scholarly journals Formation Criterion of Hydrogen-Induced Cracking in Steel Based on Fracture Mechanics

Metals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 940 ◽  
Author(s):  
Lei Fu ◽  
Hongyuan Fang
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Hydrogen Pressure ◽  
Hydrogen Atoms ◽  
Loading Effect ◽  
Hydrogen Molecules ◽  
Hydrogen Induced Cracking

A new criterion for hydrogen-induced cracking (HIC) that includes both the embrittlement effect and the loading effect of hydrogen was obtained theoretically. The surface cohesive energy and plastic deformation energy are reduced by hydrogen atoms at the interface; thus, the fracture toughness is reduced according to fracture mechanics theory. Both the pressure effect and the embrittlement effect mitigate the critical condition required for crack instability extension. During the crack instability expansion, the hydrogen in the material can be divided into two categories: hydrogen atoms surrounding the crack and hydrogen molecules in the crack cavity. The loading effect of hydrogen was verified by experiments, and the characterization methods for the stress intensity factor under hydrogen pressure in a linear elastic model and an elastoplastic model were analyzed using the finite-element simulation method. The hydrogen pressure due to the aggregation of hydrogen molecules inside the crack cavity regularly contributed to the stress intensity factor. The embrittlement of hydrogen was verified by electrolytic charging hydrogen experiments. According to the change in the atomic distribution during crack propagation in a molecular dynamics simulation, the transition from ductile to brittle fracture and the reduction in the fracture toughness were due to the formation of crack tip dislocation regions suppressed by hydrogen. The HIC formation mechanism is both the driving force of crack propagation due to the hydrogen gas pressure and the resisting force reduced by hydrogen atoms.

Development of a Novel Test Method to Characterize Material Properties in Corrosive Environments for Subsea HPHT Design

2019 ◽  
Vol 142 (3) ◽  
Author(s):  
Ramgopal Thodla ◽  
Colum Holtam ◽  
Rajil Saraswat
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Cathodic Protection ◽  
Material Properties ◽  
Test Method ◽  
Corrosive Environments

Abstract High pressure high temperature (HPHT) design is a significant new challenge facing the subsea sector, particularly in the Gulf of Mexico. API 17TR8 provides HPHT Design Guidelines, specifically for subsea applications. Fatigue endurance (i.e., S–N) and fracture mechanics design are both permitted, depending on the criticality of the component. Both design approaches require material properties generated in corrosive environments, such as seawater with cathodic protection and/or sour production fluids. In particular, it is necessary to understand sensitivity to cyclic loading frequency (for both design approaches), crack growth rates (CGR) (for fracture mechanics approach) as well as fracture toughness performance. For many subsea components, the primary source of fatigue loading is associated with the start-up and subsequent shutdown operation of the well, with long hold periods in-between, during which static crack growth (CG) could occur. These are the two damage modes of most interest when performing a fracture mechanics based analysis. This paper presents the preliminary results of a novel single specimen test method that was developed to provide fatigue crack growth rate (FCGR) and fracture toughness data in corrosive environments, in a timeframe that is compatible with subsea HPHT development projects. Test data generated on alloy 625+ in seawater with cathodic protection are presented along with a description of how the test method was developed. A crack tip strain rate based formulation was applied to the data to rationalize the effect of frequency, stress intensity factor range (ΔK), and maximum stress intensity factor (Kmax).

Development of a Novel Test Method to Characterize Material Properties in Corrosive Environments for Subsea HPHT Design

2017 ◽  
Author(s):  
Ramgopal Thodla ◽  
Colum Holtam ◽  
Rajil Saraswat
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Cathodic Protection ◽  
Material Properties ◽  
Test Method ◽  
Corrosive Environments

High pressure high temperature (HPHT) design is a significant new challenge facing the subsea sector, particularly in the Gulf of Mexico. API 17TR8 provides HPHT Design Guidelines, specifically for subsea applications. Fatigue endurance (i.e. S-N) and fracture mechanics design are both permitted, depending on the criticality of the component. Both design approaches require material properties generated in corrosive environments, such as seawater with cathodic protection and/or sour production fluids. In particular, it is necessary to understand sensitivity to cyclic loading frequency (for both design approaches), crack growth rates (for fracture mechanics approach) as well as fracture toughness performance. For many subsea components, the primary source of fatigue loading is associated with the start-up and subsequent shutdown operation of the well, with long hold periods in-between, during which static crack growth could occur. These are the two damage modes of most interest when performing a fracture mechanics based analysis. This paper presents the preliminary results of a novel single specimen test method that was developed to provide fatigue crack growth rate and fracture toughness data in corrosive environments, in a timeframe that is compatible with subsea HPHT development projects. Test data generated on alloy 625+ in seawater with cathodic protection is presented along with a description of how the test method was developed. A crack tip strain rate based formulation was applied to the data to rationalize the effect of frequency, stress intensity factor range (ΔK) and maximum stress intensity factor (Kmax).

scholarly journals Analisis Probabilistic Fracture Mechanics Pada Evaluasi Keandalan Bejana Tekan Reaktor Secara 3-D

2018 ◽  
Vol 24 (1) ◽  
Author(s):  
Entin Hartini ◽  
Roziq Himawan ◽  
Mike Susmikanti
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Probability Density Function ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Pressure Vessel ◽  
J Integral ◽  
Probabilistic Fracture Mechanics ◽  
Reactor Pressure

Analisis integritas material sangat diperlukan pada Reactor Pressure Vessel (RPV). Komponen tersebut merupakan pressure boundary yang berfungsi untuk mengungkung material radioaktif. Adanya retak pada dinding dapat mempengaruhi integritas RPV tersebut. Penelitian ini bertujuan melakukan analisis fracture mechanics menggunakan model probabilistik untuk evaluasi keandalan RPV. Model probabilistik digunakan untuk pendekatan karakter random dari kuantitas input seperti sifat mekanik material dan lingkungan fisik. Karakter random dari kuantitas input menggunakan teknik sampling berdasarkan probability density function.  Material yang digunakan pada RPV adalah baja feritik (SA 533). Analisis fracture mechanics dilakukan berdasarkan metode elemen hingga (FEM) menggunakan perangkat lunak MSC MARC. Output dari MSC MARC adalah nilai J integral untuk mendapatkan nilai stress intensity factor (SIF) pada evaluasi keandalan bejana tekan reaktor 3D. Hasil perhitungan menunjukan bahwa SIF probabilistik lebih dulu mencapai nilai batas fracture toughness  dibanding  SIF deterministik. Nilai SIF yang dihasilkan dengan metode probabilistik adalah 95,8  MPa m0,5, sedangkan dengan metode deterministik adalah 91,8 MPa m0,5, rasio crack (a/c) semakin kecil akan dihasilkan nilai SIF yang semakin besar.Kata kunci: Probabilistic fracture mechanics, bejana tekan, 3-D.

scholarly journals CIRCUMFERENTIAL INHOMOGENITY ANALYSIS IN G.A. SIWABESSY REACTOR’S PRIMARY COOLING PIPE

2016 ◽  
Vol 18 (3) ◽  
pp. 155
Author(s):  
Roziq Himawan ◽  
Mike Susmikanti
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Crack Growth ◽  
Elliptic Crack ◽  
Crack Model ◽  
Welding Part ◽  
Service Inspection

ABSTRACT In the in-service inspection conducted to G.A. Siwabessy reactor’s primary cooling system pipe, it was found the presence of inhomogenity inside of welding part. To verify whether the inhomogenity could be tolerated or not, comparative data from welding pre-service inspection is needed. Unfortunately, this weld wasn’t covered in pre-service inspection. Therefore, this inhomogenity needs to be analyzed. The purpose of this study is to evaluate the stress intensity factor of the inhomogenity, whether it is within a limit value or not and to predict the crack growth. Analysis were performed based on fracture mechanics theory using parameter of stress intensity factor. Two models were used for calculation approach that are plane crack model and semi-elliptic crack model. Hence, in order to predict the length of inhomogenity in the future, crack growth calculations were performed. The results showed that stress intensity values from both two models are remain below fracture toughness value of pipe’s material. Besides that, stress intensity factor from plane crack model is higher than those from semi-elliptic crack model. Under consideration that inhomogenity has an arc shape in actual, thus, stress intensity factor from this inhomogenity still low enough compare to the fracture toughness. Crack growth calculation’s results showed that after 300th cycle of loading, the length of inhomogenity reaches approximately 2 mm. Based on operation data of G.A. Siwabessy reactor, 300 cycle number is corresponds to 30 years operation. Based on these results it could be concluded that the presence of inhomogenity in the welding part does not affect the structure’s integrity of piping system. Keywords : Inhomogenity, fracture mechanics, fracture toughness, stress intensity factor, crack growth   ABSTRAK Pada pelaksanaan in-service inspection terhadap perpipaan sistem pendingin primer reaktor G.A. Siwabessy diketahui adanya inhomogenitas pada salah satu sambungan lasan pipa. Untuk memverifikasi apakah inhomogenitas ini dapat ditoleransi atau tidak, diperlukan data pembanding hasil pemeriksaan lasan pada saat fabrikasi. Namun, ternyata pada saat fabrikasi, sambungan lasan ini tidak mengalami pemeriksaan. Oleh karena itu, dalam rangka menetapkan apakah keberadaan inhomogentitas ini dapat ditoleransi atau tidak perlu dilakukan analisis terhadap inhomogenitas tersebut. Tujuan penelitian ini adalah untuk melakukan evaluasi stress intensity factor inhomogenitas di dalam pipa apakah masih berada di dalam batas nilai dan untuk memprediksi perambatan retak. Analisis dilakukan berdasarkan teori fracture mechanics dengan menghitung stress intensity factor inhomogenitas. Dalam perhitungan ini digunakan dua model untuk pendekatan, yaitu model retak planar dan model retak semi-ellips. Selanjutnya, untuk memprediksi panjang inhomogenitas di masa yang akan datang, dilakukan juga simulasi perambatan retak. Hasil-hasil analisis memperlihatkan bahwa nilai stress intensity factor berdasarkan model retak bentuk planar dan retak bentuk semi ellips masih jauh di bawah nilai fracture toughness material pipa. Selain itu, nilai yang dihasilkan berdasarkan model retak bentuk planar lebih besar dibandingkan dengan model retak bentuk semi ellips. Mengingat bentuk inhomogenitas yang berupa busur lingkaran, maka nilai stress intensity factor yang sesungguhnya dari inhomogenitas tersebut jauh lebih kecil dibandingkan dengan nilai fracture toughness. Sementara itu, untuk hasil simulasi perambatan retak menunjukkan bahwa pada siklus pembebanan ke-300 memberikan panjang sekitar 2 mm. Berdasarkan data operasi reaktor G.A. Siwabessy, jumlah siklus sebanyak 300 kali setara dengan pengoperasian reaktor selama 30 tahun. Berdasarkan dua hasil tersebut dapat disimpulkan bahwa keberadaan inhomogenitas pada sambungan lasan tidak berpengaruh terhadap integritas struktur sistem perpipaan. Kata kunci : Inhomogenitas, fracture mechanincs, fracture toughness, stress intensity factor, pertumbuhan retak 

The Robustness of a Simple Expression for Quantifying Fracture Initiation at a Blunt Flaw

2006 ◽  
Author(s):  
E. Smith
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Peak Stress ◽  
Critical Value ◽  
Simple Expression ◽  
Wide Range ◽  
Fracture Processes

Linear elastic fracture mechanics of cracks is well established, and is based on the stress field near a crack tip being described by the stress intensity factor, with crack extension occurring when the stress intensity factor is equal to a critical value, which is referred to as the fracture toughness of the material. This methodology has been applied to a wide range of materials and structures, with the fracture toughness being related to the micro-mechanistic fracture processes, often via the cohesive-process zone representation of these fracture processes. The author is involved in a wide-ranging research programme whose objective is to extend the fracture mechanics methodology to blunt flaws, so as to take credit for the blunt flaw geometry, the strategy being to parallel, as far as possible, the methods that have been developed for cracks. Earlier work has shown that an appropriate characterizing parameter, analogous to the stress intensity factor for a crack, is the elastic peak flaw tip stress, with fracture initiating when the peak stress attains a critical value, which is related to the flaw geometry, in particular the flaw root radius, and material parameters. A simple expression has been derived for the critical peak stress and, in this paper, we provide support for its robustness.

On notch fracture mechanics

2021 ◽  
Vol 87 (2) ◽  
pp. 56-64
Author(s):  
G. Pluvinage
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Fracture Resistance ◽  
Notch Radius ◽  
Notch Stress Intensity Factor ◽  
Blunt Notch ◽  
Notch Stress

Different stress distributions for an elastic behavior are presented as analytical expressions for an ideal crack, a sharp notch and a blunt notch. The elastic plastic distribution at a blunt notch tip is analyzed. The concept of the notch stress intensity factor is deduced from the definition of the effective stress and the effective distance. The impacts of the notch radius and constraint on the critical notch stress intensity factor are presented. The paper ends with the presentation of the crack driving force Jρ for a notch in the elastic case and the impact of the notch radius on the notch fracture toughness Jρ,c. The notch fracture toughness Jρ,c is a measure of the fracture resistance which increases linearly with the notch radius due to the plastic work in the notch plastic zone. If this notch plastic zone does not invade totally the ligament, the notch fracture toughness Jρ,c is constant. This occurs when the notch radius is less than a critical one and there is no need to use the cracked specimen to measure a lower bound of the fracture resistance.

scholarly journals Fracture toughness as an alternative approach to quantify the ageing of insulation paper in oil

Cellulose ◽  
2021 ◽  
Author(s):  
C. Fernández-Diego ◽  
I. A. Carrascal ◽  
A. Ortiz ◽  
I. Fernández ◽  
D. Ferreño ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Dielectric Materials ◽  
Superior Performance ◽  
Mechanical Resistance ◽  
Insulation Material ◽  
Cellulose Materials ◽  
Over Time

AbstractOil-immersed transformers use paper and oil as insulation system which degrades slowly during the operation of these machines. Cellulose materials are used generally as insulation solid in power transformers. The degree of polymerization (DP), defined as number of repeating β-glucose residues in the cellulose molecule, is a critical property of cellulosic insulation material used in transformers, since it provides information about paper ageing and its mechanical strength. The fast-developing electric power industry demanding superior performance of electrical insulation materials has led to the development of new materials, as well as different drying techniques performed during transformer manufacturing and service when required. Both developments have caused some practical difficulties in the DP measurement. Moreover, the increasing interest in synthetic dielectric materials replacing cellulose materials requires measuring alternative properties to the DP to quantify the degradation of insulation solids over time. In this sense, this paper proposes the possibility of analyzing paper degradation through fracture toughness. This approach is different from the study of mechanical properties such as tensile strength or strain because it provides a tool for solving most practical problems in engineering mechanics, such as safety and life expectancy estimation of cracked structures and components which cannot to be considered through the traditional assessment of the mechanical resistance of the material. An accelerated thermal ageing of Kraft paper in mineral oil was carried out at 130 °C during different periods of time, to obtain information on the kinetics of the ageing degradation of the paper. Double-edged notched specimens were tested in tension to study their fracture toughness. The evolution of the load–displacement curves obtained for different ageing times at the ageing temperature of 130 °C was utilized to the determination of the stress intensity factor. Furthermore, different kinetic models based on this stress intensity factor were applied to relate its evolution over time as a function of the temperature. Finally, the correlation between the DP and stress intensity factor, which depends on the fiber angle, was also defined. Graphic abstract

Finite Element Fracture Mechanics Study of Web Connections with Tapered Beam Flange Plates

2010 ◽  
Vol 452-453 ◽  
pp. 473-476 ◽  
Author(s):  
Hong Bo Liu ◽  
Long Jun Xu ◽  
Shuang Li ◽  
Yong Song Shao
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Bottom Surface ◽  
Seismic Load ◽  
Bottom Flange ◽  
Moment Frames ◽  
Tapered Beam

Brittle fracture was identified in many of prequalified weld joints in steel moment frames in the 1994 Nothridge earthquake. Then analyses of response and damage mechanism of beam-to-column connections under seismic load were widely studied in the world, but few people conduct the research on seismic-resistant behavior of beam-to-column web connections. To quantify the variation of stress intensity factor to weld root flaw sizes beam-to-column web connections with tapered beam flange plates, detailed 3D finite element analyses is used to study fracture toughness requirements in beam-to-column web connections, considering the large deformation, large strain, bolts pretension, bolt contact-slide, as well as material harden and soften. Fracture toughness demands are evaluated in terms of the mode I stress intensity factor. The stress intensity factor is calculated through a J-integral approach. The fracture toughness demands are studied for the flaw on the top of the beam flange and the bottom surface, respectively. Results indicate that the likelihood of top flange fractures is smaller than that of bottom flange fracture. Stress intensity factor is not uniform and is largest in the edge of beam flange. The fracture toughness in the edge of beam flange for web connections with step beam flange plates is 15% less than that for tapered beam flange plates.

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