to a 15% increase in energy absorption compared to models with reduced x-yarn densities. Moreover, as the x-yarn density increases, crack lengths at the back face of the resin matrix decrease in the y-yarn direction but increase in the x-yarn direction. The basket weave structure absorbs less energy than plain and 2 × 1 twill structures due to the less constrained weft primary yarns. These results underscore the importance of these structural parameters in optimizing 3DOW composite for better impact performance, providing valuable insights for the design of advanced composite structures.

Residual Magnetic Field Testing System with Tunneling Magneto-Resistive Arrays for Crack Inspection in Ferromagnetic Pipes.

Ferromagnetic pipes are widely used in the oil and gas industry. They are subject to cracks due to corrosion, pressure, and fatigue. It is significant to detect cracks for the safety of pipes. A residual magnetic field testing (RMFT) system is developed for crack detection in ferromagnetic pipes. Based on this background, a detection probe based on an array of tunneling magneto-resistive (TMR) sensors and permanent magnets is exploited. The probe is able to partially magnetize the pipe wall and collect magnetic signals simultaneously. First, a theoretical analysis of RMFT is presented. The physics principle of RMFT is introduced, and a finite element model is built. In the finite element simulations, the effects of the crack length and depth on the RMFT signal are analyzed, and the signal characteristics are selected to represent the crack size. Next, the validated experiments are conducted to demonstrate the feasibility of the proposed RMFT method in this paper.

Effect of Hydrogen Embrittlement on Dislocation Emission from A Bifurcation Crack Tip in Nano-metallic Materials

A theoretical model was established to investigate the interaction between hydrogen clusters and edge dislocation near bifurcation crack tip in deformed nano-metallic materials. The model’s solution was obtained by using the complex method, and the influence of hydrogen concentration, temperature, Relative crack length, material constants of nano-metallic materials and the dislocation emission angle on the critical stress intensity factor (SIFs) corresponding to the first dislocation emission from the crack tip was investigated through numerical analysis. The results show that dislocations are easy to emit from the crack tip at high hydrogen concentrations. However, under the influence of hydrogen clusters, the high temperature will make dislocation emission more difficult. At the same time, when relative cracks become longer, it becomes more difficult for dislocations to emit from the crack tip. As the angle of dislocation increased, the SIF first decreased and then increased. And as the angle between the main crack and the bifurcation crack continues to increase, the dislocation emission behavior at the tip of the bifurcation crack will be significantly promoted.

A strain gage technique for measuring the mode II stress intensity factors

In this paper, we propose a strain gage technique that allows an accurate measurement of the mode II stress intensity factors (SIFs). In order to ensure a good KII measurement, the size of the correct radial location of the strain gages is identified by using a methodology based on finite element analysis (FEA) and consolidated by solid theoretical foundations. The extent r1,max and r2,max of the validity of the five- and six-term representation of generalized Westergaard stress functions, which requires the use of two and three strain gages, respectively, is determined using the proposed method, and its dependence on the crack length to width ratio is also investigated. Numerical results obtained are in good agreement with the theoretical predictions, and confirm that the present method makes it possible to determine the KII with high precision when two (or three) strain gages are well placed within r1,max (or r2,max). Also, the numerical experiments show that the use of three strain gages is necessary when the size of the linear behavior region r1,max is very small. In addition, the effect of friction between the crack lips was checked and shown to have no effect on KII in pure mode II.

Deterioration and imperfection of the ship structural components and its effects on the structural integrity: A review

Abstract The design of ship structural safety is crucial to ensure the ship’s survivability during the operation. Extensive research has been conducted on ship structural components, including box girders, stiffened panels, and plates, beyond the ideal conditions by considering the implication of manufacturing processes, vessel usage, and aging in the form of defects like cracks, corrosion, and imperfections, both locally and globally. Previous research has also explored various methodologies, conditions, and parameters to understand the impact of damages and imperfections on ship structure and strength. However, there is a significant need to bridge the gap in prior research to advance technology and ship structural strength analysis. A comprehensive benchmark study specifically focused on improving ship structural component needs, identifying differences and gaps among existing studies as challenging. This article thoroughly reviews ship structural components, such as box girders, stiffened panels, and plates, while examining the effects of structural defects like corrosion, cracks, and imperfections on ship structural integrity. It synthesizes the influence of various defect parameters, including crack length, angle, position, corrosion severity, pit corrosion, pit diameter, and pit models, using finite element modeling and experimental investigations, particularly emphasizing ship structural components. The comparative analysis of methods and parameters presented in this review will serve as a valuable reference for future investigations and studies related to ship structural strength and design. The article’s contribution is expected to enhance the understanding of ship structural strength, contributing to the sustainability and effectiveness of vessel design in the global maritime industry.