Modeling and time delay control of shape memory alloy actuators

Shape memory alloy (SMA) actuators possess hard nonlinearities including backlash-like hysteresis and saturation. These nonlinearities result in steady-state error and limit-cycle problems when conventional controllers such as the proportional integral derivative (PID) are used for trajectory control. In this study, a dynamics for an SMA actuator was newly derived using the modified Liang's model. The derived dynamics showed continuity at the change of the phase transformation process, but the original model could not. SMA actuator characteristics could be well described using this dynamics. The derived dynamics could be also used effectively for the prediction of control performance and gain tuning of the time delay control (TDC). The dynamics consisted of first-order linear and second-order nonlinear equations. Accordingly, a control strategy was established for the TDC to regulate only the second-order nonlinear part for simplicity and for the internal closed loop to regulate the rest. The control strategy was examined from the point of view of influence of an antiwindup scheme and high gain tuning on control performance. An anti-windup scheme was essential to protect windup phenomenon and high gain tuning was effective when a temperature disturbance existed. In the robustness test, the TDC with high gains showed robustness to inertia variation and temperature disturbance in comparison with the TDC with low gains.     

Fatigue crack growth under a constant amplitude loading of Al-6061-T6 welds obtained by modified indirect electric arc technique

Abstract

The characteristics of the fatigue crack growth in the base metal, weld metal and heat affected zone (HAZ) were quantified by testing compact type specimens of 6061-T6 welds obtained by the modified indirect electric arc technique. The fatigue crack growth depends on the microstructure imposed by the welding thermal cycle and it was observed that in the HAZ the crack growth rate is lower than that in the weld metal, but higher than that in the base metal. Microhardness maps revealed that this behaviour is due to the formation of a larger plastic zone around of the crack tip produced by loss of hardening. A comparison of fatigue crack growth of weld metal and HAZ for modified indirect electric arc and friction stir welding shows that the weld metal produced by friction stir welding exhibits better resistance to crack propagation, but both processes behaved similarly in the HAZ.     

Genetic algorithm for optimisation of A-TIG welding process for modified 9Cr–1Mo steel

Abstract

It is essential to set up the activated tungsten inert gas (A-TIG) welding process parameters to produce the desired weld bead geometry and heat affected zone (HAZ) width in modified 9Cr–1Mo steel weld joints. Therefore, it becomes necessary to develop a tool for optimisation of A-TIG welding process. Genetic algorithm (GA) based model has been developed to determine the optimum process parameters. In this methodology, first independent ANN models correlating depth of penetration, weld bead width and HAZ width with current, voltage and torch speed respectively were developed. Then, GA code was developed in which the objective function was evaluated using the ANN models. There was good agreement between the target and actual values of bead geometry and HAZ width obtained using the GA optimised process parameters. Thus, a methodology using GA has been developed for optimising the A-TIG process parameters for modified 9Cr–1Mo steel.     

Influence of alloying elements on hot corrosion of superalloys and coatings: necessity of smart coatings for gas turbine engines

Abstract

Modern gas turbine engines require high performance materials and coatings to ensure high efficiency. The selection of high performance materials and coatings depends on the nature and concentration of alloying elements. The composition of materials and coatings, in particular, plays a major role in enhancing the life of gas turbine engines by exhibiting good resistance to oxidation and hot corrosion, which are major problems in gas turbine engines. The performances of several superalloys containing different alloying elements and MCrAlY type coatings containing a variety of major and minor alloying elements are described in detail. The effect of major and trace elements on the life of superalloys and coatings in the presence of pure Na₂SO₄, NaCl and vanadium containing environments is detailed. The relevant reaction mechanisms leading to the failure of superalloys and coatings are discussed. The major factors involved when selecting alloying elements for the preparation of superalloys to manufacture components intended for use under hot corrosion conditions and the selection of appropriate coatings are suggested. Finally, the necessity of innovation of 'smart coatings' to combat both oxidation and hot corrosion is discussed.     

黑米色素的性质及光稳定化剂的研究

研究了黑米色素的性质和光降解动力学方程 ,以及黑米色素的光稳定化剂对色素的辅助成色和护色的影响。结果表明 ,黑米色素光降解服从零级反应动力学方程 ,添加黄酮化合物及改性黄酮化合物可使黑米色素对光稳定性有较大提高     

Silica or fibre glass reinforced composites via photopolymerisation of acrylate systems

Abstract

Composites based on an acrylate system were cured using UV light in the presence of a radical photoinitiator, with silica powder or glass fibres as reinforcing agents. The presence of small amounts of silica or glass fibres (up to 7 wt-%), did not influence the kinetics of photopolymerisation or the final conversion of the acrylic double bonds. The properties of the materials obtained were found to depend on the type and concentration of the reinforcing agent, and the surface treatment.     

Modification of epoxy resins for improvement of adhesion: a critical review

Modification of epoxy resins for improvement of adhesion has been the subject of intense research throughout the world. Unlike for thermoplastics, physical blending is not successful for improvement of bond strength and impact strength of epoxy resins. The bond strength of an epoxy resin can be improved only by chemical modification with a suitable flexible modifier. Such chemical modification may either plasticize the epoxy matrix or lead to a two-phase microstructure. Both methods of chemical modifications are discussed critically in the present review.     

The vibration welding of poly(methyl methacrylate) to itself and to polycarbonate,poly(butylene terephthalate), and modified poly(phenylene oxide)

The weldability of poly(methyl methacrylate) (PMMA) to itself and to polycarbonate (PC), poly(butylene terephthalate) (PBT), and modified poly(phenylene oxide) (M-PPO) is assessed through 120 and 250 Hz vibration welds. Weld strengths equal to those of the base resin have been demonstrated in welds of PMMA and M-PPO to themselves. In welds of PMMA to PC and to M-PPO, weld strengths equal to those of PC and M-PPO, respectively, have been demonstrated. PMMA does not weld well to PBT; the highest weld strength obtained was 21% of the strength of PBT resin.     

Modified PID Control of a Single-Link Flexible Robot

The use of flexible links in robots has become very common in different engineering fields. The issue of position control for flexible link manipulators has gained a lot of attention. Using the vibration signal originating from the motion of the flexible-link robot is one of the important methods used in controlling the tip position of the single-link arms. Compared with the common methods for controlling the base of the flexible arm, vibration feedback can improve the use of the flexible-link robot systems. In this paper a modified PID control (MPID) is proposed which depends only on vibration feedback to improve the response of the flexible arm without the massive need for measurements. The arm moves horizontally by a DC motor on its base while a tip payload is attached to the other end. A simulation for the system with both PD controller and the proposed MPID controller is performed. An experimental validation for the control of the single-link flexible arm is shown. The robustness of the proposed controller is examined by changing the loading condition at the tip of the flexible arm. The response results for the single-link flexible arm are presented with both the PI and MPID controller used. A study of the stability of the proposed MPID is carried out.