Study on the Penetration Performance of a 5.8 mm Ceramic Composite Projectile

The penetration ability of a 5.8 mm standard projectile can be improved by inserting a ZrO₂ ceramic ball with high hardness, high temperature, and pressure resistance at its head. Thereby, a ceramic composite projectile can be formed. A depth of penetration (DOP) experiment and numerical simulation were conducted under the same condition to study the armor-piercing effectiveness of a standard projectile and ceramic composite projectile on 10 mm Rolled Homogeneous Armor (RHA) and ceramic/Kevlar composite armor, respectively. The results show that both the ceramic composite and standard projectiles penetrated the armor steel target at the same velocity (850 m/s). The perforated areas of the former (φ5 mm & φ2 mm) were 2.32 and 2.16 times larger, respectively, than those of the latter. The residual core masses of these two projectiles (φ5 mm & φ2 mm) were enhanced by 30.45% and 22.23%. Both projectiles penetrated the ceramic/Kevlar composite armor at the same velocity (750 m/s). Compared with the standard projectile, the residual core masses of the ceramic composite one (Ø5 mm & Ø2 mm) were enhanced by 12.4% and 3.6%, respectively. This paper also analyzes the penetration mechanism of the ceramic composite projectile on target plates by calculating its impact pressure. The results show that the ceramic composite projectile outperformed the standard projectile in penetration tests. The research results are instructive in promoting the application of the ZrO₂ ceramic composite in an armor-piercing projectile design.     

Study of Impact Characteristics of ZrO2 Ceramic Composite Projectiles on Ceramic Composite Armor

Exploring new armor-piercing materials is crucial for improving the penetrative ability of projectiles. Based on the process of in situ solidification injection molding through ceramic dispersant hydrolytic degradation, a ZrO₂ ceramic material suitable for use as the tip of a 12.7 mm kinetic energy (KE) projectile was prepared. The ZrO₂ ceramic tip can be matched with the metal core of a conventional projectile to form a ceramic composite projectile, increasing the damage to the Al₂O₃ ceramic composite armor. Specifically, the ZrO₂ ceramic tip can increase the impact load on the Al₂O₃ ceramic panel, prolonging the pre-damage phase and reducing the stable penetration phase, shortening the mass erosion time of the metal core compared with a 12.7 mm metal KE projectile tip. The ceramic composite projectile with the ZrO₂ ceramic tip has a lower critical penetration velocity than a 12.7 mm metal KE projectile for Al₂O₃ ceramic composite armor. Furthermore, the residual velocity, residual length, and residual mass of the metal core of the ceramic composite projectile that penetrated the Al₂O₃ ceramic composite armor are greater than those of a 12.7 mm metal KE projectile.     

Ballistic Performance of Polyurea-Reinforced Ceramic/Metal Armor Subjected to Projectile Impact

Although polyurea has attracted extensive attention in impact mitigation due to its protective characteristics during intensive loading, the ballistic performance of polyurea-reinforced ceramic/metal armor remains unclear. In the present study, polyurea-reinforced ceramic/metal armor with different structures was designed, including three types of coating positions of the polyurea. The ballistic tests were conducted with a ballistic gun; the samples were subjected to a tungsten projectile formed into a cylinder 8 mm in diameter and 30 mm in length, and the deformation process of the tested targets was recorded with a high-speed camera. The ballistic performance of the polyurea-reinforced ceramic/metal armor was evaluated according to mass efficiency. The damaged targets were investigated in order to determine the failure patterns and the mechanisms of interaction between the projectile and the target. A scanning electron microscope (SEM) was used to observe the microstructure of polyurea and to understand its failure mechanisms. The results showed that the mass efficiency of the polyurea-coated armor was 89% higher than that of ceramic/metal armor, which implies that polyurea-coated ceramic armor achieved higher ballistic performance with lighter mass quality than that of ceramic/metal armor. The improvement of ballistic performance was due to the energy absorbed by polyurea during glass transition. These results are promising regarding further applications of polyurea-reinforced ceramic/metal armor.     

Study on the Penetration Power of ZrO2 Toughened Al2O3 Ceramic Composite Projectile into Ceramic Composite Armor

This work aims to improve the penetration ability of a 14.5 mm standard armor-piercing projectile into ceramic/armor steel (Al₂O₃/RHA) composite armor. To this end, ZrO₂ toughened Al₂O₃(ZTA) is prepared as the material for bullet tips, utilizing in situ solidification injection molding that is realized via ceramic dispersant hydrolytic degradation. The penetration power of ZTA ceramic composite projectile, compared with standard armor, against 15 mm armor steel (RHA) and 30 mm Al₂O₃/RHA composite armor, is studied by ballistics testing combined with numerical simulation. The Tate theory is optimized and then employed to calculate the penetration depth and bullet core’s residual mass when ZTA ceramic composite projectile penetrates into Al₂O₃/RHA composite armor. The results show that when penetrating RHA of 15 mm, the penetration area of ZTA ceramic composite projectile into RHA increases by 27.59% and the exit area by 42.93%. While the standard projectile fails to penetrate the 30 mm Al₂O₃/RHA composite armor, the ZTA ceramic composite armor-piercing projectile succeeds, with the mass loss reduced by 66.67% over the standard one. The ZTA ceramic composite bullet has a better performance than the standard bullet in penetrating RHA and Al₂O₃/RHA composite armors. The test results, simulation, and theoretical analysis are consistent. This study has practical values for engineering applications to design new ceramic composite bullets.     

Perforation of Double-Spaced Aluminum Plates by Reactive Projectiles with Different Densities

Perforation behavior of 3 mm/3 mm double-spaced aluminum plates by PTFE/Al/W (Polytetrafluoroethylene/Aluminum/Tungsten) reactive projectiles with densities ranging from 2.27 to 7.80 g/cm³ was studied experimentally and theoretically. Ballistic experiments show that the failure mode of the front plate transforms from petalling failure to plugging failure as projectile density increases. Theoretical prediction of the critical velocities for the reactive projectiles perforating the double-spaced plates is proposed, which is consistent with the experimental results and well represents the perforation performance of the projectiles. Dimensionless formulae for estimating the perforation diameter and deflection height of the front plates are obtained through dimensional analysis, indicating material density and strength are dominant factors to determine the perforation size. High-speed video sequences of the perforation process demonstrate that high-density reactive projectiles make greater damage to the rear plates because of the generation of projectile debris streams. Specifically, the maximum spray angle of the debris streams and the crater number in the debris concentration area of the rear plate both increase with the projectile density and initial velocity.     

Microstructure Effect of Heat Input on Ballistic Performance of Welded High Strength Armor Steel

The effect of two different heat inputs, 1.2 and 0.8 kJ/ mg, on the microstructure associated with a welded high hardness armor (HHA) steel was investigated by ballistic tests. A novel way of comparing the ballistic performance between fusion zone (FZ), heat-affected zone (HAZ), and base metal (BM) of the HHA joint plate was applied by using results of the limit velocity V₅₀. These results of V₅₀ were combined with those of ballistic absorbed impact energy, microhardness, and Charpy and tensile strength revealing that the higher ballistic performance was attained for the lower heat input. Indeed, the lower heat input was associated with a superior performance of the HAZ, by reaching a V₅₀ projectile limit velocity of 668 m/s, as compared to V₅₀ of 622 m/s for higher heat input as well as to both FZ and BM, with 556 and 567 m/s, respectively. Another relevant result, which is for the first time disclosed, refers to the comparative lower microhardness of the HAZ (445 HV) vs. BM (503 HV), in spite of the HAZ superior ballistic performance. This apparent contradiction is attributed to the HAZ bainitic microstructure with a relatively greater toughness, which was found more determinant for the ballistic resistance than the harder microstructure of the BM tempered martensite.     

Design,Manufacture, and Characterization of Auxetic Yarns with Multiple Core/Wrap Structure by Braiding Method

Auxetic textiles with a negative Poisson’s ratio show significant energy absorption and synclastic curvature characteristics and potential application value in sportsmen protection material. The stability and reliability of the structure and properties of auxetic textiles is also an important factor to assess and promote the application. Thus, auxetic yarns with multiple core/wrap structure were prepared by a 16-spindle braiding machine. It mainly focused on the axial stretching behavior and the relationship between the structure and auxetic effect of yarn samples. The maximum Poisson’s ratio of auxetic yarns was −3.26. The experimental results also showed that the complex yarns still presented an auxetic effect during 30 repeats of cycle stretching. According to the study about the repeatable stretchability and auxetic effect of complex yarns, it could be expected to provide more comfortable, safer, and smarter protective textiles.     

Experiment and Numerical Simulation of Damage Progression in Transparent Sandwich Structure under Impact Load

Crack initiation and propagation is a long-standing difficulty in solid mechanics, especially for elastic brittle materials. A new type of transparent sandwich structure, with a magnesium–aluminum spinel ceramic glass as the outer structure, was proposed in this paper. Its dynamic response was studied by high-speed impact experiments and numerical simulations of peridynamics under impact loads, simultaneously. In the experiments, a light gas cannon was used to load the projectile to 180 m/s, and the front impacted the transparent sandwich structure. In the numerical simulations, the discontinuous Galerkin peridynamics method was adopted to investigate the dynamic response of the transparent sandwich structure. We found that both the impact experiments and the numerical simulations could reproduce the crack propagation process of the transparent sandwich structure. The radial cracks and circumferential cracks of the ceramic glass layer and the inorganic glass layer were easy to capture. Compared with the experiments, the numerical simulations could easily observe the damage failure of every layer and the splashing of specific fragments of the transparent sandwich structure. The ceramic glass layer and the inorganic glass layer absorbed the most energy in the impact process, which is an important manifestation of the impact resistance of the transparent sandwich structure.     

Study on the Tensile Behavior of Helical Auxetic Yarns with Finite Element Method

Complex yarns with helical wrapping structure show auxetic effect under axial tension and a wide perspective application. Experimental results suggested that initial helical angle was one of the most important structural parameters. However, the experimental method was limited and could not effectively explain the deformation behavior or auxetic mechanism. A finite element model of the helical auxetic yarn was built and used to analyze the interactive relationship between the two components and the stress distribution mode. The effectiveness and accuracy of the model was first verified by comparing with the experimental results. The simulation results showed that the complex yarn with initial helical angle of 14.5° presented the maximum negative Poisson’s ratio of −2.5 under 5.0% axial strain. Both the contact property between the two components and the radial deformability of the elastic core filament were key factors of the auxetic property. When the contact surfaces were completely smooth and the friction coefficient μ was set to 0, the complex yarn presented non-auxetic behavior. When the Poisson’s ratio of the core filament was 0, the complex yarn showed greater auxetic effect. During the axial stretching, the tensile stress was mainly distributed in the wrap filament, which led to structural deformation and auxetic behavior. A pair of auxetic yarns showed pore effect and high expansion under axial strain. Thus, it may be necessary to consider new weaving structures and preparation methods to obtain the desired auxetic property and application of auxetic yarns.     

Direct Observation of Biaxial Nematic Order in Auxetic Liquid Crystal Elastomers

Auxetic materials exhibit a negative Poisson’s ratio, i.e., they become thicker rather than thinner in at least one dimension when strained. Recently, a nematic liquid crystal elastomer (LCE) was shown to be the first synthetic auxetic material at a molecular level. Understanding the mechanism of the auxetic response in LCEs is clearly important, and it has been suggested through detailed Raman scattering studies that it is related to the reduction of uniaxial order and emergence of biaxial order on strain. In this paper, we demonstrate direct observation of the biaxial order in an auxetic LCE under strain. We fabricated ~100 μm thick LCE strips with complementary geometries, exhibiting either planar or homeotropic alignment, in which the auxetic response is seen in the thickness or width of the sample, respectively. Polarized Raman scattering measurements on the planar sample show directly the reduction in the uniaxial order parameters on strain and suggest the emergence of biaxial order to mediate the auxetic response in the sample thickness. The homeotropic sample is studied via conoscopy, allowing direct observation of both the auxetic response in the width of the sample and increasing biaxiality in the LCE as it is strained. We verified that the mechanism of the auxetic response in auxetic LCEs is due to the emergence of the biaxial order and conclude such materials can be added to the small number of biaxial nematic systems that have been observed. Importantly, we also show that the mechanical Frèedericksz transition seen in some LCEs is consistent with a strain-induced transition from an optically positive to an optically negative biaxial system under strain, rather than a director rotation in a uniaxial system.     

Ballistic injury

Wound profiles made under controlled conditions in the wound ballistics laboratory at the Letterman Army Institute of Research showed the location along their tissue path at which projectiles cause tissue disruption and the type of disruption (crush from direct contact with the projectile or stretch from temporary cavitation). Comparison of wound profiles showed the fallacy in attempting to judge wound severity using velocity alone, and laid to rest the common belief that in treating a wound caused by a high-velocity missile, one needs to excise tissue far in excess of that which appears damaged. All penetrating projectile wounds, whether civilian or military, therefore should be treated the same regardless of projectile velocity. Diagnosis of the approximate amount and location of tissue disruption is made by physical examination and appropriate radiographic studies. These wounds are contaminated, and coverage with a penicillin-type antibiotic should be provided.     

Unsteady penetration of a target by a liquid jet

It is widely acknowledged that ceramic armor experiences an unsteady penetration response: an impacting projectile may erode on the surface of a ceramic target without substantial penetration for a significant amount of time and then suddenly start to penetrate the target. Although known for more than four decades, this phenomenon, commonly referred to as dwell, remains largely unexplained. Here, we use scaled analog experiments with a low-speed water jet and a soft, translucent target material to investigate dwell. The transient target response, in terms of depth of penetration and impact force, is captured using a high-speed camera in combination with a piezoelectric force sensor. We observe the phenomenon of dwell using a soft (noncracking) target material. The results show that the penetration rate increases when the flow of the impacting water jet is reversed due to the deformation of the jet–target interface––this reversal is also associated with an increase in the force exerted by the jet on the target. Creep penetration experiments with a constant indentation force did not show an increase in the penetration rate, confirming that flow reversal is the cause of the unsteady penetration rate. Our results suggest that dwell can occur in a ductile noncracking target due to flow reversal. This phenomenon of flow reversal is rather widespread and present in a wide range of impact situations, including water-jet cutting, needleless injection, and deposit removal via a fluid jet.Ceramic materials, although having a reputation for being inherently brittle, have been used for different armor systems for almost a century. The application of ceramic-based armor ranges from protection of aircraft and personnel against small-caliber threats, to vehicle armor designed to defeat long-rod penetrators and shaped charges.Here, we consider thick, well-confined ceramic armor systems designed to withstand the high-velocity impact of heavy-metal long-rod penetrators. Such systems are extensively used to study the dynamic penetration properties of ceramics over relatively long time frames: the confinement prevents/reduces the macroscopic cracking of the ceramic target and thus provides a more controlled experimental setting where statistical effects of cracking are minimized.The time-resolved penetration behavior of ceramic armor has been extensively studied over the past 45 y using flash radiography, a technique used for impact experiments involving optically opaque targets (1–4). As sketched in Fig. 1, the typical penetration–time behavior of a ceramic target impacted by a metallic long rod is characterized by three cases depending on the impact velocity . Case I: Below a critical impact velocity, the metallic long rod erodes completely on the target surface without significant penetration (Fig. 1A). This phenomenon is commonly referred to as interface defeat and the critical transition velocity is labeled “.”Open in a separate windowFig. 1.Sketches illustrating the three regimes of penetration of ceramic targets by long-rod penetrators as a function of projectile impact velocity . (A) For , the long-rod projectile is eroded on the target surface without significant penetration. This regime is called “interface defeat.” (B) For slightly larger than , the projectile dwells on the target surface for at least 29 μs before penetration commencing at a high rate. (C) For , penetration into the target occurs after a much shorter dwell period. (D) Sketch of typical penetration rate versus time curves for the three cases I–III. (A and B adapted from ref. 10; C adapted from ref. 12.)Case II: For velocities slightly higher than the transition velocity, a phase of projectile defeat followed by penetration can be observed (Fig. 1B). The phase without penetration has been termed dwell because the penetrator “dwells” on the target surface for a duration called dwell time. Case III: As the impact velocity increases well beyond the transition velocity, dwell times decrease until they become too short to be measured (Fig. 1C) (5).The most widely used explanation for the phenomenon of dwell is cracking-induced loss of penetration resistance of the target material. This explanation is mainly based on postmortem examination of recovered targets (6, 7). A region of intense microcracking and cone cracks immediately under the impact site was observed in cross-sections of ceramic targets subjected to impacts just below the transition velocity. Consequently, it is hypothesized that dwell occurs during the time when the ceramic transitions from an intact to a damaged state (5, 8).However, three critical failings of this hypothesis can be identified. First, whereas microcracking (comminution) was observed in silicon carbide (SiC), no comminution occurred in tungsten carbide (WC) and boron carbide (B₄C) targets, even though they display the phenomenon of dwell. Second, the process of cracking takes place on a timescale of the order of 1 μs (9), whereas dwell times can be up to two orders of magnitude higher (10, 11). Finally, there is experimental evidence that the penetration rate during dwell is not zero, indicating that the target material is pushed away or removed already during dwell (12). To conclude, the cracking-induced loss of penetration resistance of the target does not provide a satisfactory explanation for the origins of dwell.In search for an alternative explanation, we note that Renström et al. (13) demonstrated that the loading from the impacting long rod on the ceramic targets is predominantly inertial (or hydrodynamic) in nature. This raises the question of whether fluid–structure interaction (FSI) between the fluid-like projectile and the deformable target might offer another possible explanation for the dwell phenomenon. FSI effects have been studied in the context of sand sprays impacting deformable structures (14, 15). Similar to the impacting long rod, the loading by the sand is also primarily inertial in nature. In such cases there is a substantial increase in the momentum transmitted by the sand to a deformable structure compared with sand impact on a rigid structure.In the ceramic target experiments with which we are concerned, the eroding projectile seems to exhibit a flow alteration due to the deformation of the target surface (Fig. 1). This flow alteration is also observed in numerical simulations of related experiments (16). The situation closely resembles a water jet hitting a dimpled rigid surface as shown in Fig. 2, a textbook example from which we know that the transmitted momentum and the impact force increase with increasing curvature of the surface (17). Considering the rate of momentum of the fluid striking the target surface and the fluid leaving the target surface, the force exerted on the target by the jet (in the direction of the incoming jet) is given bywhere is the angle between incoming and exiting fluid, is the material density of the jet, and the cross-sectional area of the jet. This simple expression can be used to gauge what phenomenon might occur when a jet impacts a deforming target (for cases when the jet velocity is much larger than the penetration rate). With increasing deformation of the surface of the target, decreases, resulting in an increase in the force ––it is this FSI effect that we hypothesize results in the unsteady penetration rate of the target. Numerical simulations, such as those in ref. 16, suggest that the impact pressure is affected by the penetration–deformation of the target surface, but they show no clear correlation between the impact pressure variations and the associated penetration rates.Open in a separate windowFig. 2.Schematic view of the proposed FSI mechanism resulting in an unsteady penetration rate due to the impact of a fluid jet with velocity . (A) During the initial stages of the jet impact, the target surface is flat and the fluid spreads horizontally. (B) As the jet deforms the target and penetrates at depth δ, it creates a dimple at the impact site; the flow pattern changes, resulting in backflow of the fluid with a velocity and a consequent increase in the impact force , which increases as the jet exit angle decreases.This study aims to explore the FSI during projectile impact by using scaled analog experiments. These are designed to circumvent the two major challenges associated with the previously described ceramic target experiments, namely: (i) to obtain direct impact force measurements, and (ii) to achieve a sufficient spatial and temporal resolution of the 3D problem with a very limited number of 2D images. We therefore perform experiments wherein a low-velocity water jet impacts on a translucent gel.We show that our scaled analog experiments reproduce the penetration versus time responses observed for ceramic targets impacted by long-rod penetrators, albeit at much lower impact velocities and consequent penetration rates. Results presented here include three impact velocities: slightly lower, slightly higher, and significantly higher than the transition velocity . Similar to the ceramic target experiments, the loading times in our scaled experiments are much longer than the time for elastic wave propagation through the target. This implies that on the timescale of the loading, the target is in static equilibrium insomuch as the force exerted by the jet on the target is equal to the reaction force between the target and the support structure. Thus, to quantify the FSI effect we perform direct impact force measurements by placing the translucent gel target on a high-sensitivity piezoelectric force sensor. The force measured by the transducer is equal to the impact force. We present these measurements in terms of a nominal impact pressure defined aswhere is the cross-sectional area of the incoming jet.We also perform a series of control creep penetration experiments wherein the penetration force is kept constant by applying a fixed load on a steel-rod penetrator with cross-sectional area , i.e., equal to that of the water jet. The control experiments are designed such that the penetration pressure is equal to that exerted by the water jet on a rigid flat target:The contrast between the water-jet penetration versus time responses and those in the control creep experiments will serve to demonstrate that it is the FSI effect that results in the observed unsteady penetration response.     

Three-Dimensional Smooth Particle Hydrodynamics Modeling and Experimental Analysis of the Ballistic Performance of Steel-Based FML Targets

In this paper, shields made of 1.3964 stainless steel bonded to a fiber laminate were subjected to ballistic impact response of 7.62 × 51 mm ŁPS (light projectile with a lead core) projectiles. Additionally, between the steel sheet metal and the laminate, a liquid-filled bag was placed, which was a mixture of ethylene glycol (C₂H₆O₂) with 5 wt.% SiO₂ nanopowder. Numerical modeling of the projectile penetrating the samples was carried out using the finite element method in the Abaqus program. The elasto-plastic behavior of the projectile material and the component layers of the shields was taken into account. Projectile penetration through glycol-filled bag has been performed using the smooth particle hydrodynamics technique. The morphology of the penetration channel was also analyzed using a scanning electron microscope. For the shield variant with a glycol-filled bag between the steel and laminate plates, the inlet speed of projectile was 834 m/s on average, and 366 m/s behind the sample. For the variant where there was no glycol-filled bag between the steel and laminate plates, the inlet and outlet average velocities were 836 m/s, after 481 m/s, respectively. Referring to the steel-glycol-laminate and steel-laminate variants, it can be concluded that the laminate-glycol-laminate is more effective.     

Effect of Heat Input on the Ballistic Performance of Armor Steel Weldments

The purpose of this study is to examine the projectile penetration resistance of the base metal and heat-affected zones of armor steel weldments. To ensure the proper quality of armor steel welded joints and associated ballistic protection, it is important to find the optimum heat input for armor steel welding. A total of two armor steel weldments made at heat inputs of 1.29 kJ/mm and 1.55 kJ/mm were tested for ballistic protection performance. The GMAW welding carried out employing a robot-controlled process. Owing to a higher ballistic limit, the heat-affected zone (HAZ) of the 1.29 kJ/mm weldment was found to be more resistant to projectile penetration than that of the 1.55 kJ/mm weldment. The ballistic performance of the weldments was determined by analyzing the microstructure of weldment heat-affected zones, the hardness gradients across the weldments and the thermal history of the welding heat inputs considered. The result showed that the ballistic resistance of heat affected zone exist as the heat input was decreased on 1.29 kJ/mm. It was found that 1.55 kJ/mm does not have ballistic resistance.     

High-performance continuous-wave room temperature 4.0-μm quantum cascade lasers with single-facet optical emission exceeding 2?W

A strain-balanced, AlInAs/InGaAs/InP quantum cascade laser structure, designed for light emission at 4.0 μm using nonresonant extraction design approach, was grown by molecular beam epitaxy. Laser devices were processed in buried heterostructure geometry. An air-cooled laser system incorporating a 10-mm × 11.5-μm laser with antireflection-coated front facet and high-reflection-coated back facet delivered over 2 W of single-ended optical power in a collimated beam. Maximum continuous-wave room temperature wall plug efficiency of 5.0% was demonstrated for a high-reflection-coated 3.65-mm × 8.7-μm laser mounted on an aluminum nitride submount.     

Structural Response of Polyethylene Foam-Based Sandwich Panels Subjected to Edgewise Compression

This study analyzes the mechanical behavior of low density polyethylene foam core sandwich panels subjected to edgewise compression. In order to monitor panel response to buckling, strains generated in the facesheets and overall out-of-plane deformations are measured with strain gages and projection moiré, respectively. A finite element (FE) model simulating the experimental test is developed. Numerical results are compared with moiré measurements. After having been validated against experimental evidence, the FE model is parameterized, and a trade study is carried out to investigate to what extent the structural response of the panel depends on the sandwich wall construction and facesheet/core interface defects. The projection moiré set-up utilized in this research is able to capture the sudden and very localized buckling phenomena occurring under edgewise compression of foam-based sandwich panels. Results of parametric FE analyses indicate that, if the total thickness of the sandwich wall is fixed, including thicker facesheets in the laminate yields a larger deflection of the panel that becomes more sensitive to buckling. Furthermore, the mechanical response of the foam sandwich panel is found to be rather insensitive to the level of waviness of core-facesheet interfaces.     

Effect of prosthetic aortic valve design on the Doppler-catheter gradient correlation: an in vitro study of normal St. Jude, Medtronic-Hall, Starr-Edwards and Hancock valves.

To evaluate the normal range of Doppler-derived velocities and gradients, their relation to direct flow measurements and the importance of prosthetic valve design on the relation between Doppler and catheter-derived gradients, five sizes of normal St. Jude bileaflet, Medtronic-Hall tilting disc, Starr-Edwards caged ball and Hancock bioprosthetic aortic valves were studied with use of a pulsatile flow model. A strong linear correlation between peak velocity and peak flow, and mean velocity and mean flow, was found in all four valve types (r = 0.96 to 0.99). In small St. Jude and Hancock valves, Doppler velocities and corresponding gradients increased dramatically with increasing flow, resulting in velocities and gradients as high as 4.7 m/s and 89 mm Hg, respectively. The ratio of velocity across the valve to velocity in front of the valve (velocity ratio) was independent of flow in all St. Jude, Medtronic-Hall, Starr-Edwards and Hancock valves when the two lowest flow rates were excluded for Hancock valves. Although Doppler peak and mean gradients correlated well with catheter peak and mean gradients in all four valve types, the actual agreement between the two techniques was acceptable only in Hancock and Medtronic-Hall valves. For St. Jude and Starr-Edwards valves, Doppler gradients significantly and consistently exceeded catheter gradients with differences as great as 44 mm Hg. Thus, Doppler velocities and gradients across normal prosthetic heart valves are highly flow dependent. However, the velocity ratio is independent of flow.(ABSTRACT TRUNCATED AT 250 WORDS)     

Penetration Fracture Mechanism of Tungsten-Fiber-Reinforced Zr-Based Bulk Metallic Glasses Matrix Composite under High-Velocity Impact

In order to adapt to the launch velocity of modern artillery, it is necessary to study the fracture mechanism of the high-velocity penetration of penetrators. Therefore, the penetration fracture mode of tungsten-fiber-reinforced Zr-based bulk metallic glass matrix composite (WF/Zr-MG) rods at a high velocity is studied. An experiment on WF/Zr-MG rods penetrating into rolled homogeneous armor steel (RHA) was carried out at 1470~1650 m/s. The experimental results show that the higher penetration ability of WF/Zr-MG rods not only results from their “self-sharpening” feature, but also due to the fact they have a longer quasi-steady penetration phase than tungsten alloy (WHA) rods. Above 1500 m/s, the penetration fracture mode of the WF/Zr-MG rod is the bending and backflow of tungsten fibers. Our theoretical calculation shows that the deformation mode of the Zr-based bulk metallic glass matrix (Zr-MG) is an important factor affecting the penetration fracture mode of the WF/Zr-MG rod. When the impact velocity increases from 1000 m/s to 1500 m/s, the deformation mode of Zr-MG changes from shear localization to non-Newtonian flow, leading to a change in the penetration fracture mode of the WF/Zr-MG rod from shear fracture to the bending and backflow of tungsten fibers.     

Right ventricular function in ischemic or idiopathic dilated cardiomyopathy.

BACKGROUND: Differentiation between ischemic (ICM) and dilated cardiomyopathy (DCM) has important therapeutic implications because the former may benefit from coronary revascularization. The aim of this study was to investigate right ventricular (RV) function using tissue Doppler echocardiography (TDE) and compare the TDE parameters of the RV among patients with ICM and DCM. METHODS AND RESULTS: Forty-two patients with ICM and 40 patients with DCM were studied with conventional echocardiography and TDE. The 2 groups did not differ in terms of New York Heart Association class, left ventricular ejection fraction and pharmacological treatment. Patients with ICM had higher pulmonary artery systolic pressure (44.4 mmHg vs 34.7 mmHg, p=0.006) and lower tricuspid annular motion systolic (RV Sa 0.06 m/s vs 0.09 m/s, p<0.0001), and diastolic velocities (RV Ea 0.05 m/s vs 0.07 m/s, p=0.0003, RV Aa 0.075 m/s vs 0.11 m/s, p=0.0016). They also exhibited a higher ratio of early transtricuspid filling velocity to early diastolic velocity of the tricuspid annulus (RV E/Ea 8.2 vs 5.7, p=0.0008). Age, pulmonary artery systolic pressure and tricuspid Sa were significant independent predictors of the diagnosis of ICM. CONCLUSIONS: RV dysfunction is more pronounced in patients with ICM than in patients with DCM. The RV TDE parameters can be used to complement clinical and conventional echocardiographic findings in the assessment of patients with ICM and DCM.