Comparing Different Metamodelling Approaches to Predict Stress Intensity Factor of a Semi-Elliptic Crack

2017 ◽  
Author(s):  
Arvind Keprate ◽  
R. M. Chandima Ratnayake ◽  
Shankar Sankararaman
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Polynomial Regression ◽  
Absolute Error ◽  
Coefficient Of Determination ◽  
Support Vector ◽  
Elliptic Crack ◽  
Maximum Absolute Error ◽  
Data Points

This paper examines the applicability of the different meta-models (MMs) to predict the Stress Intensity Factor (SIF) of a semi-elliptic crack propagating in topside piping, as an inexpensive alternative to the Finite Element Methods (FEM). Five different MMs, namely, multi-linear regression (MLR), second order polynomial regression (PR-2) (with interaction), Gaussian process regression (GPR), neural networks (NN) and support vector regression (SVR) have been tested. Seventy data points (SIF values obtained by FEM) are used to train the aforementioned MMs, while thirty data points are used as the testing points. In order to compare the accuracy of the MMs, four metrics, namely, Root Mean Square Error (RMSE), Average Absolute Error (AAE), Maximum Absolute Error (AAE), and Coefficient of Determination (R2) are used. Although PR-2 emerged as the best fit, GPR was selected as the best MM for SIF determination due to its capability of calculating the uncertainty related to the prediction values. The aforementioned uncertainty representation is quite valuable, as it is used to adaptively train the GPR model, which further improves its prediction accuracy.

Comparison of Various Surrogate Models to Predict Stress Intensity Factor of a Crack Propagating in Offshore Piping

2017 ◽  
Vol 139 (6) ◽  
Author(s):  
Arvind Keprate ◽  
R. M. Chandima Ratnayake ◽  
Shankar Sankararaman
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Polynomial Regression ◽  
Crack Depth ◽  
Absolute Error ◽  
Surrogate Models ◽  
Coefficient Of Determination ◽  
Support Vector ◽  
Data Points

This paper examines the applicability of the different surrogate-models (SMs) to predict the stress intensity factor (SIF) of a crack propagating in topside piping, as an inexpensive alternative to the finite element methods (FEM). Six different SMs, namely, multilinear regression (MLR), polynomial regression (PR) of order two, three, and four (with interaction), Gaussian process regression (GPR), neural networks (NN), relevance vector regression (RVR), and support vector regression (SVR) have been tested. Seventy data points (consisting of load (L), crack depth (a), half crack length (c) and SIF values obtained by FEM) are used to train the aforementioned SMs, while 30 data points are used for testing. In order to compare the accuracy of the SMs, four metrics, namely, root-mean-square error (RMSE), average absolute error (AAE), maximum absolute error (MAE), and coefficient of determination (R2) are used. A case study illustrating the comparison of the prediction capability of various SMs is presented. python and matlab are used to train and test the SMs. Although PR emerged as the best fit, GPR was selected as the best SM for SIF determination due to its capability of calculating the uncertainty related to the prediction values. The aforementioned uncertainty representation is quite valuable, as it is used to adaptively train the GPR model (GPRM), which further improves its prediction accuracy and makes it an accurate, faster, and alternative method to FEM for predicting SIF.

Validation of Adaptive Gaussian Process Regression Model Used for SIF Prediction

2018 ◽  
Author(s):  
Arvind Keprate ◽  
R. M. Chandima Ratnayake ◽  
Shankar Sankararaman
Keyword(s):  
Regression Model ◽  
Gaussian Process ◽  
Prediction Accuracy ◽  
Experimental Validation ◽  
Gaussian Process Regression ◽  
Absolute Error ◽  
Coefficient Of Determination ◽  
Data Sets ◽  
Maximum Absolute Error ◽  
Data Points

The main aim of this paper is to perform the validation of the adaptive Gaussian process regression model (AGPRM) developed by the authors for the Stress Intensity Factor (SIF) prediction of a crack propagating in topside piping. For validation purposes, the values of SIF obtained from experiments available in the literature are used. Sixty-six data points (consisting of L, a, c and SIF values obtained by experiments) are used to train the AGPRM, while four independent data sets are used for validation purposes. The experimental validation of the AGPRM also consists of the comparison of the prediction accuracy of AGPRM and Finite Element Method (FEM) relative to the experimentally derived SIF values. Four metrics, namely, Root Mean Square Error (RMSE), Average Absolute Error (AAE), Maximum Absolute Error (MAE), and Coefficient of Determination (R2), are used to compare the accuracy. A case study illustrating the development and experimental validation of the AGPRM is presented. Results indicate that the prediction accuracy of the AGPRM is comparable with and even higher than that of the FEM, provided the training points of the AGPRM are aptly chosen.

A Surrogate Model for Predicting Stress Intensity Factor: An Application to Oil and Gas Industry

2017 ◽  
Author(s):  
Arvind Keprate ◽  
R. M. Chandima Ratnayake ◽  
Shankar Sankararaman
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Oil And Gas ◽  
Gaussian Process Regression ◽  
Complex Loading ◽  
Oil And Gas Industry ◽  
Crack Size ◽  
Data Points ◽  
Time Required

Evaluation of the stress intensity factor (SIF) for a crack propagating in a structural component is the analytical basis of linear elastic fracture mechanics (LEFM) approach. Handbook solutions give accurate SIF results for simple crack geometries. For intricate crack geometries and complex loading conditions finite element method (FEM), is used to predict SIF. The main drawback of FEM techniques is that they are prohibitively expensive in terms of computing cost and also very time consuming. In this manuscript, authors have presented a Gaussian Process Regression Model (GPRM), which may be used as an alternative to FEM for predicting SIF of a propagating crack. The GPRM is firstly trained using 70 SIF values obtained by FEM, and then validated by comparing the values of SIF predicted by GPRM and FEM for 30 data points (i.e. combination of crack size and loading). On comparing the aforementioned values the average residual percentage between the two is 2.57%, indicating good agreement between GPRM and FEM model. Also, the time required to predict SIF of 30 data points is reduced from 30 mins (for FEM) to 10 seconds with the help of proposed GPRM.

Effect of Loading Condition on Stress Intensity Factor for Threaded Fasteners Under Helix Angle Condition

2015 ◽  
Author(s):  
Suresh Kumar Sundaram ◽  
Raghu V. Prakash
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Loading Condition ◽  
Helix Angle ◽  
Elliptic Crack ◽  
Published Data ◽  
Far Field ◽  
Loading Conditions ◽  
Deep Crack

The effect of loading condition on the stress intensity factor (SIF) solution for a metric threaded bolt with helix angle consideration is investigated. Available SIF solutions for a nut loaded bolt do not consider the effect of helix angle of thread. Various loading conditions such as: (i) far field loading, (ii) thread face loading without helix angle, (iii) thread face loading with helix angle and (iv) nut loading with helix angle are considered in the present study. 3-D contact analysis is carried out to observe the stress distribution between the bolt and nut interface. A crack was introduced at the first thread of the bolt so that the crack faces experience opening mode of fracture under nut loading condition. The SIF estimated by each loading condition was compared with the SIF values computed taking into consideration the nut loading with helix angle. SIF solutions obtained under far field loading condition are lower than those obtained under other loading conditions at short crack depths (a/d = 0.1); at deep crack depths (a/d = 0.5), SIF obtained under nut loading condition are lower than those obtained under other loading conditions. At deep crack depths (a/d = 0.5) the effect of loading condition on SIF is more pronounced for an elliptic crack (a/c = 0.2) than semi circular crack (a/c = 1). Due to the combined effect of mode II and mode III fracture which is caused by helix angle, non symmetric distribution of SIF was observed along the crack front. It is noted that, crack growth rate derived from SIF under nut loading condition is lower than published data at the middle region (P/P0 = 0).

Fracture Criteria of Fibrous Laminated Composites Under In-Plane Multidirectional Loading

1980 ◽  
Vol 47 (3) ◽  
pp. 563-569 ◽  
Author(s):  
J. Tirosh ◽  
P. Mast ◽  
L. Beaubien ◽  
D. Mulville ◽  
S. Sutton ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Laminated Composites ◽  
Combined Loading ◽  
J Integral ◽  
Fracture Criteria ◽  
Displacement Mode ◽  
Data Points ◽  
Angle Ply Laminates

A study on the validity of various fracture criteria of angle-ply-laminated composites is presented for in-plane loading. Special emphasis is given to the vectorial presentation of the J-integral as a suitable candidate for fracture characterization of composites under general combined loading. The combined loading which is composed of a simultaneous tension, shear and in-plane bending in any desired proportion, has been produced in a highly computerized fashion by a specially devised apparatus at the U.S. Naval Research Laboratory. The fracture data of several angle ply laminates of carbon/epoxy composite (T300/5208) result from prescribing the foregoing three combined radial loading until fracture. Aided by numerical stress analysis (finite-element program) the data points are cast into more well-known descriptions; namely, crack-opening displacement versus crack-sliding displacement. Mode-I stress-intensity factor (KI) versus Mode-II stress-intensity factor (KII) and energy-release rate vector Jx versus Jy. The main outcome is that the data displayed on the J-integral plane have a highly distinctive nature of aligning the data points along straight lines, thus a clear discrimination between the fracture properties of different angle-ply laminates can be characterized by only two parameters. The ability to infer fracture conditions in subcomponents from tests on small coupons is assessed.

Experimental Validation of the Adaptive Gaussian Process Regression Model Used for Prediction of Stress Intensity Factor as an Alternative to Finite Element Method

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Arvind Keprate ◽  
R. M. Chandima Ratnayake ◽  
Shankar Sankararaman
Keyword(s):  
Finite Element Method ◽  
Stress Intensity Factor ◽  
Finite Element ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Regression Model ◽  
Prediction Accuracy ◽  
Experimental Validation ◽  
Gaussian Process Regression ◽  
Absolute Error

Currently, in the oil and gas industry, finite element method (FEM)-based commercial software (such as ANSYS and abaqus) is commonly employed for determining the stress intensity factor (SIF). In their earlier work, the authors proposed an adaptive Gaussian process regression model (AGPRM) for the SIF prediction of a crack propagating in topside piping, as an inexpensive alternative to FEM. This paper is the continuation of the earlier work, as it focuses on the experimental validation of the proposed AGPRM. For validation purposes, the values of SIF obtained from experiments available in the literature are used. The experimental validation of AGPRM also consists of the comparison of the prediction accuracy of AGPRM and FEM relative to the experimentally derived SIF values. Five metrics, namely, root-mean-square error (RMSE), average absolute error (AAE), mean absolute percentage error (MAPE), maximum absolute error (MAE), and coefficient of determination (R2), are used to compare the accuracy. A case study illustrating the development and experimental validation of the AGPRM is presented. Results indicate that the prediction accuracy of AGPRM is comparable with and even higher than FEM, provided the training points of AGPRM are chosen aptly. Good prediction accuracy coupled with less time consumption favors AGPRM as an alternative to FEM for SIF prediction.

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 

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