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2019 Research Highlight: Micro-Mechanical Finite Element Modeling of Progressive Punch-Shear Behavior of Unidirectional Composite

Micro-Mechanical Finite Element Modeling of Progressive Punch-Shear Behavior of Unidirectional Composite

CMEDE Researchers
Dr. Bazle Z. (Gama) Haque
University of Delaware
Professor John. W. Gillespie, Jr.
University of Delaware
Dr. Chian-Fong Yen
CCDC Army Research Laboratory
Dr. Daniel J. O’Brien
CCDC Army Research Laboratory

Punch shear is a unique damage mechanism observed around a projectile while penetrating or perforating a composite target under high velocity impact which involves micromechanical mixed-mode transverse shear dominated fiber-fracture, fiber-matrix debonding, large deformation and cracking of matrix resin. A micromechanical finite element model of punch shear can allow the stochastic prediction of punch shear strength and associated non-linear progressive damage with the model input for stochastic fiber tensile and shear strength distribution, rate dependent mixed mode fiber-matrix interface traction laws, and rate dependent non-linear large deformation matrix behavior.

Micro punch shear experiments on unidirectional (UD) S-2 glass/DER353 composite ribbons with 6 to 7 through-thickness fibers have been conducted to determine the statistical distribution of punch shear strength, to quantify the relative fiber-fracture heights and fiber-matrix debonding lengths for model validation. An equivalent 2D FE model of the punch shear experiments of unidirectional composite has been developed and validated with experiments. The validated model is then used to run stochastic simulations in predicting the statistical distribution of punch shear strengths which matches well with the experiments. By the use of rate dependent matrix and fiber-matrix interface properties, computational simulations have also been conducted at different loading rates in determining the rate dependent punch shear strength of UD S-2 glass/DER353 composites, which shows logarithmic rate dependency.

In order to capture the 3D effects, a 3D FE model of unidirectional composites with 28 fibers in a hexagonal array has been developed. In this 3D model, each fibers are modeled as an assembly of 2 micron segments connected by zero-thickness mixed-mode traction law to mimic all probable locations of surface micro cracks on the fiber. Experimentally measured bi-modal (with 16mm & 365 micron gage length) Weibull parameters for glass fiber have been extrapolated for 4 micron gage length and randomly assigned between each fiber segments. This segmented fiber model is verified by simulating axial tension yielding the correct modulus of the unsegmented glass fiber. Furthermore, the mixed mode fiber fracture is verified by conducting a transverse impact on the fiber. The surrounding matrix is modeled as one large part with holes for the fiber array with coincident nodes for zero-thickness cohesive definition of the fiber-matrix interface between each fiber and the matrix. Punch shear of a single fiber with surrounding matrix has been simulated to verify the fiber-matrix debonding model.

The 3D FE model of the unidirectional composite is then subjected to axial tension and compression in all three material directions in predicting the non-linear progressive stress-strain for continuum model applications such as MAT162 in LS-DYNA®. In addition, inplane shear, interlaminar shear, and punch shear loading have been applied for micromechanical prediction of the shear behavior of unidirectional composites.

We are in the process of developing a 3D FE model of punch shear and axial tension in a way such that stochastic parametric computations can be performed varying the input properties. This new modeling framework will allow materials-by-design capabilities where material properties and attributes predicted in the molecular length scale will be used as input to this micromechanical model in predicting the energy dissipating damage modes and help optimize materials energy absorption both under punch shear and tensile loading.