Evaluation of Stress Wave Attenuation in a Polymer Matrix Composite Using Finite Element Analysis Technique

The dynamic behavior of polymer composites is significantly affected by the properties of their micro constituents including shape and size of inclusions and inclusions/matrix adhesion properties. Wave propagation through such a composite is a complex phenomenon as it includes random scattering, absorption and transmittance of the incident wave and is dependent upon factors such as the properties, size and placement of the inclusions inside the matrix. Finite element modeling provides a viable approach for investigating the effects of micro constituent structure on the dynamic behavior of polymer composites. In this paper, we investigate the stress wave attenuation characteristics of a particulate polymer matrix composite using Finite Element (FE) analysis approach. The wave attenuation of ultrasonic sinusoidal waves of frequency ranging from 1 MHz to 4 MHz is evaluated for different FE models. The spherical inclusions are randomly distributed inside the polymer matrix with a certain minimum distance apart from each other. Inclusion-Matrix adhesion properties are studied by modeling a small region at the interface of inclusions and matrix known as interphase region. The interphase region is modeled explicitly using the cohesive zone modeling approach to study how the properties of this region will affect the wave attenuation characteristics of the polymer composite. Cohesive zone models are governed by traction separation law which helps in the measurement of the inclusion-matrix bonding strength and also allow the study of de-bonding at the interface in the critically stressed region produced due application of load. Thus the FE models consist of three phases; polymer matrix, particulate inclusions and the interphase region. Various three dimensional FE models are created using 3D tetrahedral/hexahedral elements by varying the radius of the spherical inclusions and by varying volume fraction of the inclusions. The analyses are performed using a general purpose finite element software LS-Dyna. A rate dependent viscoelastic material model with four terms in prony series expansion is used for modeling the polymer matrix. A linear elastic isotropic material model is used for modeling the inclusions. The wave attenuation is measured as reduction in the amplitude of the wave as it passes through the composite. A comparison of results for various models is done to check for general trend of attenuation coefficient as a function of size of inclusions, volume fraction of inclusions, frequency of loading and interphase region properties. Results show that volume fraction and load frequency have a maximum effect on the wave attenuation coefficient. Interphase region stiffness and interface de-bonding also plays an important role in attenuation characteristics of the polymer composite.