Blind bolted rivets with large flange are widely used as standard fasteners for single-side connection in the aerospace industry, and their minimum tensile load is one of the clearly specified mechanical properties. However, the current method for calculating the tensile strength of blind bolted rivets with large flanges is not yet fully developed. In order to improve the forward design process of blind bolted rivets with large flanges and predict their tensile strength, the failure modes during the tensile process were investigated. First, mechanical analysis reveals three failure modes due to stress concentration:the breakage of the forming sleeve, breakage of the head, and indentation of the nut sleeve. Then, a finite element simulation was used to propose a prediction method for the tensile strength of blind rivet nuts with large flanges, which helps obtain the failure modes and predict the tensile strength. Finally, a hydraulic testing system was used to conduct tensile tests on a specific model of blind bolted rivets with a large flange, the specific failure modes and force-displacement curves are obtained. The accuracy of the proposed prediction method is verified by the test result. This study provides a reference for improving the connection strength of blind bolted rivets with large flanges and enables the prediction of tensile strength in the forward design process.

Under the background of automotive lightweighting, the use of resistance spot welding to achieve effective connection of aluminum to steel structures is an unremitting pursuit. However, in actual welding production, fluctuation of working conditions occur frequently, seriously affecting the quality of weld points. Firstly, the resistance spot welding process was adopted to connect aluminum alloy and low-carbon steel plates. The influences of different inclination angles, plate gaps,and fluctuations in cooling water flow conditions on the resistance spot welding of aluminum-steel were investigated. Then,the quality of the weld points was evaluated by comparing the diameter and thickness of the nugget, the thickness of the intermetallic compound, the coach peel performance, as well as the fracture mode. The research results show that an increase in the inclination angle and the gap between the plates within a certain range, as well as a decrease in the cooling water flow within a certain range, will both reduce the quality of the weld points. Therefore, they should be avoided as much as possible in actual production. The results of this study provide a theoretical basis and practical guidance for optimizing the resistance spot welding process of aluminum to steel.

Reaction bonded silicon carbide (RB-SiC) is widely used for manufacturing core components in nuclear energy and optics due to its excellent thermal stability, radiation resistance and chemical inertness. However, RB-SiC is highly hard and brittle, making it difficult to ensure processing quality and efficiency with traditional methods. Ultrasonic diamond wire saw cutting technology, as an efficient machining method for hard brittle materials, has been successfully applied in the processing of single crystal Si, single crystal SiC, and other hard brittle materials. However, the cutting test and process research of this technology in RB-SiC materials need to be carried out. To this end, the ultrasonic sawing test of RB-SiC was carried out for the first time. The ultrasonic wire saw cutting RB-SiC platform was built. The surface quality of parallel and vertical ultrasonic vibration directions was compared and analyzed. The effects of ultrasonic amplitude, line speed and feed speed parameters on surface roughness and surface micro-morphology were studied. Results demonstrate ultrasonic sawing has significant advantages in improving surface quality. Increasing the amplitude from 3 μm to 7 μm reduces surface roughness value by 17.4% and decreases the number of surface scratches and pits. Compared to the vertical feed direction, ultrasonic vibration sawing in the parallel feed direction is more effective in improving the surface quality of RB-SiC materials. This study can provide guidance for the research of ultrasonic sawing process of RB-SiC materials.

Taking cast iron material of cylinder head as the research object, a series of thermo-mechanical fatigue experiments under different temperature ranges were conducted through bulk sampling. The results show that the fatigue test of cast iron materials exhibits three stages: cyclic softening, cyclic stability and rapid failure. Additionally, the fatigue life of materials under inverse phase loading is significantly shorter than that under positive phase loading. Six typical supervised learning models, including artificial neural networks (ANN) and random forest (RF), were used to predict the fatigue life of the experimental data. However, the results indicate that these models failed to learn the fatigue life distribution trend of the materials. For this problem, the prediction of the thermal mechanical fatigue life of cast iron materials for cylinder heads was achieved by using the self-supervised algorithm based on the generative adversarial network (GAN), and it showed a good prediction effect under the condition of small samples. This research has strong guiding significance and reference value for cylinder head design and fatigue analysis.

Sandwich structures are widely used in aerospace, national defense and other fields due to their lightweight and energy-absorbing properties, and it is of great significance to improve their anti-explosion performance under internal explosion loads.Three structures were designed, including ring sandwich tube (R), polyurethane foam sandwich tube (F), and ring-polyurethane foam hybrid sandwich tube (RF), with the non-filled sandwich tube (A) as the control group. Through internal explosion load tests and finite element simulations, the deformation modes and energy absorption capacities of the four structures under different explosive amounts were compared and analyzed, and the influence of foam filling methods on the mechanical properties of sandwich tubes was explored.The results showed that, compared with the control group, the non-dimensional deflection of structures F, R and RF was reduced to varying degrees under TNT equivalents of 24 g, 36 g and 48 g.At a TNT equivalent of 48 g, the specific energy absorption of RF structure was 5% higher than that of R structure, exhibiting the best anti-explosion performance. In addition, when the TNT equivalent was greater than 37.39 g, the foam-filled ring structure (FR) showed the strongest deformation resistance; when it was less than this value, the foam-filled structure in the gap between the ring and the tube wall (RF) had the optimal anti-explosion performance.

To compensate for the intermittency of renewable energy generation, coal-fired power units are required to operate under low-load conditions over a long time, which causes the last stage blades of steam turbine low-pressure cylinders under small flow conditions persistently, leading to increased dynamic stresses and fatigue damage in the blades. To evaluate the safety of these last-stage blades, the fluid-structure interaction analysis of the last two-stage flow path and last stage rotating blades were conducted for a 660 MW air-cooled steam turbine under typical operating conditions. The results demonstrate that as the load decreases, both the maximum equivalent stress and deformation of the last stage rotating blades gradually diminish first, then slightly increasing. The maximum equivalent stress of the last stage rotating blades remains consistently below the material’s yield strength, indicating that the blades are in the stage of elastic deformation and no plastic deformation has occurred. Using the Goodman curve analysis method for the high-cycle fatigue life assessment of the last stage rotating blades, the dynamic stress levels of the last stage rotating blades fall within the safe zone of the Goodman curve,indicating that there is no risk of fatigue damage to the blades.

In order to improve the comprehensive mechanical properties of 960 MPa high strength steel weld metal, the optimum content of Ti element in 960 MPa high strength steel weld metal was revealed. Firstly, four kinds of weld metals with different Ti contents (0.01%-0.08%) were designed and welded. The effects of Ti content on the microstructure and mechanical properties of welds were systematically studied by scanning electron microscopy, energy dispersive spectroscopy, tensile and impact tests. The effect of Ti content on the initiation energy and propagation energy was evaluated by fracture observation and fracture morphology. The results show that when the Ti content is less than 0.06%, the microstructure of the weld metal changes from granular bainite to granular bainite + acicular ferrite. With the increase of Ti content, the content of acicular ferrite increases significantly. When the Ti content reaches 0.06%, the tensile strength reaches 939 MPa, the elongation reaches 23.5%, the elongation increases by 27% compared with Ti0.01, and the impact absorption energy at -40 ℃ reaches 104 J;when the Ti content increases to 0.08%, the formation of coarse lath bainite and the precipitation of TiN lead to a sharp decrease in plasticity and toughness, the elongation decreases to 18.2%, and the impact energy at -40 ℃ is only 25 J. Ti promotes the nucleation of acicular ferrite and improves the comprehensive mechanical properties by forming TiO₂ inclusions.However, excessive Ti will induce the precipitation of brittle phase and the formation of coarse lath bainite, which significantly deteriorates the plasticity and toughness.

To investigate the influence of structural parameters on the yield strength and deformation behavior of truss lattice structures, face-centered cubic (FCC) porous lattices were fabricated and the mechanical responses were systematically studied. A finite element model was developed to evaluate the yield strength and failure modes of structures with varying geometric parameters. The analysis revealed a correlation between the member slenderness ratio and the transition from progressive collapse to global yielding under different loading orientations. Structures with lower slenderness ratios tend to exhibit global yielding, while those with higher slenderness ratios are prone to layer-by-layer compression failure.Furthermore, lattices supported along the face diagonals demonstrate more uniform global deformation, whereas those supported along the body diagonals are characterized by localized deformation.

Exponential distribution is widely applied to describe product life in reliability engineering. Correspondingly,product failure rate is a constant (not changing with the service time of the product). Nevertheless, only the products with special property or under particular load condition have exponentially distributed life and constant failure rate. Unrealistic hypothesis of exponentially distributed life will lead to serious error in reliability and failure rate analysis results. In the situations that component life follows exponential distribution, to assume component failures being independent of each other will mislead system reliability evaluation. The the property of product failure rate was analyzed and inferred from the aspects of product strength performance and load environment.The conditions for product failure rate to follow exponential distribution were revealed, and product failure dependency issues in condition of life following exponential distribution were explained.

Aiming at the limitations of current monitoring methods in the accuracy of early fault diagnosis for rolling mill bearings, a structural design method for intelligent rolling mill bearings based on embedded multi-source microsensors was proposed.A multi-source microsensor module integrating temperature and acceleration signals was developed, and an optimized layout structure of axial sensing leads in the bearing housing was designed, breaking through the bottleneck of sensor integration under the space constraints of traditional bearings. A mechanical performance evaluation system for the slotted structure was established, and the reliability of the intelligent structure was verified through strength check and service life calculation.The results showed that when the slotted area was 10 mm×5 mm, the maximum equivalent stress was 99.71 MPa,which had sufficient safety margin compared with the material yield limit; the maximum overall deformation of the structure was only 0.24 mm, and the local deformation was less than 0.02 mm, with the theoretical service life consistent with that of conventional bearings. The optimized intelligent bearing ensured monitoring functionality while meeting industrial application requirements in terms of structural strength and service life. The research results not only provide a high-precision monitoring method for early fault diagnosis of rolling mill bearings under extreme working conditions but also achieve an integrated"monitoring-structure" process through embedded design. Its strength check standards and service life evaluation methods can directly guide the transformation and upgrading of intelligent bearings in industrial sites, holding significant engineering value for improving the operation and maintenance efficiency of rolling production lines.