Issue 50

A. Kakaliagos et alii, Frattura ed Integrità Strutturale, 50 (2019) 481-496; DOI: 10.3221/IGF-ESIS.50.40 495 the chamber is entering the yield plateau of Curve B (Fig.11). Admittedly, the situation described above occurs after one bombard shot. Additional gun shots and residual plastic dilatations caused by the combined action of temperature and internal pressure would further push point (1) in Fig.11 towards the yield plateau of Curve B, hence, increasing the potential of gun failure. After each individual gunshot, unloading would result following a typical unloading stiffness parallel to the original stiffness of the gunpowder chamber. This procedure yields residual plastic deformations of the chamber. Herein, the elastic stiffness of the gun can be computed as 101.325 MPa/169 microns, hence, 600 MPa/mm (Figs.7,11). In situations where powder chamber dilation exceeds D/500 and after repeated firing of the gun, residual plastic deformations and associated stresses and strains due to combined action of internal pressure and temperature together with successive loading and unloading in the push over curve can contribute to the overall structural deterioration of the gunpowder chamber (Curve B, Figs.7,11). Recognizing the fact that bronze material as produced during the Late Medieval Period could not exhibit a significant strain hardening behavior and considering the effect of imposed dilations due to internal blast combined with temperature, it can be concluded that exceeding deformation limit at D/100 failure of the gun can be expected. Admittedly, the situation as presented above actually occurs within a time frame of certain milliseconds. Considering the time of cannonball exit from gun bore t E at 44.8 msec, the time frame for peak blast pressure occurrence can be roughly estimated at t E /100. Although this time window is small and strain rate effects can play a role in the whole procedure, in general it is not expected that imposed stresses and strains would not produce effects as presented above. The situation as presented above supports historical reports that the bombard exploded killing both the gun crew and Orban himself (Phrantzes [6]). Figure 11: Combined effect of internal pressure and temperature. C ONCLUSIONS he objective of the analysis presented in this paper was to treat the historical records concerning the bombardment of Constantinople walls in 1453 as a full-scale numerical experiment. Its aim was to verify gun capacity as well as firing strength, check the validity of the corresponding historical records and focus on structural design aspects which potentially may have led to premature bombard failure. Orban’s gun dimensions and overall size have been reconstructed numerically based on historical reports. Gun ballistics and effect on target have been evaluated analytically. A numerical model was evaluated to assess Wall collapse mechanisms during bombardment. The analysis has verified Orban’s gun muzzle velocity, cannonball trajectory and its effect on Constantinople Walls. The analytical results have verified the authenticity of the historical reports and proved that these sources are accurate and correct. The sound effect of Orban’s gun has been evaluated numerically. The analysis confirmed the tremendous psychological effect of the Cannon’s blast on the City’s population, as mentioned in historical records. The stress situation in the powder chamber under combined action of blast internal pressure and induced temperature due to powder ignition was evaluated. It was identified that combined internal pressure and T