N.K. Gupta

• Doctor of Engineering
• Indian Institute of Technology Delhi

Crack initiation and fracture propagation of tunnel in three varying rock masses under different impact energies is discussed in detail. The small-scale physical models of tunnel are prepared using proper scaling laws. The numerical investigation of the physical model is performed under laboratory conditions, and then, the experimental and numerica...

The contribution of underground pipelines in the present time is imperative. However, in recent years, they have become a target to explosives and terrorist attacks. So, its assessment against blast loading has become very crucial. The present work is focused on the blast resistant design of pipelines. In this study, CEL (Combined Eulerian–Lagrangi...

The study is focused to investigate the behaviour of reinforced concrete slabs under low velocity impact loads. The experiment was performed on conventional reinforced concrete slab of size 1200 × 1200 mm with a thickness of 50 mm with reinforcement ratio of 0.23%. The slab was impacted under an impacted energy of 741.02 J through the hemispherical...

The threat to underground structures has emerged as a vital issue and attracts the attention of researchers worldwide. Underground tunnels prove to be an essential mode of transportation for sustainable development. Urban tunnels are primarily located in the upper few kilometers in the ground. Therefore, most of these urban tunnels are situated in...

Understanding of energy dissipation process of the selected material for a crashworthy structure is essential for its safety and reliability. Critical stress analysis for notched components of the structure is important to determine stress concentration factor. Commonly used mild steels are the primary choice of design engineers as the structural m...

Protecting occupants or payloads in crashes and blasts is of utmost importance in both moving and immobile structures. One way of achieving this is by using a sacrificial energy absorber. Composite tubes have been studied as potential energy absorbers due to their ability to fail progressively under axial compression. In this study, the energy abso...

Cylindrical pressure vessels constructed using filament winding technique are a good example of the advantages that fibre-reinforced composite materials offer over common structural materials on a unit weight basis. Their high specific properties of composite materials over metals can reduce the weight of pressure vessels with a high potential for...

For the successful development of a structure, understanding of mechanical behaviour of the selected material is an important issue to prevent damage or accidents. Mechanics of the material failure depends on its chemical composition, heat treatment, grain size, strain rate, type of loadings etc. Apart from material properties, the performance of t...

Paper presents numerical models based on detailed characterization of various uncoupled damage models in a finite element analysis (FEA) setup to assess large deformations and observed ductile fracture failure modes of fully clamped circular plates as well as transversely stiffened circular plates in cross stiffened configurations under uniform imp...

Tubular structures are the base of rational design with the improvement in high-performance and advanced structural applications. One of the biggest challenges of these parts is their complex/superior architectural geometry, therefore, knowledge is required to understand the features of each joint. In recent times, conventional metal tubular joints...

Natural fiber reinforced polymer composites are being widely used in aerospace and automotive applications. These are due to their low density and cost, better biodegradability and higher specific strength and modulus, which replace E-glass fiber reinforced polymer composites. Moreover, quasi-isotropic properties can be achieved with randomly orien...

This document reviews the recent research work on the mechanical properties of 6xxx series aluminium alloys at strain rates in the range of ∼ 10⁻⁵ – 10⁵ s⁻¹, and crashworthiness of tubes made of 6xxx series aluminium alloys under dynamic loadings (mass impact). This review endeavours to accentuate the material response (fracture toughness and dynam...

The contribution of subsurface tunnels in the present time is imperative. However, in the past few decades they have become a target to explosives and terrorist attacks. Considering the strategic importance and susceptibility of tunnels in case of internal explosion, the blast mitigating design has become very critical. In this work, a novel concep...

This study evaluates literature on mechanical response of 6xxx series aluminium alloys under dynamic loads (projectile impacts). It is mainly concerned with the ballistic behaviour of 6xxx series Al alloys fabricated through different sample processing routes involving varied heat treatments at elevated, sub-zero and cryogenic temperatures. Failure...

The production of ultrafine grained (UFG) Al alloys with improved tensile and fracture strength as compared to its bulk alloys has attracted lot of attention in aerospace and automotive industries due to the possibility of realizing very high specific strength with significant weight reduction of structural components fabricated by using these UFG...

This paper presents the effect of impact load and weathering of surrounding rockmass on the deformation behavior of urban underground structures. The FEM based numerical simulation is carried out by varying overburden depths, impact energy, and rock weathering grade. Based on this study, it is suggested that subsidence in tunnel under dynamic loadi...

Paper presents numerical models based on a detailed characterization of various uncoupled damage models in a finite element analysis (FEA) setup to assess their results and comparative performance in simulation of structural response and failure of clamped circular plates subjected to a wide range of uniform impulse loading. The significance of num...

The ballistic performance of thin concrete slabs is influenced by impact velocity, slab thickness, steel rebar content, bullet mass and prestress level. We aim to quantitatively identify which of the mentioned input variables play a major role in the ballistic response of concrete slabs, such as ballistic limit, residual velocity, and ejected concr...

Glass-epoxy Composite materials are extensively used in the complex engineering applications due to their better strength to weight ratio, corrosion and fatigue resistant properties. However, to achieve an efficient material for its adequate use, its behaviour at various strain rates is to be well understood, which could be best achieved by carryin...

This chapter discusses the impact studies of hybrid nanocomposites. Glass fibers are used as primary reinforcement, and epoxy is used as matrix and is dispersed with nanofillers which act as secondary reinforcement. Nanoclay is varied from 1 to 5 weight percentage of epoxy. The nanocomposite laminates are prepared by hand lay-up and compression mol...

The paper presents Finite Element Analysis (FEA) and simulations of large deformations and observed ductile fracture failure modes of clamped circular plates subjected to uniform impulsive loads using phenomenological failure models for damage initiation and progression. The proposed numerical setup is founded on a well-defined model of the constit...

An evaluation of mitigation strategies of underground tunnels against explosions is important to the society. Therefore, a small scale tunnel was modeled against blast loading using finite element software ABAQUS. The inelastic behavior of concrete and steel bar has been incorporated through concrete damage plasticity model and Johnson-cook models...

The manuscript is focused on the prediction of superior layer configuration on titanium and aluminium plates through numerical investigations using ABAQUS/Explicit finite element software. The target plate of titanium Ti-6Al-4V (Ti) and aluminium Al 2024-T3 (Al) were studied against 7.62 mm diameter soft lead core projectiles. The Johnson-Cook (JC)...

The paper reviews some salient research works on load characterization and structural response of thin walled metallic structures subjected to Underwater Explosion (UNDEX) highlighting the critical gaps and scope for further research work. The key aspects of an UNDEX phenomenon including Fluid Structure Interaction (FSI) and loading mechanisms on a...

This study is focused on the low-velocity impact response of 3D plate-lattices fabricated via stereolithography additive manufacturing (AM). Elementary (SC, BCC and FCC) and hybrid (SC-BCC, SC-FCC and SC-BCC-FCC) configurations were tested and the effects of impact energy, relative density, plate-thickness, multiple impacts and impact angle on the...

The performance of a structure depends on its material characteristics under various conditions of loadings, strain rate, and temperature, and therefore, it is necessary to understand these characteristics properly for the safe and reliable design of structures. In this paper, the flow stress behavior of AZ81 magnesium alloy is determined under ten...

Underground structures are divided into fully buried structure and partially buried structures which can be any structure of diverse shapes such as, shelters, basement structures, underground mall facilities, underground parking spaces, silos, storage facilities, retention basins, shafts, tunnels, pipes, underground railway, metro stations, to ment...

The ballistic resistance of a single layer alumina target has been explored numerically against eccentric ballistic impact. The alumina 99.5 was used as a single layer target that has been impacted by a steel 4340 ogival nosed projectile. The ogival projectile has a shank diameter of 10.9 mm, total length of 52.6 mm and 30 gram mass. The thickness...

The ballistic behaviour of a bi-layer ceramic-metal target against steel projectile with varying layer thicknesses has been investigated using a three-dimensional finite element model. The bi-layer target was made of alumina 99.5 % ceramic front layer and aluminium 2024-T3 metallic back layer with an areal dimension of 100×100 mm and the thickness...

The strain rate dependence of glass fiber reinforced polymer (GFRP) and carbon fiber reinforced polymer (CFRP) composites was experimentally characterized over the range of strain rates (1.6 × 10⁻³–542 s⁻¹) by performing a series of tensile tests on (0/90), (0/90/30/−60), (0/90/45/−45) and (30/−60/60/−30) laminate specimens. The Digital Image Corre...

Underground structures are proven to be one of the vital part of modern transportation system. With the growing importance of tunnels for mobility, they are being subjected to threats of severe terrorist activities. Urban tunnels are mainly located in the upper few kilometers and are highly susceptible to deformations even at very low strain rates....

The ballistic experiments have been carried out on alumina 99.5% bare ceramic plates for studying the initiation and propagation of brittle fracture and the resistance offered by the target. The ceramic tiles of size, 100 mm × 100 mm, and thickness, 5 mm, were impacted by the ogival nosed hardened steel 4340 projectiles of diameter 10.9 mm and mass...

Sandwich composites with polymeric open-celled foams or honeycomb structures as core materials have been used widely in low-weight naval, aerospace and structural applications in the past. One major drawback of such foams is skin-core debonding. To overcome this, core materials with the same matrix as the skin are studied in this paper. Sandwich co...

The lightweight metallic materials such as aluminium alloys are increasingly important for crashworthy structures due to high strength to weight ratio. These structures withstand different kinds of loads during service. Therefore, the aim of the present investigation is to study the tensile, compressive and flexural behaviours of the aluminum alloy...

An experimental investigation on the deformation behaviors of the aluminum alloy Al5052-H32 is presented under tensile, compressive, and flexure loads at different strain rates and temperatures. Quasi-static tests on tension and compression are performed using an electromechanical universal testing machine in the strain rate range 0.0001–0.1 s−1 at...

The work presents experimental and numerical results on dynamic fracture of PMMA plates subjected to impact loading. The experimental tests were conducted using steel cylinder-shaped projectile accelerated using a gas gun. In order to evaluate performance of the tested specimens, residual impactor velocity was assessed using high-speed photography...

The ballistic resistance and energy absorption characteristics of the thin hemispherical shells were evaluated against ogive and blunt nosed projectile impact with varying span and configuration of the shell. The span diameter of the 1100-H12 aluminium shell was varied as 68, 100, 150 and 200 mm whereas the configuration of the shell was varied as...

With the increase in population and the shortage of land above ground, underground exploration has become an important part of modern infrastructure. Today's civil infrastructure depends largely on underground structures. The most important of these applications are the metro tunnels. Tunnels, therefore, play a very important part in the developmen...

The efficacy of woven jute‐polyester (JP) composite tubes as structural energy‐absorbing countermeasures has been explored in the current study. In this connection, the behaviors of 3‐ply and 4‐ply JP composite tubes of square and double‐hat shaped sections subjected to axial quasi‐static and impact loads are considered, and compared with 4‐ply gla...

The ballistic resistance of 20 mm thick Armox 500T steel and 7075-T651 aluminium plates has been studied against 12.7 API projectiles through experiments and finite element simulations. The Jonson-Cook constitutive model calibrated by the authors was used in order to predict the behaviour of target. The simulations were carried out using ABAQUS fin...

For crashworthiness applications, hollow composite tubes have been proposed and studied as impact-bearing members in earlier studies to replace metal tubes and beams which resisted impact by bending. This study focusses on the effect of the addition of hollow glass microballoons (GMB) in composite tubes for compressive loading. Epoxy containing 0 t...

Sandwich panels with light-weight cores are being used widely in aerospace, marine, and other fields where weight-saving is of high priority. The main disadvantage of using conventional cores such as polymeric foams and honeycomb structures is debonding between the core and the skin. To overcome this, syntactic foams have been used as the core mate...

Underground structures are proving to be the smart structures by not only resolving various problems associated with storage and transportation but also helpful in maintaining traffic due to scarcity of land. Due to heterogeneous behavior of rock-mass, urban tunnels are highly susceptible to failure. Massive deformation in the lining is encountered...

Embedding shape memory alloys (SMAs) in composites is a promising method resistance against impact loading.In the present paper, an attempt is made to quantify the improvement in damage mitigation properties of FRP (fibre reinforced plastic)composites by embedding SMA.Numerical modelling of low velocity impact was carried out topredict the delamina...

A numerical investigation has been carried out for studying the fracture mechanics and the ballistic response of ceramic target. The ceramic considered was Alumina 95, the backing plate was Aluminium alloy 2024-T3 and the projectile was made up of Steel 4340. The diameter to length ratio of conical and blunt nosed projectiles has been varied as 0.2...

A study is based on the �nite element investigation of the response of Mild Steel (MS) and Armox 500T Steel (AS) target subjected to macro and micro size impactor. The simulations were carried out on target against pen- etrator with varying masses, sizes, shapes and di�erent in nature (rigid and deformable projectiles) using ABAQUS/Explicit. The ma...

Numerical investigation has been carried out on 2024 aluminium plate targets against 12.7 mm diameter hardened steel projectiles. The ballistic resistance of 1.27 mm thick target was studied against a spherical ball as well as the hemispherical and blunt nosed cylindrical projectiles. The simulations were performed on ABAQUS/Explicit finite element...

The effects of molybdenum disulfide (MoS2) on thermal expansion and mechanical properties of epoxy composites were investigated. MoS2 nanosheets were exfoliated by ultra-sonication and reinforced into epoxy as nanofiller by mechanical stirring. Transmission electron microscopy observations demonstrated that MoS2 exhibited better dispersion in epoxy...

The use of glass microballoon (GMB) — epoxy syntactic foams as a sandwich core material is studied. The skins and foam core are fabricated and joined instantaneously unlike the procedures followed in the previous studies. Each successive layer of the sandwich is fabricated when the previous layer is in a semi-gelled state. These sandwich samples ar...

In the present study, the calibrated Johnson-Cook material parameters proposed in our previous studies [1] has been validated through the simulations on 7075-T651 aluminium against various size, shape and mass of projectiles. Three-dimensional numerical simulations of the problem were carried out using finite element code ABAQUS. First phase, the b...

Empty hat sections, single and double, made of steel are frequently encountered in automotive body structural components such as front rails, B-Pillar, and rockers of unitized-body cars. These closed-section thin-walled components can play a significant role in terms of impact energy absorption during collisions thereby protecting occupants of vehi...

In the present work, two parameter Weibull distribution is used to measure the variability of the tensile strength of cross ply glass/epoxy, carbon/epoxy and hybrid (glass-carbon/epoxy) composites for different strain rates from 0.0083 to 542 s⁻¹. The Weibull parameters (shape and scale parameters) are obtained using linear curve fit method. The sh...

Response of circular plates under transverse impulsive load time history using a transient dynamic finite element analysis methodology employing progressive degradation has been presented. Experimental results by Nurick et al. for the prediction of onset of thinning and subsequent tearing at the boundary of clamped circular plates subjected to unif...

A coarse grained microstructure of Al6061 alloy was processed by Equal Channel Angular Pressing (ECAP) via route C (rotating the sample to 180⁰ between each pass) at room temperature. The samples were processed up to four passes through a die having channel angle of 90⁰. Mechanical behaviour was studied by the tensile testing of the specimens in th...

The present research work is to study the effect of low and medium strain rates on tensile behavior of epoxy and glass/epoxy composites. The digital image correlation (DIC) technique is employed for evaluating full-field strain contour plots using high-speed CMOS camera, which captures about 100,000 frames per second. Stress-strain measurements are...

Friction stir processing (FSP) is a prominent technique of severe plastic deformation (SPD) that can provide modification and control of microstructure to enhance the mechanical properties of Al alloys, which can be used in aerospace and aircraft applications. The present work focuses on the evaluation of mechanical and impact behavior of Al 2024 a...

This paper presents the experimental and numerical investigations of permanent large deformations on 4 mm thick Mild Steel (MS) plate due to impact-perforation of rigid spherical projectile. These investigations are made for an impact velocity range of 448 -100 m/s. AUTODYN software is used in carrying out the numerical studies. It is observed that...

In general, many numerical techniques are in place for the study of buckling and post-buckling responses of the composite structures, but these are computationally expensive. Relatively few equivalent analytical techniques are available, especially for evaluation of post-buckling responses. In this paper an analytical approach is presented for the...

This paper presents the numerical investigations of impact-perforation phenomena of a 4 mm thick mild steel plate caused by the impact of a rigid spherical projectile. AUTODYN software is used in carrying out the numerical studies. The projectile diameter is of 10 mm and the plate is of circular disc of 50 mm radius. The phenomena are described in...

The present study is devoted to the boundary value problem of coupled thermoelastoplasticity. The temperature depended yield criterion and Duhamel Neumann constitutive equation was used. The material subjected to uneven heat treatment under plane strain frameworks was considered. The new analytical solution of the problem of uneven heat treatment o...

Fundamentals of mathematical modeling of surface growth process are under consideration. Mathematical models of 3D and 2D solids that grow owing to processes of continuous influx of new elements (surfaces and fibers) are proposed. Complete systems of equations and boundary value problems are obtained. A method for solving these boundary value probl...

This study investigates energy absorption of thermally loaded composites and nanocomposites laminates during impact loading. The laminates are prepared by glass fiber/epoxy with and without nano particles in the matrix system. Nano clay and carbon nano tube are used as filliers in the epoxy matrix. The composites specimens are subjected to impact l...

Due to increase in demand for electricity usage all around the GCC there has been emphasizing on the usage of alternative sources of energy i.e. using solar, wind and ocean etc. on the other side accurate prediction of power delivery is crucial for estimating the performance of PV and return on investment. In this paper, a case study was presented...

In the present study, an attempt is made to understand the behavior and pattern of tunnel damage subjected to the static and dynamic loading conditions, through the simulation of natural as well as artificial stress states such as loads due to overburden, building, earthquake and blast. The analysis is carried out by using FEM based numerical tool...

In the present world, need for underground structures is grown many folds due to increasing population, advancement of public infrastructure, and scarcity of land,. Underground facilities are an integral part of the infrastructure of modern society and are used for a wide range of applications. Also, they provide attractive alternatives for storage...

Nuclear energy presently contributes more than 17% of global energy demand. In order to avoid the nuclear disasters, safety concern in nuclear structures is always of high concern. In the present study, response analysis of the outer containment of a typical Nuclear Power Plant (NPP) has been carried out against aircraft impact using finite element...

The present study investigates the ballistic performance and energy absorption in plastic deformation due to work done in radial, circumferential, axial and tangential directions in 1. mm thick aluminum 1100-H12 targets. The targets were impacted by single nosed; ogival, blunt and double nosed; ogival-blunt and blunt-blunt, EN-24 Steel projectiles...

In the present work, an analytical model is proposed to obtain the damage area of the composite laminates at below ballistic limit velocities. The model is based on the fact that total kinetic energy of the projectile is absorbed by different energy absorbing mechanisms taking place in laminates during impact. Depending upon the projectile velocity...

The material sensitivity of mild steel and Armox 500T steel has been studied under varying stress-triaxility, strain rate and temperature. The effect of stress triaxiality was studied on notched cylindrical specimens of initial notch radii 0.2-10 mm. The strain rate sensitivity of the material was studied on smooth cylindrical specimens at strain r...

The present paper deals with the experimental and computational analysis of the deformation behaviour of the metallic thin walled aluminium shells having dome-cone combined geometry. The specimens were tested on a universal testing machine INSTRON under axial compression to identify their modes of collapse and to study the associated energy absorpt...

The flow and fracture behavior of 7075-T651 aluminum alloy has been studied under different stress-states, strain rate and temperature in order to explore the characteristics of the material under extreme situations developed in aerospace and armor structures. Influence of stress state was studied by performing quasi-static tension tests on notched...

The present research work discusses the effect of strain rate and clay on the dynamic tensile behavior of glass/epoxy composites. Nanocomposites of different clay content in terms of 1.5, 3 and 5 wt% are chosen for the study. Characterization of the nanoclay dispersed in epoxy system is investigated by X-ray Diffraction (XRD) and Fourier Transform...

The ballistic performance of monolithic and multi-layered in contact and spaced mild steel target plates has been studied at normal and oblique impact against 7.62 AP projectiles with an objective to ascertain the effect of angle of obliquity. Numerical simulations have been performed on ABAQUS/Explicit finite element code and typical results obtai...

Conventionally, shape memory programming involves deforming the material at a temperature higher than the glass transition (Tg) and subsequently cooling the material below Tg while holding the deformation to fix the temporary shape. Alternatively materials with reversible plasticity shape memory (RPSM) property can be programmed at temperatures wel...

The ballistic resistance of mild steel plates has been studied against 7.62 AP projectiles through numerical simulations using ABAQUS/Explicit commercial finite element package. The projectiles were impacted on 4.7, 6, 10, 12, 16, 20 and 25 mm thick target plates at varying incidence angles. The material parameters proposed by authors for the Johns...

Underground facilities used for a wide range of civil and military applications such as transportation, storage, and water and sewage conveyance etc. to name a few. These structures can get damaged by the constant overburden loads and litho-static pressure of high rise buildings and apartments. Load - deformation assessment of these tunnels is impo...

The front body structure of an automobile should have sufficient stiffness and strength to protect the occupants during a high speed frontal collision; simultaneously, it should not induce unduly high impact loads during a low speed pedestrian collision. The above requirements are obviously in conflict with each other. Traditionally, the design sol...

Numerical investigations were carried out on 1.27, 3.18, 6.35, 12.7and 19.05 mm thick 2024-O aluminum target against blunt nose steel projectiles of 12.7 mm diameter and 37.7 gram mass. Three-dimensional numerical simulations of the problem are carried out using finite element code ABAQUS. The ABAQUS/Explicit finite element code in conjunction with...

Numerical investigations were carried out on 1.27mm thick 2024-O aluminum plates against hemi spherically tipped nose, steel projectiles, of 12.7mm diameter and 37.7 gram mass. Three-dimensional numerical simulations of the problem were carried out using finite element code ABAQUS. The ABAQUS/Explicit finite element code, in conjunction with Johnso...

The ballistic resistance of 12 mm thick mild steel plates has been studied against 7.62 API projectiles through numerical simulations carried out using ABAQUS/Explicit finite element code. The incidence angle was varied as 0°, 15°, 30°, 45°, 57° and 59°. The material parameters for the JC model proposed by the Authors were employed to predict the m...

Concrete is a widely used material in the construction of strategic and important structures such as nuclear containments, bridges, storage structures and military bunkers. In the present study perforation experiments and simulations on finite element code ABAQUS/Explicit have been carried out to understand the behavior of concrete against projecti...

Glass/epoxy, carbon/epoxy and hybrid (glass-carbon/epoxy) composites are subjected to quasi-static to high strain rate (542 s⁻¹) studies to obtain the tensile strength. The two-parameter Weibull distribution is employed to measure the variability of the tensile strength of cross ply laminates. The Weibull parameters are obtained using the linear cu...