Faculty Publications
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Item Effect of filler wire strength on high strength low alloy steels(Elsevier Ltd, 2021) John, M.; Kumar, P.A.; Bhat, K.U.Fusion welding of Ti-Nb microalloyed steels often leads to softening in the heat affected zone (HAZ) due to weld thermal cycles. Apart from heat input and width of HAZ, selection of filler wire also plays an important role, to achieve the minimum strength requirement of the parent material. Steel plates with 800 MPa ultimate tensile strength were butt welded using pulsed gas metal arc welding (P-GMAW) process, with undermatching, matching and overmatching strength filler wires. Welding parameters were selected in such a way that the heat input per unit weld length is almost constant. In all the samples, microstructural features were similar in the HAZ region. Static tensile tests indicated that failure in the samples welded using undermatching filler occurred at welded region, whereas the samples welded with matching and overmatching fillers failed at HAZ region. Further fracture studies indicated that, in case of under matching filler wire samples, crack propagates along the Widmanstatten ferrite present in the weld zone, whereas in other two samples, crack initiated at coarse TiN - matrix interface in the HAZ region. This study shows that overmatching fillers are recommended to overcome strength loss due to HAZ softening. © 2021 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the scientific committee of the Global Conference on Recent Advances in Sustainable Materials 2021.Item Determination of fracture toughness and fatigue crack growth rate using circumferentially cracked round bar specimens of Al2014T651(Elsevier Masson SAS infos@masson.fr 62 rue Camille Desmoulins Issy les Moulineaux Cedex 92442, 2015) Neelakantha, V.L.; Jayaraju, T.; Naik, P.; Kumar K, D.; Rajashekhar, C.R.; Kumar, M.Fracture toughness (KIC) and fatigue crack growth rate (FCGR) are the important material properties in fracture mechanics. ASTM-E399 and ASTM-E647 are the standards for determination of KIC and FCGR of metallic materials. These standards recommend the use of compact tension (CT) or single edge notched bend (SENB) test specimens. Literature review indicates that CT or SENB specimens are complex in nature, difficult to manufacture, require typical fixtures for loading during experimentation and the test procedures using CT or SENB are time consuming and cumbersome. An alternate specimen geometry which can overcome the above said drawbacks is needed by the industry which can be used as standard test specimen geometry. This research work explains use of circumferentially cracked round bar (CCRB) specimens of high strength Al2014T651 alloy for determination of KIC and FCGR.The pre-cracked round bar specimen was loaded in tensile in a universal testing machine and pulled till failure. Using suitable stress intensity factor equations the fracture toughness can be calculated. In case of crack growth test, the pre-cracked round bar specimen is allowed to rotate under fatigue load. The ratio of length of crack propagated to the number of cycles to failure was the crack growth rate. The SEM analysis of fractured surfaces was also done.The results are comparable with the values reported in the literature obtained by using standard test specimens. There are numerous advantages of using round bar specimen in KIC and FCGR tests. It is concluded that, the methodology of determination of fracture toughness and fatigue crack growth rate using CCRB specimens is relatively simple, reliable, fast and economical. CCRB specimen may be recommended as a standard test specimen for fracture toughness as well as crack growth tests. © 2015 Elsevier Masson SAS. All rights reserved.Item Strategy for refinement of nodal densities and integration cells in EFG technique(Techno-Press, 2016) Bhavana Patel, V.S.S.; Narayan, B.K.S.; Venkataramana, K.MeshFree methods have become popular owing to the ease with which high stress gradients can be identified and node density distribution can be reformulated to accomplish faster convergence. This paper presents a strategy for nodal density refinement with strain energy as basis in Element-Free Galerkin MeshFree technique. Two popular flat plate problems are considered for the demonstration of the proposed strategies. Issue of integration errors introduced during nodal density refinement have been addressed by suggesting integration cell refinement. High stress effects around two symmetrical semi-circular notches under in-plane axial load have been addressed in the first problem. The second considers crack propagation under mode I and mode II fracture loading by the way of introducing high stress intensity through line crack. The computational efficacy of the adaptive refinement strategies proposed has been highlighted. © 2016 Techno-Press, Ltd.Item Modeling of delamination in fiber-reinforced composite using high-dimensional model representation-based cohesive zone model(Springer Verlag service@springer.de, 2019) Rao, B.; Balu, A.S.Prediction of delamination failure is challenging when the researchers try to achieve the task without overburdening the available computational resources. One of the most powerful computational models to predict the crack initiation and propagation is cohesive zone model (CZM), which has become prominent in the crack propagation studies. This paper proposes a novel CZM using high-dimensional model representation (HDMR) to capture the steady-state energy release rate (ERR) of a double-cantilever beam (DCB) under mode I loading. The finite element models are created using HDMR-based load and crack length response functions. Initially, the model is developed for 51-mm crack size DCB specimens, and the developed HDMR-based CZM is then used to predict the ERR variations of 76.2-mm crack size DCB model. Comparisons have been made between the available unidirectional composite (IM7/977-3) experimental data and the numerical results obtained from the 51-mm and 76.2-mm initial crack size DCB specimens. In order to demonstrate the efficiency of the proposed model, the results of the second-order nonlinear regression model using RSM are used for the comparison study. The results show that the proposed method is computationally efficient in capturing the delamination strength. © 2019, The Brazilian Society of Mechanical Sciences and Engineering.Item Characterisation of hydrogen assisted cracking in modified 9Cr-1Mo steel welds using acoustic emission non destructive technique(Taylor and Francis Ltd., 2021) Haneef, T.K.; Chakraborty, G.; Rejeesh, R.; Mukhopadhyay, C.K.; Albert, S.K.This study aims a systematic experimental investigation using acoustic emission (AE) non-destructive technique for online monitoring of hydrogen assisted cracking (HAC) in modified 9Cr-1Mo steel (P91 steel) welds during Gap-Bead on Plate (G-BOP) and implant tests. Welds made without preheating, with different preheating and combined pre and post heating were tested using G-BOP test. AE results of G-BOP tests have shown that time duration in which HAC active varies with temperature of preheating and combined pre and post heating. Reduction of AE activity in welds made with pre and post heating compared to those only made with preheating revealed a beneficial effect of the former in reducing HAC. In the case of implant tests, crack initiation and propagation are identified for different applied loads from the AE analysis. An attempt has been made to compare HAC during G-BOP tests and implant tests using AE frequency analysis. The dominant frequency of AE signals characteristic of HAC has been identified. This study shows the potential of using AE frequency analysis for online monitoring of hydrogen assisted cracking (HAC) in welds. © 2021 Informa UK Limited, trading as Taylor & Francis Group.Item Improved Fracture Toughness and Crack Arrest Ability of Graphene–Alumina Nanocomposite(Springer, 2021) Akhil Raj, V.R.; Hadagalli, K.; Jana, P.; Mandal, S.In this work, high fracture toughness graphene–alumina composite was developed through a novel chemical method using boehmite and graphene, which is followed by extrusion and consolidation. The mixed precursors were consolidated by sintering at 1550 °C in a nitrogen atmosphere. The plate-like structures of boehmite form ?-alumina; meanwhile, graphene particles at the grain boundaries hinder the growth of alumina grains. The graphene reinforcement was bonded to ?-alumina matrix by van der Waals forces. The XRD pattern reveals the presence of graphene with a plane (002) along with ?-alumina. Properties such as fracture toughness (5.6 ± 0.01 MPa m0.5), Vickers hardness (1872 ± 25 kgf/mm2) and true density (3.8 g/cm3) were achieved in 0.5 wt.% graphene–alumina composite when compared to ?-alumina with fracture toughness (5.3 ± 0.1 MPa m0.5), Vickers hardness (1984 ± 28 kgf/mm2) and true density (3.91 g/cm3). The bridging and deviation of cracks in 0.5 wt.% graphene–alumina composite are attributed to the anchoring and dissipation of energy during crack growth, which enhances the fracture toughness, whereas ?-alumina exhibits failure caused by linear crack propagation. Meanwhile, the slight decrease in Vickers hardness and true density of 0.5 wt.% graphene–alumina composite is due to the tribological and low-density properties of graphene. The obtained properties of composite could be suitable in high-temperature, wear-resistant applications such as crucibles, bearings, etc. © 2021, ASM International.Item Effect of similar and dissimilar interface layers on delamination in hybrid plain woven glass/carbon epoxy laminated composite double cantilever beam under Mode-I loading(Elsevier B.V., 2021) Suman, M.L.J.; Murigendrappa, S.M.; Kattimani, S.Effect of similar and dissimilar interface layers on delamination in hybrid plain woven glass/carbon epoxy laminated composite double cantilever beam under Mode-I loading has been investigated experimentally and analytically. Glass-glass, glass-carbon interface layers in three different configurations of hybrid plain woven glass/carbon epoxy laminated composites were fabricated. Valvo's mode partition method from the literature is utilised to compute individual modal contributions and total fracture toughness of the hybrid composite laminates. Mode-I fracture toughness contribution is compared with standard data reduction schemes of ASTM D5528-13. The comparison reveals that Valvo's mode partition method considers mode-mixity and provides conservative results. The Valvo's mode partition does not require any correction factors including curve fitting, it provides a straightforward method for evaluating fracture toughness as they are based on the mechanics of composite materials. The comparison of R-curves of hybrid configurations reveal that the insertion of carbon with glass at the interface of symmetric hybrid configuration enhances initial fracture toughness and stabilises whereas, with the change in layer configuration of anyone arm of the double-cantilever beam, the crack growth trend is also affected irrespective of same interface layers. The fractography analysis of delamination surfaces reveals that crack propagation through a resin-rich layer creates a rougher fracture surface resulting in higher energy dissipation as compared to crack propagation through resin-rich pockets. © 2021 Elsevier LtdItem Fracture mechanics-based meshless method for crack propagation in concrete structures(Elsevier Ltd, 2025) Paul, K.; Balu, A.S.; BabuNarayan, K.S.Concrete is one of the most versatile construction materials, characterized by its high compressive strength and durability. It exhibits complex fracture behaviours in the non-linear region of the fracture process zone (FPZ) near crack tip, where micro-cracking, crack coalescence, and eventual macro-crack propagation occurs. Accurately predicting crack initiation and propagation in concrete structures is essential for ensuring their safety and performance. Traditional methods like finite element analysis (FEM) face challenges in capturing crack propagation due to the need for mesh refinement, which can be computationally expensive. This study aims to address this limitation by introducing the Element-Free Galerkin (EFG) method, which offers a more efficient approach for modelling crack behaviour in concrete beams. The maximum stress theory was used as the fracture criterion and the cohesive zone model (CZM) with a bilinear softening curve is employed to simulate the FPZ. Numerical examples of simply supported beam and cantilever beams with varying pre-notch positions and loadings were analysed. The results show that under axial and point loading, the stress intensity factor increases with crack length until unstable crack growth, leading to failure. The EFG method is found to be more accurate than FEM, particularly in regions with higher deformations, with a 13 % variation due to remeshing in FEM. Under point loading, EFG predicted deformation patterns with a 6 % variation in maximum deflection. This study demonstrates that the EFG-based model effectively predicts catastrophic failures, offering a computationally efficient solution for real-world concrete structures with pre-existing cracks or defects. © 2025 Institution of Structural EngineersItem Application of Taguchi's optimization techniques for enhancing the fracture characteristics and brittleness of self-compacting alkali-activated concrete(Elsevier B.V., 2025) Kuttagola, I.; Prashanth, M.H.Alkali-activated concrete has emerged as a promising material for energy-efficient construction, offering a technically viable and eco-efficient alternative that aligns with global sustainability goals. This study explores optimizing fracture properties in self-compacting alkali-activated concrete (SAAC) through controlled variations in maximum aggregate size (dmax) and fly ash. A systematic approach incorporating Taguchi's design of experiments (DOE) and ANOVA analysis was employed to identify optimal mix proportions that enhance fracture performance and ductility. The study employed the Weight-Compensated Work of Fracture Method (WWFM) based on curtailment of the tail of the P–? curve to determine the size-independent fracture energy (GF), enhancing the reliability of SAAC in structural applications. Additionally, the Two-Parameter Fracture Model (TPFM) evaluated the critical stress intensity factor (KsIc) and critical crack tip opening displacement (CTODc), while the MATLAB-based Box-Counting Dimension Method (BCDM) assessed the fractal dimension (D). The findings revealed a higher fracture performance with 0 % fly ash and 16 mm dmax (GF of 206.3 N/m and KsIc of 1.91 MPa?m), suitable for structural applications requiring maximum fracture energy and toughness. The study further tailored a higher ductility mix with 50 % fly ash and 16 mm dmax (CTODc of 0.032 mm and D of 1.144) offering a balanced solution for non-structural applications, providing sufficient strength with enhanced ductility. The closed-form predictive design (CPD) model enables the prediction of ft and KIc under a specified maximum fracture load, offering engineers a practical tool to optimize SAAC formulations by adjusting aggregate sizes and binder proportions for specific project needs. Regression models aligned strongly with experimental and existing literature results, affirming the reliability of predictive performance for future SAAC mix designs. © 2025 Elsevier LtdItem Effects of specimen thickness and compositions on the fracture toughness investigations of Al7075-SiC/Al2O3 hybrid composites utilizing Taguchi optimization and FEA analysis(Springer-Verlag Italia s.r.l., 2025) Bharath, P.B.; Shivakumar, S.P.; Rajesh, A.M.; Prabhuswamy, G.S.; Doddamani, S.The primary objective of this study is to investigate the influence of process parameters on the fracture toughness of aluminium–silicon carbide/alumina particulate composites. The composite is fabricated using the stir-casting method, and the study aims to explore the relationship between process parameters and the resulting mechanical properties of the material. The research seeks to answer how varying process parameters such as reinforcement composition, specimen thickness, and crack length-to-width ratio affect the fracture toughness of aluminium-based hybrid composites. A comprehensive experimental approach is employed, utilizing compact tension specimens of varying thicknesses, compositions, and crack length-to-width ratios to assess fracture toughness. Taguchi's optimization techniques, including the design of experiments with an L9 orthogonal array, analysis of variance (ANOVA), and regression analysis, are used to analyze the specified parameters. The three key factors and their respective levels considered in the study are reinforcement composition (3, 6, and 9 wt%), specimen thickness (10, 12, and 15 mm), and crack length-to-width ratio (0.45, 0.47, and 0.50). The experimental results indicate that increasing the composition of reinforcements beyond 6 wt% and certain crack length-to-width ratios decreases the fracture toughness of the hybrid composites. Through Taguchi's analysis, it is revealed that for a crack length-to-width ratio of 0.45, specimens with a thickness of 12 mm and 6 wt% reinforcements exhibit the highest fracture toughness. Further analysis underscores that the crack length-to-width ratio (a/W ratio) significantly affects fracture toughness (94%), followed by reinforcement composition and specimen thickness. The study provides valuable insights into optimizing the fracture toughness of aluminium–silicon carbide/alumina particulate composites. The identified optimized parameters 12 mm specimen thickness, 6 wt% reinforcement, and a 0.45 crack length-to-width ratio lead to enhanced fracture toughness. Additionally, finite element simulations support the experimental findings, with less than a 12% error, confirming the robustness of the optimized conditions. This research contributes to a deeper understanding of the interplay between process parameters and mechanical properties in particulate composite materials. © The Author(s), under exclusive licence to Springer-Verlag France SAS, part of Springer Nature 2025.