The M-Integral for Computing Stress Intensity Factors in Generally Anisotropic Materials

The objective of this project is to develop and demonstrate a capability for computing stress intensity factors in generally anisotropic materials. These objectives have been met. The primary deliverable of this project is this report and the information it contains. In addition, we have delivered the source code for a subroutine that will compute stress intensity factors for anisotropic materials encoded in both the C and Python programming languages and made available a version of the FRANC3D program that incorporates this subroutine. Single crystal super alloys are commonly used for components in the hot sections of contemporary jet and rocket engines. Because these components have a uniform atomic lattice orientation throughout, they exhibit anisotropic material behavior. This means that stress intensity solutions developed for isotropic materials are not appropriate for the analysis of crack growth in these materials. Until now, a general numerical technique did not exist for computing stress intensity factors of cracks in anisotropic materials and cubic materials in particular. Such a capability was developed during the project and is described and demonstrated herein

Static fracture and modal analysis simulation of a gas turbine compressor blade and bladed disk system

This paper presents a methodology for conducting a 3-D static fracture analysis with applications to a gas turbine compressor blade. An open crack model is considered in the study and crack-tip driving parameters are estimated by using 3-D singular crack-tip elements in ANSYS. The static fracture analysis is verified with a special purpose fracture code (FRANC3D). Once the crack front is perfectly defined and validated, a free vibration study is conducted by analyzing the natural frequencies and modeshapes for both a single blade and bladed disk system. Taking advantage of high performance computing resources, a high fidelity finite element model is considered in the parametric investigation. In the fracture simulation, the influence of the size of a single edged crack as well as the rotational velocity on fracture parameters (stress intensity factors and J-Integral) are evaluated. Results demonstrate that for the applied loading condition, a mixed mode crack propagation is expected. In the modal analysis study, increasing the depth of the crack leads to a decrease in the natural frequencies of both the single blade and bladed disk system, while increasing the rotational velocity increases the natural frequencies. The presence of a crack also leads to mode localization for all mode families, a phenomenon that cannot be captured by a single blade analysis.The authors gratefully acknowledge the support of the Qatar National Research Fund through Grant number NPRP 7-1153-2-432. The authors also thank Texas A&M at Qatar?s Advanced Scientific Computing (TASC) for access to the RAAD Supercomputer.Scopu

Cohesive-zone modelling of the deformation and fracture of spot-welded joints

The deformation and failure of spot-welded joints have been successfully modelled using a cohesive-zone model for fracture. This has been accomplished by implementing a user-defined, three-dimensional, cohesive-zone element within a commercial finite-element package. The model requires two material parameters for each mode of deformation. Results show that the material parameters from this type of approach are transferable for identical spot welds in different geometries where a single parameter (such as maximum stress) is not. The approach has been demonstrated using a model system consisting of spot-welded joints made from 5754 aluminium sheets. The techniques for determining the cohesive fracture parameters for both nugget fracture and nugget pullout are described in this paper. It has been demonstrated that once the appropriate cohesive parameters for a weld are determined, quantitative predictions can be developed for the strengths, deformations and failure mechanisms of different geometries with nominally identical welds.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73187/1/j.1460-2695.2005.00919.x.pd

Failure Analysis of Adhesively Bonded Structures: From Coupon Level Data to Structural Level Predictions and Verification

This paper presents a predictive methodology and verification through experiment for the analysis and failure of adhesively bonded, hat stiffened structures using coupon level input data. The hats were made of steel and carbon fiber reinforced polymer composite, respectively, and bonded to steel adherends. A critical strain energy release rate criterion was used to predict the failure loads of the structure. To account for significant geometrical changes observed in the structural level test, an adaptive virtual crack closure technique based on an updated local coordinate system at the crack tip was developed to calculate the strain energy release rates. Input data for critical strain energy release rates as a function of mode mixity was obtained by carrying out coupon level mixed mode fracture tests using the Fernlund–Spelt (FS) test fixture. The predicted loads at failure, along with strains at different locations, were compared with those measured from the structural level tests. The predictions were found to agree well with measurements for multiple replicates of adhesively bonded hat-stiffened structures made with steel hat/adhesive/steel and composite hat/adhesive/steel, thus validating the proposed methodology for failure prediction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42764/1/10704_2005_Article_0646.pd