Examining the Relationship Between Ballistic and Structural Properties of Lightweight Thermoplastic Unidirectional Composite Laminates
Abstract : The pursuit for lightweight personal protection (helmets, body armor, etc.) has been a key issue for the Army in recent years. Previous efforts have shown that the variation of orientation and architecture in ultra-high molecular weight polyethylene (UHMWPE) composite panels can significantly affect ballistic performance characteristics. In our experiments, an architecture now referred to as ARL X Hybrid emerged as the clear leader in the compromise between ballistic performance and back face deformation (BFD). For this work, thermoplastic unidirectional materials (both aramid and polyethylene based) were evaluated using 17 grain FSP V50 and 9 mm BFD testing in both typical ([0 deg/90 deg]) and X Hybrid architectures, at an areal density target 27% lighter (7.8 kg/sq m) than the currently fielded state of the art. Digital Image Correlation (DIC) was employed to characterize the materials during testing and to help elucidate the panel response as a function of architecture. Polyethylene materials in the X Hybrid architecture were shown to retain 96-99% of the [0 deg/90 deg] architecture's V50 ballistic performance, while also reducing the BFD by 36-41%. Higher fiber involvement, increased interaction area, and increased membrane stress and through-thickness compression are proposed as factors for this phenomenon.
Influence of a Steel Strike Face on the ballistic resistance of an Ultra High Molecular Weight Polyethylene fibre reinforced thermoplastic matrix composite considering energy absorption and penetration
A series of experimental target panels were constructed from ultra-high molecular weight polyethylene fibre reinforced thermoplastic using a locally developed compression moulding procedure. Half of the experimental test panels were bonded to a 1.2mm steel strike face with an acrylic adhesive forming fibre metal laminates for ballistic testing. The panels were subjected to ballistic impact loading from 55 grain jacketed soft point spitzer projectiles, fired from a rifle at velocities above 103 ms-1 under open environmental conditions. Velocity measurements were taken fore and aft with Caldwell precision chronographs, and energies calculated and normalised with areal density. Plotting of velocity, energy, thickness and areal density suggested the addition of a steel strikeface reduced the energy absorption capacity of the thermoplastic matrix laminate by approximately 50%. This result was found to be inconclusive when reviewed against high-speed video imagery. Optical microscopy was conducted on the sectioned, impacted laminates where wide area delamination was observed to initiate up to 35% earlier through thickness in fibre metal laminates. This result complimented surface profilometry observations where a 35% increase in back face deformation area was identified for fibre metal laminates. The fibre metal laminates were observed to initiate significant delamination from a thickness of 47%, with back face deflection extending to 28mm. These results illustrated a complimentary correlation with analytical calculations made using equations from previous works. Identifying this result and noting that wide area delamination is the characteristic ballistic resistance mechanisms of armour laminates, it is suggested an increase in ballistic resistance of up to 35% may be achieved by the addition of a steel strike face. To further increase the scope of results a commercial laminate was included in the testing regime qualifying the response of the panels to be consistent with commercial ballistic laminates.
Effects of Equipment Dimensions on Liquid Mixing Time of Bubble Column with Draft Tube
The liquid mixing time of a bubble column with a draft tube is experimentally studied. The diameter and height of the column, the diameter and length of the draft tube, and the mode of sparging gas were changed and the liquid mixing time was measured.The lengths of bottom and top clearances have significant effects on the liquid mixing time. The liquid mixing time increases with increasing column aspect ratio of height to diameter. The liquid mixing time of the bubble column with a draft tube is longer than that of a standard bubble column when the column aspect ratio is relatively high. The liquid mixing time has a minimum when the diameter ratio of draft tube to column is 0.5 to 0.6. These effects of equipment dimensions are expressed by an equation. In the experiment using different solutions, the liquid mixing time becomes shorter with increasing liquid surface tension, or with increasing liquid viscosity.