Behavior of confined granular beds under cyclic thermal loading

Abstract

We investigate the mechanical behavior of a confined granular packing of irregular polyhedral particles under repeated heating and cooling cycles by means of numerical simulations with the Non-Smooth Contact Dynamics method. Assuming a homogeneous temperature distribution as well as constant temperature rate, we study the effect of the container shape, and coefficients of thermal expansions on the pressure buildup at the confining walls and the density evolution. We observe that small changes in the opening angle of the confinement can lead to a drastic peak pressure reduction. Furthermore, the displacement fields over several thermal cycles are obtained and we discover the formation of convection cells inside the granular material having the shape of a torus. The root mean square of the vorticity is then calculated from the displacement fields and a quadratic dependency on the ratio of thermal expansion coefficients is established.

Transient dynamics of the thermally induced deformation of sands

“…29,30,[33][34][35] Vertical contraction has also been shown to occur for large differential expansion between the grains and the container. 31 Lastly, the present model relies solely on the mechanical behavior of sand, subjected to loading resulting from the partially restrained thermal expansion. Should different loading conditions be considered, for example, sand heated under isotropic conditions and under constant mean stress in triaxial apparatuses, the deformation would not be restrained.…”

“…[9][10][11][12][13][14][15][16][17] For coarse-grained soils (e.g., sand), thermal expansion of individual grains, which alters the contact force network and causes grain rearrangement, has been considered responsible for the thermally induced deformation of such materials within the same temperature range. [18][19][20][21][22][23][24][25][26] This peculiar nature of thermally induced deformations in coarse-grained soils has been supported by theoretical, 27 experimental, 28 and numerical evidence resorting to particle-scale simulations, [29][30][31][32][33][34][35][36] considering clean sands pertaining to classes SW or SP (i.e., wellgraded and poorly graded gravelly sands, with little or no fines) according to the Unified Soil Classification System, for which there is no potential influence of the plasticity of fine grains and their chemo-physical interaction with water.…”

Un-jamming due to energetic instability: statics to dynamics

“…Considering granular solids, their stiffness, and the elastic moduli [31,62,63] have to be considered in the presence of non-affine deformations [63]. For this, overcompression [45,49] and shear [49,60,62,[64][65][66] cyclic loading [66,67] or even thermal cyclic loading [68] were applied. When sheared granular matter starts to flow and (for large enough strain) reaches a steady state, or critical state [69][70][71], the nowadays widely accepted "classical" (I) -rheology [72] holds.…”

“…The slopes in the top panel correspond to (ss) 0 = 1 and c = 0.5 , to guide the eye, and the dashed horizontal lines in the lower panel represent the analytical values g e = 2 (dash-dotted, blue), see Eqs. (43) and (68), and various g (ss) (cyan and thin dots), see Eq. (100) 12 48 The alternative dimensionless stress:…”

Analytical and DEM studies of thermal stress in granular materials

“…buckling of rails during hot summer periods). The application of thermal cycles to granular media are also of interest since cyclic changes in stresses induced by such loadings lead to volume change as demonstrated in previous studies [1][2][3][4]. Nonetheless, there has been only limited consideration of thermal stresses in granular materials while thermal stresses in continuum materials have been well discussed in the scientific literature.…”