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Optimization-based bound tightening (OBBT) is one of the most effective procedures to reduce variable domains of nonconvex mixed-integer nonlinear programs (MINLPs). At the same time it is one of the most expensive bound tightening procedures, since it solves auxiliary linear programs (LPs)—up to twice the number of variables many. The main goal of this paper is to discuss algorithmic techniques for an efficient implementation of OBBT. Most state-of-the-art MINLP solvers apply some restricted version of OBBT and it seems to be common belief that OBBT is beneficial if only one is able to keep its computational cost under control. To this end, we introduce three techniques to increase the efficiency of OBBT: filtering strategies to reduce the number of solved LPs, ordering heuristics to exploit simplex warm starts, and the generation of Lagrangian variable bounds (LVBs). The propagation of LVBs during tree search is a fast approximation to OBBT without the need to solve auxiliary LPs. We conduct extensive computational experiments on MINLPLib2. Our results indicate that OBBT is most beneficial on hard instances, for which we observe a speedup of 17–19 % on average. Most importantly, more instances can be solved when using OBBT.

Aerospace engine is the source of power for the development of national defense and aerospace. Engine bolt tightening is an important part of the aerospace engine production process. At present, most of the bolt tightening methods of aerospace engines are manual tightening or traditional rigid tightening, which lead to the problem of low efficiency and large engine deformation. This paper proposes a process planning method for bolt tightening of aerospace engine based on digital twin, including flexible tightening mechanism design, tightening sequence optimization, the establishment of the digital twin system of the tightening mechanism, etc. The flexible tightening mechanism is suitable for different types of aerospace engines. Based on bolt tightening sequence optimization, the deformation and stress of the cabin section during the tightening process are reduced. The bolt tightening work is completed in the digital twin system, the real-time communication of physical and digital space synchronizes the operations of them. After tightening, the residual pre-tightening force of bolts are detected based on the ultrasonic method. The results show that the proposed method can solve the problems of low efficiency of aerospace engine bolt tightening and the problem of the cabin’s large deformation. Furthermore, it provides technical reference and theoretical basis for the bolt tightening technology of aerospace engine.

Bolted joints are widely used in the aerospace and automotive industries due to their ease of assembly, disassembly and design flexibility. Optimizing threaded fasteners is essential to achieve uniform load distribution and minimize the number of bolts required, thereby reducing system cost and weight. This review paper aims at summarizing the five optimization techniques available in the literature, including bolt layout, tightening strategies, tightening sequences, bolt size, and stresses. The purpose is to emphasize the importance of optimizing bolted joints via the proper selection of materials, geometry, patterns, and bolt sizes, to obtain efficient joints with low assembly time while maintaining strength.

The anchoring length and the pre-tightening force are the two main factors influencing the control effect of surrounding rock in bolt support. To study the influences, a theoretical analysis is made on the stress distribution law of the surrounding rock with different anchoring lengths and pre-tightening forces; a high pre-tightening force quantitative exerting device for high strength bolts is developed with a function of automatic anchor retreat; and four field test plans are designed and carried out with different combinations of bolt anchoring lengths and pre-tightening forces to comparatively analyze their control effect of surrounding rock. The theoretical analysis shows that as the bolt anchoring length is constant, the effective compressive stress area in the surrounding rock of the bolt non-anchoring section increases along with the increase of the pre-tightening force; a certain length of non-anchoring section is helpful to play the bolt support function, but the anchoring length should not be too short. The field test shows that increasing pre-tightening force is an effective way to improve the control effect of surrounding rock; under certain conditions, an appropriate reduction of the bolt anchoring length will not significantly weaken the control effect of surrounding rock. That verifies the theoretical analysis. The study provides some useful guidance for the selection of the parameters of the bolt support in underground engineering.

To improve the fastening effect of electronic components in mechatronic equipment, the tightening sequence and frequency have a significant impact on the structural performance of these components. This study identifies an optimal fastening method through experimental verification, although some measurement errors were noted; the method remains highly reliable. First, theoretical calculations and experimental analyses were conducted to determine the torque values under different conditions. Then, simulations were performed to study the impact on the stress of each screw. Finally, experimental validation of the simulation results was carried out, and a linear relationship (with a value of 0.82) between the measured and theoretical values was explored. Consequently, an optimized screw group fastening method is proposed, and the torque calculation process is simplified, thereby enhancing the reliability and lifespan of electronic components in mechatronic systems.

Full-ceramic ball bearings are widely used in aerospace, gas engines, and extreme working conditions. The research on vibration characteristics of full-ceramic ball bearings under different pre-tightening forces and oil supply rates is relatively rare. In this paper, silicon nitride 6206 full-ceramic deep groove ball bearing is taken as the research object, the experiment of lubrication vibration characteristics of full-ceramic bearings is carried out on a bearing vibrometer by changing different pre-tightening forces and lubricating oil supply rates with the control variable method, the dynamic model of full-ceramic deep groove ball bearing under lubrication condition is established, and the influence of factors such as lubricating oil drag force, lubricating oil film thickness, rolling friction force, and pre-tightening force on bearing vibration are analyzed in essence. The experimental results show that the large vibration ratio of the bearing in the state of lack of oil is caused by insufficient oil supply, and when the oil supply rate is too high, the rolling body is dragged by too much drag force, which leads to an obvious increase in bearing vibration. The similarity between the solution signal and the measured signal of the dynamic model of full-ceramic bearing considering the drag force of the rolling body under different lubrication conditions is over 95%, which proves the reliability and accuracy of the dynamic model.

Weakly cemented soft rock roadways are prone to severe roof lowering and floor heave, especially under strong mining. The failure of bolt (cable) supports is significant. Theoretical analysis, on-site monitoring, and numerical simulation were used in the work to solve this problem. Firstly, the work explored and obtained the failure characteristics of bolts (cables) in the weakly cemented gob-side entry. The entry was mainly composed of tension fractures and tension–shear fractures in the free section, supplemented by the shear failure of floor and roof. The failure process of bolts (cables) was explored. The insufficient pre-tightening force of bolts (cables) was the internal cause of the failure mechanism of supports based on the on-site monitoring results. The large deformation of roof sinking beyond the extended range of support materials was the external cause of the failure mechanism of support. We proposed the concept of rapid support with high pre-tightening bolt–cable synergistic deformation. The support required the deformation of bolts (cables) to be coordinated with roof deformation. A design for rapid support with bolts and cables was formed. The pre-tightening force of the weakly cemented gob-side entry was optimized based on the numerical simulation. Finally, the on-site application of our method could reduce roadway deformations and the failure of bolts (cables).HighlightsIn this paper, the failure patterns of bolt (cable) in weakly cemented gob-side entry were investigated, which mainly consisted of tension failure and tension-shear failure in the free section, supplemented by shear failure of the tray and roof. It was found that the breaking depth of bolts and cables in the roof is about 0.8~1.2m, which is located in the development area of the coal-rock interface fracture zone. The above research provided on-site measurement basis for the failure process and mechanism of roadway support.This paper analysed the failure process of bolt(cable) tensile fracture, tension-shear fracture, and shear fracture at the tray, and based on indoor experiments and on-site monitoring, it was found that the low pre-tensioning force of the bolt(cable) led to insufficient active support effect, which was the internal reason for the support failure. The external reason was that the extension amount of the bolt and cable was less than the lowering of the roof.This study proposed the concept of high pre-tensioning force bolt (cable) deformation synergistic support for the failure mechanism of the above bolt (cable) support, including two aspects: bolt (cable) and surrounding rock deformation synergistic support and high pre-tensioning force active support. The former required that the tensile deformation of the bolt (cable) be adapted to the lowering deformation of the roof, in order to avoid the failure of the bolt (cable) due to insufficient elongation; the latter adopted the high pre-tensioning force active support, which reduced the deformation of the surrounding rock by placing the bolt (cable) in a high supporting force stage.This study proposed a new support design method based on the actual anchoring characteristics of support materials, which can effectively solve the problem of large differences between theoretical strength verification and actual strength. At the same time, combined with the synergistic support design scheme of bolt and cable deformation, a fast support design method of bolt and cable suitable for weakly cemented soft rock roadways was formed. Based on numerical simulation, the roof stress distribution under different pre-tightening force conditions of the bolt (cable) was obtained, and the optimum pre-tightening force range was found. After on-site application, the effect was significant.

Coupled support technology for concrete-filled steel tube support (CFSTS) and bolt-cable (BC) used in deep roadways often fails, and increasing the length of BC is a waste of material. Therefore, changing the pre-tightening force of BC to improve the force state in CFSTS is proposed in this paper. Firstly, the damage modes of CFSTS were investigated, and the internal forces in CFSTS contained cable were obtained using the elastic centre method. And the results indicated the cable could reduce the internal force in CFSTS to ensure its high bearing capacity. And then, the numerical calculation models with different lateral pressure coefficients and coupled support conditions were established. Further, the stress and displacement law for the roadway and the support body under different lateral pressures and different support schemes, and increasing the pre-tightening force for bolt-cable in different angle ranges was investigated. And the results show that the best “CFSTS + BC” coupled support effect could be achieved with pre-tightening forces for bolts and cables of 60 and 100 kN, respectively, and the optimal reinforcement angle range is 15°–45°. Finally, “CFSTS + BC” coupled support technology was applied in the field.

The stability and integrity of the abutment-implant connection, by means of a screw, is fallible from the moment the prosthetic elements are joined and is dependent on the applied preload, wear of the components and function. One of the main causes of screw loosening is the loss of preload. The loosening of the screw-abutment can cause complications such as screw fracture, marginal gap, peri-implantitis, bacterial microleakage, loosening of the crown and discomfort of the patient. It is also reported that loosening of the screw/abutment may lead to a failure of osseointegration. It is necessary to evaluate and quantify, with in vitro studies, the torque loss before and after loading in the different connections. Aim: evaluate the influence of implant- abutment connection design in torque maintenance after single tightening, multiple tightening and multiple tightening followed by mechanical cycling. Materials and Methods: 180 Klockner implants divided in 4 groups: 15 SK2 external connection, 25 Ncm tightening torque; 15 KL external connection, 30 Ncm tightening torque; 15 Vega internal connection, 25 Ncm tightening torque; 15 Essential internal connection, 30 Ncm tightening torque. In each group removal torque values (RTV) were evaluated with a digital torque meter, in 3 distinct phases: after one single tightening, 10 multiple tightenings and 10 multiple tightenings and cyclic loading (500 N × 1000 cycles). Results: After one single tightening, and for all connections, RTV were lower than those of insertion, but only for Essential and Vega internal connections this result was statistically significant. After multiple tightening, RTV were significantly lower in all connections. After repeated tightening followed by cyclic loading, mean RTV were significantly lower, when compared to insertion torque. The multiple tightening technique resulted in higher RTV than the single tightening technique, except for Vega implant. The multiple tightening followed by cyclic load, compared to the other phases, was the one that generated the lowest RTV, for all connections. Conclusions: The connection design, in our study, did not seem to influence the maintenance of preload. Loading influenced the loss of preload, in the sense that significantly decreased the removal torque values. The multiple re-tightening technique resulted in higher removal torque values than the single tightening technique. Clinically, our results recommend to retighten retaining screws, a few minutes after insertion.

To realize the automatic tightening of nuts, a nut tightening robot system strategy based on machine vision was designed in this work. The strategy was based on three stages: nut image calibration, nut identification, and nut pose estimation. In the first stage, the template pose image of the nut and the coordinates of the nut center in this nut image were obtained by calibration. In the second stage, a nut identification algorithm based on improved the backbone feature extraction network and area generation network of Faster-RCNN was presented, which improved the efficiency and accuracy of nut identification. In the last stage, a nut pose estimation algorithm based on Fourier and log-polar coordinate transformation was presented to solve the rotation angle, translation, and scale of the nut relative to the template nut image and then obtain the rotation angle of the sleeve and the central coordinate of the nut. An experimental nut tightening robot platform was also set up in this work. The results of 50 tests showed that the proposed detection methods could identify nuts with 100% accuracy, and with the proposed pose estimation methods, the average error of the rotation angle of the nut was 0.057°, and the average error of the center position of the nut in x and y directions was ± 0.05 mm and of z direction was ± 0.5 mm. The experimental results showed that the nut tightening robot scheme and algorithm designed in this work were feasible in nut identification and pose estimation and met the requirements of insertion accuracy in the process of nut tightening.