Increasing Impact Energy Research Articles

Study of the Impact Energy Release Characteristics of Fine‐Grained Fe−Al Energetic Jets

AbstractFine‐grained Fe−Al energetic materials have high reaction enthalpies, and the release energy of the iron phase and a large portion of the active aluminium phase in sintered materials enables the replacement of conventional materials in new types of weapons. To study the energy release characteristics of fine‐grained Fe−Al energetic jets under impact loading, a dynamic energy acquisition system is established to quantify the energy generated by the response of fine‐grained Fe−Al energetic jets to impact targets. The pressure‐time curves of fine‐grained Fe−Al energetic jets with different ratios under different impact conditions are obtained, and a method for calculating the pressure differential value is proposed to quantitatively determine the energy release values of fine‐grained Fe−Al energetic jets. The energy release mechanism of the Fe−Al energetic jet is analysed at the micro‐level by recovering the reaction products. The results show that there is an optimal Fe−Al ratio that attains the greatest energy release effect from fine‐grained Fe−Al energetic jets. With increasing impact energy, the energy released by energetic jets tends to increase, and an impact energy threshold that saturates the chemical reaction of energetic materials in the jets exists. The relationship between the impact conditions and the energy release value of fine‐grained Fe−Al energetic jets is established.

Modification of mechanical properties of submerged arc welds by adding Mn2O3– or TiO2–NPs directly to the beveled surface of low-carbon steels

This work was aimed to analyze the changes in the mechanical properties of submerged arc welds due to the growth of the acicular ferrite (AF) phase promoted by addition of Mn2O3– or TiO2-nanoparticles (Mn2O3– or TiO2-NPs). Such Mn2O3– or TiO2-NPs were uniformly deposited along the V-groove, formed from joining two beveled surfaces of low-carbon steel plates to be welding. Mechanical properties of the weld beads with and without NPs were determined through Tensile, Vickers microhardness and Charpy V-Notch (CVN) impact tests; meanwhile their microstructural features changes were followed by Optical and Scanning Electron Microscopies (OM and SEM). Tensile Strength, Yield Strength and Vickers microhardness values were lower for weld beads obtained with addition of Mn2O3– or TiO2-NPs compared to those obtained without NPs additions. Namely, 13.5, 17.5 and 11.4%, respectively, lower by adding Mn2O3–NPs, and 15.8, 24.6 and 12.4%, respectively, lower by adding TiO2-NPs. In contrast, the CVN impact energy values were determined to be about 60 or 30% higher by adding Mn2O3– or TiO2-NPs, respectively. OM and SEM micrographs of weld beads with Mn2O3– or TiO2-NPs show a clear increase in the surface density and length of the AF needles, in comparison to the weld bead without NPs. Namely, it was determined that in average, the length of the AF needles increases 131 and 155% by adding Mn2O3– or TiO2-NPs, respectively. Moreover, the increase in the CVN impact energy and the surface density of AF needles can be correlated with the decrease in the average dimple diameter and with the cleavage sheets width, respectively. Thus, it can be pointed out that the addition of Mn2O3- or TiO2-NPs has a direct influence in the size of the AF needles, which caused the improvement of the corresponding weld bead toughness.

Influence of dolomite on mechanical, physical and erosive wear properties of natural-synthetic fiber reinforced epoxy composites

The study was intended to investigate the influence of dolomite content on the physical, mechanical and erosive wear properties of hybrid natural—synthetic fiber reinforced polymer composites. Therefore, epoxy composites, having fixed amount of Grewia optiva and glass fiber with varying proportion of dolomite particles (0, 5, 10 and 15 wt%) were developed with hand-layout technique. The results show that the density, void content, impact energy and hardness increases, while flexural and tensile strength decreases with the increase of dolomite content. For erosive wear analysis, Taguchi method with L16 orthogonal array was used. The experiments were performed on an air jet machine with different impingement angles (30, 45, 60 and 90°), erodent sizes (100, 150, 200 and 250 μm) and impact velocities (10, 20, 30 and 40 m s−1). The lowest wear rate was achieved under optimal condition of 10 wt% dolomite content, 30° impingement angle, 10 m s−1 impact velocity and 150 μm erodent size. Moreover, scanning electron microscopy was implemented in order to analyze the eroded composite surfaces for possible wear mechanism.

Experimental Study on the Energy-Release Characteristics of Fine-Grained Fe/Al Energetic Jets under Impact Loading.

The energy released by the active metal phase in fine-grained Fe/Al energetic materials enables the replacement of conventional materials in new types of weapons. This paper describes an experiment designed to study the energy-release characteristics of fine-grained Fe/Al energetic jets under impact loading. By means of dynamic mechanical properties analysis, the physical and chemical properties of Fe/Al energetic materials with specific content are studied, and the preparation process is determined. The energy-release properties of fine-grained Fe/Al jets subject to different impact conditions are studied based on experimental data, and energy-release differences are discussed. The results show that for fine-grained Fe/Al energetic materials to remain active and exhibit high strength, the highest sintering temperature is 550 °C. With increasing impact energy, the energy release of fine-grained Fe/Al energetic jets increases. At an impact-energy threshold of 121.1 J/mm2, the chemical reaction of the fine-grained Fe/Al energetic jets is saturated. The experimental data and microscopic analysis show that when the impact energy reaches the threshold, the energy efficiency ratio of Fe/Al energetic jets can reach 95.3%.

The role of friction in cylindrical projectile impact on fabric structure

A three-dimensional finite element analysis model for plain weave fabric was created. Impact of a rigid cylindrical projectile on a square fabric clamped along its four edges were simulated using commercially available software LS-DYNA. To reveal the role of friction in ballistic impact, comparative study was conducted in which projectile velocity, boundary condition, and material property are kept the same but friction between projectile and fabric and between yarns themselves are varied systematically. Results from the study show that the friction between projectile and fabric has little effect on fabric energy absorption but the friction between yarns themselves has apparent effect. Fabric has larger impact energy absorption capacity when friction coefficient between yarns are smaller. Smaller friction between yarns delays initiation of yarn failure, increases the duration of interaction between projectile and fabric and thus increases impact energy absorption capacity of fabric structure.

Low velocity oblique impact behavior of adhesively bonded single lap joints

This article addresses the low velocity oblique impact behavior of adhesively bonded single lap joints, and the effects of adherend strength and plastic ductility, impact energy, overlap length and oblique impact angle on the damage initiation and propagation in the adhesive layer. The experimental contact force-time, contact force-central displacement variations, axial separation lengths through the adhesive layer and permanent central deflections of overlap region, adhesive fracture surfaces were evaluated in detail. In the explicit finite element analyses, the adhesive layer was divided into three zones: upper and lower adhesive interfaces and the adhesive layer between these interfaces. The adhesive interfaces were modeled with cohesive zone approach to predict the failure initiation and propagation along both upper and lower adhesive–adherend interfaces, whereas the elastic-plastic material model was implemented for the middle adhesive region between the upper and lower adhesive interfaces. The proposed finite element model predicted reasonably the damage initiation and propagation through the adhesive layer, and the contact force-time/central displacement variations. Especially, the test and analysis results were compared with those of the adhesively bonded single lap joints under a normal transverse impact load. Increasing oblique impact angle resulted in lower peak contact forces, shorter contact durations and earlier damage initiation and propagation through the adhesive layer. The peak contact forces increased, the contact duration decreased with increasing impact energy. The strength and plastic deformation capability of adherend materials also affected the damage initiation and propagation through the adhesive layer as well as the after-impact joint geometry.

On the damage mechanism of high-speed ballast impact and compression after impact for CFRP laminates

Single and multiple track-ballast impacts are investigated for the CFRP laminates used in train carbodies. Numerical simulations have been performed to study the damage behaviors of CFRP laminates during ballast impacts and compressions after ballast impact (CABI). Intralaminar and interlaminar damages are successfully predicted using continuum damage mechanics and cohesive zone model, respectively. It reveals that, for a high-speed ballast impact, delamination occurs during the damage initiation and appears at several interfaces nearby the impacted side of the specimen. After that, fiber breakage and matrix cracking appear, while delamination continuously extends until the failure. Repeated ballast impacts on the same site and different sites of specimens show significant increase of delamination while indicating less intralaminar damage. Furthermore, CABI simulations show that, the residual compression strength decreases in a nonlinear manner with the increase of impact energy. To bear the same impact energy, less detrimental effect is caused when one impact is replaced by two or more impacts.

Influence of Tempering Temperature on the Microstructure and Mechanical Properties of a Cr–Ni–Mo‐Alloyed Steel for Rock Drill Applications

This research investigates the mechanical properties of a Cr–Ni–Mo‐alloyed rock drill steel tempered at different temperatures from 150 to 550 °C. The highest strength, hardness, and impact energy occur when the steel is tempered at 180 °C. Strength, hardness, and impact energy decrease with increasing tempering temperature from 180 to 400 °C. For tempering temperatures higher than 400 °C, the steel exhibits: 1) an increase in impact energy; 2) an increase in strength and hardness when tempered at 420, 450, and 480 °C; and 3) a gradual decrease in strength and hardness when tempered at temperature higher than 480 °C. The mechanism of the changes of impact energy and hardness with tempering temperature is proposed.

Theoretical and experimental cross sections for electron scattering from halothane

We report a joint theoretical and experimental study on elastic scattering of electrons from halothane (CF3CHBrCl). The theoretical differential, integral and momentum transfer cross sections were obtained with the Schwinger multichannel method implemented with pseudopotentials (SMCPP), and with the independent atom model with screening corrected additivity rule including interference effects (IAM-SCAR+I). The differential cross sections measurements were conducted for incident electron energies of 10, 20, 30 and 50 eV, while the scattered electron angular range varied from 7° to 100°. At these energies the present experimental differential cross sections are in reasonable agreement with both SMCPP and IAM-SCAR+I calculations. As expected, the two theoretical methodologies agree well with each other as the electron impact energy increases. We also discuss the presence of low-energy resonances and a bound anion state identified in our SMCPP calculations.

Elastic wave mode conversion phenomenon in glass fiber-reinforced polymers

PurposeThe purpose of this paper is to present the results of experimental analysis of the elastic-guided wave mode conversion phenomenon in glass fiber-reinforced polymers. The results of this research presented in this paper are strictly focused on S0/A0’ mode conversion phenomenon caused by discontinuities in the form of circular Teflon inserts (artificial delaminations) and impact damage. Results of this research could be useful in problems of damage detection and localization.Design/methodology/approachIn the research, guided waves are excited using a piezoelectric transducer and sensed in a non-contact manner using a scanning laser Doppler vibrometer. Full wavefield measurements are analyzed. Analysis of the influence of investigated discontinuities on S0/A0’ mode conversion is based on the elastic wave mode filtration in frequency-wavenumber domain. Mode filtration process allows us to remove the effects of the propagation of unwanted type of mode in forward or backward direction. Effects of S0/A0’ mode conversion are characterized by a mode conversion indicator (MCI) based on the amplitude of new mode A0’ and the amplitude of incident S0 mode.FindingsIt was noticed that the magnitude of MCI depends on the depth at which the Teflon inserts were located for all analyzed excitation frequencies and diameters of inserts (10 and 20 mm). The magnitude of MCI also increases with increasing impact energies. The S0/A0’ mode conversion phenomenon could be utilized for the detection of surface and internal located discontinuities.Originality/valueThis paper presents the original results of this research related to the influence of discontinuity location with respect to the sample thickness and severity of discontinuity on S0/A0’ mode conversion.

Behavior of ultra-high performance fiber-reinforced concrete (UHPFRC) filled steel tubular members under lateral impact loading

This study investigates the behavior of ultra-high performance fiber-reinforced concrete (UHPFRC) filled steel tubular (UHPFRCFST) members under lateral impact loading. A total of five specimens were prepared and tested under lateral impact loading. All specimens were 168 mm in diameter and 2000 mm in length. In addition to UHPFRCFST members, normal strength concrete (NSC) filled steel tubular (NSCFST) members were also tested for comparison purpose. Other investigated parameters in this study include the impact energy and the presence of an inner void. The test results show that as compared to the NSCFST members, the UHPFRCFST members exhibit higher lateral impact resistance with higher peak and plateau impact forces, smaller deflection, and less local indentation. With the increase of impact energy, the peak impact force, the impact duration, and the deflection of the UHPFRCFST members are increased, while the plateau impact force is almost kept constant. Moreover, the presence of an inner void does not deteriorate the lateral impact resistance of the UHPFRCFST members. Finite element (FE) model was then developed and validated by the test results in this study. Afterwards, full-range analysis was performed to investigate the damage evolution, sectional bending moment distribution, and the interactions between the steel tube and the concrete during the impact process. Finally, detailed parametric analyses were carried out to investigate the influences of different parameters on the lateral impact behavior of UHPFRCFST members.

Impact Damage Investigation on Glass Fiber-Reinforced Plate Laminates at Room and Lower Temperatures through Ultrasound Testing and Electronic Speckle Pattern Interferometry

In this work, the evaluation of damage area due to low-velocity impact tests at different impact energy values and different temperatures on glass fiber-reinforced plate laminates was investigated by two nondestructive evaluation (NDE) techniques, electronic speckle pattern interferometry (ESPI) and ultrasound testing (UT). Composites are characterized by several interacting failure modes such as matrix breakage, fiber failure and delaminations, which can be simultaneously induced by low-velocity impacts and can be different depending on the temperature. It can be complicated to detect by visual inspections of the structures for such phenomena. This paper aims to investigate the dependence of the damaged area with respect to temperature variation on glass fiber composite laminates. GF composite laminates were impacted with three energy levels (5, 10, 20 J) and at different temperatures (room temperature, − 25, − 50 °C) by a drop weight impact machine. The results show that at decreasing temperature, a decrease in the damage extension was observed, which is more evident at increasing impact energy. Moreover, as expected, the results confirm UT and ESPI techniques are able to identify the barely visible low-velocity impact damage. However, some limitations for detection were found in ESPI. Nonetheless, the ESPI technique can be considered as one of the useful NDE methods if the calibration and the post-processing methods are improved.

Axial impact behaviors of stub concrete-filled square steel tubes

Existing research on the widely used concrete-filled steel tubes is mainly focused on static or cyclic loading, and the studies on effects of high strain rate are relatively rare. In this article, seven stub concrete-filled steel tubular columns with square section were tested under both static and impact loads, using a large-capacity drop-weight testing machine. The research parameters were variable height of the drop-weight and different load types. The experimental results show that the failure modes of the concrete-filled steel tube columns from the impact tests are similar with those under static load, characterized by the local buckling of the steel tube. The time history curves of impact force and steel strain were investigated. The results indicate that with increasing impact energy, the concrete-filled steel tube stub columns had a stronger impact-resistant behavior. The dynamic analysis software LS-DYNA was employed to simulate the impact behaviors of the concrete-filled steel tube specimens, and the finite element results were reasonable compared with the test results. The parameter analysis on the impact behavior of concrete-filled steel tube columns was performed using the finite element model as well. A simple method was proposed to calculate the impact strength of square concrete-filled steel tube columns and compared favorably with experimental results.

Failure mechanisms in carbon fiber reinforced plastics (CFRP) / aluminum (Al) adhesive bonds subjected to low-velocity transverse pre-impact following by axial post-tension

The present study aimed to explore the effects of impact surface and impact energy on the residual characteristics of the carbon fiber reinforced plastics (CFRP)/aluminum (Al) adhesive bonded joints. The adhesive specimens were manufactured in the hot pressing machine with specific curing temperature and curing pressure of the adhesive. In the experiments, a transverse low velocity pre-impact was carried out first and then followed by the axial (longitudinal) tensile test. The results divulged that CFRP, as an impact surface, could generate better structural integrity and decrease loss of joint strength in comparison with the aluminum impact surface. The mechanism for alternating residual tensile strength resulting from transverse impact load was the combined effect of both damage and mechanical interlocking effectiveness. The residual tensile strength and failure displacement decreased with increasing impact energy except for the joint strength impacted onto the aluminum surface at 10 J due to the prominent mechanical interlocking effect. The strain evolution paths in the adherends at the overlap region presented the different forms when impacted onto the different surfaces. In the tensile tests, the fracture surfaces for the joints with impacting on the aluminum surface can be classified as shear failure zone, annular failure zone and mixed failure zone, while the fracture surfaces for the joints with impacting onto the CFRP surface classified to be shear failure zone and crossed impact zone. This study is expected to provide systematic understanding on crashing behavior of adhesive joints with dissimilar materials for multiple impacts from different directions.

Low-velocity impact behaviour of woven laminate plates with fire retardant resin

The understanding of the damage mechanisms for woven laminate plates under low-velocity impact is challenging as the damage mechanisms at the interface of adjacent layers are dominated by the fibre architecture. This work presents an experimental investigation of the behaviour of woven glass and carbon fibre composite laminates in a matrix of fire retardant resin under low-velocity impact. The performance is evaluated in terms of damage mechanisms and force time history curves. Six impact energy levels were used to test standard plates to identify the type of damage observed at various energy levels. Scanning electron microscopy (SEM) along with C-scans were used to characterise the damage. It has been observed that in woven composites, the damage occurs mostly between the fibre bundles and matrix. As the impact energy increases, the failure involves extended matrix cracking and fibre fracture. Moreover, due to the fibre architecture, both the contact forces between bundles of fibres and stretching of the bundles are responsible for the dominant matrix cracking damage mode observed at the low-impact energy level. As the impact energy increases, the damage also increases resulting in fibre fracture. The experimental evidence collected during this investigation shows that for both the carbon fibre and the glass fibre woven laminates the low-velocity impact behaviour is characterised by extended fibre fracture without a noticeable sudden load drop.

Comparison of damage resistance of thermoplastic and thermoset carbon fibre-reinforced composites

The research presented in the article concerns the resistance to damage of thermosetting and thermoplastic fabric carbon composites. A comparison of these materials resistance was made on the basis of the results of residual strength tests which include impact tests and static compression of samples after impact. The impact tests consisted of two impact criteria: specimens impacted with energy adjusted to the specimen thickness, determined on the basis of ASTM D7136 (energy criterion) and specimens impacted in such a way so as to obtain a specific depth of indentation (indentation depth criterion). The specimens struck according to the indentation depth criterion were additionally divided into two subgroups: with the indentation depth of 1.3 mm and the indentation depth of 2.6 mm. In addition, after impact tests, each specimen was subjected to ultrasonic phased array testing in order to obtain information about the extent of the damage. Experimental results showed that with less impact energy, the thermoplastic laminate has a higher residual strength than the thermosetting composite. This difference decreases as the impact energy increases.

Investigations on low-energy impact and post-impact fatigue of adhesively bonded single-lap joints using composites substrates

ABSTRACT This paper presents an extensive investigation on the low-energy impact damage and post-impact fatigue of composite/steel and composite/composite adhesive joints experimentally and numerically. Using carbon-fiber and glass-fiber reinforced plastics (CFRP and GFRP) as well as high-strength steel (HSS), four kinds of adhesive joints were fabricated, i.e., CFRP/CFRP, CFRP/HSS, GFRP/GFRP and GFRP/HSS single-lap joints (SLJ). The impact damage of the joints under different energy impacts was analyzed and introduced into the fatigue simulation. A multi-step coupling numerical method was proposed and validated to predict the post-impact fatigue life of the adhesive joints cost-effectively and conveniently. The effects of the impact energy density and the adherend/adhesive stiffness ratio were studied. The results show that the post-impact fatigue life decreases with the increasing impact energy density. The life decrease percentage of 1275 mJ/g impact condition is approximately more than seven times that of 425 mJ/g impact condition. The post-impact fatigue life of composite/steel joints is more susceptible to low-energy impact damage than that of the composite/composite joints. Reducing the flexural stiffness difference between two adherends as well as the adhesive can improve the post-impact fatigue life of the adhesive joints in composites.

Low Velocity Response of GFRP and Hybrid Laminates Under Impact Testing

This paper analyses the improvements in falling weight impact resistance characteristics of the laminates when highly flexible Polycarbonate (PC) sheet is sandwiched between Glass Fiber Reinforced Polymer (GFRP) laminates. Towards this, low-velocity impact (LVI) tests at different impact energies were conducted on various thicknesses of GFRP and hybrid laminates. For each given incident impact energy, the load—time data were extracted and the transient absorbed energy, as well as displacement, are computed by numerical integration. The impact energy obtained from this data is computed for all the laminates. Experimental investigation reveals that the hybrid laminate shows a significant increase in the maximum impact energy that can be absorbed before complete perforation as compared to bare GFRP laminate. Other impact resistance characteristics such as initial stiffness and peak load as a function of incident impact energy have been analyzed and the influence of PC insertion in the laminate (hybrid) on these parameters are experimentally investigated.

Soft body armor time-dependent back face deformation (BFD) with ballistics gel backing

This paper presents a method for obtaining time dependent back face deformation (BFD) data for body armor during ballistic impact using a clear ballistics gelatin backing and high-speed cameras to capture the deformation profile. Using this method, baseline fabric characterization data was obtained for samples comprised of varying layers of 467 g/m2 Kevlar K29 fabric impacted with 8.24 g steel ball projectile and backed with NATO standard 20% clear ballistics gelatin. For these tests, deformation depths were seen to increase with increasing impact energy and decreasing total areal density. A limited study of the various test parameters was performed by testing one additional fabric, projectile, and ballistics gelatin. From these comparisons, it was observed that 122 g/m2 Kevlar KM2+ fabric performs better per weight than 467 g/m2 Kevlar K29 fabric in terms of BFD, 9 mm FMJ projectiles produce deeper BFDs than 12.7 mm steel ball projectiles, and backing a sample with FBI standard 10% ballistics gel increases the BFD considerably over NATO standard 20% ballistics gel.

Research on impact toughness of 105SS drill pipe in wet H2S environment

In order to investigate the corrosion behavior and impact toughness of 105SS drill pipe steel in the wet H2S environment, the impact and corrosion testing were carried out. The results show that the diffusible hydrogen concentration is mainly influenced by the morphology of the corrosion scales and the dynamic fracture toughness loss of 105SS drill pipe steels increases with the increase of diffusible hydrogen concentration. However, when hydrogen was released, the impact energy increases. The area of quasi-cleavage features on the fracture surfaces increases with the increase of hydrogen concentration.