Mixed-Mode Dynamic Crack Growth in a Functionally Graded Particulate Composite: Experimental Measurements and Finite Element Simulations

Abstract

Mixed-mode dynamic crack growth behavior in a compositionally graded particle filled polymer is studied experimentally and computationally. Beams with single edge cracks initially aligned in the direction of the compositional gradient and subjected to one-point eccentric impact loading are examined. Optical interferometry along with high-speed photography is used to measure surface deformations around the crack tip. Two configurations, one with a crack on the stiffer side of a graded sheet and the second with a crack on the compliant side, are tested. The observed crack paths are distinctly different for these two configurations. Furthermore, the crack speed and stress intensity factor variations between the two configurations show significant differences. The optical measurements are examined with the aid of crack-tip fields, which incorporate local elastic modulus variations. To understand the role of material gradation on the observed crack paths, finite element models with cohesive elements are developed. A user-defined element subroutine for cohesive elements based on a bilinear traction-separation law is developed and implemented in a structural analysis environment. The necessary spatial variation of material properties is introduced into the continuum elements by first performing a thermal analysis and then by prescribing material properties as temperature dependent quantities. The simulated crack paths and crack speeds are found to be in qualitative agreement with the observed ones. The simulations also reveal differences in the energy dissipation in the two functionally graded material (FGM) cases. T-stresses and hence the crack-tip constraint are significantly different. Prior to crack initiation, larger negative T-stresses near the crack tip are seen when the crack is situated on the compliant side of the FGM.

A peridynamic model for dynamic fracture in functionally graded materials

“…Such a modeling approach may not be appropriate for modeling failure processes in certain FGMs under certain loading conditions. Part of our goal here is to see to what extent the proposed peridynamic model of a locally homogenized FGM is able to reproduce experimentally-observed dynamic fracture behavior for an FGM prepared by varying the volume fraction of small inclusions (glass spheres) in an epoxy matrix as used in [22] and [25]. For the type of FGM used in [22] and [25], the fracture behavior under impact conditions reveals a very high repeatability in terms of the crack path (see Fig.…”

“…Kim and Paulino [24] used local remeshing technique to predict the crack path forthe mixed-mode quasistatic fracture test in reference [23]. Kirugulige and Tippur [25] have reexamined the mixed-mode dynamic fracture experiment reported in [22] by using the cohesive-zone finite element method. Zhang and Paulino [26] have conducted mode-I and mixed-mode dynamic fracture simulations in FGMs by cohesive finite elements.…”

Experimental investigation on the radial and circular crack propagation of PVB laminated glass subject to dynamic out-of-plane loading

“…The dynamic crack propagation (along the material distribution axis) in homogeneous and inhomogeneous materials is thoroughly studied [15][16][17][18][19][20][21][22][23][24][25][26][27]. Singh et al [18] have investigated the fracture behavior of a dynamically loaded edge crack in a brittle-ductile layered material.…”

Experimental Fracture Mechanics of Functionally Graded Materials: An Overview of Optical Investigations

“…Nevertheless, it is noted that despite the high eccentricity of the imposed dynamic loading, the mode-II component of the response remains as a small portion of the overall stress field. These experiments were further supported by the implementation of a finite element simulation wherein cohesive elements based on a bilinear traction separation law were dispersed within the broad vicinity of expected crack growth [57]. Good agreement was achieved with the experimentation, thereby providing further validation to the derived solution.…”