The ergonomic design of helmets is very important for those who wear them for long periods on the job; for example, construction workers and security personnel. A helmet's weight, stability, and ability to protect are especially important. According to our case study, fitting design according to head shape can significantly reduce the weight and enhance the stability of a helmet. The traditional helmet design process takes a long time, and is thus unsuitable for individually customized shape design. In this paper, a rapid preliminary design method for the helmet shell and a corresponding toolkit are introduced, taking advantage of three-dimensional (3D) anthropometric head scans. A 3D head model is first generated from the 3D head scan of the intended user or representative user of an intended population group. Then a semi-parametric surface modelling tool is applied to quickly generate the helmet shell by simply inputting several parameters related to helmet protection, size, and shape requirements and adjusting several key curves. In a case study, the new design by the proposed method and the existing design by the traditional method were compared with regard to weight, centroid, and moments of inertia to demonstrate the effectiveness of the proposed method.

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High pressure common rail system is the state-of-the art technology for modern diesel engines to achieve energy conservation and emission reduction. The economy and emission performance of the diesel engines are influenced by the fuel injection stability of the high pressure common rail system. In this work, a high pressure common rail injector numerical model based on bond graph theory has been proposed. The comparisons between experimental results and numerical simulations show that the numerical model could reasonably predict the injection characteristics of the system. In order to reveal the essential rules and inherent characteristics of the fuel injection stability for high pressure common rail system, the rank variations of the state matrix at different injection pulse widths during fuel injection are obtained by means of a linear analysis. In addition, the distributions of eigenvalues for the state matrix in complex plane are investigated using Lyapunov method. The results show that the rank is influenced mainly by the movements of control valve and needle. Furthermore, the variation rule of the rank is independent of the injection pulse width before the needle is opened. The needle channel orifice of the injector plays a dominant role in transformation of the system from strong damping oscillation to underdamping oscillation. The opening and closing of control valve have significant effect on the stability of the system because its movement breaks the stability, and the movement of needle has remarkable effect on the oscillating characteristics of the system. High pressure common rail system is a complicated time-variant system with unstable pressure relief and strong oscillation injection.

1Cr11Ni2W2MoV is a new martensitic heat-resistant stainless steel utilized in the manufacturing of aero-engine high-temperature bearing components. Welding of this type of steel using fusion welding techniques causes many defects. Friction stir welding (FSW) is a valuable alternative. However, few investigations have been performed on the FSW of steels because of the high melting point and the costly tools. Numerical simulation in this regard is a cost-effective solution for the FSW of this steel in order to optimize the parameters and to reduce the number of experiments for obtaining high-quality joints. In this study, a 3D thermo-mechanical finite element model based on the Coupled Eulerian Lagrangian (CEL) approach was developed to study the FSW of 1Cr11Ni2W2MoV steel. Numerical results of metallurgical zones’ shape and weld appearance at different tool rotation rates of 250, 350, 450 and 550 rpm are in good agreement with the experimental results. The results revealed that the peak temperature, plastic strain, surface roughness and flash size increased with an increase in the tool rotation rate. Lack-of-fill defect was produced at the highest tool rotation rate of 650 rpm. Moreover, an asymmetrical stir zone was produced at a high tool rotation rate.

An effective method to improve the thermal stability of Ni(Ge 1-x Sn x ) by carbon pre-stanogermanidation implant into GeSn substrate is investigated systematically. As-prepared samples were characterized by means of sheet resistance measurement, X-ray diffraction (XRD), scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (X-TEM) and secondary ions mass spectroscopy (SIMS). The incorporation of carbon leads to significantly improved thermal stability of Ni(Ge 1-x Sn x ) by about 100 • C as well as tends to change the preferred orientations of polycrystalline Ni(Ge 1-x Sn x ). The robust thermal stability can be attributed to the segregation of C in grain boundaries and at Ni(Ge 1-x Sn x )/GeSn interface after stanogermanidation.