## 5 Concluding Remarks  
The new simulations were satisfactorily validated using experimental work and a previously validated modelling approach [17]. The peak bearing velocity were not influenced by the improved bearing damage model of the finer bearing mesh. This confirmed that momentum transfer is mainly influenced by the charge mass to ball bearing mass ratio and the aspect ratio of the charge. Larger ball bearings require extra momentum to accelerate them to higher velocities due to their increased mass, but their higher surface area also means that a greater portion of the explosive charge is involved in momentum transfer. The drop in velocity observed part-way through the bearing flight due to interaction with the reflected pressure was influenced by bearing diameter charge diameter. Higher momentum required greater reflected pressures to decelerate the bearing, but the reflected pressure acted over a larger surface area. Additionally, less of the charge mass directly contributed to the reflected pressure front in low diameter charges; this was due to the increased bearing surface area meaning that less of the blast pressure moved past the ball bearing in the early stages of blast wave formation.  
Figure 14: Simulated pressure contour plots from detonating a 27.16 g charge (30 mm diameter) embedded with a 10 mm diameter ball bearing at (**a**) 1.8 \(\upmu\)s, (**b**) 2.55 \(\upmu\)s, (**c**) 2.99 \(\upmu\)s, (**d**) 4.53 \(\upmu\)s.  
Using a post-test damage analysis and an enhanced ball bearing modelling approach, tensile spalling was found to be the major damage mechanism within the ball bearings. The charge aspect ratio affected the initial compressive hydrostatic pressure propagation within the ball bearing itself; the compressive stress was then reflected from the free surface of the bearing as a tensile wave. The focusing effect due to bearing curvature and charge geometry influenced the magnitude and shape of the tensile spalling wave, affecting the location and degree of internal cracking within the bearings. In some cases, it may be possible to cause the bearing to break apart due to extensive internal cracking caused by tensile spalling. These findings will prove valuable to blast protection engineers considering the effects of embedded projectiles in improvised explosive devices, enabling projectile velocities and trajectories to be estimated for future injury estimates from IED events.  
Conceptualization, G.S.L. and T.J.C.; methodology, T.J.C., S.C.K.Y., G.S.L. and R.Q.; investigation, R.Q., G.S.L., T.J.C. and S.C.K.Y.; resources, G.S.L.; data curation, R.Q.; writing--original draft preparation, G.S.L. and R.Q.; writing--review and editing, T.J.C. and S.C.K.Y.; supervision, G.S.L. and T.J.C.; project administration, G.S.L.; funding acquisition, G.S.L. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Research Foundation (NRF) of South Africa, grant number 111737.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors are grateful to the National Research Foundation (NRF) of South Africa for their financial support. Opinions expressed and conclusions arrived at are those of the authors and are not necessarily attributable to the NRF. The authors would also like to thank the staff of the Mechanical Engineering workshop at UCT for their assistance in machining the specimens and pendulum parts.  
The authors declare no conflict of interest.