Search Results (25)

Fire safety design for steel beams is crucial in the construction of steel structures. However, there remains a significant gap in the fire resistance testing of insulated steel beams. This study focuses on full-scale experimental research examining the fire resistance performance of steel beams with varying fire protection methods, cross-sectional dimensions, and heating curves. During the tests, the furnace temperature, specimen temperature, and deflection at mid-span were measured. The test results indicated that specimens mainly failed in lateral–torsional buckling. Additionally, a markedly non-uniform temperature distribution was observed across the cross-section, and the predictions made by GB 51249-2017 were found to be unsafe. The use of fiber cement board for fire protection may be ineffective, as it tends to become brittle at elevated temperatures, making it susceptible to breakage and detachment when the beams begin to bend. Furthermore, due to potential creep deformation, specimens subjected to longer heating durations exhibited lower critical temperatures compared to those with shorter heating durations. Finally, the design method outlined in BS EN 1993-1-2 and ANSI/AISC 360-22 was evaluated against the test results, indicating an accurate prediction of these methods for specimens with shorter heating durations, but an unconservative prediction for specimens with longer heating durations due to ignorance of creep deformation. Full article

The intricate and dynamic cutting behavior observed in titanium alloy turning leads to non-uniform surface and subsurface properties in the workpiece, impacting torsional strength and fatigue life. A transient pose model, founded on the configuration of a turning tool, is developed to elucidate the evolution of the transition surface during transient turning. Through finite element simulation, the plastic deformation, residual stress, and work hardening rate of the machined surface and subsurface of a titanium alloy are quantitatively examined. The torsional strength and fatigue life calculation method is developed based on initial performance parameters derived from the finite element model. This method enables the correlation identification between surface morphology characteristics, surface and subsurface performance parameters, and fatigue properties. Surface morphology, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) are employed to quantitatively analyze the surface features and elemental composition of the titanium alloy turning surface, unveiling their influence on torsional fatigue properties. The findings demonstrate the efficacy of the proposed models and methodologies in identifying the torsional fatigue properties and their distribution patterns of titanium alloy turning surfaces. Full article

Carbon fiber-reinforced epoxy composites, known for their high specific stiffness, specific strength, and toughness are one of the primary materials used for composite nozzles in aerospace industries. The high temperature vibration behaviors of the composite nozzles, especially those that withstand internal pressures, are key to affecting their dynamic response and even failure during the service. This study investigates the changes in frequencies and the vibrational modes of the carbon fiber reinforced epoxy nozzles, focusing on a three-dimensional (3D) orthogonal woven composite, with high internal temperatures from 25 °C to 300 °C and non-uniform internal pressures, up to 5.4 MPa. By considering the temperature-sensitive parameters, including Young’s modulus, thermal conductivity, and thermal expansion coefficients, which are derived from a self-built representative volume element (RVE), the intrinsic frequencies and vibrational modes in composite nozzles were examined. Findings reveal that 2 nodal diameter (ND) and 3ND modes are influenced by $E_{xx}$ and $E_{yy}$ while bending and torsion modes are predominantly affected by shear modulus. Temperature and internal pressure exhibit opposite effects on the modal frequencies. When the inner wall temperature rises from 25 °C to 300 °C, 2ND and 3ND frequencies decrease by an average of 30.39%, while bending and torsion frequencies decline by an average of 54.80%, primarily attributed to the decline modulus. Modal shifts were observed at ~150 °C, where the bending mode shifts to the 1st-order mode. More importantly, introducing non-uniform internal pressures induces the increase in nozzle stiffening in the xy-plane, leading to an apparent increase in the average 2ND and 3ND frequencies by 17.89% and 7.96%, while negligible changes in the bending and torsional frequencies. The temperature where the modal shifts were reduced to ~50 °C. The research performed in this work offers crucial insights for assessing the vibration life and safety design of hypersonic flight vehicles exposed to high-temperature thermal vibrations. Full article

This paper presents an extended method for determining flow curves under shear loading using torsion tests, a technique often used to characterize plastic behavior in metal forming. Torsion tests are advantageous due to their ability to achieve flow curves up to large strains (~3) while maintaining stable specimen geometry during deformation. However, the strain and strain rate distribution across the specimen are non-uniform, increasing radially from the rotation axis. Traditional analytical methods, such as the Fields and Backofen approach, address this non-uniformity by considering average strain and strain rates. Conversely, inverse approaches, which rely on fitting constitutive equations through iterative procedures, are more sensitive to the choice of empirical equations and can be computationally expensive. To address these issues, this study adapts an inverse piecewise flow curve determination method from compression tests for use in torsion tests. A stepwise methodology is proposed to calculate constant strain rates and isothermal flow curves, where flow curves for the lowest strain rates are first determined and subsequently used to derive flow curves at higher strain rates. The proposed approach was applied to the case-hardened steel 16MnCrS5, with tests conducted at temperatures ranging from 900 °C to 1100 °C and strain rates from 0.01 s⁻¹ to 1 s⁻¹. The experimental data obtained were successfully replicated by the flow curves with a maximum deviation of only 1%. The results demonstrate the efficiency and accuracy of the stepwise inverse approach for determining flow curves in torsion tests, making it appropriate for characterizing material behavior for metal-forming applications. Full article

This study utilizes the inverse finite element method (iFEM) to investigate the strain field reconstruction of ship stiffened plates under multiple loading conditions. The aim is to enhance the monitoring, safety, and reliability of ship structures through multi-condition strain field reconstruction. By applying iFEM, this research addresses the challenge of reconstructing strain fields from discrete strain measurements using a least-squares variational equation derived from elastic mechanics principles. The performance of iFEM was evaluated under five loading conditions: axial compression, non-uniform loading, torsion, combined axial compression with non-uniform loading, and combined axial compression with symmetric uniform loading. To mitigate boundary effects, an extended stiffened plate design was implemented. The results show significant improvements in reconstruction accuracy: under two specific loading conditions, the precision improved by 38.82% and 11.25%, respectively, compared to the original plate. This study underscores the potential of iFEM in improving the monitoring and safety of marine structures. Future work could explore the applicability of iFEM to other marine structures and scenarios, ensuring broader practical applications. Full article

Computational crystal plasticity (CP) models are widely utilized in the literature to analyze the deformation responses of materials at the microstructural level under macroscopic loading conditions. The challenge of connecting changes in texture with macroscopic loading can be effectively addressed through a multiscale CPFE approach. This research focuses on bridging changes in texture and macroscopic loading in pure aluminum wire under torsional loading through the innovative use of the multiscale CP finite element simulation approach and integration with experimental data. The study deals with the effects of the initial average grain size, strain rate, and strains on microstructural evolution at room temperature and mechanical properties. An inhomogeneous initial texture for an as-received specimen was extracted using EBSD measurements and assigned to a CP code to solve the multiscale CPFEM simulations. Changes in texture obtained from pole figures indicated that the $A (11\overline{1})[1\overline{1}0],B (11\overline{2})[1\overline{1}0], \overline{B} (\overline{1}\overline{1}2)[\overline{1}10], C (100)[0\overline{1}1], A_1^{\ast } (11\overline{1})[2\overline{1}1],$ and $A_2^{\ast }$($1\overline{1}1$) [$\overline{2}\overline{1}1$] components had the highest frequencies among the torsional tests. The analysis of the resulting texture through the Taylor factor (TF) revealed that the average TF distribution increased from 2.65 to 3.04 when the local strain increased from 0.5 to 2.5 revolutions. Furthermore, an increase in the number of rotations from 0.5 to 2.5 resulted in an 11% increase in average hardness near the outer surface of specimens with an average grain size of 55 µm. Full article

To study the aerodynamic and vibration characteristics of iced conductors under the influence of wind fluctuations, a harmonic superposition method is used to simulate nonuniform wind speeds. A user-defined function is written on the basis of the secondary development function of the Fluent 2021 R1 software to determine the displacement and velocity of the conductor at each time step, and a two-way fluid–structure interaction (FSI) numerical simulation of an iced conductor under a nonuniform wind field is performed via an overset mesh method. In the analysis, the aerodynamic coefficients and galloping characteristics of iced conductors under different degrees of freedom (DOFs) are investigated by considering different combinations of quasi-steady theory, unsteady theory, a uniform wind field, and a nonuniform wind field. The results show that in a nonuniform wind field, the mean, standard deviation (SD), and peak values of the drag and torsion coefficients of the conductors calculated via unsteady theory are significantly larger than those calculated via quasi-steady theory, indicating that the obtained aerodynamic coefficients of the latter (the mean values are typically used) conceal the characteristics of the iced conductors in an actual wind environment and ignore the adverse effects of the variability. Full article

Three titanium alloys with 0.5, 6, and 9 wt.% iron were investigated, and the samples were pre-annealed in three different regions of the Ti–Fe phase diagram, namely β, α+β, and α+FeTi. After annealing, five samples of different phases and structural compositions were studied. They were then subjected to the high-pressure torsion (HPT). The microstructure of the samples before and after HPT treatment was studied using transmission and scanning electron microscopy. The microstructure of the samples obtained during heat treatment before HPT treatment had a fundamental effect on the microstructure after HPT. Grain boundary layers and chains of particles formed during the annealing process made it difficult to mix the material during HPT, which led to the formation of areas with non-uniform mixing of components. Thus, the grain boundary layers of the α-phase formed in the Ti–6wt % Fe alloy after annealing at 670 °C significantly decreased the mixing of the components during HPT. Despite the fact that the microstructure and phase composition of Ti–6wt % Fe alloys pre-annealed in three different regions of the Ti–Fe phase diagram had significant differences, after HPT treatment, the phase compositions of the studied samples were quite similar. Moreover, the measured micro- and nanohardness as well as the Young’s modulus of Ti–6wt % Fe alloy had similar values. It was shown that the microhardness of the studied samples increased with the iron content. The values of nanohardness and Young’s modulus correlated well with the fractions of β- and ω-phases in the studied alloys. Full article

Marine vessels rely heavily on propeller shaft systems to adjust the engine torque and propeller thrust. However, these systems are subjected to various dynamic excitations during operation, such as transverse, longitudinal, and torsional excitations. These excitations can arise from factors like non-uniform stern flow fields, misaligned components, and the whirling motion of the shafts, which can affect the integrity and reliability of the vehicle. To analyze the dynamic response of the propulsion shaft system and ensure its reliability, numerical/analytical models are currently in practice. The finite element method (FEM) is a popular choice, but uncertainties in bearings and connectors stiffness lead to inaccuracies in the Finite Element model, resulting in significant differences between the experimental and theoretical models. This paper proposes the response surface optimization (RSO) technique to estimate unknown bearing stiffness in the propulsion shaft system. The experimental model of the propeller shaft system is constructed using steady-state response with step sine excitation. The RSO technique is then used to update the natural frequencies and vibration amplitude of the FE (Finite Element) model. The updated model shows less than a 10% difference in natural frequencies and vibration amplitude compared to the experimental model, demonstrating that the proposed technique is an efficient tool for marine shaft dynamic analysis. Full article

During the operational phase of a bridge, the crossbeam, acting as a supporting member, plays an important role in keeping the cross-sectional shape constant in addition to resisting against various lateral and longitudinal loads and distributing the dead and the live loads to the adjacent main girders. The complex functional requirements lead to a complex internal force composition of the crossbeam. When subjected to torque, the two main beams of the twin I-girder bridge will have deformation in opposite longitudinal directions (known as warping deformation) to counteract the torque. The existing research has not considered the impact of main beam warping deformation on the internal force of the crossbeam. Based on the existing research, this article further considers the impact of main beam warping deformation on the internal force of the crossbeam, making the calculation of the internal force of the crossbeam more accurate. The results show that the torsional characteristics of the continuous twin I-girder bridge can be calculated using Vlasov’s theory of thin-walled structures combined with the displacement method. As for the effect of the crossbeam on the torsional stiffness of the structure, it can be managed by making the crossbeam stiffness continuous; however, in general, the equivalent stiffness is small compared to the stiffness of the main beam and it can be ignored. The crossbeam can be simplified to a bar with two solid ends for the internal force calculation whose formula is proposed in this paper, based on the existing frame model, and it can further consider the influence of warping deformation of the main beam on the internal force of the beam, and the calculation accuracy is high. Full article

The research on structural features, microhardness distribution, and deformation features of Vit105 bulk metallic glass (BMG) before and after high-pressure torsion (HPT), as well as after relaxing annealing, has been carried out. HPT n = 1 leads to an increase in free volume ΔV, and relaxing annealing leads to a decrease in ΔV and non-uniformity relative to the initial state of BMG. In the initial BMG and in the BMG after relaxing annealing, microhardness is uniformly distributed over the surface, while in the material subjected to HPT, the microhardness distribution is more heterogeneous. The bonded-interface indentation of the BMG has been conducted in different states. The formation of numerous concentric bands around the indenter is observed. The pattern of band distribution is more homogenous in Vit105 BMG alloy before HPT. In relaxed samples, the bands often have fractures and irregularities, as well as cracks that can be seen under the indents. After HPT, the formation of several intensity bands can be observed, as well as a number of low-intensity ones between the main intensity bands. The average distance between the bands in the initial BMG and BMG after HPT is close to identical, while the distance between the bands is smaller in the relaxed state, which reflects the lower plasticity of the material after annealing. Full article

The present work aims to design a robust method to detect and certify the deterministic chaos or ergodic process for the forced torsional vibrations (FTV) of a double tripod industrial driveshaft (DTID) in transition through the principal parametric resonance region (PPRR) which is considered by the researchers in the field as one of the most important resonance regions for the systems having parametric excitations. The DTID’s model for FTV considers the following effects: nonuniformities of inertial characteristics of the DTID’s elements, the harmonic torque excitation induced by the asynchronous electrical motor used for a heavy-duty grain mill, and the harmonic reaction torque generated by different granulation of the substance needed to be milled. Based on these aspects, a model of the FTV for the DTID was designed which was a modified, physically consistent model already used by the authors to investigate the FTV of automotive driveshafts (homokinetic transmission). For the DTID elements, the dynamic instability for nonstationary FTV in the PPRR using time–history analysis (THA) was analyzed—THA represents the phase portraits. Time–history analysis is a detection method for possible chaotic dynamic behavior for the nonstationary FTV (NFTV) in transition through PPRR. If this dynamic behavior was seen, a new robust method LEA–PM was created to certify and confirm the deterministic chaos for the NFTV of DTID. The new method, LEA–PM, is composed of the Lyapunov exponent’s approach (LEA) coupled with the Poincaré Map (PM) applied to the global system of differential equations that describe the FTV of DTID in the PPRR. This new robust method, which embeds LEA and PM, LEA–PM, establishes if the mechanical system has a deterministic chaotic dynamic behavior (strange attractor) or an ergodic dynamic process in this resonant region. LEA represents a new method that includes not only the maximal Lyapunov exponent method (MLEM) but also new mathematical criteria that is “the sum of all Lyapunov exponents has to be negative” which, coupled with MLEM, indicates the presence of deterministic chaos (strange attractors). THA–LEA–PM had been used for the NFTV of DTID computing the phase portraits, the Lyapunov exponents, and representing the Poincaré Maps of the NFTV for the DTID’s elements in transition through PPRR, founding deterministic chaos or ergodic dynamic behavior. Based on the obtained results, numerical simulations revealed the pitting manifestations of the DTID’s elements, typical for the geared systems transmission, mentioned recently in experimental data research for the homokinetic transmissions. Using the new robust method, THA–LEA–PM (time–history analysis coupled with LEA–PM) can be used in future research for chaotic dynamic analysis of DTID’s NFTV transition through superharmonic resonances, subharmonic resonances, combination resonances, and internal resonances. Time–history analysis as a detection method for chaos and LEA–PM as a certifying method for deterministic chaos can be integrated as a design tool for DTID’s FTV control of the homokinetic transmission. Full article

Unstiffened steel plate walls (SPWs) are prone to buckling in practical engineering and will invariably be subjected to vertical loads. The use of stiffeners can improve the buckling behavior of thin plates. Considering the effect of the torsional stiffness of C-shaped stiffeners, the elastic buckling of the diagonally stiffened steel plate wall (DS-SPW) under combined shear and non-uniform compression is investigated. The interaction curves for the DS-SPW under combined action are presented, as well as a proposed equation for the elastic buckling coefficient. In addition, the effects of the stiffener’s flexural and torsional stiffness on the elastic buckling stress were investigated, and the threshold stiffness formulae were proposed. The results show that the interaction curve of the DS-SPW under combined shear and non-uniform compression is approximately parabolic. The critical buckling stress of the DS-SPW can be increased by increasing the stiffener’s torsional-to-flexure stiffness ratio and the non-uniform compression distribution factor, while the buckling stress can be decreased by increasing the non-uniform compression-to-shear ratio. Simultaneous action of shear and axial compression will increase the threshold stiffness by approximately 40% when compared to the plate under pure shear action. Therefore, the safety threshold stiffness formula is suggested, considering the combined action of shear and non-uniform compression. Full article

The aim of this research was to design a physically consistent model for the forced torsional vibrations of automotive driveshafts that considered aspects of the following phenomena: excitation due to the transmission of the combustion engine through the gearbox, excitation due to the road geometry, the quasi-isometry of the automotive driveshaft, the effect of nonuniformity of the inertial moment with respect to the longitudinal axis of the tulip–tripod joint and of the bowl–balls–inner race joint, the torsional rigidity, and the torsional damping of each joint. To resolve the equations of motion describing the forced torsional nonlinear parametric vibrations of automotive driveshafts, a variational approach that involves Hamilton’s principle was used, which considers the isometric nonuniformity, where it is known that the joints of automotive driveshafts are quasi-isometric in terms of the twist angle, even if, in general, they are considered CVJs (constant velocity joints). This effect realizes the link between the terms for the torsional vibrations between the elements of the driveshaft: tripode–tulip, midshaft, and bowl–balls–inner race joint elements. The induced torsional loads (as gearbox torsional moments that enter the driveshaft through the tulip axis) can be of harmonic type, while the reactive torsional loads (as reactive torsional moments that enter the driveshaft through the bowl axis) are impulsive. These effects induce the resulting nonlinear dynamic behavior. Also considered was the effect of nonuniformity on the axial moment of inertia of the tripod–tulip element as well as on the axial moment of inertia of the bowl–balls–inner race joint element, that vary with the twist angle of each element. This effect induces parametric dynamic behavior. Moreover, the torsional rigidity was taken into consideration, as was the torsional damping for each joint of the driveshaft: tripod–joint and bowl–balls–inner race joint. This approach was used to obtain a system of equations of nonlinear partial derivatives that describes the torsional vibrations of the driveshaft as nonlinear parametric dynamic behavior. This model was used to compute variation in the natural frequencies of torsion in the global tulip (a given imposed geometry) using the angle between the tulip–midshaft for an automotive driveshaft designed for heavy-duty SUVs as well as the characteristic amplitude frequency in the region of principal parametric resonance together the method of harmonic balance for the steady-state forced torsional nonlinear vibration of the driveshaft. This model of dynamic behavior for the driveshaft can be used during the early stages of design as well in predicting the durability of automotive driveshafts. In addition, it is important that this model be added in the design algorithm for predicting the comfort elements of the automotive environment to adequately account for this kind of dynamic behavior that induces excitations in the car structure. Full article

Due to structural irregularity, curved bridgesaremore likely to cause non-uniform collisions and unseating between adjacent components when subjected to earthquakes. Based on the analysis of the collision response of curved bridges duringearthquakes, and according to the seismic characteristics of curved bridges, research was carried out on pounding mitigation and unseating prevention measures. A curved bridge with double column piers was taken as an engineering example, and a finite element model of curved bridges thatcould consider the non-uniform contact collision between adjacent components was built with ABAQUS software. Viscoelastic dampers, viscous dampers, and a lead rubber bearing were selected as the damping devices, and a steel wire rope-rubber mat was used as the pounding mitigation device to form the combinatorial seismic mitigation system. Based on the principle of energy dissipation combined with constraints, three kinds of combined seismic mitigation case were determined; a seismic response analysis was then performed. The results indicated that the three kinds of combined seismic case were effective atreducing the response topounding force, stress, damage, girder torsion and displacement, and achieved the goals of seismic mitigation and unseating prevention. Full article