Influence of Vibrational Loading on Deformation Behavior of Metallic Glass: A Molecular Dynamics Study

The influence of vibrational loading on the deformation behavior of a Zr50Cu46Al4 metallic glass (MG) was characterized via molecular dynamics approaches. High-frequency (1 GHz) vibrational loading was imposed on the elastoplastic deformation stage during the uniaxial tension of the MG conducted at 50 K. It was found that imposing vibrational loading scarcely reduces the average deformation resistance. On the contrary, it results in a notable residual hardening effect after the vibrational loading is removed, which differs significantly from the previously reported acoustic softening mechanisms. Vibrational loading can increase the fraction of STZed atoms and enhance the shear localization degree, which is beneficial to the shear deformation of MGs. Meanwhile, the influence of vibrational loading on the local microstructure of MG is negligible. A plausible explanation of these phenomena is given by considering the accelerated aging of MG stemming from the β relaxation.

Assessment Procedures for Mechanical Securing Components of LNG Cargo Containment System With Potential Damages

This research has been performed to evaluate the structural integrity of the LNG cargo containment system. The structural integrity under vibrational loading and hull deflection was evaluated for damaged and undamaged systems. The test Mock-ups had been constructed for vibrational loading tests and hull deflection tests to compare the system behaviors under the damaged and the undamaged conditions. The damaged Mock-up was constructed with particular damages at the mechanical joints of the top and the bottom boards. The damages of the joints were applied at the designated points, which were selected based on the FEM analysis that compares the stress levels for the various damaged systems. The static tests were performed when the bottom board and the top board was installed, respectively. The visual inspection had been performed to compare the structural integrity of the damaged and the undamaged system during and after the tests. The vibrational loading tests had also been performed to compare the fatigue performance of both the damaged and the undamaged system. Endurance tests were performed for both vertical and lateral directions based on the results of resonance search tests. The specimens were vibrated at the resonant frequencies determined to most seriously affect the structural integrity. Abnormality of the acceleration time history had been monitored during the endurance tests and the acceleration level at the beginning of the test was compared with the level at the end of the test. After the endurance tests, the structural integrity of both systems had been thoroughly investigated by visual inspection.

Fatigue Life Prediction for Caliper Guide Pin under Random Vibrational Loading

A fatigue life prediction tool was developed for caliper guide pins under random vibrational loading. The Pie-Slice model was designed to provide detailed information about the failure location, orientation, and damage magnitude. A component test fixture was developed to determine the strain-life curve for a given guide pin design. Statistical analysis was conducted to insure the repeatability of the failure mode and the robustness of the setup. Weibull analysis was performed to the measured guide pin strain-life in order to insure that the developed strain-life data to insure that developed strain-life curve will account for all the manufacturing process variations, from a component, assembly, and a system level to a certain level of reliability and confidence. Rainflow cycle count was used to bin the damaging and non-damaging cycles based on their stain level. Fatigue life calculation was performed using the Smith-Watson-Topper strain-life approach. The predictive tool was able to accurately estimate the cumulative fatigue damage for guide pins under random loading conditions. The Pie-Slice model was also able to predict the failure location and orientation of a crack, as well as the damage magnitude. Both tools were validated using a pre-designed random block-load sequence at constant amplitude..