High impact velocity

Meir and Clifton [12] study shocked <100) LiF (high purity) with peak longitudinal stress amplitudes 0.5 GPa. A series of experiments is reported in which surface damage is gradually eliminated. They find that, while at low-impact velocities the dislocations in subgrain boundaries are immobile and do not affect the dislocation concentration in their vicinity, at high-impact velocities ( 0.1 km/s) dislocations emitted from subgrain boundaries appear to account for most of the mobile dislocations. 

The particles must hit the accumulating bed with a high impact velocity. 

Figure 3.30. Schematic showing the impact phenomena of multiple droplets on a substrate surface spreading pattern at low impact velocities (fop) and splashing mechanism at high impact velocities (bottom).

Figure 9 demonstrates the load-displacement diagrams for the two cases of the impact velocity and for both cases of with and without the use of the rubber bumper. The results show that the indentation, which represents the local deformation at the vicinity of an impact, is much larger in the case of having the rubber shock absorber due to the reduced impact stiffness. Furthermore, in the case of the relatively high impact velocity of 1.0 m/s, the deformation exceeds the maximum compressive capacity of the 5 cm thick rubber bumper, and the impact force begins to rise rapidly, since the postyield linear impact stiffness is used. 

R. Shakeshaft, "Atomic Rearrangement Collisions at Assymtoti-cally High Impact Velocities in "Physics of Electronic and Atomic Collisions , S. Datz, ed. (North Holland Press, 1982) pp. 123-138. 

Shakeshaft, R., 1982, Atomic rearrangement collisions at asymptotically high impact velocities, "Invited Papers of the XII International Conference on the Physics of Electronic and Atomic Collisions", Gatlinberg, Tennessee, July 1981, S. Datz (editor). North Holland, Amsterdam. 

Shakeshaft, R. and L. Spruch, 1979, Mechanism for charge transfer (or for the capture of any light particle) at asymptotically high impact velocities. Rev. Mod. Phys., 51 369. 

There are many remaining topics on impact phenomena of adhesively bonded joints, which should be solved in the future. One of rising and promising research areas is impact problems of composite materials bonded adhesively. This analysis will be more important due to the increase of composite aircrafts, althor it has difficulties of high impact velocity and the anisotropy of composite materials. In contrast, lower impact velocity will also become more important. Dropping impact problem of mobile phones has been analyzed (Akiba et al. 2006), but joining parts in the structure was not modeled. Even in low impact velocities, the modeling of adhesive joints is still a big problem and a material for research. 

The morphology of the oxide scale that forms during erosion plays an important role, as noted by the extensive work of Levy and co-workers [47, 49,53,58,59]. Segmented scales have better erosion resistance than thick, continuous and dense scale, since in the former case the spalled area is confined to crystalline oxide only. This observation is validated by adding Si to the steel. Addition of Si to low chromium steel results in the formation of a segmented scale even at high impact velocity and thereby reduces the erosion rate substantially as compared to the same steel without Si [59]. 

Based on the above kinetic description of fracture as observed from the SEM fractographs, it can be realized that at the high impact velocity, the fracture occurred dominantly in brittle modes. Also, less energy pulses were needed for the completion of the fracture event than those at the low impact velocity. It should be noted that the impact energy input at failure exponentially increases with relaxed stiuctural constraint (namely increasing x, see Fig. 2) and fracture would become less brittle or even unlikely. Above certain x value, the flexible tube may be able to absorb the impact energy without any damage. 

At high impact velocities (2 and 3m/s) the superinposed oscillations due to dynamic effects were so important, that it was very difficult to describe sample behavior. However, fracture surfaces exhibited the same features as sanples evaluated at 1 m/s. 

---