Application of the Laplace transform dual reciprocity boundary element method in the modelling of laser heat treatments

The Laplace Transform Dual Reciprocity Boundary Element Method (LTDRM or LT-DRBEM) provides with an alternative numerical technique to finite difference (FDM) or finite element methods (FEM) for solving transient diffusion problems. With this method, solutions are calculated directly at any specific time thus avoiding the use of time-stepping schemes. Besides, domain integrals are removed from the problem formulation.In this work we study the applicability of the LT-DRBEM method for laser heat treatment modelling purposes. A simple model was developed based on a two dimensional transient heat conduction equation, in which the laser beam is included as a heat flux boundary condition of gaussian shape. Results corresponding to a stationary and a moving beam are presented and discussed. Non-linear formulations of the problem as those given by temperature dependent material properties are also considered. Good accuracy results were obtained for the stationary beam approach, whereas severe limitations were found for the moving beam case.     

A refined dynamic stiffness element for free vibration analysis of cross-ply laminated composite cylindrical and spherical shallow shells

An exact free vibration analysis of doubly-curved laminated composite shallow shells has been carried out by combining the dynamic stiffness method (DSM) and a higher order shear deformation theory (HSDT). In essence, the HSDT has been exploited to develop first the dynamic stiffness (DS) element matrix and then the global DS matrix of composite cylindrical and spherical shallow shell structures by assembling the individual DS elements. As an essential prerequisite, Hamilton’s principle is used to derive the governing differential equations and the related natural boundary conditions. The equations are solved symbolically in an exact sense and the DS matrix is formulated by imposing the natural boundary conditions in algebraic form. The Wittrick–Williams algorithm is used as a solution technique to compute the eigenvalues of the overall DS matrix. The effect of several parameters such as boundary conditions, orthotropic ratio, length-to-thickness ratio, radius-to-length ratio and stacking sequence on the natural frequencies and mode shapes is investigated in details. Results are compared with those available in the literature. Finally some concluding remarks are drawn.     

Influence of Ag on TCR and MR of La0.7(Ca0.27Sr0.03)MnO3:Ag0.2 ceramics subjected to cross magnetic fields

In this account, polycrystalline La_0.7(Ca_0.27Sr_0.03)MnO₃:Ag_0.2 (LCSMO:Ag) ceramics were synthesized by the sol-gel method followed by solid-state doping. The Ag amounts doped into grain boundary and cell lattice could be adjusted by changing the sintering temperature from 1000 °C to 1500 °C. The temperature coefficient of resistivity (TCR) and magnetoresistance (MR) of the obtained LCSMO:Ag ceramics were tested under cross magnetic field with directions parallel and perpendicular to the flat of bulk. The difference between TCR and MR values reached their maxima at sintering temperature of 1450 °C, meaning that degree of lattice distortion reached maximum value. The combined data from X-ray diffraction (XRD) and scanning electron microscopy (SEM) demonstrated that Ag was doped into the grain boundary and lattice cell, and Ag played an important role during the process. The influence of Ag-doping on TCR and MR suggested that degree of lattice distortion can be adjusted by doping, leading to change in isotropic ceramics into anisotropic ceramics without damage. Application of parallel magnetic fields shifted the application temperature to room temperature, and response sensitivity of the ceramics to magnetic field further increased. Overall, these findings look promising for future applications in photoelectric and magnetic devices.     

A predictive energy-bounding approach for Haptic teleoperation

In this paper, a predictive energy-bounding approach (EBA) is presented for haptic bilateral teleoperation that is robustly stable for any time delay and data losses as well as for any uncertain environments over any network. The proposed scheme (termed as Predictive EBA) combines the bilateral EBA with Smith predictor (SP) architecture in the master site which predicts the slave (site) states on the master site to improve the force tracking transparency using the SP while the bilateral EBA guarantees robust stability against any uncertainties. Quantitative and qualitative transparency analyses of bilateral EBA and Predictive EBA shows significant improvement in phase of feedback force and consequently the perceived impedance if the slave/environment dynamics are well known. The proposed predictive EBA also allows any feedback signals such as measured contact forces/torques, position error based forces, and obstacle avoidance forces from slave sites. Experimental results show the effectiveness of the proposed predictive EBA for any large time delay while keeping robust stability of the overall system.     

In-situ investigation of EMC relaxation behavior using piezoresistive stress sensor

The relaxation behavior of an epoxy molding compound (EMC) subjected to a constant strain can cause new reliability challenges in automotive electronics. This problem will be exacerbated due to the ever-increasing demand in modern electronics systems for miniaturization with more functionality, yet it has not been studied extensively to mitigate its effect on reliability. In this study, a piezoresistive silicon-based stress sensor is used to understand the stress state in an electronic control unit (ECU), more specifically the relaxation behavior of EMC caused by the storage time of an ECU (i.e., duration between production and actual usage). Mechanical stresses are measured by the piezoresistive stress sensor that is encapsulated in a standard microelectronic 3 × 3 mm land grid array (LGA) package. The relaxation behavior is observed at three different temperatures for 1 week: 75 °C, 100 °C and 125 °C. The relaxation behavior is measured continuously for one more week after cooling the package to room temperature (at 25 °C). An additional test is conducted at 85 °C with 85% relative humidity to investigate the effect of moisture diffusion on the package. The experimental results clearly indicate that the proposed approach can be used for better understanding of the evolution of stresses in molded packages during their lifetime, especially during storage, which in turn can lead to more optimal designs in the future.     

Applying genetic algorithm to a new bi-objective stochastic model for transportation,location, and allocation of hazardous materials

In 2013, approximately 15,600 HAZMAT accidents with 158 injuries and fatalities have been reported in the USA (“Transportation Statistics Bureau”). Managing hazardous material (HAZMAT) transportation and locating the disposal sites for these materials properly can significantly reduce the risk of accidents and its environmental and social aspects. In this research, a new stochastic model for transportation, location, and allocation of hazardous materials is proposed. The cost of transportation is considered to be of a stochastic nature. The objective function minimizes the total cost and risk of locating facilities and transportation of HAZMATs. The decisions which have to be made are: (1) where to open the facilities and disposal sites; (2) to which facilities every customer should be assigned; (3) to which disposal site each facility should be assigned; and (4) which routes a facility should choose to reach the customers and disposal sites. A novel genetic algorithm (GA) is applied to the model. The results show the efficiency of the proposed GA in terms of finding high quality solutions in a short time.     

Mechanical property of Ti-6Al-4V sheet in one-sided electric hot incremental forming

Although Ti-6Al-4V titanium can be quickly and easily formed by electric hot incremental forming, the material property is the key factor for industrial application. In the current work, mechanical properties of Ti-6Al-4V sheet in one-sided electric hot incremental forming, such as microstructure, hardness, and tensile strength, were investigated. The results show that the current is obviously the most important factor to elevate temperature, so a higher feed rate can be adopted if the current is increased. In order to keep a constant processing temperature, an online temperature detector and current feedback system should be adopted. After observation and analysis of the microstructure of forming workpieces, the electric hot incremental forming is an integrated process, which involves plastic hardening and annealing. The temperature of the tool–workpiece contact side reached the β-transus one, α phase disappeared, and the basket weave structure was formed because of the fast air-cool. A composite organization with superior property which includes elongated α phase grains and basket weave structure can be acquired by one-sided electric hot incremental forming. If a uniform metal structure is obtained, special heat treatment must be adopted. Micro-hardness analysis shows that electric hot incremental forming is an enhanced processing. In order to improve the tensile strength, the oxidation of sheet must be prevented and inert gas protection should be adopted in future research.     

A framework for effective management of condition based maintenance programs in the context of industrial development of E-Maintenance strategies

CBM (Condition Based Maintenance) solutions are increasingly present in industrial systems due to two main circumstances: rapid evolution, without precedents, in the capture and analysis of data and significant cost reduction of supporting technologies. CBM programs in industrial systems can become extremely complex, especially when considering the effective introduction of new capabilities provided by PHM (Prognostics and Health Management) and E-maintenance disciplines. In this scenario, any CBM solution involves the management of numerous technical aspects, that the maintenance manager needs to understand, in order to be implemented properly and effectively, according to the company’s strategy. This paper provides a comprehensive representation of the key components of a generic CBM solution, this is presented using a framework or supporting structure for an effective management of the CBM programs. The concept “symptom of failure”, its corresponding analysis techniques (introduced by ISO 13379-1 and linked with RCM/FMEA analysis), and other international standard for CBM open-software application development (for instance, ISO 13374 and OSA-CBM), are used in the paper for the development of the framework. An original template has been developed, adopting the formal structure of RCM analysis templates, to integrate the information of the PHM techniques used to capture the failure mode behaviour and to manage maintenance. Finally, a case study describes the framework using the referred template.     

微米CeO2的细化及其悬浮液的分散稳定性研究

首先使微米CeO2在乙醇中球磨分散,然后向悬浮液中加入一定量去离子水,最后对悬浮液进行超声分散,使用这种方法制备出了分散稳定性较好的微米CeO2悬浮液,探讨了其增强微米CeO2分散稳定性的机制。结果表明:微米CeO2以不同方式分散时在不同比例醇水混合介质中的分散行为各不相同;微米CeO2在纯乙醇中的球磨分散性能最好,其起始分散率可以达到80%左右,而在醇水混合介质中的超声分散性能比在纯乙醇或纯水中的超声分散性能要好,但其起始分散率不高,只能达到20%左右。球磨后加水再超声分散的方法可以显著地提高微米CeO2悬浮液体系的分散性能,其中加入去离子水的最佳体积分数为40%,最佳超声时间为15 min。球磨后加水再超声分散的方法可以进一步打破微米CeO2粉体颗粒间的团聚,使粉体粒径得到进一步的细化,由于去离子水的加入悬浮液体系的表面电位得到了较大提高,乙醇水合团簇的形成使颗粒周围的溶剂化膜变厚。     

High-velocity walk-through programming for industrial applications

Traditionally, industrial robots are programmed by highly specialized workers that either directly write code in platform-specific languages, or use dedicated hardware (teach-pendant) to move the robot through the desired via-points. Unsurprisingly, the inherently complex and time-consuming nature of this task is one of the factors that are still preventing industrial manipulators from being massively adopted by companies that require a high degree of flexibility in order to cope with limited production volumes and rapidly changing product requirements. In this context, the introduction of sensor-based walk-through programming approaches represents the ideal solution as far as the need to reduce programming complexity and time is concerned. Nevertheless, the main shortcomings of these solutions typically consist in limited reachable velocities during the programming phase due to safety constraints and in relying on open robot controllers. To this regard, this paper proposes a control architecture for walk-through programming of industrial manipulators specifically designed in order to (i) reach high velocities while guaranteeing the operator’s safety; (ii) allow straightforward integration with a generic closed robotic controller. The proposed solution is extensively validated on an industrial manipulator.