Carbon-fiber reinforced polymer (CFRP) composites offer benefits of reduced weight and increased specific strength; however, these materials can have relatively weak interlaminar toughness. The first modes of composite material failure often remain undetected, since failure is not always visually apparent on the surface of composite materials. In this study, several nano-sized materials and integration approaches are investigated as nanoreinforcement for composite materials. Performance is characterized by the ability of each nanoreinforced composite type to improve Mode I interlaminar toughness. The nanomaterials include 1) commercially available surface-modified silica nanoparticles and 2) continuous polyacrylonitrile (PAN) nanofibers. Test articles are manufactured using hand-layup vacuum bagging and feature either reinforced unidirectional carbon fiber or woven carbon fiber material and one of two investigated epoxy-based resin systems. The nanosilica particles were integrated into the fiber composite structure by mixing with the resin system prior to layup. The PAN nanofibers were produced by an electrospinning process; these fibers were integrated by either collecting the fibers of various areal densities as respective “nanomats” on an interim substrate for subsequent transfer during layup, or directly electrospun onto dry carbon fiber ply surfaces. Test articles were characterized according to ASTM D5528 for finding Mode I strain energy release rates. Results were compared to baseline coupons to determine fracture toughness performance. Results showed that the nanosilica-reinforced coupons increased an average of 35% and 25% in strain energy release rates for the coupons featuring unidirectional fibers and woven fibers, respectively, as compared to the corresponding baseline, whereas the nanomat-reinforced and directly deposited nanofiber-reinforced composites decreased. Low strain energy release rates for the PAN nanofiber-reinforced coupons is attributed to voids in the test coupons as a result of unconventional composite coupon manufacturing.
Continuous polyacrylonitrile (PAN) nanofibers fabricated via the electrospinning process and commercially available
silica nanoparticles were investigated and compared for their impact mitigating effects when incorporated into composite
materials. The nanofibers were introduced at ply interfaces using two different approaches while the nanoparticles were
mixed into the matrix material. Behavior was experimentally characterized by determining the fracture toughness of flat
carbon-fiber composite coupons using the double cantilever beam (DCB) test according to ASTM D5528. The
nanofibers were introduced to the composite coupons by directly electrospinning the fibers onto the ply surfaces or
transferring the fibers from an interim substrate, or "nanomat", while the nanosilica particles were mixed into the resin
system during vacuum bagging hand layup. Testing facilitated the calculation of Mode I strain energy release rates.
Preliminary results show that when compared to a baseline coupon without nanoreinforcement, there is a 54.5%, 43.1%,
and 26.9% reduction in Gavg for the nanomat, nanosilica, and directly deposited nanomaterial coupons, respectively.
Directly deposited nanofibers outperformed the nanosilica reinforcement by 16.2% and the nanomat approach by 27.6%.
Basic materials (carbon-fiber ply material and matrix system) and incomplete composite consolidation were cited as
contributors to poor test coupon quality and detrimental to Mode I performance.
Dip Pen Nanolithography (DPN<sup>TM</sup>) is a scanning probe technique for nanoscale lithography: A sharp tip is coated with a functional molecule (the “ink”) and then brought into contact with a surface where it deposits ink via a water meniscus. The DPN process is a direct-write pattern transfer technique with nanometer resolution and is inherently general with respect to usable inks and substrates including biomolecules such as proteins and oligonucleotides. We present functional extensions of the basic DPN process by showing actuated multi-probes as well as microfluidic ink delivery. We present the fabrication process and characterization of such active probes that use the bimorph effect to induce deflection of individual cantilevers as well as the integration of these probes. We also developed the capability to write with multiple inks on the probe array permitting the fabrication of multi-component nanodevices in one writing session. For this purpose, we fabricate passive microfluidic devices and present microfluidic behavior and ink loading performance of these components.
A sonar transducer, 28 mm in diameter and 40 mm long, has been built using composite Terfenol-D, consisting of grains of Terfenol-D embedded in an epoxy and magnetically aligned while the epoxy is setting. The transducer has been tested in air, where it has a resonant frequency of 18 kHz, and Q equals 18 at low amplitudes. In water it is expected to have Q equals 4.5, an acoustic output power of 48 watts, a power efficiency of 32 percent, and a maximum duty cycle of 6 percent. Surprisingly, hysteresis losses appear to be negligible when the bias field is greater than 800 oersteds, and 90 percent of the power dissipation is due to eddy currents, with 10 percent due to ohmic losses in the coil. The anomalously high eddy currents, still much lower than in monolithic Terfenol-D, can be understood in terms of the arrangement of Terfenol-D grains in the composite. At this time we have no explanation for the anomalously low hysteresis loss. It should be possible to greatly reduce the eddy currents, increasing the power efficiency to 76 percent, the output power to 69 watts, and the maximum duty cycle to 60 percent. Composite Terfenol-D should be superior to both monolithic Terfenol-D and PZT in transducers for sonar arrays operating in the 20 to 30 kHz range.