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The objective of the present study is to develop cost effective thermoplastic hybrid laminate using Dyneema® HB50 and Tensylon®HSBD 30A through structural hybridization method. Laminates having 20 mm thickness were fabricated and subjected to 7.62 × 39 mm mild steel core projectile with an impact velocity of 730 ± 10 ms−1. Parameters such as energy absorption, back face deformation and rate of back face deformation were measured as a function of hybridization ratio. It was observed that hybrid laminate with 50:50 ratio (w/w) of Tensylon® and Dyneema® with Tensylon® as front face showed 200% more energy absorption when compared to 100% Tensylon® laminate and showed equal energy absorption as that of expensive 100% Dyneema® laminate. Moreover, hybrid laminate with TD50:50 ratio showed 40% lower in terms of final back face deformation than Dyneema® laminate. Rate of back face deformation was also found to be slow for hybrid laminate as compared to Dyneema® laminate. Dynamic mechanical analysis showed that, Tensylon® laminate has got higher stiffness and lower damping factor than Dyneema® and hybrid laminates. The interface between Tensylon® and Dyneema® layers was found to be separating during the penetration process due to the poor interfacial bonding. Failure behaviour of laminates for different hybridization ratios were studied by sectioning the impacted laminates. It was observed that, the Tensylon® laminate has undergone shear cutting of fibers as major failure mode whereas the hybrid laminate showed shear cutting followed by tensile stretching, fiber pull out and delamination. These inputs are highly useful for body armour applications to design cost effective armour with enhanced performance.

The objective of this research is to investigate the dynamic flow behavior of Ti-5553 alloy at elevated temperatures using Crystal plasticity and Johnson-Cook (J-C) models. Compression tests were carried out at different temperatures of 25 °C, 200 °C, 400 °C and 600 °C at various strain rates of 0.01–2000/s. A physically-based Modified Crystal plasticity model was then adopted to describe the flow behavior in the Work hardening (WH)-Dynamic recovery (DRV) regime in conjunction with Arrhenius equation. The model well established the flow behavior of the titanium alloy, mainly the strain hardening and thermal softening effects. Microstructural study has also been undertaken. The mechanisms of dynamic recrystallization and adiabatic shear bands are discussed. Numerical simulations were carried out using the ABAQUS/Explicit code. The developed crystal plasticity model was implemented in ABAQUS using user sub-routine UMAT.

To investigate the dynamic mechanical behavior of Ti-10-2-3 alloy, the material was subjected to quasi static and dynamic compression testing. The results confirm that material exhibits strain rate sensitivity at low and high strain rates. The deformation mechanisms are elucidated by thermal activation theory. Voyiadjis-Abed (V-A) model is proposed to establish the thermo mechanical response of Ti-10-2-3 alloy. The developed model is compared with Johnson-Cook (J-C) model at different strain rates and temperatures. The V-A model well established the quasi-static and dynamic behavior of the Ti-10-2-3 alloy, mainly the effects of strain hardening and thermal softening. This model is embedded in ABAQUS/Explicit code in the form of a VUMAT user-subroutine to perform ballistic impact simulations. It is found that the predicted residual velocities are well matching with the experimental results. Adiabatic shear bands were observed in specimens deformed at higher strain rates. The tensile specimen is broken in a manner of ductile fracture presenting typical dimple structure, while the compressive specimen fails in a manner of localized shearing failure.

In the present paper, the high velocity impact of 9 mm soft lead projectile on 10 mm and 30 mm thick E-glass/epoxy composites was studied using a 450 kV Flash X-ray radiography (FXR) system. The basic parameters of FXR imaging, such as effect of ratio of target to film (TF) and source to target (ST) distances and X-ray penetration thickness of the composite material were optimized based on clarity and the actual dimensions of the objects. The optimized parameters were used in the FXR imaging of the ballistic event of 9 mm soft projectile on E-glass/epoxy composite. The real time deformation patterns of both the projectile and composite target during the ballistic impact were captured and studied at different time intervals. The notable failure modes of the 10 mm thick target with time include fibre breakage, bulging on the back side, delamination, recovery of the bulging, reverse bulging and its recovery. However, with increase in thickness of the target to 30 mm the only failure mechanism observed is the breaking of fibres. The ballistic impact event was also numerically simulated using commercially available LS-DYNA software. The numerically simulated deformation patterns of the projectile and target at different time intervals are closely matching with the corresponding radiographic images. Keywords: Flash X-ray radiography, E-Glass/epoxy composite, Ballistic impact, Numerical simulation

Hot-rolled high-nitrogen steel (HNS) plates were evaluated against AK-47 mild steel core (7.62 mm × 39 mm, deformable) and 14.5 mm armour piercing (AP) (14.5 mm × 114 mm, hard steel core) projectiles. The ballistic results of HNS plates were compared with conventionally used Rolled Homogeneous Armour (RHA) steel plates. The ballistic tests on HNS and RHA steel plates with different thicknesses were conducted against AK-47 mild steel core and 14.5 mm AP projectiles at velocities of 740 ± 10 m/s and 1000 ± 10 m/s respectively, in order to find out the minimum thickness required to stop the projectile without perforation. In comparison to RHA steel, HNS exhibited higher ballistic performance (in terms of minimum areal density required) against both AK-47 mild steel core and 14.5 mm armour piercing projectiles. The ballistic results against 14.5 mm AP was studied using an analytical model reported in literature. Detailed post ballistic (microstructural and hardness measurements) investigations were carried out to understand the ballistic performance of the two steels. Further, an attempt has been made to correlate the initial microstructure and mechanical properties with the failure mechanisms activated during ballistic impact and the resulting ballistic performance.

A comparative study on ballistic performance of hot pressed boron carbide (HPBC) and reaction bonded boron carbide (RBBC) tiles were performed using depth of penetration (DOP) configuration against...

The objective of the study is to understand the dynamic flow behavior of Ti–22Al–25Nb alloy at high temperatures using a modified Zerilli–Armstrong (Z-A) model. To investigate the dynamic mechanical behavior of titanium alloy, the material was subjected to quasi static and dynamic compression testing. It is found out that the modified Z-A models possess better predictability in evaluating the flow behavior of the Ti–22Al–25Nb alloy at elevated strain rates and temperatures. The model well established the quasi-static and dynamic behavior of the titanium alloy, mainly the effects of strain hardening and thermal softening. The regimes of high strain rate deformation behavior represented by dynamic recrystallization (DRX), lamellar globularization and the instability flow have been discussed. Using transmission electron microscopy (TEM) studies, it is found that the dislocation density is directly associated with strain rate.

The purpose of this study is to describe the dynamic behavior of near alpha titanium alloy at elevated temperatures using Crystal plasticity and other models. Three constitutive models: Johnson-Cook (J-C), Zerilli–Armstrong (Z-A), Cowper-Symonds (C–S) and J-C fracture models are established. Experimental results observed that material displayed strain rate sensitivity at various strain rates. The generated model constants have been incorporated into finite element code. Finite Element simulations of tensile tests under different strain rates have been performed using Autodyn software. A crystal plasticity model is established and shows that it can predict the stress strain response under dynamic loading conditions. The developed crystal plasticity model was implemented in the ABAQUS code to simulate high strain rate compression and showed good agreement. Subsequently, a Charpy impact test on specimen has also been simulated. The fracture surfaces of specimens tested under quasi static state at various temperatures were studied under scanning electron microscopy (SEM).

Static indentation and uniaxial compression tests have been conducted on Armox500T steel and its weldments to predict the constraint factor (CF), i.e., ratio of Meyer’s hardness to uniaxial flow stress. Series of dynamic indentation experiments were carried out at impact velocities ranging from 5 to 300 m/s to estimate dynamic hardness as a function of average strain. Subsequently, dynamic indentation (DI) test data and CF determined under static indentation conditions have been used to study the high strain rate plastic flow behavior of Armox500T weldments in comparison with the base metal. It was observed that flow stress for Armox500T and its weldments under dynamic loading conditions (104 s−1) are significantly higher than flow stress measured under static loading conditions (10−3 s−1). The plastic flow behavior computed from DI is in good agreement with the data evaluated through conventional split Hopkinson pressure bar technique. Further, the study of the microstructure of base metal and weldments by optical microscopy and SEM revealed a considerable variation in the microstructure.

Study of tribological characteristics of multi-pass shielding metal arc-welded (SMAW) Armox 500T steel joints in comparison with its counterpart base metal was carried out. Series of dry sliding wear tests were carried out as a function of applied loads ranging from 30 to 120 N and sliding distances from 1000 to 6000 m at a constant sliding velocity using pin-on-disk tribometer. It was observed that specific wear rate and lost volume in SMAW joints significantly high compared to Armox 500T base metal in the range of loads and sliding distances considered in the present study. The scanning electron micrographs indicated that wear of Armox 500T base metal occurred due to micro-grooving and adhesion, on the other hand, micro-delamination was observed in SMAW joints. Microstructural investigations revealed that base metal exhibits superior tribological properties as compared to SMAW joints due to the formation of martensite lath in acicular form with coarse and fine precipitates.

In this investigation, comparative study of tensile and impact properties of multi-pass SMAW Armox 500T steel joints fabricated by austenitic stainless steel (ASS) and low hydrogen ferritic steel (LHF) consumables vis-a-vis base metal was carried out. The tensile tests were conducted on computer controlled Walter + Bai Ag UTM at a nominal strain rate of 10−3 s−1. Subsequently, charpy impact tests were carried out on an instrumented Zwick-Roell test setup to obtain load vs. displacement and maximum energy absorbed vs. displacement of the specimen. It was observed that, the joint efficiency of weldment processed by LHF consumable was 41.7% and weldment processed by ASS was 30.6% of its base metal indicating the influence of electrode consumable on tensile properties of the joints. On the contrary, impact toughness of weldment processed by ASS was 20% more and weldment processed by LHF was 12% less than that of base metal. Microstructural studies also revealed that, ASS can be considered as a candidate welding consumable for good strain hardening and toughness of the welding joint in impact applications. However, LHF steel consumable is recommended for welding joints that requires higher joint efficiency under tensile loading conditions. Keywords: Armox500T, Multi-pass SMA welding, ASS and LHF welding consumables, Mechanical properties, Microstructural characterization

The effect of backing material, projectile velocity and tile thickness on the ballistic efficiency of ceramic materials was studied against 7.62 mm AP projectile in depth of penetration (DOP) test configuration. An analysis on variation in differential efficiency factor (DEF) with respect to backing material was carried out. The factor responsible for variation in DEF was eliminated using a normalization method. A new definition (NDEF/ NBE) is proposed for calculation of ballistic efficiency. Using the new definition a comparison of ballistic efficiency of hot pressed boron carbide, alumina and zirconia toughened alumina were done for different projectile velocities and tile thickness. The DEF was found to increase with increase in projectile velocity, but NDEF and NBE were found to decrease with increase in projectile velocities. Even though the DEF, NDEF and NBE have produced different ballistic efficiencies they all have produced similar trends with respect to tile thickness.

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 obtained have been validated by earlier experimental results, Gupta and Madhu [1] , [2] . The Johnson–Cook elasto-viscoplastic material model calibrated by the authors for mild steel was employed in the numerical simulations. Close correlation of typical experimental and numerical results validated the numerical procedure and the calibrated model. Ballistic limits of monolithic mild steel targets of thicknesses 4.7, 6, 10, 12 and 16 mm each impacted at 0, 30 and 45ᵒ obliquity were numerically computed. The ballistic limits of in contact layered and spaced targets of equivalent thickness 10 mm (3.33 + 3.33 + 3.33 mm) were also computed at 0, 30 and 45° obliquity. For 60° angle of obliquity, the monolithic target experienced project ricochet, in contact layered target, projectile embedment, and the spaced target, projectile perforation. At low angles of obliquity, the difference between the ballistic performance of monolithic, layered in contact and spaced targets was not significant. As the angle of obliquity increased, each studied configuration was found to have distinct ballistic performance. Simulations were also done for three layered target of 4.7 and 6 mm thick plate and spacing was varied to study its effect on their ballistic resistance. The variation of spacing at normal impact was found to have influence as long as the spacing was smaller than the projectile length.

A comprehensive study has been performed for understanding the constitutive behavior of titanium alloy IMI 834 under different strain rates, stress triaxialities and temperatures. Results confirmed an improvement in its strength with increase in strain rate and stress triaxiality. Experimental results obtained from the specimens of materials were employed to calibrate the material parameters of Johnson–Cook (J-C) strength and fracture model. The microstructure study has been undertaken to discuss the shear band and grain growth mechanisms. Three constitutive models: Johnson-Cook (J-C), Zerilli–Armstrong (Z-A) and Cowper-Symonds (C-S) models are established to determine the flow stress using dynamic compression data. The ballistic tests were performed in which 8 mm thick target plates were impacted by 7.62 AP projectiles with a velocity of 830 m/s. The ballistic test results were replicated through numerical simulations carried out using ABAQUS finite element code. It is observed that the residual velocities generated by simulations were in good agreement with the experimental results.

The dynamic compression tests were performed at various strain rates (0.01, 1700, 2700 and 3500/s) and temperatures (25, 200, 400 and 600 °C) for a biomedical Ti–13Nb-13Zr alloy. Based on experimental data, constitutive models were established using the Modified Johnson-Cook (J-C) model, Modified Khan–Huang–Liang (KHL) model and Artificial neural network (ANN) model, respectively. The new modified J-C model considers the coupled effects of strain hardening, strain rate hardening and thermal softening. In this work, a radial basis function artificial neural network (RBF-ANN) model was also developed to predict the high strain rate flow curves of Ti–13Nb-13Zr alloy. The results demonstrate that the flow behavior of Ti–13Nb-13Zr alloy is considerably influenced by the strain rate and temperature. The modified KHL model and ANN significantly enhance the predictability. The deformation behavior represented by dynamic recrystalization (DRX) and the instability flow has been discussed with reference to microstructural evolution during high strain rate compression. The validation of the developed constitutive model is embedded in the finite element analysis (FEA) to perform numerical simulations with ABAQUS/Standard to obtain the charpy impact energy.

The objective of the study is to perform experiments on FeCoNiCr high entropy alloy under different strain rates ranging from 0.01 to 3500/s and also at temperatures of 25, 200, 400 and 600 °C. Considering the effects of work hardening and thermal softening at high strain rates, the flow behavior is characterized by employing the modified Johnson-Cook (J-C) and Zerilli–Armstrong (Z-A) models. The triaxiality data showed the decrease in effective plastic strain at failure as triaxiality increases for all strain rates. Fracture constants have been evaluated.

Hot compression tests of Ti-10-2-3 alloy were carried out in the temperature range of 900–1050 °C, at strain rates of 0.001–1 s−1 on a Gleeble thermo mechanical-simulator. The experimental results demonstrate that the flow stress of the titanium alloy is significantly influenced by temperature, strain and strain rate. A physically-based constitutive model was established, based on the dislocation density theory and dynamic recrystallization kinetics. The comparison between the experimental and predicted flow stresses shows that the established model has high accuracy. The statistical study confirmed the predicting capability of the model. The presented constitutive model, as well as the dynamic recrystallization (DRX) kinetics, was incorporated into ABAQUS to provide an effective means to study hot deformation. Results confirm that the constitutive model considering dynamic recovery (DRV) and DRX provides high accuracy. DRX results of the Finite Element Method (FEM) are in good agreement with the experimental results.

Sandwich panels with cellular cores are being widely used as blast mitigation materials, due to their light weight and good energy absorption properties. In the present study, the behaviour of sandwich panels against different shock loadings is evaluated using piston driven shock tube. The sandwich panels are fabricated using aluminium(Al) foam core and E-glass/epoxy composite face sheets of different thicknesses. Different shock loads were generated by varying the driven gas pressures. The foams and sandwich panels were subjected to peak shock reflected pressures ranging from 50 bars to 150 bars and the corresponding transmitted pressure pulses were recorded. The behaviour of the foams and sandwich panels under shock wave loading was evaluated by post test visual damage assessment. The effect of face sheet thickness on failure mechanisms of sandwich panel is also studied. The failure mechanisms of foams at higher shock pressures were observed to be core crushing and core fracture, whereas sandwich panels exhibited face sheet deflection, core crushing, fibre breakage at back face sheet and back face delamination.

The present study describes the experimental results pertinent to the penetration of AA-2024, AA-6061 and AA-7017 plates with two different non-deformable steel projectiles. The diameters of the projectiles used for ballistic impact testing are 7.62 and 12.7 mm. The projectiles are impacted on the aluminium targets of 70 mm thickness with velocities in the range of 840±10 m/s. The results presented include variation in damage pattern in experimental alloys with respect to different projectiles. The microstructures and micro-hardness values along the projectile penetration path have been investigated to understand the material deformation behaviour. Some observations relating to the adiabatic shear band formation have also been presented. From the ballistic testing experiments, it is observed that AA-7017 plates display higher ballistic resistance among the tested aluminium alloys. The ballistic performance of the aluminium alloy plates have been correlated with their respective mechanical properties.

Energy absorption of two different types of composite laminates i.e. glass composite (E-glass/epoxy) and ultra high molecular weight polyethylene (UHMWPE) (Dyneema®) laminates were studied under low and high velocity impact. Instrumented drop weight impact tester was used for low velocities and sub machine carbine (SMC) gun was used for high velocity impact. Failure behaviour of both E-glass/epoxy and dyneema laminates during impact was studied and results of the energy absorption of the tested composite laminates have been presented. Dyneema laminates showed 2 times higher energy absorption than E-glass/epoxy laminate under high velocity impact. However, both the laminates have showed higher energy absorption at high velocity impact as compared to low velocity impact. Failure analysis on impacted laminates reveals that the E-glass/epoxy laminate undergoes elastic deformation, delamination and brittle failure of fibres, whereas dyneema laminates undergo plastic deformation and associated tensile stretching of fibres. The results obtained from this study bear significance in the development of light weight add-on and structural composite armours for the real time applications.

The present study is aimed at developing Carbon and E- glass based hybrid composite lamiantes for armour applications in order to get advantages of both the types of fibers. Three hybrid composite laminates based on carbon and E-glass in the weight ratio of 75:25, 50:50 and 25:75 with epoxy resin matrix were fabricated. For comparison purpose all carbon (C 100) and all E-glass (E 100) composites were also fabricated. High velocity impact tests were performed on laminates keeping carbon as strike face against 7.62 mm mild steel projectile. Present study revealed that the composite laminates comprising carbon and E-glass in the ratio of 50:50 (CE 50-50) has shown maximum performance in terms of energy absorption. It showed 17% & 30% higher energy absorption than C 100 and E 100 composites respectively. Damage areas at front and rear sides as well as damage volume are determined and found that its increase with increase in thickness.

The ballistic performance of bilayer silicon carbide/aluminium (SiC/Al) armour is assessed and compared with the alumina/aluminium (Al 2 O 3 /Al) armour using numerical analysis. For the numerical simulation of impact phenomena, ANSYS/AUTODYN software and phenomenological material models are used. The phenomenological models are JH-1 and JH-2 for brittle materials such as silicon carbide and alumina respectively and Johnson Cook (JC) model for ductile materials such as steel and aluminium. This study results shows that the ballistic performance of SiC/Al armour is higher than the Al 2 O 3 /Al armour and also SiC/Al target made severe damage to the projectile. The failure modes of these armours against blunt and ogive nose projectile are also evaluated.

The high hardness combined with its lower density makes boron carbide an attractive candidate for armour material. The ballistic performance of hot pressed boron carbide tiles were evaluated using standard Depth of Penetration (DOP) test method against hard steel armour piercing (AP) projectile of 12.7 mm caliber. Aluminium alloy 2024-T351 was used as backing material. The effect of tile thickness on ballistic efficiency was studied for tile thickness from 7.1 mm to 14.6 mm. Also projectile velocity effect was studied for velocities between 700 to 825 m/s. The ballistic efficiency with respect to tile thickness was initially found to increase and then decreases. Results on ballistic efficiency along with results of post ballistic analysis have been presented.

Steel containing 0.65 wt % nitrogen has been investigated for armour applications by subjecting it to different percentages of hot rolling. The effect of percentage reduction during hot rolling on microstructures, mechanical properties and ballistic performance has been studied. The ballistic performance of 6.5 mm, 7.5 mm thick plates against 7.62 ball and 16 mm, 17 mm thickness against 7.62AP projectiles were assessed. The nature of damage has been studied by varying percentage reduction during hot rolling of these plates for providing full protection.

To understand the flow and fracture behavior of near-α titanium alloy, the influence of stress triaxiality and strain rate on the failure behavior of this alloy was considered. The combined effect of strain rate, temperature and stress triaxiality on the behavior was studied by testing both smooth and notched specimens. Johnson-Cook (J-C) constitutive and fracture models were established based on high strain rate tensile data obtained from Split hopkinson tension bar (SHTB) and quasi-static tests. The Johnson Cook constitutive and fracture models have been calibrated. A modified Johnson–Cook model was established and proved to have high accuracy. The calibrated model has been validated by simulating the tension tests at various triaxialities using ANSYS autodyn software. Finite element simulations were used to predict the effective plastic strain versus triaxiality history within the deforming specimens. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).

The dynamic recrystallization (DRX) behavior of a biomedical titanium Ti-13Nb-13Zr alloy has been investigated using the high temperature compression tests under wide range of strain rates (0.001-1/s) and temperatures 900-1050°C. A constitutive equation represented as a function of temperature, strain rate and true strain is developed and the hot deformation apparent activation energy is calculated about 534kJ/mol. By considering the exponential relationship between work-hardening rate (θ) and stress, a new mathematical model was proposed for predicting flow stress up to the critical strain during hot deformation. The mathematical model for predicting flow stress up to the critical strain exhibits better consistency and accuracy. The DRX kinetic equation of Ti-13Nb-13Zr alloy is described as XDRX=1-exp[-0.32(Ɛ-ƐcƐ(*))(2.3)] . The DRX kinetic model was validated by microstructure observation. It was also found that the process of DRX was promoted by decreasing strain rate and increasing deformation temperature. Eventually, the continuous dynamic recrystallization (CDRX) was identified to be the DRX mechanism using transmission electron microscope (TEM).

In this study, Split hopkinson tension bar (SHTB) has been employed to investigate the dynamic tensile flow behavior of Ti-10-2-3 alloy at high strain rates and elevated temperatures. The combined effect of stress triaxiality, strain rate and temperature and on the tensile behavior of the alloy was evaluated. Johnson-Cook (J-C) constitutive and fracture models were developed based on high strain rate tensile data. A modified Johnson–Cook model was established and proved to have high accuracy. A comparative assessment has been done to confirm the accuracy of modified J–C model based on finite element method (FEM). The improved model provides better description on the influence of equivalent plastic strain rate and temperature on the plastic flow. The simulation results proved to be in good agreement with the experimental data. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).

In the present work, a comparative study is carried out on the energy absorption ability of phenolic and epoxy matrices reinforced with glass fibres. E-glass/phenolic and E-glass/epoxy laminates having different thickness (5 mm, 10 mm, 15 mm, 20 mm & 25 mm) were fabricated and subjected to ballistic impact against 7.62 × 39 mm mild steel core projectile. Dynamic Mechanical Analysis (DMA) of E-glass/phenolic and E-glass/epoxy laminates was also carried out. It was observed that, E-glass/phenolic laminates which have shown higher storage and loss modulus were found to show higher energy absorption than E-glass/epoxy laminates which have shown lower storage and loss modulus. This is observed to be because of ease of delamination and transverse stretching of fibres in E-glass/phenolic laminates as the matrix at the interface is allowing easy sliding. However this effect is found to be significant only when the laminate thickness to projectile diameter ratio (t/d) is more than two. Mechanisms influencing the observed trend in results are analyzed in the present paper with the help of DMA and high speed video imaging during impact. Failure analysis of laminates was studied by using microscopy techniques. Keywords: E-glass/phenolic, E-glass/epoxy, Ballistic impact, Energy absorption, High speed video

The hot isothermal compression tests of high-strength armor steel under a wide range of deformation temperatures (1100-1250 °C) and strain rates of (0.001-1/s) were performed. Based on the experimental data, constitutive models were established using the original Johnson-Cook (JC) model, modified JC model, and strain-compensated Arrhenius model, respectively. The modified JC model considers the coupled effects of strain hardening, strain rate hardening, and thermal softening. Moreover, the prediction accuracy of these developed models was determined by estimating the correlation coefficient (R) and average absolute relative error (AARE). The results demonstrate that the flow behavior of high-strength armor steel is considerably influenced by the strain rate and temperature. The original JC model is inadequate to provide good description on the flow stress at evaluated temperatures. The modified JC model and strain-compensated Arrhenius model significantly enhance the predictability. It is also observed from the microstructure study that at low strain rates (0.001-0.01/s) and high temperatures (1200-1250 °C), a typical dynamic recrystallization (DRX) occurs.

The purpose of the current study is to perform quasi static and high strain rate tensile tests on Al-4.8Cu-1.2Mg alloy under different strain rates ranging from 0.01–3500/s and also at temperatures of 25,100, 200 and 300 °C. The combined effect of strain rate, temperature and stress triaxiality on the material behavior is studied by testing both smooth and notched specimens. Johnson–Cook (J–C) constitutive and fracture models are established based on high strain rate tensile data obtained from Split hopkinson tension bar (SHTB) and quasi-static tests. By modifying the strain hardening and strain rate hardening terms in the Johnson–Cook (J–C) constitutive model, a new J–C constitutive model of Al-4.8Cu-1.2Mg alloy was obtained. The improved Johnson–Cook constitutive model matched the experiment results very well. With the Johnson–Cook constitutive and fracture models, numerical simulations of tensile tests at different conditions for Al-4.8Cu-1.2Mg alloy were conducted. Numerical simulations are performed using a non-linear explicit finite element code autodyn. Good agreement is obtained between the numerical simulation results and the experiment results. The fracture surfaces of specimens tested under various strain rates and temperatures were studied under scanning electron microscopy (SEM).

Failure mechanism of 7.62 mm AP projectile impacting boron carbide tiles was studied by post ballistic examination of the failed projectiles. It is found that the projectile failure originates simultaneously from at least two locations in the projectile during ballistic impact, one originating from the target interaction front of the projectile and another from a location near the tail end of the projectile. The failure origination from the target interaction front of the projectile is due to severe deformation at the interaction front. The second failure origination from locations near tail end of the projectile is due to stress wave generated micro-cracks. At the target interaction front of the projectile a temperature rise of above 1160 °C has been estimated. No remarkable change in failure mechanism of the hard steel projectile with respect to tile thickness (5–9.2 mm) or projectile velocity (600–820 m/s) has been observed. The variation in remnant projectile weight with respect to tile thickness and projectile velocity can be attributed to the change in duration of dwell or total projectile interaction time with ceramic target.

The isothermal hot compression tests of high-strength armor steel over wide ranges of strain rates (0.01-10 /s) and deformation temperatures (950-1100 °C) are carried out using Gleeble thermo-simulation machine. The true stress-strain data obtained from the experiments are employed to establish the constitutive equations based on the strain-compensated Arrhenius model. With strain-compensated Arrhenius model, good agreement between the experimental and predicted values is achieved, which represents the highest accuracy in comparison with the other models. The hot deformation activation energy is estimated to be 512 kJ/mol. By employing dynamic material model, the processing maps of high-strength armor steel at various strains are established. A maximum efficiency of about 45% of power dissipation is obtained at high temperature and low strain rate. Due to the high power dissipation efficiency and excellent processing ability in dynamic recrystallization zone for metal material, the optimum processing conditions are selected such that the temperature range is between 1050 and 1100°C and the strain rate range is between 0.01 and 0.1/s. Transmission electron microscopy observations show that the dislocation density is directly associated with the value of processing efficiency.

The use of light weight armor against ballistic threats is very important for increasing mobility and survivability. This paper describes ballistic performance of an E-glass/phenolic composite as a function of laminate thickness and projectile impact velocity using mild steel core projectile. The results show that there is a nonlinear relationship between the energy absorption and laminate thickness. The effect of thickness and velocity on energy absorption in the laminates has been explained in terms of interaction time between target and projectile. It is also observed that deformation of the projectile is more dependent on the target thickness than the strike velocity. Changes in failure mechanisms with change in target thickness are also described. Keywords: Polymer composites, Ballistic impact, Delamination, High speed video

Planar shock loading of rolled homogeneous armour (RHA) steel has been studied at high pressures in the range of 20-100 GPa using an explosive-driven plate impact system. Shock velocities and flyer velocities are measured using time of arrival pins embedded in the target at known depths. The shock equation of state of RHA steel has been determined. α → e phase transition stress and hugoniot elastic limit (HEL) of RHA steel have been determined through manganin gauge and found to be 12.2 ±0.6 GPa and 4.1 ± 0.2 GPa, respectively. The experimental stress of phase transition has been compared with the stress calculated using ThermoCalc software. The shock properties have been incorporated in the Autodyn simulation package and simulations were performed to determine flyer velocity, pressures and the results are compared with that of experiments. Defence Science Journal, Vol. 65, No. 3, May 2015, pp.196-202, DOI: http://dx.doi.org/10.14429/dsj.65.7952

A study was carried out to compare the ballistic performance of high purity alumina and zirconia-toughened alumina (ZTA) using depth of penetration (DoP) test configuration against 7.62 mm armour piercing (AP) ammunition. The effect of tile thickness on the differential efficiency factor (DEF) was studied for tile thickness in the range of 3 mm to 6 mm for alumina tiles and 3 mm to 5 mm for ZTA tiles. The DEF is found to increase as tile thickness increases. An analysis on the failed shots showed that the residual shot weight does not follow a single linear relationship with ceramic tile thickness unlike the residual DoP for all thicknesses of tiles. Post-ballistic analysis on ceramic powder for particle size distribution was carried out and the results are presented. Defence Science Journal, Vol. 64, No. 5, September 2014, pp.477-483, DOI:http://dx.doi.org/10.14429/dsj.64.6745

This work presents the influence of machining parameters on surface roughness (SR) and material removal rate (MRR) of high strength armor steel using wire cut electrical discharge machining (WEDM). Tests have been carried out with six process parameters: pulse-on time, pulse-off time, wire feed, flushing pressure, spark voltage, and wire tension. Taguchi's technique has been employed for experimental investigation. Results show that pulse-on time, pulse-off time, and spark voltage are significant variables to MRR and surface roughness (SR). The confirmation experiments have also been conducted to validate the results obtained by the Taguchi technique.

In the present work the effect of size and shape of regularly spaced holes on the ballistic impact behavior of high hardness steel plates has been studied. Thick backing technique was used to evaluate the efficiency of these plates when subjected to ballistic impact of 7.62 mm non-deformable hard steel core projectiles. The ballistic efficiency of these steel plates was found to be sensitive to size of the holes. Higher efficiency was found for plates with hole sizes close to the diameter of the projectile. Damage patterns and microstructure of the perforated steel plate have been compared with those of non-perforated steel plates. It has been found that presence of holes inhibits shear band formation in the target plates.

Armour steel plates of 25 mm thickness were tempered at various temperatures from 200 °C to 600 °C and tested against ballistic impact of 7.62 mm AP projectiles. Hardness decreases with increase in tempering temperature resulting in corresponding increase in depth of penetration. Least depth of penetration was observed in the plate tempered at 200 °C. Post-impact microstructure of the crater region in the tested plates show adiabatic shear band (ASB) induced cracking for tempering temperatures up to 400 °C and no ASB is seen for 600 °C. ASB induced cracking was also observed in the crater region of a 5 mm thick plate tempered at 200 °C and tested under similar conditions. Plates of thickness 5 mm with drilled holes of diameter nearly equal to that of the projectile were also tested. The result showed that ASB formation can be partially inhibited in these plates due to presence of holes.

Ballistic impact performance of aramid fiber fabric-epoxy and aramid fiber fabric-polypropylene (PP)-based composite laminates has been studied against 7.62 mm armor piercing projectiles. Twaron® was used as aramid fiber fabric in the composites. Role of matrix on the damage pattern has been investigated by impacting the composites of different thickness with projectiles having different strike velocity (SV). Ballistic limit (BL) for each composite has been estimated through correlation of SV and residual velocity (RV) of the projectile by usual V50 method. Ballistic limit was found to vary linearly with composite laminate thickness. Twaron®-PP composites exhibited higher ballistic limit compared toequivalent thickness of Twaron®-epoxy composites. Epoxy-based composites exhibited localized damage mode compared to a global mode of failure in PP-based composites. Scanning electron microscopy revealed that fibers in Twaron®-epoxy composites failed largely by shear while tensile mode of failure was observed for Twaron®–PP composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Protection creates a shift in the internal paradigm of the soldier and leads to multiplied psychological stamina for moving fearlessly in the battlefield which generates a major force-multiplier effect. Hence, the mechanized forces are still likely to be one of the dominant forces on the futuristic battlefield and would be the primary target of enemy forces capable of engaging from tank guns up to 4-5 km in a direct fire mode and up to 8-10 km in an indirect fire modes. Increased protection is possible only using advanced armour technology. Throughout the history of warfare, materials technologies have had a significant impact on land-combat force capabilities. Armour materials have progressed through improvements in metallic systems and development of advanced, lightweight (low areal density) composite materials. The advancements in ceramic systems have further improved the performance. Similarly, the advances in development of explosive reactive armour has generated efficient armour system against all contemporary high explosive antitank (HEAT) ammunition and missile threats for armoured vehicles. Yet, to achieve armour performance exceeding that of the current light combat vehicles and main battle tanks for new vehicular systems, weighing significantly less than the present combat vehicles, advances in new armour materials, systems, and survivability technologies are required. This paper describes various approaches and advancements in the metallic, ceramic, and composite armour materials and new dynamic armour systems that are essential to improve the survivability of armoured vehicles in the futurisitic multi-spectral battlefied scenarios. Defence Science Journal, 2011, 61(4), pp.394-402 , DOI:http://dx.doi.org/10.14429/dsj.61.365

Boron carbide is an attractive candidate for use as armour material because of its lower density combined with high hardness. The ballistic performance of boron carbide tiles were evaluated using standard Depth of Penetration (DOP) test method against hard steel 7.62 mm armour piercing (AP) projectiles. The effect of variation in thickness of tile and the projectile velocity on the ballistic efficiency of the material was studied. It has been found that the differential efficiency factor (DEF) increases with increase in projectile velocity from 600 to 820 m/s. And an insignificant or marginal increase in efficiency was observed for increase in tile thickness from 5.2 mm up to 7.3 mm. The effect of the type of radial confinement on the residual DOP was also studied. It was found that the steel radial confinement produces lower residual DOP values compared to aluminium alloy and with no radial confinement. Results along with photographs have been presented.

An experimental study has been carried out on the ballistic performance of 95% and 99.5% alumina ceramic tiles backed by metal plates, when subjected to normal impact of hard steel 12.7 mm armour piercing (AP) projectiles at velocities ranging from 500 to 830 ms−1. Typical damaged targets and broken projectiles are presented. The depth of penetration is measured in all the experiments, and the ballistic efficiency factor of the ceramic plates are determined. Results show that the efficiency factor increases with increase in projectile velocity. With the increase in thickness of the ceramic tile, the ballistic efficiency factor for a given velocity is observed to decrease in the case of 99.5% grade and increase in the case of 95% grade ceramic. The higher purity alumina (99.5%) shows higher ballistic performance when compared with the 95% alumina. The 99.5% alumina exhibited a predominantly transcrystalline fracture while the 95% alumina showed a less defined fracture surface. Experiments on 7.62 mm AP shots were also done keeping the ( d / t ) ratio same as in 12.7 mm AP experiments and results are presented.

The ultimate goal of armour research is to create better armour for battle worthy combat plat forms such as main battle tanks, infantry combat vehicles and light combat vehicles. In each of these applications, the main aim boils down to one of the two things; either reduce the weight without sacrificing protection or enhance the performance at same or even reduced weight. In practice, these ambitions can be fulfilled only if we have with us, appropriate improved armour materials, advanced and innovative technologies and also improved designs, which enable us to use them for creating next generation armour modules. Armour systems have progressed through improvements in metallic, ceramic and lightweight (low areal density) composite materials. Similarly, the advances in development of explosive reactive armour (ERA) and non-explosive reactive armour (NERA) have generated efficient armour system against contemporary high explosive antitank ammunition and missile threats for the armoured vehicles. Yet, to achieve armour performance exceeding that of the current light combat vehicles and main battle tanks, further advancements in armour materials, systems, and survivability technologies are required for new vehicular systems that weigh significantly less than the present combat platforms. Various approaches and advancements in the metallic and composite armour materials, ERA and NERA systems to improve the survivability of armoured vehicles in the futuristic multi-spectral battlefield scenarios are described.