In pressurized-water reactor nuclear power plants, the vessel nozzles of large carbon steel equipment such as reactor pressure vessel (RPV), steam generator (SG), and main pumps are connected to austenitic steel pipes through dissimilar metal welds (DMWs). The thick-walled DMW has material inhomogeneity and complex weld residual stress (WRS), which easily leads to the generation of fatigue or stress corrosion cracks.Firstly, the WRS of DMW in nuclear power plants obtained through international measurements and numerical analyses was investigated. Then, based on a rapid WRS simulation method for volume uniform heating of unit cells, the WRS of DMW in the hot leg of the primary loop (the connecting pipe section from RPV outlet to SG inlet, which is the pipe section with the highest operating parameters in the primary loop pressure boundary) was obtained.The numerical simulation results are consistent with the trend of the fitting envelope curve recommended by the United States, and the overall results can be enveloped by the fitting curve recommended by the United States, indicating that the described rapid WRS simulation method is feasible. The WRS of thick-walled DMW is relatively high, and the stress values at the inner and outer surfaces of the pipe are more conservative than the recommended values of the United States, suggesting that more safety margins can be obtained in actual structural analyses.

Metro gearbox is a key component for torque transmission in vehicles, and its failure will directly affect the safety of train operation. The vibration characteristics of tooth breakage faults in metro gearbox were studied by combining dynamic simulation and vibration test. Firstly, based on the dynamic relationships and constraint characteristics between various components of metro gearbox, a rigid-flexible coupling dynamic model of metro gearbox with tooth breakage faults was established through the impact function method, Coulomb friction model, bearing modeling, flexible body of the housing and gear system dynamics theory. The dynamic response of the gearbox under different types of tooth breakage faults was studied, and the influence of operating parameters on the vibration characteristics of tooth breakage was analyzed. Then,through vibration test, the dynamic response of metro gearbox under normal state and broken tooth fault was obtained,verifying the accuracy of the dynamic simulation model. The results indicate that the rigid-flexible coupling dynamic model can effectively calculate the acceleration response of gearbox in different operating states, provide diagnostic basis for the prediction and identification of tooth breakage faults in the gearbox.

The fatigue limit of 7085 aluminum alloy was tested by four-point bending fatigue test for samples of different sizes and roughness. The results show that the greater the thickness of the specimen, the greater the ultimate fatigue strength of the material. The higher the surface roughness of the sample, the lower the ultimate fatigue strength of the material. The stress analysis and calculation of the specimen show that the dangerous cross section occurs at the position where the indenter contacts the specimen, where the specimen is subjected to the combined action of bending normal stress and shear force. With the increase of the thickness of the specimen, the shear force on the specimen decreases, and the bending normal stress on the specimen increases under the same fatigue limit. And vice versa. The relation between the surface roughness and the radius of curvature of the sample is shown by establishing a simplified model, and then the relationship between the surface roughness and the fatigue ultimate strength of the material is obtained.

The subsurface damage depth of grinding WC-10Co-4Cr coating with a cup wheel was investigated in an effort to address the issue that the subsurface damage will cause the coating's performance to deteriorate. The theoretical formula of single particle grinding force was obtained based on the principles of indentation fracture mechanics and grinding material removal theory. A theoretical subsurface damage depth prediction model was developed based on the cup wheel's surface grinding properties. The design of the single factor surface grinding test and the single point polishing test was to confirm the model's accuracy. Analysis was done on how various grinding parameters affected the workpiece's surface roughness and depth of subsurface damage. The maximum relative error is 15. 8%, and the predicted subsurface damage depth agrees with the measured value, according to the results. Surface roughness and subsurface damage depth rise with feed speed and grinding depth, but fall with spindle speed. The study has some theoretical significance for directing the process parameter optimization of cup wheel grinding of WC-10Co-4Cr coatings.

To investigate the mechanical properties of woven composite hybrid bonded/bolted joints, a mechanical failure model for hybrid bonded/bolted joints based on 3D progressive damage model and cohesive force model was developed to simulate the mechanical behavior and damage evolution of the joints. Based on the Abaqus finite element software, a finite element simulation model for hybrid bonded/bolted joints woven composites was established. The damage initiation and propagation of the composite material were judged using the three-dimensional Linde criterion. The cohesive force model was used to simulate the damage failure process of the adhesive layer. On the basis of test verification of the model accuracy, the strength and damage failure process of the joints were analyzed under different tightening torques. The test and simulation results indicate that as the tightening torque increases, the extension of adhesive layer damage can be effectively suppressed.However, the shear strength of the adhesive layer in the hybrid bonded/bolted joints firstly increases and then decreases,because increasing the tightening torque can reduce the peeling stress of the adhesive layer in the joints. However, the excessive tightening torque will strengthen the stress around the adhesive layer hole, leading to a decrease in the shear srength of the adhesive layer and a decrease in the strength of the connection structure. The load-displacement curve of the numerical simulation is consistent with the test results, and the predicted adhesive layer fracture load is equivalent to the test results. At the same time, the fiber damage, matrix damage, and delamination damage on the laminated plate can also be well reflected in the numerical model, which is similar to the damage form after the connection test, verifying the effectiveness of the damage prediction model.

As a common material for flow components, 17-4PH(0Cr17Ni4Cu4Nb) martensitic stainless steel is vulnerable to serious cavitation damage. Based on the corrosion inhibition effect of array texture structure，this study focused on the cavitation characteristics and inhibition mechanism of 17-4PH material under the surface structure of hundred-micron groove array. Based on the ultrasonic cavitation test platform, the experimental data were obtained by the weight loss method, and the data points were fitted by Logistic equation to obtain the nominal incubation period and other parameters. The results show that the surface groove target with groove spacing W and groove width L in the range of hundred-micron has a good inhibitory effect on cavitation damage. The geometric parameters of the groove array structure with the appropriate ratio can further reduce the cavitation damage of the material. The groove array target with groove width L=700 μm and groove spacing W=400 μm has the longest incubation period (22. 79 h) and the smallest cumulative mass loss (10.92 mg) after continuous cavitation for 50 h, thereby exhibiting the best cavitation resistance. This study can provide reference for practical engineering applications in preventing cavitation erosion.

After low-velocity impact at the edge, delamination and matrix extrusion occur inside the composite laminates,which will have a serious impact on the safe use and life of the composite laminates. Therefore, it is of practical engineering significance to establish a fatigue life prediction model for low-velocity impact at the edge. The dent damage size, compressive residual strength and fatigue life of the fatigue life prediction model were obtained by low-speed impact test, compression test and compression-compression fatigue test. Based on the average stress failure criterion, the impact damage area of the laminated plate was equivalent to the corresponding aperture by combining the opening equivalent method, and the equivalent damage coefficient of different impact energy was proposed. A fatigue life prediction model considering the compressive residual strength of impact damaged laminates was established, and the prediction results were compared with the test results.The results show that the fatigue life prediction accuracy of the model is high, the error is controlled within 10%, and the model has good prediction ability.

In order to investigate the stress concentration phenomenon and analyze the distribution characteristics of the interlaminar stress in the hole edge region of composite laminates. Based on the generalized mixed variational principle, the generalized mixed finite element model for laminated plates with various stacking modes were established. The stress field variables were divided into the interlaminar stress and the in-plane stress, with the introduction of stress boundary conditions to ensure the physical continuity of interlaminar stresses between layers and the discontinuity of in-plane stresses between layers.The interlaminar stresses at the edge of the laminated plate hole were respectively analyzed through the thickness direction and the circumferential direction. Numerical examples demonstrated that the incompatible generalized mixed element could obtain more accurate stress singularity results than the 8-node three-dimensional solid incompatible displacement element results solved by the finite element software Abaqus. Stresses on both upper and lower surfaces of the laminated plate consistently reflected actual situations. The research indicates that compared with the displacement element, the incompatible generalized mixed element can more effectively capture the high stress gradient of the interlaminar stresses at the edge of the laminated plate hole, which provides a new idea for the optimal design of the laminate.

The eccentric installation of high-lock titanium alloy bolts (an assembly angle between the bolt head and the fastening plate) leads to premature failure, which seriously affects the safe operation of aerospace aircraft. Currently, the test research is difficult to obtain the bolt fracture process, which in turn limits the revealing of fracture mechanism. Meanwhile,test research cannot obtain the fracture strength variation value of bolts with different assembly angles. Therefore, in response to the problem of premature fracture of high-lock bolts in the eccentric installation, finite element analysis method was employed and the model was verified by test. The verified finite element model was used to visualize the fracture process of eccentric installation bolts and predict the tensile strength of eccentric installation bolts with different angles. The research results indicate that the tensile strength and fracture position of bolts with installation angles of 0° and 3° obtained from finite element analysis are consistent with the test results, which show that the finite element model has good accuracy. As the installation angle increases, both the bolt head and thread are subjected to eccentric loads, and the bending moment generated aggravates the stress concentration in these two areas. When the assembly angle is less than 3°, the stress at the thread is larger,and when the angle is over 3°, the stress on the head is greater. The finite element model successfully predicts the tensile strength of bolts with an assembly angle of 1°, 2°, and 4°. The research results effectively reveal the fracture mechanism of high-lock titanium alloy bolts under the eccentric load. Meanwhile, the simulation model can predict the tensile strength of bolts under different installation angles, and provide technical specifications for the service of eccentric bolts.

Porous metals are widely used in filtration, catalysis, adsorption and heat transfer because of their excellent mechanical properties. However, creep failure is a primary failure mode for porous metal parts experiencing the high temperature and constant stress. The research progress of the creep resistance of porous metal materials was summarized from four aspects, pore structure，edge structure, micro-defect and creep life prediction. The effects of pore structure, such as porosity, pore shape and pore diameter, on the stress index, creep resistance and deformation mechanism of porous metals were expounded. The creep resistance of the hollow and solid edge under different stress conditions was analyzed, and the effect law of edge size on the creep rate of porous metals was revealed. The effect of micro-defects on the creep mechanism of porous metals was clarified, and the constitutive model for predicting the creep life of porous metals was introduced. These studies provide scientific guidance for the long-life service and reliable operation of porous metal structures.