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    25 December 2016, Volume 4 Issue 4
    Dissimilar titanium/aluminum friction stir welding lap joints by experiments and numerical simulation
    G. Buffa, M. De Lisi, E. Sciortino, L. Fratini
    2016, 4(4):  287-295.  doi:10.1007/s40436-016-0157-2
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    Dissimilar lap joints were produced by friction stir welding (FSW) out of Ti6Al4V titanium alloy and AA2024 aluminum alloy sheets. The joints, welded with varying tool rotation and feed rate, were studied by analyzing the maximum shear strength, Vickers microhardness and optical observations. A dedicated numerical model, able to take into account the presence of the two different alloys, was used to highlight the effects of the process parameters on temperature distribution, strain distribution, and material flow. The combined analysis of experimental measurements and numerical predictions allowed explaining the effects of tool rotation and feed rate on the material flow. It was found that tool rotation had a larger impact on the joint effectiveness with respect to feed rate. A competition between material mixing and heat input occurs with increasing tool rotation, resulting in higher joint strength when lower values of tool rotation are used.

    A comparison between friction stir welding, linear friction welding and rotary friction welding
    Achilles Vairis, George Papazafeiropoulos, Andreas-Marios Tsainis
    2016, 4(4):  296-304.  doi:10.1007/s40436-016-0163-4
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    Three friction welding processes are compared for temperature, stresses and strains, as well as strain rates developed in the early phases of the processes, which are essential in their successful development. These are friction stir welding (FSW), linear friction welding (LFW) and rotary friction welding (RFW). Their common characteristic is the use of friction to generate adequate energy and raise temperature locally in order to create favorable conditions for welding at the interface between two parts. Although the mode of movement is different for each one of them, welds are produced through plastic deformation. The Lagrangian and coupled Eulerian-Lagrangian numerical models developed have produced results which are in qualitative agreement with experiments and have shed a light on the commonalities of these friction welding processes.

    Experimental characterization of Ti6Al4V T joints welded through linear friction welding technique: microstructure and NDE
    Antonello Astarita, Mario Coppola, Sergio Esposito, Mariacira Liberini, Leandro Maio, Ilaria Papa, Fabio Scherillo, Antonino Squillace
    2016, 4(4):  305-313.  doi:10.1007/s40436-016-0160-7
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    Linear friction welding (LFW) is an innovative solid-state welding technique that allows to manufacture joints with high mechanical properties. This technology has various applications in the aerospace field; in particular it is used to weld massive structural components made of Ti6Al4V. This paper deals with the experimental study of Ti6Al4V T-joints welded through LFW, with particular focus on the effectiveness of ultrasonic control in detecting and distinguishing welding defects within the joints. Aiming to this scope, joints with different properties were manufactured and tested:some were free from defects but with different metallurgy, and some had different types of defects. The results obtained proved that the ultrasonic control was an effective method to detect and identify defects in linear friction welded titanium joints, moreover it was possible to get information regarding the microstructure and in particular the extension of the different metallurgical zones induced by the welding process.

    The effects of forging pressure and temperature field on residual stresses in linear friction welded Ti6Al4V joints
    Ying Fu, Wen-Ya Li, Xia-Wei Yang, Tie-Jun Ma, Achilles Vairis
    2016, 4(4):  314-321.  doi:10.1007/s40436-016-0161-6
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    Linear friction welding (LFW), as a solid state joining process, has been developed to manufacture and repair blisks in aeroengines. The residual stresses after welding may greatly influence the performance of the welded components. In this paper, the distribution of residual stresses in Ti6Al4V joints after LFW was investigated with numerical simulations. The effects of applied forging pressure and temperature field at the end of the oscillating stages on the residual stresses within the joints were investigated. The results show that, the residual tensile stresses at the welded interface in the y-direction are the largest, while the largest compressive stresses being present at the flash root in the z-direction. Furthermore, the forging pressure and temperature field at the end of the oscillating stages strongly affect the magnitude of the residual stresses. The larger forging pressure produced lower residual stresses in the weld plane in all three directions (x-, y-, and z-directions). Larger variance, σ, which decides the Gaussian distribution of the temperature field, also yields lower residual stresses. There is good agreement between simulation results and experimental data.

    Measurement and analysis technologies for magnetic pulse welding: established methods and new strategies
    J. Bellmann, J. Lueg-Althoff, S. Schulze, S. Gies, E. Beyer, A. E. Tekkaya
    2016, 4(4):  322-339.  doi:10.1007/s40436-016-0162-5
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    Magnetic pulse welding (MPW) is a fast and clean joining technique that offers the possibility to weld dissimilar metals, e.g., aluminum and steel. The high-speed collision of the joining partners is used to generate strong atomic bonded areas. Critical brittle intermetallic phases can be avoided due to the absence of external heat. These features attract the notice of industries performing large scale productions of dissimilar metal joints, like automotive and plant engineering. The most important issue is to guarantee a proper weld quality. Numerical simulations are often used to predict the welding result a priori. Nevertheless, experiments and the measurement of process parameters are needed for the validation of these data. Sensors nearby the joining zone are exposed to high pressures and intense magnetic fields which hinder the evaluation of the electrical output signals. In this paper, existing analysis tools for process development and quality assurance in MPW are reviewed. New methods for the process monitoring and weld characterization during and after MPW are introduced, which help to overcome the mentioned drawbacks of established technologies. These methods are based on optical and mechanical measuring technologies taking advantage of the hypervelocity impact flash, the impact pressure and the deformation necessary for the weld formation.

    Application of thermodynamics in designing of advanced automotive steels
    Lin Li, Hu Jiang
    2016, 4(4):  340-347.  doi:10.1007/s40436-016-0156-3
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    Advanced automotive steels were designed with alloy concept and thermodynamics. Several phases were taken for the designing of transformation induced plasticity(TRIP) steels in accordance with the practical metallurgy process. Al was firstly chosen to substitute Si for improving galvanizing property, afterwards P was proved to be another alternative of Si by thermodynamic calculation and kinetic estimation. Thermodynamic investigation in the third phase revealed the effective function of Al to increase carbon solubility in austenite as well as TRIP effect of steel. Stack fault energy was calculated, in combination with heat treatment and microstructure measurement, which led to a successful composition designing of twin induced plasticity (TWIP) steel.

    A new color image encryption scheme based on chaos synchronization of time-delay Lorenz system
    Hua Wang, Hang-Feng Liang, Zhong-Hua Miao
    2016, 4(4):  348-354.  doi:10.1007/s40436-016-0159-0
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    In this paper, a new image encryption scheme is presented based on time-delay chaos synchronization. Compared with existing methods, a new method is proposed and a lot of coupled items can be taken as zero items to simplify the whole system. A simple linear controller is introduced to realize time-delay chaos synchronization and image encryption. The positions of the image pixels are firstly shuffled and then be hidden in the carrier image. The address codes of the chaotic sequences are adopted to avoid the disturbances induced by the initial value and computer accuracy error. Simulation results for color image are provided to illustrate the effectiveness of the proposed method. It can be seen clearly that the system can converge quickly and the image can be encrypted rapidly.

    Study of the thermal influence on the dynamic characteristics of the motorized spindle system
    Song-Sheng Li, Yuan Shen, Qiang He
    2016, 4(4):  355-362.  doi:10.1007/s40436-016-0158-1
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    The severe internal heat generation of the motorized spindle system causes uneven temperature distribution, and will affect the vibration characteristics of the system. Based on the thermal analysis about the motorized spindle by finite element method (FEM), the thermal deformations of the spindle system are calculated by the thermal structure coupling simulation, and the thermal deformations of the rotor and the bearing units are extracted to analyze the bearing stiffness changes so that the modal characteristics of the rotor can be simulated in different thermal state conditions. And then the rotor thermal deformation experiment and the modal experiment of spindle by exciting with hammer are performed. The result shows that the thermal state of the motorized spindle system has a significant influence on the natural frequency of the rotor, which can be carefully treated when a spindle system is designed.

    Accuracy analysis of omnidirectional mobile manipulator with mecanum wheels
    Shuai Guo, Yi Jin, Sheng Bao, Feng-Feng Xi
    2016, 4(4):  363-370.  doi:10.1007/s40436-016-0164-3
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    This article is based on the omnidirectional mobile manipulator with mecanum wheels built at Shanghai University. The article aims to find and analyze the parameters of kinematic equation of the omnidirectional system which affects its motion accuracy. The method of solving the parameter errors involves three phases. The first step is equation operation to achieve the equation of relative errors. The second step is to obtain the displacement errors of the system via experiment and combine the error results with kinematic equation deduction to solve the geometric parameter errors in two methods. The third step is to verify its validity via comparing experiments. We can then revise its kinematics equation afterwards.