Issue 50

A. Kakaliagos et alii, Frattura ed Integrità Strutturale, 50 (2019) 481-496; DOI: 10.3221/IGF-ESIS.50.40 494 Figure 9: Temperature effect on gunpowder cylinder – von Mises combined stresses powder chamber without connection to gun breech. The temperature stresses used in the combined stress effect from Fig.6 were combined with the corresponding stresses from internal pressure in Fig.5 and presented in Fig.10. The formation of a plastic zone is recorded, extending from 240 mm up to chamber exterior surface (Fig.10). As the temperature stresses were evaluated for chamber without connection to the breech, the radial stresses which are typically zero at the internal and external chamber surface, are expected to rise when the corresponding radial constraint is activated to the connected gun breech. This procedure would increase the effect of radial stresses in the evaluation of the von Mises combined stress as presented previously with a simultaneous increase of the plastic zone width. It should be emphasized that during the cooling procedure, which is typically executed fast during a battle situation, residual stresses are expected to develop in the powder chamber at the interior and exterior chamber surface. These residual stresses would combine their effect with the subsequent shot, hence, deteriorating the situation as presented in Figs.5,10. Figure 10 : Combined effect of internal pressure and temperature – von Mises combined stress powder chamber without connection to gun breech. To capture the temperature effect on the chamber considering the connection to cannon breech it was decided to apply a displacement-based procedure. Herein, the evaluated radial displacement, as computed with Eq.(23) at 200 o C, was used as imposed displacement on the push over curve B from Fig.11. The evaluated radial displacement δ Τ at the inner chamber surface was at 159 microns and 991 mm at the outer surface correspondingly. For ensuing considerations, the average value of evaluated radial displacements was used, hence, at 575 microns. Considering the radial displacement at 169 microns due to internal pressure together with the average imposed displacement due to temperature at 575 microns the total displacement results at 744 microns. Using this value as imposed displacement in Fig.11 the plastic radius r p is at 218 mm with the corresponding stress situation (Point 1, Fig.11) at Curve B close to D/250, thus, yielding a situation where