Thermomechanical behaviour of ceramic breeder and beryllium pebble beds

Status of ceramic breeder pebble bed thermo-mechanics R&D and impact on breeder material mechanical strength

“…Also note that the high frequency oscillations during loading in the stress-plateau region represent the failure of new pebbles. The current analysis also shows a creep-like behavior of the stress-strain response and hence the stress-plateaus observed in the experiments [24] may indicate the presence of pebble crushing in addition to the thermal creep mechanism. Furthermore, the residual strain after unloading is large for the system with sudden damage than the system with gradual damage.…”

“…[17] have studied similar pebble assemblies in a cubic box with periodic boundary conditions. In both the above studies, a non-linear stress-strain response and a characteristic residual strain after unloading (analogous to plastic strain in continuum systems) has been observed akin to the experimental results [24]. It has been shown that the average coordination number, average normal contact force and the maximum normal contact force in the assembly has a unique functional relation (nonlinear, linear and linear, respectively) with the hydrostatic pressure or the applied pressure independent of the packing factor [17,16].…”

Mechanics of binary and polydisperse spherical pebble assembly

“…This suggests that the counter intuitive behavior of the assemblies studied above should be arising from the difference in the values of relative volume fraction V * . The presence of small pebbles between two large pebbles introduces a ball-bearing like effect also observed in experiments [10] resulting in a softer response. A large value of V * indicates the presence of more such ball-bearing like sites in the assembly resulting in a complaint behavior of the assembly.…”

“…On the contrary, the binary and polydisperse assemblies exhibit a rather soft behavior (in comparison to mono size assembly) along with a residual strain of approximately 0.3%. In the uni-axial compression tests carried out by [10], the assembly shows a rather soft behavior with a residual strain of approximately 0.35%. However, in the present study of polydisperse pebble assemblies, a much stiffer response during loading is observed.…”

Packed bed heat storage: Continuum mechanics model and validation

“…One key parameter for the continuum model is the effective Young's Modulus of the packed bed. Reimann [7] provided a correlation of the effective Young's Modulus as a function of temperature and stress for a variety of packed bed materials used in ceramic breeder blankets:…”