Prediction Of Mechanical Properties Of The Short-fiber Reinforced Injection Molding Products

Because of their good mechanical properties and convenient processing technics, the short-fiber-reinforced injection molding products are widely used in many fields, for example, aviation, spaceflight, automobile and shipping. In order to design the products that can answer for the producing requirement, this paper is to study the products' macro-mechanical properties and its different forecasting methods on the basis of micro-mechanics, and compare the results of different methods to each other.At first, the classical problems in micro-mechanics-----the problem of Eshelby'ssingle inclusion in infinite matrix and equivalent inclusion are introduced. Then, the mechanical models of unidirectional short-fiber reinforced composites developed by the former researchers are analyzed and corresponding computer program of some of these models are built too. It is found that the Tandon-Weng model's results are relatively precise. The results of Tandon-Weng model can exactly reflect the relationship between the macro-mechanical properties of unidirectional short fiber reinforced composites' and the properties of the components or fiber volume fraction, aspect ratio.At present, there is a method of predicting misaligned fiber reinforced mechanical properties which is widely used in most of simulation softwares-MoldFlow and so on. It can be divided into three steps. First, the fiber orientation function is transformed to orientation tensor; then, the tensor's eigenvalues and corresponding eigenvectors can be numerated, the eigenvectors shows the fibers orientation, the corresponding eignevalues means the probability of the fiber orientation; finally, the summation of the stiffness matrix of the fiber orientation multiply the eigenvalue is the composites stiffness matrix. The method is used for improving the numerating efficiency, consequently the results of this method is not exact enough. We will compare this method to the laminated method that was not predigested, in order to know if the used method can answer for the engineering requirement.Usings several different fiber orientation functions, the laws of how the differences of the results of two methods change with the fibers' volume fraction, aspect ratio, will be discussed.