Advances in Science and Technology Vol. 158

Abstract: A single pocket cage is the SKF product, which is used in Large Size Bearings for wind industry. The function of a bearing cage is to hold, guide and separate rolling elements, and differently from the conventional cage, the current one consists of segments, which eases the bearing assembly and reduces its weight. The long life challenge (25 years!) requires considering fatigue, and since the single pocket cage is made of PEEK polymer, it is also susceptible to creep (in near room temperature), which enhances fatigue damage. The current work proposes the numerical model capturing non-linear viscoelasticity of PEEK. The mechanical behavior of this material is identified in uniaxial tension test and is modeled in Finite Elements (FE) by means of the Parallel Rheological Framework (this numerical tool has been recently implemented in the commercial software ABAQUS). The current FE model enables to apply cyclic loading, simulating the material response of cage when it operates in running bearing. By applying sub-modeling technique only a small domain is modeled which improves the computational time efficiency. The sub-model domain corresponds to the cage region, where the stress is high resulting to the material yielding, fatigue/creep degradation (due to inelastic cyclic deformation) and initiation of fatigue crack. The FE results were combined with the test data, in attempt to relate the numerically predicted damage to the cage life. The development of irreversible deformation during cyclic loading, shakedown analysis and the stress volume effect, are the main focuses of the current work.

Abstract: In industrial settings, the use of frictional noise to improve wear monitoring is highly promising. It enables the identification of changes in friction and wear conditions, the assessment of different phases of wear, and the examination of the impact of wear on machine performance. By analysing acoustic signatures, it is conceivable to continuously monitor the wear characteristics and surface conditions. This helps in predicting wear and detecting aberrant wear regimes in real-time. The data demonstrate that in dry conditions, the aluminum disc has higher coefficients of friction relative to cast iron and mild steel, likely due to the absence of graphite flakes in aluminum. Under lubricated conditions, a layer of lube significantly decreases the coefficient of friction, with no apparent deviations across the materials, demonstrating that complete lubrication avoids direct metal contact. In lubrication-starved applications, oily depictions nevertheless help minimize friction, though less efficiently than complete lubrication. In dry conditions, frictional sound levels for mild steel are higher due to direct surface hits, while lubrication reduces noise by eliminating metal-on-metal contact. As a result, monitoring noise levels is a helpful indicator of lubrication difficulties, aiding in maintenance and repairs.

Abstract: Carrier-based aircraft takeoff and landing devices endure repeated high-speed, high-energy, and high-load impacts during operation. This repeated impact results in fatigue damage, a primary cause of failure in these devices, commonly known as impact fatigue. To address multiple impact fatigue failures in the takeoff and landing process of carrier-based aircraft, an investigation into the three-point bending impact fatigue characteristics of ultra-high-strength steel 23Co14Ni12Cr3MoE (abbreviated as A100 material) was conducted using experimental and microscopic techniques. A reproducible impact loading device for three-point bending tests was devised, leveraging a drop hammer impact tester. This innovative setup enabled the proposal of a three-point bending impact fatigue testing method. Test specimens featuring U-shaped, V-90°, and V-60° notches were designed, drawing inspiration from the Charpy pendulum impact test for metallic materials (GB/T 229-2007). Impact fatigue testing was then performed on the drop hammer tester across five distinct energy levels: 25J, 30J, 35J, 40J, and 45J.The study comprehensively examined the load response, energy absorption, and fatigue life of the A100 material in relation to the number of notches and impacts. Post-experiment analysis using a light microscope and SEM electron microscope revealed key morphological features of the A100 material's impact fatigue fracture surface: the crack initiation zone, stable crack propagation zone, rapid crack propagation zone, and shear lip area. Notably, as impact energy rose, the crack propagation zone expanded, while the shear lip area contracted.These findings contribute significantly to understanding the fatigue behavior of A100 material under repeated impact conditions, critical for enhancing the durability and safety of carrier-based aircraft takeoff and landing devices.

Abstract: Thermal property of carbon fiber-reinforced polymer composites (CRFPs) fabricated through vacuum assisted resin transfer molding method (VARTM) is investigated using Thermo Gravimetric Analysis/Differential Scanning Calorimetry tool. These analysis on laminate composites with three different orientations are carried out at room temperature up to 800°C. Also, mechanical and water absorption behavior of polymeric composites are determined. Among the orientation effect, a longitudinal direction sample including 39 vol. % carbon fiber in epoxy resin indicated that the mass loss in percentage was lower while decomposition temperature was higher than those of others due to higher mechanical strength. These composites revealed the most thermally stable among the others. Further, lower amounts of water absorption rates were obtained at 0^o-orientation, followed by 0/90^o-orientation composites, but no significant variations occurred with these orientations while some variations occurred for 30^o-orientation with increasing the soaking times.

Abstract: Sterling silver commonly uses copper as its primary alloying element, which enhances hardness. However, the presence of copper can cause a fire stain—a red spot microstructure—leading to tarnishing issues. This research focuses on reducing the copper content and developing suitable processes to enhance hardness through the use of three different alloy compositions within the AgCu and AgCuZnNi systems: Alloy SA (92.5 wt% Ag - 7.5 wt% Cu), Alloy A (93.5 wt% Ag - 5.01 wt% Cu - 0.79 wt% Zn - 0.70 wt% Ni), and Alloy B (94.5 wt% Ag - 4.24 wt% Cu - 0.63 wt% Zn - 0.63 wt% Ni). Precipitation hardening was measured at temperatures of 250 °C, 350 °C, and 450 °C for various durations ranging from 15 to 180 minutes. The results demonstrated an improvement in hardness, increasing from 60-70 HV to 120-160 HV after the heat treatment, with optimal results achieved for Alloy B at a temperature of 350 °C for one hour. This refined alloy composition presents a viable alternative, offering reduced copper content while maintaining enhanced mechanical strength and long-term durability post-heat treatment. Furthermore, the CIELAB test confirmed that Alloy B exhibits superior tarnish resistance. The composition and optimized process outlined in this research can serve as a guideline for producing sterling silver for commercial applications.

Abstract: Structural health monitoring (SHM) is a burgeoning area of interest among modern research endeavors, motivated by the application of state-of-the-art machine learning models. During the last few years, many researchers have proposed techniques for the analysis of SHM datasets, particularly those corresponding to sequence data collected from sensors. Following the flow of this research, in this work, we introduce an effective approach utilizing eXtreme Gradient Boosting (XGBoost), a potent ensemble learning framework rooted in gradient boosting for damage detection. A dataset of damage cases from the Nam O bridge, a steel truss bridge for railways, is applied to assess damages. To evaluate the effectiveness of the method used, common DL models such as One-Dimensional Convolutional Neural Network (1DCNN) and Long Short-Term Memory (LSTM) are also considered. Moreover, the influence of the boosting round on the overall result will be analyzed. The results from the validation set and the test set both illustrate that XGBoost performs better in accuracy than 1DCNN and LSTM with 100% and 95.7%, respectively. Besides, XGBoost is the model that achieved the lowest mean square error (MSE) of only 4.3% in the test set. These results demonstrate the significant potential of utilizing the XGBoost model in SHM and truss bridge structures, especially through the utilization of time-series data.

Abstract: Fire produces unique effects on steel structures which can compromise the residual capacity and therefore the structural response if they impact jointly with other natural hazards, such as earthquakes. This work presents a procedure that allows for the extension of the analysis method introduced in the 1990s by Fajfar and Gaspersic and outlined in EC8 (referred to as the N2 method) for the case of Multi-Hazard (MH) analysis, specifically for hazard-chain scenarios involving earthquake and fire. The goal is to assess the structural performance at the end of the sequence of considered events. By appropriately modeling the structure considering elasto-plastic behaviour, it becomes possible to observe the structural response as the plasticization of structural elements progresses: in this context, accounting for material and geometric nonlinearities has proven essential, since the material and structure's behaviour under fire are governed by complex phenomena, due to the significant deformations and distortions involved. The hazard-chain scenario here discussed is characterised by the consecutiveness of main earthquake event and fire; the proposed procedure is then applied to a 2D steel structure. Results highlight that neglecting possible hazard interactions could lead to an erroneous evaluation of the residual structural capacity.

Abstract: Next generation rolls such as super-cermet rolls and all-ceramic rolls can be manufactured using only sleeve assembly type rolls, which have the advantage of being able to reuse the shaft by replacing the damaged sleeves. However, in some cases, failures with unknown causes may occur such as circumferential slippage, shaft pull-out or residual bending deformation at the shrink-fit interface. Such slipping failures cannot be prevented by conventional design concept. This is because even if the resistant torque is greater than the motor torque, the circumferential slippage will occur. Through numerical simulation and miniature roll experiment, the following results are obtained. 1) Even under free rolling condition without motor torque, the circumferential slippage occurs. 2) The slippage is caused by the accumulation of irreversible slip during the roll rotation. 3) The motor torque accelerates the sip amount significantly. 4) The geometry of slippage defect can be identified experimentally. 5) The fatigue strength of sleeve assembly rolling rolls can be evaluated by using √area parameter characterizing the identified slip defects. 6) By preventing the slip damage, the fatigue strength of sleeve rolls can be nearly equal to that of conventional solid rolls without shrink-fit.

Abstract: In this article, the mechanism of moving the doors of a passenger elevator with a poly-V-belt drive is studied and their disadvantages are examined, and a new type of driven door movement mechanism is designed, manufactured and tested. In the proposed new design, instead of a two-stage poly V- belt transmission with a large gear ratio, a three-stage package of gear box with metal-polymer gears is preferred. Each pinions are made from steels while gears are made from polymers. It fundamentally consists only of two shafts and three stages spur gearings. Due to making the prototype of gear box with three-stages, overall size of door mechanism decreases about 1.8 times in compare to the old driven door mechanism. Further, sound level is around 68 dB, which is lower than the maximum limit of door mechanism. The overall velocity ratio is reduced slightly through a new designed/produced with three-stages of spur gear system. The field tests have confirmed that the developed a prototype of gear box with three-stages has been used successfully.