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The flexural behavior of lightweight concrete two-way slabs repaired or strengthened with externally bonded carbon fiber-reinforced polymer (CFRP) sheets is the subject of this study. The experiment included five reinforced lightweight concrete slab specimens with dimensions of 1000 mm in length, 1000 mm in width, and 120 mm in thickness. Tested one specimen without any strengthening and reinforced another specimen with a single layer of CFRP. The other specimens were repaired with a single layer of CFRP, applying damage ratios of 50%, 60%, or 70% of the ultimate load. Intentionally designed each slab to collapse under bending forces and maintained comparable dimensions. According to the experiment results, changing the degree of damage from 70% to 50% increases the ultimate load capacity by about 17.7%, and the ultimate deflection decreases by about 31.4%. CFRPs have the potential to fix structural damage under static stress testing conditions. However, it is essential to make sure that they stick well to surfaces that do not have suitable geometric properties or have been deformed. CFRP sheets effectively repaired the specimens, increasing the failure stress of the reinforced concrete slabs and preventing the spread of cracks.

Overall structural integrity and load transfer between concrete and reinforcement enabling composite action relies on the bond between concrete and reinforcement. Bond strength determination of reinforced concrete is an essential task that a pullout test can determine. Experimental pullout behaviour can be affected by various parameters, such as concrete and steel strength, boundary conditions, etc. Therefore, a parametric study on pullout tests is time-consuming. In addition, measurements of internal stress-strain components and damages of constitutive materials are also difficult in experimental endeavours. In this context, finite element (FE) models should be developed to perform a parametric study with cost and time-saving. This study proposes a finite element modeling strategy of reinforced concrete under pullout force by using the expected failure mechanism to predict bond-slip behaviour in ABAQUS. In FE models, surface-to-surface cohesive interaction behaviour was used to assign interaction between reinforcement and concrete. The proposed modelling strategy was validated with available experimental data from four reference specimens, having all possible failures (i.e., pullout, splitting, and splitting-pullout) under pullout loading. The finite element analysis showed that the proposed FE modeling strategy performed well in predicting bond-slip behaviour in elastic regions. Additionally, maximum bond stresses were predicted satisfactorily, except for the splitting failure pattern, using the proposed FE modelling strategy.

This paper proposes a methodology to evaluate and optimize the dynamic response of tall buildings under wind loading, controlled through semi-active Magneto-Rheological dampers (MR dampers). For this, a tall building, modeled as a 2D frame, is taken as case study and three structural control configurations are proposed. The original structural configuration of the building is the first configuration analyzed, called Uncontrolled Original (C1). In the second configuration, called Uncontrolled Optimized (C2), the fundamental frequency of the building is optimized via PSO algorithm as a function of its mass. Then, in the third configuration, Controlled Optimized (C3), a set of MR dampers with behavior formulated via the modified Bouc-Wen rheological model and controlled through the Linear Quadratic Regulator associated with the Clipped Optimal control strategy (LQR-CO) is applied to the structure. Finally, the dynamic response of the three scenarios under wind action is analyzed and compared to performance criteria established in the literature. The results demonstrate that the C3 configuration is the only one able of satisfying all the established performance criteria, proving that the proposed methodology y that combines structural optimization with MR dampers is a powerful tool for vibration control.

This study reports an experimental investigation of the fatigue and fracture resistance of R350HT, a heat-treated pearlitic rail steel with refined microstructure used in rails. Monotonic tensile, rotating bending, linear elastic plane strain fracture toughness, and fatigue crack growth rate tests are presented. The results are used to outline the basic properties and are corroborated by fractographic investigation. This enables the identification of the dominant type of fracture. Regarding fatigue and fracture resistance, the investigated material shows similar properties as other pearlitic rail steels, such as R260. At room temperature, the dominating fracture is of brittle cleavage type, showing some ductile regions associated with pro-eutectoid.

Mechanical processing of hole edges in large-size hull structures of single and double curvature for welding saturation parts into them is an urgent task of shipbuilding. A considerable amount of such machining has to be performed directly on the slipway on a fully assembled structure. To perform such works non-stationary technological machining complexes are used, which have reduced rigidity in comparison with stationary equipment. The article summarizes the results of mathematical modeling of cutting forces during face milling of a workpiece made of high-strength high-viscosity shipbuilding steel. The application of high-speed face milling in order to reduce the value and non-uniformity of cutting forces is theoretically substantiated. Recommendations for selection of technological cutting modes and tool geometry are determined. The obtained experimental data confirm the possibility and expediency of high-speed face milling of hull structures made of hard-to-machine materials under conditions of a low-rigid technological system.

The article describes the results of laboratory studies on the unfrozen water content and ultimate long-term strength of frozen clay and chalk samples in the temperature range from −10 to −25 °C. The soil samples contained dissolved salt in the pore space, with three types of salts (NaCl, KCl, and CaCl2) being considered. The findings indicate that the influence of the content and type of dissolved salt on the ultimate long-term strength of soils is realized indirectly through the unfrozen water content. In this case, the soil freezing characteristic curve in the region of negative temperatures significantly depends on both the type of dissolved salt and its quantity. The experimental data obtained were used to parameterize the model and calculate the maximum bearing capacity of the frozen wall (FW) in the presence of dissolved salts in the volume of frozen soils. It has been demonstrated that the decrease in the maximum FW bearing capacity is substantial with the appearance of dissolved salt in the pore space of the soils. This decrease is at-tributed to the combined effects of two factors: 1) a reduction in the FW thickness and 2) a decrease in the frozen soil strength due to an increase in the amount of unfrozen water content in the soil pore space. The second factor is deemed more significant.

The research focuses on examining the impact of technological defects, specifically "dry-spot" and "wrinkles," on the mechanical behavior and buckling resistance of structural composites. The investigation of the buckling phenomenon was carried out through a compression test on a thin plate fabricated from carbon-fiber-reinforced polymer (CFRP) laminate. This test was performed using a specialized fixture designed in accordance with ASTM 3410 standard. For the analysis, the study employed a three-dimensional digital optical system, Vic-3D, in conjunction with the AMSY-6 acoustic emission system. The research showcases findings from acoustic emission signals that verify the shear-based mechanism of buckling in plates constructed from CFRP featuring "dry-spot" type defects. In the case of "wrinkles" defects, it was observed that transverse shear transpires at the stress concentration points created by the "excess" layers.

This work is devoted to an experimental investigation of fatigue behavior of pultruded fiberglass tubes under uniaxial tension, compression and torsion. Static tests were carried out; a presence of postcritical deformation stage during torsion is noted. Regularities of inhomogeneous strain fields evolution are analyzed using digital image correlation method. Fatigue curves are built for four cyclic loading modes: tension-tension, compression-compression, tension-compression and torsion. An analysis of specimens' fractures is carried out, typical damaging mechanisms are revealed. Residual dynamic stiffness data is obtained and studied using a previously proposed fitting model. Results demonstrate model's high descriptive capability and its flexibility to describe two-staged and three-staged stiffness degradation curves. An influence of loading mode on a shape of these curves is found out. Model parameters' dependence on maximum stress value during the loading cycle is studied using the Pearson's correlation coefficient. The necessity of multiaxial fatigue behavior investigation of pultruded fiberglass tubes is concluded.

Partial confinement can provide sufficient reinforcement to enhance the compressive strength and ductility of concrete with lesser confining material. This paper presents the results of an axial compression test conducted on eighteen plain concrete cylinders of 150 mm diameter and 300 mm height partially confined with a Stainless-Steel Wire Mesh (SSWM) strip of different widths. The study included two specimens without wrapping, two fully wrapped specimens, and others wrapped with two SSWM strips of varying widths at both the ends of concrete cylinder. The strain on SSWM up to failure is measured to understand the effectiveness of lateral confining pressure on the behaviour of concrete cylinders. The peak axial compressive strength and corresponding strain of unconfined and SSWM-confined concrete cylinders are compared. The result shows a significant increase in peak confined compressive stress as compared to an unconfined concrete cylinder. However, the confinement efficiency is reduced when the height of the unconfined region exceeds the diameter of the cylinder, and significant strain localisation is detected within the unwrapped region. Based on experimental investigation, a confinement coefficient is suggested for a partial wrapping of SSWM on the concrete cylinder.

The present study aims to develop a novel hybrid composite by incorporating clamshell as a secondary reinforcing filler into a bamboo-epoxy composite. The primary objective of this hybridization is to optimize the synergistic benefits of each component, harnessing the strength of bamboo fibres, the durability of epoxy, and the cost-effective repurposing of the waste clamshell. Compression moulding was employed to develop composites with varying filler content (0- 9 wt%). The effect of filler on the physical and mechanical properties of bamboo-epoxy composites was evaluated by conducting tests as per ASTM standards. Experimental results show that the addition of clamshell filler significantly improved composites' properties, but there was a limitation to the addition. Hardness, tensile, and flexural properties were increased, whereas impact strength was reduced. Composites with 6 wt% clamshell exhibited optimum properties, enhancing tensile strength by 20.5% and flexural strength by 24.4 % compared to composites without filler. SEM analysis of fractured tensile and bending specimens revealed an enhanced fibre-matrix bonding with the inclusion of filler and supported the experimental results obtained. The outcome of this study contributes to sustainable development by using natural resources like bamboo fibre and repurposing seashell waste to create cost-effective composite material with enhanced properties.

In the past five years, the implementation of machine learning (ML) techniques has surged in civil engineering applications, particularly for optimizing and predicting solutions to various challenges. More robust prediction models may be produced by combining test data collected in the laboratory or field with ML. These models may be used to estimate the compressive strength of masonry or repair mortars, probable damage scenarios in buildings, concrete models, beams, and columns for determining the mechanical characteristics of materials, damage detection in civil structures, and so on. This comprehensive review aims to clarify the array of ML-based methods employed in civil engineering, specifically focusing on their efficacy in strengthening energy efficiency and cost-effectiveness. In combination with ML, the review explores corresponding soft computing methodologies such as fuzzy logic (FL) and design of experiments (DOE). A variety of case examples that highlight the versatility of these approaches, particularly in applications linked to structural reinforcement, enhance the story. The review navigates difficulties associated with the integration of soft computing in civil engineering and expands its scope to include emerging research directions. This synthesis of advanced artificial intelligence (AI) serves as a guide, providing new researchers with knowledge about a developing field. These methods could revolutionize the current situation by providing creative answers to complex problems that arise in civil structural applications.

Most techniques of measuring the stress intensity factor (SIF) in the cracking process assume a crack in a planar medium. Currently, there is no effective approach for curved brittle shells, particularly for non-developable cases, i.e., shapes with non-vanishing Gaussian curvature. This paper introduces a novel approach to obtaining material properties related to fracture by experimentally observing weakly curved surfaces. Based on the DIC record of the displacement field around the crack tip, the truncated Williams expansion is fitted to the data adjusted according to the shallow shell equations. The convergence properties of the method are investigated by comparing experimental data of PMMA cylinders to theoretical and numerical predictions. The applicability of the technique to non-developable surfaces is verified. It is demonstrated that robust convergence requires the number of terms in the Williams expansion exceeding 6. For different geometries, the ratio of the data selection radius and the length of the crack should exceed 0.3.

Adopting novel sandwich structures with FRP (Fibre Reinforced Polymer) skins and a metallic lattice core, both of which have high specific strength and stiffness, is one way to achieve better mechanical performance while remaining lightweight. Flexural stress is a load pattern that frequently occurs in the structural frame components of automobiles; nonetheless, while the in-plane load scheme has scarcely been examined, the out-of-plane load one has. As a result, the former configuration received consideration in this work. Moreover, short beam specimens were taken into account. The mechanical response of specimens with three different kinds of composite materials as skin material was analysed. The skins were made of CFRP (Carbon Fiber Reinforced Polymer), with two different weaving styles, and AFRP (Aramid Fiber Reinforced Polymer). All-titanium specimens were studied, too. Similar maximum loads and maximum displacement at break were recorded for both CFRP and AFRP specimens, while the all-titanium one resulted stronger. In terms of the load-displacement curves, the first section featured an initial linear phase, followed by a minor load drop, likely attributed to the breakage of fibres. The CFRP specimens showed a sharp fracture of the skin fibres, while for the AFRP, a fraying was observed.

Most techniques of measuring the stress intensity factor (SIF) in the cracking process assume a crack in a planar medium. Currently, there is no effective approach for curved brittle shells, particularly for non-developable cases, i.e., shapes with non-vanishing Gaussian curvature. This paper introduces a novel approach to obtaining material properties related to fracture by experimentally observing weakly curved surfaces. Based on the DIC record of the displacement field around the crack tip, the truncated Williams expansion is fitted to the data adjusted according to the shallow shell equations. The convergence properties of the method are investigated by comparing experimental data of PMMA cylinders to theoretical and numerical predictions. The applicability of the technique to non-developable surfaces is verified. It is demonstrated that robust convergence requires the number of terms in the Williams expansion exceeding 6. For different geometries, the ratio of the data selection radius and the length of the crack should exceed 0.3.

The phenomenon of ignition and explosive failure of specimens from high-entropy alloys (HEAs) of systems Ti-Zr-Hf-Ni-Cu, Ti-Zr-Hf-Ni-Cu-Co at quasi-static compression tests was found. It physical model is proposed. It is exhibited that the reason for this phenomenon is the release of energy of the oxidation reaction; such reaction is initiated due to the heat released ahead of the shear crack tip at brittle fracture of the specimens under quasi-static compression. It is shown that ignition and failure by explosion are the specific features of brittle fracture for high-entropy alloys containing Ti-Zr-Hf, in general. This phenomenon is realised when certain critical levels of strength and ductility of these alloys are reached. The importance of these critical levels of strength and ductility lies in the fact that they predetermine the maximum permissible level of strength and brittleness for this class of HEAs, above which they lose their structural and functional properties, turning to the energetic alloys capable of explosive release of a significant amount of thermal energy. This specific feature of the high-entropy alloys containing Ti-Zr-Hf outlines the scope of their application and defines the boundary separating structural and functional high-entropy alloys from energetic high-entropy alloys.

Taking advantage of the interevent time intervals, namely the time intervals between two successive acoustic events recorded during mechanical loading of structural elements, it is attempted to detect indices warning about upcoming failure. The innovative aspect of the study is that the analysis is implemented in the frame of Non-Extensive Statistical Mechanics, a discipline founded on a class of entropies violating the additivity principle, which is the cornerstone of the Boltzmann-Gibbs Statistical Mechanics. The specimens used for the experiments were marble blocks simulating either fragmented and restored epistyles or mutually interconnected intact epistyles of the Parthenon Temple on the Acropolis of Athens. The specimens consisted of three mate­rials (marble, metallic connectors and cementitious pastes) exhibiting, thus, a strongly non-homogeneous nature. The entropic index, i.e., the parameter quantifying the degree of non-additivity, was used for the analysis of the ex­pe­rimental data. The results were considered in juxtaposition to the re­spective ones from experimental protocols with specimens of macroscopically homo­geneous nature. It was concluded that the temporal evolution of the entropic index provides very good insight into the level of damage ac­cumu­lated in the loaded structure, independently of whether the structure is homogeneous or not, providing an interesting pre-failure indicator.

The present work investigates the crack-induced degradation of the dynamic characteristics in plain concrete elements subjected to mixed-mode fracture conditions. Specifically, a discrete fracture model, based on an inter-element cohesive approach, has been improved and implemented into a 2D finite element framework to evaluate the progressive variation of the static and dynamic properties as the damage level increases. The obtained numerical results highlight the effectiveness of the proposed model in determining the load-carrying capacity and the degradation of natural vibration frequencies during damage propagation, demonstrating its applicability in the framework of structural health monitoring.

This study focuses on ductile fracture behavior prediction for Ti6Al4V alloys fabricated via Selective Laser Melting (SLM). A modified Gurson-Tvergaard-Needleman (GTN) model characterizes void growth and shear mechanisms under uniaxial stress. The research explores the impact of Artificial Neural Network (ANN) architecture, specifically hidden layers and neurons, on predicting fracture parameters. Results reveal that increasing hidden layers substantially enhances accuracy, particularly for fracture displacement. Notably, predicting maximum force requires fewer layers than fracture displacement. Using selected layers and neurons, the system consistently achieved R2-values exceeding 0.99 for both maximum force and fracture displacement. The study identifies the initial void volume fraction (f0) parameter as having the most significant influence on both properties.

Nodular cast iron (GJS) represents one of the most widely used materials for vehicle, energy and heavy machinery industry. Nevertheless, foundries struggling with the influence of local material defects in GJS like pores, shrinkages and dross often leading to a locally reduced fatigue strength of the entire component. One measure to tackle those negative effects is the welding of the affected areas. This measure is then successful when locally achieved material strengths and surface qualities are higher than the component with the casting defect. Unfortunately, data for the lifetime and fatigue assessment of welded GJS are not present right now. Thus, the research project »nodularWELD« assessed the local stress- and strain-based fatigue data of different thick-walled GJS grades for building a basis for a successful usage even of defect affected components. So, three ferritic and pearlitic GJS grades were investigated in the heat-affected zone, the base material, the welding filler and more over in an integral material state comprising all those three aforementioned states based on axial and bending investigations. Additionally metallographic and fractographic analysis were conducted.

Various input variables, including corrosion time, fretting force, stress, lubrication, heat-treating, and nano-particles, were evaluated by modeling of stress-controlled fatigue lifetimes in AlSi12CuNiMg aluminum alloy of the engine pistons with different machine learning (ML) techniques. Bending fatigue experiments were conducted through cyclic loading with zero mean stress, and then experimental data was predicted by five different ML-based models. Moreover, when the optimal ML prediction model was found, it was analyzed using the Shapley additive explanation (SHAP) values method. Results illustrated that extreme gradient boosting (XGBoost) had superior data for estimations, with average training coefficients of determination of at least 63% and 90%, respectively for fatigue lifetime and its logarithmic value. The SHAP values interpretation of the XGBoost model revealed that fretting force, stress, and corrosion time were the most significant inputs in estimating the logarithm values of fatigue lifetimes, respectively.

In this study, ultrasonic welding (USW) of lap joints of polyetherimide (PEI) plates (adherends) with carbon fiber (CF) prepregs impregnated with PEI was investigated. No energy director (ED) was used, so binder contents were varied in the prepregs to compensate for the lack of the polymer in the fusion zone. In addition, the effect of the USW parameters on the structure and the mechanical properties of the lap-joints were analyzed. The most homogeneous macrostructure, the maintained structural integrity of both the CF-fabric in the prepregs and the lap-joined PEI adherends, as well as the maximum strength properties (tensile strength) were revealed for the USW joints with the minimum polymer content in the prepreg. In this case, rising the USW time from 400 up to 800 ms radically changed the macrostructure of the fusion zone, while the strength properties did not vary significantly (shear stresses were 42–48 MPa). Computer simulation of the influence of the PEI/CF-fabric ratios in the prepregs on the deformation response of the USW joints showed that the prepreg thicknesses and, accordingly, the PEI/CF ratios did not exert a noticeable effect on the strain–stress (tensile) diagrams, while the determining factor was the adhesion level.

In the last four decades, bonded composite repair has proven to be an effective method for addressing crack damage propagation. On the other hand, machine learning (ML) has made it possible to employ a variety of approaches for mechanical and aerospace problems and such significant approach is the repair mechanism and hence ML algorithms used to enhance in the present work. The current work investigates the effect of the single-sided composite patch bonded on a thin plate under plane stress conditions. An analytical model was formulated for a single-sided composite patch repair using linear elastic fracture mechanics and Rose's analytical modelling. From the analytical model, the stress intensity factors (SIF) were calculated by varying all possible parameters of the model. Next, ML algorithms were selected, and comparative studies were conducted for the best possible performance and to identify the parametric effects on optimum SIF. Also, the analytical model is validated with existing work, and it shows good agreement with less than 10% error. This study is particularly important for designing the single-sided composite patch repair method based on analytical modelling. Also, it is important to compare ML algorithms with analytical solutions in regression applications.

This work is devoted to the fracture processes numerical modeling of elastic-brittle bodies taking into account the statistical distribution of subregions strength values and stress concentration. The novel formulation of the boundary value problem and its solution algorithm are developed. The loading diagrams obtained in computational simulations, the corresponding growth curves of the destroyed elements relative number and the damaging process kinetics are analyzed. The presence of the postcritical deformation stage at the macro-level is noted. The influence of the strength properties distribution range and the depth of the concentrator on the maximum load value and the damage evolution is determined. The significant influence of the finite elements’ properties distribution on the fracture processes modeling results is concluded.

Modern technological make it possible to produce three-dimensional (3D) reinforcement for polymer composite materials. The tasks of experimental research and analysis of the deformation process of new composite materials for aviation purposes taking into account the nonlinearity of mechanical behavior become actual. The paper presents an experimental study of the mechanical compression behavior of composite material specimens made of 3D woven carbon fiber preforms using the pressure impregnation technology (Resin Transfer Molding method with a pairwise interlayer reinforcement and a longitudinal layer). Compression mechanical tests were carried out on specimens using a universal system of electromechanical testing Instron 5882 and a system of 3D analysis of displacement and strain fields on the surface. Tests were conducted in accordance with ASTM D 3410 recommendations and using specialized tooling. Consideration of nonlinearity parameter during experimental data processing is proposed. The importance of determining the values of critical deformation in compression as a parameter characterizing the moment of the beginning of fracture is noted. The comparison of strength, elastic and deformation properties of carbon-fiber composite materials made using the same technology from fibers and binders from different manufacturers is carried out. The experimental diagrams "stress-strain" and their approximating dependences taking into account the nonlinearity function ? are obtained. The type of functions ? of the studied materials is defined, the linear approximation of dependence of functions ? on strain is substantiated. Values of strength limits, elastic modulus, nonlinearity coefficient and critical damage were obtained, statistical processing of the obtained results and their analysis were carried out

The work is devoted to the study of the Zr-1Nb alloy in coarse-grained and ultrafine-grained states under laser-induced shock-wave loading. This material is of interest due to the application for the manufacture of shells for fuel elements of nuclear reactors. The properties of this alloy in the ultrafine-grained state is attracted for the reliability improvement of fuel rods in wide range of load intensity. Shock wave loading was carried out using a Beamtech SGR-Extra-10 high-energy nanosecond laser. The free surface velocity profiles were registered by the VISAR system. Mechanical characteristics are obtained using velocity profiles. It is shown that the spall strength and dynamic elastic limit for the coarse-grained state are higher than for the ultrafine-grained state. In general, the Zr-1Nb alloy in the ultrafine-grained state is more susceptible to spall fracture, including laser shock peening. Numerical simulation of the process under study has been carried out using statistically based nonlinear model of solid with defects and finite element method to describe the deformation behavior and fracture of the material under shock-wave loading. Simulation results are qualitatively consistent with experiments in the prediction of the conditions of spall failure.

Al6061 and its composites are widely employed in applications requiring high strength and impact resistance. Heat treatment, particularly ageing, is a well-established method for enhancing the mechanical properties of these composites. However, the influence of post-ageing cooling methods on the impact energy absorption capacity of Al6061 and its composites is not well understood. This investigation aims to examine the impact energy absorption of Al6061 and its composites after ageing at 460�C for 2 hours, employing different cooling methods, including furnace cooling, air cooling, and water cooling. The composites were produced using the stir casting technique with varying weight fractions of graphite and SiC particles based on Taguchi's design of experiments. Charpy impact tests were conducted using a specialised testing machine. The results reveal that the impact energy absorption capacity of the composites is influenced by the cooling method used after the ageing treatment. Furnace cooling demonstrated the highest impact energy absorption capacity compared to the other cooling methods, exhibiting a 28% increase relative to the monolithic aluminium alloy. Furthermore, it was observed that the impact energy absorption capacity of the composites did not improve with an increase in the weight fraction of SiC particles, while the addition of graphite negatively impacted the absorption capacity

This paper addresses the estimation of critical loads in FFF (Fused Filament Fabrication) printed polymers and composites containing notches. Particularly, the analysis is focused on the fracture load estimations of 39 PLA (polylactic acid) and 39 graphene reinforced PLA (PLA-Gr) printed plates containing two different types of notches (U- and V-notches) and combining different plate thicknesses and defect length to plate width (a/W) ratios. The addition of graphene (1 wt.%) increases both the yield stress and the ultimate tensile strength, also reducing the strain at rupture and, thus, generating a material whose behavior is closer to linear elasticity. Among the different assessment tools that may be used to estimate critical loads, this work applies the well-known Averaged Strain Energy Density (ASED) criterion, which compares the averaged strain energy over a certain control volume at the notch tip with the corresponding critical value, the latter being a material property. This approach has a linear-elastic nature, so its application to non-fully linear materials may require the use of specific corrections or calibrations. For the two materials analyzed here, PLA and PLA-Gr, it has been observed that the ordinary linear-elastic ASED criterion provides good estimations for the PLA-Gr material, whereas the pristine PLA, with more evident non-linear behavior, the obtainment of accurate results requires a previous specific calibration of the ASED material parameters

This research examines the performance of reinforced lightweight concrete beams subjected to several degrees of damage (50%, 60%, 70%, and 100%). It can use a sheet made of Carbon Fiber Reinforced Polymer (CFRP) to reinforce. The Full U-wrapping rehabilitation method was tested in the presented experimental program. In this method, CFRP sheets are attached to the bottom only and the side and bottom of the beam section. Experiments proved that the service load (Ps) increases by 7.06 % from a damage level of 50 % to 70 %, rises by 1.21 % from a damage level of 60 % to 70 %, and falls by 3.07 % from a damage level of 100 %. The result also rose for the fortified sample by 11.99%. Increases of 42.67 %, 33.07 %, and 23.73 % in the stiffness ratio (k) were observed at damage intensities of 50, 60, and 70 %, respectively. Damage at lower severity levels is increasing at a faster rate. The ductility of the restored LWC beams is more excellent than the control, as with the stiffness. Damage levels of 50%, 60%, and 70% saw increased ductility of 35.60, 34.92, and 34.69 %, respectively.

This is the first part of a short three-paper series, aiming to revisit some classical concepts of Linear Elastic Fracture Mechanics. The motive of this first paper is to highlight some controversial issues, related to the unnatural overlapping of the lips of a �mathematical� crack in an infinite plate loaded by specific combinations of principal stresses at infinity (predicted by the classical solution of the respective first fundamental problem), and the closely associated issue of negative mode-I Stress Intensity Factor. The problem is confronted by superimposing to the first fundamental problem of Linear Elastic Fracture Mechanics for an infinite cracked plate (with stress-free crack lips) an �inverse� mixed fundamental problem. This superposition provides naturally acceptable stress and displacement fields, prohibiting overlapping of the lips (by means of contact stresses generated along the crack lips, which force the overlapped lips back to naturally accepted position) and, also, non-negative mode-I Stress Intensity Factors. The solutions of this first paper form the basis for the next two papers of the series, dealing with the respective problems in finite domains (recall, for example, the cracked Brazilian disc configuration) weakened by artificial notches (rather than �mathematical� cracks), by far more interesting for practical engineering applications.

Due to the substantial need to continuously ensure safe excavations and sustainable operation of deep engineering structures, structural health monitoring based on remote sensing techniques has become a prominent research topic in this field. Indeed, throughout their lifetime, deep tunnels are usually exposed to many complex situations which inevitably affect their structural health. Therefore, appropriate and effective monitoring systems are required to provide real-time information that can be used as a true basis for efficient and timely decision-making. Since sensors are at the heart of any monitoring system, their selection and conception for deep rock tunnels necessitates special attention. This work identifies and describes relevant structural health problems of deep rock tunnels and the applicability of sensors employed in monitoring systems, based on in-depth searches performed on pertinent research. The outcomes and challenges of monitoring are discussed as well. Results show that over time, deep rock tunnels suffer several typical structural diseases namely degradation of the excavation damaged areas, corrosion of rock bolts and cable bolts, cracks, fractures and strains in secondary lining, groundwater leaks in secondary lining, convergence deformation and damage provoked by the triggering of fires. Various types of remote sensors are deployed to monitor such diseases. For deep rock tunnels, it is suggested to adopt comprehensive monitoring systems with adaptive and robust sensors for their reliable and long-lasting performance

In this study, a new method for identifying and characterizing straight cracks in plate-like structures is presented. The method combines the finite element method (FEM) using the software Abaqus and the success history-based adaptive differential evolution algorithm (SHADE). The objective of the method is to minimize the mean relative error between the measured experimental frequencies of a plate with an unknown crack identity and the numerical frequencies obtained using the Shade-FEM approach. The crack identity is defined by its length, orientation, and centre coordinates. To validate the effectiveness of the proposed approach, two strategies are applied. In the first strategy, the inverse problem is solved using the natural frequencies of a plate with a known crack identity obtained through modal simulation in Abaqus. In the second strategy, the experimental frequencies of a cracked plate are used. The results of the study demonstrate that the proposed approach achieves promising results with just a population size of 25 and 150 iterations. The outcomes show high accuracy, as indicated by a relative error of the objective function below 0.8%. Overall, the study demonstrates the effectiveness of using the Shade-FEM approach for identifying and characterizing straight cracks in plate-like structures, offering potential applications in various engineering and structural integrity fields.

The aim of this study is to analyze the effect of different geometries and sections on the mechanical properties of epoxy specimens. Five tensile tests were carried out on three types of series. The experimental results obtained were 1812.21 MPa, 3.90% and 41.91 MPa for intact specimens, 1450.41 MPa, 2.16% and 21.28 MPa for specimens with hole and 750.77 MPa, 2.77% and 11.89 MPa for specimens with elliptical -notched for Young's Modulus , strain and stress respectively. In addition, the experimental results indicated that the mechanical properties of both (Young's Modulus value and stress value) were higher in an intact specimen. Afterwards, the nonlinear functional relationship of input parameters between epoxy sample geometries and sections was established using the response surface model (RSM) and the artificial neural network (ANN) to predict the output parameters of mechanical properties (Young's Modulus and stress). In addition, the design of experiment was developed by the Analysis of the Application of Variance (ANOVA). The results showed the superiority of the ANN model over the RSM model, where the correlation coefficient values for the model datasets exceed ANN (R2 = 0.984 for Young's Modulus and R2 = 0.981 for the stress)

A DIC-based method was employed for assessing the fatigue induced degradation of mechanical properties of neat polyetheretherketone (PEEK) and its laminated composite reinforced with unidirectional carbon fibers. Its operation principle is based on the remote measurement and calculation of the maximum and minimum strains in a cycle, as well as both dynamic and secant moduli estimated from mechanical hysteresis loops. It is shown that these parameters reflect the degree of material damaging, enabling to predict its current mechanical state.

The aim of this paper is to characterize the mechanical characteristics of chlorinated PVC (CPVC). Tensile tests were carried on the compounds at different temperatures ranging from -20 to 90�C and crosshead speeds from 5 to 500 mm/min. The results were analyzed to determine how crosshead speed and temperature affected on the mechanical characteristics of CPVC specimens. Two damage models are then developed, one model obtained by adapting the unified theory version and the other quasi-experimental static model based on ultimate stress. These models allow us to evaluate the damage evolution of CPVC samples and to determine the safety and maintenance intervals of this material.

The present paper deals with the prediction of the fatigue life of a planar tubular truss, when geometrical parameters, material properties, and live loads are non-deterministic. A multi-level calculation uncertainty quantification framework code was designed to aggregate the finite element method and fatigue-induced sequential failures. Due to the incompleteness of the aleatory-type inputs, the maximum entropy principle was applied. Two sensitivity analyses were performed to report the most influencing factors. In terms of variance, the results suggest that the slope of the curve crack growth rate � stress intensity factor range is the most influencing factor related to fatigue life. Furthermore, due to the application of the entropy concept, the fatigue crack growth boundaries and fatigue crack semi-width boundaries obtained provide the most unbiased fatigue crack design mapping. These boundaries allow the designer to select the worst-case fatigue scenario, besides being able to predict the crack behavior at a required confidence level.

In recent studies, piezoelectric actuators have been recognized as a practical and effective material for repairing cracks in thin-walled structures, such as plates that are adhesively bonded with piezoelectric patches due to their electromechanical effects. In this study, we used the finite element method through the ANSYS commercial code to determine the stress intensity factor (SIF) at the crack tip of a cracked plate bonded with a piezoelectric actuator under a plane stress model. By running various simulations, we were able to examine the impact of different aspects that affect this component, such as the size and characteristics of the plate, actuator, and adhesive bond. To optimize performance, we utilized machine learning algorithms to examine how these characteristics affect the repair process. This study represents the first-time machine learning has been used to examine bonded PZT actuators in damaged structures, and we found that it had a significant impact on the current problem. As a result, we were able to determine which of these parameters were most helpful in achieving our goal and which ones should be adjusted to improve the actuator's quality and reduce significant time and costs.

Eccentrically Braced Frames (EBFs) outperform moment-resisting frames in seismically active regions because of their strength, stiffness, energy dissipation, and ductility. Conventional bracing systems, such as X, Y, V, or K types, are utilized to enhance structural integrity. This study employs computational modelling to analyze multi-story steel buildings featuring an eccentric X-brace system. In this investigation, 120 multi-story steel frame buildings were selected. These multi-story structures comprise six-, nine-, and twelve-story geometries. ETABS built a full-scale FE model of multi-story structures. The study's parametric variables are the X-brace eccentricity, steel X-brace section size, and X-braced placement. Steel X-braces may have an eccentricity of 500, 1000, or 1500 millimeters. The ETABS model was validated when its findings matched experimental data. According to the data, the eccentric X-brace increases top-story displacement more for 6-story multi-story structures than for 9- and 12-story ones. Eccentric X-braces reduced lateral stiffness, allowing more significant floor movement. Eccentric and diagonal braces offer less lateral rigidity than concentrically braced frames due to their flexibility. Eccentricity reduces stiffness, even if the X-braced component has a larger cross-section. EBFs may migrate horizontally. Since the EBF absorbs more energy, changing the X-brace section size and eccentricity affects its ductility.

Onyx � is a new material composed of Polyamide 6 reinforced with short carbon fiber, used in the novel additive manufacturing composites technique. This paper aims to presents the axial fatigue performance of this material with and without U-notches. The experimentally determined S-N fatigue curve was obtained under axial load with a load inversion ratio, R = 0.1, and compared to fatigue performance of U-notched samples ranging from 0.25 to 2 mm radius. In addition, the stress concentration factor was compared for static and alternative loading to obtain the notch sensitivity in terms of the U-notch radius, showing that there is indeed a difference in stress concentration between them. The advantage of the approach is that it permits using commonly used dimensioning methods for this AM material.�

New developments in thermal spraying processes may offer higher-quality alternatives to hard chrome plating and possibilities for hard chrome plating in a range of coating applications. These include spraying with high-velocity air fuel (HVAF) and new spray consumables. The low operating temperatures and accelerated particle velocity of the HVAF process enable investigation and development of a wide range of novel coating materials and applications. The High-velocity Air Fuel Process' quality and efficiency are primarily due to the broad combustion chamber and axial injection of the feedstock through it, as well as the relatively low combustion temperature of an air-fuel mixture and the low gas velocity that provides enough time for the mild heating of the powder particles. The current work discusses the inventive thermal spray procedure used for SAE 1008 carbon steel, a cost-effective substrate material. All of the compositions that were treated have undergone microstructure investigations. A scratch test is conducted in accordance with ASTM guidelines. Assessment of surface morphology clearly demonstrates the relationship between the evaluated parameters. According to the occurrence, scratch methods such as�delamination, cracking, plastic deformation, and elastic deformation are highlighted. However, the findings of the scratch test showed that the samples' scratch resistance increased as the coating thickness rose. In comparison to samples with thinner coating, those with thicker coating demonstrated a stronger resistance to scratching. This is explained by the fact that coatings with a higher thickness and density can support the subsurface more effectively and stop cracks from scattering. This can retain the coating's integrity and stop more damage from occurring, improving scratch resistance. Better scratch resistance was displayed by the samples with denser microstructures and smoother surface morphologies. The outcome is greater scratch resistance because a higher density covering can withstand deformation and fracture better than a lower density layer. This is due to the mechanism of deformation and fracture in the coating material. This improvement in scratch resistance can be due to the composites' increased HVAF coating's hardness and adherence. The findings imply that using an HVAF coating to increase the scratch resistance of new nanocomposites�may constitute a successful strategy.

The purpose of this study was to understand the behavior of martensitic H13 steel in accordance with the microstructural evolution, mechanical properties and wear in repeated tempering cycles. The microstructures were characterized by an axio image observer microscope, scanning electron microscope (SEM), and x-ray diffraction (XRD). Uniaxial tensile test, Charpy v-notch impact test, rockwell hardness test and wear test were conducted to analyze the changes in mechanical properties, impact properties, hardness and wear in repeated tempering cycles. The specimens prepared were subjected to hardening at 1030 �C for 20 minutes, oil quenched and subjected to repeated tempering cycles at 570 �C for 2hrs holding time each. The mechanical properties recorded indicate that the maximum ultimate tensile strength obtained was at double tempering due to secondary hardening effect i.e., alloy carbides precipitation offering strength to the matrix and corresponding wear was found to be minimum. The annealed specimen revealed bainitic microstructure and with hardening and repeated tempering cycles, fine needle like structure and carbides were observed in the microstructure and retained austenite was converted into martensite and martensite was converted into tempered martensite. Carbide size and martensite lath distribution control the strength

Research in innovative construction materials has focused on utilising supplementary materials in cementitious composites to promote sustainable development and reduce CO2 emissions. Within this context, this study aims to investigate the fresh properties and assess the pozzolanic activity of ternary blended cement by incorporating two industrial waste materials, namely waste glass (WG) and granulated blast furnace slag (GBS), as cement replacements up to 30%. A mixture design approach was employed for composition optimisation, and mathematical models were implemented to achieve this. XRD and SEM/EDS analyses were conducted to examine the structure and composition of the cementitious matrix. The results indicate that the setting time was prolonged compared to the reference mixture. Furthermore, based on the results of the SAI (Strength Activity Index) test, an acceptable level of strength development was demonstrated, confirming that WG and GBS possess the potential to replace cement while meeting the minimum strength requirements outlined in the specifications. Microstructure analyses revealed good adhesion between WGP, GGBS, and the cementitious binder. This research contributes to the development of eco-efficient binders that exhibit increased cement replacement ratios and qualities comparable to, or even superior to, traditional cement systems.

In this paper, an experimental and numerical study was achieved to investigate the behavior of masonry beams internally reinforced using carbon fiber-reinforced polymer (CFRP) and hybrid steel/CFRP reinforcements. Three beams were built using concrete bricks and grout mortar. The brick was designed with two holes that were filled with grout before placing the rebar inside. One beam was built without shear reinforcement, and the other two were with shear reinforcement. Material characterization tests were performed to evaluate the compressive strength of the brick and the masonry cube and the flexural strength of the masonry prism. The masonry cubes were prepared and tested to evaluate their equivalent mechanical properties. The beams were tested in three-point bending with an effective simply supported span of 840 mm where the load deformations and failure loads were monitored. Finite element models were built using ANSYS and validated with experimental results. Additional beam models were analyzed to study the effect of shear reinforcement spacing from 0.78d to 0.39d and more hybrid reinforcement configurations. Results showed that using equivalent material properties in numerical modeling instead of modeling bricks and mortar was acceptable. In addition, using shear reinforcement with a spacing of 0.78 d didn't enhance the shear behavior of the spacing. Finally, the hybrid steel/CFRP-reinforced beam with shear reinforcement achieved the highest capacity compared to the two other beams.

The use of elastomers has become increasingly important in a variety of industries, including automotive, medical, and food packaging. The adaptability of elastomers to different mechanical stresses has made them a popular choice for these applications. However, the mechanical properties of elastomers can be further enhanced by adding suitable fillers. In this study, the effects of different carbon fillers, namely carbon black, carbon graphite, and carbon nanotubes, on the tensile strength of elastomeric materials were investigated. Different combinations of plain silicone with varying concentrations of CB, CG, and CNT fillers were prepared using a solution casting method. The concentrations of the fillers ranged from 5% to 15% with an interval of 5%. The tensile strength of each combination was measured, and the results showed that the maximum tensile strength was achieved with the combination of CNT at 15% loading. The results of this study highlight the importance of filler selection in enhancing the mechanical properties of elastomers. Carbon fillers, particularly CNTs, have shown to be effective in improving the tensile strength of elastomeric materials. This has important implications for various industries, particularly in the development of new materials for applications in automotive and medical fields. The use of elastomers in the automotive industry has become increasingly important due to their ability to absorb mechanical shocks and vibrations. Elastomeric materials have also found applications in the medical field, such as in the development of artificial skin, blood pumps, drug delivery systems, and implants. The use of elastomers in food packaging has also become popular due to their ability to provide a barrier against oxygen and moisture. The use of carbon fillers in elastomeric materials has the potential to significantly enhance their mechanical properties, particularly their tensile strength. This study provides valuable insights into the effects of different carbon fillers on the tensile strength of elastomers, which can help in the development of new materials for various industrial applications.

The use of miniaturized specimen testing methods is a promising way to solve the problem of limited materials in RPV monitoring programs. The use of miniature specimens allows the evaluation of fracture toughness from other specimen materials used. In particular, the small-size compact tensile test specimen (0.16T CT) is promising for the determination of fracture toughness, as it can be produced from the standard size Charpy specimen that has already been tested. However, if we have only 0.16T CT test, we cannot investigate the dimensional response and also have only one restricted deformation state, which may pose problems in verifying geometry independence and determining local parameters for state-of-the-art analyses. It is therefore recommended to prepare at least two tests with two different restricted deformation specimens. Therefore, the testing of mini single edge notched bending (SENB) is also required and can be worked out from the Charpy specimens. The paper presents the determination of fracture toughness for these miniaturized specimens by modifying the virtual crack closure technique (VCCT) simulation method using GTN parameters instead of energy release as the driving force. This allows the calculation of the J-integral to proceed in parallel with the crack propagation.

The mechanical methods for measuring residual stresses typically rely on so-called destructive techniques where some stress components can be determined based on part deflection after material removal (cutting, etching, drilling, etc.). While these methods don't provide a comprehensive representation of residual stresses within the entire part, they can be readily applied in most manufacturing labs. In this study, we propose an efficient method for determining residual stress within additively manufactured cylindrical samples of stainless steel. The method is based on the assumption of a relation between the axial component of residual stress (normal to cross-section) and the cylinder radius. The general form of this relation is proposed based on data from numerical simulations using linear, parabolic or piecewise approximations. The parameters for the proposed relation are defined using equilibrium equations for total force and moment. The proposed method relies on an experiment with a mechanical cut along the cylinder. Consequently, the deflection of the cylinder halves after the cut allows for obtaining the equivalent bending moment.

The escalating importance of lightweight design in engineering demands innovative strategies to tackle this challenge. Traditionally, the joining of these materials involves rivets, bolts, or adhesives. However, contemporary manufacturing techniques, such as 3D printing, present the potential to fabricate joints without the necessity for additional binding mechanisms. This paper delves into a promising initiative concerning the joining of multimaterial systems, specifically composites and metals. The fabrication of the metal component of the joint through additive manufacturing (AM) enables the manipulation of surface geometry by incorporating patterned anchors. This, in turn, facilitates the direct co-curing of the composite onto the modified metallic surface. The primary objective is to enhance mechanical interlocking without relying on traditional fastening elements or adhesives. The study evaluates various anchor geometries to assess their efficacy in increasing the overall joint strength. This assessment employs the cohesive zone modeling (CZM) method to simulate joint specimens, followed by comparative analyses to quantify the strengths of the joints.

New conception of adiabatic shear bands (ASB) and adiabatic shear failure mechanisms are proposed as special type of critical phenomen, structural-scaling transition, in the ensembles of microshears, governed by the characteristic non-linearity (metastability) of stored (free) energy of solid with mesodefects. Corresponding free energy release kinetics provides experimentally observed ASB induced staging of plastic strain localization and transition to adiabatic shear failure. ASB staging follows to collective properties of microshears ensemble given by the self-similar solutions of evolution equation providing spatial-temporal microshears localization, momentum transfer and damage localization. The criticality of ASB induced plastic strain localization and failure allows us to avoid the discrepancy in the interpretation of ASB effects as thermo-plastic instability in the balance of the stored energy and structural DRX transformation. The microshear ensemble is considered as the second phase and initiation of collective modes provide different staging according to the metastability decomposition and ASB scaling properties following to the self-similar solutions. Self-similar nature of microshears collective modes providing the ASB dynamics is analyzed as the mechanism of steady plastic wave front unversality in shocked materials. The dynamic split Hopkinson pressure bar tests were conducted with AlMg6 alloy combined with “in-situ” imaging of temperature kinetics by CEDIP Silver 450M high-speed infrared camera with conclusion of the secondary role of thermoplastic instability at the ASB staging. The microstructural study performed by an electron microscopy revealed the correlated behavior of the ensemble of defects, which can be classified as a structural transition and precursor of ASB induced strain localization and failure. The modeling reflecting the links of self-similar solutions in microshear ensembles with relaxation properies and damage localization was applied for the comparative analysis of ASB staging and temperature dynamics given be the infrared imaging.

This is the second part of a short three-paper series, aiming to revisit some classical concepts of Linear Elastic Fracture Mechanics. Being the intermediate step of the analysis between infinite domains (discussed in Part-I) and finite bodies (that will be discussed analytically in the third part of the series), the present part offers an alternative theoretical approach for the confrontation of problems dealing with both infinite and finite bodies with geometrical discontinuities. The method is here applied to a stretched, single-edge notched strip. Assuming that the strip is made of a linearly elastic and isotropic material, the complex potentials technique is used. The solution is achieved by extending Mushkelishvili’s procedure, for the confrontation of the prob­lem of an infinite perforated plane. Closed form, full-field formulae are obtained for the stresses all over the notched strip. Using these formulae, the stress concentration factor at the base (tip) of the notch is quantified and studied in terms of the geometrical features of the notch and its dimensions relatively to the respective ones of the strip. The stress distributions plotted along characteristic loci, resemble closely, from a qualitative point of view, the respective ones provided by well-established analytical solutions. Preliminary numerical analyses in progress provide results in very good agreement with those of the present analysis.

The bonded composite repair has proven to be an effective method for addressing crack damage propagation. Numerous studies have employed experimental and simulation techniques to demonstrate the repair performance through the composites. These studies have explored various parameters related to bonded composites, such as size and properties, to enhance repair effectiveness. However, one aspect that has not been thoroughly investigated is the impact of fiber orientation within the composites. Therefore, the current work investigates the effect of the fiber direction of the composite patch bonded on a thin plate under plane stress conditions. Three types of fiber orientation of composite patch have been considered. In this investigation, the finite element method was used to determine the stress intensity factor using the ANSYS commercial code. The research findings showed that the fiber direction influenced the mitigation of stress intensity factor. This study is particularly important for designing the composite patch based on the fiber direction.

Designing tooling and cooling systems to prevent cutting tool damage is crucial while machining difficult-to-cut nickel alloys. This study investigates the machining effects during turning Inconel 718 using unitary aluminum oxide (Al2O3) and hybrid aluminum oxide+multi-walled carbon nanotube type (Al2O3+MWCNT) nanofluids under minimum quantity lubrication (NFMQL) through mathematical modeling and multi-objective optimization. The worn-out tools were analyzed for damage and wear mechanisms through images captured using optical and scanning electron microscopes. The study indicates that hybrid nanofluids outperform unitary nanofluids, which could be attributed to the better lubricating and cooling capabilities of MWCNT and the higher surface tension and thermal conductivity of Al2O3 nanoparticles. The cutting parameters were optimized by combining the Technique for Order of Preference by Similarity to the Ideal Solution (TOPSIS) and genetic algorithm. The study reveals an average error of less than 10% between experimental and predicted responses from the proposed optimization model. This study found lower cutting force up to 80 N, surface roughness of 0.6–0.7 µm, and tool life over 10 minutes with a cutting speed of 50–70 m/min and a lower feed and depth of cut of 0.1 mm/rev and 0.2 mm, respectively, using a hybrid Al2O3+MWCNT nanofluid under NFMQL conditions.