Low velocity blunt impacts on composite aircraft structures

As composites are increasingly used for primary structures in commercial aircrafts, it is necessary to understand damage initiation for composites subject to low velocity impacts from service conditions, maintenance, and other ground equipment mishaps. In particular, collisions with ground vehicles can present a wide area, blunt impact. Therefore, the effects of bluntness of an impactor are of interest as this is related to both the external visual detectability of an impact event, as well as the development of internal damage in the laminate. The objective of this investigation is to determine the effect of impactor radius on the initiation of damage to composite panels. A pendulum impactor was used to strike 200 mm square woven glass/epoxy composite plates of 3.18mm and 6.35mm thicknesses. Hemispherical steel tips with radius 12.7mm to 152.4mm were mounted to a piezoelectric force sensor which measures the contact force history. Impacts were conducted with and without rubber bumpers to mimic the bumpers used on ground vehicles. Strain gauges were mounted to select panels. Experimental data show distinct threshold energy for the onset of delamination and fiber breakage. These energy levels increase with increasing tip radius. Strain increases with decreasing tip radius. Strains at the panel center are less affected by the presence of rubber bumpers with increasing tip radius. Finite element simulations match the experimentally measured contact force and strain data. Curved FE panels show peak contact forces independent of impactor radius and incident angle. In-plane compressive stresses decrease with increasing radius tips and incident angl

A Non-Explosive Methodology for Generating Wide Area Close -in Dynamic Blast Pressure Loads on Flexible Armor Panels /

Dynamic blast testing of armor components often requires explosives to generate the high pressure, wide area impulses. While explosives provide the most realistic loading conditions, they are difficult to replicate consistently and necessitate remote test facilities for safety. Non-explosive methodologies, such as gas guns and shock tubes, can produce high impulse dynamic events with higher repeatability and increased safety, but are often limited to smaller-sized targets. To impact wide area flexible armor panels with the blast characteristics of a close-in detonation, a non-explosive methodology was investigated using the U.C. San Diego Blast Simulator. The objective was to create a consistent, economical, and scalable methodology for comparing conventional steel and prototype sandwich panel performance with validation of damage modes and extent of damage using actual blast tests and finite element modeling. A tiled projectile array having spatially and temporally varying pressure pulses was developed to replicate the spherical loading profile of a close-in detonation. Using a high speed servo- hydraulic actuator, the projectile was launched at 23.0 - 24.6 m/s, equivalent to 7,520 - 8,460 Pa-s with less than 1.9% standard deviation over 43 tests. This was comparable to 1.37 kg of C4 at 305 mm standoff, which was also used to test five armor panels. Sandwich panel transmitted pressures, measured indirectly via transmission plate acceleration, showed up to 75% reduction in maximum values compared to the steel armor panels, with up to 49% weight savings. Deformation profiles of the non-explosive tested panels were similar in both shape and magnitude compared to the blast tested panels, but with more consistency and symmetry. Blast tested panels showed more extensive core crushing for the sandwich panels but no difference for steel. Finite element modeling predicted similar deformation profiles and transmission plate velocities and accelerations. The models showed higher core crush for the blast tested panels and stress concentrations that matched both sets of test results. The applied impulses for the non-explosive tests were also predicted to be higher than the blast tests. The UCSD Blast Simulator was able to achieve similar levels of damage compared to an actual blast test, with greater repeatability between test

Role for GDNF in Biochemical and Behavioral Adaptations to Drugs of Abuse

AbstractThe present study examined a role for GDNF in adaptations to drugs of abuse. Infusion of GDNF into the ventral tegmental area (VTA), a dopaminergic brain region important for addiction, blocks certain biochemical adaptations to chronic cocaine or morphine as well as the rewarding effects of cocaine. Conversely, responses to cocaine are enhanced in rats by intra-VTA infusion of an anti-GDNF antibody and in mice heterozygous for a null mutation in the GDNF gene. Chronic morphine or cocaine exposure decreases levels of phosphoRet, the protein kinase that mediates GDNF signaling, in the VTA. Together, these results suggest a feedback loop, whereby drugs of abuse decrease signaling through endogenous GDNF pathways in the VTA, which then increases the behavioral sensitivity to subsequent drug exposure