Finite Element Investigation of Quasi-Static Crack Growth in Functionally Graded Materials Using a Novel Cohesive Zone Fracture Model

2002 ◽  
Vol 69 (3) ◽  
pp. 370-379 ◽  
Author(s):  
Z.-H. Jin ◽  
G. H. Paulino ◽  
R. H. Dodds,
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Functionally Graded Materials ◽  
Material Properties ◽  
Growth Response ◽  
Functionally Graded ◽  
Fracture Model ◽  
Cohesive Fracture ◽  
Graded Materials ◽  
Cohesive Fracture Model

This work studies mode I crack growth in ceramic/metal functionally graded materials (FGMs) using three-dimensional interface-cohesive elements based upon a new phenomenological cohesive fracture model. The local separation energies and peak tractions for the metal and ceramic constituents govern the cohesive fracture process. The model formulation introduces two cohesive gradation parameters to control the transition of fracture behavior between the constituents. Numerical values of volume fractions for the constituents specified at nodes of the finite element model set the spatial gradation of material properties with standard isoparametric interpolations inside interface elements and background solid elements to define pointwise material property values. The paper describes applications of the cohesive fracture model and computational scheme to analyze crack growth in compact tension, C(T), and single-edge notch bend, SE(B), specimens with material properties characteristic of a TiB/Ti FGM. Young’s modulus and Poisson’s ratio of the background solid material are determined using a self-consistent method (the background material remains linear elastic). The numerical studies demonstrate that the load to cause crack extension in the FGM compares to that for the metal and that crack growth response varies strongly with values of the cohesive gradation parameter for the metal. These results suggest the potential to calibrate the value of this parameter by matching the predicted and measured crack growth response in standard fracture mechanics specimens.

A Simplified Method for Calculating the Crack-Tip Field of Functionally Graded Materials Using the Domain Integral

1999 ◽  
Vol 66 (1) ◽  
pp. 101-108 ◽  
Author(s):  
P. Gu ◽  
M. Dao ◽  
R. J. Asaro
Keyword(s):  
Finite Element ◽  
Functionally Graded Materials ◽  
Material Properties ◽  
Crack Tip ◽  
Functionally Graded ◽  
Crack Tip Field ◽  
Graded Materials ◽  
Fine Mesh ◽  
Domain Integral ◽  
Standard Domain

A finite element based method is proposed for calculating stress intensity factors of functionally graded materials (FGMs). We show that the standard domain integral is sufficiently accurate when applied to FGMs; the nonhomogeneous term in the domain integral for nonhomogeneous materials is very small compared to the first term (the standard domain integral). In order to obtain it, the domain integral is evaluated around the crack tip using sufficiently fine mesh. We have estimated the error in neglecting the second term in terms of the radius of the domain for the domain integration, the material properties and their gradients. The advantage of the proposed method is that, besides its accuracy, it does not require the input of material gradients, derivatives of material properties; and existing finite element codes can be used for FGMs without much additional work. The numerical examples show that it is accurate and efficient. Also, a discussion on the fracture of the FGM interlayer structure is given.

Numerical Simulation of Mixed-Mode Crack Propagation in Functionally Graded Materials

2009 ◽  
Vol 631-632 ◽  
pp. 121-126 ◽  
Author(s):  
Li Ma ◽  
Zhi Yong Wang ◽  
Lin Zhi Wu
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Crack Propagation ◽  
Crack Growth ◽  
Functionally Graded Materials ◽  
Mixed Mode ◽  
Fracture Criterion ◽  
Functionally Graded ◽  
Graded Materials ◽  
Specific Fracture

This paper addresses the numerical simulation of mixed-mode crack propagation in Functionally Graded Materials (FGMs) by means of eXtended Finite Element Method (XFEM), endowed with elastic and toughness properties which gradually vary in space. The method allows to follow crack paths independently of the finite element mesh, this feature is especially important for FGMs, since the gradation of the mechanical properties may lead to complex propagation paths also in simple symmetric tests. Each step of crack growth simulation consists of the calculation of the mixed-mode stress intensity factor by means of a non-equilibrium formulation of the interaction integral method, determination of the crack growth direction based on a specific fracture criterion. A specific fracture criterion is tailored for FGMs based on the assumption of local homogenization of asymptotic crack-tip fields in FGMs. The present approach uses a user-defined crack increment at the beginning of the simulation. Crack trajectories obtained by the present numerical simulation agree well with available experimental results for FGMs. The computational scheme developed here serve as a guideline for fracture experiments on FGM specimens (e.g. initiation toughness and R-curve behavior).

Model Development of the Application of Finite Element – Eigenvalue Method to the Determination of Transient Temperature Field in Functionally Graded Materials

2007 ◽  
Vol 18-19 ◽  
pp. 253-261
Author(s):  
John A. Akpobi ◽  
C.O. Edobor
Keyword(s):  
Finite Element ◽  
Temperature Field ◽  
Functionally Graded Materials ◽  
Model Development ◽  
Element Model ◽  
Steady State Solution ◽  
Functionally Graded ◽  
Transient Temperature ◽  
Graded Materials ◽  
Eigenvalue Method

In this paper, a finite elment-eigenvalue method is formulated to solve the finite element models of time dependent temperature field problems in non-homogeneous materials such as functionally graded materials (FGMs). The method formulates an eigenvalue problem from the original finite element model and proceeds to calculate the associated eigenvectors from which the solution can be obtained. The results obtained highly accurate and are exponential functions of time which when compared with the exact solution tended fast to the steady state solution.

Designing Optimal Volume Fractions For Functionally Graded Materials With Temperature-Dependent Material Properties

2006 ◽  
Vol 74 (5) ◽  
pp. 861-874 ◽  
Author(s):  
Florin Bobaru
Keyword(s):  
Functionally Graded Materials ◽  
Material Properties ◽  
Volume Fraction ◽  
Effective Properties ◽  
Functionally Graded ◽  
Dominant Factor ◽  
Temperature Dependent ◽  
Graded Materials ◽  
Critical Stresses ◽  
Non Linear

We present a numerical approach for material optimization of metal-ceramic functionally graded materials (FGMs) with temperature-dependent material properties. We solve the non-linear heterogeneous thermoelasticity equations in 2D under plane strain conditions and consider examples in which the material composition varies along the radial direction of a hollow cylinder under thermomechanical loading. A space of shape-preserving splines is used to search for the optimal volume fraction function which minimizes stresses or minimizes mass under stress constraints. The control points (design variables) that define the volume fraction spline function are independent of the grid used in the numerical solution of the thermoelastic problem. We introduce new temperature-dependent objective functions and constraints. The rule of mixture and the modified Mori-Tanaka with the fuzzy inference scheme are used to compute effective properties for the material mixtures. The different micromechanics models lead to optimal solutions that are similar qualitatively. To compute the temperature-dependent critical stresses for the mixture, we use, for lack of experimental data, the rule-of-mixture. When a scalar stress measure is minimized, we obtain optimal volume fraction functions that feature multiple graded regions alternating with non-graded layers, or even non-monotonic profiles. The dominant factor for the existence of such local minimizers is the non-linear dependence of the critical stresses of the ceramic component on temperature. These results show that, in certain cases, using power-law type functions to represent the material gradation in FGMs is too restrictive.

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