CAE Analysis Of Mechanical Properties Of Thin-walled Composite Products

Composite materials have been widely used in aerospace and other fields due to the merits of light weight,high strength,fatigue resistance,and flexible design.The development of science and technology continuously improves the quality and greatly reduces the cost,which lays a foundation for composite materials to be popular in various market applications.Meanwhile,as more and more attention is paid to environment protecting,energy saving and cost reducing,it has become an ongoing trend to use advanced composite materials instead of traditional metals to raise the quality and sustainability of economic development.The anisotropic feature of composite materials increases the complexity of the stress-strain constitutive relations and the mechanical performance.As a result,it is not easy to design products of high quality,and the demand for numerical simulation of mechanical properties is increasingly urgent.Although some commercial CAE tools currently available are relatively matured,there are still some deficiencies in the mechanical analysis of thin-walled composite products.On the one hand,the complexity of the composite materials causes new problems.For example,for an injection molded thin-walled composite product,the element material data used in mechanical analysis are obtained from flow analysis,but how to do it is still a key problem to be solved.On the other hand,the available software tools are not powerful enough to deal with thin-walled composite products due to limited function and poor extensibility.For instance,composite materials usually show a certain degree of anisotropy,it is,in theory,necessary to define material data for each element independently,which is a hard work in practice especially when the model is large.Furthermore,it is not suitable to use commercial software in some situation.Such as the stress detecting equipment of the space-suit mask,it is a domestic self-developed instrument,into which only the stress-strain algorithm is integrated.All of these indicate it is meaningful in engineering application and scientific research to develop our own mechanical analysis software that is flexible in function expansion according to the needs of thin-walled composite products design.For these reasons,this paper studies on the basic theory of the mechanical simulation for shell-structured composite products.Based on the previous research works,the FEM model of structural analysis was established with flat shell element,and then the corresponding software was developed with Visual C++.The main content is summarized as follows:(1)A new method for predicting the elastic constants of composite materials containing transversely isotropic matrix is proposed.By using Mura tensor instead of Eshelby tensor in the Mori-Tanaka model,its application is extended to materials with transversely isotropic matrix.(2)The CST film element and the DKT bending element are used to establish the mechanical FEM model that consisting of pure triangular elements while the Q4 film element and Mindlin element are used for that consisting of pure quadrilateral elements.The combination of the two models can be used when the above elements co-exist.(3)The Jacobi method and QR method are used to calculate the principal stress and its direction instead of exhaust enumeration.Test results show its results are stability and reliability.(4)Based on the above theory,the software HTStress was developed with Visual Studio 2013 C++.Its results are also testified from ANSYS.(5)In the engineering application,the kernel of the HTStress,which is the stressstrain calculation algorithm,is embedded into the stress detection equipment of the space-suit mask to calculate the stress and strain after assembly.