Effect of Geometrical Parameters on the Mechanical Performance of Bamboo-Inspired Gradient Hollow-Strut Octet Lattice Structure Fabricated by Additive Manufacturing.

Hollow-strut metal lattice structures are currently attracting extensive attention due to their excellent mechanical performance. Inspired by the node structure of bamboo, this study aimed to investigate the mechanical performance of the gradient hollow-strut octet lattice structure fabricated by laser powder bed fusion (LPBF). The effect of geometrical parameters on the yield strength, Young's modulus and energy absorption of the designed octet unit cells were studied and optimized by FEA analysis. The hollow-strut geometrical parameters that deliver the best mechanical property combinations were identified, and the corresponding unit cells were then redesigned into the 3 × 3 × 3 type lattice structures for experimental evaluations. Compression tests confirmed that the designed gradient hollow-strut octet lattice structures demonstrated superior mechanical properties and deformation stability than their solid-strut lattice structure counterparts. The underlying deformation mechanism analysis revealed that the remarkably enhanced bending strength of the gradient hollow-strut lattice structure made significant contributions to its mechanical performance improvement. This study is envisaged to shed light on future hollow-strut metal lattice structure design for lightweight applications, with the final aim of enhancing the component's mechanical properties and/or lowering its density as compared with the solid-strut lattice structures.

The J2 evolution model and control technology of the main roadway surrounding rock under superimposed influence of double-coal seam mining.

Under double-seam mining, the main roadway surrounding rock is affected by the superposition of the advanced stress of the two-seam coal working faces. The stress superposition mode and degree are of great significance to the width calculation of the protective coal pillar and the determination of the critical control direction of the surrounding rock. This paper uses theoretical analysis, numerical simulation, and site engineering practice to carry out targeted research. The conclusions are as follows: Under different lateral pressure coefficients, the superposition evolution law of maximum principal stress direction of two coal seams with different offsets; Two developmental trends and three types of evolution models of J2 peak zone (the critical area of the stress increase and deflection changes) under different superimposed loading modes are summarized. Based on the typical asymmetric evolution model of the J2 peak zone, an asymmetric truss-cable co-anchoring method is proposed aimed at the J2 critical zone. The field monitoring results show that the main roadway surrounding rock is stable after support when the upper coal seam protective coal pillar is left 80 m, and the lower one is 60 m wide. It is of great reference importance for similar engineering practices.

Enhanced High-Temperature Wear Performance of H13 Steel through TiC Incorporation by Laser Metal Deposition.

High-temperature wear failure has been a major challenge to die parts. This work provides a comprehensive study on the high-temperature wear performance of a TiC/H13 composite coating prepared by laser metal deposition (LMD). The microstructures of wrought H13 samples, LMD-processed H13 and TiC/H13 samples were systematically investigated. The refined martensite size, the uniform distribution of TiC ceramic particles, as well as their bonding with the matrix endowed the fabricated composite coating with superior hardness. The LMD-prepared TiC/H13 composite coating material demonstrated outstanding wear resistance when compared with other counterparts, mainly due to the high thermal stability and the load-transferring effect triggered by the introduced TiC ceramic particles. The dominated wear mechanism transition from severe ploughing in the wrought H13 material to mild delamination in the TiC/H13 composite coating was confirmed. The present study is expected to shed light on high-temperature wear-resistant coating material design and applications within the highly demanding mould industry.

Precipitation kinetics, microstructure evolution and mechanical behavior of a developed Al-Mn-Sc alloy fabricated by selective laser melting.

The dynamic metallurgical characteristics of the selective laser melting (SLM) process offer fabricated materials with non-equilibrium microstructures compared to their cast and wrought counterparts. To date, few studies on the precipitation kinetics of SLM processed heat-treatable alloys have been reported, despite the importance of obtaining such detailed knowledge for optimizing the mechanical properties. In this study, for the first time, the precipitation behavior of an SLM fabricated Al-Mn-Sc alloy was systematically investigated over the temperature range of 300-450 °C. The combination of in-situ synchrotron-based ultra-small angle X-ray scattering (USAXS), small angle X-ray scattering (SAXS) and X-ray diffraction (XRD) revealed the continuous evolution of Al6Mn and Al3Sc precipitates upon isothermal heating in both precipitate structure and morphology, which was confirmed by ex-situ transmission electron microscopy (TEM) studies. A pseudo-delay nucleation and growth phenomenon of the Al3Sc precipitates was observed for the SLM fabricated Al-Mn-Sc alloy. This phenomenon was attributed to the preformed Sc clusters in the as-fabricated condition due to the intrinsic heat treatment effect induced by the unique layer-by-layer building nature of SLM. The growth kinetics for the Al6Mn and Al3Sc precipitates were established based on the in-situ X-ray studies, with the respective activation energies determined to be (74 ± 4) kJ/mol and (63 ± 9) kJ/mol. The role of the precipitate evolution on the final mechanical properties was evaluated by tensile testing, and an observed discontinuous yielding phenomenon was effectively alleviated with increased aging temperatures.

Hypoxia decrease expression of cartilage oligomeric matrix protein to promote phenotype switching of pulmonary arterial smooth muscle cells.

Extracellular matrix proteins play important roles in the development of pulmonary hypertension(pH). However, the role of Cartilage oligomeric matrix protein (COMP) in the development of hypoxia-induced pH is largely unknown. We tested the hypothesis that COMP deficiency induced by hypoxia leads to the phenotype switching of pulmonary arterial smooth muscle cells (PASMCs). The expression of COMP decreased in a chronic hypoxia rat pH model (P<0.05) and in PASMCs under hypoxia (3%O2) (P<0.05). The expressions of differentiated marker proteins reduced in the pulmonary arteries from 5 month old COMP-/- mice and in PASMCs under hypoxia or with the siRNA of COMP treatment under normoxia, but increased in PASMCs with adenovirus-increased COMP under hypoxia. The absorbance of cell counting kit-8 at 450nm and the expressions of proliferating cell nuclear antigen (PCNA) and osteopontin increased in PASMCs with the siRNA of COMP under normoxia (P<0.05). PCNA and osteopontin decreased in PASMCs with adenovirus-increased COMP under hypoxia (P<0.05). Additionally, the expression of bone morphogenetic protein receptor 2 (BMPR2) was reduced in COMP-/- mice (P<0.01). Both mRNA and protein levels of bone morphogenetic protein 2 (BMP2) were lower in PASMCs with the siRNA of COMP (P<0.05). The protein level of BMP2 could be reversed by adenovirus-increased COMP under hypoxia (P<0.05). These data suggest that COMP could normally have a protective role against PASMC phenotype switching and maintain BMP2/BMPR2 signaling, and these protective actions could be lost as a result of hypoxia promoting a depletion of COMP.

[The influence of rhAng-1 on endothelial junctions of BBB after focal cerebral ischemia/reperfusion in rats].

OBJECTIVE: This study was performed to determine whether recombinant human angiopoietin-1 (rhAng-1) decreases the permeability of the blood-brain barrier (BBB) in focal cerebral ischemia and reperfusion rats, whether RhAng-1 opens the BBB by affecting tight junction associated proteins zonnula occludin-1 (ZO-1), occludin and adherens junction protein vascular endothelial (VE)-cadherin. METHODS: The rats were divided into eight groups randomly( n = 10): (1) sham-operated group; (2) ischemia group; (3)-(5) ischemia/reperfusion (middle cerebral artery occlusion and reperfusion (MCAO/R) 12 h, 48 h, and 7 days) and 0.9% saline groups; (6)-(8) ischemia/reperfusion (MCAO/R 12 h, 48 h, and 7 days) and rhAng-1 groups. The Bee permeability was assessed by Evans blue extravasation. The messenger RNA and protein expressions of ZO-1, occludin, and VE-cadherin were determined by reverse transcription-polymerase chain reaction, Western blot, and immunohistochemistry assays. RESULTS: The BBB permeability and the brain infarct volume were significantly decreased after rhAng-1 injection. The expressions of ZO-1, occludin, and VE-cadherin were increased after rhAng-1 injection. CONCLUSION: rhAng-1 may decrease the permeability of BBB in MCAO/R rats by upregulation of ZO-1, occludin, and VE-cadherin.