Nylon Projectiles Research Articles

Impact Study on Composite Targets by a Nylon Projectile

In the present paper, impact study of nylon projectile on composite targets using a water-jet disruptor was addressed with damage mechanism. The three different composite targets such as teak, ply and pine woods were used in the experiment. The strength of wood and the damage under impact load is very crucial. The failure under load is very intricate as it is made up of natural composite. The composite target damage mechanism depends on characterisation and impact velocity of projectile. Simultaneously stresses and strains are generated which makes it responsible to cause the damage. Disruptor using water-jet plays a very crucial role in neutralising Improvised Explosive Devices (IEDs) with the minimum risk. These devices are designed to generate a high velocity water-jet using an electrically initiated gas generator cartridge. This helps in separating the critical components of IED’s and avoiding them from operating as anticipated. The damage caused by a waterjet disruptor is not quantified in assessing the performance. However, at present no technique was available to evaluate the performance. The terminal ballistics tests at the target end are found appropriate for solid projectiles, such as penetration of bullet into target plates or impact of fragments. These terminal effects are the good indicators considering the destruction. The available alternative measurement techniques are cost effective that forms a basis for future common test protocols. The authors suggested that craters made by a nylon projectile using the disruptor provide a quantitative measure. This should be considered as a potential for upcoming standard test for evaluating the performance. The impact caused by a nylon projectile is dependent on projectile kinetic energy and the dissemination of stress wave in the surrounding zone. The energy dissipated by a nylon projectile gets absorbed by the targets through a certain mechanisms. Ballistic velocities for various targets are also worked out. Pinewood has less ballistic velocity limit as compared to other two targets. Study and methods for the disruptor performance on various composite targets (plywood, teak wood and pinewood with 15 mm thickness) at 0.5 and 1m stand-off distances are evaluated. This compares with the respective common target tests. From the experiments, it is concluded that a nylon projectile has potential to penetrate through composite targets.

Numerical Analysis of Nylon Projectile Engraving into Rifle

The parametric model of projectile and rifled barrel is established by using finite element software ABAQUS. The numerical simulation of the projectile engraving into the bearing band under the maximum chamber pressure of 10 MPa and 15 MPa is carried out respectively. he force condition and morphological changes of projectile during extrusion at different times are analyzed and explained. The variation of velocity and displacement of projectile is obtained in the chamber, respectively. Simultaneously, the velocity and displacement components of rifled barrel and slippery barrel after muzzle exit are presented. It is verified that the rifling structure can effectively reduce the emission dispersion of the launching system under gravity free.

Experimental Research of Electrical Output Characteristics of Stacked PZT-5H Under High-Overload Conditions

Stacked piezoelectric ceramics (PZT-5H) are often used as sensors and pulsed power sources in moving objects. They will be subjected to a larger overload force when the moving objects collide with the target. In order to study the influence of the connection mode (parallel/series) of ceramic chips on the electrical output characteristics of stacked PZT-5H during overload, many experiments were performed using a nylon projectile to impact the stacked piezoelectric ceramic with different impact velocities by using a one-stage light gas gun as the loading device. The influence of a full bridge rectifier circuit on electrical output characteristics of the stacked PZT-5H was analyzed.

Oblique impact cratering experiments in brittle targets: Implications for elliptical craters on the Moon

Most impact craters observed on planetary bodies are the results of oblique impacts of meteoroids. To date, however, there have only been very few laboratory oblique impact experiments for analogue targets relevant to the surfaces of extraterrestrial bodies. In particular, there is a lack of laboratory oblique impact experiments into brittle targets with a material strength on the order of 1MPa, with the exception of ice. A strength on the order of 1MPa is considered to be the corresponding material strength for the formation of craters in the 100m size range on the Moon. Impact craters are elliptical if the meteoroid's trajectory is below a certain threshold angle of incidence, and it is known that the threshold angle depends largely on the material strength. Therefore, we examined the threshold angle required to produce elliptical craters in laboratory impact experiments into brittle targets. This work aims to constrain current interpretations of lunar elliptical craters and pit craters with sizes below a hundred meters. We produced mortar targets with compressive strength of 3.2MPa. A spherical nylon projectile (diameter 7.14mm) was shot into the target surface at a nominal velocity of 2.3km/s, with an impact angle of 5°‐90° from horizontal. The threshold angle of this experiment ranges from 15° to 20°. We confirmed that our experimental data agree with previous empirical equations in terms of the cratering efficiency and the threshold impact angle. In addition, in order to simulate the relatively large lunar pit craters related to underground cavities, we conducted a second series of experiments under similar impact conditions using targets with an underground rectangular cavity. Size and outline of craters that created a hole are similar to those of craters without a hole. Moreover, when observed from an oblique angle, a crater with a hole has a topography that resembles the lunar pit craters. The relation between the impact velocity of meteoroids on the Moon and the probability of elliptical crater formation was investigated based on our experimental results and an existing empirical equation. The results suggest a distinct possibility that most craters in the 100m size range on the Moon, given their elliptical shape, originated as secondary craters.

Fragment shapes in impact experiments ranging from cratering to catastrophic disruption

Laboratory impact experiments have found that impact fragments tend to be elongated. Their shapes, as defined by axes a, b and c, these being the maximum dimensions of the fragment in three mutually orthogonal planes (a⩾b⩾c), are distributed around mean values of the axial ratios b/a∼0.7 and c/a∼0.5. This corresponds to a:b:c in the simple proportion 2:√2:1. The shape distributions of some boulders on Asteroid Eros, the small- and fast-rotating asteroids (diameter <200m and rotation period <1h), and asteroids in young families, are similar to those of laboratory fragments created in catastrophic disruptions. Catastrophic disruption is, however, a process that is different from impact cratering. In order to systematically investigate the shapes of fragments in the range from impact cratering to catastrophic disruption, impact experiments for basalt targets 5–15cm in size were performed. A total of 28 impact experiments were carried out by firing a spherical nylon projectile (diameter 7.14mm) perpendicularly into the target surface at velocities of 1.60–7.13km/s. More than 12,700 fragments with b⩾4mm generated in the impact experiments were measured. We found that the mean value of c/a in each impact decreases with decreasing impact energy per unit target mass. For instance, the mean value of c/a in an impact cratering event is nearly 0.2, which is considerably smaller than c/a in a catastrophic disruption (∼0.5). The data presented here can provide important evidence to interpret the shapes of asteroids and boulders on asteroid surfaces, and can constrain current interpretations of asteroid formation. As an example, by applying our experimental results to the boulder shapes on Asteroid Itokawa’s surface, we can infer that Itokawa’s parent body must have experienced a catastrophic disruption.

Ejecta velocity distribution of impact craters formed on quartz sand: Effect of projectile density on crater scaling law

In order to clarify the effects of projectile density on ejecta velocity distributions for a granular target, impact cratering experiments on a quartz sand target were conducted by using eight types of projectiles with different densities ranging from 11gcm−3 to 1.1gcm−3, which were launched at about 200ms−1 from a vertical gas gun at Kobe University. The scaling law of crater size, the ejection angle of ejecta grains, and the angle of the ejecta curtain were also investigated. The ejecta velocity distribution obtained from each projectile was well described by the π-scaling theory of v0gR=k2x0R-1μ, where v0, g, R and x0 are the ejection velocity, gravitational acceleration, crater radius and ejection position, respectively, and k2 and μ are constants mostly depending on target material properties (Housen, K.R., Holsapple, K.A. [2011]. Icarus 211, 856–875). The value of k2 was found to be almost constant at 0.7 for all projectiles except for the nylon projectile, while μ increased with the projectile density, from 0.43 for the low-density projectile to 0.6–0.7 for the high-density projectile. On the other hand, the π-scaling theory for crater size gave a μ value of 0.57, which was close to the average of the μ values obtained from ejecta velocity distributions. The ejection angle, θ, of each grain decreased slightly with distance, from higher than 45° near the impact point to 30–40° at 0.6 R. The ejecta curtain angle is controlled by the two elementary processes of ejecta velocity distribution and ejection angle; it gradually increased from 52° to 63° with the increase of the projectile density. The comparison of our experimental results with the theoretical model of the crater excavation flow known as the Z-model revealed that the relationship between μ and θ obtained by our experiments could not be described by the Z-model (Maxwell, D.E. [1977]. In: Roddy, D.J., Pepin, R.O., Merrill, R.B. (Eds.), Impact and Explosion Cratering. Pergamon, NY, pp. 1003–1008). Therefore, we used the extended Z-model by Croft (Croft, S.K. [1980]. Proc. Lunar Sci. Conf. 11, 2347–2378), which could be applied to the crater excavation process when the point source was buried at the depth of d under the target surface, and then all the experimental results of μ and θ were reasonably explained by suitable Z and d values of the extended Z-model.

Impact cratering experiments in brittle targets with variable thickness: Implications for deep pit craters on Mars

High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1–6cm, and a bulk density of 1550kg/m3 by using a mixture of cement, water and sand (0.2mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2±0.9MPa. A spherical nylon projectile (diameter 7mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead.

A New Online Resource for the Hypervelocity Impact Community and the Change of Debris Cloud Impact Patterns With Impact Velocity

We announce the creation of a new online archive containing high resolution images, and measurements of over 200 metal plates impacted with a variety of projectiles at velocities between 1 and 8.5km s−1. This archive is being made freely accessible for use by the shock physics and hypervelocity impact research communities.During the course of this archival work, it was discovered that debris cloud impact patterns from nylon projectiles form distinct geometric patterns, and that these patterns seem to fall into a distinct group depending on the projectile impact velocity. Complementary hydrocode modelling (using Ansys’ AUTODYN) has been performed to try to recreate the patterns, but was not entirely successful, indicating that there is some physics that is not simulated within the hydrocode. Full details of the online archive and the hydrocode modelling are detailed in a much longer manuscript published by Loft K, Price M. C. et al. in the special HVIS 2012 edition of the Int. J. of Impact Engineering (DOI: 10.1016/j.ijimpeng.2012.07.007).

Impacts into metals targets at velocities greater than 1 km s−1: A new online resource for the hypervelocity impact community and an illustration of the geometric change of debris cloud impact patterns with impact velocity

We announce the creation of a new online archive containing high resolution images, and measurements of over 200 metal plates impacted with a variety of projectiles at velocities between 1 and 8.5 km s−1. This archive is being made freely accessible for use by the shock physics and hypervelocity impact research communities.During the course of this archival work, it was discovered that debris cloud impact patterns from nylon projectiles form distinct geometric patterns, and that these patterns seem to fall into a distinct group depending on the projectile impact velocity. Complementary hydrocode modelling (using Ansys' AUTODYN) has been performed to try to recreate the patterns, but was not entirely successful, indicating that there is some physics that is not simulated within the hydrocode.

The effect of a thin weak layer covering a basalt block on the impact cratering process

To clarify the effect of a surface regolith layer on the formation of craters in bedrock, we conducted impact-cratering experiments on two-layered targets composed of a basalt block covered with a mortar layer. A nylon projectile was impacted on the targets at velocities of 2 and 4kms−1, and we investigated the crater size formed on the basalt. The crater size decreased with increased mortar thickness and decreased projectile mass and impact velocity. The normalized crater volume, πV, of all the data was successfully scaled by the following exponential equation with a reduction length λ0: πV=b0πY-b1exp(-λ/λ0), where λ is the normalized thickness T/Lp, T and Lp are the mortar thickness and the projectile length, respectively, b0 and b1 are fitted parameters obtained for a homogeneous basalt target, 10−2.7±0.7 and −1.4±0.3, respectively, and λ0 is obtained to be 0.38±0.03. This empirical equation showing the effect of the mortar layer was physically explained by an improved non-dimensional scaling parameter, πY∗, defined by πY∗=Y/(ρtup2), where up was the particle velocity of the mortar layer at the boundary between the mortar and the basalt. We performed the impact experiments to obtain the attenuation rate of the particle velocity in the mortar layer and derived the empirical equation of upvi=0.50exp-λ1.03, where vi is the impact velocity of the projectile. We propose a simple model for the crater formation on the basalt block that the surface mortar layer with the impact velocity of up collides on the surface of the basalt block, and we confirmed that this model could reproduce our empirical equation showing the effect of the surface layer on the crater volume of basalt.

Impact experiments of porous gypsum–glass bead mixtures simulating parent bodies of ordinary chondrites: Implications for re-accumulation processes related to rubble-pile formation

Laboratory impact experiments were conducted for gypsum–glass bead targets simulating the parent bodies of ordinary chondrites. The effects of the chondrules included in the parent bodies on impact disruption were experimentally investigated in order to determine the impact conditions for the formation of rubble-pile bodies after catastrophic disruption. The targets included glass beads with a diameter ranging from 100 μm to 3 mm and the volume fraction was 0.6, similar to that of ordinary chondrites, which is about 0.65–0.75. Nylon projectiles with diameters of 10 mm and 2 mm were impacted at 60–180 m s −1 by a single-stage gas gun and at 4 km s −1 by a two-stage light gas gun, respectively. The impact strength of the gypsum–glass bead target was found to range from 56 to 116 J kg −1 depending on the glass bead size, and was several times smaller than that of the porous gypsum target, 446 J kg −1 in low-velocity collisions. The impact strengths of the 100 μm bead target and the porous gypsum target strongly depended on the impact velocity: those obtained in high-velocity collisions were several times greater than those obtained in low-velocity collisions. The velocities of fragments ejected from two corners on the impact surface of the target, measured in the center of the mass system, were slightly dependent on the target materials, irrespective of impact velocity. These results suggest that chondrule-including planetesimals (CiPs) can reconstruct rubble-pile bodies in catastrophic disruptions at the size of the planetesimal smaller than that of planetesimals without chondrules.

Experimental study on the impact fragmentation of core–mantle bodies: Implications for collisional disruption of rocky planetesimals with sintered core covered with porous mantle

Impact experiments of inhomogeneous targets such as layered bodies consisting of a dense core and porous mantle were conducted to clarify the effect of the layered structure on impact strength. The layered structure of small bodies could be the result of the thermal evolution of planetesimals in the solar nebula. So, the impact disruption of thermally evolved bodies with core–mantle structure is important for the origin of small bodies such as asteroids. We investigated the impact strength of rocky-layered bodies with porous mantle-sintered cores, which could be formed at an initial stage of thermal evolution. Spherical targets composed of soda-lime glass or quartz core and porous gypsum mantle were prepared as an analog of small bodies with a core–mantle structure, and the internal structure was changed. A nylon projectile was impacted at the impact velocity from 1 to 5 km/s. The impact strength of the core–mantle targets decreases with the increase of the core/target mass ratio ( R CM ) in the specific energy range from 1 × 10 3 to 4 × 10 4 J / kg . We observed two distinct destruction modes characterized by the damage to the core: one shows a damaged core and fractured mantle, and the other shows an intact core and broken mantle. The former mode was usually observed with increasing R CM , and the boundary condition of the core destruction ( Q t _ b ∗ ) was experimentally found to be Q t _ b ∗ [ J / kg ] = Q c ∗ ( R CM ) −2 , where Q c ∗ is the specific energy required to disrupt a glass core. From this empirical equation, it might be possible to discuss the destruction conditions of a thermally evolved body with a porous mantle-sintered core structure. We speculate that the impact strength of the body could be significantly reduced with the progress of internal evolution at the initial stage of thermal evolution.

Study on microwave emission mechanisms on the basis of hypervelocity impact experiments on various target plates

It was formerly confirmed by experiment that hypervelocity impacts on aluminum plates cause microwave emission. In this study, we have carried out experiments in order to clarify the mechanism of the emission. The microwave is detected by heterodyne detection scheme at 22 and 2 GHz with an intermediate frequency bandwidth of 500 and 120 MHz, respectively. A nylon projectile is accelerated using a light-gas gun to impact a target. First, aluminum plates with ten different thicknesses ranging from 1 to 40 mm were used as a target, and microwave signals were detected. The experimental results are statistically analyzed assuming a Gaussian distribution of the emitted power. The standard deviation of pulse voltage is calculated to show the existence of two kinds of signals: sharp pulse and thermal noise. It is shown that the emitted energy and the dispersion have a relation with the extent of the target destruction. Next, nylon projectiles are impacted on different metals such as aluminum, iron, and copper. These results suggest that microcracks are essential to microwave emission. Finally, in order to clarify the mechanism of charging and discharging across the microcracks, the experimental results are compared with this model for the following factors: (1) the thermally excited electrons and the emitted power, and (2) the bond dissociation energy of target material and emitted power. The analytical results suggest that electrons are excited thermally and by transition from a crystalline state to an atomic state.

Momentum Transfer in Oblique Impacts: Implications for Asteroid Rotations

We calculate the momentum transfer efficiency for small cratering impacts from 59 high-velocity (0.76–4.4 km/s) oblique impact experiments using nylon projectiles and targets made of basalt, aluminum, mild steel, mortar, and nylon. High-speed video frames show an initial luminous stream downrange of impact point for all the target materials. For basaltic and mortar targets there follows axi-symmetric ejection of target material around surface normal at the impact point. Our results suggest that: (1) momentum carried away by the axi-symmetric ejecta would significantly contribute to the normal component of momentum transfer efficiency; and (2) thepenetration depth of the projectile into target could determine the tangential momentum transfer efficiency. We calculated the efficiency of angular momentum transfer from the translational motion of projectiles to the rotation of ellipsoidal asteroids using the efficiencies for the linear momentum. The efficiency is more than four times that for spherical asteroid at their principal axis ratio of 2 : 1.4 : 1. If the experimental results hold for the impact that formed the largest crater on 253 Mathilde, the largest projectile estimated may have despun the asteroid to the present slow rotation by chance.

Angular momentum transfer in oblique impacts: Implications for 1989ML

We conducted 10 shots of high-velocity oblique impact experiments (1.95–3.52 km/s) using nylon projectiles and spherical mortar targets. Large craters were formed, but these targets were not disrupted by the impacts. We then calculated the efficiencies of momentum transfer from the projectile to the post-impact target for each experiment. The efficiencies of angular momentum transfer from the translational motion of the projectiles to the rotation of the post-impact targets were also derived. A representative efficiency of angular momentum transfer was calculated to be 0.17 for random successive collisions. The efficiency was applied to an equation expressing the precession angle of asteroids. It is shown that 1989ML, target of Japan-US asteroid-sample-return-mission (MUSES-C) would be tumbling.

Collisional Disruption of Ice by High-Velocity Impact

High-velocity impact among icy planetesimals is a physical phenomenon important to the planetary evolution process in the outer Solar System. In order to study this phenomenon, impact experiments on water ice were made by using a two-stage light gas gun installed in a cold room (−10°C) to clarify the elementary processes of collisional disruption and to study the reaccumulation and the escape conditions of the impact fragments. Cubic ice targets ranging in size from 15 to 100 mm were impacted by a nylon projectile of 7 mg with an impact velocity ( v i) from 2.3 to 4.7 km/s. The corresponding mass ratio of the projectile to the target ( m p/ M t) ranged from 10 −3 to 10 −6, which is two orders of magnitude lower than that used in previous studies (Arakawa et al. 1995, Icarus 118, 341–354). As a result, we obtained data on elementary processes such as attenuation of the shock wave and fragmentation dynamics. We found that the shock pressure attenuates in the ice target according to the relation of P∝( L p/ r 2, irrespective of the mass ratio between 10 −3 and 10 −5, where L p is the projectile size and r is a propagation distance. The largest fragment mass ( m l) normalized by the original target mass has a good relationship to a nondimensional impact stress ( P I, NDIS) defined as the ratio of the antipodal pressure to the material strength. This relationship is described as m l/ M t ∝ P I −1.7 for a wide range of impact conditions (50 m/s< v i<4 km/s and 10 −1< m l/ M t<10 −6), and shows the utility of NDIS. Using a measured shock wave decay constant of 2, the reaccumulation and the escape conditions of icy bodies in high-velocity collisions were estimated. As a result, it was clarified that a rubble pile could be formed when large icy bodies (radius>20 km) reaccumulated. On the other hand, when smaller icy bodies (radius<2 km) disrupted catastrophically, all fragments escaped and a rubble pile was never formed.

Experimental investigations on neutron emission from projectile-impacted deuterated solids

Deuterated polycrystalline solids (LiD, TiD x and PdD x , etc.) were impacted by nylon projectiles of < 1 km/s velocity to look for and characterize possible neutron emissions from fracto-fusion type reactions. Emission of < 100 neutrons from impacted 6–8 mm size lithium deuteride samples is inferred by monitoring signals from a bank of BF 3 detectors in various ways.

Velocity Measurements of Impact Ejecta from Regolith Targets

We performed new experiments with impacts on regolith-like layers of glass spheres to investigate the spatial and velocity distributions of ejecta with velocities higher than several hundred m sec−1. Spherical nylon projectiles of 7.0 mm diameter were accelerated to about 4 km sec−1using a two-stage light-gas gun. The ejecta were detected by thin Al foil targets of different thickness, and the resulting holes on the foil were counted to derive the velocity distribution using an empirical threshold penetration formula. The spatial distribution of the ejecta was also derived from the analysis of the position of the penetration holes. The high velocity ejecta were concentrated toward the downrange azimuth of the impacting projectile because of the oblique impacts of the projectiles into the targets. In order to estimate the total volume of ejecta with velocity higher than a given velocity, the measured spatial distributions were extrapolated to regions where no Al targets were exposed. The results were compared to a scaling formula based on low velocity data of the ejecta from sand targets. Though our results on the volume of ejecta with higher velocity lie below the extrapolation of the lower velocity data, the differences were within about one order of magnitude.

Fragment Mass Distribution of Platelike Objects

The fragment mass distributions of platelike objects are investigated by conducting two types of experiments. The first is a ``sandwich'' experiment in which thin glass and plaster plates are inserted between two larger stainless steel plates and an iron projectile is dropped onto the target plate at normal incidence. The second is a ``lateral impact'' experiment in which a hypervelocity nylon projectile collides at the side of the plaster plates. There is a discrepancy in the power-law exponent of fragment mass distribution between the sandwich experiment and the lateral impact experiment. A model that agrees with the experimental results is proposed.

Observation of expanding vapor cloud generated by hypervelocity impact

Observations of the expanding vapor cloud generated by the hypervelocity impact have been carried out. Under usual laboratory conditions, rock or ice materials cannot be vaporized completely. In order to investigate the expansion of a large amount of the vapor by complete vaporization caused by hypervelocity impact, we used a nylon projectile and measured the fundamental quantities of the vapor, that is, the expansion velocity, the shape of the vapor cloud, the temperature, and the light energy, by observing the light radiating from the vapor. The expansion velocity of the leading edge of the vapor is almost constant with time and is about twice that of the isothermal sound velocity, which is defined from the pressure and the density of the nylon projectile after passing of the shock wave. The shape of the cloud is not always hemispherical but depends on the combination of the material of the projectile and target, and impact velocity and angle. Inside the vapor cloud are not only the vapor but also the solid ejecta, which travel with the same velocity as the leading edge of the cloud. The temperature of the cloud in the case of nylon impacting on nylon decreases with the power law exponent of time of −0.04 to −0.2. The light energy radiating from the cloud is about 10−4 to 10−5 times the initial projectile kinetic energy.