Fatigue failure transition evaluation of load carrying cruciform welded joints by effective notch energy model

This paper investigates fatigue failure transition boundary of Load-carrying Cruciform Weld Joint (LCWJ) with different yield strength mismatch ratios and geometrical sizes of welded joints under cyclic loading conditions using a semi-empirical analytical method, which is based on the obtained fatigue test data and finite element analysis. To examine the fatigue failure mode transition relationship in CLWJs, different mismatch ratios and local geometries (plate thickness, weld size, and penetration ratio) were designed and fabricated to evaluate potential fatigue initiations (weld toe or weld root). The numerical simulations of cyclic responses at weld toe and weld root were conducted by material cyclic plastic properties from fatigue data of standard coupon specimens. A uniform effective notch energy indicator in the previous investigation was utilized to characterize the low and high cycle fatigue life by extending the SED method on the combination of generalized Neuber concept of Fictitious Notch Rounding (FNR). The related analytical formulations for potential failure points were used to predict the fatigue assessment indicator of LCWJ, considering the effects of plasticity and mechanical heterogeneity and geometry configurations. The effective notch energy relationship between the weld toe and weld root in LCWJ was determined by the established analytical solutions, verified by the fatigue data. The strategy is expected to provide some insights into assessing fatigue life for various types of weld joints for different potential failure locations

Controlling Welding Residual Stress and Distortion of High-Strength Aluminum Alloy Thin Plates by a Trailing Hybrid High-Speed Gas Fluid Field

This paper presents an investigation of the welding residual stress and distortion of LY12 high-strength aluminum alloy (6061) by improving the local welding thermal and mechanical fields. A trailing hybrid high-speed gas fluid method was proposed and applied to decrease the welding residual stress and distortion of 6061 aluminum alloy efficiently. Firstly, the temperature and stress fields were calculated using the finite element simulation method, considering a trailing hybrid high-speed gas fluid field. The distance between the aerodynamic load and the heat source action was a key factor determined by the simulation method. In addition, the reasonable effective range of gas pressure was obtained. Subsequently, welding and distortion tests were conducted on the self-developed device under conventional welding and high-speed gas fluid field conditions. The results showed that an aerodynamic load under 30 MPa of gas pressure was available near the area at a distance of 20–28 mm from the heat source for thin plate welding distortion. The peak longitudinal residual tensile stresses in the weld’s mid-length section decreased by 77.73%, the peak residual compressive stresses decreased by 69.23% compared with conventional welding, and the deflection distortion disappeared almost entirely. The maximum deflection of the distortion was only 1.79 mm, which was 83.76% lower than the 11.02 mm of the conventional welding distortion. This validates that the method can simultaneously and greatly eliminate the welding residual stress and distortion

A Vps21 endocytic module regulates autophagy

In autophagy, the double-membrane autophagosome delivers cellular components for their degradation in the lysosome. The conserved Ypt/Rab GTPases regulate all cellular trafficking pathways, including autophagy. These GTPases function in modules that include guanine-nucleotide exchange factor (GEF) activators and downstream effectors. Rab7 and its yeast homologue, Ypt7, in the context of such a module, regulate the fusion of both late endosomes and autophagosomes with the lysosome. In yeast, the Rab5-related Vps21 is known for its role in early- to late-endosome transport. Here we show an additional role for Vps21 in autophagy. First, vps21Δ mutant cells are defective in selective and nonselective autophagy. Second, fluorescence and electron microscopy analyses show that vps21Δ mutant cells accumulate clusters of autophagosomal structures outside the vacuole. Third, cells with mutations in other members of the endocytic Vps21 module, including the GEF Vps9 and factors that function downstream of Vps21, Vac1, CORVET, Pep12, and Vps45, are also defective in autophagy and accumulate clusters of autophagosomes. Finally, Vps21 localizes to PAS. We propose that the endocytic Vps21 module also regulates autophagy. These findings support the idea that the two pathways leading to the lysosome—endocytosis and autophagy—converge through the Vps21 and Ypt7 GTPase modules

Monolayer Bismuthene-Metal Contacts: A Theoretical Study

Bismuthene, a bismuth analogue of graphene, has a moderate band gap, has a high carrier mobility, has a topological nontriviality, has a high stability at room temperature, has an easy transferability, and is very attractive for electronics, optronics, and spintronics. The electrical contact plays a critical role in an actual device. The interfacial properties of monolayer (ML) bismuthene in contact with the metal electrodes spanning a wide work function range in a field-effect transistor configuration are systematically studied for the first time by using both first-principles electronic structure calculations and quantum transport simulations. The ML bismuthene always undergoes metallization upon contact with the six metal electrodes owing to a strong interaction. According to the quantum transport simulations, apparent metal-induced gap states (MIGSs) formed in the semiconductor–metal interface give rise to a strong Fermi-level pinning. As a result, the ML bismuthene forms an n-type Schottky contact with Ir/Ag/Ti electrodes with electron Schottky barrier heights (SBHs) of 0.17, 0.22, and 0.25 eV, respectively, and a p-type Schottky contact with Pt/Al/Au electrodes with hole SBHs of 0.09, 0.16, and 0.38 eV, respectively. The effective channel length of the ML bismuthene transistors is also significantly reduced by the MIGSs. However, the MIGSs are eliminated and the effective channel length is increased when ML graphene is used as an electrode, accompanied by a small hole SBH of 0.06 eV (quasi-Ohmic contact). Hence, an insight is provided into the interfacial properties of the ML bismuthene–metal composite systems and a guidance is provided for the choice of metal electrodes in ML bismuthene devices