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Kaplan turbines, as one of the well-known hydraulic turbines, are generally utilized worldwide for low-head and high-flow conditions. Any failure in each of the turbine components can result in long-term downtime and high repair costs. In a particular case, if other parts are damaged due to the impact of the broken blades (e.g., the main shaft of the turbine), the whole power plant may be shut down. On the other hand, further research on the primary causes of failures in turbines can help improve the present failure evaluation methodologies in power plants. Hence, the main objective of this paper is to present the major causes of Kaplan turbine failures to prevent excessive damage to the equipment and provide practical solutions for them. In general, turbines are mainly subjected to both Internal Object Damage (IOD) and Foreign Object Damage (FOD). Accordingly, this paper presents a state-of-the-art review of Kaplan turbine failures related to material and physical defects, deficiencies in design, deficits in manufacturing and assembly processes, corrosion failures, fatigue failure, cavitation wear, types of cavitation in hydro turbines, hydro-abrasive problems, and hydro-erosion problems. Eventually, the authors have attempted to discuss practical hints (e.g., nanostructured coatings) to prevent damages and improve the performance of Kaplan turbines. [ABSTRACT FROM AUTHOR]

The alternate load path method for progressive collapse analysis ignores the cause and mechanism of member failure and its influence on the dynamic effect of the remaining structures. It must assume the location of member failure, which is unsuitable for grid structures with many members. In this paper, by using the double broken line follow-up strengthening model and the proposed VUMAT material constitutive model, taking the member instability and material failure as the member failure criteria and considering the geometric nonlinearity and material nonlinearity, the instantaneous member removal method for deleting the failure member in real time was proposed. On this basis, nonlinear dynamic analysis for a three-layer space truss was used to compare the effects of different member failure criteria on the structural responses, such as the member failure sequence and the occurrence time of the continuous structural collapse. The results show that when considering the instability of members, the initial member failure and the final progressive collapse occur earlier than when using the material failure criterion, which is more similar to the actual situation. Furthermore, the proposed VUMAT material constitutive model can apply to study the progressive collapse behavior of space truss structures. [ABSTRACT FROM AUTHOR]

The influence of tool wear on cutting force in turning glass–ceramics was studied, and a theoretical model of turning force considering tool wear was established in this paper. Firstly, the crack propagation behavior and the form of energy dissipation were analyzed during chip formation, and the model of the force due to chip formation was established based on the fracture mechanics of brittle solids and the principle of energy transfer. Secondly, the mechanical model caused by the flank wear was established by analyzing the microscopic wear mechanism of the tool and the source of friction. Finally, the theoretical model of turning force considering the tool wear was established. The model is only applicable to brittle removal mode. Two different cutting tools were selected to carry out the experiment of turning fluorophlogopite glass–ceramics. The relationship between cutting force and tool wear was discussed, and the accuracy of the model was verified. The results showed that the tool wear has a direct impact on the cutting force, and the theoretical model of cutting force established is in good agreement with the experimental data in this paper. [ABSTRACT FROM AUTHOR]

Valve failure is a big risk and a costly phenomenon in the offshore sector of the oil and gas industry. It results in severe negative consequences such as loss of asset; loss of production due to plant shutdown; health, safety and environmental (HSE) issues such as hydrocarbon (oil and gas) spillage; environmental pollution; and sometimes loss of human life. Different types of valve failures have occurred in the Norwegian offshore industry for various reasons such as poor material selection, corrosion, mechanical failure of valve components due to high stresses and loads, lack of coating and lack of inspection. The aim of this paper is to review and critique some of the wrong material selection approaches for industrial valves in the offshore sector of the oil and gas industry that lead to the corrosion and failure of valves, and to provide an appropriate material selection solution to mitigate these failures. Seven cases of material failures due to corrosion, including a valve gear box in coated cast iron, bolting made of low alloy steel with hot dip galvanized coating, a stem key made of a low alloy steel, stem material in 17-4 PH, spring material in Inconel X750, duplex, super duplex and hard nickel alloys in subsea as well as graphite packing in seawater, are reviewed, and preventive measures are proposed to avoid corrosion risk. In general, the use of carbon and low alloy steel for valves in the offshore environment should be limited and the use of corrosion-resistant alloys (CRAs) is proposed. [ABSTRACT FROM AUTHOR]

This paper is a consecutive work based on the last paper "Finite element analysis of viscoelastic/damage behaviors of composite solid propellant for underwater intelligent equipment". This paper studies adhesive failure behaviors of multi-material structure in underwater intelligent equipment, which includes the propellant layer/lining layer/adiabatic layer/aluminum layer. First, the hyperelastic mechanical properties for ethylene–propylene–diene monomer for adiabatic layer are predicted by using the Mooney–Rivlin constitutive model, where the material parameters are fitted by combining with theoretical and experimental load curves. Second, the adhesive failure between the propellant layer and the lining layer is predicted for the designed multiple material layers under shear loads by combining with the bilinear cohesive model, the constitutive models for the propellant and adiabatic layer materials. Finally, the adhesive failure mechanisms and the load responses are studied for the shear specimens. [ABSTRACT FROM AUTHOR]

Announces the publication of the research paper `The Quantitative Bridge Safety Assessment Utilizing Fracture Mechanics and Ultrasonic Stress Measurements,' by the National Institute of Standards and Technology. Contents of the paper; Ordering information.

In a recent paper in Structural Concrete, the authors Dönmez and Bažant explain that the theoretical background of the Model Code 2010 equations for one way and punching shear are not sufficiently grounded in theory and should instead use an energy‐based size effect law in their formulation to match behavior. To support this claim, finite element simulations were presented. In this paper the basic assumption that an energy‐based method must govern the shear failure of beams without stirrups is questioned. These questions are shown to be based on the hardening behavior of aggregate interlock tests and the inability for slip strains to localize during shear failure. In addition to these theoretical arguments finite element analyses were conducted with a constitutive model that is energy‐based but that also does an appropriate job at modeling aggregate interlock, an aspect that appears to be lacking in the analyses of Dönmez and Bažant. These new results are shown to better model the test results and confirm that aggregate interlock is important in explaining shear strength and therefore the size effect in shear for slender members. As such any concerns about the safety of the Model Code shear equations appear unwarranted. [ABSTRACT FROM AUTHOR]

Smoothed particle hydrodynamics (SPH) has its unique advantages in simulating large deformation. However, in its calculation, it is easy for some regional particles to break off. This paper puts forward the concept of virtual crack boundary to solve crack propagating problems in the framework of SPH. The parameters of virtual crack boundary are determined by the projection method of descending dimension, which improves the support domains of crack tip particles. Based on the principle of minimum strain energy density factor in fracture mechanics, the initiation and extended directions of cracks in materials are estimated. By simulating the generation and expansion of three modes of cracks in materials, the SPH calculation results of the three types of support domain forms are compared with the ABAQUS simulation results and experiment results. It indicates that the method of virtual crack boundary method is more stable than the one based on discontinuous medium. And it can generate more reasonable results than the method based on continuous medium. This paper proves the effectiveness of strain energy density factor based on fracture mechanics theory in searching the direction of crack expansion using SPH, and explores the application of new support domain model in SPH crack solution. [ABSTRACT FROM AUTHOR]

High forming force is often needed when high-strength and low-plasticity materials are processed by fine blanking. Too high forming force increases the load of the die and greatly increases the risk of die failure. If the forming force is reduced, the material will fracture prematurely, which will lead to poor quality parts. Aiming at this problem, a new force variation load fine-blanking technology is proposed in this paper. During the loading process, the forming force does not remain constant but changes with the blanking stroke. A 2D finite element fine-blanking model was established for the TC4 material. The mechanism of force variation fine blanking is also revealed. This paper proposes a method to design the loading route of the forming force with variable load. This method combines finite element simulation with neural network and a multi-objective genetic algorithm. Finally, the application of variable load fine blanking production and the application of traditional fine blanking production parts are verified by the experimental method. The same results are obtained from both simulation and experiment. It is found that the variable load fine blanking process can greatly reduce the load of the die on the premise of ensuring the quality of fine-blanking parts. [ABSTRACT FROM AUTHOR]

This paper put forward a fast pavement crack recognition algorithm based on support vector machine classification. This algorithm uses the gauss filter to reduce the image noise firstly, and according to the characteristics of the pavement distress, eliminate the interference factors, such as lane line, shadow, etc. The 3024 × 2048 pixel size crack image is divided into 252 blocks each contain 168 × 152 pixels. Then using the support vector machine as the basic classifier, bagging method was used to generate several classifiers for predicting. This paper realized the accurate location of the crack area and the fast classification of the crack finally. Experimental results show that the proposed algorithm's performance is better than the minimum error method, OSTU threshold method, maximum entropy method and other classical algorithms. [ABSTRACT FROM AUTHOR]

This paper presents the physics of crack-path formation in single-crystalline 3 C -SiC containing an isolated pore as a combination of three physical processes: bifurcation, arrest, and renucleation. Results show that, depending on the symmetry of the crystal structure, three distinctive crack paths form: (i) crack bifurcates and propagates in the domain without being affected by the pore, (ii) crack bifurcates and interacts strongly with the pore leading to a termination of the propagating crack, and (iii) crack does not bifurcate, retains its propagation path on the symmetry plane, and gets arrested at the pore. The continued growth of the terminated crack requires crack renucleation at the pore edge, and the renucleation event enhances the effective toughness of the domain. The degree of toughness enhancement depends on the pore diameter, the crack length, and the crack–pore distance. While the crystallographic anisotropy forms the basis for bifurcation, the conditions for bifurcation and arrest are governed by the strength of elastic interactions emanating from the crack tip and the pore edge. As such, there exists a critical crack–pore distance of 40 nm below which the crack–porosity interaction is strong enough to enforce the bifurcated crack to divert toward the pore, leading to instant termination of its growth. [ABSTRACT FROM AUTHOR]

Metallic materials are widely employed in engineering constructions, and one of the most common failure mechanisms in metals is fatigue failure. Even though metal fatigue has been studied for almost 160 years, many problems remain unsolved. Fatigue in metal occurs when the metallic material is subjected to varying loads, resulting in failure due to damage accumulation. The fatigue process consists of a buildup of damage that leads to crack initiation, followed by a period of crack growth until the critical flaw size is reached. The sum of a start phase and a propagation phase represents the total life. To better understand the fatigue phenomenon at its different stages and predict the fatigue life, various types of prediction models have been developed and reported in the literature. This paper reviewed the different models that include microstructure scale parameters that can be used to predict how fatigue cracks start under variable amplitude loading, including the Modified Tanaka-Mura Model, Acoustic Second Harmonic Generation, and the Probability of Crack Initiation on Defects. For perfect life prediction under variable amplitude loading, a stress-based approach, a strain-based approach, and a continuum damage mechanics approach are reviewed. The purpose of this paper is to get overview of the current state of approaches to the life prediction of fatigue crack initiation with variable amplitude. Finally, gaps in knowledge about the prediction of fatigue crack initiation under variable loading at high temperatures are pointed out. [ABSTRACT FROM AUTHOR]

At present, PE pipelines are widely used in urban gas pipeline networks. As pipeline safety is of great importance to the gas supply, this paper focuses on the safety and reliability of PE pipes during service. First of all, this paper analyzes the aging factors of PE materials and the failure forms and mechanisms of PE pipes. Second, the performance testing methods of PE pipelines are summarized, including pipeline pressure tests, pipeline condition inspections, welded joint inspections, mechanical performance tests, and physical performance tests. In addition, life prediction methods for PE pipelines are introduced and analyzed. The methods and applicability of tensile experiments and DSC experiments based on thermal oxygen aging are both analyzed, and the corresponding experiments are also carried out. On the basis of the above research, the technical system of the integrity detection and evaluation of urban gas pipelines is finally established. The system includes the integrity detection method of urban gas pipelines and the applicability evaluation and determination of retest cycles, which can provide a reference for the safe operation of urban gas pipeline networks. [ABSTRACT FROM AUTHOR]

The durability assessment of additively manufactured parts needs to account for both surface-breaking material discontinuities and surface-breaking porosity and how these material discontinuities interact with parts that have been left in the as-built state. Furthermore, to be consistent with the airworthiness standards associated with the certification of metallic parts on military aircraft the durability analysis must be able to predict crack growth, as distinct from using a crack growth analysis in which parameters are adjusted so as to match measured data. To partially address this, the authors recently showed how the durability of wire arc additively manufactured (WAAM) 18Ni-250 maraging steel specimens, where failure was due to the interaction of small surface-breaking cracks with surface roughness, could be predicted using the Hartman–Schijve variant of the NASGRO crack growth equation. This paper illustrates how the same equation, with the same material parameters, can be used to predict the durability of a specimen where failure is due to surface-breaking porosity. [ABSTRACT FROM AUTHOR]

With the growth of various microdefects in bodies, complex systems of cracks of arbitrary configuration can be generated. This paper presents a technique for numerical simulation of complex branched cracks, which makes it possible to analyze such systems. Using the method proposed by the authors, it is possible to find the stress and displacement fields as well as the stress intensity factors, the analysis of which leads to the conclusion about the influence of the considered configuration on the crack stability. The paper also contains the comparison with the results of other authors in the problem of a two-link crack. [ABSTRACT FROM AUTHOR]

In this paper, the short-term behaviour of innovative aluminium–timber composite beams was investigated. Laminated veneer lumber panels were attached to aluminium beams with screws. Recently conducted theoretical, experimental, and numerical investigations have focused on aluminium–timber composite beams with almost full shear connections. However, no experiments on aluminium–timber composite beams with partial shear connections have yet been conducted. For this reason, composite action in composite beams with different screw spacing was studied in this paper. Four-point bending tests were performed on aluminium–timber composite beams with different screw spacing to study their structural behaviour (ultimate load, mode of failure, load versus deflection response, load versus slip response, and short-term stiffness). The method used for steel–concrete composite beams with partial shear connection was adopted to estimate the load bearing capacity of the investigated aluminium–timber composite beams. The resistance to sagging bending of the aluminium–timber composite beams with partial shear connections from the theoretical analyses differed by 6–16% from the resistance in the laboratory tests. In addition, four 2D numerical models of the composite beams were developed. One model reflected the behaviour of the composite beam with full shear connection. The remaining models represented the composite beams with partial shear connections and were verified against the laboratory test results. Laminated veneer lumber was modelled as an orthotropic material and its failure was captured using the Hashin damage model. The resistance to sagging bending of the aluminium–timber composite beams with partial shear connections from the numerical analyses were only 3–6% lower than the one from the experiments. [ABSTRACT FROM AUTHOR]

Machine learning has the potential to enhance damage detection and prediction in materials science. Machine learning also has the ability to produce highly reliable and accurate representations, which can improve the detection and prediction of damage compared to the traditional knowledge-based approaches. These approaches can be used for a wide range of applications, including material design; predicting material properties; identifying hidden relationships; and classifying microstructures, defects, and damage. However, researchers must carefully consider the appropriateness of various machine learning algorithms, based on the available data, material being studied, and desired knowledge outcomes. In addition, the interpretability of certain machine learning models can be a limitation in materials science, as it may be difficult to understand the reasoning behind predictions. This paper aims to make novel contributions to the field of material engineering by analyzing the compatibility of dynamic response data from various material structures with prominent machine learning approaches. The purpose of this is to help researchers choose models that are both effective and understandable, while also enhancing their understanding of the model's predictions. To achieve this, this paper analyzed the requirements and characteristics of commonly used machine learning algorithms for crack propagation in materials. This analysis assisted the authors in selecting machine learning algorithms (K nearest neighbor, Ridge, and Lasso regression) to evaluate the dynamic response of aluminum and ABS materials, using experimental data from previous studies to train the models. The results showed that natural frequency was the most significant predictor for ABS material, while temperature, natural frequency, and amplitude were the most important predictors for aluminum. Crack location along samples had no significant impact on either material. Future work could involve applying the discussed techniques to a wider range of materials under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

A review of nonlocal theories utilized in the fatigue and fracture modeling of solid structures is addressed in this paper. Numerous papers have been studied for this purpose, and various nonlocal theories such as the nonlocal continuum damage model, stress field intensity model, peridynamics model, elastic-plastic models, energy-based model, nonlocal multiscale model, microstructural sensitive model, nonlocal lattice particle model, nonlocal high cycle fatigue model, low cycle fatigue model, nonlocal and gradient fracture criteria, nonlocal coupled damage plasticity model and nonlocal fracture criterion have been reviewed and summarized in the case of fatigue and fracture of solid structures and materials. [ABSTRACT FROM AUTHOR]

Based on fracture mechanics theory, a finite element method was used to determine the stress intensity factors of the inclined crack on the inner surface of the pipe under axial compression load and external pressure. The effects of different influencing factors on the stress intensity factor along the crack front considering crack closure were systematically explored, which were different to those under internal pressure. The effects of high aspect ratio on KII, the crack inclination asymmetry caused by curvature and the effects of the friction coefficient on the stress intensity factors of the pipe with an inclined inner surface crack under axial compression load and external pressure were explored in this paper. To be fit for defect assessment, the solutions for stress intensity factors KII and KIII were derived, and new correction factors fθ and fμ were proposed in the empirical solutions to accommodate the crack inclination asymmetry and the friction coefficient, respectively. [ABSTRACT FROM AUTHOR]

Proof testing is used to remove weak ceramic components from a manufactured batch in turn truncating the lower end of the strength‐failure probability distribution. With proof testing, components are subjected to stresses comparable to those observed during service load histories resulting in the remaining ones having assured minimum reliabilities. The degree to which the reliability of the remaining parts is assured depends on the proof test protocol, which includes multiple variables such as stress level, realistic sampling of flaws, complex geometries, multiaxial stresses, transient loading histories, time‐dependent damage due to slow crack growth and/or fatigue, and change in material behavior due to temperature and/or environmental conditions. This paper advances the early work done on proof test theory, which was limited to simple stress states, to include general stress and material states. The theory introduced in this paper takes into account practical conditions often encountered in industrial applications. This advanced proof test theory was coded into the CARES/Life code (Ceramics Analysis and Reliability Evaluation of Structures/Life). Examples are provided to demonstrate the theory. [ABSTRACT FROM AUTHOR]

The article discusses a study which was carried out to investigate the local and effective fracture behaviour of polycrystalline silicon for microelectromechanical systems (MEMS). The apparent mode I critical stress intensity factor was determined from MEMS-scale tension specimens. The distribution of values was attributed to local cleavage anisotropy and to enhanced grain boundary toughening.

Abstract: We employ the carbon paper technique with the aim of investigating the effect of spherical-agglomerate (pellet) strength on force distributions, through confined compression of approximately 1mm sized pellets formed from microcrystalline cellulose and polyethylene glycol. The carbon paper technique relies on the transference of imprints from compressed pellets onto white photo quality paper, which are digitised and processed via image processing software. The investigated pellets can both deform plastically and develop localised cracks in response to an applied stress, while remaining largely intact during confined compression. Our results indicate that such crack formation – henceforth referred to as fracture – has a decisive influence on force distributions. Previous work on non-fracturing systems has found that the distribution of normalized forces tends to narrow with increasing particle deformation. No narrowing is observed after the point of fracture in this study and the width of the distributions – as quantified by the standard deviation of non-normalized forces – is found to increase with the difference between non-normalized mean force and fracture force. Additional corroborative results show that spatial force–force correlations typically exhibit a marked change once the fracture force is exceeded. [ABSTRACT FROM AUTHOR]

A finite element model (FEM) of the bracket arm of wrecker is developed and the mechanical behavior under six representative conditions is studied in this paper. Stress test experiment is carried out to validate the presented FEM. Comparison analyses show that results predicted from the FEM are in good agreement with those obtained from the test experiment. Moreover, the mechanical behavior analyses also give the danger working conditions for each component of the bracket arm. Based on the stress distributions under the danger working condition, structural improvement is conducted for the component which is prone to material failure. Mechanical behavior analyses of the improved structures are also carried out in this paper. Numerical analysis results show that the maximum stresses of each improved component of the bracket arm are all reduced to close or below the allowable stress. This indicted that the load bearing capacities of each component are improved effectively and meet the requirements of engineering applications. [ABSTRACT FROM AUTHOR]

The method of backfill in underground mining is important for ground control as well as material recycling and energy efficiency. Even though extensive testing and field studies of backfill have been conducted, less is known about the detailed damage and fracturing that occurs directly at the rock/backfill interface. In this paper, cylindrical specimens containing an inner diameter of backfill and an outer diameter of rock (RB) were tested under triaxial compression. Acoustic emissions (AE) were used throughout testing, and X-ray computed tomography (CT) scanning was conducted before loading was applied and after the specimens had failed. The high-resolution CT images were then converted into point clouds to isolate the fractures and visualize them in three dimensions. The point clouds clearly show that fracturing occurred both in the rock and along with the contact between rock and backfill, while very little fracturing was found to occur in the backfill. Based on the point cloud and AE results, a unique evolution of fracturing is found to occur that includes two stages of shear fracturing in the rock, tensile fracturing along with the rock/backfill interface, and final tensile fracturing in the rock after delamination from the backfill, all of which contributed to the nonlinear stress–strain response. This paper presents a novel approach for investigating the initiation and propagation of 3D fractures in laboratory testing and can offer a useful reference for further studies on the mechanics of bi-material structures. [ABSTRACT FROM AUTHOR]

The paper presents the results of standard specimen fracture made of anisotropic carbon fiber plastic with an epoxy matrix. Static stepwise loading of the specimen was carried out on an Instron 8801 testing machine to determine the characteristics of ductile fracture G1C in the first mode in accordance with ASTM D5528. During loading, the parameters of acoustic emission (AE) signals, such as AE impulse amplitudes and their energy were synchronously recorded. At the same time, the magnitude of the opening and the growth of the crack initiated by the artificial cut at the end of the specimen were recorded. According to the analysis of the acoustic emission signals, three zones with different G1C behaviour were identified: initial crack propagation, its stationary growth and accelerated fracture of the specimen. The zonal character of the change in the acoustic emission signals made it possible to determine the energy of the acoustic emission signals as diagnostic evidence for the onset of rapid destruction of the specimen. The amplitude of the AE-signals in the zones, however, remained constant. Online monitoring of changes in the energy of acoustic emission signals will prevent the onset of rapid destruction of an object in places of its deformations. The paper does not aim at defining G1C as usual. It presents the investigation of the fracture stages for a composite material using an acoustic emission method. [ABSTRACT FROM AUTHOR]

This paper starts with an overview of the application of the three guidelines (GL) of the German Research Association of Mechanical Engineers (FKM). Each of these provides algorithms for calculating fatigue lives of components under constant or variable amplitude loading, however, with underlying different failure criteria, that is, technical crack initiation life (GL‐nonlinear), fatigue crack growth life (GL‐fracture mechanics), and total fracture life (GL‐linear). Since the GL‐linear only considers linear‐elastic material behavior in the fracture fatigue life calculation, the guideline is not capable for the LCF and is not able to take sequence effects into account. For a better approximation of fracture fatigue lives, the elastic–plastic material behavior has to be taken into account. This paper introduces the U‐Concept which has been evaluated from a large structural durability database from the literature with more than 1,500 experiments for constant and more than 700 experiments for variable amplitude loading. The U‐Concept is a small add‐on to the local strain approach (LSA) which is the backbone of the GL‐nonlinear. It enables (1) to directly calculate the fatigue life to total fracture based on elastic–plastic material behavior according to the LSA or (2) to estimate the remaining fatigue life from crack initiation to fracture without a crack growth simulation. Furthermore, the U‐Concept needs no experimental determined crack growth parameters, the only necessary material parameter is the ultimate tensile strength Rm. The U‐Concept is therefore easy applicable for industrial users and increases the accuracy of the approximated fatigue lives by considering the elastic–plastic material behavior. [ABSTRACT FROM AUTHOR]

This paper reports on a new method for the measurement of sheet fracture toughness. In this method, samples cut in DENT geometry are cyclically loaded. The maximum load for each cycle is incremented after each cycle until the sample fractures. The work in the final cycle is then the work required to fracture the sample. The fracture toughness determined using the new cyclic technique is compared with that determined using the Essential Work of Fracture (EWF) technique, for samples with a wide range of fracture toughness, and it is shown that cyclic technique gives a fracture toughness around 8% lower than the EWF technique. For 3 samples, cyclic fracture toughness values were measured for ligament lengths from 3.3 to 14.0 mm and compared with the EWF fracture toughness in each case. The cyclic fracture toughness was found to be independent of the ligament length, except for very weak samples, and to be 5–10% lower than the EWF fracture toughness. The differences between the EWF and cyclic fracture toughnesses were probably due to the development of damage zones around the crack tips before the fracture. The advantages of the new cyclic technique over the EWF technique are that it requires less sample area as only one ligament length is required, is quicker and can be readily automated. [ABSTRACT FROM AUTHOR]

An introduction to the journal is presented in which the editor discusses various reports published within the issue, including "Development of an Efficient Maintenance Strategy for Corroded Steel Bridge Infrastructures," "Instrumentation and Modeling of I-35W St. Anthony Falls Bridge," and "Fatigue Crack Formation and Repair Strategies for Steel Cantilever Bracket Tie Plates."

In this section, the dynamic propagation behavior of a penny-shaped interface crack in piezoelectric bimaterials is analyzed. The objective of this paper is to use the boundary conditions of the penny-shaped interface crack to study the dynamic propagation of the crack under the action of load, so as to provide some valuable implications for the fracture mechanics of the piezoelectric bimaterials and simulate the interface crack between piezoelectric bimaterials, it is necessary to establish a suitable model and give appropriate boundary conditions according to the actual situation. The elastic displacement and potential equations are constructed according to the structural characteristics of the circular crack. In the case of a given displacement or stress, the Laplace transform and Hankel transform are used to simplify the problem into an integral equation with unknown functions. According to the boundary conditions, the corresponding unknowns are obtained, and the closed solution is derived. The results show that the fracture toughness of a penny-shaped interface crack in piezoelectric bimaterials is related to the thickness of the material, the impact time, the material characteristics, and the electric field. At the same time, it can be found that different materials have different roles in the crack propagation, so it is very important to study the crack opening displacement (COD) intensity factor of the crack for safety design. [ABSTRACT FROM AUTHOR]

Fracture of viscoelastic materials is considered to be a complex phenomenon due to their highly rate sensitive behavior. In this context, we are interested in the quasi-static response of a viscoelastic solid subjected to damage. This paper outlines a new incremental variational based approach and its computational implementation to model damage in viscoelastic solids. The variational formalism allows us to embed the local constitutive equations into a global incremental potential, the minimization of which provides the solution to the mechanical problem. Softening damage models in their local form are known to result in spurious mesh-sensitive results, and hence, non-locality (or regularization) has to be introduced to preserve the mathematical relevance of the problem. In the present paper, we consider two different regularization techniques for the viscoelastic damage model: a particular phase-field and a lip-field approach. The model parameters are calibrated to obtain some equivalence between both these approaches. Numerical results are then presented for the bidimensional case and both these approaches compare well. Numerical results also demonstrate the ability of the model to qualitatively represent the typical rate-dependent behaviour of the viscoelastic materials. Besides, the novelty of the present work also lies in the use of lip-field approach for the first time in a viscoelastic context. [ABSTRACT FROM AUTHOR]

In recent years, Additive Manufacturing (AM) has emerged as a transformative technology, with the process of Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M) gaining substantial attention for its precision and versatility in fabricating metal components. A major challenge in PBF-LB/M is the failure of the component or the support structure during the production process. In order to locate a possible residual stress-induced failure prior to the fabrication of the component, a suitable failure criterion has to be identified and implemented in process simulation software. In the work leading to this paper, failure criteria based on the Rice-Tracey (RT) and Johnson-Cook (JC) fracture models were identified as potential models to reach this goal. The models were calibrated for the nickel-based superalloy Inconel 718. For the calibration process, a conventional experimental, a combined experimental and simulative, and an AM-adapted approach were applied and compared. The latter was devised to account for the particular phenomena that occur during PBF-LB/M. It was found that the JC model was able to capture the calibration data points more precisely than the RT model due to its higher number of calibration parameters. Only the JC model calibrated by the experimental and AM-adapted approach showed an increased equivalent plastic failure strain at high triaxialities, predicting a higher cracking resistance. The presented results can be integrated into a simulation tool with which the potential fracture location as well as the cracking susceptibility during the manufacturing process of PBF-LB/M parts can be predicted. [ABSTRACT FROM AUTHOR]

The leak-before-break design concept is based on J-R curves, which are obtained by J-R tests on various types of specimens and are known to be dependent on the cyclic load history. The J-R curves of standard specimens suggested by the American Society for Testing Materials are determined based on quasi-static tensile loading. However, seismic loading induces a reverse cyclic loading that alternately applies a tensile and a compressive load to nuclear plant piping. Therefore, it is very important to obtain the fracture toughness characteristics under reverse cyclic loading for the integrity estimation of nuclear plant piping. The objective of this paper is to study the effects of reverse cyclic loading on the fracture toughness characteristics of SA312 TP316L stainless steel, which is a nuclear plant piping material. J-R tests on a flat, equivalent stress gradient specimen with varying incremental displacement were carried out. The test results were reviewed by comparing the J-R test results under quasi-static loading. In addition, the safety margin of the nuclear plant piping was evaluated using a crack driving force diagram method. For the SA312 TP316L stainless steel, the results showed that the J-R curves were decreased with a decrease in the incremental displacement. When the incremental displacement was set to 0.25 mm, the unstable crack growth point value was about 73.0% of those for the quasi-static loading conditions. [ABSTRACT FROM AUTHOR]

This paper deals with the study of the mechanical responses of ductile metals under biaxial non-proportional cyclic loading tests. The biaxially loaded HC specimens manufactured from 4 mm thick aluminum alloy sheets (EN AW 6082-T6) are subjected to various loading paths, including monotonic and cyclic loading conditions. The aim is to investigate the plastic, damage, and fracture behavior of the material under these different loading scenarios. In terms of numerical aspects, a modified anisotropic two-surface cyclic plastic–damage continuum model is used to predict the material behavior in the load-displacement field and different strain fields. Numerically predicted stress states are analyzed in detail to gain a better understanding of the damage mechanisms. Moreover, the scanning electronic microscopy (SEM) pictures taken from the fracture surfaces confirm the dependency of the damage mechanisms on the loading histories. The present work indicates the importance of considering different loading conditions for the accurate prediction of material responses. [ABSTRACT FROM AUTHOR]

This paper presents the results of centrifuge model tests to investigate the deformation behaviour of unreinforced and reinforced transparent soil foundations under strip loading. A digital image analysis technique was employed to obtain the soil displacement field and strain distribution of reinforcements. Two-dimensional (2D) numerical models were developed and verified using the test results. The soil was modelled as a linearly-elastic perfectly-plastic material with Mohr–Coulomb failure criterion. The reinforcement was characterised using a linearly-elastic model considering rupture behaviour. Moreover, a parametric study was conducted to investigate the load–settlement response of foundations, distribution of reinforcement tension and failure sequence of reinforcements. The experimental and numerical studies show that the results obtained from the numerical simulations are in good agreement with the results of the centrifuge model tests. The 2D finite difference model developed using the user-defined functions coded into the FLAC programme can better simulate the progressive failure of the reinforcement layers in the tests. The failure sequence of reinforcement layers is not affected by the modulus and internal friction angle of soil and the reinforcement length, but is closely related to the combined effect of spacing and number of reinforcement layers and the combined effect of reinforcement stiffness and strength. [ABSTRACT FROM AUTHOR]

Previous studies demonstrated coupling of acoustic guided waves from one optical fiber to another through a simple adhesive bond coupler. This paper experimentally utilizes such an adhesive bond coupler to easily extend an already existing sensor network. We experimentally demonstrate this concept for detecting simulated cracks growing from circular holes in a thin aluminum plate. A single, remotely bonded FBG sensor is used to detect the original crack growth, followed by the addition of other optical fiber segments using adhesive couplers to detect new crack growth locations on the plate. A laser Doppler vibrometer is also used to measure the guided wave propagation through the plate to verify that the changes in the FBG sensor measurements are due to the growth of the cracks. [ABSTRACT FROM AUTHOR]

Internal subsurface cracks in continuously cast slabs can lead to catastrophic failure of the material when it is subjected to further rolling or shaping. The interplay of multiple factors contributes to the formation of these cracks, making it occasionally challenging to accurately assess slab quality based solely on surface appearance. This paper presents an in-depth exploration of the internal quality of slabs, that aimed to identify the critical parameters responsible for initiating and propagating these cracks. The investigation employs a range of methodologies, including macro- and micro-metallographic analysis, thermo-mechanical simulations, that aid in characterizing defects and understanding material vulnerability. To prevent such failures in cast products, the study also proposes optimized operational parameters. [ABSTRACT FROM AUTHOR]

Three types of initial microcracks have been clearly observed in concrete: those that developed around aggregate/coarse sand, those that developed perpendicular to the aggregate, and those that developed in the cement paste. However, the evolution of each of these microcrack types has not yet been separately studied. The variations among these microcrack types and their effect on the microstructures of the interfacial transition zone (ITZ) and cement paste have not been further investigated. Accordingly, this study presents an experimental and statistical study of the systematic and quantitative analysis of the initial microcrack characteristics of the concrete ITZ and cement paste, focusing on the aforementioned core scientific deficiencies. First, the initial microcracks within concrete are quantitatively and statistically evaluated. This is achieved by developing an image recognition algorithm and interactive algorithm for boundary recognition based on the experimental results of the fluorescent epoxy impregnation method (FEIM). Then, the different behaviors of each microcrack type are identified based on the statistical analysis of the number, area, length, width, and axis orientation of the microcracks. Accordingly, the effect of each type of microcrack on the microstructure and macroproperties of concrete can also be deduced. Finally, the initial microcrack characteristics within the ITZ is examined. The proportion of the total length of microcracks to the corresponding aggregate/coarse sand perimeter (α) and the parameter RL , which can reflect the location distributions of microcracks, is used to evaluate the characteristics of the initial microcracks within the ITZ statistically and quantitatively. The statistical approach employed in this study establishes the experimental and theoretical foundation for evaluating the initial characteristics of microcracks in concrete. Concrete is a three-phase composite material consisting of coarse/fine aggregates, cement paste, and interfacial transition zone. The concept of interfacial transition zone has been widely accepted of concrete technology for many years. An interfacial transition zone is often considered a weak link because its increased microcracks may serve as a path for the ingress of aggressive species and provide preferential and easier pathways for crack growth. Because the interfacial transition zone plays a significant role in the macroproperties of concrete, further investigations focusing on the microcrack evolutions distributed in the interfacial transition zone are urgently needed. In this paper, the fluorescent epoxy impregnation method was used to obtain the real microcrack distributions within concrete. An image recognition algorithm and interactive algorithm for boundary recognition have been developed to evaluate the microcrack characteristics quantitatively. Thus, statistical analysis of microcracks distributed in the interfacial transition zone is conducted. Microcracks developed perpendicular to the aggregate and in cement paste are also analyzed for comparison. The statistical approach establishes the experimental and theoretical foundation for evaluating the microcrack characteristics and its effect on the strength, durability, and service safety of concrete engineering structures. [ABSTRACT FROM AUTHOR]

The most common classification method of drill cores is the Rock Quality Designation (RQD) value, which indicates the percentage of rock cores longer than 10 cm in a given core section. This core logging procedure is the basic parameter in the most useful rock mass classification methods like Rock Mass Rate (RMR) and Rock Mass Quality (Q). It is also used to determine the Geological Strength Index (GSI), which has become widely used in the last 20 years. One of the basic problems of the RQD value is that it does not distinguish different rock cores longer than 10 cm (100% is obtained for one piece of 1 m length and 10 pieces of 10 cm length) and a uniform result is obtained for shorter units. In this paper, the so-called Integrated RQD (Int_RQD) factor is introduced to eliminate these problems and to provide a better description of fracture density in the core logging procedure. As it uses the original core logging procedure, historical RQD data can also be reevaluated. Considering that RQD is an input parameter for most rock engineering classifications, these systems such as GSI can be reviewed based on the new RQD definition proposed herein. [ABSTRACT FROM AUTHOR]

The material network in the chemical process has the characteristics of a complex network. Once the fault occurs, it will spread and lead to cascading failures, causing the chemical production process to not proceed normally. Previous studies of cascading failures have been limited by the size and characteristics of the network, which prevented the definition of the fault propagation capacity of the edge based on the actual situation. Studies on the effects of network topology and certain risk factors on the amount of fault propagation still need to be completed. Because of the above shortcomings, this study constructs a chemical material network cascading failure invulnerability analysis model that considers the failure propagation ability. Through the study of the chemical material network topology structure and the analysis of various flammable and explosive chemicals, the paper defines the fault propagation coefficient, which affects the load propagation quantity on the connecting edge. Then, based on the load‐capacity nonlinear cascading failure model, the chemical material network's invulnerability was analyzed by adjusting the model parameters. The effectiveness of the model is verified through case analysis. Compared to the existing model, the model in this paper effectively improves the invulnerability of the material network and can reduce the phenomenon of large‐scale failure of the material network due to the failure propagation capability is not considered. [ABSTRACT FROM AUTHOR]

Discrete element models are being increasingly applied to model rock failure processes. Bonded-particle models, based on circular or spherical particle systems, have been successfully used for two decades. More recently, bonded-block models, using polygonal or polyhedral elements, have proven to be a powerful alternative. This paper describes the basis of the application of these models in the numerical simulation of failure in rock materials. The critical governing parameters are identified, and their influence is discussed. The model calibration procedure based on the analysis of laboratory tests is discussed. An application example of an underground excavation problem is presented using a simple bonded-block model employing rigid blocks and a bilinear softening contact model. The results show the capability of this approach to reproduce observed failure modes involving block fractures. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the impact of transient velocity changes on sealing performance during reciprocating sealing processes. Design/methodology/approach: Establish a model of transient mixed lubrication, solve the transient Reynolds equation, consider the effect of temperature rise at the seal interfaces, and determine the behavior of the seal interfaces, such as film thickness and fluid pressure. Evaluation with friction and leakage rate, calculate the variation of sealing performance with reciprocating velocity under different working conditions, and verify it through bench experiments. Findings: Within a reciprocating stroke, the frictional force decreases with increasing velocity, and the frictional force of the outstroke is greater than that of the instroke; at the time of the stroke transition, the fluid pressure is smallest and the rough peak contact pressure is greatest. At present, the dynamic pressure effect of fluids is the largest, and the friction force also increases, which increases the risk of material wear and failure. Friction and leakage increase with increasing pressure and root mean square roughness. As temperature increases, friction increases and leakage decreases. In studying the performance variations of seal components through a reciprocating sealing experiment, it was found that the friction force decreases with increasing velocity, which is consistent with the calculated results and more similar to the calculated results considering the temperature rise. Originality/value: This study provides a reference for the study of transient sealing performance. [ABSTRACT FROM AUTHOR]

Featured Application: Creation of statistically significant reference sample sets for validation, optimization, and demonstration of non-destructive testing techniques, particularly for the additive manufacturing sector. Techniques for the controlled seeding and growth of cracks are urgently required for non-destructive testing technique evaluation, particularly for additive manufactured (AM) samples. This paper describes a method that uses a combination of the tensile load and the resonance excitation of notched AM samples, with in situ monitoring of the resonance frequency serving to track the crack dimensions. Mechanical low-cycle fatigue cracks, ranging in length from ~0.3 mm to ~5 mm, were successfully created in five AM samples using this technique. The samples were non-destructively characterized using optical microscopy and Nonlinear Resonance (NLR) testing. The exploitation of resonance enabled the concentration of a significant number of stress cycles on the samples in much shorter timespans than conventional fatigue testing, enabling a high throughput while utilizing compact components. Furthermore, the tracking of the resonance frequency shift throughout the process enabled non-invasive and no-contact real-time condition monitoring. [ABSTRACT FROM AUTHOR]

This paper is devoted to showing a discrete adaptive finite element approximation result for the isotropic two-dimensional Griffith energy arising in fracture mechanics. The problem is addressed in the geometric measure theoretic framework of generalized special functions of bounded deformation, which corresponds to the natural energy space for this functional. It is proved to be approximated in the sense of T-convergence by a sequence of discrete integral functionals defined on continuous piecewise affine functions. The main feature of this result is that the mesh is part of the unknown of the problem, and it gives enough flexibility to recover isotropic surface energies. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the axial compression behaviour of perforated glass fibre reinforced plastic (GFRP) circular tubes. A total of 12 GFRP medium-length tubes with and without circular holes were tested under axial compression. The influence of hole size and hole quantity on the failure mode and mechanical behaviour of perforated GFRP tubes were carefully evaluated. The overall buckling failure and material strength failure, mainly determined by the hole size, were observed in the axial compression tests. The critical load and axial stiffness of the perforated tubes decreased further with the increase of hole sizes and quantities, compared to those of the intact GFRP tubes. To reveal the damage mechanism of perforated GFRP tubes, three-dimensional digital image correlation (3D-DIC) technique was used to analyse the evolution of full-field strain around the hole. It was demonstrated that the damage mechanisms of the overall buckling failure and material strength failure were respectively compression-shear destruction and tension-shear destruction in the high strain concentration regions around the hole. Finally, design-oriented equations were proposed to predict the critical load and axial stiffness of perforated GFRP tubes under axial compression, and 95% confidence interval was used for interval estimation. The proposed equations were in good agreement with the test results. In addition, the prediction results of axial stiffness are generally more accurate than that of critical load. [ABSTRACT FROM AUTHOR]

Concrete is among the most widely used structural materials in buildings and bridges all over the world. During their service life, concrete structures may inevitably display cracks due to long-term fatigue loads, leading to the degradation of structural integrity. Thus, it is very important to detect cracks and their growth in concrete structures using an automated structural health monitoring system. In this paper, experimental research on crack detection and imaging of concrete structures by using sensing skin and electrical resistance tomography (ERT) is presented. Carbon ink is screen-printed on the surface of concrete as a conductive material to form sensing skins. With these sensing skins, when cracks occur on or near the surface, it breaks the continuity of the sensing skins and significantly reduces conductivity in cracking areas. Then, after exciting small currents in sensing skins and measuring related voltage data, an inverse analysis based on total variation (TV) regularization is adopted to reconstruct tomographic images showing conductivity changes in sensing skins, to detect the occurrence and growth of cracks. The effectiveness of conductive sensing skins and our related crack detection method is validated in experimental studies on a concrete beam subjected to fatigue tests. [ABSTRACT FROM AUTHOR]

Residual stress is an important factor that affects the properties of cold spray coatings. The study performed 2D single-, 3D single-, and 3D multiple-particle finite element simulations based on the Eulerian method, and hole drilling measurements to study residual stress in cold-sprayed copper coatings. The study examined how the basic modeling parameters affect residual stress in the 2D system. It found that the mesh size, substrate dimension, and simulation duration change the residual stress; while material failure does not have much effect because failure is localized. It also found that thermal softening, which occurs when the initial temperature and/or plastic deformation increase, helps to reduce the residual stress. In addition, the residual stress along the axisymmetric axis of the particle changes from being compressive at first to being compressive-tensile-compressive along the through-depth thickness direction with the interfacial stress being tensile that mainly originates from friction shear of the interfacial layers. For the 3D single-particle simulations, the average residual stress to the through-depth thickness shows tension to compression transition and is similar to the 2D cases. For the 3D multiple-particle simulations, the residual stresses in the coatings/substrate are all compressive because of the repeated and strong impact of the particles, which agree with the experimental measurements. The study also found that the compressive stresses decrease when the coating thickness increases because of more plastic deformation-induced thermal softening. This paper clarifies the effects of Eulerian-based finite element parameters on simulating residual stress in cold spray and will serve as a valuable reference for future studies. [ABSTRACT FROM AUTHOR]

In earthquake-prone areas, pile-anchor structures are widely employed for slope reinforcement due to their reliable performance. Current research has primarily focused on static and quasi-static analyses of slopes reinforced by using pile-anchor structures, with limited investigation into their dynamic response. In this work, the finite element method (FEM) is used to study the dynamic behavior of a pile-anchor slope system, and the extended finite element method (XFEM) is used to simulate the progressive failure processes of piles. Three different reinforcement schemes, which include no support, pile support, and pile-anchor support, are considered to examine the performance of the pile-anchor structure. The simulation results suggest that the pile-anchor structure displays a reduction of 39.6% and 40.6% in the maximum shear force and bending moment of the piles, respectively, compared to the pile structure. The XFEM is utilized to model the progressive failure process of the piles subjected to seismic loading. We find that crack initiation in the pile body near the slip surface, for both the pile supported and the pile-anchor supported conditions, occurs when the peak ground acceleration arrives. Crack growth in the piles completes in a very short period, with two distinct increments of crack area observed. The first increment occurs when the peak ground acceleration arrives and is significantly larger than the second increment. Consequently, for the seismic design of piles, it is necessary to strengthen the pile body around slip surfaces. The novelty of this paper is that we realize the simulation of crack initiation and propagation in piles subjected to seismic loading. [ABSTRACT FROM AUTHOR]

This paper introduces a robust algorithm that efficiently generates high-quality unstructured triangular meshes to model complex two-dimensional crack growth problems within the framework of linear elastic fracture mechanics (LEFM). The proposed Visual Fortran code aims to address key challenges in mesh generation including geometric complexity, required simulation accuracy, and computational resource constraints. The algorithm incorporates adaptive refinement and updates to the mesh structure near the crack tip, resulting in the formation of rosette elements that provide accurate approximations of stress intensity factors (SIFs). By utilizing the maximum circumferential stress theory, the algorithm predicts the new crack path based on these SIFs. Throughout the simulation of crack propagation, a node splitting approach was employed to represent the progression of the crack, while the crack growth path is determined by successive linear extensions for each crack growth increment. To compute stress intensity factors (SIFs) for each increment of crack extension, a displacement extrapolation method was used. The experimental and numerical results demonstrated the algorithm's effectiveness in accurately predicting crack growth and facilitating reliable stress analysis for complex crack growth problems in two dimensions. The obtained results for the SIF were found to be consistent with other analytical solutions for standard geometries. [ABSTRACT FROM AUTHOR]