Accurate Values Of Stress Intensity Factors Research Articles

Estimation of stress intensity factors from crack flank displacements

In the present numerical investigation, the efficacy of a recently proposed displacement based method for estimation of mixed mode (I/II) stress intensity factors of 2D configurations are demonstrated using additional benchmark examples. The proposed displacement based technique is simple, efficient and robust and can be used for the fatigue crack growth simulations. This technique uses the crack opening and crack sliding displacements obtained from the finite element analysis to determine the mode I, mode II and mixed mode (I/II) stress intensity factors (SIFs). This technique can provide the sign of the mode II stress intensity factors which enables it to be used for the fatigue crack growth simulations involving numerous computational steps. Quarter point elements (QPEs) are employed around the crack tip. Convergence of the present method is studied and the performance is assessed by comparing the extracted SIFs using other methods such as displacement extrapolation, J-integral and interaction integral techniques. The present study indicates that very accurate values of SIFs can be computed using the proposed technique and the accuracy of the SIF solutions are of the order of the path independent integrals

Acoustic Emission Assessment of Fatigue Crack Growth from a Transverse Weld Toe

AbstractAcoustic emission (AE) has been increasingly used for assessment and prediction of fatigue cracks in steel bridge members. Fatigue cracks develop at the transverse weld toe of stiffeners, attachments, and cover plates in steel bridge members. Effectiveness of AE to assess fatigue crack initiation from weld toe is investigated in this study, and an attempt is made to predict the crack growth behavior using AE signal features. Cruciform specimens consisting of a single tension pull plate with transverse fillet-welded plates attached at midspan are tested in this study. The transverse plates represent stiffeners and/or short attachments typical of welded steel bridge details. The specimen provides realistic initial conditions of fatigue crack initiation and growth from high stress concentration regions. Consequently, AE waveform characteristics representative of those expected on bridge structures are produced. Accurate stress intensity factor values are difficult to obtain because of the small, nonu...

Approximation method for the calculation of stress intensity factors for the semi-elliptical surface flaws on thin-walled cylinder

A simple approximation method for the stress intensity factor at the tip of the axial semi-elliptical cracks on the cylindrical vessel is developed. The approximation methods, incorporated in VINTIN (Vessel INTegrity analysis-INner flaws), utilizes the influence coefficients to calculate the stress intensity factor at the crack tip. This method has been compared with other solution methods including 3-D finite element analysis for internal pressure, cooldown, and pressurized thermal shock loading conditions. For these, 3-D finite-element analyses are performed to obtain the stress intensity factors for various surface cracks witht/R=0.1. The approximation solutions are within ±2.5% of the those of finite element analysis using symmetric model of one-forth of a vessel under pressure loading, and 1–3% higher under pressurized thermal shock condition. The analysis results confirm that the approximation method provides sufficiently accurate stress intensity factor values for the axial semi-elliptical flaws on the surface of the reactor pressure vessel.

Experimental and numerical analysis of fatigue behaviour for tubular K-joints

In this paper, a full-scale K-joint specimen was tested to failure under cyclic combined axial and in-plane bending loads. In the fatigue test, the crack developments were monitored step by step using the alternating current potential drop (ACPD) technique. Using Paris` law, stress intensity factor, which is a fracture parameter to be frequently used by many designers to predict the integrity and residual life of tubular joints, can be obtained from experimental test results of the crack growth rate. Furthermore, a scheme of automatic mesh generation for a cracked K-joint is introduced, and numerical analysis of stress intensity factor for the K-joint specimen has then been carried out. In the finite element analysis, J-integral method is used to estimate the stress intensity factors along the crack front. The numerical stress intensity factor results have been validated through comparing them with the experimental results. The comparison shows that the proposed numerical model can produce reasonably accurate stress intensity factor values. The effects of different crack shapes on the stress intensity factors have also been investigated, and it has been found that semi-ellipse is suitable and accurate to be adopted in numerical analysis for the stress intensity factor. Therefore, the proposed model in this paper is reliable to be used for estimating the stress intensity factor values of cracked tubular K-joints for design purposes.

A Finite Element Study on the Integrity Evaluation Method of Subclad Cracks Under Pressurized Thermal Shock Transients

The reactor pressure vessel is usually clad with stainless steel to prevent corrosion and radiation embrittlement, and thus, the population of subclad cracks is higher than that of surface cracks. In fact, a number of subclad cracks have been found during in-service-inspections. These subclad cracks should be assumed for a safe operation under normal conditions and faulted conditions such as pressurized thermal shock (PTS). There are several elastic stress intensity factor (SIF) solutions for subclad cracks which are used for ASME fracture assessment procedures. However, these solutions are known to be overly conservative due to intrinsic assumptions. In this paper, full 3-D elastic-plastic finite element analyses were performed to investigate the validity of the present ASME code in evaluating the integrity of vessel under PTS conditions. The solution in ASME Section XI code gives accurate SIF values when the crack tip is close to cladding. However, the difference between the code solution and elastic plastic finite element analysis (EPFEA) results become significant with increasing crack depth. This difference is caused by the stress discontinuity at the interface between cladding and parent material. Elastic finite element analysis (EFEA) results, which do not consider plastic deformation at the clad material, also showed a big difference compared to those from EPFEA. Therefore, it is recommended to perform EPFEA for the accurate assessment of subclad cracks under PTS which causes plastic deformation at the cladding.

THE USE OF A NEW LINE‐SPRING SHELL ELEMENT FOR ELASTIC SURFACE CRACK ANALYSIS

AbstractIn this paper, the Line‐Spring concept developed by Rice and Levy[l] is used to build a new elastic surface cracked shell element in the general purpose Finite Element code CASTEM 2000. The implementation is described and an energy release rate technique is proposed to arrive at more accurate Stress Intensity Factor values at the crack front‐free surface intersection. A comparison with existing accepted numerical solutions is made on various plane and cylindrical configurations and a discussion on the applicability of the model is presented.