Estimation Of Stress Intensity Factors Research Articles

Evaluation of Mixed-Mode Stress Intensity Factors Using a Small Punch Specimen with a Circular Crack: Preliminary Experiment and an Estimation of Stress Intensity Factors

Evaluation of Mixed-Mode Stress Intensity Factors Using a Small Punch Specimen with a Circular Crack: Preliminary Experiment and an Estimation of Stress Intensity Factors

Experimental and numerical estimation of complex stress intensity factor for the completely debonded anti-crack embedded into a weak matrix using domain integral method

The problem of interface debonding is of fundamental importance in understanding the stress transfer mechanism and behavior of weak interfaces present due to rigid stiffeners. A domain integral method based on Betti’s reciprocal theorem was adopted to compute the complex stress intensity factor (SIF) for the completely debonded anti-crack (discontinuity) with mixed boundary conditions. The domain integral approach is based on two admissible mechanical states, which comprise of actual and auxiliary elastic fields. The singular auxiliary fields in terms of angular variations for the completely debonded anticrack were obtained using the full-field solution. The obtained angular variations were compared with the Williams eigenvalue problem for completeness. The displacement and strains were obtained using digital image correlation (DIC) experiments and numerical simulation for parallel and perpendicular orientations of the discontinuity. The obtained DIC strain contours revealed the presence of anti-symmetric and symmetric variation on the bonded side of the anti-crack. The complex SIF is estimated experimentally and numerically based on the domain integral method to seek a better comparison with the analytical estimate. The SIF estimated for the perpendicular orientation is higher than the parallel orientation.

Modeling of Mode I crack-tip dislocation nucleation in three FCC materials: Ni, Cu and Al

An accurate estimation of the critical stress intensity factor for crack tip dislocation nucleation under Mode I loading is of great importance to determine whether a material is intrinsically ductile or not. Here, shear displacements and energy change at crack tip in FCC nickel, copper and aluminum are investigated during Mode I fracture process using atomistic simulations. In light of our simulation results, a new shear resistance model is formulated by a general Fourier expansion with coefficients identified by the computed energy curve. The new model involving the step formation energy which can be regarded as a new parameter and unstable stable stacking fault energy, reduces to Rice theory if no step exists. The criterion for nucleation is developed based on the idea that crack tip behaviors are controlled by the shear resistance and the maximum point serves as an obstacle to conquer. The predictions of the critical shear displacement corresponding to maximum shear resistance position and the critical nucleation energy show good agreement with simulation results. In addition, the new model can be further utilized to study the effect of complex stress state on Mode I crack tip dislocation nucleation.

Estimation of stress intensity factor for surface cracks in the firtree groove structure of turbine disk using pool-based active learning with Gaussian Process Regression

Estimation of stress intensity factor for surface cracks in the firtree groove structure of turbine disk using pool-based active learning with Gaussian Process Regression

Quantifying 3D crack propagation in nodular graphite cast iron using advanced digital volume correlation and X-ray computed tomography

Advanced digital volume correlation (DVC) combined with X-ray computed tomography (XCT) was utilized to investigate the 3D crack propagation in nodular graphite cast iron under tensile loading. The objective of this work was to quantify crack growth at the voxel-scale and extract fracture mechanics parameters such as the 3D crack front, crack opening displacements (CODs), and stress intensity factors (SIFs). By employing a crack growth updating strategy and an adaptive multiscale mesh, the 3D crack shape and propagation were accurately captured throughout the entire process. Von Mises strain and COD fields were characterized to provide insights into plastic zones and variations in crack opening behavior. Estimation of SIFs revealed a mode I dominant regime and limited influence from modes II and III. This study provides comprehensive insights into crack propagation and crack opening behavior, providing valuable information to fracture mechanics.

Optimization of damage repair with piezoelectric actuators using the Taguchi method

Over the last two decades, piezoelectric actuators have emerged as a promising solution for structural repair. In this work, initially the stress intensity factor (SIF) estimation using the finite element (FE) approach at crack tips in aluminium 2024-T3 plates. Based on Taguchi’s L9 orthogonal array the FE simulation has been conducted. Later, this study uses the optimization method via the design of experiments to systematically evaluate the effect of various dimensions and material qualities, especially under the conditions of Mode-I crack propagation. It also investigated the complex interaction of factors impacting adhesive bonds, piezoelectric actuators, and aluminium plates, The study not only analyses the parameter relationships but also examines their controls, identifying those best aligned with primary objectives. This sensitivity enhances the piezoelectric actuator's efficacy and quality. The research determines an optimal parameter combination, developing active repair performance and establishing an essential SIF benchmark. This research explores the complex world of piezoelectric actuator-assisted repairs, providing a road map for better structural rehabilitation.

Implementation of the Displacement Discontinuity Method in Geotechnical Case Studies

This paper uses the displacement discontinuity method, one of the boundary element methods, to solve two major engineering problems. The first one addresses the safe design of underground excavations in fractured rock masses. The implemented method was used to control the slip of discontinuities passing through a circular opening at 45°. Special contact elements were used to simulate a possible slip on the cracks. At the same time, stress intensity factors (SIFs) were calculated using the gradient elasticity theory (special tip elements where numerical integrations are needed were excluded). The crack propagation due to shear slip occurrence was defined using the criterion of maximum tangential stress at an angle of 71° from the initial crack direction. The second one involved in the crack’s propagation was solved by applying pressure to the circular opening, while a part of it was transferred to the cracks, approximating the mechanism of hydraulic fracture. Finally, the implementation of higher elasticity elements in the cracks provided an accurate estimation of SIFs, showing an error of about 4%, as confirmed by comparisons with existing type I loading solutions.

A Method on Estimates of Stress Intensity Factors of Outer Circle and Inner Ellipse Submarine Pipeline Under Bending Moment

The slender circle submarine pipeline possesses both shell and beam characteristics, which are widely used in practical engineering. Unfortunately, for some reason, there will be some geometric defects in the cross-section of the pipeline (such as machining errors and seawater corrosion, etc.), resulting in the stiffness of the circular submarine pipeline being different. The cracked variable stiffness pipeline is actually a typical three-dimensional complex crack problem. In this paper, taking the outer circle and inner ellipse submarine pipeline as an example, a method based on elementary mechanics and the concept of the conservation law is proposed to determine the stress intensity factors (SIFs) of variable stiffness pipeline, and a series of closed-form expressions of SIF are derived for the cracked pipeline. The results from the present method are shown to agree well with available solutions and FEM. In particular, the present method can also be easily applied to other similar variable stiffness submarine pipelines.

Analytical expressions to estimate rapidly the notch stress intensity factors at V‐notch tips using the Peak Stress Method

AbstractThe Peak Stress Method (PSM) enables a rapid estimation of the notch stress intensity factors (NSIFs) for the fatigue strength assessment of sharp V‐notches and notably welded joints. It takes advantage of the linear elastic peak stresses calculated at the V‐notch tip using coarse finite element (FE) mesh patterns, thanks to properly calibrated coefficients depending on the V‐notch opening angle, FE type, formulation, and FE mesh pattern typical of the employed FE code. The original calibration was performed only for few master values of opening angle; therefore, in the present study, the coefficients have been calibrated by using Ansys® FE code for the full range of notch opening angles to generalize the PSM. In particular, polynomial expressions have been fitted on the results of FE analyses and implemented in a tool that automates the application of the PSM. Two case studies have been analyzed highlighting the benefits of the new polynomial expressions.

Simple crack tip and stress intensity factor determination method for model I crack using digital image correlation

In the past three decades, quantitative characterization of cracks attracted much attention with the development of digital image correlation (DIC), especially for estimation of crack tip position (CTP) and stress intensity factor (SIF). Quantifying CTP and SIF is of great importance in the damage tolerance assessment of fracture-critical components and structures. In previous research, multivariate fitting is performed on the displacement field to determine CTP and SIF. However, high gradient deformation near the crack tip causes inaccurate results and an involving complex estimation process. In this paper, a simple method is proposed to determine the CTP and SIF based on the displacement field calculated by DIC. Instead of the full-field fitting method, two lines symmetrically distributed on both sides of the crack tip are selected to fit the CTP. Vertical displacement differences between two lines are fitted with the theoretical solutions of mode I crack. Compared with the actual position observed by the micrograph, the estimation error is less than 2 pixels (about 6 μm). Additionally, a similar method is proposed to estimate the SIF utilizing the CTP results. To avoid the bias errors caused by the plastic zone, two lines are selected in the elastic zone away from the crack tip. Vertical displacements on two lines are fitted with the theoretical solutions to obtain SIF. The fitting results of the proposed method are close to that of the full-field fitting method. Compared with the previous methods, the computation burden of the proposed method is greatly reduced while the accuracy is not affected.

Effect of Mesh Density on the Estimation of Stress Intensity Factors Evaluated by Interaction Integral in the Experiment

Effect of Mesh Density on the Estimation of Stress Intensity Factors Evaluated by Interaction Integral in the Experiment

Prediction of Fatigue Crack Growth Rate and Stress Intensity Factors Using the Finite Element Method

This study investigates crack growth and stress intensity factors via finite element methods in linear elastic fracture mechanics. The procedure involves estimating stress intensity factors (SIFs), crack trajectory, and fatigue life, using two different softwares in both two and three-dimensional analyses. Crack modeling was done in a variety of ways depending on the software. ANSYS Mechanical R19.2 and FRANC2D/L software were used to prognosticate fatigue crack growth, fatigue life, and associated stress intensity factors under plane stress state. Fatigue analysis was governed by Paris’s law and crack growth direction by the theory of maximum circumferential stress. The results show that the fatigue growth was attracted to the hole and either changes its direction to reach the hole or floats by the hole and grows as the hole is missed. The findings of the study agree with other experimental and numerical crack propagation studies presented in the literature.

Digital shearography approach for stress intensity factors calculation in friction stir welded nugget of AA2024 aluminum alloy

The purpose of this paper is to calculate the stress intensity factor and fatigue life estimation in AA2024-T351 aluminum alloy welded specimens under uniaxial load with low-cycle fatigue, using digital shearography method. For this purpose, using optomechanical relations and failure mechanics concepts, the relationship between surface displacement derivatives and stress intensity factors in uniaxial loading mode is extracted analytically. To prove the validity of the model results, numerical and experimental studies have been performed on compact tension (CT) specimens that have been welded using friction stir welding (FSW) method. First, friction stir welding with different welding speeds was performed on AA2024-T351 aluminum alloy specimens. Then CT specimens were prepared and after setting the overlay arrangement, CT specimens were subjected to uniaxial loading with low-cycle fatigue. Then, by preparing images of the specimen surface while loading and processing these images, the field of surface displacement derivatives and stress intensity factors near the crack tip are extracted simultaneously. The difference between the test results and the digital shearography method indicates the appropriate ability of this optical method to calculate the stress intensity factors.

Stress intensity factor estimation of cracks originating from square, circular or elliptical hole in a plate subjected to tension

The use of Linear Elastic Fracture Mechanics (LEFM) in the assessment of reliability and performance, with the help of the concepts from Finite Elements Method, provides practical and convenient ways to study the growth of crack and fracture in the materials. While the Boundary Element Method is another tool usually used to deal with elastic fracture problems, the Finite Element Method has many powerful means to simulate and conduct experiments virtually. In this work, the influence of cracks originating from different hole shapes on the mode I Stress Intensity Factor (SIF) is analysed in Abaqus simulation package. To accomplish this, a two-dimensional finite element model of a plate containing cracks originating from square, circular or elliptical hole is created and then subjected to tension. The objective is to investigate the effect of crack length on the mode I SIF for the different shapes of holes. As the crack length is increased by 367% in all the three cases of square, circular and elliptical holes, the SIF increased respectively by 170.7%, 170.6% and 167.3%. These outcomes indicate that the magnitude of SIF increases by increasing the crack length and vice-versa. However, in the case of elliptical hole, the percent increase in SIF, is slightly less than the other two hole shapes.

FATIGUE ASSESSMENT OF CORRODED DECK LONGITUDINALS OF TANKERS


 
 
 Fatigue life of deck longitudinals of oil tankers is analysed based on linear elastic fracture mechanics. A parametric formulation for the estimation of stress intensity factors and the Paris-Erdogan law are applied. Long-term effects of corrosion are modelled based on regression equations fitted to thickness measurements made during inspections of two tankers. Parametric studies are performed in order to investigate the importance of the governing parameters of crack propagation. A comparison of the fatigue analyses performed by linear fracture mechanics and S-N approaches is presented.
 
 

On the behaviour of small fatigue cracks emanating from corrosion pits: Part I – The influence of mechanical factors

The initiation and propagation behaviour of cracks emanating from corrosion pits in a high strength low alloy steel is investigated by testing pre-pitted specimens in the high cycle fatigue regime in an air environment. This was complemented with finite element analysis of electrochemically generated pit profiles. Fatigue cracks were found to initiate from the mouth of pits due likely to strain localisation at this region. Crack initiation lifetime and fatigue endurance decreased with increasing pit depth. Fatigue behaviour of the steel was found to be crack initiation dominated. A fracture mechanics methodology that provides a satisfactory estimation of critical threshold stresses and threshold stress intensity factor required for fatigue failure from corrosion pits is discussed.

Characteristic-tensor method for efficient estimation of stress-intensity factors of three-dimensional cracks

A practically simple characteristic-tensor method (CTM) is proposed for evaluation of the stress state at crack tips subjected to arbitrary loading conditions. Stress-intensity factors (SIFs) in several representative types of three-dimensional cracks (such as the circular crack, elliptical crack, and inclined circular crack) were computed by the finite-element method. Even using a relatively coarse mesh, SIFs for mixed-mode crack problems could be estimated by the CTM with high accuracy. The results show that the CTM is a practical and reliable approach to the estimation of SIFs of 3D cracks that are important to the industrial application.

Fatigue reliability assessment of a pearlitic Grade 900A rail steel subjected to multiple cracks

In this paper, a reliability analysis of fatigue crack growth for a pearlitic Grade 900A rail steel subject to the growth of multiple cracks is presented. The stress intensity factors (SIFs) at the tip of the cracks, by considering all possible combinations of all different cracks, are calculated by the boundary element method (BEM). A 3D boundary element analysis model has been applied to estimate stress intensity factors of the rail under the influence of cyclic loading conditions. For this purpose, an UIC60 rail with accurate geometry is studied. Paris Equation is used as a criterion of fatigue crack growth rate and the maximum tangential stress was considered as the crack growth direction. The geometry correction functions of the five cracks in rail steel, as a function of a crack size are determined by using nonlinear regression analysis estimating the statistical descriptors of the five geometry correction functions. Also, Morgan law is used to describe the failure probability of the series system. Fatigue reliability is evaluated for each failure mode due to multiple site fatigue cracks propagation in rail steel.

Two-dimensional weight function of stress intensity factors for corner cracks emanating from a circular hole

The weight function method is adopted to calculate stress intensity factors along the corner crack front rather than at only two end points, which are pre-requisites in evaluating fatigue growth of corner cracks emanating from a circular hole. Two-dimensional weight function is derived for corner cracks emanating from a circular hole, based on reference stress intensity factors modified by Newman (2018) and corresponding accurate stress distribution on virtual crack face formulized by authors (Guo and Guo, 2019). The obtained weight function is validated against numerical results in the literature and finite element calculations and shows high accuracy. For quick fatigue crack growth prediction in engineering structures, explicit formulae are obtained for typical corner crack shapes with wide ranges of aspect ratio 0.2 ≤ a/c ≤ 2, crack depth ratio 0.1 ≤ a/B ≤ 0.95, crack front angular parameter 0.05 ≤ 2ϕ/π ≤ 0.95 and plate thickness to hole radius ratio B/R = 2. The process can be thereby extended to the estimation of stress intensity factors for corner cracks emanating from a circular hole contained in complicated structures under arbitrary stress distribution.

A new numerical approach to estimate stress intensity factors under very high cycle fatigue testing

Ultrasonic very high cycle fatigue testing finds many advantages in fatigue studies especially in very low fatigue crack growth rate investigations. In this application, the determination of the stress intensity factor has a key role and presenting a general approach to calculate stress intensity factor in reasonable time and ultimate accuracy is necessary. The present research proposes a new numerical approach (hybrid method) based on reduce order modeling (dynamic substructuring), multi-harmonic balance method, and M-integral to evaluate stress intensity factors under very high cycle fatigue testing in the most accurate and fast way possible. The verification of the hybrid method was done through a benchmark and implicit solver implemented in ABAQUS commercial software as the reference solution. Investigations proved that the presented hybrid method here could determine stress intensity factor in ultrasonic regime with the ultimate accuracy and save computational time at least 50%.