EnginSoft - Conference Abstracts

EnginSoft Users' Meeting 2007
Le Tecnologie CAE nell'Industria

Development and validation of an algorithm for the numerical implementation of the Virtual Crack Closure Technique

Meneghin Ivan - University of Bologna, Aerospace Engineering
Troiani Enrico - University of Bologna, Aerospace Engineering
Gianotti Stefano - University of Bologna, Aerospace Engineering

Abstract

An algorithm is developed for the implementation of the Virtual Crack Closure Technique (VCCT) in order to predict the crack growth accurately.

Griffith’s criterion is employed to evaluate the crack propagation by means of the computation of Strain Energy Release Rate (SERR) values. These values are directly connected to the Stress Intensity Factors (SIFs) for isotropic materials.

The VCCT is a powerful tool to estimate efficiently the actual SERR values at the crack tip, by means of the implementation of the Irwin energy balance.

The ANSYS Parametric Design Language (APDL) is employed to generate a local mesh and to simulate the crack growth along a user defined path, by means of automatic release of paired nodes. The SERR values, for all fracture modes, are calculated during the process.

The numerical results are compared with three well - known closed form solutions, in order to validate the tool and to optimize the element dimensions,

• the single - edge notched (SEN) tensile specimen;
  
• the central cracked (CCT) tensile specimen;
  
• the double - edge notched (DEN) tensile specimen.

The definition of the optimum crack to element size ratio allows to reduce the free - edge effect by means of an accurate refinement of the local mesh.

An application study of the tool is the evaluation of the critical fracture points in a single - lap joint. This evaluation is performed by the comparison of the SERR values versus crack length curves. Several different locations of crack initiation and growth are considered.