Tensile and fracture characterization using a simplified digital image correlation test set-up

Abhishek Kumar,S. Vishnuvardhan,A. Rama Chandra Murthy,G. Raghava 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.4

Digital image correlation (DIC) is now a popular and extensively used full-field metrology technique. In general, DIC is performed by using a turnkey solution offered by various manufacturers of DIC. In this paper, a simple and economical set-up for DIC is proposed which uses easily accessible digital single-lens reflex (DSLR) camera rather than industrial couple-charged device (CCD) cameras. The paper gives a description of aspects of carrying a DIC experiment which includes experimental set-up, specimen preparation, image acquisition and analysis. The details provided here will be helpful to carry DIC experiments without specialized DIC testing rig. To validate the responses obtained from proposed DIC set-up, tension and fatigue tests on specimens made of IS 2062 Gr. E300 steel are determined. Tensile parameters for a flat specimen and stress intensity factor for an eccentrically-loaded single edge notch tension specimen are evaluated from results of DIC experiment. Results obtained from proposed DIC experiments are compared with those obtained from conventional methods and are found to be in close agreement. It is also noted that the high resolution of DSLR allows the use of proposed approach for fracture characterization which could not be carried out with a typical turnkey DIC solution employing a camera of 2MP resolution.

Studies on the effect of thermal shock on crack resistance of 20MnMoNi55 steel using compact tension specimens

Thamaraiselvi, K.,Vishnuvardhan, S. Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.9

One of the major factors affecting the life span of a Reactor Pressure Vessel (RPV) is the Pressurised Thermal Shock (PTS). PTS is a thermo-mechanical load on the RPV wall due to steep temperature gradients and structural load created by internal pressure of the fluid within the RPV. Safe operating life of a nuclear power plant is ensured by carrying out fracture analysis of the RPV against thermal shock. Carrying out fracture tests on RPV/large scale components is not always feasible. Hence, studies on laboratory level specimens are necessary to validate and supplement the prototype results. This paper aims to study the fracture behaviour of standard Compact Tension [C(T)] specimens, made of RPV steel 20MnMoNi55, subjected to thermal shock through experimental and numerical investigations. Fracture tests have been carried out on the C(T) specimens subjected to thermal transient load and tensile load to quantify the effect of thermal shock. Crack resistance curves are obtained from the fracture tests as per ASTM E1820 and compared with those obtained numerically using XFEM and a good agreement was found. A quantitative study on the crack tip plastic zone, computed using cohesive segment approach, from the numerical analyses justified the experimental crack initiation toughness.

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%.

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.

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.

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.

Preparation, Characterization and Low Frequency a.c. Conduction of Polypyrrole-Lead Titanate Composites

Basavaraja, C.,Choi, Young-Min,Park, Hyun-Tae,Huh, Do-Sung,Lee, Jae-Wook,Revanasiddappa, M.,Raghavendra, S.C.,Khasim, S.,Vishnuvardhan, T.K. Korean Chemical Society 2007 Bulletin of the Korean Chemical Society Vol.28 No.7

Conducting Polypyrrole-lead titanate (PPy/PbTiO3) composites have been prepared by in situ deposition technique by placing different wt.% of fine grade powder of PbTiO3 (10, 20, 30, 40, and 50%) during polymerization of pyrrole. The composites formed were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), and these data indicate that PbTiO3 particles are dominating with an increase in crystallinity as well as thermal stability of the composites. The results on the low frequency dielectric studies which are obtained in the form of pressed pellet state are interpreted in terms of Maxwell Wagner polarization, which are responsible for the dielectric relaxation mechanism and frequency dependence of conductivity.

Preparation, Characterization and Low Frequency a.c. Conduction of Polypyrrole-Lead Titanate Composites

바사바,Young Min Choi,Hyun Tae Park,Do Sung Huh*,이재욱,M. Revanasiddappa,S. C. Raghavendra,S. Khasim,T. K. Vishnuvardhan 대한화학회 2007 Bulletin of the Korean Chemical Society Vol.28 No.7

Conducting Polypyrrole-lead titanate (PPy/?PbTiO3) composites have been prepared by in situ deposition technique by placing different wt.% of fine grade powder of PbTiO3 (10, 20, 30, 40, and 50%) during polymerization of pyrrole. The composites formed were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), and these data indicate that PbTiO3 particles are dominating with an increase in crystallinity as well as thermal stability of the composites. The results on the low frequency dielectric studies which are obtained in the form of pressed pellet state are interpreted in terms of Maxwell Wagner polarization, which are responsible for the dielectric relaxation mechanism and frequency dependence of conductivity.