Fatigue Pre-Cracking Curved Wide Plates in Bending

2010 ◽  
Author(s):  
Mark D. Richards ◽  
Timothy S. Weeks ◽  
J. David McColskey ◽  
Bo Wang ◽  
Yong-Yi Wang
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Stress Field ◽  
Crack Growth ◽  
Field Analysis ◽  
Four Point Bending ◽  
Stress Field Analysis

Curved wide plate (CWP) testing in tension, on API 5L X100 pipes of 36-inch (916-mm) diameter and 0.75-inch (19-mm) wall thickness, has been initiated in support of strain-based design using high strength steel for oil and gas pipeline applications. The CWP tests are being used to optimize and validate welding procedures and to determine the defect tolerance within the girth welds. A traditional pre-requisite for fracture mechanics testing is a final extension of a crack via fatigue pre-cracking to produce a representative flaw. A method of fatigue pre-cracking CWP specimens for final notch preparation in bending was developed to meet ASTM guidelines for fracture mechanics testing. Fatigue pre-cracking for the present specimen geometry was possible in bending due to lower requisite force capacity equipment which allowed for greater cyclic loading frequencies. In order to achieve sufficient stress levels for fatigue crack growth in the curved plate, a stress field analysis was performed to optimize the loading support configuration in four-point bending. In addition to the stress field analysis, a 3-D finite element model of the CWP specimen was generated to analyze the notched CWP specimen in four-point bending. Finite element analysis (FEA) results and experimental data were used to confirm the hypothesis that, under the proposed loading arrangement, the closed-form solutions for stress-intensity (K) of flat plates in bending can be used to approximate the K for CWP specimens in bending. Validation of a solution for stress-intensity factor subsequently allowed the determination of force amplitude levels for fatigue crack growth. Force and crack mouth opening displacement (CMOD) data were analyzed to correlate compliance with crack length measurements. From experimental results, a method was developed that enable the repeatable and well characterized extension of surface flaws by fatigue pre-cracking in curved wide plate specimens in bending.

Effective Modeling of Fatigue Crack Growth in Pipelines

2012 ◽  
Author(s):  
Steven J. Polasik ◽  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Models ◽  
Critical Parameters ◽  
Operating Pressure ◽  
Mechanics Model ◽  
Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

The Model of Fatigue Crack Growth in High Pressure Cylinder Wall

2010 ◽  
Author(s):  
Jan Brumek ◽  
Bohumir Strnadel ◽  
Ivo Dlouhy´
Keyword(s):  
Stress Intensity Factor ◽  
Finite Element ◽  
High Pressure ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Cylinder Wall ◽  
High Pressure Cylinder ◽  
Pressure Cylinder

This paper presents numerical study to predict crack growth rate under fatigue loading in a high pressure cylinder wall made of high strength steel. Experimental fatigue crack growth data on three point bending test samples were applied to simulate and predict crack growth process using detailed three dimensional parametric finite element models. The fatigue crack propagation was based on linear elastic fracture mechanics and stress intensity factor determination. Finite element model provides results of crack growth analysis optimized for the stress levels of operating pressure level. Results are plotted on S-N curves and the disparity was explained in terms of crack growth rates near threshold stress intensity factor range. Results were compared with an experimental fatigue test.

Augmenting Generic Fatigue Crack Growth Models Using 3D Finite Element Simulations and Gaussian Process Modeling

2019 ◽  
Author(s):  
Adrian Loghin ◽  
Shakhrukh Ismonov
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Gaussian Process ◽  
Crack Growth ◽  
Life Assessment ◽  
Growth Path ◽  
3D Fem

Abstract Assessing the crack propagation life of components is a critical aspect in evaluating the overall structural integrity of a mechanical structure that poses a risk of failure. Engineers often rely on industry standards and fatigue crack growth tools such as NASGRO [1] and AFGROW [2] to perform life assessment for different structural components. A good understanding of material damage tolerant capabilities, and the component’s loading mission during service conditions are required along with the availability of generic fracture mechanics models implemented in the lifing tools. Three-dimensional (3D) linear elastic fracture mechanics (LEFM) finite element modeling (FEM) is also a viable alternative to simulate crack propagation in a component. This method allows capturing detailed geometry of the component and representative loading conditions which can be crucial to accurately simulate the three dimensionality of the propagating crack shape and further determine the associated loading cycles. In comparison to a generic model, the disadvantage of the 3D FEM is the extended runtime. One feasible way to benefit from 3D modeling is to employ it to understand the crack front evolution and growth path for the representative loading condition. Mode I stress intensity factors (KI) along the predetermined crack growth path can be generated for use in fatigue crack growth tools such as NASGRO. In the current study, such a 3D FEM lifing process is presented using a classical bolt-nut assembly, components that are commonly used in engineering design. First, KI solutions for a fixed crack aspect ratio a/c = 1 are benchmarked against a similar solution available in NASGRO. Next, a predefined set of crack shapes and sizes are simulated using 3D FEA. A machine learning model Gaussian Process (GP) was trained to predict the KI solutions of the 3D model, which in turn was used in the crack propagation simulation to accelerate the life assessment process. Verification of the implemented procedure is done by correlating the crack growth curves predicted from GP to the results obtained directly from 3D FE crack propagation method.

Study on Fatigue Crack Growth Model of 7075-T7410 Aluminum Alloy Straight Attachment Lug

2011 ◽  
Vol 66-68 ◽  
pp. 82-89
Author(s):  
Li Ming Wu ◽  
Yu Ting He ◽  
Xin Bo Wang ◽  
Hai Wei Zhang ◽  
Jin Qiang Du ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Model ◽  
Outer Radius ◽  
Finite Element Software ◽  
Inside Radius ◽  
Crack Growth Model

The finite element model of a 7075-T7410 straight attachment lug is built by using the finite element software ANSYS, a cosine distribution pin-bearing pressure is applied on the surface of the pin-hole as a boundary condition. The stress intensity factor (SIF) expression for the straight attachment lug with a single through-the-thickness crack and subjected to an axial pin-load is determined by studying on the effect of the geometric parameters (the dimensionless crack length a/R1，the ratio of outer radius to inside radius R2/R1 and the inside radius R1) on SIF value. The fatigue crack growth velocity (da-dN) and the stress intensity factor’s amplitude (ΔK) is calculated by the SIFs equations to get the values of the Paris constants, offering an analytical method for establishment of the fatigue crack growth model of the typical straight lugs. The paper can be helpful in assessing and designing damage tolerant attachment lugs.

scholarly journals Application of a New, Energy-Based ΔS* Crack Driving Force for Fatigue Crack Growth Rate Description

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 518 ◽  
Author(s):  
Grzegorz Lesiuk
Keyword(s):  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Engineering Practice ◽  
Stress Effect ◽  
New Energy

This paper presents the problem of the description of fatigue cracking development in metallic constructional materials. Fatigue crack growth models (mostly empirical) are usually constructed using a stress intensity factor ΔK in linear-elastic fracture mechanics. Contrary to the kinetic fatigue fracture diagrams (KFFDs) based on stress intensity factor K, new energy KFFDs show no sensitivity to mean stress effect expressed by the stress ratio R. However, in the literature there is a lack of analytical description and interpretation of this parameter in order to promote this approach in engineering practice. Therefore, based on a dimensional analysis approach, ΔH is replaced by elastic-plastic fracture mechanics parameter—the ΔJ-integral range. In this case, the invariance from stress is not clear. Hence, the main goal of this paper is the application of the new averaged (geometrically) strain energy density parameter ΔS* based on the relationship of the maximal value of J integral and its range ΔJ. The usefulness and invariance of this parameter have been confirmed for three different metallic materials, 10HNAP, 18G2A, and 19th century puddle iron from the Eiffel bridge.

On the Stress Intensity Factor of Cracks in Residual Stress Field

2007 ◽  
Vol 353-358 ◽  
pp. 1078-1081
Author(s):  
Liang Wang ◽  
Ya Zhi Li ◽  
Hong Su
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Stress Field ◽  
Residual Stresses ◽  
Weight Function ◽  
Crack Growth ◽  
Function Technique ◽  
Residual Stress Field

The use of weight function technique in fatigue crack growth subjected to external cyclic loading and residual stress field has been questioned by several researchers in that the technique is unable to account for the residual stress redistribution during the crack growth. In this paper a center cracked tension specimen containing residual stresses was analyzed by finite element method. The crack growth was simulated by releasing the nodes ahead of crack tip in stepwise and the stress intensity factors induced by residual stresses at different crack lengths were estimated. The results from the numerical analysis are identical to the weight function solution, which demonstrates that the weight function technique can be used for the fatigue crack growth analysis in residual stress field, unless the residual stress distribution is disturbed by the plastic yield.

Numerical Analysis of JNES Seismic Tests on Degraded Combined Piping System

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Tao Zhang ◽  
Frederick W. Brust ◽  
Gery Wilkowski ◽  
Do-Jun Shim ◽  
Jinsuo Nie ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Small Scale ◽  
Cycle Fatigue ◽  
Small Scale Yielding ◽  
Scale Yielding

Nuclear power plant safety under seismic conditions is an important consideration. The piping systems may have some defects caused by fatigue, stress corrosion cracking, etc., in aged plants. These cracks may not only affect the seismic response but also grow and break through causing loss of coolant. Therefore, an evaluation method needs to be developed to predict crack growth behavior under seismic excitation. This paper describes efforts conducted to analyze and better understand a series of degraded pipe tests under seismic loading that was conducted by Japan Nuclear Energy Safety Organization (JNES). A special “cracked-pipe element” (CPE) concept, where the element represented the global moment-rotation response due to the crack, was developed. This approach was developed to significantly simplify the dynamic finite element analysis in fracture mechanics fields. In this paper, model validation was conducted by comparisons with a series of pipe tests with circumferential through-wall and surface cracks under different excitation conditions. These analyses showed that reasonably accurate predictions could be made using the abaqus connector element to model the complete transition of a circumferential surface crack to a through-wall crack under cyclic dynamic loading. The JNES primary loop recirculation piping test was analyzed in detail. This combined-component test had three crack locations and multiple applied simulated seismic block loadings. Comparisons were also made between the ABAQUS finite element (FE) analyses results to the measured displacements in the experiment. Good agreement was obtained, and it was confirmed that the simplified modeling is applicable to a seismic analysis for a cracked pipe on the basis of fracture mechanics. Pipe system leakage did occur in the JNES tests. The analytical predictions using the CPE approach did not predict leakage, suggesting that cyclic ductile tearing with large-scale plasticity was not the crack growth mode for the acceleration excitations considered here. Hence, the leakage was caused by low-cycle fatigue with small-scale yielding. The procedure used to make predictions of low-cycle fatigue crack growth with small-scale yielding was based on the Dowling ΔJ procedure, which is an extension of linear-elastic fatigue crack growth methodology into the nonlinear plasticity region. The predicted moments from the CPE approach were used using a cycle-by-cycle crack growth procedure. The predictions compare quite well with the experimental measurements.

Study on Fatigue Crack Growth Model of Attachment Lug Subjected to Oblique Pin-Load

2011 ◽  
Vol 291-294 ◽  
pp. 1043-1050 ◽  
Author(s):  
Li Ming Wu ◽  
Yu Ting He ◽  
Hai Wei Zhang ◽  
Rong Hong Cui ◽  
Jin Qiang Du ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Growth Model ◽  
Outer Radius ◽  
Finite Element Software ◽  
Inside Radius ◽  
Crack Growth Model

The finite element model of a straight attachment lug subjected to an oblique loading less than 45 degrees is built by using the finite element software ANSYS, a cosine pin-bearing pressure distribution is applied on the hole of lug as a boundary condition. The stress intensity factor (SIF) expression for the straight attachment lug with a single through-the-thickness crack, which is subjected an oblique pin-load less than 45 degrees, is determined by studying on the influence law of dimensionless crack length (a/R1)，ratio of outer radius to inside radius (R2/R1), inside radius (R1) and pin-load angle (β) on the SIFs values. The expression is validated by contrasting with the ANSYS results and the data of residual strength test. The stress intensity factor’s amplitude (ΔK) are calculated by the SIF equation to get the values of the Paris constants. The fatigue crack growth model of attachment lug subjected to oblique pin-load is established, offering an analytical as well as experimental method for assessing and designing damage tolerant attachment lugs.

Sign in / Sign up

Export Citation Format

Share Document