In order to gain insight into the stability of the tracking frame structure of shipborne large-aperture telescopes,the stability of typical ground-level telescope tracking frames was studied. According to the external load borne by the equipment in the case of ship, the external load was parameterized and entered into the finite element software. The pretreatment software and finite element software were used to analyze the structural deformation under static wind load. Then,the natural frequency of the structure was solved, and a simple response spectrum analysis calculation was proposed instead of the tedious random response analysis to analyze the stability of the equipment under dynamic wind load and wave excitation. According to the stress and deformation values obtained from the results, it was ensured that the shipborne telescope tracking frame theoretically meets the strength requirements and design accuracy requirements under shipborne conditions. Under the static wind load, the maximum stress value of the tracking frame structure is about 14.07 MPa, which was less than the yield strength of steel 355 MPa, the maximum deformation variable was about 0.02 mm, which was less than the design accuracy error coaxiality ϕ0.1 mm, and the natural frequency 1st-6th order mode value was 40.15, 49.65, 66.86, 82.93, 91.38,115.89 Hz. Under dynamic wind load, the peak value of structural stress was 3.92 MPa and the maximum deformation variable was 0.01 mm, and under the excitation of ocean waves, the peak of structural stress was 5.88 MPa and the maximum deformation variable was 0.02 mm, which was less than the yield strength and design accuracy error coaxiality of steel. The error between the modal value obtained by the modal test and the calculated modal value is within 10%. Combining theoretical simulation and practical tests, the tracker structure can work normally under shipborne conditions.

In order to clarify the dynamic response, damage situation, and failure mode of titanium/steel corrugated composite plates and interfaces under impact loads, small energy (53 J）impact experiments were conducted on titanium/steel corrugated composite plates using a light air cannon. On the basis of verifying the effectiveness of the numerical calculation model, numerical simulations were conducted on composite plates under various velocities to study the impact mechanical response of composite plates and their interfaces under various energies. The results show that, under low energy impact conditions, the front of the corrugated composite plate shows plastic expansion damage, and the back plate has protrusions with cracks at the raised areas. The corrugated interface layer is tightly bonded and overall concave; cut the target plate along the impact center and observe that there are no cracks, delamination, or other damages on the cross-section. This is different from fiber reinforced composite laminates. There will generally be obvious delamination inside when there is barely visible damage on the impact surface. In numerical simulation, the cohesive force interface damage area of the corrugated composite plate under impact is less than that of the planar interface composite plate. When subjected to low energy impact, the absorption of bullet kinetic energy by the corrugated plate is mainly dominated by overall deformation energy absorption, and the damage to the titanium/steel composite plate at the corrugated interface is relatively small. Under various energy impacts,corrugated interface composite plates have tighter interface bonding, better structural integrity, and are less prone to damage compared to planar interface composite plates.

Low-cycle fatigue is a typical failure mode of engine pistons. In order to study the influence of multi-source uncertainty factors on the reliability of low-circumference fatigue of pistons and improve the efficiency of the reliability analysis, a new reliability calculation method is constructed based on the polynomial-chaos-based Kriging (PC-Kriging) model and the Monte Carlo simulation (MCS), and the accuracy and efficiency of this method are proved by numerical examples.Taking the piston group structure of a certain diesel engine as the research object, a finite element model of the piston is established based on the thermal-mechanical coupling analysis, and the reliability analysis of the piston for low-cycle fatigue is carried out by using this method, taking into account the critical dimensions, the material properties, and the uncertainty of the load. The results of the reliability analysis show that, compared with the same type of method, this method is more efficient in calculation, requiring only 20+93 finite element calculations, and the probability of fatigue failure is 1.053% when the expected design life of the piston is 1.4×10⁴. The sensitivity analysis shows that, the height of the piston, the piston diameter,the elasticity modulus of the material, and the parameters of the fatigue calculation model have a greater influence on the reliability. The analysis results can provide a guidance for the reliability design of the piston.

The slat of aircraft is subjected to the combined action of thermal load and aerodynamic force during its service, which has an impact on the safety of the structure. The typical aluminum alloy structure widely used in slat structure is taken as the main research object, and the stress distribution and structural strength under the combined action of heat and force were studied by experiment and finite element method. Firstly, in order to explore the influence of temperature on material properties, the linear tensile test of 2024-T62 rectangular thin plate and the high temperature tensile failure test of perforated thin plate were carried out under four different temperature conditions. The test shows that the high temperature environment has a reduction effect on the elastic modulus of the material, and at 190 °C, the bearing strength of the test piece decreased by 15%. Therefore, considering the reduction effect of temperature on material parameters can establish a more accurate model for predicting structural strength. Secondly, aiming at the thermal stress problem of aluminum alloy parts and structures, the test and simulation of aluminum alloy sheet and simplified slat structure under the combined action of heat and force were carried out respectively. A set of modeling method and thermal stress measurement test technology under the combined action of heat and force were established. The maximum error between the simulation and test results of aluminum alloy sheet is 10%. The thermal stress simulation of the simplified slat structure has a good trend compared with the experimental results, and the maximum error is 20%. In addition, through the experiment, it is also found that the thermal stress is particularly sensitive to the setting of boundary conditions. For the model with complex constraints, it is necessary to expand the modeling range to the stable boundary conditions to simulate the actual thermal stress.

The creep behavior of 7050-T7451 aluminum alloy under different temperatures and stresses was studied by the uniaxial tensile creep test. Based on continuum damage mechanics, a constitutive model describing the creep behavior of aluminum alloy at high temperature was established. The model took into account the precipitation coarsening, dislocation multiplication/annihilation and microvoid formation during the creep process, and introduced the corresponding damage factor evolution formula to reflect these three damage processes. In addition, the model took into account the additional damage caused by stress increase to reveal the effect of stress on the creep damage. Based on the comparative analysis of the test results and the predicted results, it was verified that the established physical constitutive model can accurately describe the creep behavior of 7050 aluminum alloy under different temperatures and stresses.

The bearing section of the work roll neck often suffers burnout failure due to bearing seizure, and additive manufacturing is usually used in the field to repair it. Life prediction of the repaired roll neck is the key to predict the safe service of the work roll in the field production and carry out overhaul，but there is a lack of research on the related issues. In view of the above problems, the stress analysis and multi-axis life prediction of the working roll neck bearing section of the four-high mill were carried out. Based on the SIMS model and the influence function method, the rolling force and the stress between the rolls were calculated. The moment balance equation of the roll neck end was established in the bearing section,and the bending stress model of the roll neck bearing section was established. The deformation resistance was regarded as the plastic deformation energy per unit volume to calculate the rolling torque in the deformation zone, and the torsional shear stress model of the roll neck bearing section was established. Using the first strength theory, the equivalent stress was obtained by combining the bending stress and the torsional shear stress. On the basis of proving the calculation accuracy of the model,the multi-axis fatigue model was used to predict the fatigue life of the roll neck bearing section, and compared with the service life of the actual roll in the production line. The results show that the stress calculation model of the working roll neck bearing section of the four-high mill is in line with the actual stress state of the roll neck. The error between the expected service life predicted by the theoretical model and the actual service life is less than 20%, which meets the actual engineering error requirements.

In view of the difficulty of obtaining durability test specifications for axle components, a method of constructing driving load of the front axle dynamic model was proposed to provide the input for system-level bench test and life verification of front axle components. The life of front axle was obtained based on the whole vehicle dynamics model and the measured road load, and the useful information and life prediction results in the above process were employed to guide the construction of driving load applied on front axle. Firstly, the frequency band of the measured six-component forces at the wheel center was adjusted. Then, with the goal of minimizing the difference between the damage/life of the front axle and the reference value under each working condition, the adjustment coefficient of the amplitude of the three-way forces at the wheel center was optimized by combining the response surface method and genetic algorithm. The optimized three-way forces at the wheel center and the other three-way torques constituted the driving signal of the front axle model. The results show that the constructed wheel center drive signal is used to simulate the dynamic load of the front axle model. The life of the front axle,the failure sequence of risk points and the damage contribution ratio of various road conditions to dangerous points are obtained and in good agreement with the reference results, which verified the effectiveness of the proposed method and provided reference for the drive signal construction and component life evaluation of system-level bench durability test.Finally, the damage distribution of the front axle can be consistent with the reference results by modifying the main damage load of the shaft tube.

Aiming at the storage life evaluation of photodetectors, a new evaluation method for multi-parameter competitive failure storage life assessment based on Monte-Carlo method was proposed. This method comprehensively considered whether the key performance parameters of the sample have deteriorated or improved trend. Firstly, the optimal degradation model with a single parameter was selected by performance degradation modeling, so that the pseudo-life of the sample with increasing degradation trend was calculated according to the failure threshold, and the pseudo-life was regarded as the right-censored data for the sample with decreasing degradation trend. Furthermore, the optimal distribution of a single performance parameter was selected based on the pseudo-life data combined with the expectation maximization(EM)algorithm, and then the competitive failure evaluation of multi-parameters was carried out by Monte-Carlo sampling method.According to the case analysis of the photodetector storage, the feasibility of this method was verified.

The mechanical response of external rotor direct drive generator under time-varying loads is analyzed theoretically, calculated by simulation and verified by test. Firstly, the source of magnetic pull of the rotor core of the external rotor generator and its variation with load were analyzed. The expression of magnetic pull of the rotor and the characteristics of time and space order were determined. The basic vibration model of the external rotor core was analyzed, and the basic vibration equation of the external rotor core was determined. Then the simulation model of the external rotor generator was established, and the spatiotemporal order characteristics of the magnetic pull and the typical daily variation rule with time were obtained. The magnetic pull density obtained from the electromagnetic field was used as the input load to guide the structure field. The magnetic-solid coupling simulation was carried out, and the deformation and stress distribution and noise response of the external rotor core were calculated and analyzed. Finally, a simulation example of a 13 kW external rotor direct-drive generator proved the correctness of the analysis and simulation. The results of the study determined the time-varying load on the outer rotor core and its mechanical response distribution. It is found that the time and position of the rotor core should be tested emphatically when the generator is running. Noise characteristics under time-varying loads are also analyzed. The analysis provides reference for the maintenance and design of the generator.

The gearbox of wind turbine is in the complex environment such as random wind load for a long time, and the gear contact fatigue becomes a key factor limiting the stability and reliability of wind turbine equipment. The research on the gear contact damage evolution mechanism is faced with difficulties such as complex stress states, damage anisotropy and failure modeling. Material configurational force theory can describe the effect of defect configurational change on the free energy of materials and can be used to predict the damage and failure behavior of materials. A wind turbine gear contact damage model was constructed based on this theory. The gear contact interface stress field simulation analysis was carried out for the key bearing area of gear contact, and the gear contact damage evolution process under contact load was simulated. The results show that the configurational force theory damage model can effectively simulate the contact damage phenomenon of gear and explain the pitting and spalling of gear surfaces. It has significance to predict contact fatigue life of gears accurately.