Yingjie Xu

Microstructure modelling and prediction of effective elastic properties of 3D multiphase and multilayer braided composite

Abstract This paper is focused on the microstructure modelling and evaluation of effective elastic properties of three-dimensional multiphase and multilayer braided composite. Regarding the multiscale characteristics of the composite, the microstructure modelling is carried out sequentially from fibre to tow scale. The geometrical configuration of the microstructure is first analysed, and mathematical relations among different geometrical parameters are derived on each scale. Second, effective elastic properties are obtained based on the sequential homogenisation from fibre to tow scale. A strain energy based method is proposed to evaluate effective elastic properties with specific boundary conditions imposed on the microstructure. Numerical results obtained by the proposed method and the microstructure model show a good agreement with the results measured experimentally.

Experimentation and Modeling of the Tension Behavior of Polycarbonate at High Strain Rates

A comprehensive understanding of the mechanical behavior of polycarbonate (PC) under high-rate loadings is essential for better design of PC products. In this work, the mechanical behavior of PC is studied during tensile loading at high strain rates, using a split Hopkinson tension bar (SHTB). A modified experimental technique based on the SHTB is proposed to perform the tension testing on PC at rates exceeding 1000 s−1. The effect of strain rates on the tension stress–strain law of PC is investigated over a wide range of strain rates (0.0005–4500 s−1). Based on the experiments, a physically based constitutive model is developed to describe the strain rate dependent tensile stress–strain law. The high rate tensile deformation mechanics of PC are further studied via finite element simulations using the LSDYNA code together with the developed constitutive model.

FE Analysis of Dynamic Response of Aircraft Windshield against Bird Impact

Bird impact poses serious threats to military and civilian aircrafts as they lead to fatal structural damage to critical aircraft components. The exposed aircraft components such as windshields, radomes, leading edges, engine structure, and blades are vulnerable to bird strikes. Windshield is the frontal part of cockpit and more susceptible to bird impact. In the present study, finite element (FE) simulations were performed to assess the dynamic response of windshield against high velocity bird impact. Numerical simulations were performed by developing nonlinear FE model in commercially available explicit FE solver AUTODYN. An elastic-plastic material model coupled with maximum principal strain failure criterion was implemented to model the impact response of windshield. Numerical model was validated with published experimental results and further employed to investigate the influence of various parameters on dynamic behavior of windshield. The parameters include the mass, shape, and velocity of bird, angle of impact, and impact location. On the basis of numerical results, the critical bird velocity and failure locations on windshield were also determined. The results show that these parameters have strong influence on impact response of windshield, and bird velocity and impact angle were amongst the most critical factors to be considered in windshield design.

Processing-Induced Inhomogeneity of Yield Stress in Polycarbonate Product and Its Influence on the Impact Behavior

In this study, an integrated methodology for impact analysis of polycarbonate (PC) product is proposed which incorporates the processing-induced inhomogeneity of yield stress. A previously developed model is extended to predict the inhomogeneous yield stress distribution along the specimen by using the thermal history experienced during injection molding. A strain rate-dependent elastic-plastic model combining the processing-induced yield stress is applied to model the mechanical behavior of PC. Finite element simulation for notched Izod impact test is then conducted to analyze the impact behaviors of PC specimens with different thermal histories. Numerical results of the fracture energies are compared with experimental measurements.

A research methodology for crashworthiness evaluation of aero-structures under impact loading

The present work describes a methodical approach of material characterization and constitutive modeling with intent to apply it in finite-element (FE) solver to simulate the impact behavior of critical aircraft structures. The dynamic response analysis of a military aircraft windshield and canopy manufactured from Poly-methyle-methacrylate (PMMA) polymer was undertaken. The work is divided in three integral phases. In the first phase the material characterization was carried out at low and high strain-rates using universal testing machine and Split Hopkinson pressure bar (SHPB) respectively. In second phase of work, the material testing results were used to constitute a material model that can predict the deformation behavior of polymer under different loading conditions. The last phase of work deals with numerical implementation of constitutive model by incorporating a user-defined material subroutine in LS-DYNA, an explicit finite-element program. After successful implementation, the model was employed to determine the impact behavior of a military aircraft windshield and canopy against bird impact. The close experimental and simulation results encourages that the proposed model can effectively be used to assess the dynamic behavior of polymer based aero-structures under high velocity impact applications.

High-Speed Bird Impact Analysis of Aircraft Windshield by Using a Nonlinear Viscoelastic Model

In this study, a numerical model was established to predict the dynamic response of PMMA based polymeric aircraft windshield against high speed bird impact. A detailed nonlinear viscoelastic constitutive model with tensile failure criterion was used to predict the damage and failure of windshield structure. The numerical model was implemented by employing user defined material subroutine (UMAT) in explicit finite element (FE) solver LS-DYNA 3D. Numerical results were validated against experimental data and further investigations were carried out to study the influence of increased bird velocity and impact location on windshield. On the basis of numerical results, the limiting bird velocity and critical impact location on windshield were determined. The study will help to optimize the design of windshields against high speed bird strikes.

Integrative Analysis of the Injection Molding Process and Mechanical Behavior of Plastic Part

For parts made of plastics, injection molding is a common manufacturing process. Warpage and residual stress induced during the injection molding process have very important influences on the mechanical performance of injection products. In this paper, an integrative analysis of the injection molding process and mechanical performance of plastic parts is proposed. This integrative approach incorporates the effects of the manufacturing process in the mechanical simulation: (a) firstly, the finite element package MoldFlow is used to simulate the injection molding process and obtain the warpage and residual stress results. (b) Then the finite element model of plastic part including the process induced warpage and residual stress is established. Explicit dynamic finite element program LS-DYNA is used to simulate the mechanical behaviors of the molded part. Based on the integrative analysis, the influences of injection molding process parameters on mechanical behavior of a PC windshield against impact loading are studied.