The effect of manufacturing defects on the fatigue life of selective laser melted Ti-6Al-4V structures

SUMMARY Automated simulation of arbitrary, non-planar, 3D crack growth in real-life engineered structures requires two key components: crack representation and crack growth mechanics. A model environment for representing the evolving 3D crack geometry and for testing various crack growth mechanics is presented. Reference is made to a specific implementation of the model, called FRANC3D. Computational geometry and topology are used to represent the evolution of crack growth in a structure. Current 3D crack growth mechanics are insufficient; however, the model allows for the implementation of new mechanics. A specific numerical analysis program is not an intrinsic part of the model; i.e., finite and boundary elements are both supported. For demonstration purposes, a 3D hypersingular boundary element code is used for two example simulations. The simulations support the conclusion that automatic propagation of a 3D crack in a real-life structure is feasible. Automated simulation lessens the tedious and time-consuming operations that are usually associated with crack growth analyses. Specifically, modifications to the geometry of the structure due to crack growth, re-meshing of the modified portion of the structure after crack growth, and re-application of boundary conditions proceeds without user intervention.

Automated 3‐D crack growth simulation

Safe life and damage tolerance aspects of railway axles – A review

A review on 3D-FE adaptive remeshing techniques for crack growth modelling

Modified NASGRO equation for physically short cracks

The behavior of part-through flaws with regard to failure under monotonic loading and their growth under fatigue loading was studied experimentally and analytically. Comparisons are made of experimental values of toughness obtained using surface and corner cracked specimens with those obtained using standard test specimens, and also experimental growth cycles were compared with numerical predictions using the NASA/FLAGRO computer program. Tests were conducted on various types of surface and corner cracks under tensile and bending loads. Room temperature lab air provided the test environment. The material used in this study was the Ti-6Al-4V alloy in the solution treated and aged (STA) and stress relieved condition. Detailed tabulation of the fracture toughness data and results of life prediction using the NASA/FLAGRO program are presented. Fatigue crack growth rates for the part-through cracked specimens are compared with a base curve fitted from the data obtained using standard specimens. The fatigue loading used in the crack growth testing was constant-amplitude sinusoidal type.

https://ntrs.nasa.gov/api/citations/19910009960/downloads/19910009960.pdf

Behavior of surface and corner cracks subjected to tensile and bending loads in Ti-6Al-4V alloy

This viewgraph presentation describes NASGRO, which is a fracture mechanics and fatigue crack growth analysis software package that is used to reduce risk of fracture in Space Shuttles. The contents include: 1) Consequences of Fracture; 2) NASA Fracture Control Requirements; 3) NASGRO Reduces Risk; 4) NASGRO Use Inside NASA; 5) NASGRO Components: Crack Growth Module; 6) NASGRO Components:Material Property Module; 7) Typical NASGRO analysis: Crack growth or component life calculation; and 8) NASGRO Sample Application: Orbiter feedline flowliner crack analysis.

https://ntrs.nasa.gov/api/citations/20100042296/downloads/20100042296.pdf

NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

Flaws resulting from improper welding and forging are usually modeled as cracks in flat plates, hollow cylinders or spheres. The stress intensity factor solutions for these crack cases are of great practical interest. This report describes some recent efforts at improving the stress intensity factor solutions for cracks in such geometries with emphasis on hollow cylinders. Specifically, two crack configurations for cylinders are documented. One is that of a surface crack in an axial plane and the other is a part-through thumb-nail crack in a circumferential plane. The case of a part-through surface crack in flat plates is used as a limiting case for very thin cylinders. A combination of the two cases for cylinders is used to derive a relation for the case of a surface crack in a sphere. Solutions were sought which cover the entire range of the geometrical parameters such as cylinder thickness, crack aspect ratio and crack depth. Both the internal and external position of the cracks are considered for cylinders and spheres. The finite element method was employed to obtain the basic solutions. Power-law form of loading was applied in the case of flat plates and axial cracks in cylinders and uniform tension and bending loads were applied in the case of circumferential (thumb-nail) cracks in cylinders. In the case of axial cracks, the results for tensile and bending loads were used as reference solutions in a weight function scheme so that the stress intensity factors could be computed for arbitrary stress gradients in the thickness direction. For circumferential cracks, since the crack front is not straight, the above technique could not be used. Hence for this case, only the tension and bending solutions are available at this time. The stress intensity factors from the finite element method were tabulated so that results for various geometric parameters such as crack depth-to-thickness ratio (a/t), crack aspect ratio (a/c) and internal radius-to-thickness ratio (R/t) or the crack length-to-width ratio (2c/W) could be obtained by interpolation and extrapolation. Such complete tables were then incorporated into the NASA/FLAGRO computer program which is widely used by the aerospace community for fracture mechanics analysis.

/pdf/stress-intensity-factors-for-part-through-surface-cracks-in-2ba16wec1m.pdf

Stress Intensity Factors for Part-Through Surface Cracks in Hollow Cylinders

A recently developed numerical method based on the strip yield analysis approach was used to calculate the Crack Tip Opening Displacement (CTOD) and Crack Tip Opening Angle (CTOA) for a number of complex crack configurations of practical interest. This method is an adaptation of the dislocation-density based boundary element method. In this Boundary Element approach, crack-face opening displacements are obtained at any point on a crack using a series of definite integrals evaluated exactly in closed form for a variety of crack geometries, including infinite or finite extent, with arbitrarily applied loading conditions.

/pdf/numerical-strip-yield-calculation-of-ctod-and-ctoa-3xpr1grjm4.pdf

Royce Forman

Papers

Behavior of surface and corner cracks subjected to tensile and bending loads in Ti-6Al-4V alloy

NASGRO(registered trademark): Fracture Mechanics and Fatigue Crack Growth Analysis Software

Stress Intensity Factors for Part-Through Surface Cracks in Hollow Cylinders

Numerical Strip-Yield Calculation of CTOD and CTOA