scholarly journals Analysis of the Fatigue Crack Evolution of Corrugated Web Girders

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 869
Author(s):  
Guoqian Wei ◽  
Fan Ye ◽  
Shanshan Li ◽  
Siwen Chen
Keyword(s):  
Fatigue Crack ◽  
Crack Front ◽  
Small Region ◽  
Initial Crack ◽  
Evolution Process ◽  
Crack Evolution ◽  
Element Analysis ◽  
Bending Load ◽  
Corrugated Web ◽  
Weld Toe

Based on linear elastic fracture mechanics (LEFM), the fatigue crack evolution process and behavior of corrugated web girders were studied. The global finite element analysis (FEA) model of corrugated web girders was first developed and the equivalent structural stress method was used to reveal the dangerous locations along the weld under the bending load. The weld toe between the tension flange and the web weld, which is near the intersection of the inclined fold and the parallel fold, was determined as the fatigue crack easy-initiating location. Then a small region containing the crack-prone site was extracted as the sub-model for a crack propagating simulation. A semi-circle initial crack with 0.1 mm radius was inserted at the crack easy-initiating location. The stress intensity factors (SIFs; KI, KII, and KIII) of some discrete points along the crack front were calculated by the M-integral method. Based on Nasgro law, the geometry of the new crack front with a given extension length was obtained. Finally, the complete evolution process of the crack propagation was simulated. Results showed that the dominant crack propagating mode is open type (Mode I) and KI is the most important propagating driving force. According to the crack front shape evolution, the whole propagating process was divided into 6 stages. An obvious kink of the crack was found in stage 1, which covered only a very short time. The stages 3, 4 and 5 accounted for the majority of life, among which the stage 3 accounted for as high as 81% of the total life. Therefore, the cycles of the weld toe crack propagating from 0.1 mm to the thickness of the flange can be defined as the prediction life of this kind of structures.

Automatic Fatigue Crack Growth

2009 ◽  
Author(s):  
S. C. Mellings ◽  
J. M. W. Baynham
Keyword(s):  
Fatigue Crack ◽  
Cyclic Loading ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Initial Crack ◽  
Design Stage ◽  
Load Spectrum ◽  
Forensic Investigations ◽  
Crack Faces

One of the critical requirements of fatigue crack growth simulation is calculation of the remaining life of a structure under cyclic loading. This paper presents a method which predicts the remaining fatigue life of a part, and gives information on the eventual mode of failure. The path of a growing crack needs to be understood so that informed assessment can be made of the structural consequences of eventual fast growth, and the likelihood of leakage and determination of leakage rates. For these reasons the use of standard handbook solutions for crack growth is generally not adequate, and it is essential to use the real geometry and loading. The reasons for performing such simulation work include preventive investigations performed at the design stage, forensic investigations performed after failure, and sometimes forensic investigations performed during failure-when the results provide input to the planning of remedial work. This paper focuses on the 3D simulation of cracks growing in metal structures exposed to cyclic loading, and explains the techniques which are used. The loading might arise from transients of pressure or other mechanical forces, or might be caused by thermal-stress variations. The simulation starts from an initial crack which can be of any size and orientation. The relevant geometry of the cracked component is modelled, and the loading is identified using one or more load cases together with a load spectrum which shows how the loading cycles. The effects of the crack are determined by calculating stress intensity factors at all positions along the crack front (it would be called the crack tip if the modelling was performed in 2D). The rate and direction of crack growth at each part of the crack front are calculated using one of the available crack growth laws, together with appropriate material properties. The effects of such growth are accumulated over a number of load cycles, and a new crack shape is determined. The process is repeated as required. The use of multi-axial and mixed mode techniques allows the crack to turn as a result of the applied loading, and the resulting crack path is therefore a consequence of both the detail of the geometry and the loading to which the structure is subjected. Gas or other fluid pressures acting on the crack faces can have significant impact, as can the contact between opposing crack faces when a load case causes part of the crack to close.

Numerical Investigation on the Fatigue Behavior of the Multi-Planar Tubular DX-Joint under Combined Loads

2014 ◽  
Vol 1006-1007 ◽  
pp. 11-17
Author(s):  
Gui Jie Liu ◽  
Yu Zhang ◽  
Basit Farooq
Keyword(s):  
Finite Element ◽  
Hot Spot ◽  
Fatigue Behavior ◽  
Combined Loading ◽  
Element Analysis ◽  
Hot Spot Stress ◽  
Bending Load ◽  
Weld Toe ◽  
Plane Bending ◽  
Stress Concentration Factors

The stress concentration factors (SCFs) is used in the fatigue design for calculating hot-spot stress. However a major issue can be noted that the majority of research results are focused on the SCF distribution of uni-planar tubular joints subjected to the single basic load. By aiming to find the solution of this problem, the distribution of SCFs at the weld toe of a multi-planar tubular DX-joint which is subjected to the two set of the balanced combined loading components at the end of in-plane braces is studied by the finite element method. Thus it is concluded that for the axial plus in-plane bending load case, hot-spot stress location varies between saddle and crown position; while the location is invariably at the saddle position under combined axial plus out-of-plane bending loads. At last the API RP2A equation for predicting hot-spot stress is used for comparison with the finite element analysis results. Meanwhile the distribution of SCFs is also provided, that information indicates the-hot spot location along the weld toe affects the crack initiation.

Finite element analysis of cracked and uncracked tubular T-joint

1986 ◽  
Vol 13 (3) ◽  
pp. 261-269 ◽  
Author(s):  
G. S. Bhuyan ◽  
M. Arockiasamy ◽  
K. Munaswamy ◽  
O. Vosikovsky
Keyword(s):  
Finite Element ◽  
Crack Front ◽  
Three Dimensional ◽  
Singular Element ◽  
Singular Stress ◽  
Element Analysis ◽  
Joint Stress ◽  
Weld Toe ◽  
Singular Stress Field ◽  
Bending Loads

A welded tubular T-joint is analysed using finite element methods to obtain through-thickness and surface stresses due to axial and in-plane bending loads. The effects of a shallow weld toe crack on the stress redistribution are studied. The two-dimensional analysis of the joint includes the membrane stiffness representation by plane stress element and the flexural stiffness by plate bending element. For the three-dimensional analyses, the joint is modelled using incompatible solid elements to improve flexural characteristics. The embedded elliptical crack front is modelled by straight-line segments. The region at the vicinity of the crack is discretized using special elements, which produce a singular stress field at the crack front. Key words: tubular joint, stress analysis, weld toe crack, incompatible element, singular element.

scholarly journals Analysis of Fatigue Crack Propagation of an Orthotropic Bridge Deck Based on the Extended Finite Element Method

2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Ying Wang ◽  
Zhen Wang ◽  
Yuqian Zheng
Keyword(s):  
Residual Stress ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Crack Propagation ◽  
Bridge Deck ◽  
Fatigue Cracks ◽  
Initial Crack ◽  
Residual Stress Field ◽  
Scale Feature ◽  
Weld Toe

As one of the most fatigue-sensitive parts of an orthotropic steel bridge deck, the weld between the U-rib and the top deck is prone to fatigue cracking under the actions of the stress concentration, welding residual stress, and vehicle load. To investigate the mechanism of fatigue crack propagation and the influence of the welding residual stress on the propagation patterns of fatigue cracks, a multiscale modeling method was proposed, and the static analysis and the dynamic propagation analysis of fatigue crack were carried out in this paper. First, a multiscale finite element model was established, including whole bridge models with a scale feature of 102 m, orthotropic bridge deck models with a scale feature of 100 m, and crack models with a scale feature of 10−3 m. Then, a segmental model of the bridge deck was extracted, which is regarded as a critical location of the bridge, and the shell-solid coupling method is adopted in the segmental model in order to further analyze the crack propagation rule. Moreover, based on the extended finite element method (XFEM), the static crack and dynamic crack propagation in this critical position were analyzed. Finally, thermoelastoplastic analysis was carried out on the connection of the U-rib and deck with a length of 500 mm to obtain the residual stress, and then the results of residual stress were introduced into the segmental model to further study its influence on the evolution of fatigue crack propagation. The analysis of the welding process shows that near the weld region of the connection of the U-rib and deck, the peak value of the residual tensile stress can reach the material yield strength. The static analysis of fatigue cracks shows that under the single action of a standard fatigue vehicle load, the fatigue details at the weld toe of the deck cannot reach the tensile stress required for fatigue crack propagation, and only the fatigue details at the weld toe of the U-rib can meet the requirements of fatigue crack propagation. The dynamic analysis of fatigue cracks reveals that the crack in the weld toe of the U-rib is a mixed-mode crack with modes I, II, and III. The propagation of a fatigue crack without a residual stress field will be terminated until the crack length is extended to a certain length. Nevertheless, when the residual stress field was introduced, the growth angle and size of the fatigue crack would increase, and no crack closure occurs. For the crack in the weld toe of the deck, the crack is in the closed state under the standard fatigue vehicle load. When the residual stress field is introduced, the tensile stress of the fatigue details increases. Meanwhile, the fatigue crack will become a mixed-mode crack with modes I, II, and III that will be dominated by mode I and extend toward the weld at a slight deflection angle. The results of various initial crack sizes at the weld toes of the top deck are analyzed, which shows that the initial crack size has a certain effect on the fatigue crack growth rate, especially the initial crack depth.

Modeling of Pipeline Repair Sleeves

2002 ◽  
Author(s):  
Robert Lazor ◽  
L. Blair Carroll ◽  
Michael E. Bloom ◽  
Robert F. Booth
Keyword(s):  
Fatigue Crack ◽  
Internal Pressure ◽  
Pipe Wall ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Stress Fields ◽  
Element Analysis ◽  
Weld Toe ◽  
Line Pressure ◽  
Local Stiffness

Full encirclement repair sleeves with fillet-welded ends are used as a permanent repair on pipelines to reinforce areas with defects such as cracks or corrosion which may penetrate the pipe wall subsequent to the installation of the repair. CSA standards require that these sleeves be tapped to relieve the stress field surrounding the defect unless an engineering assessment indicates that the defect will not extend beyond the ends of the sleeve during future operation of the pipeline. This paper describes an engineering assessment recently completed to establish the relative performance of a sleeved pipe with and without a pressurized annulus. Finite element analysis (FEA) was used to relate changes in stresses in the weld region to internal pressure fluctuations. The FEA included an estimate of the effects of circumferential fillet weld shrinkage on local stiffness due to residual stress fields. Relationships between stress and internal pressure were used to convert the line pressure history to local weld stress fluctuations. This stress history was then used to assess the potential for fatigue crack propagation of possible circumferentially-oriented weld flaws using a fatigue crack growth algorithm. The results showed that the highest stresses were developed in the weld toe and root regions. The operating conditions of the line, as well as the pipe and sleeve dimensions, were considered when making recommendations concerning sleeve tapping.

Controlled Weld Toe Profiles for Fatigue Life Extension in FSO’s and FPSO’s

2007 ◽  
Author(s):  
J. Efrai´n Rodri´guez-Sa´nchez ◽  
Alejandro Rodri´guez-Castellanos ◽  
Manuel F. Carbajal-Romero ◽  
Efre´n Ayala-Uraga
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fracture Mechanics ◽  
Fatigue Cracking ◽  
Life Extension ◽  
Element Analysis ◽  
Profile Control ◽  
Hull Structure ◽  
Weld Toe ◽  
Plate Connection

Application of controlled weld toe profiles can be considered an option to extend the fatigue life of welded connections when ongoing tankers are converted in dry docks to serve like offshore ships (FPSOs and FSOs). Very slim chances to implement such fatigue improvement will arise when these vessels are in service, since a converted ship is designed to be inspected, maintained and repaired in situ and not in dry dock as it is uneconomical to interrupt production. Codes recognize fatigue life extension by means of a controlled weld toe profile, e.g. [1]. Application of a controlled weld toe profile during conversion in selected areas previously identified by stress analysis of the hull structure can lead to extend the converted vessel fatigue life to comply with an expected field life. The American Bureau of Shipping S-N curves allow a credit of 2.2 on fatigue life when suitable toe grinding and NDE are provided. A controlled weld toe profile can be applied in fatigue crack repaired welds during ship conversion or even on those that during ship conversion are found in a non-cracked condition but were identified prone to fatigue cracking in a stress assessment analysis under in-service conditions. Credit on fatigue life in various codes and results from experimental data obtained from fatigue tested specimens with a controlled weld toe profile are given. Comments on the design of a controlled weld toe profiles and recommendations based on experimental experience for the implementation of equipment to perform a controlled weld toe profile are also given. A Fracture Mechanics approach for the assessment of controlled weld toe profiles for fatigue life extension purposes is described. Initially, a comparison of SCFs for a typical ship hull plate connection with and without weld toe profile control determined by Finite Element Analysis (FEA) is presented. Then, results obtained from the FEA connection such as through plate stress distribution are used in a Fracture Mechanics Analysis to compare the fatigue crack growth curve in as-welded condition to that with controlled weld toe profile.

Fatigue crack propagation analysis for multiple weld toe cracks in cut-out fatigue test specimens from a girth welded pipe

2017 ◽  
Vol 94 ◽  
pp. 158-165 ◽  
Author(s):  
John H.L. Pang ◽  
Hsin Jen Hoh ◽  
Kin Shun Tsang ◽  
Jason Low ◽  
Shawn Caleb Kong ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Propagation ◽  
Fatigue Test ◽  
Fatigue Crack Propagation ◽  
Propagation Analysis ◽  
Weld Toe ◽  
Welded Pipe

Comparison of DBEM and FEM Crack Path Predictions with Experimental Findings for a SEN-Specimen under Anti-Plane Shear Loading

2007 ◽  
Vol 348-349 ◽  
pp. 129-132 ◽  
Author(s):  
Roberto G. Citarella ◽  
Friedrich G. Buchholz
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Front ◽  
Crack Path ◽  
Shear Loading ◽  
Crack Growth Behaviour ◽  
3D Crack Growth ◽  
Corner Points ◽  
Experimental Findings

In this paper detailed results of computational 3D fatigue crack growth simulations will be presented. The simulations for the crack path assessment are based on the DBEM code BEASY, and the FEM code ADAPCRACK 3D. The specimen under investigation is a SEN-specimen subject to pure anti-plane or out-of-plane four-point shear loading. The computational 3D fracture analyses deliver variable mixed mode II and III conditions along the crack front. Special interest is taken in this mode coupling effect to be found in stress intensity factor (SIF) results along the crack front. Further interest is taken in a 3D effect which is effective in particular at and adjacent to the two crack front corner points, that is where the crack front intersects the two free side surfaces of the specimen. Exactly at these crack front corner points fatigue crack growth initiates in the experimental laboratory test specimens, and develops into two separate anti-symmetric cracks with complex shapes, somehow similar to bird wings. The computational DBEM results are found to be in good agreement with these experimental findings and with FEM results previously obtained. Consequently, also for this new case, with complex 3D crack growth behaviour of two cracks, the functionality of the proposed DBEM and FEM approaches can be stated.

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