Hypervelocity Impact Events Research Articles

Globally distributed iridium layer preserved within the Chicxulub impact structure.

The Cretaceous-Paleogene (K-Pg) mass extinction is marked globally by elevated concentrations of iridium, emplaced by a hypervelocity impact event 66 million years ago. Here, we report new data from four independent laboratories that reveal a positive iridium anomaly within the peak-ring sequence of the Chicxulub impact structure, in drill core recovered by IODP-ICDP Expedition 364. The highest concentration of ultrafine meteoritic matter occurs in the post-impact sediments that cover the crater peak ring, just below the lowermost Danian pelagic limestone. Within years to decades after the impact event, this part of the Chicxulub impact basin returned to a relatively low-energy depositional environment, recording in unprecedented detail the recovery of life during the succeeding millennia. The iridium layer provides a key temporal horizon precisely linking Chicxulub to K-Pg boundary sections worldwide.

Hypervelocity impact monitoring and location identification on aluminum plate based on FBG sensing system

To achieve the real-time detecting and localization of hypervelocity impact events, a monitoring and localization system was designed based on fiber Bragg grating (FBG) sensor network. First, the simulation model was built to study the damage evolution and wave propagation process. Subsequently, based on the response mechanism of FBG to strain, the corresponding high frequency demodulation system was designed. Furthermore, a hypervelocity impact experiment was performed to verify the effectiveness of the designed system. Finally, combined with the diamond sensor array localization algorithm, the accurate position of hypervelocity impact source can be achieved.

Modelling and Analyses of Fiber Fabric and Fabric-Reinforced Polymers under Hypervelocity Impact Using Smooth Particle Hydrodynamics

In a hypervelocity impact (HVI) event, fiber fabrics and the fabric-reinforced polymers (FRP) would undergo shock compression, large deformation and fragmentation. The smooth particle hydrodynamics (SPH) approach was applied to assess the shielding performance of the fabric and its composite structure in a Whipple shield. In the fabric model, a fiber is built by SPH particles to properly reproduce the spreading feature of fragmented fabric under HVI. The simulations display that an aluminum panel, serving as the bumper of a Whipple, has the better performance in debris spreading than fabric layers. In the stuffed layer of a Whipple, the widely used plain weave fabric has the similar performance as the 3D weave both in debris spreading and speed retarding. The fabric model is further developed and extended to FRP by building fiber and polymer materials separately based on specific geometries. The computations illustrate that the FRP/Aluminum hybrid laminate can efficiently reduce the shock peak under HVI and meanwhile produce large deformation for kinetic energy absorption, in good agreement with experimental measurements. It applies to the rear wall of a Whipple which should resist the HVI of a debris cloud, forming a high but short shock pulse. The further optimization of the hybrid laminate was made by using a corrugated aluminum plate, a gap and a Kevlar fabric layer, leading to the considerable reduction of the laminate areal mass in a prescribed thickness.

Prediction of micrometeoroid damage to lunar construction materials using numerical modeling of hypervelocity impact events

The use of Lunar regolith for the creation of construction materials to build habitats and other infrastructure required for a Lunar base is an example of in situ resource utilization (ISRU), an important strategy for minimizing the launch mass associated with a NASA mission to the Moon. One class of solidified regolith, Biopolymer-bound Soil Composites (BSC), consists of regolith mixed with a small amount of biopolymer binding agent (10% w/w). This paper characterizes BSC's micrometeoroid impact performance using experimental and numerical methods. Micrometeoroids are a notable hazard of the Lunar environment and pose a challenging design consideration. A total of 17 hypervelocity impact experiments were conducted on BSC targets at NASA's White Sands Testing Facility. Numerical simulations of the hypervelocity impact experiments were carried out using CTH, a shock physics code developed by Sandia National Laboratories. Comparisons between the experimental craters and the simulation results indicate that there is good agreement between crater dimensions of the hypervelocity impact experiments and the CTH model. The CTH model developed in this paper provides (1) a damage prediction tool that allows for the necessary extrapolation of micrometeoroid impact velocities beyond what is experimentally achievable and into the velocity regime that is relevant for micrometeoroids and (2) a material design tool that is capable of varying material parameters computationally, ultimately allowing for the engineering and optimization of BSC's performance under impact loading.

Statistics of energy dissipation in the hypervelocity impact shock failure transition

In the hypervelocity impact event, shock waves subject material to failure transitions with the attendant dissipation of the imparted energy. Under shock compression, failure and dissipation entail intense inelastic shear and compaction. Through shock interactions, states of dynamic tension are achieved and further failure dissipation involves fracture and fragmentation. The nature of failure of solids in the shock environment has encouraged considerable experimental effort through the past several decades. Such efforts have yielded results that suggest a level of universality in the shock failure transition over significant spans of shock intensity and solid material types. Examples include the fourth-power relation between pressure and strain rate in solid-material compressive shock waves, and power-law relations capturing spall fracture strength and fragmentation size scale in dynamic tensile failure. Comparable power-law relations also describe the shock compaction of distended solids. The present paper explores a statistical perspective of the underlying micro failure dynamics for the purpose of achieving better understanding of the macro failure trends noted above. A statistical correlation function description of the random micro velocity field is introduced. Through the attendant kinetic dissipation, the statistical fluctuation-dissipation principle is applied to the shock failure transition. From this statistical approach, power-law relations for compressive and tensile shock failure emerge that replicate the reported experimental behaviors. Results are compared with selected experimental data.

Nanoscale constraints on the shock-induced transformation of zircon to reidite

In a hypervelocity impact event, the temperatures and pressures generated by the shock waves far exceed the values produced by endogenic processes. The shock-induced processes can modify the distribution of trace elements in zircon grains located in target rocks, potentially affecting the geochemical reliability of zircon, but also providing an opportunity to better understand the mechanisms of shock deformation. The formation of reidite lamellae by the shock-induced phase change of zircon has previously been proposed to be a diffusionless, martensitic transformation, with no associated atomic mobility over nanometre length scales. However, nanoscale characterization of the zircon–reidite interface and a low-angle boundary within the reidite by atom probe tomography, transmission electron microscopy and correlative analytical techniques, shows localised enrichment of particular trace elements (Y, Al, Ca, Be, Mg, Mn, and Ti). These observations indicate the presence of additional short-range diffusional components to explain the local compositional variations observed at the nanoscale for the high-pressure transformation of zircon to reidite lamellae. A new model for this transformation is proposed that consists of two stages: 1) the early stage of the impact event where the shock waves induce defects in the zircon grain and trigger a phase transformation, resulting in trace element segregation by interface migration; and 2) the recovery stage where the trace elements and shock induced defects migrate to areas of lower energy.

Characterizing hypervelocity (>2.5 km/s)-impact-engendered damage in shielding structures using in-situ acoustic emission: Simulation and experiment

Pervasive in outer space, hypervelocity impact (HVI), caused by man-made debris (a.k.a. space junk) and natural micrometeoroids, poses a clear and tremendous threat to the safe operation of orbiting spacecraft, and it will possibly lead to the failure of a space exploration mission. Addressing such an issue, damage in a downscaled two-layer space shielding assembly, engendered by HVI events with an impact velocity up to 4 km/s, was characterized quantitatively, using in-situ measured acoustic emission (AE) induced under HVI. A hybrid model, based on three-dimensional smooth-particle hydrodynamics and finite element, was developed, to achieve insight into the traits of HVI-induced AE waves and HVI-caused damage. Proof-of-concept simulation was accomplished using the hybrid model, in which a projectile, at various impact velocities, impinged a series of shielding assembly of different thicknesses, in a normal or oblique manner. Experimental validation was implemented, and HVI-induced AE waves were in-situ acquired with a built-in piezoelectric sensor network integrated with the shielding assembly. Results from simulation and experiment show qualitative consistency, demonstrating the capability of the hybrid model for depicting HVI-produced shock waves, and the feasibility of in-situ measurement of HVI-induced AE signals. Taking into account the difference and uniqueness of HVI against other ordinary impact cases, an enhanced, delay-and-sum-based imaging algorithm was developed in conjunction with the built-in sensor network, able to “visualize” HVI spots in pixelated images accurately and instantaneously.

Racemization of Valine by Impact-Induced Heating.

Homochirality plays an important role in all living organisms but its origin remains unclear. It also remains unclear whether such chiral molecules survived terrestrial heavy impact events. Impacts of extraterrestrial objects on early oceans were frequent and could have affected the chirality of oceanic amino acids when such amino acids accumulated during impacts. This study investigated the effects of shock-induced heating on enantiomeric change of valine with minerals such as olivine ([Mg0.9, Fe0.1]2SiO4), hematite (Fe2O3), and calcite (CaCO3). With a shock wave generated by an impact at ~0.8km/s, both D- and L-enriched valine were significantly decomposed and partially racemized under all experimental conditions. Different minerals had different shock impedances; therefore, they provided different P-T conditions for identical impacts. Furthermore, the high pH of calcite promoted the racemization of valine. The results indicate that in natural hypervelocity impacts, amino acids in shocked oceanic water would have decomposed completely, since impact velocity and the duration of shock compression and heating are typically greater in hypervelocity impact events than those in experiments. Even with the shock wave by the impact of small and decelerated projectiles in which amino acids survive, the shock heating may generate sufficient heat for significant racemization in shocked oceanic water. However, the duration of shock induced heating by small projectiles is limited and the population of such decelerated projectiles would be limited. Therefore, even though impacts of asteroids and meteorites were frequent on the prebiotic Earth, impact events would not have significantly changed the ee of proteinogenic amino acids accumulated in the entire ocean.

Effect of honeycomb core under hypervelocity impact: numerical simulation and engineering model

Honeycomb sandwich panels (HC/SP) are the most common used structures for space vehicle. Under the threat of meteoroid and space debris, the distribution of the fragments produced in a hypervelocity impact event on HC/SP is critical to the vulnerability assessment of space vehicle. CISAS developed an engineering model to describe fragments clouds propagating inside spacecraft in consequence of space debris impact on HC/SP. In this model, the effect of the honeycomb core was modeled by an empirical corrective factor, which was not related to the physical of the impact. To improve this model, a new model to describe the effect of the honeycomb core was developed. In the new model, the honeycomb core was equaled to multi-parallel thin plates, which can represent the discontinuity of honeycomb core without complex boundary. Based on the knowledge of hypervelocity impact on a simple thin plate and approximation supported by numerical simulation results, the model was deduced. The coefficient of the model was fitted by the numerical simulation results.

Stress-wave propagation and damage formation associated with hypervelocity penetration into polycarbonate

Hypervelocity impact experiments have been performed on polycarbonate to observe the impact-induced damage process progressing inside polymer material. Impact experiments have been conducted by impacting a sphere made of several kinds of materials using a two-stage light-gas gun. The damage evolution and stress wave propagation associated with hypervelocity impact have been observed via shadowgraphy using an ultra-high-speed camera. Recoded images clearly demonstrate how damages form during the hypervelocity impact event. The obtained time evolution of penetration show that the behavior of stress wave propagation associated with impact vary according to the penetrating motion, and the impact velocity dependence of penetration length and shape change depending on the deformation and fracture behavior of impactor during penetrating process. From these results, it is indicated that not only the mechanical characteristics of impactor material but also the change of penetrating motion associated with the deformation and fragmentation of impactor are key factors for impact-damage formation.

Saqqar: A 34 km diameter impact structure in Saudi Arabia

AbstractHere we present the first proof of an impact origin for the Saqqar circular structure in northwestern Saudi Arabia (Neville et al. ), with an apparent diameter of 34 km, centered at 29°35′N, 38°42′E. The structure is formed in Cambrian–Devonian siliciclastics and is unconformably overlain by undeformed Cretaceous and Paleogene sediments. The age of impact is not well constrained and lies somewhere between 410 and 70 Ma. The subsurface structure is constrained by 2‐D reflection seismic profiles and six drilled wells. First‐order structural features are a central uplift that rises approximately 2 km above regional datums, surrounded by a ring syncline. The crater rim is defined by circumferential normal faults. The central uplift and ring syncline correspond to a Bouguer gravity high and an annular ring‐like low, respectively. The wells were drilled within the central uplift, the deepest among them exceed 2 km depth. Sandstone core samples from these wells show abundant indicators of a shock metamorphic overprint. Planar deformation features (PDFs) were measured with orientations along (0001), {103}, and less frequently along {101} and {104}. Planar fractures (PFs) predominantly occur along (0001) and {101}, and are locally associated with feather features (FFs). In addition, some shocked feldspar grains and strongly deformed mica flakes were found. The recorded shock pressure ranges between 5 and 15 GPa. The preserved level of shock and the absence of an allochthonous crater fill suggest that Saqqar was eroded by 1–2 km between the Devonian and Maastrichtian. The documentation of unequivocal shock features proves the formation of the Saqqar structure by a hypervelocity impact event.

Machine learning methods for predicting the outcome of hypervelocity impact events

The outcome of projectile impacts on spaced aluminium armour (i.e. Whipple shield) at hypervelocity is traditionally predicted by semi-analytical equations known as ballistic limit equations (BLEs). For spherical aluminium projectiles impacting aluminium Whipple shields, the state-of-the-art BLE has been found to correctly reproduce the perforation/non-perforation result of approximately 75% of tests contained within a database with over 1100 entries. For such high-dimensional, complex problems, machine learning methods may be a superior approach over such semi-analytical/empirical methods. Towards this end an artificial neural network (ANN) and support vector machine (SVM) have been developed to better classify the outcome of hypervelocity impact events on aluminium Whipple shields. The ANN was found to correctly reproduce the perforation/non-perforation result of over 93% of the training exemplars, generalizing at 92.2% when applied with an optimized architecture. The SVM was not able to reach comparable levels of generalization error as the ANN, peaking at 83% after the removal of a small number of test exemplars which induced conflict within the SVM pattern recognition. Although providing a significant improvement in predictive accuracy over the conventional BLE, the performance of both the ANN and SVM were highly sensitive to the population density of the parameter space described by the training data. Within highly populated regions the qualitative trends of the machines are demonstrated to accurately identify patterns associated with projectile fragmentation and melting, while in sparsely populated regions the accuracy significantly decreases and the qualitative trends can become nonsensical. Further improvements in accuracy are limited by the inhomogeneous sampling of the parameter space defined by the current impact test database—a problem expected to be typical of any terminal ballistics problem in which the cost of performing experiments limits their scope to, for example, materials and geometries of interest, impact conditions expected during operation, and a limited range about the perforation threshold (i.e. ballistic limit). A combined novelty-detecting neural net and hetero-associate neural net have been applied to iteratively improve the performance of the ANN without requiring an inordinate number of additional tests. This process, referred to as bootstrapping, has been successfully demonstrated through the design of ‘optimized’ Whipple shields for given impact conditions, hypervelocity impact testing of the designed shields, and re-training of the critic net to incorporate the results of the new impact tests.

Stress Wave and Damage Propagation in Transparent Materials Subjected to Hypervelocity Impact

Hypervelocity impact experiments have been conducted on transparent materials, SiO2 glass and polycarbonate, to observe directly the impact-induced damage process progressing inside materials. Stress wave propagation and damage evolution associated with hypervelocity impact are visualized by employing the Edge-on Impact technique coupled with an ultra-high-speed video camera. Recorded images clearly show how stress wave propagate and interact each other, and how damages form and propagate during hypervelocity-impact event. In the impacted SiO2 glass, the damages on the ballistic direction are formed associated with the propagation of a shear wave. And, the interaction of the shear wave with the longitudinal wave reflected from free surface initiates the drastic nucleation of damage points. In the impacted polycarbonate, in addition to penetration damage and spall fracture, the delamination-like fracture is initiated by the interaction of the reflected rarefaction waves from both side free surfaces. However, such delamination fracture does not extended inside the plastic deformed region induced by the penetration of the impacted projectile.

On the Fluidic Response of Structures in Hypervelocity Impacts

Abstract In a hypervelocity impact (HVI) event, the shock pressures exceed the strength of common aerospace materials, and brief shock-induced temperature rises cause melting and vaporization of most structural bodies. Under these extreme conditions, the failure and deformation of solids can resemble fluid flow. By using meshless Lagrangian models in an explicit computational framework, this work identifies analogous fluidic interactions and further quantifies the role of shear and inertial forces in HVIs.

Damage Evolution in SiO2 Glass Subjected to Hypervelocity Impact

Hypervelocity-impact experiments are performed on SiO2 glass plates to investigate its damage process. The damage propagation behavior induced by a hypervelocity impact is observed using a high-speed video camera. The postmortem observations reveal that the damage structure of the impacted plates consists mainly of crater, internal failure zone, and radial cracks. The sequence of the damage formation and propagation during a hypervelocity-impact event is revealed using the images of the high-speed video camera. The propagation velocities of surface fracture show a nearly constant value regardless of impacting conditions. The propagation velocities of internal failure zone increase with decreasing target thickness. The formation of radial cracks is affected by the projectile kinetic energy normalized by the target thickness. The radial crack velocities increase with increasing the normalized kinetic energy and approach asymptotically to the terminal velocity.

Imaging Ejecta and Debris Cloud Behavior Using Laser Side-lighting

The Caltech Small Particle Hypervelocity Impact Range (SPHIR Facility) utilizes a two-stage, light gas gun to accelerate Nylon 6/6 right cylinders (d = 1.8mm, L/D=1, 5.5mg) and spheres (d = 1.8mm, 3.6mg) to impact speeds of 5km/s and above. The projectiles impact aluminum 6061-T6 plate targets. An optical technique was employed to produce images of the hypervelocity impact event with short exposure times (20ns) and short inter-frame times (<1μs). The technique uses coherent illumination, orthogonal to the projectile flight direction, to provide a series of shadowgraph images of the impact on the target. An expanded beam from a 532nm continuous wave laser is used as the illumination source. The beam is expanded to illuminate a 10cm diameter area and is then directed to a gated, intensified high-speed CCD camera. The front ejecta and debris clouds created behind the target are simultaneously imaged with this system. An edge-finding algorithm has been developed to provide a consistent method for identifying the position of the debris-front in sequential images. This technique enables a regular method to investigate the debris cloud evolution and to characterize its asymmetrical features. Furthermore, with the Laser Side-lighting system atmospheric waves emanating from the impact site are also visible. Increasing the atmospheric pressure in the target chamber (above the nominal 1.5 Torr) significantly increases the observable features of these shock waves. The behaviour of these waves provides an improved understanding of the temporal sequence of the impact phenomena.

Survival of yeast spores in hypervelocity impact events up to velocities of 7.4 km s−1

We report on the survivability in hypervelocity impacts of yeast in spore form, and as mature cultures, at impact velocities from 1 to 7.4kms−1, corresponding to an estimated peak shock pressure of ∼43GPa. Spores from a yeast strain (BY4743), deficient in an enzyme required for uracil production, were fired into water (to simulate oceanic impact from space) using a light gas gun. The water was then retrieved and filtered and the resulting retentate and filtrate cultured to determine viability and survival rates of remnant spores. Yeast growth (confirmed as coming from the original sample as it had the same enzyme deficiency) was found in recovered samples at all impact speeds, albeit in smaller quantities at the higher speeds. The survival probabilities were measured as ∼50% at 1kms−1, falling to ∼10−3% at 7.4kms−1. This follows the pattern observed in previous work on survival of microbial life and spores exposed to extreme shock loading, where there is reasonable survival at low peak shock pressures with more severe lethality above a critical shock pressure at the GPa scale (here between 2 and 10GPa). These results are explained in the context of a general model for survival against extreme shock and are relevant to the hypotheses of panspermia and litho-panspermia, showing that extreme shocks during transfer across space are not necessarily sterilising.

Validation of the Preston–Tonks–Wallace strength model at strain rates approaching ∼1011 s−1 for Al-1100, tantalum and copper using hypervelocity impact crater morphologies

Data from hypervelocity impact experiments shows that the size of an impact crater is a non-linear function of the projectile diameter for micrometre-scale and smaller sized impactors. This non-linearity is thought to arise due to the strain rate hardening of the target materials at the ultra-high strain rates experienced during the impact event (approaching 1010 s−1). Here we investigate this ultra-high strain regime using a combination of experimental and simulated results. The experimental work involved samples of monodisperse silica and sodalime glass spheres with diameters between 500 nm and 22 μm which were fired onto aluminium 1100 alloy, high purity (99.5+%) tantalum and copper targets at a velocity of ca. 6 km s−1 using a light gas gun. Precise measurements of the resulting crater diameters were made using scanning electron microscopy (with a resolution of a few tens of nanometers). We also ran hydrocode simulations of the impact events using ANSYS’ AUTODYN to compare the modelled results against the experimental data. The Preston–Tonks–Wallace (PTW) constitutive model was used in the hydrocode as it specifically deals with loading events at very high strain rates. Comparison is also made with results obtained using the Steinberg-Guinan strength model which is also applicable at high strain rates.The results demonstrate that current literature values for the PTW model need refining in order to accurately model micrometre-scale (and below), hypervelocity impact events. We present updated model parameters for Al, Cu and Ta and thus show that impact craters give an indirect measurement of the yield strength of a material at strain rates approaching 1011 s−1.

Shock‐induced silicate vaporization: The role of electrons

We conducted a spectroscopic study of shock‐heated silicate (diopside) and obtained the time evolution of the spectral contents, the line widths of emission lines, and the time‐ and irradiance‐averaged peak shock temperatures. The peak shock pressures ranged from 330 to 760 GPa. Time‐resolved emission spectra indicated that the initial spectrum was blackbody radiation; the spectrum evolved to yield several ionic emission lines, which in turn evolved to yield atomic lines at the later stages. The shock‐heated diopside was highly dissociated and ionized, even though it is likely to have been subjected to high‐pressure conditions near the liquid–vapor phase boundary. The time evolution of the spectra, from ions to atoms, strongly suggests that electron recombination occurred in the expanding shock‐induced diopside vapor. The time‐ and irradiance‐averaged peak shock temperatures at &gt;330 GPa were lower than the theoretical Hugoniot curve, with a constant isochoric specific heat, indicating endothermic shock‐induced ionization. Thus, we conclude that electrons behave as an important energy reservoir in energy partitioning via endothermic shock‐induced ionization and subsequent exothermic electron recombination. This electron behavior leads to a higher degree of vaporization after isentropic release and a lower cooling rate due to the exothermic electron recombination in expanding impact‐induced silicate vapors than previously expected. These results will affect the predictions associated with hypervelocity impact events in planetary science, such as the origin of the Moon and chemical reactions and production of silicate dust particles in impact‐generated silicate vapor clouds.

Lithium in tektites and impact glasses: Implications for sources, histories and large impacts

Lithium (Li) abundances and isotope compositions were determined in a representative suite of tektites (moldavites, Muong Nong-type tektites and an australite, Ivory Coast tektites and bediasites), impact-related glasses (Libyan Desert Glass, zhamanshinites and irghizites), a glass fragment embedded in the suevite from the Ries impact crater and sedimentary materials in order to test a possible susceptibility of Li to fractionation during hypervelocity impact events and to de-convolve links to their potential parental sources. The overall data show a large spread in Li abundance (4.7–58 ppm Li) and δ 7Li values (−3.2‰ to 26.0‰) but individual groups of tektites and impact glasses have distinctive Li compositions. Most importantly, any significant high-temperature Li isotope fractionation can be excluded by comparing sedimentary lithologies from central Europe with moldavites. Instead, we suggest that Li isotope compositions in tektites and impact-related glasses are probably diagnostic of the precursor materials and their pre-impact geological histories. The Muong Nong-type tektites and australite specimen are identical in terms of Li concentrations and δ 7Li and we tentatively endorse their common origin in a single impact event. Evidence for low-temperature Rayleigh fractionation, which must have operated prior to impact-induced melting and solidification, is provided for a subset of Muong Nong-type tektites. Although Li isotope variations in most tektites are broadly similar to those of the upper continental crust, Libyan Desert Glass carries high δ 7Li ⩾24.7‰, which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater. Lithium isotopes in impact-related glasses from the Zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies, which is also consistent with their major and trace element patterns. Extreme shock pressures and the related extreme post-shock temperatures alone appear not to have any effect on the Li isotope systematics; therefore, useful information on parental lithologies and magmatic processes may be retrieved from analyses of Martian and lunar meteorites. Moreover, lack of significant Li depletion in tektites provides further constraints on the loss of moderately volatile elements during the Moon-forming impact.