Strengthening of RC Beams and Frames by External Prestressing

Ph.DDOCTOR OF PHILOSOPH

Edge-pinning effect of graphene nanoflakes sliding atop graphene

Edge effect is one of the detrimental factors preventing superlubricity in laminar solid lubricants. Separating the friction contribution from the edge atom and inner atom is of paramount importance for rational design of ultralow friction across scales in van der Waals heterostructures. To decouple these contributions and provide the underlying microscopic origin at the atomistic level, we considered two contrast models, namely, graphene nanoflakes with dimerized and pristine edges sliding on graphene monolayer based on extensive ab initio calculations. We found the edge contribution to friction is lattice orientation dependence. In particular, edge pinning effect by dimerization is obvious for misaligned contact but suppressed in aligned lattice orientation. The former case providing local commensuration along edges is reminiscent of Aubry's pinned phase and the contribution of per edge carbon atom to the sliding potential energy corrugation is even 1.5 times more than that of an atom in bilayer graphene under commensurate contact. Furthermore, we demonstrated that the dimerized edges as high frictional pinning sites are robust to strain engineering and even enhanced by fluorination. Both structural and chemical modification in the tribological system constructed here offers the atomic details to dissect the undesirable edge pinning effect in layered materials which may give rise to the marked discrepancies in measured friction parameters from the same superlubric sample or different samples with the same size and identical preparation.Comment: 18 pages,6 figure

Ultra-high strength metal matrix composites (MMCs) with extended ductility manufactured by size-controlled powder and spherical cast tungsten carbide

The main challenge of particle reinforced metal matrix composites (MMCs) is balancing strength and ductility. This research uses type 420 stainless steel and spherical cast tungsten carbide (WC/W2C) with a similar powder size and range as raw powders to manufacture laser powder bed fusion (LPBF) 420 + 5 wt% WC/W2C MMCs. LPBF 420 + 5 wt% WC/W2C MMCs contain austenite, martensite, and W-rich carbides (WC/W2C, FeW3C, M6C, and M7C3) from nanometre to micrometre scale. The well-balanced composition creates a crack-free reaction layer between the reinforced particles and matrix. This reaction layer consists of two distinct layers, depending on the element concentration. The LPBF 420 + 5 wt% WC/W2C MMCs achieved an excellent compressive strength of ∼5.5 GPa and a considerable fracture strain exceeding 50 %. The underlying mechanisms for the improved mechanical properties are discussed, providing further insight to advance the application of MMCs via additive manufacturing

Unveiling the additive-assisted oriented growth of perovskite crystallite for high performance light-emitting diodes.

Solution-processed metal halide perovskites have been recognized as one of the most promising semiconductors, with applications in light-emitting diodes (LEDs), solar cells and lasers. Various additives have been widely used in perovskite precursor solutions, aiming to improve the formed perovskite film quality through passivating defects and controlling the crystallinity. The additive's role of defect passivation has been intensively investigated, while a deep understanding of how additives influence the crystallization process of perovskites is lacking. Here, we reveal a general additive-assisted crystal formation pathway for FAPbI3 perovskite with vertical orientation, by tracking the chemical interaction in the precursor solution and crystallographic evolution during the film formation process. The resulting understanding motivates us to use a new additive with multi-functional groups, 2-(2-(2-Aminoethoxy)ethoxy)acetic acid, which can facilitate the orientated growth of perovskite and passivate defects, leading to perovskite layer with high crystallinity and low defect density and thereby record-high performance NIR perovskite LEDs (~800 nm emission peak, a peak external quantum efficiency of 22.2% with enhanced stability)

A Driving Behavior Planning and Trajectory Generation Method for Autonomous Electric Bus

A framework of path planning for autonomous electric bus is presented. ArcGIS platform is utilized for map-building and global path planning. Firstly, a high-precision map is built based on GPS in ArcGIS for global planning. Then the global optimal path is obtained by network analysis tool in ArcGIS. To facilitate local planning, WGS-84 coordinates in the map are converted to local coordinates. Secondly, a double-layer finite state machine (FSM) is devised to plan driving behavior under different driving scenarios, such as structured driving, lane changing, turning, and so on. Besides, local optimal trajectory is generated by cubic polynomial, which takes full account of the safety and kinetics of the electric bus. Finally, the simulation results show that the framework is reliable and feasible for driving behavior planning and trajectory generation. Furthermore, its validity is proven with an autonomous bus platform 12 m in length

Passivity breakdown on copper: Influence of borate anion

Passivity breakdown on copper: Influence of borate anio

Pit growth kinetics of additively manufactured MoNi over-alloyed type 316L stainless steel

The microstructure and corrosion performance of wrought, laser powder bed fusion (LPBF), and MoNi over-alloyed LPBF type 316L stainless steel is compared. Adding Mo and Ni to LPBF 316L stainless steel resulted in ẟ-ferrite. Potentio-dynamic polarisation was used to rank all microstructures, with LPBF + MoNi has more resistant than LPBF and wrought material. Bipolar electrochemistry was applied, with LPBF samples having the lowest critical pitting potential and highest pit growth kinetics. The best corrosion performance was for LPBF + MoNi stainless steel. Different pitting corrosion resistance as function of process directions were found. The tiny pores negatively impacted the pitting performance

Optimized wear behaviors and related wear mechanisms of medium entropy alloy-based composite coatings

In this work, the (10 wt%, 30 wt%, 50 wt%) TiC reinforced AlFeCrCo medium entropy alloy (MEA) lightweight composite coatings with the extremely low porosity were successfully fabricated on Mg alloy substrate by resistance seam processing. The results showed that the microstructure of composite coating was consisting of a BCC-based MEA matrix and TiC particles, and a good metallurgical bonding with a semi-coherent relationship was formed between the coating and Mg alloy. Furthermore, the lightweight composite coatings (5.6–6.5 g cm−3) showed improved corrosion resistance over Mg alloy substrate. Specifically, the composite coatings exhibited optimized wear performance in the dry, deionized water and 3.5 wt% NaCl solution conditions with the increasing TiC content, surpassing related high/medium entropy alloy coatings, which is attributed to the formation of a coherent interface between the MEA matrix and the TiC particles. The first-principles calculations were performed to elucidate the nature for the higher bonding strength of TiC/MEA interface. In these wear conditions, the main wear mechanisms of composite coatings were discussed in terms of adhesive wear, oxidative wear and/or corrosive wear, in connection with their microstructure features and electrochemical behaviors. Based on the elevated anti-corrosion ability, this work has provided a strategy to fabricate advanced coatings on Mg alloys endowing with lower density, interfacial metallurgical bonding and optimized wear resistance, substantially contributing to the development of high-performance composite coatings