The release load of holdback bar will affect the safety of catapult-assisted takeoff of carrier-based aircraft, and the accurate control of releasing the load will ensure success. The magnitude and the control accuracy of release load are important parameters which impact the takeoff performance, therefore unstable release load and insufficient release precision are the main factors affecting the takeoff safety. In this paper, mechanical models of the carrier-based aircraft in the catapult-assisted takeoff tensioning state and gliding state after release are established based on multi-body dynamics, contact mechanics and tribological theory, and the influence of the release load of the holdback bar on the catapult-assisted takeoff performance is analyzed. Furthermore, a kinetic model of the holdback bar device is established, and the kinetic characteristics of the release process of the holdback bar are studied. Based on the kinetic model and friction model of the holdback bar, the influencing factors of the sensitivity of the holdback bar release load are analyzed and the structural parameters are optimized. The results show that the released load decreases slowly with the increase of the contact surface angle of the holdback bar structure and increases rapidly when that angle reaches the critical value; besides, the release load increases slowly with the increase of the friction coefficient of the contact surface and increases faster when the critical friction coefficient is reached.
This study concentrates on the fatigue performance of ultra-high-strength steel Aermet100 under different loading rates. The standard specimen measured the static mechanical properties of Aermet100 steel, based on which the basic mechanical properties and fracture characteristics of the sample before and after necking was obtained. To take the strain rate effect into account, this study uses the dynamic constitutive model Johnson-Cook. The equation parameters are fitted through dynamic mechanical tests and quasi-static tests. This model is input into ABAQUS user-defined program afterward. Referring to the work done above, along with the extended finite element method (XFEM), this study establishes the dynamic fracture finite element model of the Aermet100 steel specimen on the basis of the continuous damage mechanics. Five groups of specimen fatigue tests were carried out in the laboratory. Simulation results show the feasibility and accuracy of the integrated XFEM model with the same loading and boundary conditions. The experimental data and simulation results prove that, in the loading time range of 0.0001 ~ 1s, the life cycles increase as the loading rate increases. It is worth mentioning that when the loading time is in the order of 0.0001s, the life changes significantly.
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