Crack Problems Research Articles

Construction characteristics and reinforcement and maintenance technology of native earth buildings in Liling area

ABSTRACT Traditional earth dwellings in Weishan Village, Liling City, Hunan Province, China, have experienced hundreds of years of wind and rain. In order to asses their seismic performance, a field survey was conducted on representative traditional rammed earth buildings in Liling Kiln area of Weishan Village. The research uses a variety of methods, including on-site investigation, 3D laser scanner tilt analysis, deformation chromatography analysis, wood material detection, and stress wave analysis, to obtain the main structural forms and material characteristics of local earth buildings. The main structural problems of rammed earth buildings were summarized through the investigation: the foundation and roof were no longer stable, the problems of sag, tilt and cracking were common in rammed earth walls, and the wood parts were gradually rotting and splitting. According to the investigation results, the seismic measures to improve rammed earth buildings were proposed from different parts of the damaged houses, in order to provide guidance for the local villagers’ residential construction, house reinforcement and renovation design.

Effect of Gradient Transition Layer on the Cracking Behavior of Ni60B (NiCrBSi) Coatings by Laser Cladding.

Laser cladding technology is an effective method for producing wear-resistant coatings on damaged substrates, improving both wear and corrosion resistance, which extends the service life of components. However, the fabrication of hard and brittle materials is highly susceptible to the problem of cracking. Using gradient transition layers is an effective strategy to mitigate the challenge of achieving crack-free laser-melted wear-resistant coatings. This study presents the cracking issue of laser cladding Ni60B (NiCrBSi) coatings on 38CrMoAl (18CrNiMo7-6) steel by designing a gradient transition layer infused with varying amounts of Ni powder. We examine how different levels of Ni doping in the transition layer influence the fabrication of the Ni60B coating. The results indicate that the cracking mechanism of Ni60B is primarily due to the brittleness and hardness of the fusion cladding layer, which can result in cold cracks under residual tensile stress. Increasing the nickel content in the transition layer reduces the difference in thermal expansion coefficients between the cladding layer and the substrate. Additionally, the nickel in the transition layer permeates the cladding layer due to the laser remelting effect. The physical phase within the cladding layer transitions from the initial CrB, M7C3, and γ-Ni solid solution to γ-Ni solid solution and Ni-B-Si eutectic, with a small amount of boride and carbide hard phases. As the nickel doping in the transition layer increases, the proportion of the toughness phase dominated by Ni elements significantly rises, leading to a decrease in the hardness of the fused cladding layer. However, the average hardness of the fusion cladding layer in crack-free samples was measured at 397.5 ± 5.7 HV0.2, which is 91% higher than that of the substrate.

Finite Element Analysis of a Dynamic Linear Crack Problem

This work investigates the problem of a linear crack in the middle of a uniform elastic medium under normal tension-compression loading. The direct Finite Element numerical procedure is used to solve the fractured media deformation problem, which also includes an examination of the dynamic field variables of the problem. A Finite Element algorithm that satisfies the unilateral Signorini contact constraint is also described for solving the crack faces' contact interaction, as well as how this affects the qualitative and quantitative numerical results while calculating the dynamic fracture parameter.

Interfacial crack analysis in piezoelectric bi-material using coupled FE-XEFG approach

The current paper emphasizes the study of interface crack problems in piezoelectric bi-material having k-class singularity using coupled finite element (FE) and extended element free Galerkin (XEFG) technique. Heaviside and asymptotic crack-tip functions are incorporated to capture crack-tip singularity and discontinuities across crack surfaces for local enrichment within FE-XEFG framework. Few fracture problems are numerically simulated to extract mixed mode intensity factors (IFs) by modified form of domain-based interaction integral. Parametric studies based on geometrical parameters and loading conditions, such as mechanical loading effect, electrical loading effect, effect of crack length, and aspect ratio on fracture parameters have been simulated.

Comparing numerical simulation methods for evaluating hysteretic response of self-centering shear walls reinforced with SMA-ECC under cyclic loading

Under the action of earthquake, the traditional shear wall structure has the problems of excessive residual deformation and macroscopic cracks. The SMA-ECC composite material formed by the combination of smart materials such as shape memory alloy (SMA) and high ductility engineered cementitious composite (ECC) not only has good energy dissipation capacity, but also can obtain superior self-centering ability and damage self-healing ability, thereby improving the seismic performance and durability of shear wall structures. In this paper, in order to explore the nonlinear behavior of the self-centering shear wall under earthquake action and accurately simulate it, ECC and SMA material tests are carried out to establish the uniaxial constitutive relationship of the material. Using OpenSees finite element analysis platform, considering the micro and macro perspectives, a variety of finite element models are established, namely layered shell model, fiber model and multi-vertical rod model. Combined with the low-cycle reciprocating loading test of shear walls, the numerical simulation results are compared with the experimental data. By considering the parameters such as yield load, peak load and simulation time, the feasibility, stability and calculation efficiency of these models are evaluated. The results show that among the three models, the model based on fiber element can capture well the hysteretic response of new materials, and simulate the hysteretic performance, pinch effect and stiffness degradation of various shear wall members. The simulated values and experimental values can be well matched. Compared with the microscopic model, the computational efficiency of the fiber model is greatly improved, and the model has good feasibility, accuracy and efficiency.This work provides a basis for further research on the optimization of design parameters of SMA-ECC shear wall.

Effect of double-layer formwork curing on the early temperature field and properties of precast concrete components in environments with large diurnal temperature variations

An efficient double-layer formwork curing method using an “inner supporting formwork + outer insulation formwork” was proposed in this study to address the early cracking of precast concrete components in high altitude regions. Steel and plywood formwork were designed as inner support formwork, while polystyrene (PS) and polyurethane (PU) were used as outer insulation formwork. Indoor experiments and two finite element methods (The complete simulation method focuses on computational accuracy, and the equivalent simulation method emphasizes computational efficiency) were employed to analyze the evolution of the concrete temperature field under different double-layer formwork curing methods throughout the curing period, combined with compressive strength and pore structures testing. The results show that steel + 5-mm-thick PU insulation formwork curing method can significantly mitigate the impact of large diurnal temperature variations on the internal temperature of concrete. Unlike traditional steam-curing, this method does not deteriorate the pore structure or compressive strength of the concrete. This study is of great significance in addressing the problem of early cracking of precast concrete components exposed to large diurnal temperature vriations in high altitude regions.

Towards a More Reliable Identification of Non-Conformities in Railway Cars: Experiments with Mask R-CNN, U-NET, and Ensembles on Unbalanced and Balanced Datasets.

In every business, equipment requires repair services. Over time, equipment wears out; however, with well-conducted and guided maintenance, this degradation can be controlled, and failed equipment can be restored to operational status. Preventive maintenance allows this concept to be applied, given the great advantages for large companies in reusing equipment and machinery, always putting the worker's health and safety first. Rail transport has several pieces of equipment that can be reused if they are in a regular and well-defined maintenance cycle. In this sense, this article sought to create a method using real data for identifying cracks in wagons. Through the use of computer vision algorithms to prepare the data, along with several machine learning classification algorithms to locate cracks in train cars, the classification used properly annotated images and obtained great results, with a best case 98.10% hit-rate when wagons had a crack problem.

Multiscale approaches for optimizing the impact of strain on Na-ion battery cycle life

Abstract The high costs and geopolitical challenges inherent to the lithium-ion (Li-ion) battery supply chain have driven a rising interest in the development of sodium-ion (Na-ion) batteries as a potential alternative. Unfortunately, the larger ionic radius of Na limits the reversibility of cycling because of the extensive atomic rearrangements that accompany Na-ion insertion, which in turn limit diffusion and charging speed, and lead to rapid degradation of the electrodes. The Center for Strain Optimization for Renewable Energy (STORE) was established to address these challenges and develop new electrode materials for Na-ion cells. This article discusses the current state-of-the-art materials used in Na-ion cells and several directions that STORE believes are critical to understand and control the structural and volumetric changes during the reversible (de)insertion of large cations. Graphical abstract Highlights Understanding the fundamental way materials respond to localized strains at the atomic length-scale is a critical first step in the development of highly reversible, long cycle life, Na-ion insertion hosts. This perspective explores a variety of methods that can be employed to mitigate the detrimental effects of large strain. The insights gained from these investigations should help lay the foundation for the creation of more economical and sustainable batteries that could have immediate impact on global energy infrastructure. Discussion Although there is near universal agreement that electrochemical energy storage must be an integral part of a green-energy future, there is less agreement about how to reduce the cost of energy storage. Replacing high-cost lithium-ion cells with lower-cost sodium-ion batteries is one option frequently considered in future energy models, but the details of what can be achieve with optimized sodium cell performance remains unclear. Here we posit that developing methods to mitigating strain on the electrode particle length scale is a key factor for achieving long-cycle-life sodium-ion batteries. Mitigating strain on the atomic scale suppress electrode-level volume change. Allowing for fast cycling in materials without the problems of electrode cracking or delamination. We further posit that understanding volume change in sodium-ion electrodes at a fundamental level will lead to the designing new sodium-ion electrode materials that will allow for efficient, stable, lower-cost energy storage.

Nanosecond laser ablation of micro-pits in Ni60/WC coatings with coupled thermal-stress simulation and parameter optimization

In order to solve the problem of crack sprouting inside the micro-pit caused by improper design of laser ablation process parameters, this study establishes a thermal-stress coupling simulation model of nanosecond laser ablation of micro-pits on Ni60/WC coated surfaces. It researches the influence of laser process parameters (laser power, scanning speed, processing times) on the index parameters of micro-pit diameter, depth, and maximum residual stress. The weighting of diameter, depth and maximum residual stress sub-objectives in the comprehensive evaluation objectives of micro-pits are calculated. The response surface method of Central Composite Design (CCD) and regression analysis are used to fit the response surface functions of micro-pit diameter, depth, and maximum residual stress as a function of the variation of laser ablation process parameters. The Genetic Algorithm (GA) is used to minimize value of the maximum residual stress sub-objective function and to optimize the process parameters of laser ablation of micro-pits, using the values interval of the micro-pit diameter and depth functions as nonlinear constraints. The results show that the maximum residual stress varies quadratically with laser power and scanning speed, increases linearly with the processing times, and is coupled with the ablation process parameters. A design method for optimizing the parameters of nanosecond laser ablation by maximum residual stress is established, and the process parameters are optimized to meet the design parameters and quality requirements of micro-pits: laser power of 12 W, scanning speed of 276 mm/s, and 4 times of processing. The optimized process is provided for the parameter tuning nanosecond laser ablation of micro-pits on Ni60/WC coating surfaces.

Shear mode solutions to penny-shaped crack problems in two-dimensional hexagonal piezoelectric quasicrystal media

This study investigates shear mode penny-shaped crack problems in an infinite three-dimensional body composed of a two-dimensional hexagonal quasicrystal medium with piezoelectric effect. The crack is subjected to a set of shear phonon and phason loadings within the crack plane. This shear mode crack problem is transformed into a mixed boundary value problem in the upper half space. Subsequently, it is elegantly solved utilizing Fabrikant’s potential theory method. The boundary integral–differential equations governing three-dimensional shear mode crack problems in two-dimensional hexagonal piezoelectric quasicrystals are derived with the phonon and phason displacement discontinuities serving as unknown variables. Closed-form solutions for all physical field quantities are presented, not merely limited to the crack surface, but rather extended comprehensively to the entire space. Key fracture mechanics parameters, such as phonon and phason displacement discontinuities, stress intensity factors at the crack tip, and energy release rate, are explicitly derived. Numerical results are provided to validate the obtained analytical solutions and illustrate the distribution of the electric-phason-phonon coupling field around the crack in graphical form. Additionally, these numerical results also compare the fracture mechanics parameters of the chosen piezoelectric quasicrystal with its corresponding non-piezoelectric quasicrystal, thereby investigating the influence of piezoelectric effect on quasicrystals. The obtained solution can be used as a benchmark for the experimental and numerical study of shear mode cracks in piezoelectric quasicrystals.

Research on the Propagation Law of Temperature-Induced Reflective Cracks in Semi-Rigid Base Asphalt Pavement

In order to solve the problem of reflection cracks in semi-rigid base asphalt pavement, a study of temperature-type reflection crack expansion is carried out according to the typical climatic characteristics of Guilin, Guangxi Province. According to the theory of fatigue fracture mechanics, the stress intensity factor analysis at the crack tip is carried out, the reflection crack propagation life under single-factor and multi-factor changes is calculated using the Paris fatigue growth formula, and the prediction model of the propagation life of reflected crack under the action of a temperature gradient is established. The results show that the propagation life of temperature-type reflective cracks increases with an increase in the thickness of the middle course and bottom course, and decreases with an increase in the surface course modulus, base course modulus, base course thickness, and temperature decrease. The prediction model includes the factors that have a great influence on the reflection crack extension and provides a theoretical supplement and reference for the design and calculation of asphalt pavement structure in areas with large temperature differences.

Preparation and artificial weathering properties of Ce/TiO2/BTA-HALS coating on heat-treated wood surface

Heat-treated wood has only short-term weathering resistance, while wood cracking, discoloring and other problems will appear in long-term outdoor environments. Therefore, it is necessary to enhance the anti-weathering properties of heat-treated wood. In this study, organic ultraviolet absorbers, light stabilizers and inorganic Cerium/Titanium dioxide (Ce/TiO2) ultraviolet shielding agents were compounded by the simple physical blending method, and the modifiers were loaded on the surface of heat-treated wood by brushing method. The UV-Vis spectrum showed the high transparency and UV shielding of the composite coating. After artificial weathering, the color difference (ΔE) of Ce/TiO2/BTA-HALS coated sample was only 1.64 and 2.68, which is significantly lower than 2.3 and 6.1 of the heat-treated sample. The surface roughness, scanning electron microscope and X-ray energy spectrum also showed that the stability of the coating was significantly improved, and the loss of inorganic particles has decreased. Fourier transform infrared spectroscopy and electron paramagnetic resonance proved that the modifier was successfully grafted on the surface of heat-treated wood. The composite coating has a certain synergistic effect in improving the weathering resistance of heat-treated wood and improves the film-forming property of the modifier and the stability of the coating during weathering.

Multiple edge cracks in a coated semi-infinite medium due to non-Fourier thermal shock

In this wok, based on the non-Fourier C-V model, the problem for multiple edge cracks is investigated for a coating-substrate pair subjected to a sudden temperature drop at the surface of coating. The temperature and resulting thermal stresses without cracks are obtained by the method of Laplace transform. By numerically solving the singular integral equations, the thermal stress intensity factors (SIFs) are evaluated. The results from the Fourier model and C-V heat conduction model are presented for comparison. Two dimensionless quantities are proposed to account for the coupling effects of heat conduction parameters (i.e., thermal conductivity, thermal diffusivity, and thermal relaxation time). Numerical results are presented for the thermal SIF as a function of normalized quantities such as time, crack depth, material constants and crack spacing. The findings in this work are expected to provide references for maintaining the integrity of the coating-substrate pair in the extreme heat transfer applications.

Effect of lanthanum on inclusions and solidification structure of alloy 800H

Alloy 800H is commonly used in high temperatures and corrosive environments due to its exceptional strength and resistance to high temperatures, but the ingots are prone to longitudinal cracking during the hot working process because of its coarse solidification structure. Based on the heterogeneous nucleation effect of rare earth inclusions, a strategy is proposed to refine the solidification structure of alloy 800H by La treatment to solve the crack problem. In this study, four kinds of alloy 800H ingots (0, 120, 260 and 470 ppm La) were prepared to investigate the effect of La on the solidification structure. After adding La, the types of inclusion were changed, and the modification path of inclusions was Al2O3 (0 ppm La) → LaAlO3 (120 ppm La) → LaAlO3·La2O2S and La2O2S (260 ppm La) → La2O2S and La2O3 (470 ppm La). After adding La, the inclusion morphology tended to be more spherical and the average size smaller. The lattice misfit calculation indicated that La-containing inclusions can serve as heterogeneous nucleation cores, and the number of effective heterogeneous nucleation also increased with La content increased. The columnar to equiaxed transition occurred early with La treatment, the ratio of the equiaxed zone increased from 2.1% to 36.5%, and the average equiaxed grain size decreased from 2.56 to 0.43 μm with La content increased from 0 to 470 ppm. The solidification structure of alloy 800H was significantly refined by adding La, and can thus provide a new strategy to solve the crack problem.

Recent Advances in Additive Friction Stir Deposition: A Critical Review.

Additive friction stir deposition (AFSD) is a novel solid-state additive manufacturing method developed on the principle of stirring friction. Benefits from its solid-phase properties, compared with traditional additive manufacturing based on melting-solidification cycles, AFSD solves the problems of porosity, cracks, and residual stress caused by the melting-solidification process, and has a significant improvement in efficiency. In AFSD, the interaction between feedstocks and high-speed rotating print heads suffers severe plastic deformation at high temperatures below the melting point, ending up in fine, equiaxed recrystallized grains. The above characteristics make components by AFSD show similar mechanical behaviors to the forged ones. This article reviews the development of AFSD technology, elaborates on the basic principles, compares the macroscopic formability and material flow behavior of AFSD processes using different types of feedstocks, summarizes the microstructure and mechanical properties obtained from the AFSD of alloys with different compositions, and finally provides an outlook on the development trends, opportunities, and challenges to the researchers and industrial fields concerning AFSD.

Method of understanding for investigation of crack propagation trajectory and fracture aspects in dental cracks on view of fracture mechanics theories.

Current research introduces understanding of dental-cracks mechanistic with fundamental fracture behavior in natural-teeth and orthodontics including mode I crack under both tension and compression, mode II crack under both clockwise-shear and anticlockwise-shear and mixed-mode cracks under both compression-shear and tension-shear. It depends on experimental models of transparent-Plexiglas including pre-cracks of different orientations angle (b) based on fundamental theoretical fracture analysis with comparison. Problem-concept, cracking aspects of fracture-initiation, propagation-direction, fracture-increment length, critical external-load and fracture path are predicted experimentally and theoretically using directional fracture approach and directional strain-energy density theory. Tests are carried out for (36) samples for compression and tension in LEFM. Friction-resistance between crack-surfaces is considered with derivation of equations and charts. Negative stress-intensity factor (-KI) is developed for solving complicated problems of cracks under occlusal compression loads. The occlusal loads are compression and shear producing lateral tensile mixed mode cracks. The critical propagation angle (qc), critical propagation load (sc) and critical propagation envelope of stress intensity factors (KI-KII) are developed with respect to crack orientation angle (b) with comparisons. They are necessary to predict the fracture propagation early before teeth-failure. It helps for prevention and control of dental-cracks, correct-restoration, prosthodontics, orthodontics, and development of new dental-materials and technologies.

A Study on the Mechanical Behavior of a Wind Turbine Foundation with a Constrained Structural Shear Connector

Aiming to solve the problems that a wind turbine foundation with a foundation pipe may suffer from grouting, where the concrete around the interface collapses and the interface disintegrates under a long-term wind load, a kind of wind turbine foundation with a constrained structural shear connector is proposed. In this article, the scaling model tests and a finite element simulation of a traditional stud foundation pipe, perforated steel shear connector foundation pipe, and three groups of constrained structural shear connector foundation pipes with different anchored depths are presented. The force transmission mechanism and damage mechanism of constrained structural shear connector wind turbine foundations are revealed, and the shear resistance of a constrained structural shear connector is analyzed. The influences of buried depth and other parameters on the mechanical properties of the shear connector are also investigated. The results show that the constrained structural shear connector has the advantages of stronger interfacial stiffness and significant force transfer and diffusion, and can more effectively connect the foundation pipe and concrete foundation to work together. It can give full play to the material advantages of concrete and reinforcements, and effectively improve the embedded stiffness and durability of concrete foundations. It can solve the problem of cracks in concrete caused by local pressure. At the same time, it is suggested that the diameter of the surrounding concrete should be in the range of 3 to 4 D, and the embedment depth of the stud should not be less than 0.4 D to give full play to the performance of the constrained structural shear connector.

Stress-constrained concurrent multiscale topological design of porous composites based on discrete material optimisation

Porous composites have attracted increasing attention in recent decades. This study develops a concurrent multiscale topology optimisation (CMTO) method under a prescribed stress constraint for designing porous composites with multi-domain microstructures. First, to address the difficulty of predicting local stress due to varying of microstructural type throughout the optimisation process, a continuous and differentiable stress measure is proposed to effectively approximate the local stress. Second, an inverse homogenisation method based on isogeometric analysis (IGA) is developed to improve the accuracy of stress prediction, and then it is integrated into a CMTO which is developed based on the discrete material optimisation (DMO) interpolation scheme. Third, a stress constraint which is differentiable with respect to both macro and micro design variables is proposed to enable the stress-constrained concurrent optimisation of the macrostructural configuration, microstructural configuration and distribution. Fourth, a novel post-processing approach is established to achieve smooth while volume preserving contour of unit cells with layouts. Finally, two benchmark design examples, namely l-bracket and Crack problems, are implemented using the presented CMTO under a global stress constraint to demonstrate the effectiveness of the proposed method. The result indicates that the proposed method can effectively decrease the stress concentration via three design manners, i.e., the macrostructural configuration, microstructural configuration and distribution. Also, an “interface-enlarging” phenomenon was interestingly but reasonably found in those cases when subjected to stress-constraint considerations.

Research status of crack problem in laser brazing diamond

Research status of crack problem in laser brazing diamond

An in-depth analysis of the Radial Point Interpolation Method’s parameters in relation to the accuracy of fracture problem

The fracture problem has been modeled using Radial Point Interpolation Method (RPIM) to examine the effects of support domain size and shape parameter value on the calculation of Stress Intensity Factor (SIF). The study focuses on an edge crack problem subjected to normal load and shear loads, determining that the support domain size of ‘ α ≥ 3.5 and shape parameter value between ‘ n = 1.9 -2.1’ yield results of accuracy with error % ≤ 3 % . Additionally, research extended by varying the problem domain size and crack location to verify consistency. The findings indicate that selecting the optimal shape parameter value will ensure better accuracy over the enrichment techniques with lesser computational cost.