Temat: oblique impact - Prolib Integro

Skocz do pozycji: 1.

Tytuł:: Experimental analysis of interfacial properties of sphere oblique impact with initial spin
Autorzy:: Wang, Qing-Peng
Wang, Zheng-Feng
Wang, Heng
Li, De-Feng
Gao, Xian-Kun
Xu, Guang-Yin
Tematy:: sphere
spin
oblique impact
contact surface
slip ratio; Pokaż więcej
Wydawca:: Polskie Towarzystwo Mechaniki Teoretycznej i Stosowanej
Powiązania:: https://bibliotekanauki.pl/articles/2086967.pdf Link otwiera się w nowym oknie
Opis:: Experiments of a sphere oblique impact with and without an initial spin have been carried out to obtain properties of the impact interface. The contact surface is recorded with a piece of thin carbon paper. The interfacial parameters measured are expressed as axis length, contact area and slip ratio. It is found that for the impact between steels the forward spin can make geometrical sizes of the contact surface increase compared with the case of no initial spin, however, just the reverse for the backward spin. The effect of the initial spin becomes more apparent for the impact with a rubber cushion. Whether the initial spin promotes or hinders the sphere sliding depends on the parameters of tangential velocity and force at the interface.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 2.

Tytuł:: Numerical study of the projectile trajectory disturbing during the oblique impacts
Autorzy:: Morka, A.
Niezgoda, T.
Tematy:: computational mechanics
impact problem
armour perforation
ballistic resistance
oblique impact; Pokaż więcej
Wydawca:: Instytut Techniczny Wojsk Lotniczych
Powiązania:: https://bibliotekanauki.pl/articles/244096.pdf Link otwiera się w nowym oknie
Opis:: The numerical investigations have been performed to determine the effect of the projectile trajectory disturbing during oblique impacts. An impact of the 14.5x118 mm B32 armour piercing projectile on the A12O3 different shape elements backed by 7017 aluminum alloy plate was analyzed. The oblique impact was realized by different shapes of the frontal ceramic elements, including hemispheres and pyramids, with respect to standard flat tiles. The influence of the impact point location was also under considerations. The Computer simulations were performed with the Element Free Galerkin Method (EFG) implemented in LS-DYNA code. full 3D models of the projectile and targets were developed with strain rate and temperature dependent material constitutive relations. The Johson-Cook model was applied to describe the metallic parts, while the ceramic was modelled by Johnson-Holmquist constitutive relations. The models of the projectile, ceramic and aluminium alloy targets were validated with utilization of the experimental datafound in literature. The obtained results confirmed that the projectile trajectory undergoes essential deviation because of the projectile angular velocity. The conditions for maximizing the value of this angular velocity were studied and it is possible to reach several radians per millisecond. The conclusions presented in this paper can be applied to develop modern impact protection panels where the appropriate balance between the mass and protection level must be accomplished.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 3.

Tytuł:: Kratery Morasko w świetle wiedzy na temat ukośnych impaktów
Morasko craters base on knowledge related to oblique impacts
Autorzy:: Walesiak, Tomasz
Tematy:: Morasko meteorite
asymmetry
craters
ejecta
oblique impact
penetration funnels
strewnfield; Pokaż więcej
Wydawca:: Polskie Towarzystwo Meteorytowe
Powiązania:: https://bibliotekanauki.pl/articles/1033091.pdf Link otwiera się w nowym oknie
Opis:: It is considered that The Morasko meteorite shower happened about 5400 years BP with a trajectory from NE to SW (Bronikowska et al. 2015). Recent studies not only prove that this fall could be observed in Februrary 14, 1271, but also that location of most findings in the area to the east side of the craters, should not be taken as the main indicator of impact direction. The proper answer can be given base on knowledge related to oblique impacts, supported by understanding of complicated fragmentation process. The largest crater in Morasko Meteorite Restricted Area has main ejecta plume located in SE, side walls in SW and NE, and free of ejecta Zone of Avoidance (ZoA) in NW. This clearly shows that impact trajectory was approximatelly from NW to SE. There were also discovered other structures, 2 km North from Restricted Area, having common features. Their ejecta plumes as well as few raised ducts (possible traces of underground penetration) are directed to SE, pointing the largest structure – Umultowskie Lake, located approx. 2 km ESE from known main Morasko crater. Shapes of cavities, their walls and ejecta asymmetry allow estimating trajectories and defining new Morasko strewnfield, which matches not only location of impact strucures and discovered meteorite fragments, but also explains smaller (3–4 kg) findings in the neighborhood of Oborniki Wielkopolskie.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 4.

Tytuł:: Kratery Morasko – obrona hipotezy ukośnego impaktu w kontekście dostępnej wiedzy i wyników badań
Morasko craters – in defense of oblique impact origin based on knowledge and research
Autorzy:: Walesiak, Tomasz
Tematy:: bilateral symmetry
crater field
elliptical craters
forbidden zone
meteorite Morasko
oblique impact; Pokaż więcej
Wydawca:: Polskie Towarzystwo Meteorytowe
Powiązania:: https://bibliotekanauki.pl/articles/1830330.pdf Link otwiera się w nowym oknie
Opis:: Over 2 years ago there was published an article (Bronikowska 2018a) challenging some results of research related to Morasko meteorite fall. Those results are huge problem for scientists who are not able to explain them using simplified models and maybe do not want to admit that some assumptions should be verified and redefined. One of hypothesis discussed in the paper was article manifesting that Morasko craters were created during oblique impact (Walesiak 2017) and that initial trajectory can be estimated by elongation of almost all cavities, their bilateral symmetries according to longer axis and observed asymmetries of rims. By comparison to Campo del Cielo craters Walesiak suggested that impact angle could be very shallow (10–20°), as ellipticity of all smaller Morasko structures is approx. 1,3. Further analysis of topography in neighborhood of Morasko revealed that there may exist more impact craters around this area, which may explain discovery of two iron meteorites near Oborniki village (17 km NW from Meteorite Morasko Restricted Area), unfortunately lost during World War II. In fact, Bronikowska confused definitions “oblique impact” and “elliptical craters”, what can be supported by given references (Elbeshausen et al. 2009) confirming Walesiak hypothesis. Unfortunately, this misunderstanding touches also another article of this author (Bronikowska et al. 2017), where obliquity was neglected. However, estimated during that modeling pre-impact angle (30–43°), according to known definitions written in many publications, should be classified as oblique impact. All elongated craters, as well as morphology of the largest structure in Meteorite Morasko Restricted Area suggest impact from NW while during reconstruction of meteoroid parameters Bronikowska assumed impactor coming from NE (based on existing strewn field). Considering not clear relation between meteorites and craters (e.g., lack of findings in cavities, relatively poor number of shrapnel fragments around structures and possibility that craters may be much older than fall of meteorites), it may be not enough reliable justification. Even if relation exists, example of Whitecourt (with distribution of meteorites downrange), compared with abundance of Morasko shrapnel fragments collected hundreds of meters NE from Restricted Area, undermines parameter used in modelling. Also, single fragmentation is doubtful, concluded after unreasonable omitting known craters outside Restricted Area (e.g., crater no 8 described by Pokrzywnicki (1964) and structure no 9 mentioned by Hodge (1994)). Finally, use of iSALE-2D shock physics code (valid for vertical impacts only) for modelling of elliptical craters formed during highly oblique impact (angle lower than 12°), even considering vertical component (which approximation is only applicable for impact into materials with a friction coefficient of about f=0,7 with no or very little cohesion) (Elbeshausen et al. 2009), also should not be considered as proper applied method leading to get valuable results. In this article there is proposed new strewn field definition for Morasko meteorite, based on elongation of all known and unconfirmed (yet) craters. Surprisingly, estimated (redefined) pre-impact trajectory gives convincing explanation for bilaterally symmetrical distribution of documented findings.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 5.

Tytuł:: Wykorzystanie danych Numerycznego Modelu Terenu do poszukiwania i wstępnej identyfikacji struktur impaktowych
Use of the digital elevation models (DEM) as a tool for searching and preliminary identification of impact structures
Autorzy:: Walesiak, Tomasz
Tematy:: cardioid pattern
crater field
impact structures
morphometry
oblique; Pokaż więcej
Wydawca:: Polskie Towarzystwo Meteorytowe
Powiązania:: https://bibliotekanauki.pl/articles/1033155.pdf Link otwiera się w nowym oknie
Opis:: Is it possible that in Poland, instead of Morasko and still unconfirmed structures Porzadzie, Jaszczulty and Ochudno, may exist some other impact craters? To answer this question, investigations were performed, which were based on the digital elevation models. There are plenty of cavities, having different origin (e.g. a result of past glaciations, human activities or the Second World War), where some criteria may be applied, which could help to distinguish one from another. The main assumption was that during oblique impact (low angle in relation to the surface) there may develop special type of craters having cardioid (heart-shaped) ejecta pattern (as well as shape of cavity), with axis of symmetry parallel to the initial trajectory. Such structures were observed many times during experiments as well as can be easily found on other celestial bodies. Having preserved rims, even if they are much shallower than typical craters (because of secondary changes), such cavities are perfect candidates to be suspected of the impact origin. As a result of research between 2015 and 2017 there were discovered 3 locations (instead of Ochudno) with heart-shaped structures, which may represent combined effect of ejection angles, velocities and directions, known from experiments and confirmed craters. In all cases there are noticeable rims. The largest “spoon-like” structure, discovered near the Rowista village, is almost perfect copy of a very unusual elongated crater located north of the Acheron Fossae on Mars.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 6.

Tytuł:: Analiza cech impaktu ukośnego na przykładzie struktur Porządzie, Jaszczułty i Ochudno
Analysis of oblique impact features. A case study of Porzadzie, Jaszczulty and Ochudno structures
Autorzy:: Walesiak, Tomasz
Tematy:: asymmetry
cardioid
craters
ejecta
experiments
impact structures
oblique; Pokaż więcej
Wydawca:: Polskie Towarzystwo Meteorytowe
Powiązania:: https://bibliotekanauki.pl/articles/1033069.pdf Link otwiera się w nowym oknie
Opis:: It’s considered that one half of all projectiles are striking surface of planets at the angle lower than 45°. Our knowledge of oblique impact events is based on computer modelling, laboratory experiments and observation of craters on the Moon, Mars, Venus and other celestial bodies. Recent discovery in northeast Poland, reveals at least four structures with features reserved for low-angle impacts. In this article we show and explain them using high-quality laser air scanning data (LiDAR) in comparison to results of experiments and similar real known objects on other planets. Also we try to verify by analyzing historical sources if multiple impact event could occur in our area and, if it was noticed and reported in the papers.
Dostawca treści:: Biblioteka Nauki

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Skocz do pozycji: 7.

Tytuł:: Dalsze badanie struktur w okolicach Wyszkowa – wyniki prac terenowych
Further investigation of structures near Wyszkow – field research results
Autorzy:: Walesiak, Tomasz
Tematy:: crater
impact
oblique
planar deformation features
shatter cones
shocked quartz; Pokaż więcej
Wydawca:: Polskie Towarzystwo Meteorytowe
Powiązania:: https://bibliotekanauki.pl/articles/1033139.pdf Link otwiera się w nowym oknie
Opis:: There are specified criteria used to verify if some geological structure was developed during hypervelocity impact. Some of them are related to the passage of a shock wave through rocks, so are considered as definitive. Porządzie, Jaszczulty & Ochudno are structures discovered in 2014 (based on LiDAR data). They have many features suggesting possible impact origin. In shape of Porządzie there can be even recognized possible traces of shock waves, similar to those present during hypersonic flow (similar to observed e.g. in an airburst shape of extraordinary bright meteors). Unfortunately, this kind of observations (morphometry) on Earth is still considered as not enough to confirm the crater. The aim of recent study was to search for additional traces, which may help to prove that mentioned structures were created during common oblique impact event. Initially there were chosen 3 locations for outcrops, but finally samples were collected from 6 smaller pits. In Porzadzie structure there were discovered cemented rocks with various shape and size (concretions or lithic, parautochtonous breccias) and 2 rocks with possibly shocked quartz, having basal sets of thin and straight lamellae. On once surface there were recognized hierarchal branched (including spoon-like) structures resembling shatter cones. In uprange, at depth of about 50–70 cm, soil was rich in small charcoal pieces (like in other relatively small craters: e.g. Campo del Cielo, Whitecourt, Kaali, Ilumetsa, Morasko). All these observations, taken together with previous results, are about to confirm impact origin of Porzadzie crater.
Dostawca treści:: Biblioteka Nauki

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