Search Results (51)

The SBPDN (Steel Bar Prestressed Deformed Normal relaxation) bar, which has ultra-high yield strength yet much lower bond resistance than conventional deformed bars, has been recently proposed to be used as the longitudinal rebar instead of a normal-strength deformed bar to simply realize strong earthquake-resilient concrete components. To facilitate and promote the application of concrete components reinforced with SBPDN rebars to the structures located in earthquake-prone regions, it is indispensable to develop reliable and effective anchoring means and clarify the bond strength of SBPDN bars embedded in concrete and/or grout mortar. This paper presents experimental information on the pull-out tests of fifteen SBPDN bars embedded in grout mortar, along with a discussion on the effective anchorage details and the bond strength of SBPDN bars. The tested SBPDN bars have a nominal diameter of 22.2 mm, the maximum diameter currently available on the market. All SBPDN bars were embedded in high-strength grout mortar with a targeted compressive strength of 60 MPa. The primary experimental variables included the end anchorage details, the diameter of sheath ducts, and the embedded length of the bars. Test results demonstrated that either screwing two nuts and a washer at the end of SBPDN bars or providing a rolling-threaded end region was effective in preventing them from premature slip from grout mortar. If the embedment length was 20 times the bar diameter or longer, the proposed two anchorages could ensure the SBPDN bar to fully develop its specific yielding strength as high as 1275 MPa. In addition, it has also been experimentally revealed that the bond strength of SBPDN bars embedded in grout mortar was much lower than that of conventional deformed bars and varied between 2.84 MPa and 3.98 MPa. Full article

Three-wheeled vehicles are increasingly adopted as sustainable transport solutions, but their asymmetric design and lightweight structure make them vulnerable to ride discomfort and rollover instability. This study develops a high-fidelity 12-degrees-of-freedom (DOF) dynamic model in MATLAB/Simulink and MSC ADAMS to analyze and improve ride comfort, handling, and roll stability. The model captures longitudinal, lateral, vertical, roll, pitch, and yaw motions, along with tire dynamics represented through the Magic Formula, and is validated using real-world data from an instrumented test vehicle. In this research, both active and passive control strategies were separately implemented and studied. The active strategy involves an Active Vehicle Roll Dynamics Control (VRDC) system with an active rear suspension to suppress roll and yaw during aggressive maneuvers. The passive strategy focuses on improving rollover resistance by modulating throttle input based on sensor data from gyroscopes, accelerometers, and compasses. Simulation and experimental results show that each strategy, when applied independently, enhances roll stability, reduces yaw rate deviations, and improves handling performance. These findings demonstrate the effectiveness of both approaches in improving the safety and dynamic behavior of electric three-wheeled vehicles under real-world conditions. Full article

This paper presents a stability analysis of single-channel, slow-rolling, Semi-Automatic Command to Line of Sight (SACLOS) missiles using a comparison of the Routh–Hurwitz and the Frank–Wall stability criteria and a nonlinear analysis. Beginning with a six-degree-of-freedom (6-DOF) model in the Resal frame, a linearized model for the commanded motion is developed. This linearized model, which features complex coefficients due to the coupling of longitudinal channels in rolling missiles, is used to define the structural scheme of the commanded object and its flight quality parameters. The guidance kinematic relations, guidance device equations, and actuator relations, incorporating a switching function specific to slow-rolling, single-channel missiles, are also defined and linearized within the Resal frame to construct a comprehensive structural diagram of the SACLOS missile. From this, the characteristic polynomial with complex coefficients is derived and analyzed by comparing the Routh–Hurwitz and the Frank–Wall stability criteria. This analysis determines a stability domain for the guidance gain and establishes a minimum limit for the guidance time. The stability domain defined through the linear model is then validated using a nonlinear model in the body frame. Full article

Current passive anti-rollover systems exhibit inadequate adaptability to complex operational environments. Additionally, due to unidentified critical factors driving rollover incidents during landing, the design of active anti-tipping systems for airdrop remains constrained. Given the foregoing circumstances, this paper divides the landing impact process of the vehicle into the airbag cushioning stage and the rigid collision stage. In the airbag cushioning stage, a vertical impact test bench and a fluid–structure interaction (FSI) model is built up to obtain the terminal impact velocity when the airbag’s touching down speed is set as around 8 m/s. An oblique impact test bench and a dynamic model are proposed to investigate the influence of terminal sideslip angles and impact velocities on the vehicle’s roll/pitch stability during the rigid collision phase. Experimental and numerical analyses reveal that the peak overload during the airbag cushioning stage reaches approximately 11 g while the terminal impact velocity in this stage is around 2 m/s. In the rigid collision stage, higher initial descent velocities amplify the peak roll angles and significantly compromise the roll stability. Notably, adjusting the terminal sideslip angle from 90° to 0°/180° triples the critical horizontal velocity threshold from 5.3 m/s to 14.7 m/s which markedly enhances the vehicle’s stability. To address this, an active sideslip angle control system activated at a 250 m altitude is developed to align the vehicle’s horizontal velocity vector with its longitudinal axis to nearly 0°/180° and thus improves the roll/pitch stability. This study establishes a technical foundation for the design of a highly reliable anti-rollover device for the airdrop vehicle. Full article

The present study examines the effect of a modified oval–round rolling scheme incorporating inclined oval calibers on the mechanical behavior and microstructural evolution of Mn–Si low-alloy steel (25G2S). Cylindrical billets were hot rolled through both classical and modified sequences under identical thermal and kinematic conditions. Tensile testing demonstrated that, relative to the unrolled condition (σ_0.2 ≈ 269 MPa; σᵤ ≈ 494 MPa), the classical route increased yield and ultimate strengths to ~444 MPa and ~584 MPa, respectively, whereas the modified scheme yielded comparable values (~433 MPa and ~572 MPa) while providing superior ductility (δ ≈ 26.8%, ψ ≈ 68.6%). Vickers microhardness decreased systematically from 244 HV (unrolled) to 213 HV (classical) and 184 HV (modified), with the modified scheme exhibiting the lowest scatter (±4.8 HV), confirming enhanced structural uniformity. Scanning electron microscopy revealed ferrite–pearlite refinement under both rolling sequences, with the modified scheme producing finer equiaxed ferrite grains (~3–5 µm) and attenuated longitudinal banding. These features are indicative of shear-assisted dynamic recrystallization, activated by the inclined oval calibers. The findings highlight that the modified rolling strategy achieves a favorable strength–ductility balance and improved homogeneity, suggesting its applicability for advanced thermomechanical processing of low-alloy steels. Full article

Rice membrane-covered cultivation offers notable agronomic advantages, including effective weed suppression and improved moisture retention. However, current mechanized approaches remain constrained by high labor requirements, low operational efficiency, and the inherent fragility of biodegradable membranes. To address these limitations, this study integrates a high-speed synchronous membrane-covering device, governed by a PSO-Fuzzy PID control algorithm, into a conventional rice transplanter. This integration enables precise coordination between membrane-laying and transplanting operations. The mechanical properties of the membranes were analyzed, and a tension evaluation model was developed considering structural parameters and roll diameter variation. Experimental tests on three biodegradable membranes revealed an average thickness of 0.012 mm, a longitudinal tensile force of 0.57 N, and a tensile strength of 2.85 N/mm. The PSO algorithm was employed to optimize fuzzy PID parameters (K = 5.3095, K_p = 10.6981, K_i = 0.0100, K_d = 8.2892), achieving adaptive synchronization between membrane output speed and transplanter travel speed. Simulation results demonstrated that the PSO-Fuzzy PID reduced rise time by 53.13%, stabilization time by 90.58%, and overshoot by 3.3% compared with the conventional PID. In addition, a dedicated test bench for the membrane-covering device was designed and fabricated. Orthogonal experiments determined the optimal parameters for the speed-measurement system: a membrane pressure of 5.000 N, a roller width of 28.506 mm, and a placement angle of 0.690°. Under these conditions, the minimum membrane-stretching tension was 0.55 N, and the rotational speed error was 0.359%. Field tests indicated a synchronization error below 1.00%, a membrane-width variation rate below 1.50%, and strong anti-interference capability. The proposed device provides an effective solution for intelligent and fully mechanized rice transplanting. Full article

It is important to accurately characterize the plane-stress state of pipe walls for evaluating the bearing capacity of the pipe and ensuring the structural safety. This paper describes a novel ultrasonic technique for evaluating anisotropic pipe-wall plane stresses using three-directional longitudinal critical refracted (LCR) wave time-of-flight (TOF) measurements. The connection between plane stress and ultrasonic TOF is confirmed by examining how the anisotropy of rolled steel plates affects the speed of ultrasonic wave propagation, which is a finding not previously documented in spiral-welded pipes. Then based on this relationship, an ultrasonic stress coefficient calibration experiment for spiral-welded pipes is designed. The results show that the principal stress obtained by the ultrasonic method is closer to the engineering stress than that obtained from the coercivity method. And, as a nondestructive testing technique, the ultrasonic method is more suitable for in-service pipelines. It also elucidates the effects of probe pressure and steel plate surface roughness on the ultrasonic TOF, obtains a threshold for probe pressure, and reveals a linear relationship between roughness and TOF. This study provides a feasible technique for nondestructive measurement of plane stress in anisotropic spiral-welded pipelines, which has potential application prospects in the health monitoring of in-service pipelines. Full article

Friction behaviour at the wheel–rail interface is of critical importance for railway operations and maintenance and is generally characterised by creep curves. The V-Track test rig was used in this study to measure both the lateral and longitudinal creep curves with uncontaminated dry interface conditions, utilising contact pressures representative of operational railway wheel–rail systems. The novelties of this study are threefold. 1. With proper representations of train/track components, the V-Track tests revealed the effects of structural dynamics on measuring wheel–rail creep curves in real life. 2. Pure lateral and longitudinal creepage conditions were produced with two distinct experimental principles—displacement- and force-controlled—on the V-Track, i.e., by carefully controlling the angle of attack and the traction/braking torque, respectively, and thus the coefficient of friction from lateral and longitudinal creep curves measured on the same platform could be cross-checked. 3. The uncertainties in the measured creep curves were analysed, which was rarely addressed in previous studies on creep curve measurements. In addition, the measured creep curves were compared against the theoretical creep curves obtained from Kalker’s CONTACT. The influence of wheel rolling speed and torque direction on the creep curve characteristics was then investigated. The measurement results and findings demonstrate the reliability of the V-Track to measure wheel–rail creep curves and study the wheel–rail frictional rolling contact. Full article

Buffer stops have always been installed on blind tracks to mitigate the hazards associated with overruns due to insufficient or wrong braking. Conventional buffer stops fixed to the rails may absorb only limited energy while Energy-Absorbing Buffers Stops (EABS) dissipate higher energy hydraulically and/or by friction from sliding blocks clamped to the rail head. The assessment of EABS performances in terms of maximum stopping distance and maximum allowed deceleration is usually performed by using the common kinematic rules of motion and considering the overrunning train as a single mass hitting the buffer stop. This paper studies the dynamic characteristics of the collision of entire trains with a friction EABS applying a Longitudinal Train Dynamics (LTD) approach. Several realistic scenarios using the UIC approved TrainDy software were simulated considering various train compositions, with different types of vehicles (locomotives, freight wagons and passenger coaches) and different kinds of buffers. The results show that high dynamic loads are exerted on the vehicles within the train, while the average deceleration and the stopping distance are not greatly influenced when compared with a simpler Finite Element Method (FEM) approach that does not consider the train composition. The progressive application of the EABS braking force increases the stopping distance but can reduce the peak deceleration of about 50%. The results may be used to tune the design parameters of friction EABS according to the currently available specifications and standards for rolling stock structural assessment considering that no international standards for EABS exist currently. Full article

The construction industry faces increasing pressure to reduce energy consumption and carbon emissions. Promoting sustainable practices, such as using hot-rolled H-shapes and minimizing welding, can address these challenges. This study introduces low-carbon H-shape bolted composite beams (HBCBs) as a sustainable alternative. Experimental and numerical investigations into the lateral-torsional buckling behavior of HBCBs demonstrated that high-strength bolts significantly enhance structural stability and capacity. A reliable simulation method was developed and validated based on experimental results. The study reveals that bolt spacing exceeding 1/15 of the beam span has negligible effects on load-bearing capacity, and HBCB performance reaches approximately 95% of plug-welded counterparts. Despite this, longitudinal slip reduction remains challenging, warranting further research to optimize performance. Full article

The paper starts by describing the manufacturing process of cups thermoformed from extruded foils of 80% recycled PET (80r-PET), which comprises heating, hot deep drawing and cooling. The 80r-PET foils were heated up to 120 °C, at heating rates of the order of hundreds °C/min, and deep drawn with multiple punchers, having a depth-to-width ratio exceeding 1:1. After puncher-assisted deformation, the cups were air blown away from the punchers, thus being “frozen” in the deformed state. Due to the high cooling rate, most of the polymer’s structure reached a rigid, glassy state, the internal stresses that tended to recover the flat undeformed state were blocked and the polymer remained in a temporary cup form. When heating was applied, glass transition occurred, and the polymer reached a rubbery state and softened. This softening process released the blocked internal stresses and the polymer tended to recover its flat permanent shape. This relative volume contraction quantitatively describes the shape memory effect (SME) which can be obtained either with free recovery (FR-SME) or with work generation (WG-SME) when the cups lifted their bottoms with different loads placed inside them. The paper discusses the results obtained by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), room-temperature tensile failure tests (TENS) and scanning electron microscopy (SEM). The DSC charts emphasized a glass transition, responsible for SME occurrence. The DMA thermograms and the TENS curves revealed that there are slight differences between the storage modulus and the tensile strains of the specimens cut on longitudinal, transversal, or 45° to the film rolling direction. The SEM micrographs enabled to observe structural differences between the specimens cut parallelly and transversally to the film’s rolling direction. The thermoformed cups were heated on a special experimental setup, which enabled the determination of FR-SME and WG-SME after applying different maximum temperatures and loads placed into the cups, respectively. Full article

Automotive structural components from Advanced High-Strength Steels (AHSS) can be manufactured with Flexible Roll Forming (FRF). The application of FRF in the automotive industry is limited due to flange wrinkling defects that increase with material strength. The new Incremental Shape Rolling process (ISR) has been shown to reduce wrinkling severity compared to FRF and therefore presents a promising alternative for the manufacture of high-strength automotive components. The current work analyzes for the first time the mechanisms that lead to wrinkling reduction in ISR based on the critical stress conditions that develop in the flange. For this, finite element process models are validated with experimental forming trials and used to investigate the material deformation and the forming stresses that occur in FRF and ISR when forming a variable-width automotive component. The results show that in ISR, the undeformed flange height decreases with increasing forming; this increases the critical buckling and wrinkling stresses with each forming pass and prevents the development of wrinkles towards the end of the forming process. In contrast, in FRF, the critical buckling or wrinkling stress is constant, while the longitudinal compressive stress in the flange increases with the number of forming passes and exceeds the critical stress. This leads to the development of severe wrinkles in the flange. Full article

Evaluating the current technical condition and residual life of structures that may have reached or exceeded the end of their design life is a challenging issue in many industrial sectors. This paper focuses on the assessment of the structural integrity of structural elements of a seaport portal crane after operation for about 33 years. Test specimens were extracted from two crane elements, a jib (element A) as the most seriously loaded unit and, for comparison, a boom (element B) as the less loaded one, and machined in two different orientations, longitudinal and transversal. Both crane elements were made of a low-carbon rolled steel. The analysis was performed according to the FAD approach of FITNET Procedures. The basic level of analysis was used. For this purpose, the strength and fracture toughness characteristics of the steel from tested elements were determined experimentally. The strength and plasticity properties of the steel of both elements were similar. At the same time, the fracture toughness characteristics differ for the elements A and B and for the longitudinal and transverse specimen directions. The results of the FAD (FITNET) analysis performed for the elements containing a central crack loaded by tensile stress showed that they are not susceptible to failure. The relative length of cracks for which the critical state will be reached is also estimated. Full article

In this paper, nonlinear system identification using Bayesian network has been implemented to discover open-loop lateral-directional aerodynamic model parameters of an agile aircraft using a grey box modelling structure. Our novel technique has been demonstrated on simulated flight data from an F-16 nonlinear simulation of its Flight Dynamic Model (FDM). A mathematical model has been obtained using time series analysis of a Box–Jenkins (BJ) model structure, and parameter refinement has been performed using Bayesian mechanics. The aircraft nonlinear Flight Dynamic Model is adequately excited with doublet inputs, as per the dictates of its natural frequency, in accordance with non-parametric modelling (Finite Impulse Response) estimates. Time histories of optimized doublet inputs in the form of aileron and rudder deflections, and outputs in the form of roll and yaw rates are recorded. Dataset is pre-processed by implementing de-trending, smoothing, and filtering techniques. Blend of System Identification time-domain grey box modelling structures to include Output Error (OE) and Box–Jenkins (BJ) Models are stage-wise implemented in multiple flight conditions under varied stochastic models. Furthermore, a reduced order parsimonious model is obtained using Akaike information Criteria (AIC). Parameter error minimization activity is conducted using the Levenberg–Marquardt (L-M) Algorithm, and parameter refinement is performed using the Bayesian Algorithm due to its natural connection with grey box modelling. Comparative analysis of different nonlinear estimators is performed to obtain best estimates for the lateral–directional aerodynamic model of supersonic aircraft. Model Quality Assessment is conducted through statistical techniques namely: Residual Analysis, Best Fit Percentage, Fit Percentage Error, Mean Squared Error, and Model order. Results have shown promising one-step model predictions with an accuracy of 96.25%. Being a sequel to our previous research work for postulating longitudinal aerodynamic model of supersonic aircraft, this work completes the overall aerodynamic model, further leading towards insight to its flight control laws and subsequent simulator design. Full article

Under the background of dual carbon policy as well as energy conservation, blanks with variable thicknesses (BVTs) which act as structural components have drawn extensive attention due to their excellent strength and formability and reasonable load-bearing distribution characteristics, particularly in the field of automotive manufacturing. With these advantages, the manufacturing technologies of these plates using more efficient rolling methods have thus emerged. This article summarizes four methods and their characteristics for manufacturing plates with variable thicknesses based on rolling technology. In addition, a review is conducted on the latest research progress of the metal flow and rolling theories of existing plates with different thicknesses in the longitudinal and transverse direction. Full article