International audienceThe paper presents investigations on the penetration tests in granular material. A discrete numerical study is proposed for the modeling of penetration tests in constant velocity conditions and also in impact conditions. The model reproduces qualitatively the mechanical response of samples of granular material, compared to classical experimental results. Penetration tests are conducted at constant velocity and from impact, with similar penetration rates ranging from 25 mm.s-1 to 5000 mm.s-1. In constant velocity condition, the value of tip force remains steady as long as the penetration velocity induces a quasi–static regime in the granular material. However, the tip force increases rapidly in the dense flow regime corresponding to higher penetration rate. Impact tip force increases with the impact velocity. Finally, the tip forces obtained from impact penetration tests are smaller compared to the one obtained in constant velocity conditions in both quasi–static and dense flow regimes

Penetration tests are widely used in geotechnical engineering for the on site characterization of mechanical properties of soils. This paper proposes a numerical study of static penetration tests on granular material using Discrete Element Method and in particular molecular dynamics in 2 dimensions (Cundall and Strack, 1979). The results first showed the ability of the model to reproduce qualitatively the results of penetration tests classically obtained in experimental conditions. Then, the energy balance of the test is analyzed at the macroscopic and microscopic to understand local parameters influencing this test and how to interpret this test. The most part of the source energy is irreversibly lost and dissipated by friction in the contacts between particles; the remaining part of energy is stored by the upper confining wall. The sample area mobilized by frictional dissipation remains approximately the same as penetration velocity increases but the dissipated energy level increases for particles in this area.

No abstract

No abstract