Issue 50

A. Kakaliagos et alii, Frattura ed Integrità Strutturale, 50 (2019) 481-496; DOI: 10.3221/IGF-ESIS.50.40 489 G UNPOWDER CHAMBER STRUCTURAL RESPONSE he pressure inside the gunpowder chamber due to gunpowder ignition is increasing the atmospheric pressure of 101,325 Pa by a factor R (Eq.(1)). Consequently, the internal pressure q results at 101.325 MPa (14.70 ksi), with R at 1,000. Considering the gunpowder chamber as a thick cylinder under internal pressure, maximum stresses result at the inner surface of the cylinder (Timoshenko and Goodier [13]). Herein, for a cylinder without connection to cannon breech, the circumferential stress is at 107 MPa, the radial stress at 101 MPa and the axial stress at 2.7 MPa, respectively. These stresses produce a maximum von Mises stress σ v at 180 MPa (Fig.4). Under this plane stress condition, with both cylinder ends capped, the dilatation of the inner gunpowder cylinder surface results at 169 microns and 35 microns at the outer gunpowder cylinder surface, respectively. Stress concentration appears at the connection of gunpowder cylinder to cannon breech along the gunpowder cylinder inner perimeter. At this location the circumferential stresses bottleneck in order to further stream into the connected cannon breech solid and typically act locally as shear stresses. As a result of this, the von Mises stress peaks at 211 MPa (Fig.4). In order to verify the local von Mises stress increase at the connection of gunpowder chamber to cannon breech, a finite element computer model under internal pressure was employed. The internal pressure q was set at 101.325 MPa. Herein, a 10 o cylinder slice was used, with the finite element mesh tuned to yield the theoretically stresses derived previously for a cylinder under internal pressure without connection to cannon breech (Figs.4,5a). The model had fixed base supports, whereby 24,026 eight node solid elements and 48,813 nodes were employed. Figure 4: Gun powder chamber stresses under internal pressure during powder ignition. Figur e 5 : (a) Computer model; (b) gunpowder chamber stresses and (c) gunpowder chamber internal surface distortions. T