The Comparison of Measurement Methods for Air-Kerma Rate in Narrow-Spectrum Series

The air-kerma is one of the most important physical quantities in ionizing radiation dosimetry. The measurement of airkerma rate in narrow-spectrum series is th...     

THEORETICAL ANALYSIS OF COORDINATES MEASUREMENT BY FLEXIBLE 3D MEASURING SYSTEM

The system mathematical model of flexible 3D measuring system is built by theoretical analysis,and the theoretical formula for measuring space point coordinate is also derived. Frog-jumping based coordinate transform method is put forward in order to solve measuring problem for large size parts. The frog-jumping method is discussed,and the coordinate transform mathematical model is method of the space point coordinate compared to original value,and an advanced method is provided. Form the space point coordinate transform formula can derive the calculation measuring method for measuring large size parts.     

The Do's and Don'ts of Wettability Characterization in Textiles

Surface treatments introduce chemical modifications to the fiber surface that affect the surface free energy (SFE). This is done either with the obvious aim to change the wetting behavior, or to affect related properties, such as, e.g., adhesion phenomenon, surface conductivity, adsorption of proteins, etc. On planar substrates, the measurement of contact angles of specific liquids and making use of formalisms such as Neumann or Owens–Wendt equations is a commonly used approach to determine the surface free energy. It is to be observed that this direct approach is often and lightheartedly applied to porous and textured samples, such as textiles, too. The geometry of a textile is extremely complex and defined by the topography of the fiber, the construction of the yarn, and the construction of the fabric. In addition, polymer fibers may be porous and take up water from the environment. Accordingly, wetting is the result of simultaneous spreading on a rough surface, penetration, and capillary motion in the multi-porous system. Therefore, the critical consideration of any analytical method for wettability measurements cannot be overemphasized, and the present paper is meant to critically discuss the pros and cons of various methods common to the textile researcher. It can be summarized that contact angles can be useful for comparative measurements on hydrophobic samples, while the established drop penetration tests characterize the effects of fabric finishing, fiber surface modifications, etc. with limited quantification. By no means can these test be used to derive the SFE, and in all cases it is essential to avoid accidental distortions of the fabric. The single fiber micro-Wilhelmy method can be regarded as the only reliable method to obtain advancing and receding contact angles.     

Experimental study of joint performance in spot friction welding of 6111-T4 aluminium alloy

Abstract

The effect of process parameters (cycle time, tool speed and axial force) on the specimen temperature measured 2 mm away from the weld in spot friction welding (SFW) of Al 6111-T4 is investigated. The temperatures were correlated to the lap shear load. Results revealed that, to achieve a good joint strength with the maximum lap shear load >2˙5 kN, temperatures should be greater than a threshold value, which is 350°C at a location close to the SFW joint in this study. By studying the specimen macrographs, two internal weld geometric features based on the cross-section area were identified and correlated to the shear and mixed failure modes of the lap shear tested specimens. A model was developed and validated using experimental data of the cross section area of SFW joint with either shear or mixed mode fracture. The model predicts that the SFW joint strength is maximised at the transition region between the shear and mixed mode fracture.     

Solidification and microstructure of ZA27/SiCp composite fabricated by mechanical–electromagnetic combination stirring process

Abstract

The solidification behaviours and microstructural characteristics of both ZA27/SiC_p composites and monolithic ZA27 alloy were studied by using differential scanning calorimetry, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis, and X-ray diffraction. It was found that there were differences in the transformation temperature and volume fraction of the phases, although the solidification process was almost identical for the composite and the monolithic alloy. The incorporation of SiC particles in the ZA27 alloy led to slight refinement of primary grains and reduced volume fraction of eutectic-like phase. The SiC particles obstructed Zn diffusion in the residual melt during the formation of proeutectic β phase, but promoted Zn diffusion from (Al) to η (Zn) phase during eutectoid transformation. During solidification, Cu was mainly segregated in the final solidification regions; Mg was present not only in the matrix but also on SiC particles; and oxide inclusions were mainly distributed around SiC particles. The matrix microstructure for both materials mainly consisted of primary cores of Al rich +η eutectoid; β′ phase resulting from the eutectoid transformation of the proeutectic β phase; and Zn rich +η eutectoid resulting from the eutectoid transformation of the eutectic-like phase. The SiC particles were mainly distributed around the primary grains. Several new phases based on the Al–Zn–Mg–Cu system and interfacial reaction products, including Al₂₁Fe₃Si, Cu₅Zn₈, Mg₆Cu₃Al₇, MgAl₂O₄, and amorphous oxide inclusions, were identified in the final solidification regions. The nucleation of both primary phase and eutectic-like +η phase at the surface of SiC particles and their crystallographic orientation relationships were investigated theoretically and experimentally. No distinct crystallographic orientation relationship between the matrix and SiC has been identified, although the mismatch between (0001)_SiC and (111)_ was calculated to be as small as 7·6%.     

Experimental characterisation of a semi-solid A356 alloy during solidification and remelting

Abstract

Within the general framework of hot tearing research in casting processes the tensile behaviour of the semi-solid aluminium alloy A356 under remelting and solidification conditions is studied. In order to measure true-stress versus true-strain curves of the semi-solid metal, a new experimental technique has been developed to perform hot tensile tests in the mushy regime between the coherency and the solidus temperatures. The local true-strain in the semi-solid region of the tensile specimen is measured optically with a laser speckle extensometer (LSE). During the solidification tests measurement is done by using a transparent aero-gel mould. The resulting stress–strain curves and the corresponding microstructure are compared for the remelting and solidification condition.     

Interfacial instabilities in multimaterial co-injection mouldings Part 1 – Background and initial experiments

Abstract

Interfacial adhesion between the skin and core is vital for successful co-injection moulding. This is the first paper in a series, which introduces and describes an in mould method of mixing that is applicable regardless of the compatibility of the materials. It works by inducing turbulent mixing at the interface between the skin and core materials. It makes use of the change that occurs from laminar to turbulent flow at high injection speeds in co-injection moulding. This novel approach takes advantage of the moulding parameters already available within the co-injection system to offer an expanded range of material combinations for multimaterial moulding. Comparisons are made between multimaterial mouldings made with miscible polymers, immiscible polymers with no compatibiliser, and immiscible polymers bonded by compatibilisers.