Microcellular PP-CaCO3 Nanocomposites: Relationship Between Nanocomposite Morphology and Foam Morphology

Polymeric nanocomposites exhibit high potential as a new material for carbon dioxide (CO2) foaming. In this paper, a polypropylene (PP)/nano-calcium carbonate (nano-CaCO3) composite was selected to investigate the relationship between nanocomposite morphology and foam morphology. Nanocomposites were prepared using a twin-screw extruder with screw including both shearing and mixing elements. Nanocomposites with different morphology via changing the nano-CaCO3 content were then foamed by using supercritical CO2 in a batch system. Effect of nano-CaCO3 content on the volume expansion ratio, and cell coalescence were studied.

Processing and Characterization of Hybrid Nanoparticle Infused Structural Fiber Composites

Effective conventional manufacturing techniques are required to integrate the nanomaterial configurations into material systems at a larger component and structural level to obtain the enhanced benefits offered by the material configurations at the nano length scale. A low cost manufacturing process based on vacuum assisted resin transfer molding (VARTM) is demonstrated for the effective processing of fiber composite laminates using modified epoxy resin systems dispersed with nano and sub-micron alumina oxide particles. The effect of alumina oxide particles on the thermo physical properties (glass transition temperature, etc), are studied via differential scanning calorimetry and thermal gravimetric analysis. Higher glass transition temperatures with the alumina oxide and other nano particulate systems provide an opportunity to use conventional resin systems in high temperature applications. Ultrasonic mixing is employed to uniformly disperse the particles into an epoxy resin system. The flow characteristics of the modified resin system are not significantly different than the neat resin system and allowed the use of traditional VARTM processes successfully. The details of the resin modification and current studies on particulate modification for better interfacial bond are discussed in this paper. Wear performance for reinforced plastics are also investigated in this paper. Composite laminates with S2 glass and modified resins are fabricated. The mechanical behavior of the fabricated composite laminates with the neat and modified resin system using different sized and loading of alumina oxide particles are presented and discussed.

Relaxation in Nanoscale Freestanding Gold Films Using MEMS

We present experimental results to describe the stress relaxation behavior of thin (125 nm) freestanding gold films at room temperature. The experiments were performed inside a field emission scanning microscope using a MEMS-based test bed which is only 3mm × 10mm in size. The effect of stress relaxation on the young’s modulus of gold thin films is observed. The thin film specimen used in the experiment is co-fabricated with the micromechanical loading device and hence eliminates problems of alignment and gripping. Freestanding thin films provide us with information about the mechanical behavior of thin films in the absence of substrate effects.

Dielectrostriction and Piezoresistance Response in Liquid Polymers

Variations of dielectric and resistive responses of a material with deformation are called dielectrostriction and piezoresistance respectively. Both phenomena have the same microscopic foundation — they involve the change of relative positions of polarizable or conductive species, leading to change in the material’s electric properties. Since both dielectrostriction and piezoresistance are determined by the pair distribution function of inclusions, these two phenomena are sensitive to a material’s microstructure, which renders them effective for monitoring liquid polymer and polymer suspension processing and mixing. In this study, a planar sensor is implemented to detect the dielectrostriction effect in shear flow of pure silicone elastomer and piezoresistance effect in silicone/graphite suspensions. In both measurements, the electric responses are found to be scaled with the flow-induced stresses, which constitute new approaches to study the rheological properties of bulk materials and suspensions and compliment each other for revealing the microstructure in various systems.

Elastic Properties of Composites Based on Tree Root Fibers

The in plane mechanical properties of composites based on fibres which shape is that of a tree root has been investigated. The number of fibrils as well as the angle between them have been shown to influence significantly the effective properties of the composite. It can be shown that there is an optimal number of fibrils and an optimal angle for which the stiffness of the material is maximum

Suppression of Edge Delamination Through Meso-Scale Structuring

We are developing a new class of fiber-reinforced polymer composite materials to facilitate imbedding multifunctional features and devices in material systems, and to manage interlaminar stresses at free edges and cut-outs. The idea is centered on introducing one more level of design space by composing plies with individual tiles possessing the same degrees of design freedom that are associated with individual plies. In this work, we have focused on tiling schemes that will allow blending of laminates (lay-ups), where a lay-up suitable for suppressing interlaminar stresses could be placed at necessary locations whereas another lay-up could be used for the main objective. This results in the introduction of matrix-rich tile-to-tile interface pockets in the blending region. Preliminary mechanical testing shows that uniaxially reinforced tiled composites attain stiffness levels near those of their traditional counterparts, yet with a potential degradation of strength. We used the finite element method to investigate the effects of resin-rich pocket size, the use of supporting continuous layers, tile size, and tile overlapping (interface stacking) schemes on stress distribution around interfaces in uniaxially reinforced tiled composites, with the aim to identify parameters controlling overall strength. We discovered that alignment of the resin-rich pockets through the thickness exacerbates stress-concentration and that outer continuous layers on the composite may help in better load transfer. As a first step in the application of this technique for the suppression of delamination at the free edges of holes in laminates, a bilaminate material was modeled, and the concept was shown to be effective in the suppression of edge delamination.

Intralaminar Reinforcement for Biomimetic Toughening of Bismaleimide Composites Using Nanostructured Materials

Many conventional composite materials are composed of multiple layers of continuous fiber reinforced resin produced by lamination of b-staged prepreg and subsequent cure. These materials exhibit very high strength and stiffness in the plane, dominated by the properties of the fibers. The Achilles heel of such composites is the interlaminar strength, which is dependent on the strength of the unreinforced resin, often leading to failure by delamination under load. Current methods for increasing the interlaminar shear strength of composites consist of inserting translaminar reinforcement fibers through the entire thickness of a laminated composite, such as z-pin technology developed by Foster-Miller [1]. While effective, this technique adds several processing steps, including ultrasonic insertion of the z-pins into the laminate, subsequently causing a significant cost increase to laminated composites. Described in this paper is a process utilizing single-walled carbon nanotubes (SWNTs) and vapor grown carbon nanofibers as reinforcing elements promoting interlaminar shear strength and toughness in carbon fiber/bismaleimide (BMI) resin composites. The resulting composites mimic the natural reinforcing mechanism utilized in insect cuticles. Three different methods of increasing the affinity of these carbon nanofillers for the BMI matrix were explored. The mechanical properties of these composites were assessed using end notch flexure testing. The results indicated that including nanofiller at the laminae interface could increase the interlaminar shear strength of carbon fiber/BMI composites by up to 58%. SEM micrographs revealed that the nanofiller successfully bridged the laminae of the composite, thus biomimicking the insect cuticle. Composite fabrication techniques developed on this program would have a wide variety of applications in space and aerospace structures including leading and trailing edges of aircraft wings.

Enhancement of Dimensional Stability of Polymer Composites Manufacturing Using Carbon Nanofibers

Process induced residual stress arises in polymer composites as a result of resin shrinkage during cure cycle. When a shell-like composite part is demolded, these residual stresses result in change of dimensions such as spring-in, which is a phenomenon that the enclosed angles of the composite part are reduced due to process-induced residual stress. To have good precision in the composite part, the dimensional instability of enclosed angles must be controlled and/or compensated. The traditional approach is to estimate the spring-in and consequently correct the mold geometry to counterbalance the predicted dimensional instability. The success of such mold design practice relies on the past experience or by costly trial and error approach. In this paper, we present a new approach to reduce the spring-in by using Carbon Nanofibers (CNF). CNF have remarkable physical and mechanical properties and have excellent dimensional stability and hence may be useful in improving the dimensional stability of polymer composites. In this experimental study, we dispersed different fractions of CNF into fiberglass/polyester composite parts with corner angles and compared their spring-in angles after the composite parts were demolded. The results show that the CNF can effectively restrain the undesired deformation and improve the dimensional stability of polymer composites during manufacturing process.

Origami Fabrication of SU-8 Supercapacitors

The Nanostructured Origami™ 3D Fabrication and Assembly Process was developed as a novel method of creating three-dimensional (3D) nanostructured devices using two-dimensional micro- and nanopatterning tools and techniques. The origami method of fabrication is a two-part process in which two-dimensional (2D) membranes are first patterned and then folded into the desired 3D configuration. This paper reports on the use of the Nanostructured Origami™ process to create a functional electrochemical energy storage device. An electrochemical capacitor, or a supercapacitor, is selected because its performance can be readily improved by the addition of 3D geometry and nanoarchitecture. In addition to improved performance, the origami fabrication method allows such devices to be integrated into preexisting MEMS and IC processes, thus enabling the fabrication of complete micro- and nanosystems with an integrated power supply. The supercapacitors were created by selectively depositing carbon-based electrode materials on the SU-8 membrane and then folding the structure so that oppositely-charged electrode regions face each other in a 3D arrangement. The fabrication process, electrochemical testing procedure, and analysis of the results are presented.

Study on the Drilling of Titanium/Graphite Hybrid Composites

Titanium/graphite hybrid composites (TiGr) are a potentially enabling technology which satisfies the low structural weight fraction and long operational lifetime required for the High Speed Civil Transport. TiGr composites are made of thermoplastic polymer matrix composite (PMC) plies with titanium foils as the outer plies. The two materials are assembled by bonding the polymer matrix composite plies and titanium foils to form a hybrid composite laminate. Both experimental and analytical work has been performed to characterize major hole quality parameters and cutting mechanisms encountered in drilling of TiGr composites. The effects of consolidation processing, such as induction heating press and autoclave processe, on drilling characteristics of TiGr composites were examined. The hole quality parameters and hole exit damage was investigated and discussed.