Crack Growth by Dimensional Reduction Methods

2012 ◽  
Vol 525-526 ◽  
pp. 17-20
Author(s):  
P.H. Wen ◽  
M.H. Aliabadi
Keyword(s):  
Crack Growth ◽  
Dimensional Reduction ◽  
Crack Extension ◽  
Initial Growth ◽  
Stress Criterion ◽  
The Maximum Principle ◽  
Reduction Methods ◽  
Small Increments ◽  
Crack Growth Path ◽  
Crack Paths

This paper presents a new fatigue crack growth prediction by using the dimensional reduction methods including the dual boundary element method (DBEM) and element-free Galerkin method (EFGM) for two dimensional elastostatic problems. One crack extension segment, i.e. a segment of arc, is introduced to model crack growth path. Based on the maximum principle stress criterion, this new prediction procedure ensures that the crack growth is smooth everywhere except the initial growth and the stress intensity factor of mode II is zero for each crack extension. It is found that the analyses of crack paths using coarse/large size of crack extension are in excellent agreement with analyses of the crack paths by the tangential method with very small increments of crack extension.

scholarly journals Finite Element Simulation of a Crack Growth in the Presence of a Hole in the Vicinity of the Crack Trajectory

Materials ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 363
Author(s):  
Abdulnaser M. Alshoaibi ◽  
Yahya Ali Fageehi
Keyword(s):  
Crack Growth ◽  
Crack Path ◽  
Circumferential Stress ◽  
Crack Arrest ◽  
Growth Direction ◽  
Stress Criterion ◽  
Crack Trajectory ◽  
Linear Elastic ◽  
New Feature ◽  
Crack Growth Path

The aim of this paper was to present a numerical simulation of a crack growth path and associated stress intensity factors (SIFs) for linear elastic material. The influence of the holes’ position and pre-crack locations in the crack growth direction were investigated. For this purpose, ANSYS Mechanical R19.2 was introduced with the use of a new feature known as Separating Morphing and Adaptive Remeshing Technology (SMART) dependent on the Unstructured Mesh Method (UMM), which can reduce the meshing time from up to several days to a few minutes, eliminating long preprocessing sessions. The presence of a hole near a propagating crack causes a deviation in the crack path. If the hole is close enough to the crack path, the crack may stop at the edge of the hole, resulting in crack arrest. The present study was carried out for two geometries, namely a cracked plate with four holes and a plate with a circular hole, and an edge crack with different pre-crack locations. Under linear elastic fracture mechanics (LEFM), the maximum circumferential stress criterion is applied as a direction criterion. Depending on the position of the hole, the results reveal that the crack propagates in the direction of the hole due to the uneven stresses at the crack tip, which are consequences of the hole’s influence. The results of this modeling are validated in terms of crack growth trajectories and SIFs by several crack growth studies reported in the literature that show trustworthy results.

Analysis of Crack Growth Path under Simple and Mixed-Mode Loading in Specimens with Rectangular Section

2016 ◽  
Vol 251 ◽  
pp. 194-199 ◽  
Author(s):  
Sebastian Faszynka ◽  
Dariusz Rozumek
Keyword(s):  
Crack Growth ◽  
Stress Ratio ◽  
Rectangular Cross Section ◽  
Fatigue Tests ◽  
Test Results ◽  
Growth Path ◽  
Rectangular Section ◽  
Α Phase ◽  
Crack Growth Path ◽  
Crack Paths

The paper presents the test results on the fatigue crack growth under bending, torsion and proportional bending with torsion. The tests were performed at the fatigue test stand MZGS-100 at the constant amplitude of moment MB = MT = MBT = 15.84 N⋅m and stress ratio R = -1. Specimens with rectangular cross-section in fatigue tests were used and were made of EN AW-2017A aluminium alloy. The EN AW-2017A alloy consists of α grains and the Al2Cu phase. The effect of the microstructure on the crack paths in specimens was observed. Transcrystalline cracks through grains of the α phase have been usually observed on the fractures.

Ductile Crack Extension Analysis for X80 Bending Deformation Using Damage-Based Model

2014 ◽  
Author(s):  
Satoshi Igi ◽  
Mitsuru Ohata ◽  
Takahiro Sakimoto ◽  
Kenji Oi ◽  
Joe Kondo
Keyword(s):  
Plastic Strain ◽  
Simulation Model ◽  
Crack Growth ◽  
Crack Extension ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Notch Tip

This paper presents experimental and analytical results focusing on the strain limit of X80 linepipe. Ductile crack growth behavior from a girth weld notch is simulated by FE analysis based on a proposed damage model and is compared with the experimental results. The simulation model for ductile crack growth accompanied by penetration through the wall thickness consists of two criteria. One is a criterion for ductile crack initiation from the notch-tip, which is described by the plastic strain at the notch tip, because the onset of ductile cracking can be expressed by constant plastic strain independent of the shape and size of the components and the loading mode. The other is a damage-based criterion for simulating ductile crack extension associated with damage evolution influenced by plastic strain in accordance with the stress triaxiality ahead of the extending crack tip. The proposed simulation model is applicable to prediction of ductile crack growth behaviors from a circumferentially-notched girth welded pipe with high internal pressure, which is subjected to tensile loading or bending (post-buckling) deformation.

Application of the R-Curve Concept to Fatigue Crack Growth

1978 ◽  
Vol 100 (4) ◽  
pp. 416-420 ◽  
Author(s):  
D. P. Wilhem ◽  
M. M. Ratwani
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Extension ◽  
Stress Ratio ◽  
Cyclic Stress ◽  
Crack Growth Resistance ◽  
Resistance Curve ◽  
Cyclic Stress Ratio ◽  
Wide Range

Crack growth resistance for both static (rising load) and for cyclic fatigue crack growth has been shown to be a continuous function over a range of 0.1 μm to 10 cm in crack extension for 2024-T3 aluminum. Crack growth resistance to each fatigue cycle of crack extension is shown to approach the materials ordinary undirectional static crack resistance value when the cyclic stress ratio is zero. The fatigue crack extension is averaged over many cycles and is correlated with the maximum value of the crack tip stress intensity, Kmax. A linear plot of crack growth resistance for fatigue and static loading data shows similar effects of thickness, stress ratio, and other parameters. The effect of cyclic stress ratio on crack growth resistance for 2219 aluminum indicates the magnitude of differences in resistance when plotted to a linear scale. Prediction of many of these trends is possible using one of several available crack growth data correlating techniques. It appears that a unique resistance curve, dependent on material, crack orientation, thickness, and stress/physical environment, can be developed for crack extensions as small as 0.076 μm (3 μ inches). This wide range, crack growth resistance curve is seen of immense potential for use in both fatigue and fracture studies.

scholarly journals Evaluation of ductile tearing for API-5L X70 pipeline grade steel using SENT specimens

2015 ◽  
Vol 6 (3) ◽  
pp. 8
Author(s):  
Nicholas Ohms ◽  
Diego Belato Rosado ◽  
Wim De Waele
Keyword(s):  
Crack Growth ◽  
Crack Extension ◽  
Crack Growth Resistance ◽  
Fracture Surfaces ◽  
Edge Notch ◽  
Resistance Curves ◽  
Unloading Compliance ◽  
Inner Diameter ◽  
Tearing Resistance ◽  
Hardness Map

Pipelines in harsh environments may be subjected to large deformations. Classic stress-based design needs to be complemented with strain-based design. An important parameter in the design is the crack growth resistance. SENT testing (Single Edge Notch Tension) allows to determine the so-called material’s tearing resistance curve. Very recently the first standard on SENT testing, BS 8571:2014, has been published. SENT testing is however still subject to extensive research and different approaches with respect to eg. notch placement, crack extension measurement and analysis exist. In this paper two methods for calculating crack extension based on the unloading compliance procedure are used and compared, proving that they show little difference. This is performed on an API-5L X70 steel grade and this for different configurations, namely an inner diameter notch and a through thickness notch. The results showed little difference between the different configurations, although the inner diameter showed higher crack growth resistance. Furthermore, the results are compared to visual observations of the fracture surfaces and a hardness map. The fracture surfaces corresponded to the obtained resistance curves. However, no real correlation between the hardness map and the other results could be seen.

The Influence of Creep Strain on Crack Length Measurements Using the Potential Drop

2015 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
K. M. Nikbin ◽  
D. W. Dean
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Material Properties ◽  
Crack Extension ◽  
Electrical Potential ◽  
Creep Crack Growth ◽  
Potential Drop ◽  
Fe Model ◽  
Creep Properties ◽  
Length Measurements

One of the most common methods for estimating crack extension in the laboratory is electrical potential drop (PD). A key limitation of this technique is that it is sensitive to strains at the crack tip as well as crack extension. When producing J-R curves the onset of crack growth may be identified from a point of inflection on a plot of PD vs. CMOD. For creep crack growth (CCG) tests however, the effects of strain are often ignored. This paper investigates whether a similar method may be applied to CCG testing. A single CCG test was performed on type 316H stainless steel and a point of inflection, similar to that observed during J-R curve testing was identified. A finite element (FE) based approach was used to investigate this phenomenon further. A 3D sequentially-coupled structural-electrical FE model was used to reproduce the experimental PD vs. CMOD plot up to the point of inflection. The model was capable of predicting the general relationship between strain and PD. It predicted the magnitude of the change in PD to within 30%. A simplified 2D FE model was then used to perform a parametric study to investigate whether a similar trend may be expected for a range of materials. Power law tensile and creep properties were investigated with stress exponents of 1, 3 and 10. The results confirm that a point of inflection should be observable for the range of material properties considered.

scholarly journals Cruciform specimens for the determination of crack growth behaviour in biaxial stress fields: calculation of K-factors

2019 ◽  
Vol 300 ◽  
pp. 11008
Author(s):  
Carl H. Wolf ◽  
Andreas Burgold ◽  
Sebastian Henkel ◽  
Meinhard Kuna ◽  
Horst Biermann
Keyword(s):  
Crack Growth ◽  
Steel Specimen ◽  
Biaxial Stress ◽  
Transmission Factor ◽  
Crack Growth Behaviour ◽  
Aluminum Specimen ◽  
Small Influence ◽  
Simplified Calculation ◽  
Crack Paths

The aim of this study is to propose a simplified calculation of the Mode I stress intensity factor K for the cruciform specimen design proposed by Brown and Miller. To calculate K, both cracks have to grow with a similar crack growth rate and the crack paths of the two single cracks with the length a should also be similar. The calculations are carried out on an aluminum specimen and a steel specimen. For all load cases and materials, the stresses resulting from the forces are first considered. It was found that the elastic constants E and ν have only a small influence of less than 3 %. In addition, the coupling between the forces of the load axes, which should be minimized by the slotted arms, is considered. Furthermore K-factors are calculated by FE for different crack lengths. These K-values together with the transmission factor allow to find a K-factor formula for cruciform specimens, which is based on the prescribed forces. Finally, the results of the FE calculation of the exact straight crack paths were compared to experimentally determined crack paths.

Explicit and Implicit Lifetime Assessment Methods of 9Cr-1Mo Steel Under Combined Creep and Fatigue Loads Using a Strip Yield Model

2014 ◽  
Author(s):  
B. Andrews ◽  
G. P. Potirniche
Keyword(s):  
Experimental Data ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Constitutive Equations ◽  
Crack Extension ◽  
Cyclic Loads ◽  
Yield Model ◽  
Creep Crack ◽  
Strip Yield Model

Growing demand for clean, affordable energy has driven the power industry towards generation plants with higher thermal efficiency and higher operating temperatures. ASTM Grade 91 is a high chromium (9Cr-1Mo) creep resistant steel commonly used in high temperature pressure vessel and piping applications. These service conditions often involve a combination of stationary and cyclic loads at elevated temperatures. Lifecycle assessments of components under such conditions require modeling of both creep and fatigue behaviors. This paper develops two approaches to modeling mixed creep and fatigue crack growth for lifetime assessment of high service temperature components. Both approaches model fatigue crack growth using the Paris law integrated over the number of lifetime cyclic reversals to obtain crack extension. A strip yield model is used to characterize the crack tip stress-strain fields. The first approach employed an explicit method to approximate creep crack growth using C* as a crack tip parameter characterizing creep crack extension. The Norton power law was explicitly solved to model the primary and secondary stages of creep. The second approach used an implicit method to solve a set of constitutive equations based on properties of the material microstructure to model all creep stages. Constitutive equations were fit to experimental data collected at stresses 10–60% of yield and temperatures 550–650°C. These methods were compared to published experimental data under purely stationary loads, purely cyclic loads and mixed loading. Both models showed good agreement with experimental data in the stress and temperature conditions considered.

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