In this licentiate thesis the work done in the TURBO POWER project Influence of high temperature hold times on the fatigue life of nickel-based superalloys will be presented. The overall objective of this project is to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. Firstly, the constitutive beh...

This paper presents a meshless point collocation method for three-dimensional crack propagation. The meshless point collocation method is based on direct discretization of strong-form governing equations to achieve a truly meshless scheme that does not require mesh structures or a numerical integration procedure. These characteristics of the point collocation method enable the direction of an a...

Paris law constants are commonly obtained with a well established procedure based on standard specimens, notched and pre-cracked. Pre-cracking produces through cracks with stable shapes, nearly straight, similar during all propagation. However, in several situations specimens with corner and surface cracks are recommended. In these cases cracks having significant propagation will continuously m...

A series of molecular-dynamics simulations using a many-body interatomic potential has been performed to investigate the behavior under load of several ^001& and ^011& symmetrical tilt grain boundaries ~GB’s! in diamond. Cohesive energies, the work for fracture, maximum stresses and strains, and toughness as a function of GB type are evaluated. Results indicate that special short-period GB’s po...

Effect of thermal treatment on the fatigue crack propagation behavior of a new Ni-base superalloy Xingbo Liu a,*, ling Xu a, Ever Barbero a, Wei-Di Cao b, Richard L. Kennedy b a West Virginia University, Morgantown, WV 26506-6106, USA b Allvac, an AT! Technologies Company, Monroe, NC 28111-5030, USA Received 22 October 2006; received in revised form 23 March 2007; accepted 10 May 2007 The effec...

BACKGROUND Slow crack growth can be described in a v (crack velocity) versus KI (stress intensity factor) diagram. Slow crack growth in ceramics is attributed to corrosion assisted stress at the crack tip or at any pre-existing defect in the ceramic. The combined effect of high stresses at the crack tip and the presence of water or body fluid molecules (reducing surface energy at the crack tip)...

The aim of the present paper is to simulate the propagation of diffuse ultrasonic energy in concrete in the presence of a real crack. The numerical model is presented and validated by the comparison with experimental data from the literature. Unlike most of the studies which consider a crack as a notch, a realistic crack morphology exhibits partial contacts along its lips. These contacts are mo...

We propose a minimal nonlinear model of brittle crack propagation by considering only the motion of the crack-tip atom. The model captures many essential features of steady-state crack velocity and is in excellent quantitative agreement with many-body dynamical simulations. The model exhibits lattice-trapping. For loads just above this, the crack velocity rises sharply, reaching a limiting valu...

The experimentally determined marked rise of the stress intensity factor required to initiate crack propagation in brittle solids under variably high loading rates, is analyzed. This problem of fracture initiation at the tip of a crack is considered in terms of activating a flaw at some distance away from the tip. By using a semi-infinite crack in an unbounded two-dimensional solid subjected to...

Finite element method (FEM) is one of the most famous methods which has many applications in varies studies such as the study of crack propagation in engineering structures. However, unless extremely fine meshes are employed, problem arises in accurately modelling the singular stress field in the singular element area around the crack tip. In the present study, the crack growth simulation has b...