This paper presents an experimental and numerical study to understand ballistic behavior of plain-weave hybrid and non-hybrid composites. The effect of hybridization on ballistic limit ( V 50 ) was investigated. The hybrid S2 glass-IM7 graphite fibers/toughened SC-79 resin, non-hybrid S2 glass-fiber/toughened SC-79 resin, and non-hybrid IM7 graphite fibers/toughened SC-79 resin composites plates were impacted at various velocities. The three-dimensional dynamic nonlinear finite element code, LS-DYNA, modified with a proposed user-defined nonlinear-orthotropic damage model, was adopted to simulate the experimental results. The combined results obtained from experiments and finite element simulations were then used for determining V 50 for each lay-up configuration. Good agreement between experimental and FE results was found from the comparison of dynamic strain and damage patterns. The hybridization found to be very effective on ballistic limit velocities of woven composites.
Impact-induced delamination and fracture in 6061-T6 aluminum/cast acrylic sandwich plates adhered by epoxy were generated in an instrumented drop-weight impact machine. Although only a small dent was produced on the aluminum side when a hemispherical penetrator tup was dropped onto it from a couple of inches, a large ring of delamination at the interface was observed. The delamination damage was often accompanied by severe shattering in the acrylic substratum. Damage patterns in the acrylic layer include radial and ring cracks and, together with delamination at the interface, may cause peeling-off of acrylic material from the sandwich plate. Theory of stress-wave propagation can be used to explain these damage patterns. The impact tests were conducted at various temperatures. The results also show clearly that temperature effect is very important in impact damage. For pure cast acrylic nil-ductile transition (NDT) occurs between 185-195 F. Excessive impact energy was dissipated into fracture energy when tested at temperature below this range or through plastic deformation when tested at temperature above the NDT temperature. Results from this study will be used as baseline data for studying fiber-metal laminates, such as GLARE and ARALL for advanced aeronautical and astronautical applications.
The main objective of this NASA FAR project is to conduct ultrasonic assessment of impact-induced damage and microcracking in polymer matrix composites at various temperatures. It is believed that the proposed study of impact damage assessment on polymer matrix composites will benefit several NASA missions and current interests, such as ballistic impact testing of composite fan containment and high strain rate deformation modeling of polymer matrix composites. Impact-induced damage mechanisms in GLARE and ARALL fiber-metal laminates subject to instrumented drop-weight impacts at various temperatures were studied. GLARE and ARALL are hybrid composites made of alternating layers of aluminum and glass (for GLARE) and aramid- (for ARALL) fiber-reinforced epoxy. Damage in pure aluminum panels impacted by foreign objects was mainly characterized by large plastic deformation surrounding a deep penetration dent. On the other hand, plastic deformation in fiber-metal laminates was often not as severe although the penetration dent was still produced. The more stiff fiber-reinforced epoxy layers provided better bending rigidity; thus, enhancing impact damage tolerance. Severe cracking, however, occurred due to the use of these more brittle fiber-reinforced epoxy layers. Fracture patterns, e.g., crack length and delamination size, were greatly affected by the lay-up configuration rather than by the number of layers, which implies that thickness effect was not significant for the panels tested in this study. Immersion ultrasound techniques were then used to assess damages generated by instrumented drop-weight impacts onto these fiber-metal laminate panels as well as 6061-T6 aluminum/cast acrylic sandwich plates adhered by epoxy. Depending on several parameters, such as impact velocity, mass, temperature, laminate configuration, sandwich construction, etc., various types of impact damage were observed, including plastic deformation, radiating cracks emanating from the impact site, ring cracks surrounding the impact site, partial and full delamination, and combinations of these damages.
Abstract Fiber-metal laminated cantilever beams, made of glass-fiber reinforced GLARE and aramid-fiber reinforced ARALL laminates interlaced with aluminum layers, were first excited by a shaker at various frequencies surrounding resonances. Dynamic Young’s moduli and damping ratios were then evaluated using both free-vibration (resonance) and forced-vibration (non-resonance) schemes. Results from both schemes are in good agreement. Compared to aluminum alloys, the dynamic Young’s moduli of fiber-metal laminates are relatively lower. For all types of fiber-metal laminates tested in this study, their values are almost constant within an excitation frequency range up to 5,000 Hz whereas the damping ratios oscillate within a narrow range of 0 to 0.02. The obtained dynamic moduli are in excellent agreement with their static counterparts. Better results were obtained when using a strain gage near the clamped end, as compared to a piezoelectric accelerometer at the tip.
In this paper, GLARE 5 fiber-metal laminates (FMLs) of two different geometries: 152.4mm×101.6mm (6″×4″) plate and 254mm×25.4mm (10″×1″) beam and with various thicknesses and stacking sequences were impacted by a 0.22 caliber bullet-shaped projectile using a high-speed gas gun. Velocities of the projectile along the ballistic trajectory were measured at different locations. For both geometries, the incident projectile impact velocity versus the residual velocity was plotted and numerically fitted according to the classical Lambert–Jonas equation for the determination of ballistic limit velocity, V50. The results showed that V50 varied in a parabolic trend with respect to the metal volume fraction (MVF) and the specimen thickness for both geometries. It was found that by changing the geometry from a plate to a beam, the ballistic limit velocity increased. On the other hand, changing the stacking sequence had a less pronounced effect on V50 for both geometries. The quasi-isotropic beam and plate specimens offered relatively higher ballistic limit velocities compared to other types of stacking sequences in their own geometrical groups. Furthermore, the cross-ply and unidirectional beam specimens showed relatively higher V50 compared to their plate counterparts. Experimental results showed that the ballistic limit was almost the same for the quasi-isotropic layup FMLs of both plate and beam geometries.
Beginning in the Fall 1994 semester, the Department of Mechanical Engineering at The City College of The City University of New York has introduced the utilization of computer animated modules in its undergraduate dynamics course which are intended to help the students visualize and obtain a better understanding of important concepts covered in the course. The software which these modules are based on is called Working Model and is commercially available from Knowledge Revolution, San Francisco, CA. The software allows the user to create two dimensional mechanical systems on the screen containing devices such as springs, masses, pulleys, dampers, motors and actuators. Various types of forces may be simulated including gravitational, frictional and electrostatic forces. Clicking a RUN button animates the experiment. Controls may be introduced which allow the user to vary physical parameters such as initial position, velocity, and acceleration of objects, magnitude and direction of applied forces and torques, etc. Physical quantities such as velocity, acceleration, linear and angular momentum and kinetic energy may be measured and displayed while an animation is in progress. Several illustrative modules have been developed covering a variety of topics. In addition, as the students became acquainted with the software, they were given specific topics and asked to develop their own modules. The paper describes some of the modules developed and the students' reactions to this learning experience.
