Detection method for contact stress distribution of tapered roller bearings.

The axle box of high-speed train adopts double row tapered roller bearings as transmission parts, and the reliability of bearings directly affects the safety of train operation. Tapered roller bearings can withstand axial and radial loads, their service life being closely related to the distribution of contact stress. The test object is the axle box bearing of high-speed train. According to bearing's structural characteristics, based on the digital speckle correlation method (DSCM) and machine vision, the contact stress distribution detection devices for rollers and complete sets of bearings are developed respectively and an effective detection method is proposed. The contact stress data of the bearing which has reached the service life and the new bearing under the condition of no lubrication and grease lubrication are collected and normalized. Through the geometric relationship, based on the measured data of the selected detection points, the normal and tangential contact stress distribution of the roller and raceway under different contact conditions is obtained by data fitting. The test can be used as an evaluation basis for the effectiveness of bearing modification and provide reference for bearing design.

Influence of Sulfur Atoms on TADF Properties from Through-Space Charge Transfer Excited States.

The harnessing of heavy atom effect of chalcogen elements offers a way for boosting the thermally activated delayed fluorescence (TADF) of purely organic luminescent materials that can harvest triplet excitons. However, the conformational and electronic variations induced by the heavy and large atoms may also have adverse effects on the TADF properties. Herein, the design, synthesis, and structures of a new type of through-space charge transfer (TSCT) emitters containing benzothiazino[2,3,4-kl]phenothiazine (DPTZ) as the donor unit are reported. The influences of S atoms on the emission properties have been systematically investigated by means of theoretical simulations, electrochemical and spectroscopic studies. Although the presence of π-stacking interactions and calculated spin-orbit coupling (SOC) values are beneficial for TSCT-TADF properties, the triplet TSCT states are uplifted to above the locally excited (LE) state of the acceptor moieties. As a result, the new emitters display longer delayed fluorescence lifetimes (τDF ) of 255.0-114.3 µs and lower PLQYs of 45-61 % in comparison with the O-containing congeners (τDF =26.9-6.8 µs; PLQYs=74-71 %). This work highlights that a full consideration of various effects is essential when making use of heavy chalcogen atoms for the design of TADF emitters.

Acceptor-Donor-Acceptor π-Stacking Boosts Intramolecular Through-Space Charge Transfer towards Efficient Red TADF and High-Performance OLEDs.

Organic push-pull systems featuring through-space charge transfer (TSCT) excited states have been disclosed to be capable of exhibiting thermally activated delayed fluorescence (TADF), but to realize high-efficiency long-wavelength emission still remains a challenge. Herein, we report a series of strongly emissive orange-red and red TSCT-TADF emitters having (quasi)planar and rigid donor and acceptor segments which are placed in close proximity and orientated in a cofacial manner. Emission maxima (λ em) of 594-599 nm with photoluminescence quantum yields (PLQYs) of up to 91% and delayed fluorescence lifetimes of down to 4.9 µs have been achieved for new acceptor-donor-acceptor (A-D-A) molecules in doped thin films. The presence of multiple acceptors and the strong intramolecular π-stacking interactions have been unveiled to be crucial for the efficient low-energy TSCT-TADF emissions. Organic light-emitting diodes (OLEDs) based on the new A-D-A emitters demonstrated electroluminescence with maximum external quantum efficiencies (EQEs) of up to 23.2% for the red TSCT-TADF emitters. An EQE of 18.9% at the brightness of 1000 cd m-2 represents one of the highest values for red TADF OLEDs. This work demonstrates a modular approach for developing high-performance red TADF emitters through engineering through-space interactions, and it may also provide implications to the design of TADF emitter with other colours.

Colossal Magnetoresistance in Ti Lightly Doped Cr2Se3 Single Crystals with a Layered Structure.

Stoichiometric Cr2Se3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr2Se3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr2Se3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr2Se3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr2Se3 crystal from strong out-of-plane to weak in-plane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr2Se3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.