Quasi-zero stiffness （QZS） vibration isolation，by introducing stiffness nonlinearity，effectively addresses the inherent contradiction between load-bearing capacity and isolation bandwidth in conventional linear isolators. As a result，it exhibits superior low-frequency isolation performance. The core challenge in realizing QZS isolation lies in designing mechanical structures whose force-displacement curves simultaneously demonstrate high static stiffness and low dynamic stiffness. Focusing on QZS isolation design methodologies，this paper first outlines the fundamental principles of QZS isolation and categorizes the traditional approaches according to the means of stiffness nonlinearization into four groups： geometric motion nonlinearity，geometric deformation nonlinearity，magnetic nonlinearity，and stress-strain nonlinearity. Subsequently，it introduces emerging design strategies based on nonlinear positive-stiffness structures，including hardening and softening types，and compares them with conventional approaches，with particular attention to their differences in static and dynamic behavior. Finally，the paper summarizes and discusses future directions from the perspectives of negative-stiffness structure design，QZS characteristic tuning，and potential applications，aiming to provide a comprehensive overview of the latest research progress and to offer insights into future development trends of QZS isolation systems.

The friction block of high-speed train brake pads exist in two configurations： holed and non-holed. To investigate the influence of the holed structure on the braking performance，drag braking tests using both types of friction blocks are carried out on a self-developed scaled brake dynamometer for high-speed trains. In addition，finite element simulations are carried out to analyze vibration noise and interface thermal distribution during braking. Experimental and numerical results indicate that the non-holed friction blocks produces continuous self-excited vibration and excites high-intensity squeal noise，whereas the perforated block effectively suppress system instability and reduce squeal noise to some extent. Moreover，the holed structure improves the interfacial thermal distribution，leading to more uniform temperatures on both the friction block surface and the matching brake disc compared to the non-holed blocks.

In response to the challenge of quantitatively diagnosing corrosion damage thickness within pipelines，a quantitative imaging method for pipeline corrosion damage using ultrasonic guided waves is proposed. Firstly，based on the frequency domain finite difference method，a numerical model for multi-path helical propagation of guided waves in pipes is established，enabling rapid calculation of guided wave reception signals when thickness map is known. Secondly，by calculating the received signals in the presence of randomly distributed damage，a database comprising 3 500 samples of damage signals is generated through iteratively running the numerical model. Subsequently，a one-dimensional convolutional neural network imaging model is constructed. The model is trained using the generated database to establish a mapping relationship between thickness maps and reception signals，and inputting the reception signals into the imaging model yields corresponding thickness maps. Finally，the feasibility of the proposed method is experimentally validated. The mean square error between experimental imaging results and actual values is 8.6048×10^-4，the correlation coefficient is 0.711 6，and the imaging model runtime is 0.538 5 seconds. The results indicate that the proposed method can achieve quantitative imaging of corrosion damage thickness within pipelines with high imaging efficiency.

Nonlinear structures exhibit multiple responses under steady-state excitation，making it challenging to directly obtain their dynamic characteristics using traditional vibration test methods. To address this issue，a constant-force dynamic characteristics testing method based on acceleration-response-controlled step-sine frequency sweep test technology is proposed. First，the acceleration response at the excitation point is selected as the control signal，and a step-sine frequency sweep experiment is performed by maintaining a constant response amplitude. Secondly，the resulting simple harmonic excitation spectrum and acceleration response spectrum are obtained through experiments under various acceleration amplitude conditions，and a smooth simple harmonic force surface is constructed using linear interpolation. Then，by extracting the contour lines corresponding to constant force amplitude from this surface，the frequency response curve of the nonlinear structure under constant-force conditions is derived. Finally，the dynamic characteristics of a typical bolted nonlinear structure are investigated. The results show that the proposed approach can accurately capture the frequency response characteristics of bolted nonlinear structures，revealing the pronounced nonlinear dependence on force amplitude. Furthermore，bolt preload and structural reassembly are found to significantly influence the dynamic characteristics of the connection structure.

To investigate the data-driven evolution of rail corrugation in subways，a spatio-temporally dense measurement method is proposed for rapid detection. First，high-precision sensors are used to measure car-body vibration，collecting triaxial acceleration data. Second，vehicle speed and mileage position are estimated by fusing triaxial vibration acceleration from different car bodies. Then，the vertical vibration acceleration of the car body is decomposed via wavelet packet analysis，and a vibration energy ratio index is defined as the ratio of the energy in the characteristic frequency band excited by rail corrugation wavelength to the total vibration energy. The vibration energy ratio threshold is set to automatically identify rail corrugation and output mileage information. Finally，the corrugation wavelength is derived from the ratio of vehicle speed to characteristic frequency，and the relationship between vibration energy ratio and corrugation amplitude is analyzed. Results show that using a vibration energy ratio threshold of 0.2 yields corrugation mileage distribution consistent with that from noise-based identification，and the calculated corrugation wavelength matches the measured value of 175 mm from a corrugation analyzer. Statistical clustering reveals that the relationship between rail corrugation amplitude and vibration energy ratio is not purely linear. Line-wide rapid detection shows that non-corrugated sections account for 76.56% of the track，while corrugation sections account for 23.44%. Among the corrugated sections，those with wavelengths below 60 mm dominate （77.88%），whereas those above 60 mm account for 22.12%.

To study the influence of subway wheel polygons on low-frequency vibration of the car body，the polygon wear of wheels of a subway line is investigated，on the basis of grasping the distribution characteristics of wheel polygons of subway lines. A vertical dynamic model of elastic car body considering wheel polygons is established，by the time-domain integral solution method. The relationship between wheel polygon excitation frequency and low frequency vibration of vehicle body is studied. By comparing the low-frequency vibration of wheel polygons of different orders，the effect of changes in the operating speed of metro vehicles under service conditions and changes in the radius of wheel wear on the polygonal action of the wheel body is discussed separately. It is shown that a wheel polygon of order 1—3 at common operating speeds generate a low-frequency excitation frequency of 0—20 Hz，and when the excitation frequency is close to the first-order droop frequency of 10.2 Hz resonance will occur. At the beginning of service，the influence of the second order wheel polygon becomes severe on the low frequency vibration of the car body. With the wear of the wheel radius during service，the influence of the first three order wheel polygon changes on the vibration law of the car body. This paper provides a good reference value for service subway operation and wheel maintenance.

The theoretical framework of Hertzian contact model for soft sphere collisions is well-established； however limited research has been done on the collision between rigid particles and elastoplastic materials. In this study，a novel damping form is introduced by incorporating the elastoplastic half-space contact constitutive relationship，and a viscoelastoplastic collision model between hard spherical particles and polyurethane surfaces is established. The nonlinear dynamic equations for particle and elastoplastic surface collision are derived. Furthermore，by conducting experiments to measure the coefficient of restitution for coal pellets colliding with polyurethane，the Meyer's index of the polyurethane material and the damping coefficient in the dynamic equations are determined. Additionally，the correctness of the damping model proposed in this study is validated by considering different damping forms in the equations. The changes in contact force at different stages are analyzed under various damping coefficients. The variations of displacement，velocity，and contact force during the collision process between particles and elastoplastic polyurethane are investigated. The results reveal that with an increase in the initial collision velocity，the irreversible plastic deformation of polyurethane increases from 1.636×10^-4 m to 5.657×10^-4 m，the coefficient of restitution decreases from 0.583 2 to 0.501 2，the collision time decreases from 6.963×10^-4 s to 4.737×10^-4 s，and the proportion of plastic compression stage decreases from 59.81% to 59.04%.The model established in this paper can be used in scenarios where particles collide with softer planes，such as the separation of metal ores and particle dampers. This paper provides theoretical support for the transportation，collision，impact，and separation of particle systems.

In order to analyze the reliablility of hypersonic flight vehicles，the longitudinal model of the vehicle is simplified as a cantilever beam structure，and a limit state function is formulated. To address the uncertainty of variable parameters within the limit state function，a hybrid reliability analysis method based on a two-stage Kriging model is proposed. For the first stage，initial sample points are selected to construct an initial Kriging model centered on potential failure points meeting specified accuracy requirements，ensuring the model satisfies this accuracy criterion. For the second stage，a hybrid reliability analysis of the flight vehicle is performed using the initial Kriging model and the first-order reliability method. The Kriging model is adaptively updated by incorporating learning functions，thereby enhancing the efficiency and accuracy of reliability calculations. Comparing the results with existing methods under different parameters of ultimate strength，cantilever beam height，and width，it is demonstrated that the proposed method can meet the requirements for real-time and accurate reliability analysis of the hypersonic vehicle.

To address the issue of metallic objects around a balise affecting its electromagnetic transmission performance，a balise antenna model is established in electromagnetic simulation software. The simulation experiments are carried out by varying three parameters：the metal surface area，the vertical distance between the metal surface and the balise，and the metal surface thickness. The uplink signal amplitude curves of the balise under different parameters are obtained，and the transmission performance metrics are calculated to analyze the impact. Results show that： a larger metal surface area leads to lower performance metrics，such as a reduced number of safety message frames received by the balise transmission module （BTM），with a more significant degradation and greater interference from the sidelobe region. When the metal area is greater than 320 mm×320 mm，the uplink field strength consistency requirement can no longer be met. A greater absolute distance between the metal surface and the balise results in less interference from the sidelobe region，and the distance must be greater than 123 mm to satisfy the field strength consistency requirement. Increased metal surface thickness causes greater interference from the sidelobe region，and the thickness should not exceed 1 mm.

For tip clearance measurement，a multi-section tip clearance measurement and verification simulation rotor test bench is established，and multi-channel tip clearance online measurement software is developed. First，tip clearance is measured using a customized dual-fiber sensor based on laser triangulation. Second，a high-precision displacement platform is utilized to change the tip clearance value，and accurate tip clearance values are measured at different rotational speeds. Last，to address the trigger threshold voltage issue of the acquisition card for measuring tip clearance with dual-fiber sensors，a multi-channel integrated voltage comparator has been designed，which eliminates the time difference on the order of 10^-5 s caused by simultaneous measurement of the two channels of the dual-fiber sensor. The results show that，based on the tip timing principle，the tip clearance can be calculated by measuring only the arrival time of the tip. The mean error of each set of clearances is within 5%，and the standard deviation of the tip clearance measurements in each group is less than 22 µm，demonstrating the accuracy and repeatability of the tip clearance measurement system.