Du Xingwen

Simulation Analysis of Vibration Characteristics of Wrinkled Membrane Space Structure

Flexible membrane space structures have received the widest attention due to their small packaging volume and low launching cost, but wrinkles as the common deformation state, are the main failure mode of such structures. They also affect the vibration characteristics which are the main factor of the structural analysis and design. So a better understanding of the vibration characteristics of the wrinkled membrane structure is essential and desirable. In this paper, a modal analysis, incorporating the wrinkling analysis, is presented to model the vibration characteristics of the wrinkled square membrane structure subjected to the asymmetric tension. The effects of the wrinkles on the vibration characteristics of the wrinkled membrane structures are considered in detail. Some important conclusions are also summarized in detail at last. The results of this paper are very important when used in the structural design and optimization of the membrane space structure.

Mesh-dependence of Material with Softening Behavior

Abstract The issue of mesh-dependence emerges when the conventional continuum damage model is applied to handling the softening behavior. In order to circumvent the mesh-dependence, the non-local theory is introduced into the conventional damage model and the finite element formulas are derived for two-dimensional gradient-enhanced damage model. A new element is proposed in which the basic unknown quantities are displacement, non-local equivalent strain and the gradient of non-local equivalent strain. The element and constitutive equation proposed in this article are added to the finite element software ABAQUS through user subroutine UEL. Numerical results show that the gradient-enhanced damage model can eliminate the mesh-dependence and is effective for dealing with the issue of softening behavior.

Method of model analysis for flexible head impacting with elastic plane

To consider the head is a flexible multi-layer structure and the contact-impact is flexible, the Hertz Contact Law is unsuitable for analyzing the dynamic response of human head impacts elastic plane with initial speed. In this paper, the process of head impacting with elastic plane is modeled as a response of vibrant system, and methods like mechanical network figure and mechanical impedance is taken to resolve this dynamic response problem. Based on the actual head structure, head is modeled as a vibrant model, which concludes the masses of scalp and bone in the impact area, the masses in the other part of the head and the brain, the stiffness of the head, and the damp coefficient of the scalp and brain. At the same time, the elastic plane is simplified as a vibrant model including mass, stiffness and damp. These two vibrant models are linked into one vibrant systematic model. In order to calculate the elastic deformation and the impact acceleration of the head, the models are transformed into mechanical girding figure at violent vibration point. The dynamic impact force of the system, the impact acceleration of the head, the elastic deformation of the plane and the fixed frequency of the system can be worked out by calculating the velocity impedance at the violent vibration point when the initial impact speed is known. The results fit the test data well, which proves that this method is available for the analysis of the dynamic response of the system under impact.

The Analytical Model of Shear Properties of the Pre-impregnated Woven Fabric Composite

The pre-impregnated woven fabric composite is the material which is used in the space inflatable structures for the state of uncured. So studying on properties of the pre-impregnated woven fabric composite is important for the space inflatable structures. The pre-impregnated woven fabric composite has its own properties which are not similar with the fabric or the fabric reinforced composite because of the existence of the uncured resin. In this paper, a picture frame analytical model is developed to account for large shear deformation and to calculate the stress and stiffness of the fabric. A mesostructure model which explains the uncured resin impede the structure to deform is also proposed. The picture frame experiment results are presented to validate this model. Results show the equation explains the properties of the material well. This paper may provide useful information for the further investigation in the characteristics of the space inflatable structures’ materials.

Viscoelastic constitutive model of unvulcanized rubber

Based on rheological test results, a new viscoelastic constitutive equation for unvulcanized rubber has been set up, with mathematical justification to describe its mechanical properties in relation to the yield stress and shear-thinning effect. In this model, every term or coefficient has an explicit physical meaning. The proposed model indicates that the yield stress is one of the main causes for the shear-thinning effect and reveals why some materials possess double-Newtonian regions with the shear viscosity in the first region higher than that in the second region. The yield stress makes the flow index of the power law fluid model vary widely, so that it needs to be eliminated from the power law fluid model. The model can also distinguish the true shear viscosity from the apparent shear viscosity effectively. The parameters of the equation are determined by the step fitting method, which is the precondition for quantitative analysis. However, the equation is a one-dimensional model, so further research is needed.