Crack growth analysis and remaining life prediction of dissimilar metal pipe weld joint with circumferential crack under cyclic loading

Murthy, A. Ramachandra,Gandhi, P.,Vishnuvardhan, S.,Sudharshan, G. 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.12

Fatigue crack growth model has been developed for dissimilar metal weld joints of a piping component under cyclic loading, where in the crack is located at the center of the weld in the circumferential direction. The fracture parameter, Stress Intensity Factor (SIF) has been computed by using principle of superposition as K_H + K_M. K_H is evaluated by assuming that, the complete specimen is made of the material containing the notch location. In second stage, the stress field ahead of the crack tip, accounting for the strength mismatch, the applied load and geometry has been characterized to evaluate SIF (K_M). For each incremental crack depth, stress field ahead of the crack tip has been quantified by using J-integral (elastic), mismatch ratio, plastic interaction factor and stress parallel to the crack surface. The associated constants for evaluation of K_M have been computed by using the quantified stress field with respect to the distance from the crack tip. Net SIF (K_H + K_M) computed, has been used for the crack growth analysis and remaining life prediction by Paris crack growth model. To validate the model, SIF and remaining life has been predicted for a pipe made up of (i) SA312 Type 304LN austenitic stainless steel and SA508 Gr. 3 Cl. 1. Low alloy carbon steel (ii) welded SA312 Type 304LN austenitic stainless-steel pipe. From the studies, it is observed that the model could predict the remaining life of DMWJ piping components with a maximum difference of 15% compared to experimental observations.

Relevance vector based approach for the prediction of stress intensity factor for the pipe with circumferential crack under cyclic loading

A. Ramachandra Murthy,S. Vishnuvardhan,M. Saravanan,P. Gandhi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.1

Structural integrity assessment of piping components is of paramount important for remaining life prediction, residual strength evaluation and for in-service inspection planning. For accurate prediction of these, a reliable fracture parameter is essential. One of the fracture parameters is stress intensity factor (SIF), which is generally preferred for high strength materials, can be evaluated by using linear elastic fracture mechanics principles. To employ available analytical and numerical procedures for fracture analysis of piping components, it takes considerable amount of time and effort. In view of this, an alternative approach to analytical and finite element analysis, a model based on relevance vector machine (RVM) is developed to predict SIF of part through crack of a piping component under fatigue loading. RVM is based on probabilistic approach and regression and it is established based on Bayesian formulation of a linear model with an appropriate prior that results in a sparse representation. Model for SIF prediction is developed by using MATLAB software wherein 70% of the data has been used for the development of RVM model and rest of the data is used for validation. The predicted SIF is found to be in good agreement with the corresponding analytical solution, and can be used for damage tolerant analysis of structural components.

Fracture analysis and remaining life prediction of aluminium alloy 2014a plate panels with concentric stiffeners under fatigue loading

A. Ramachandra Murthy,Rakhi Sara Mathew,G.S. Palani,Smitha Gopinath,Nagesh R. Iyer 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.4

Fracture analysis and remaining life prediction has been carried out for aluminium alloy (Al2014A) plate panels with concentric stiffener by varying sizes and positions under fatigue loading. Tensioncoupon tests and compact tension tests on 2014A have been carried out to evaluate mechanical propertiesand crack growth constants. Domain integral technique has been used to compute the Stress intensity factor(SIF) for various cases. Generalized empirical expressions for SIF have been derived for various positions ofstiffener and size. From the study, it can be concluded that the remaining life for stiffened panel for particularsize and position can be estimated by knowing the remaining life of corresponding unstiffened panel.

Fracture analysis and remaining life prediction of aluminium alloy 2014A plate panels with concentric stiffeners under fatigue loading

Murthy, A. Ramachandra,Mathew, Rakhi Sara,Palani, G.S.,Gopinath, Smitha,Iyer, Nagesh R. Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.4

Fracture analysis and remaining life prediction has been carried out for aluminium alloy (Al 2014A) plate panels with concentric stiffener by varying sizes and positions under fatigue loading. Tension coupon tests and compact tension tests on 2014A have been carried out to evaluate mechanical properties and crack growth constants. Domain integral technique has been used to compute the Stress intensity factor (SIF) for various cases. Generalized empirical expressions for SIF have been derived for various positions of stiffener and size. From the study, it can be concluded that the remaining life for stiffened panel for particular size and position can be estimated by knowing the remaining life of corresponding unstiffened panel.

Plastic viscosity based mix design of self-compacting concrete with crushed rock fines

Kalyana Rama J S,Sivakumar M V N,Vasan A,Sai Kubair,Ramachandra Murthy A 사단법인 한국계산역학회 2017 Computers and Concrete, An International Journal Vol.20 No.4

With the increasing demand in the production of concrete, there is a need for adopting a feasible, economical and sustainable technique to fulfill practical requirements. Self-Compacting Concrete (SCC) is one such technique which addresses the concrete industry in providing eco-friendly and cost effective concrete. The objective of the present study is to develop a mix design for SCC with Crushed Rock Fines (CRF) as fine aggregate based on the plastic viscosity of the mix and validate the same for its fresh and hardened properties. Effect of plastic viscosity on the fresh and hardened properties of SCC is also addressed in the present study. SCC mixes are made with binary and ternary blends of Fly Ash (FA) and Ground Granulated Blast Slag (GGBS) with varying percentages as a partial replacement to Ordinary Portland Cement (OPC). The proposed mix design is validated successfully with the experimental investigations. The results obtained, indicated that the fresh properties are best achieved for SCC mix with ternary blend followed by binary blend with GGBS, Fly Ash and mix with pure OPC. It is also observed that the replacement of sand with 100% CRF resulted in a workable and cohesive mix.

Prediction of stress intensity factor range for API 5L grade X65 steel by using GPR and MPMR

A. Ramachandra Murthy,S. Vishnuvardhan,M. Saravanan,P. Gandhi 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.5

The infrastructures such as offshore, bridges, power plant, oil and gas piping and aircraft operate in a harsh environment during their service life. Structural integrity of engineering components used in these industries is paramount for the reliability and economics of operation. Two regression models based on the concept of Gaussian process regression (GPR) and Minimax probability machine regression (MPMR) were developed to predict stress intensity factor range (K). Both GPR and MPMR are in the frame work of probability distribution. Models were developed by using the fatigue crack growth data in MATLAB by appropriately modifying the tools. Fatigue crack growth experiments were carried out on Eccentrically-loaded Single Edge notch Tension (ESE(T)) specimens made of API 5L X65 Grade steel in inert and corrosive environments (2.0% and 3.5% NaCl). The experiments were carried out under constant amplitude cyclic loading with a stress ratio of 0.1 and 5.0 Hz frequency (inert environment), 0.5 Hz frequency (corrosive environment). Crack growth rate (da/dN) and stress intensity factor range (K) values were evaluated at incremental values of loading cycle and crack length. About 70 to 75% of the data has been used for training and the remaining for validation of the models. It is observed that the predicted SIF range is in good agreement with the corresponding experimental observations. Further, the performance of the models was assessed with several statistical parameters, namely, Root Mean Square Error (RMSE), Mean Absolute Error (MAE), Coefficient of Efficiency (E), Root Mean Square Error to Observation’s Standard Deviation Ratio (RSR), Normalized Mean Bias Error (NMBE), Performance Index (ρ) and Variance Account Factor (VAF).

Prediction of fatigue crack initiation life in SA312 Type 304LN austenitic stainless steel straight pipes with notch

A. Ramachandra Murthy,S. Vishnuvardhan,K.V. Anjusha,P. Gandhi,P.K. Singh 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.5

In the nuclear power plants, stainless steel is widely used for fabrication of various components such aspiping and pipe fittings. These piping components are subjected to cyclic loading due to start up and shutdown of the nuclear power plants. The application of cyclic loading may lead to initiation of crack atstress raiser locations such as nozzle to piping connection, crown of piping bends etc. of the pipingsystem. Crack initiation can also take place from the flaws which have gone unnoticed duringmanufacturing. Therefore, prediction of crack initiation life would help in decision making with respectto plant operational life. The primary objective of the present study is to compile various analyticalmodels to predict the crack initiation life of the pipes with notch. Here notch simulates the stress raisersin the piping system. As a part of the study, Coffin-Manson equations have been benchmarked to predictthe crack initiation life of pipe with notch. Analytical models proposed by Zheng et al. [1], Singh et al. [2],Yang Dong et al. [25], Masayuki et al. [33] and Liu et al. [3] were compiled to predict the crack initiationlife of SA312 Type 304LN stainless steel pipe with notch under fatigue loading. Tensile and low cyclefatigue properties were evaluated for the same lot of SA312 Type 304LN stainless steel as that of pipe test. The predicted crack initiation lives by different models were compared with the experimental results ofthree pipes under different frequencies and loading conditions. It was observed that the predicted crackinitiation life is in very good agreement with experimental results with maximum difference of ±10.0%.

Fracture energy and tension softening relation for nanomodified concrete

A. Ramachandra Murthy,P. Ganesh,S. Sundar Kumar,Nagesh R. Iyer 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.54 No.6

This paper presents the details of size independent fracture energy and bi-linear tension softening relation for nano modified high strength concrete. Nano silica in powder form has been used as partial replacement of cement by 2 wt%. Two popular methods, namely, simplified boundary effect method of Karihaloo et al. (2003) and RILEM (1985) fracture energy with P-δ tail correction have been employed for estimation of size independent fracture energy for nano modified high strength concrete (compressive strength ranges from 55 MPa to 72 MPa). It is found that both the methods gave nearly same values, which is an additional evidence that either of them can be employed for determination of size independent fracture energy. Bi-linear tension softening relation corresponding to their size independent fracture energy has been constructed in an inverse manner based on the concept of non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams.

Flexural behaviour of GFRP reinforced concrete beams under cyclic loading

A. Ramachandra Murthy,P. Gandhi,D.M. Pukazhendhi,F. Giftson Samuel,S. Vishnuvardhan 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.84 No.3

This paper examines the flexural performance of concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars under fatigue loading. Experiments were carried out on concrete beams of size 1500×200×100 mm reinforced with 10 mm and 13 mm diameter GFRP bars under fatigue loading. Experimental investigations revealed that fatigue loading affects both strength and serviceability properties of GFRP reinforced concrete. Experimental results indicated that (i) the concrete beams experienced increase in deflection with increase in number of cycles and failed suddenly due to snapping of rebars and (ii) the fatigue life of concrete beams drastically decreased with increase in stress level. Analytical model presented a procedure for predicting the deflection of concrete beams reinforced with GFRP bars under cyclic loading. Deflection of concrete beams was computed by considering the aspects such as stiffness degradation, force equilibrium equations and effective moment of inertia. Nonlinear finite element (FE) analysis was performed on concrete beams reinforced with GFRP bars. Appropriate constitutive relationships for concrete and GFRP bars were considered in the numerical modelling. Concrete non linearity has been accounted through concrete damage plasticity model available in ABAQUS. Deflection versus number of cycles obtained experimentally for various beams was compared with the analytical and numerical predictions. It was observed that the predicted values are comparable (less than 20% difference) with the corresponding experimental observations.

Prediction of flexural behaviour of RC beams strengthened with ultra high performance fiber reinforced concrete

Murthy A, Ramachandra,Aravindan, M.,Ganesh, P. Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.3

This paper predicts the flexural behaviour of reinforced concrete (RC) beams strengthened with a precast strip of ultra-high performance fiber-reinforced concrete (UHPFRC). In the first phase, ultimate load capacity of preloaded and strengthened RC beams by UHPFRC was predicted by using various analytical models available in the literature. RC beams were preloaded under static loading approximately to 70%, 80% and 90% of ultimate load of control beams. The models such as modified Kaar and sectional analysis predicted the ultimate load in close agreement to the corresponding experimental observations. In the second phase, the famous fatigue life models such as Papakonstantinou model and Ferrier model were employed to predict the number of cycles to failure and the corresponding deflection. The models were used to predict the life of the (i) strengthened RC beams after subjecting them to different pre-loadings (70%, 80% and 90% of ultimate load) under static loading and (ii) strengthened RC beams after subjecting them to different preloading cycles under fatigue loading. In both the cases precast UHPFRC strip of 10 mm thickness is attached on the tension face. It is found that both the models predicted the number of cycles to failure and the corresponding deflection very close to the experimental values. It can be concluded that the models are found to be robust and reliable for cement based strengthening systems also. Further, the Wang model which is based on Palmgren-Miner's rule is employed to predict the no. of cycles to failure and it is found that the predicted values are in very good agreement with the corresponding experimental observations.