Rapid Penetration into Soils

NYU

Visualization and Penetration by NYU

Travel of projectiles in soils has been a subject of interest in science and engineering, dating at least as far back as the mid-eighteenth century. Impact and penetration is important for many engineering applications, including subsurface investigations, planetary impact, and offshore foundations and anchors, among others. Significant progress has been made over the past 50 years in understanding the fundamental mechanisms involved in penetration into soils, and a wealth of knowledge has been accumulated. The study of rapid penetration provides both qualitative and quantitative insights into the mechanical properties of granular materials at high stresses and high strain rates.

In order to further investigate the formation and role of a false nose in penetration, an additional penetration test was performed using a tungsten sphere into a color-coded target consisting of aragonite sand.  The test results showed that a false cone was formed in front of the projectile. The cone had an angle of approximately 82°, and was highly symmetric, as shown in the figure below. Inspection of the cone revealed that the crushed material adhered to form a densely packed kernel.

Image of false cone formed ahead of the projectile: (a) spherical projectile and retrieved
cone and (b) scanning electron microscope image of the false cone

Snapshots of penetration into the embedded plane transparent soil sample are shown in the figure below for penetration of blunt and cone nose rods. The penetrators were propelled with an initial velocity of 21 and 22.5 m/s for the blunt and conical penetrators, respectively. It can be seen that at the impact velocity considered, impact and initial penetration results in cavity formation, which appears as an opaque region in the images. During this initial stage of penetration, the penetrator tip is in contact with the impeding soil, whilethe afterbody (projectile shank) moves in the cavity void. As the penetrator velocity decays, supercavitation ceases, and the penetrator afterbody comes in contact with the surrounding soil.

During initial embedment and penetration, an opaque region forms ahead of the penetrator, with a base diameter greater than that of the penetrator. This opaque region is larger for the blunt nose projectile. The opaque region immediately ahead of the penetrator takes the form of an approximate cone in the case of the blunt nose projectile, and persists ahead of the penetrator during later stages of penetration. However, in the case of the conical projectile, the opaque region does not persist during later stages of penetration. The formation of these opaque regions may be explained by one or more hypotheses,
including pressure-induced change in RI, cavitation due to tensile hoop strains, and cavitation due to shear-induced dilation.

Snapshots of penetration of blunt nose (a, b, c/top) and conical nose (d, e, f/bottom) into
embedded plane transparent soil sample, at penetration times (a, d) t¼1.00 ms, (b, e) t¼5.50 ms,
(c, f) t¼8.50 ms following impact (t=0)

 

 

REFERENCES

JOURNAL ARTICLES (VISUALIZATION)
  1. Omidvar, M., M. Iskander, and S. Bless (2016), “Soil-projectile interactions during low velocity penetration,” International Journal of Impact Engineering, doi: 10.1016/j.ijimpeng.2016.02.015, Elsevier [link]
  2. Omidvar, M., J. Doreau Malioche, Z. Chen, M. Iskander, and S. Bless (2015), “Visualizing kinematics of dynamic penetration in granular media using transparent soils”, Geotechnical Testing Journal, Vol. 38, No. 5, doi: 10.1520/GTJ20140206, ASTM [link]
  3. Guzman, I., M. Iskander, S. Bless (2015), “Observations of projectile penetration into a transparent soil”, Mechanics Research Communications, Vol. 70, Dec., pp. 4-11, doi:10.116.j.mechrescom.2015.08.008, Elsevier [link]
  4. Guzman, I., M. Iskander, S. Bless, C. Qi (2014), “Terminal depth of penetration of spherical projectiles in transparent granular media”, Granular Matter, Vol. 16, No. 6, pp. 829-84, doi: 10.1007/s10035-014-0528-y [link]
  5. Chen, Z., M. Omidvar, and M. Iskander, and S. Bless (2014), “Modelling of projectile penetration into transparent sand”, International Journal of Physical Modelling in Geotechnics, Vol. 14, No. 3, pp. 68-79, doi:10.1680/ijpmg.14.00003, ICE [link]
JOURNAL ARTICLES (EXPERIMENTAL & NUMERICAL DETAILS)
  1. Cave, A., S. Roslyakov, M. Iskander, and S. Bless (2016), “Design and performance of a laboratory pneumatic gun for soil ballistic applications”, Experimental Techniques, doi: 10.1111/ext.12091, Wiley [link]
  2. Carvalho, T., E. Suescun-Florez, M. Omidvar, and M. Iskander (2015), “A nonviscous water-based pore fluid for modeling with transparent soils”, Geotechnical Testing Journal., Vol. 38, No. 5, doi: 10.1520/GTJ20140278, ASTM [link]
  3. Omidvar, M., Z. Chen, and M. Iskander (2014), “Image based lagrangian analysis of granular kinematics”, Journal of Computing in Civil Engineering, Vol. 29, No. 6, doi: 10.1061/cp.1943-5487.0000433, ASCE [link]
  4. Guzman, I., Iskander, M., E. Suescun and Omidvar, M. (2014), “A transparent aqueous-saturated sand-surrogate for use in physical modeling”, Acta Geotechnica, Vol. 9, No. 2, pp. 187-206, doi: 10.1007/s11440-013-0247-2, Springer [link]
  5. Guzman, Iskander, M. (2013), “Geotechnical properties of sucrose-saturated fused quartz for use in physical modeling”, Geotechnical Testing Journal, Vol. 36, No. 3, pp. 448-454, doi: 10.1520/GTJ20120182, ASTM [link]
  6. Peden, R. M. Omidvar, S. Bless, S, and M. Iskander (2014), “Photonic doppler velocimetry for study of rapid penetration into sand,” Geotechnical Testing Journal, Vol. 37, No. 1, pp. 139–150, doi:10.1520/GTJ20130037, ASTM [link]
CONFERENCE PAPERS
  1. Omidvar, M. and  Iskander, M. (2017), “Modeling of projectile penetration using transparent soils”, Proceedings, 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul [link]
  2. Chen, Z., M. Omidvar, Iskander, M. and Bless, S. (2015),  “Visualizing the fundamental physics of rapid earth penetration, using transparent soils”, IFCEE 2015, GSP No. 256, pp. 2617-2626, doi: 10.1061/9780784479087.243, ASCE [link]
  3. Peden, R, S. Bless and M. Iskander (2013), “Penetration of granular materials: new experimental techniques,” Proceedings,  Ballistics 2013: 27th International Symposium on Ballistics, April 22-26, Freiburg, Germany, Vol. 2, ed. Matthias Wickert and Manfred Salk, ISBN: 978-1-60595-106-5, DEStech Publications