Finite Element Simulation of a Crack Growth in the Presence of a Hole in the Vicinity of the Crack Trajectory

The aim of this paper was to present a numerical simulation of a crack growth path and associated stress intensity factors (SIFs) for linear elastic material. The influence of the holes’ position and pre-crack locations in the crack growth direction were investigated. For this purpose, ANSYS Mechanical R19.2 was introduced with the use of a new feature known as Separating Morphing and Adaptive Remeshing Technology (SMART) dependent on the Unstructured Mesh Method (UMM), which can reduce the meshing time from up to several days to a few minutes, eliminating long preprocessing sessions. The presence of a hole near a propagating crack causes a deviation in the crack path. If the hole is close enough to the crack path, the crack may stop at the edge of the hole, resulting in crack arrest. The present study was carried out for two geometries, namely a cracked plate with four holes and a plate with a circular hole, and an edge crack with different pre-crack locations. Under linear elastic fracture mechanics (LEFM), the maximum circumferential stress criterion is applied as a direction criterion. Depending on the position of the hole, the results reveal that the crack propagates in the direction of the hole due to the uneven stresses at the crack tip, which are consequences of the hole’s influence. The results of this modeling are validated in terms of crack growth trajectories and SIFs by several crack growth studies reported in the literature that show trustworthy results.

On the Fatigue and Fracture of Bladed and Integrally Bladed Rotors of Aircraft Engine Compressors

The fatigue and fracture for bladed and integrally bladed rotors (IBR) of aircraft engine compressors has been studied. For IBRs, a new distinct finite element technique was developed to model crack propagation under combined low cycle and high cycle fatigue loading. The crack trajectory, aspect ratio, and shape resulting from the method agreed very well with airfoils which fractured in service. The technique can be extended on other compressor disk applications. For bladed rotors limited by fretting fatigue, a unique fracture mechanics based methodology was developed for obtaining an evolved coefficient of friction (COF) resulting from fretting motion between the fan blade and hub. The predicted nucleation location, nucleation life, crack trajectory, shape and propagation life agreed well with the fractured components. The study confirms that the fretting-specific modified Smith-Watson-Topper (SWT) parameter more accurately predicts the nucleation location and life of the crack compared to the plain fatigue SWT parameter.

On the Fatigue and Fracture of Bladed and Integrally Bladed Rotors of Aircraft Engine Compressors

The fatigue and fracture for bladed and integrally bladed rotors (IBR) of aircraft engine compressors has been studied. For IBRs, a new distinct finite element technique was developed to model crack propagation under combined low cycle and high cycle fatigue loading. The crack trajectory, aspect ratio, and shape resulting from the method agreed very well with airfoils which fractured in service. The technique can be extended on other compressor disk applications. For bladed rotors limited by fretting fatigue, a unique fracture mechanics based methodology was developed for obtaining an evolved coefficient of friction (COF) resulting from fretting motion between the fan blade and hub. The predicted nucleation location, nucleation life, crack trajectory, shape and propagation life agreed well with the fractured components. The study confirms that the fretting-specific modified Smith-Watson-Topper (SWT) parameter more accurately predicts the nucleation location and life of the crack compared to the plain fatigue SWT parameter.

Identification and Prediction of Mixed-Mode Fatigue Crack Path in High Strength Low Alloy Steel

The trajectory of fatigue crack growth is influenced by many parameters and can be irregular due to changes in stress distribution or in material properties as the crack progresses. Images of the surface of a standardized test specimen can be used to visualize the crack trajectory in a non-destructive way. Accurately identifying the location of the crack tip, however, is challenging and requires devoted image postprocessing. In this respect, digital image correlation allows to obtain full field displacement and strain fields by analysing changes of digital images of the same sample at different stages of loading. This information can be used for the purpose of crack tip tracking. This paper presents a combined experimental-numerical study of detection and prediction of fatigue crack propagation path by means of digital image correlation (DIC) and the extended finite element method (X-FEM). Experimental validation and analyses are carried out on a modified C(T) specimen in which a curved crack trajectory is triggered by introducing mixed-mode (tension + shear) loading. The developed tools are used for validating an automated framework for crack propagation prediction.

ANALYTICAL DESCRIPTION OF THE INCLINED CRACK TRAJECTORY BY THE METHOD OF NONLINEAR DEFORMATION MODEL

The article proposes an analytical solution to determine the trajectory of inclined crack with the use of nonlinear deformation model in the area of the transverse bending of a reinforced concrete beam. The use of nonlinear deformation model for the analysis of stress-strain state of the beam in the zone of the transverse bending allows to determine the coordinates of the inclined crack trajectory, the position of its vertex, and the angle of inclination to the longitudinal axis of the beam. It is then possible to move from the empirical dependences for calculating the strength of the inclined sections to precise analytical techniques. The proposed algorithms calculate and analyze the stress-strain state of reinforced concrete beams create preconditions for the implementation of the physical model of a power resistance of reinforced concrete elements under transverse bending.