Liangmo Wang

Parametric analysis of a cylindrical negative Poisson's ratio structure

Much research related to negative Poissons ratio (NPR), or auxetic, structures is emerging these days. Several types of 3D NPR structure have been proposed and studied, but almost all of them had cuboid shapes, which were not suitable for certain engineering applications. In this paper, a cylindrical NPR structure was developed and researched. It was expected to be utilized in springs, bumpers, dampers and other similar applications. For the purpose of parametric analysis, a method of parametric modeling of cylindrical NPR structures was developed using MATLAB scripts. The scripts can automatically establish finite element models, invoke ABAQUS, read results etc. Subsequently the influences of structural parameters, including number of cells, number of layers and layer heights, on the uniaxial compression behavior of cylinder NPR structures were researched. This led to the conclusion that the stiffness of the cylindrical NPR structure was enhanced on increasing the number of cells and reducing the effective layer height. Moreover, small numbers of layers resulted in a late transition area of the load–displacement curve from low stiffness to high stiffness. Moreover, the middle contraction regions were more apparent with larger numbers of cells, smaller numbers of layers and smaller effective layer heights. The results indicate that the structural parameters had significant effects on the load–displacement curves and deformed shapes of cylindrical NPR structures. This paper is conducive to the further engineering applications of cylindrical NPR structures.

Finite element analysis of a jounce bumper with negative Poisson’s ratio structure

Jounce bumpers in automotive suspension are key components that can improve the noise, vibration, and harshness performance of entire vehicle. Traditional jounce bumper made of polyurethane usually cannot satisfy the mechanical performances required by noise, vibration, and harshness optimization. In addition, the application of hyperelastic material influenced the efficiency and reliability of numerical calculations of polyurethane jounce bumper. In this paper, an engineering negative Poisson’s ratio structure was introduced and applied on the jounce bumper. The negative Poisson’s ratio jounce bumper can be mainly defined by few structure parameters. The finite element analysis of the negative Poisson’s ratio jounce bumper was conducted applied explicit method. The influences of loading velocity and material densities on computational time and numerical results were researched. The results indicated that enlargements of material densities and loading velocity can improve the computational efficiency and have limited influence on reliability. Furthermore, a negative Poisson’s ratio jounce bumper prototype was manufactured and tested to verify the numerical results. It was proved that the finite element analysis of the negative Poisson’s ratio jounce bumper was reliable both in load–displacement curve and deformation shapes. Compared to the traditional jounce bumper, the negative Poisson’s ratio jounce bumper can achieve similar mechanical behavior but with a smoother load–displacement curve, which is beneficial to the vehicle’s noise, vibration, and harshness performance.

A finite element stratification method for a polyurethane jounce bumper

The primary problem in the finite element analysis of polyurethane jounce bumpers, bumper stops, or similar structures is the identification of a mathematical model for the constitutive material. The densities of the exterior polyurethane area and the interior polyurethane area usually differ owing to the manufacturing process. This difference results in inaccuracy when predicting the mechanical behavior of the jounce bumper and bumper stop if a homogeneous material model is used. Thus, this work proposes a stratification method for finite element analysis of a polyurethane jounce bumper. The polyurethane structure was divided into three regions (the ‘skin layer’, the ‘transition layer’, and the ‘core area’) with different material properties. A foam model was utilized as the constitutive relationship. The foam model coefficients of the core area were obtained by a curve-fitting process using uniaxial compression test results. Subsequently, the material properties of the skin layer and the transition layer were also obtained. The finite element analysis results show that the proposed stratification strategy improves the prediction of the deformed shapes of the polyurethane jounce bumper. Furthermore, the calculated load–displacement curve is reliable for small to medium strains (0–0.4). Therefore, the proposed stratification method can be applied to enhance the reliability of jounce bumper simulations and to simplify the design process.

Assessment of the locations of fatigue failure in a commercial vehicle cab using the virtual iteration method

In this paper, fatigue damage analysis and structural improvement of a commercial vehicle cab were carried out, in which a simulation technique and durability road tests were combined. A full-scale finite element model of the cab was established and then validated by means of physical testing and analysis of its stiffness and its modal performance. The loading spectra, in accordance with the durability road test, were obtained by adopting the virtual iteration method. With the established finite element model, the stress distributions in the cab under unit excitation were determined. The obtained stress distributions were then used to assess the total fatigue life of the cab by employing the strain–life (ε–N) method; thus, the critical regions were determined. The results showed that some components near the pillars and mounts are easy to damage because of the stress concentrations. It was also demonstrated that the predicted regions are reliable, which was verified by comparison with the physical durability road tests. Finally, structural improvements in the critical structures were made; the fatigue life assessment of the improved cab showed an obvious improvement in its durability performance.

Multi-objective optimization of a tapered elliptical tube under oblique impact loading:

All types of thin-walled tube with different configurations were studied to determine their crashworthiness performances. A novel single-cell tapered elliptical tube is proposed in this paper. First, the crashworthiness performance of the single-cell tapered elliptical tube subjected to different oblique impacts was compared with those of other tubes with different configurations (straight, tapered, and multi-cell tapered) and different cross-sections (square, rectangular, and circular). It can be found that the single-cell tapered elliptical tube shows a better crashworthiness performance at multiple loading angles by comparing the specific energy absorption values and minimizing the peak crushing force. Second, to simplify the optimization process, the radial basis function model combined with the design-of-experiments method was utilized. Third, to determine the ideal radial rate f, the taper angle θ and the thickness t of the wall of the single-cell tapered elliptical tube, this paper adopted the non-dominated sorting genetic algorithm II to maximize the specific energy absorption and to minimize the peak crushing force. When determining the effect of the uncertainty in the loading angle, two different weighting-factor cases (case 1 and case 2) can be considered. In both cases, the optimized single-cell tapered elliptical tube has a better crashworthiness performance than tubes with other different cross-sections do. The design has a great influence on the optimization results. In comparison with the original single-cell tapered elliptical tube, in case 1, the composite specific energy absorption index under multiple oblique loading of the optimal tube increases by 12.81% and the peak crushing force at 0° decreases by 16.66% and, in case 2, the specific energy absorption index under multiple oblique loading increases by 11.8% and the peak crushing force at 0° decreases by 12.83%.

Homogenized modeling and micromechanics analysis of thin-walled lattice plate structures for brake discs

Periodic cellular structures, especially lattice designs, have potential to improve the cooling performance of brake disk system. In this paper, the method of two scales asymptotic homogenization was used to indicate the effective elastic stiffnesses of lattice plates structures. The arbitrary topology of lattice core cells connected to the back and front plates which are made of generally orthotropic materials, due to use in brake disc design. This starts with the derivation of general shell model with consideration of the set of unit cell problems and then making use of the model to determine the analytical equations and calculate the effective elastic properties of lattice plate concerning the connected back and front plates. The analytical and numerical method allows determining the stiffness properties and the internal forces in the trusses and plates of the lattice. Three types of core-based lattice plates, which are pyramidal, X-type and I-type lattices, have been studied. The I-type lattice is characterized here for the first time with particular attention on the role that the cell trusses and plates plays on the stiffness and strength properties. The lattice designs are finite element characterized and compared with the numerical and experimentally validated pyramidal and X-type lattices under identical conditions. The I-type lattice provides 4% higher strength more than the other lattice types with 9% higher truss fraction coefficient. Results show that the stiffness and yield strength of the lattices depend upon the stress–strain response of the parent alloy of trusses and plates, the truss mass fraction coefficient, the face carriers thickness and the core elements parameters. The study described here is limited to a linear analysis of lattice properties. Geometric nonlinearities, however, have a considerable impact on the effective behavior of a lattice and will be the subject of future studies.