The Reliability Life of 7B04 Aluminum Alloy under Alternate Action of Corrosion and Fatigue

Experiment of alternate action of corrosion and fatigue on 7B04 aluminum alloy was carried out in this paper and fatigue life was obtained. One of the characteristics about fatigue life is that it is not always decreasing with the increasing of corrosion time. The surface splits caused by the corrosion of intruding and extruding slip steps on the surface and decreasing of stress concentration around corrosion pits were the main reasons. Single side allowance factor k was proposed to calculate reliability fatigue life with both reliability and confidence. Reliability, confidence, and specimen number had affection on the value of k. The reliability influences more greatly the reliability fatigue life compared to the confidence. The safe fatigue life is smaller than median life and it was safe to administrate aircraft life using safe fatigue life

Hybrid Structure Based Tracking and Consensus for Multiple Motors

This paper investigates a hybrid structure based synchronous control strategy for multimotor system of shaftless-driven printing press. Many existing algorithms can obtain a stable synchronous system; however, the obtained stable system may encounter a large enough disturbance that can destroy the synchronization. Focusing on this challenging technological problem about how to receive more robust synchronization during steady-state process, this paper first proposes a state-dependent-switching based leader-following control approach, in which synchronization includes two parts, one associated with tracking control for all members, and the other one associated with consensus maintained among followers in the case that one follower loses synchronization with the leader during steady-state motion. By employing the algebra graph theory, matrix theory, and Lyapunov analysis, the convergence and stability of the given multimotor system are proved. Finally, simulation examples are presented to demonstrate the effectiveness and robustness of the theoretical results

Fault Reconstruction Based on Sliding Mode Observer for Nonlinear Systems

This paper presents a precision fault reconstruction scheme for a class of nonlinear systems involving unknown input disturbances. First, using the coordinate transformation algorithm, the disturbances and faults of the system are fully decoupled. Therefore, it is possible to eliminate the influence of disturbances to the system, namely, better disturbances robustness. On this basis, the design of a sliding mode state observer makes the most genuine reconstruction realizable, instead of estimation of faults. Furthermore, with the equivalent principle of sliding mode variable structure, the precision reconstruction of arbitrary nonlinear faults is achieved. Finally, the applications of fault reconstruction in a third-order nonlinear theoretical model with disturbances and in a single-link robot system, respectively, have demonstrated the validity of the proposed scheme

A Design Method for Fault Reconfiguration and Fault-Tolerant Control of a Servo Motor

A design scheme that integrates fault reconfiguration and fault-tolerant position control is proposed for a nonlinear servo system with friction. Analysis of the non-linear friction torque and fault in the system is used to guide design of a sliding mode position controller. A sliding mode observer is designed to achieve fault reconfiguration based on the equivalence principle. Thus, active fault-tolerant position control of the system can be realized. A real-time simulation experiment is performed on a hardware-in-loop simulation platform. The results show that the system reconfigures well for both incipient and abrupt faults. Under the fault-tolerant control mechanism, the output signal for the system position can rapidly track given values without being influenced by faults

ASSESSMENT ON INITIAL FATIGUE QUALITY OF AIRCRAFT TYPICAL CONNECTED STRUCTURE

Durability experimental study is performed on single-piece specimens with through-hole and double-piece specimens with fastening holes of three different lengths on random loading. The weak area of structures is gained through threedimensional finite element analysis,considering pre tightening force of bolts and the interference fit between bolts and holes.Based on the results of durability experimental analysis,a new method is put forward to assess the initial fatigue quality（ IFQ） of structures and controlled stress curves are drawn to compare with this method. As a result,the method to assess IFQ of structures in this paper is proved to be effective. The IFQ of double-piece specimens with fastening holes is higher than that of single-piece specimens with through-hole. Furthermore,the IFQ increases with the decreasing of the length of the structure

Effect of Alternate Corrosion and Fatigue on Fatigue Crack Growth Characterization of 2024-T4 Aluminum Alloy

To investigate the effect of alternate corrosion and fatigue on fatigue crack growth characterization of 2024-T4 aluminum alloy, the pure fatigue test, “corrosion + fatigue” test (commonly known as pre-corrosion fatigue), and the “fatigue + corrosion + fatigue” alternating test of single-sided notched specimen of 2024-T4 aluminum alloy were carried out. The fatigue crack life of alternate corrosion and fatigue is longer than that of the pre-corrosion fatigue when the corrosion time is the same. And the more the times of alternating, the longer the crack growth life will be. This is mainly because the fatigue crack growth rate will change suddenly, which will have a certain hysteresis effect on the fatigue crack growth. The corrosion and fracture morphology characteristics of the alternate test were examined by scanning electron microscopy (SEM), and the composition of corrosion products was examined by the energy dispersion spectrum (EDS). The prediction model of fatigue crack growth rate considering the alternating hysteresis effect of corrosion and fatigue based on the Paris formula was established, and the parameters and precision of the model were calculated and verified. The results show that the model has certain engineering application value

Online Estimation of the Adhesion Coefficient and Its Derivative Based on the Cascading SMC Observer

The adhesion coefficient of wheel-rail surface cannot be directly measured, so a cascaded sliding-mode observer is proposed to observe adhesion coefficient and its derivative. A kinetic model for running heavy-duty locomotive is also established. The state equation of wheel adhesion control system is derived from the equation of traction motor torque balance, and adhesion coefficient is proposed to be calculated by load torque. Then, the cascaded sliding-mode observer is designed, and its stability is justified by Lyapunov stability. Based on the equivalence control principle for sliding-mode variable structure, an algorithm to estimate adhesion coefficient and its derivative is established. The simulation and experimental results are used to verify the effectiveness of the observer with load variations or wheel-rail status changes

Design of Sliding Mode Variable Structure Servo Driver Based on Hardware

Based on sliding mode control theory, in this paper a control method of tension control system in printing machine is presented. Firstly, a sliding mode controller for decreasing steady-state error is designed based on the servo motor model in the tension control system of printing machine, and the simulation verification is carried out in the MATLAB/Simulink. Further the hardware circuit is implemented through the design of operational amplifier to reduce the chattering of the system, and the trapezoidal wave is served as the input signal to reduce the overshoot of printing machine generated at the moment of start and stop, ensuring the smooth start and stop of the system. With the simulation results and the experimental results being consistent, it illustrates the correctness and practicality of the proposed method

STUDY ON THE EQUIVALENCE RELATION BETWEEN THE ACCELERATED CORROSION OF SALT SPRAY AND THE COASTAL ATMOSPHERIC ENVIRONMENT

The fatigue feature of LY12-CZ aluminum alloy under atmospheric corrosion environment is studied and the corrosion law is analyzed. Atmosphere data of the service place is collected and the accelerating environment spectrum is built through weighting analysis. The accelerating experiment of LY12-CZ aluminum alloy is carried out and the accelerating factor of spectrum is calculated by analyzing the effective theory of corrosion and declining rule of fatigue life