Yielding and Locking of Confined Sand

Historical review of high strain rate and shock properties of ceramics relevant to their application in armour

“…116,117,[161][162][163][164][165][166][167] It should be emphasised that sand (or comminuted ceramic) does not have zero strength because the grains can interlock. 168 Direct evidence for this in glass has been obtained using flash X-ray and high-speed photography: 169 a steel rod was seen to be strongly resisted by glass up for at least 40 ms despite the glass having been completely comminuted within about 5-6 ms.…”

Loading rate effects on compressibility of sand

“…Below this rate, the stress -strain curve "stiffens" (curvature concave to the stress axis), whereas above this rate, the curve "yields" (curvature concave to the strain axis). Such changes in curvature would have significant effects on propagation velocities ~nd rise times at the fronts of blast-induced stress waves (4,11). A variety of simple viscoelastic and hysteretic models have been used to study the effects of time-dependent, inelastic and nonlinear stress-strain behavior on stress wave propagation through laterally confined soils (12,13); a model incorporating all of these characteristics is needed in order to replicate the behavior shown in Fig.…”

“…Experimental results for dry sands show that the stress-strain curves , starting from some initial prestress , are S-shaped , with yielding for small stress changes and stiffening for large stress changes (4) . The secant modulus of dry sand for a rapid loading (say 10-msec rise time) is usually on the order of 5 to 40 percent greater than that for a slow loading (several minutes rise time) ; typical values previously reported for such dynamic-to-static modulus ratios are given in Table 1 .…”