A Vibration Model of Ball Bearings with a Localized Defect Based on the Hertzian Contact Stress Distribution

To study the vibration mechanism of ball bearings with localized defects, a vibration model of a ball bearing based on the Hertzian contact stress distribution is proposed to predict the contact force and vibration response caused by a localized defect. The calculation of the ball-raceway contact force when the ball passes over the defect is key to establishing a defect vibration model. Hertzian contact theory indicates that the contact area between the ball and the raceway is an elliptical contact surface; therefore, a new approach is used to calculate the ball-raceway contact force in the defect area based on the stress distribution and the contact area. The relative motion between the inner ring, the outer ring, and the balls is considered in the proposed model, and the Runge-Kutta algorithm is used to solve the vibration equations. In addition, vibration experiments of a bearing with an outer ring defect under different loads are performed. The numerical signals and experimental signals are compared in the time and frequency domains, and good correspondence between the numerical and experimental results is observed. Comparisons between the traditional model and the proposed model reveal that the proposed model provides more reasonable results

Measurement and Analysis of the Diffusible Hydrogen in Underwater Wet Welding Joint

The diffusible hydrogen in steel weldments is one of the main reasons that led to hydrogen assisted cracking. In this paper, the results of literatures survey and preliminary tests of the diffusible hydrogen in underwater wet welding joint were presented. A fluid-discharge method of for measuring the diffusible hydrogen in weldment was introduced in detail. Two kinds of underwater welding electrode diffusible hydrogen are 26.5 mL/100g and 35.5 mL/100g by fluid-discharge method, which are high levels. The diffusible hydrogen of underwater welding is higher than atmospheric welding, and the result is closely related to welding material. The best way to control the diffusible hydrogen is adjusting welding material and improving fluidity of slag

Measurement and Analysis of the Diffusible Hydrogen in Underwater Wet Welding Joint

The diffusible hydrogen in steel weldments is one of the main reasons that led to hydrogen assisted cracking. In this paper, the results of literatures survey and preliminary tests of the diffusible hydrogen in underwater wet welding joint were presented. A fluid-discharge method of for measuring the diffusible hydrogen in weldment was introduced in detail. Two kinds of underwater welding electrode diffusible hydrogen are 26.5 mL/100g and 35.5 mL/100g by fluid-discharge method, which are high levels. The diffusible hydrogen of underwater welding is higher than atmospheric welding, and the result is closely related to welding material. The best way to control the diffusible hydrogen is adjusting welding material and improving fluidity of slag

Improved Energy Storage Performance of Linear Dielectric Polymer Nanodielectrics with Polydopamine coated BN Nanosheets

Polymer-based nanodielectrics have been intensively investigated for their potential application as energy storage capacitors. However, their relatively low energy density (Ue) and discharging efficiency (η) may greatly limit their practical usage. In present work, high insulating two-dimensional boron nitride nanosheets (BNNS), were introduced into a linear dielectric polymer (P(VDF-TrFE-CTFE)-g-PMMA) matrix to enhance the energy storage performance of the composite. Thanks to the surface coating of polydopamine (PDA) on BN nanosheets, the composite filled with 6 wt% coated BNNS (mBNNS) exhibits significantly improved breakdown strength (Eb) of 540 MV/m and an energy density (Ue) of 11 J/cm3, which are increased by 23% and 100%, respectively as compared with the composite filled with the same content of pristine BNNS. Meanwhile, η of both composites is well retained at around 70% even under a high voltage of 400 MV/m, which is superior to most of the reported composites. This work suggests that complexing polymer matrix with linear dielectric properties with surface coated BNNS fillers with high insulating 2D structure might be a facile strategy to achieve composite dielectrics with simultaneously high energy density and high discharging efficiency