• Wang, Huaijun
  The Graduate School, University of Maine
  

A mathematical model based on stochastic principles was developed to simulate the three dimensional geometric microstructure of wood fiber composite materials. Several computer programs were created to generate, analyze and visualize the simulated three dimensional (3D) fiber networks. The Model assumed ideal rigid and cylindrical fibers. The microstructure model input variables include 1) distribution of fiber length (lognormal); 2) distribution of fiber diameter (normal); 3) distribution of fiber horizontal orientation (von Mises); 4) size of composite to simulate; and 5) target density of composite. Simulation results include the information needed to describe individual fibers within the modeled space, specifically length, diameter and position in a 3D coordinate system. Functions to generate lognormal, normal, von Mises and Poisson random samples were written using a Monte Carlo simulation method.

Quantitative analysis of the simulated composite microstructure was accomplished by describing the distribution of the local void fraction, density, number of fiber segments and fiber contact area within the modeled space. A program was written to scan the simulated microstructure. The influence of model inputs such as fiber dimension and orientation on the microstructure properties were determined. Void size distributions were estimated by varying the size of the sub-units.

Three dimensional images of the microstructure were generated by two methods. The first technique consisted of reconstructing the pixel slice information into a voxel representation. Commercial software was then used to obtain and quantify volumetric renderings. the second 3-D visualization technique involved representation of the surface of individual fibers through calculation of control points on the fiber periphery. The resultant data structure was converted to a Virtual Reality Modeling Language (VRML) file which can be viewed and manipulated using appropriate viewers (available for windows and UNIX platforms). This approach, while not quantitative, permits interested parties to interact with the simulated 3-D structure from any computer in the world with suitable software and an internet connection.

This modeling approach can be extended to include alternate geometries (e.g. flattened fibers, flakes) and will further serve as geometrical input to finite element procedures to analyze the microstructure performance of composite materials.