Corrosion Fatigue Failure Analysis and Life Prediction

2003 ◽  
Author(s):  
Fred V. Ellis ◽  
Sebastian Tordonato
Keyword(s):  
Yield Strength ◽  
Failure Analysis ◽  
Corrosion Fatigue ◽  
Life Prediction ◽  
Crack Depth ◽  
Bending Moment ◽  
Failure Criteria ◽  
Initial Crack ◽  
Crack Geometry ◽  
Stress Curve

A metallurgical failure analysis and life prediction was performed for an economizer tube. The tube failed after approximately nine years of service. The failure was a pin hole leak, elliptically shaped with the long axis in the circumferential direction. On the inside surface of the tube, there were several circumferential cracks and numerous oxygen pits on the top half. The cracks were transgranular and initiated at pits. The failure mechanism is corrosion fatigue and is believed to be due to a cyclic applied bending moment. Life predictions were performed using two crack geometries and zero-tension loading cycle. The geometries were a thumbnail shaped ID crack with an a/c of 0.2 and a 360° ID cracked cylinder. A parametric approach was used with two initial crack depths based on the measured pit depths and three remote stresses centered around the minimum yield strength of the SA-178-A tube material. The failure criteria was the reference stress equal to the flow stress. For the thumbnail crack geometry at a remote load of 179 MPa (equal to minimum specified yield strength), the calculated lives were 15,960 cycles for an initial crack depth of 5% and 3,450 cycles for an initial crack depth of 10%. The cyclic lives of the 360° crack geometry were approximately half of those for the thumbnail crack geometry. The slope of the log life-log stress curve was approximately −5.8.

Corrosion-Fatigue of High Strength Steel Bars: Evolution of Crack Aspect Ratio

2011 ◽  
Vol 488-489 ◽  
pp. 1-4
Author(s):  
Jesús Toribio ◽  
Juan Carlos Matos ◽  
Beatriz González ◽  
J. Escuadra
Keyword(s):  
Aspect Ratio ◽  
Corrosion Fatigue ◽  
Crack Front ◽  
Crack Depth ◽  
High Strength ◽  
Initial Crack ◽  
Crack Advance ◽  
Prestressing Steel ◽  
Steel Wires ◽  
Steel Bars

Abstract. This paper shows the evolution of the surface crack front in prestressing steel wires subjected to fatigue in air and to corrosion-fatigue in Ca(OH)2+NaCl. To this end, a numerical modelling was made on the basis of a discretization of the crack front (characterized with elliptical shape), considering that the crack advance at each point is perpendicular to such a front according to a Paris-Erdogan law, and using a three-parameter stress intensity factor (SIF). Each analyzed case (a particular initial crack geometry) was characterized by the evolution of the semielliptical crack aspect ratio (relation between the semiaxes of the ellipse) with the relative crack depth and by the variation of the maximum dimensionless SIF at the crack front

Corrosion Fatigue and Life Assessment of Tube Bends

2007 ◽  
Author(s):  
Fred V. Ellis
Keyword(s):  
Corrosion Fatigue ◽  
Crack Depth ◽  
Initial Crack ◽  
Neutral Axis ◽  
Life Assessment ◽  
Inside Surface ◽  
Straight Tube ◽  
Tube Shape ◽  
Stress Amplification ◽  
Life Predictions

Metallurgical examinations and life predictions were performed for six water-cooled tubing bends. All of the tubes had axially oriented cracks on the inside surface of the tube bends near the neutral axis position and one of the tubes had failed. The cracking was intermittent or semi-continuous indicating multiple crack initiation sites. The cracks were transgranular, oxide-filled, and branched. One sample was cold fractured and examination of the fracture surface in the SEM revealed beachmarks and thumbnail shaped cracks. The tube shape is nominally oval and the ovality varied from 5% to 8-1/2%. Increased hoop stresses are expected on the inside surface at the neutral axis of a bend due to ovality. The failure mechanism is corrosion fatigue. Life predictions were performed as an aid in inspections and fitness for service assessments. Because the cracking was near the neutral axis, the straight tube geometry was used for the crack growth calculations. A parametric approach was used with three initial crack depths and stress amplification values of 1, 1.2, and 1.5 to account for stress increases due to ovality. The failure criterion was the reference stress equal to the minimum flow stress of carbon steel. For a stress amplification of 1.5 times the pressure induced stress, the calculated lives were 2,420 cycles for an initial normalized crack depth of 10% and 130 cycles for an initial normalized crack depth of 30%.

scholarly journals High-Strength Bolt Corrosion Fatigue Life Model and Application

2014 ◽  
Vol 2014 ◽  
pp. 1-5 ◽  
Author(s):  
Wang Hui-li ◽  
Qin Si-feng
Keyword(s):  
Fatigue Life ◽  
Yield Strength ◽  
Applied Stress ◽  
Corrosion Fatigue ◽  
Stress Amplitude ◽  
Crack Depth ◽  
High Strength ◽  
Corrosion Fracture ◽  
High Strength Bolt ◽  
Life Model

The corrosion fatigue performance of high-strength bolt was studied. Based on the fracture mechanics theory and the Gerberich-Chen formula, the high-strength bolt corrosion fracture crack model and the fatigue life model were established. The high-strength bolt crack depth and the fatigue life under corrosion environment were quantitatively analyzed. The factors affecting high-strength bolt corrosion fatigue life were discussed. The result showed that the high-strength bolt corrosion fracture biggest crack depth reduces along with the material yield strength and the applied stress increases. The material yield strength was the major factor. And the high-strength bolt corrosion fatigue life reduced along with the increase of material strength, the applied stress or stress amplitude. The stress amplitude influenced the most, and the material yield strength influenced the least. Low bolt strength and a low stress amplitude level could extend high-strength bolt corrosion fatigue life.

scholarly journals Numerical Failure Analysis and Fatigue Life Prediction of Shield Machine Cutterhead

Materials ◽  
2021 ◽  
Vol 14 (17) ◽  
pp. 4822
Author(s):  
Jie Li ◽  
Zengqiang Zhang ◽  
Chuang Liu ◽  
Kang Su ◽  
Jingbo Guo
Keyword(s):  
Stress Intensity ◽  
Failure Analysis ◽  
Stress Intensity Factors ◽  
Life Prediction ◽  
Crack Detection ◽  
Crack Depth ◽  
Intensity Factors ◽  
Mathematical Methods ◽  
Different Shapes ◽  
Shield Machine

This paper presents numerical failure analysis on cracking of shield machine cutterhead structure during a metro-tunnel construction. The stress intensity factors (SIFs) of surface cracks with different shapes and location angles were analyzed by a finite element simulation method based on linear elastic fracture mechanics (LEFM) theory. The ratios of variation in stress intensity factors of cracks with different shapes were analyzed. The maximum allowable crack depth of the cutterhead panel is 50.23 mm by dynamic stress calculation, and the damage tolerance criterion of the cutterhead panel was proposed. The influence of the Paris model parameter values was analyzed based on mathematical methods. It is proven that the location of the cutterhead cracking angle is mainly determined by the mixed-mode SIF. In practice, the crack section basically expanded into the semi-elliptical shape. The cutterhead structure may directly enter the stage of crack propagation due to welding defects during tunneling. The research results provide a theoretical basis and important reference for crack detection in the key parts of the cutterhead, as well as maintenance cycle determination and life prediction of the cutterhead mileage, both of which have important engineering value.

Influence of Yield Strength Variability over Cross-Section to Steel Beam Load-Carrying Capacity

2005 ◽  
Vol 10 (2) ◽  
pp. 151-160 ◽  
Author(s):  
J. Kala ◽  
Z. Kala
Keyword(s):  
Yield Strength ◽  
Cross Section ◽  
Carrying Capacity ◽  
Bending Moment ◽  
Statistical Characteristics ◽  
Load Carrying Capacity ◽  
Load Carrying ◽  
Strength Variability ◽  
Hot Rolled ◽  
Hot Rolled Steel

Authors of article analysed influence of variability of yield strength over cross-section of hot rolled steel member to its load-carrying capacity. In calculation models, the yield strength is usually taken as constant. But yield strength of a steel hot-rolled beam is generally a random quantity. Not only the whole beam but also its parts have slightly different material characteristics. According to the results of more accurate measurements, the statistical characteristics of the material taken from various cross-section points (e.g. from a web and a flange) are, however, more or less different. This variation is described by one dimensional random field. The load-carrying capacity of the beam IPE300 under bending moment at its ends with the lateral buckling influence included is analysed, nondimensional slenderness according to EC3 is λ¯ = 0.6. For this relatively low slender beam the influence of the yield strength on the load-carrying capacity is large. Also the influence of all the other imperfections as accurately as possible, the load-carrying capacity was determined by geometrically and materially nonlinear solution of very accurate FEM model by the ANSYS programme.

Failure behavior of aerial bomb lifting lug under variable amplitude loading: Failure analysis and life prediction

2021 ◽  
Vol 120 ◽  
pp. 105000
Author(s):  
Bowen Wang ◽  
Liyang Xie ◽  
Jiaxin Song ◽  
Xuehong He ◽  
Weifeng Luo ◽  
...  
Keyword(s):  
Failure Analysis ◽  
Life Prediction ◽  
Failure Behavior ◽  
Variable Amplitude Loading ◽  
Variable Amplitude

Effect of Yield Strength and Crack Depth on COD-Decrease-Parameter m

2000 ◽  
Vol 183-187 ◽  
pp. 589-594
Author(s):  
Qing Fen Li ◽  
Huocai Ni ◽  
Sang Lin Yang ◽  
Maoyuan Ma ◽  
Ping Long ◽  
...  
Keyword(s):  
Yield Strength ◽  
Crack Depth

Elastic-Plastic Analysis of an Elbow With Axial Part-Through Internal Crack at Crown Under In-Plane Bending

2008 ◽  
Author(s):  
K. M. Prabhakaran ◽  
S. R. Bhate ◽  
V. Bhasin ◽  
A. K. Ghosh
Keyword(s):  
Finite Element ◽  
Crack Depth ◽  
Bending Moment ◽  
Internal Crack ◽  
J Integral ◽  
Finite Element Analyses ◽  
Integrity Assessment ◽  
Elastic Plastic ◽  
Axial Part ◽  
Plane Bending

Piping elbows under bending moment are vulnerable to cracking at crown. The structural integrity assessment requires evaluation of J-integral. The J-integral values for elbows with axial part-through internal crack at crown under in-plane bending moment are limited in open literature. This paper presents the J-integral results of a thick and thin, 90-degree, long radius elbow subjected to in-plane opening bending moment based on number of finite element analyses covering different crack configurations. The non-linear elastic-plastic finite element analyses were performed using WARP3D software. Both geometrical and material nonlinearity were considered in the study. The geometry considered were for Rm/t = 5, and 12 with ratio of crack depth to wall thickness, a/t = 0.15, 0.25, 0.5 and 0.75 and ratio of crack length to crack depth, 2c/a = 6, 8, 10 and 12.

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