Search

This paper focuses on the multi-scale modelling method for strain rate dependent behaviour of long fibre reinforced thermoplastics based on the Mori–Tanaka scheme. In the present work, the anisotropic and nonlinear viscoelastic–viscoplastic behaviour of an injection moulded plate are experimentally characterised, and the sensitive range of strain rates is discussed. Fibre orientation tensors, content and fibre length are measured and analysed based on micro computed tomography images at different positions of the plate. Further, a multi-scale material model considering microstructure variables, constitutive models of two phases and failure criteria, is proposed. The accuracy of the model is validated by finite element simulations, including five strain rates and three loading directions. The comparison results indicate that the calculated stress–strain curves show a good consistency with the experimental data.

This paper focuses on the crushing collapse theory of externally fiber-reinforced twelve right-angle section (TTRS) tubes based on the kinematic approach. This paper presents the crushing energy dissipation mechanism of metal TTRS tubes and derives the expression of mean crushing force. Considering the contribution of the composite-metal wall and the final crushing deformation, which affected by the accumulation of the composite after failure, the expression describing the mean crushing force for externally fiber-reinforced TTRS tubes is presented. The accuracy of the theoretical predictions is validated by finite element simulations, including four different metal wall thicknesses and three different amounts of composite plies. The results indicate that the mean crushing forces calculated by the proposed theory show a good consistency with the simulation results.

The current design and optimization of the occupant restraint system (ORS) are based on numerous actual tests and mathematic simulations. These two methods are overly time-consuming and complex for the concept design phase of the ORS, though they’re quite effective and accurate. Therefore, a fast and directive method of the design and optimization is needed in the concept design phase of the ORS. Since the airbag system is a crucial part of the ORS, in this paper, a theoretical model for the vehicle airbag is established in order to clarify the interaction between occupants and airbags, and further a fast design and optimization method of airbags in the concept design phase is made based on the proposed theoretical model. First, the theoretical expression of the simplified mechanical relationship between the airbag’s design parameters and the occupant response is developed based on classical mechanics, then the momentum theorem and the ideal gas state equation are adopted to illustrate the relationship between airbag’s design parameters and occupant response. By using MATLAB software, the iterative algorithm method and discrete variables are applied to the solution of the proposed theoretical model with a random input in a certain scope. And validations by MADYMO software prove the validity and accuracy of this theoretical model in two principal design parameters, the inflated gas mass and vent diameter, within a regular range. This research contributes to a deeper comprehension of the relation between occupants and airbags, further a fast design and optimization method for airbags’ principal parameters in the concept design phase, and provides the range of the airbag’s initial design parameters for the subsequent CAE simulations and actual tests.

Throughout the vehicle crash event, the interactions between vehicle, occupant, restraint system (VOR) are complicated and highly non-linear. CAE and physical tests are the most widely used in vehicle passive safety development, but they can only be done with the detailed 3D model or physical samples. Often some design errors and imperfections are difficult to correct at that time, and a large amount of time will be needed. A restraint system concept design approach which based on single-degree-of-freedom occupant-vehicle model (SDOF) is proposed in this paper. The interactions between the restraint system parameters and the occupant responses in a crash are studied from the view of mechanics and energy. The discrete input and the iterative algorithm method are applied to the SDOF model to get the occupant responses quickly for arbitrary excitations (impact pulse) by MATLAB. By studying the relationships between the ridedown efficiency, the restraint stiffness, and the occupant response, the design principle of the restraint stiffness aiming to reduce occupant injury level during conceptual design is represented. Higher ridedown efficiency means more occupant energy absorbed by the vehicle, but the research result shows that higher ridedown efficiency does not mean lower occupant injury level. A proper restraint system design principle depends on two aspects. On one hand, the restraint system should lead to as high ridedown efficiency as possible, and at the same time, the restraint system should maximize use of the survival space to reduce the occupant deceleration level. As an example, an optimization of a passenger vehicle restraint system is designed by the concept design method above, and the final results are validated by MADYMO, which is the most widely used software in restraint system design, and the sled test. Consequently, a guideline and method for the occupant restraint system concept design is established in this paper.

In this study PLASIMO program developed by Eindhoven University of Technology was used to investigate the effects of argon flow velocity on argon plasma in the cascaded arc. The simulation results are in good agreement with available experimental data that along the symmetry axis, the pressure decreases but the electron temperature increases from the inlet to the outlet. The effects of flow velocity of argon on plasma properties were investigated. The simulation results show that for argon arc discharges, with increasing the flow velocity, the electron density and the heavy particle temperature increases, while the electron temperature decreases. Along the symmetry axis, the electron temperatures are all above 1 eV and the heavy particle temperatures are all about 1 eV at differe

The microstructure changes brought by the addition of Nd element to AM60 magnesium alloy were studied, the precipitating phases were identified and their influences on the mechanical properties of alloys were investigated. Results show that Nd addition makes the refinement of microstructure of the AM60 alloy, and decreases the size of Mg17Al12 phase. Nd element takes a priority to react with Al element over Mg, Mn and Zn forming binary phase Al11Nd3 with high melting point. Certain content of Nd can increase tensile strength, yield strength and elongation of the alloy. But with too much addition, Nd would combine with more Al in matrix and decrease strengthening effect because Al11Nd3 phase would become coarsening. The mechanical property tests indicate that AM60-0.9Nd alloy has the best properties. Maximum tensile strength, maximum yield strength, maximum elongation are 230 MPa, 127 MPa and 14% respectively, increased by 28%, 48% and 250% respectively.

To explore the possibility to automatically update the 1:250,000 river network data, this paper chooses the Oujiang Watershed in Zhejiang Province as a study case, extracts automatically the river network based on 90m SRTM DEM, and assesses its accuracy in terms of point positional accuracy, river morphology parameters, and river-network-matching-difference. Since the accuracy of extracted river network is highly correlated with the drainage area threshold, this paper proposes the average drainage branching ratio to determine this threshold, which can improve the data accuracy by 1.24%. The results show that under any topography, the positional accuracy of automatically extracted river network is high than that of 1:250,000 data, which accounts for 21.4% on plains, 15.7% on hills, and 53.0% on mountains, respectively. Furthermore, the greater the relief, the higher the accuracy of extracted data. In terms of river morphology, the river-network-matching-difference is less than 1.2%, which implies the automatically extracted river network seems to best match 1:250,000 data. Therefore, automatically extracted waterlines based on SRTM DEM can basically meet the update requirements of 1:250,000 river network data.

The aim of this study was to enhance head-injury prediction, this paper investigated the behavior of cerebrospinal fluid (CSF) in finite element (FE) modeling. Nine different material properties selected according to material definitions and property values were used to represent CSF in FE head models. To evaluate the influence of CSF material parameters on brain mechanical responses, the models were validated against available cadaver experiment data. Results showed that coup pressure increased whereas contrecoup pressure decreased when the head sustained purely translational impact with increased bulk modulus when CSF was modeled as fluid. However, with increased bulk modulus, coup pressure, contrecoup pressure and relative skull-brain motions decreased under rotational impact. When CSF was assumed to be an elastic material, coup pressure increased whereas contrecoup pressure decreased with increased elastic modulus when the head was subjected to purely translational impact. However, the variation trend was not obvious during head rotation. Results also indicated that when subjected to brain strain and von Mises stress, the model was prone to underestimate brain injury when CSF was modeled as an elastic material, especially during purely translational impact to the head. The model with CSF as fluid reduced the strain rate of brain, which was more likely to be realistic than the model with CSF as a viscoelastic material. These findings suggested that significantly higher values of the bulk modulus of CSF modeled as fluid were needed to predict intracranial dynamic responses and brain injury during head impact.