Search Results (233)

Widely employed in diverse engineering applications, stiffened steel plates are often subjected to biaxial compressive loads. Under these conditions, buckling may occur, initially within the elastic range but potentially progressing into the elasto-plastic domain, which can lead to permanent deformations or structural collapse. To increase the ultimate buckling stress of plates, the implementation of longitudinal and transverse stiffeners is effective; however, this complexity makes analytical stress calculations challenging. As a result, numerical methods like the Finite Element Method (FEM) are attractive alternatives. In this study, the Constructal Design method and the Exhaustive Search technique were employed and associated with the FEM to optimize the geometric configuration of stiffened plates. A steel plate without stiffeners was considered, and 30% of its volume was redistributed into stiffeners, creating multiple configuration scenarios. The objective was to investigate how different arrangements and geometries of stiffeners affect the ultimate buckling stress under biaxial compressive loading. Among the configurations evaluated, the optimal design featured four longitudinal and two transverse stiffeners, with a height-to-thickness ratio of 4.80. This configuration significantly improved the performance, achieving an ultimate buckling stress 472% higher than the unstiffened reference plate. In contrast, the worst stiffened configuration led to a 57% reduction in performance, showing that not all stiffening strategies are beneficial. These results demonstrate that geometric optimization of stiffeners can significantly enhance the structural performance of steel plates under biaxial compression, even without increasing material usage. The approach also revealed that intermediate slenderness values lead to better stress distribution and delayed local buckling. Therefore, the methodology adopted in this work provides a practical and effective tool for the design of more efficient stiffened plates. Full article

Crack damage can significantly reduce the ultimate strength of marine structures, potentially leading to progressive collapse. This study employs finite element analysis to investigate how cracks affect the strength of plates and stiffened panels under uniaxial and biaxial compression, providing insights essential for robust structural design. The effects of crack size and orientation are explored through a systematic evaluation of longitudinal, transverse, and bidirectional cracks—sized at 10%, 25%, and 50% of structural dimensions (plate length and plate breadth/web height)—in both plates and unstiffened panels. The analysis identifies key parameters governing strength degradation and reveals that stiffened panels are more resistant to cracking, whereas plates are more sensitive to crack orientation and loading direction. These findings underscore the role of crack characteristics and structural reinforcement in maintaining residual strength and provide guidance for improving the accuracy and reliability of ultimate strength predictions. Full article

The aim of translucency-enhancing liquids (TEL) is to locally influence the phase composition of zirconia in order to increase its translucency. This study aimed to determine the influence of TEL on 3Y- and 4Y-TZP zirconia concerning roughness, hardness, wear, flexural strength, dynamic stability and fracture force of fixed dental prostheses after thermal cycling and mechanical loading. Two zirconia materials (4Y-TZP; 3Y-TZP-LA, n = 8 per material and test) were investigated with and without prior application of TEL. Two-body wear tests were performed in a pneumatic pin-on-block design (50 N, 120,000 cycles, 1.6 Hz) with steatite balls (r = 1.5 mm) as antagonists. Mean and maximum vertical loss as well as roughness (Ra, Rz) were measured with a 3D laser-scanning microscope (KJ 3D, Keyence, J). Antagonist wear was determined as percent area of the projected antagonist area. Martens hardness (HM; ISO 14577-1) and biaxial flexural strength (BFS; ISO 6872) were investigated. The flexural fatigue limit BFSdyn was determined under cyclic loading in a staircase approach with a piston-on-three-ball-test. Thermal cycling and mechanical loading (TCML: 2 × 3000 × 5 °C/55 °C, 2 min/cycle, H₂O dist., 1.2 × 10⁶ force á 50 N) was performed on four-unit fixed dental prostheses (FDPs) (n = 8 per group) and the fracture force after TCML was determined. Statistics: ANOVA, Bonferroni test, Kaplan–Meier survival, Pearson correlation; α = 0.05. TEL application significantly influences roughness, hardness, biaxial flexural strength, dynamic performance, as well as fracture force after TCML in 3Y-TZP. For 4Y-TZP, a distinct influence of TEL was only identified for BFS. The application of TEL on 3Y- or 4Y-TZP did not affect wear. TEL application has a strong effect on the mechanical properties of 3Y-TZP and minor effects on 4Y-TZP. All effects of the TEL application are of a magnitude that is unlikely to restrict clinical application. Full article

Significant progress has been made in the low-temperature toughness and crack resistance of polypropylene fiber-reinforced composites. However, there is still a gap in the research on damage evolution under freeze–thaw cycles and complex stress ratios. To solve the problem of durability degradation of traditional rubble masonry in cold regions, this paper focuses on the study of polypropylene fiber-mortar-masonry blocks with different fiber contents. Using acoustic emission and digital image technology, the paper conducts a series of tests on the scaled-down polypropylene fiber-mortar-masonry structure, including uniaxial compressive tests, three-point bending tests, freeze–thaw cycle tests, and tests with different stress ratios. Based on the Kupfer criterion, a biaxial failure criterion for polypropylene fiber mortar-masonry stone (PPF-MMS) was established under different freeze–thaw cycles. A freeze–thaw damage evolution model was also developed under different stress ratios. The failure mechanism of PPF-MMS structures was analyzed using normalized average deviation (NAD), RA-AF, and other parameters. The results show that when the dosage of PPF is 0.9–1.1 kg/m³, it is the optimal content. The vertical stress shows a trend of increasing first and then decreasing with the increase in the stress ratio, and when α = 0.5, the degree of strength increase reaches the maximum. However, the freeze–thaw cycle has an adverse effect on the internal structure of the specimens. Under the same number of freeze–thaw cycles, the strength of the specimens without fiber addition decreases more rapidly than that with fiber addition. The NAD evolution rate exhibits significant fluctuations during the middle loading period and near the damage failure, which can be considered precursors to specimen cracking and failure. RA-AF results showed that the specimens mainly exhibited tensile failure, but the occurrence of tensile failure gradually decreased as the stress ratio increased. Full article

Thin plates are commonly used in mechanical structures such as ship hulls, offshore platforms, aircraft, automobiles, and bridges. When subjected to in-plane compressive loads, these structures may experience buckling. In some applications, perforations are introduced, altering membrane stress distribution and buckling behavior. This study investigates the elasto-plastic buckling behavior of perforated plates using the Finite Element Method (FEM), Constructal Design (CD), and Exhaustive Search (ES) techniques. Simply supported thin rectangular plates with central elliptical perforations were analyzed under biaxial elasto-plastic buckling. Three shapes of holes were considered—circular, horizontal elliptical, and vertical elliptical—along with sixteen aspect ratios and two different materials. Results showed that higher yield stress leads to higher ultimate stress for perforated plates. Regardless of material, plates exhibited a similar trend: ultimate stress decreased as the aspect ratio dropped from 1.00 to around 0.40 and then increased from 0.35 to 0.25. A similar pattern was observed in the stress components along both horizontal (x) and vertical (y) directions, once the y-component became considerably higher than the x-component for the same range of 0.40 to 0.25. For longer plates, in general, the vertical elliptical hole brings more benefits in structural terms, due to the facility in the distribution of y-components of stress. Full article

This study focuses on optimizing cruciform specimen configurations for the biaxial tensile testing of soft composite materials used in the aerospace industry under conditions of large deformation. A comprehensive evaluation system based on stress–strain uniformity and load transfer efficiency was established, and the stability of these metrics during the tensile process was analyzed. Using finite element simulation and multi-parameter analysis, the main parameter set affecting specimen performance was identified. The influence of different parameters on stress–strain uniformity and load transfer efficiency was investigated. Based on the optimization criteria, an optimized planar cross-shaped specimen configuration was developed. This configuration demonstrated excellent performance stability during deformation, with final stress uniformity error controlled to within 2.2%. The final strain uniformity error was maintained at 2.9%. The fluctuation range of load transfer efficiency did not exceed 1.5%. This study provides guidelines for designing specimens for large deformation testing of soft composite materials and can be used as a reference for future work on optimizing specimens. Full article

Traditional fiber-reinforced polymer (FRP) retrofit methods can restore the strength of reinforced concrete columns well, but stiffness is also partly restored. To increase the initial stiffness of retrofitted columns, this study investigated the seismic behavior of retrofitted resilient reinforced concrete (RRC) columns that were retrofitted by different methods, including high-strength mortar retrofit, carbon fiber-reinforced polymer (CFRP) retrofit, and CFRP and steel plate retrofit. In addition, the effect of the axial load was also considered. Quasi-static tests were conducted twice on five specimens, i.e., before and after repairing. The first test was used to create earthquake damage, and the second test was used to compare the seismic behavior of the retrofitted columns. The experimental results indicated that the CFRP retrofit method, whether with a steel plate or not, can restore the lateral resistance capacity well; furthermore, the drift-hardening behavior and self-centering performance were well maintained. The residual drift ratio of the CFRP-retrofitted column was less than 0.5%, even at a drift ratio of 3.5%, and less than 1% at the 6% drift ratio. However, the initial stiffness was only partly restored using the CFRP sheet. The introduction of steel plates was beneficial in restoring the initial stiffness, and the stiffness recovery rate remained above 90% when CFRP sheets and steel plates were used simultaneously. The strain distribution of the CFRP sheet showed that the steel plate did work at the initial loading stage, but the effect was limited. By using the steel plate, the CFRP hoop strain on the south side was reduced by 68% at the 6% drift ratio in the push direction and 38% in the pull direction. The axial strain of CFRP cannot be ignored due to the larger value than the hoop strain, which means that the biaxial stress condition should be considered when using an FRP sheet to retrofit RC columns. Full article

(1) Background: The work aims to determine different chemical and mechanical properties with and without BPA dental resin–matrix composites under the same curing and testing conditions. (2) Methods: Disc-shaped specimens were prepared from six resin–matrix composites used in dentistry, three with BPA (BE-Brilliant EverGlow^TM, ED-IPS Empress Direct, FS-Filtek^TM Supreme XTE) and three without (AF-Admira Fusion, BF-Enamel Plus HRi Bio Function Enamel, N/C). Specimens were photoactivated using an LED light-curing unit. The chemical and mechanical properties were analysed. (3) Results: The FS group exhibited the most significant water sorption (31.17 µg/mm³), while the BF showed the lowest (12.23 µg/mm³). Regarding the diffusion coefficient, the result recorded for the group AF is faster-absorbing water, and the group NC is slower. In both test methods (biaxial flexural strength and compressive strength), the resistance to flexural loading of the AF group was significantly lower than all other resin composites evaluated. (4) Conclusions: According to all the parameters studied, we verified that the BF presents the best chemical–mechanical behaviour. Resins free of BPA may not influence chemical–mechanical performance. However, the inorganic matrix has more influence on mechanical properties than the organic matrix. Full article

This paper presents an optimal model for the design of elliptical isolated footings subjected to biaxial bending under the minimum cost criterion, assuming that the footing rests on elastic soils and that the soil pressure distribution is linear. The methodology is developed in two parts. The first is used to obtain the minimum area, and the second is used to determine the minimum cost. Some authors show the equations for circular and elliptical footings for moments, bending shear, and punching shear. However, they do not present the minimum cost, and the numerical examples are presented only for circular footings and not for elliptical footings. Two numerical problems are given (each problem presents five variants), and the optimal cost design for elliptical isolated footings subjected to biaxial bending are shown. Problem 1: Modifying the moment on the Y axis. Problem 2: Modifying the axial load. In addition, a comparison is made between elliptical footings and circular footings. The results show that the minimum area is smaller for elliptical footings than for circular footings, and the minimum cost appears in elliptical footings when the footing dimensions are governed by the minimum pressure. Therefore, the new model for elliptical footings will be of great help to foundation engineering specialists. Full article

The presence of mixed-mode stresses, combining both opening and shearing components, complicates fatigue life estimation when applying the Paris law. To address this, the crack path, along with Mode-I (opening) and Mode-II (shear) components, was numerically analyzed using Fracture Analysis Code (Franc2D) based on the linear elastic fracture mechanics (LEFM) approach. Accordingly, fatigue life and stress intensity factors (SIFs) under various biaxial loading ratios (λ) were calculated using the Paris law and compared with available data in the literature. The results show that crack growth is primarily driven by the Mode-I component, which exhibits the largest magnitude. Thus, the Mode-I stress intensity factor (K_I) was adopted for the numerical integration of the fatigue life equation. Furthermore, the influence of normal and transverse loads (σ_y and σ_x, respectively) on the crack path plane and SIF was examined for λ. The analysis revealed that lower λ values led to faster crack propagation, while higher λ values resulted in extended fatigue life due to an increased number of cycles to failure. The comparison demonstrated good agreement with reference data, confirming the reliability of the proposed modeling approach over a wide range of biaxial loading conditions. Full article

Q345 steel is usually used on structures working under high temperature where creep deformation could endanger their structural integrity. In order to support the application of steel structures made of Q345 under high temperature, a fracture analysis on defective Q345 steel in the process of small-scale creep crack propagation has been performed. Three-dimensional finite element models with a semi-elliptical surface crack have been established, and the crack propagation process of Q345 steel has been simulated at 400 °C. The constraint effect near the crack tip in the process of creep crack propagation has been analyzed using the J-A₂ two-parameter method in which the influence of the crack aspect ratio, loading level, and biaxial loading ratio was studied. The previously developed constraint-based R6 procedure was adopted to assess the structural integrity of the cracked structure under small-scale creep conditions. The results showed that small-scale creep crack propagation behavior exhibits great influence on both crack tip fields and a constraint effect near the crack tip. The increase in the biaxial loading ratio, loading level, and aspect ratio of the crack could lead to an increase in the J integral, an enhancement of the constraint effect, and a decrease in the safe area in the failure assessment diagram for the cracked structure in the process of small-scale creep crack propagation. Full article

This study established a dynamic impact simulation system for a coral limestone cement composite subjected to bidirectional stress confinement conditions by using a coupled method of continuous medium FDM (a coupled continuum-discontinuum approach integrating finite difference continuum modeling (FDM) and the discrete element method (DEM) granular analysis), and verified its accuracy through indoor experiments. The study first conducted dynamic mechanical performance tests on reef limestone concrete using an SHPB experimental device, exploring the effects of the strain-rate governed high-rate response, energy evolution, and failure modes. Subsequently, an FDM-DEM coupled model was used to simulate the impact-induced behavior of concrete at multiaxial stress conditions and constraint conditions, analyzing the strain-rate dependent performance of concrete exposed to biaxial monotonic loading. Test outcomes indicate that the increase in strain rate significantly enhanced the dynamic peak stress, and the collapse behavior shifted from type I to type II. As static loading in the σ₂ direction increased, the dynamic peak stress in the σ₁ direction decreased, while the dynamic peak stress in the σ₂ direction increased, indicating that the constraint stress in the σ₂ direction had an inhibitory effect on the sample’s failure. Through the time-history monitoring and analysis of cracks, it was found that the internal crack growth rate accelerated as the stress increased, while the crack growth tended to stabilize when the stress decreased. Additionally, this study explored the effect of stress constraints on the fragmentation patterns, revealing changes in the failure modes and crack distributions of the sample under different stress states, providing a theoretical basis and technical support for island and reef construction and engineering protection. Full article

The accuracy of numerical predictions in sheet metal processes involving multiaxial stress–strain states (e.g., blanking, riveting, and incremental forming) heavily depends on the characterisation of plastic anisotropy under multiaxial loading conditions. A fully calibrated 3D plastic anisotropy model is essential for this purpose. While in-plane material behaviour can be conventionally characterised through uniaxial and equi-biaxial tensile tests, calibrating out-of-plane material behaviour remains a significant challenge. This behaviour, governed by out-of-plane shear stress and associated material parameters, is typically described by out-of-plane shear yielding. These parameters are notoriously difficult to determine, leading researchers to frequently assume isotropic behaviour or identical shear parameters for in-plane and out-of-plane responses. Although advanced calibrations may utilise crystal plasticity modelling, there remains a critical need for macro-mechanical characterisation methods. This paper presents an out-of-plane shear testing and material characterisation procedure based on full-field strain measurements using digital image correlation (DIC). Strains within the shear zone are measured via DIC and employed in the Finite Element Model Updating (FEMU) to identify out-of-plane shear parameters of a 2.42 mm thick, cold-rolled AW5754-H22 aluminium alloy sheet, using the Yld2004-18p yield criterion. Given that the characteristic strain response at this scale may be influenced by local crystal structure behaviour on the surface, this paper evaluates the feasibility of such measurements. Finally, to test the validity of the full-field-based approach, the FEMU-identified parameters are compared against results obtained through a classical optimisation procedure based on force-elongation measurements from the shear zone. Full article

The size of ships has increased considerably in recent decades. This growth impacts the stress magnitude in the bottom hull plates, which constantly suffer from biaxial compression and lateral water pressure, potentially leading to buckling. Adding stiffeners is an effective alternative to increase mechanical buckling resistance if placed in a proper way. Several researchers have investigated the influence of stiffeners on plates under different loading conditions. However, the behavior under combined biaxial compression and lateral pressure has not yet been widely explored. This work aims to verify and validate a computational model to analyze the elastoplastic buckling of plates under biaxial compression and lateral pressure, applying it in a case study to define the ideal geometric configuration to increase ultimate buckling resistance, using the constructal design method and exhaustive search technique. In this study, a portion of the volume from a reference plate without stiffeners was converted into stiffeners to determine the optimal geometry for maximizing ultimate buckling resistance. The numerical model was verified and validated, and the case study identified the optimal plate configuration with five longitudinal and four transverse stiffeners, with a height-to-thickness ratio of 8.70, achieving a 284% increase in ultimate buckling resistance compared to the reference plate. These results highlight the importance of geometric evaluation in structural engineering problems. Full article

The growing demand for electricity in developing countries has called attention and interest to renewable energy sources to mitigate the adverse environmental effects caused by energy generation through fossil fuels. Among different renewable energy sources, such as photovoltaic, wind, and biomass, hydraulic energy represents an attractive solution to address the demand for electricity in rural areas of Colombia that are not connected to the electrical grid. In the current paper, the fluid–structure interaction (FSI) of a recently designed Vertical-Axis Hydrokinetic Turbine (VAHT) Straight-Bladed (SB) Darrieus-type, modified with symmetric winglets, was studied by implementing the sliding mesh method (SMM). By coupling with Computational Fluid Dynamics (CFD) numerical simulations, the FSI study demonstrated that the hydrodynamic loads obtained can cause potential fatigue damage in the blades of the Straight-Bladed (SB) Darrieus VAHT. Fatigue life was assessed using the stress–life (S-N) approach, and materials such as structural steel, short glass fiber reinforced composites (SGFRC), and high-performance polymers (HPP), such as PEEK, were studied as potential materials for the construction of the blades. FSI results showed that the biaxiality index (BI) provides a good understanding of the dominant stresses in the blades as the azimuth angle changes. It was also shown that structural steel and PEEK are good materials for the manufacturing of the blades, both from a fatigue resistance and modal perspective. Full article