Intrinsic Heat Treatment Induced Graded Surficial Microstructure and Tribological Properties of Selective Laser Melted Titanium

In the course of the selective laser melting (SLM) process, the part is built layer by layer involving partial remelting/heating of the previous layer, called as intrinsic heat treatment. Therefore, superficial properties of as-built parts are somewhat different from that of the inside of the part. In this work, the nano-tribological behavior of the commercial pure Ti (CP-Ti) sample built using SLM was investigated considering the near-surface regions with focus on the effect of intrinsic heat treatment. Microstructure and nano-testing allow identifying specific sliding behaviors in three attitude regions: (I) surface (0–50 µm), (II) subsurface (50–200 µm), and (III) inner-part (below 200 µm). The average hardness drops slightly when moving from Regions I and II (3.35 GPa) to Region III (3.09 GPa). The coefficient of friction (COF) values vary from 0.18 to 0.45 for all three regions, and the Region III presents highest worn trace width of 5.8 μm. Regions I and III promote a stick-and-slip behavior while sliding is smooth and continuous in Region II. This gradient microstructural characterization enables associating the behavior of Region II to large-sized lath martensite α′ morphology, which is different from the Regions I and III with finer microstructure. A finite element analysis (FEA) thermal model suggests that the existence of the three identified regions is the consequence of the intrinsic heat treatment induced by the SLM process, in which the remelting/heating and recrystallization have been considered as the main reasons for microstructure coarsening and refinement between Regions I and II, Regions II and III, respectively.

HIGHER-ORDER SLIDING MODE DYNAMICS DESIGN FOR A CLASS OF SINGLE-INPUT LINEAR SYSTEMS

The paper considers a higher-order sliding mode dynamics design in a class of single-input linear systems having the invertible system matrix. The proposed sliding manifold selection method simultaneously provides a necessary relative degree of the sliding variable for a specific sliding mode order and the desired system dynamics after establishing that sliding mode. It is shown that the found unique solution satisfies these requirements. The theoretically obtained result is validated through a numerical example and illustrated by digital simulations.

Optimization of Friction Behavior Characteristics by Coating with Solid Lubricants

Increasing the lifetime of machine elements whose operation involves the development of friction processes and diminishing energy losses by friction can be achieved by using solid lubricants. In this regard, a method applied to improve the friction behavior of machine elements is electrostatic coating of the surfaces of interest with polyester layers that include particles of solid lubricants, such as molybdenum disulfide or graphite. Experimental research was conducted to highlight the influence of normal force, the concentration of solid lubricant particles in polyester, and specific sliding between surfaces involved in the friction process on the deposited layer’s lifetime and on the friction coefficient. Grey analysis was employed to identify sets of input factors that would lead to the most convenient values of the lifetime and energy friction losses when using polyester layers that incorporate molybdenum or graphite particles. Specialized software was elaborated in a MATLAB environment to use the grey relational analysis in identifying the optimal values of the process input factors for distinct weights of the output parameters.

Improved calculation of load-dependent gear losses by consideration of so far disregarded influences

The topic of this study was subject to the efficiency calculation of gearboxes. Additional analyses were performed with regard to an existing calculation approach, to improve the calculation of load-dependent gear losses by so far disregarded influences. On the one hand, the influence of the driving direction was investigated. During this, the driving and driven test gears considered showed high differences of the specific sliding at tooth root and tooth tip. On the other hand, the influence of the change of contact ratio under load was studied. Both influences showed considerable influence on the load-dependent gear losses. An equation for an optimized calculation of the load-dependent gear losses is given.

Comparison between the AFNOR Method and the Imposition of Balanced Maximum Specific Sliding in the Imposed Centre Distance Problem

Successive editions of Henriot’s treatise on gears, and an AFNOR document, present an approximate procedure for the choice of profile shift values for the pinion and wheel when a center distance value is imposed in a cylindrical gear pair. That procedure aims at achieving an approximate balancing of the maximum specific sliding values of the pinion and of the wheel. The method involves a loosely defined choice of an auxiliary parameter, but no information is available relating this choice with the level of attainment of the intended balancing of maximum specific sliding values. This assessment, if needed, requires a subsequent analysis for verification.Since no information is available evaluating the procedure, the purpose of this work is to provide a thorough rigorous analysis of the method, highlighting its qualities but also its shortcomings.

A Specific Sliding Mode Control for Autopilot Design of Bank-to-Turn Missiles

This paper studies the BTT missile's sliding mode flight controller. Firstly, the control model is established according to dynamic inverse method and the general dynamic equation of the missile flying in the atmosphere. Then, the sliding mode controller is designed and it adopts the time-varying sliding mode surface, the self-defined reaching law and the adaptive control parameters. Finally, three sets of simulation are carried out to prove the flight controller designed in this paper for BTT missile can follow the guidance instructions and meet operational needs.