Mechanics of Composite, Hybrid & Multi-functional Materials, Volume 5

The interlaminar fracture of carbon fiber reinforced composites is a leading cause of failure while in service. In an effort to overcome this weakness, carbon nanotubes were embedded into HexPly^® IM7/8552 Prepreg in an attempt to increase the interlaminar strength. The present work experimentally analyzed the mechanical properties of the composite materials with and without carbon nanotubes. A systematic curing process was designed to fabricate composite laminates in either an 8-ply quasi-isotropic or 12-ply unidirectional configurations. Property variations at 0°, 30°, 45°, 60°, and 90° were investigated using the unidirectional laminates. Samples were subjected to supersonic impact and 4-point bending tests. Scanning electron microscopy was used to analyze the postmortem specimens. The 4-point bending tests were analyzed using digital image correlation to measure displacement, strain fields, and calculate flexural strength.

In this research, recycled natural rubber (NR) based composites reinforced with the doped nano boron nitride (NBN) with the high resolution in thermal conductive and electrical-insulating field were designed, and their properties were studied. Good distribution of doped NBN in the matrix has shown substantial increments of thermal conductivity and high electrical insulation depending on the quantity in the matrix. Additionally, the thermal analysis indicates that NR/NBN composites have excellent heat-transfer capacity during heating and cooling processes, which suggests great potential application in thermal conductive and electrical insulating fields. The procedure can find multiscale particle-matching ways to achieve the maximum effective thermal conductivity under a given filler load. It should be emphasized that the optimized effective thermal conductivity obviously can be improved with the increase in the volume fraction of the reinforcement.

In this research, recycled rubber-based composites are considered with glass bubble (GB) and fine gamma alumina fiber (γ-Al₂O₃) reinforcements. The effect of the reinforcements with matrix, fracture characteristics of the composite are studied by impact-loading tests (i.e., drop-weight tests). These test results are simulated by finite element analysis (FEM) and the results are compared with the experimental results. Microstructural and fracture surface analysis are carried out by means of scanning electron microscopy (SEM). Mechanical test results show that the reinforcement with glass bubbles and aluminum oxide ceramic fibers generally increase the damping capacity and fracture toughness of the composites.

In this study, the microstructural formation and static/dynamic compression behaviour of recycled Ni-Al-Cu matrix hybrid composites reinforced with silicon whiskers and alumina (Al₂O₃) fibres will be studied. It is intended to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites generally are produced using by combined “sintering + forging” processes. The static and dynamic properties will be evaluated in detail, considering the relevant scanning electron microscopy (SEM) microstructures (including the distribution of reinforcement elements).

Titanium-based composites have potential applications in the aeronautical industry as multifunctional materials and/or magnetic shape memory composites (MSMCs). In this work, gas-atomized recycled pure iron (1–5 μ) and fine magnetic iron oxide (<1 μ-Fe₃O₄) were used as reinforcements for pure titanium (VWR) Two types of composites were fabricated by using a powder metallurgy-combined method: sintering + forging. Two types of processes were carried out at two different sintering temperatures (600 °C and 850 °C). As known, the Ti-Fe eutectic temperature is ~750 °C. Increasing of the pure iron to 45 wt% gives rise to the formation of Ti-Fe intermetallic in the composites. As a result, mechanical properties of the sintered forging composites were considerably improved. Electrical and thermal behaviour and magnetic permeability were measured. The microstructure analyses and the diffusion mechanism at the Ti-Fe interface are also investigated by using scanning electron microscopy (SEM).

In this study, the microstructural formation and static/dynamic compression behaviour of the recycled Ti-Al-Cu matrix hybrid composites reinforced with silicon whiskers and alumina (Al₂O₃) fibres are examined. It is intended to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites are generally produced using combined sintering + forging processes. The static and dynamic properties are evaluated in detail, taking into account the relevant scanning electron microscopy (SEM) microstructures, including the distribution of reinforcement elements.

In this study, the microstructural formation and static/dynamic compression behaviour of the recycled Ni-Al/Nb₂Al/ZrO₂ matrix-hybrid composites reinforced with Nb and ZrO₂ will be studied. It is intended to be an alternative to traditional alloys/composites used in the aeronautical industry. These composites are generally produced by using combined sintering + forging processes. The static and dynamic properties will be evaluated in detail, considering the relevant scanning electron microscopy (SEM) microstructures, including the distribution of reinforcement elements.

The development and description of a test fixture designed to restrict out-of-plane motion in the center region of tension-loaded carbon-epoxy panels are presented herein. The test fixture was used to impose displacement conditions consistent with those in an analytical tool being developed to predict panel behavior in the vicinity of a central notch, which included the assumption that there would be no out-of-plane displacement and no buckling. However, pretest analysis using finite element models for a panel loaded without any out-of-plane restraint in the region of the notch indicated that with an imperfection magnitude equal to 20% of the thickness of the thin-skin panel, an unacceptable amount of out-of-plane deformation would occur as Poisson effects induced compression loads in the region of the notch. Therefore, to validate this tool in a test program, a restraint fixture which would suppress out-of-plane motion was required. The panel could not be encased in restraining plates because instrumentation and visibility were required in the vicinity of the notch. Therefore, a fixture that would restrict out-of-plane motion while still allowing access to the surface of the panel at the notch edges for instrumentation and line-of-sight access for cameras was required. To satisfy these requirements, a fixture was designed to restrict only out-of-plane motion near the center of the notch. Two 1.78-m-long test panels were loaded in tension to failure using this fixture. Out-of-plane deformations were not directly measured during testing, so back-to-back strain gages were used to obtain an indication of buckling. Strain results indicated that the restraint fixture performed as designed and buckling did not occur.

Bacteria can proliferate orthopedic implants, resulting in infection rates as high as 5%. A consistent problem across implantology is the development of surfaces which successfully promote the adhesion and propagation of healthy fibroblast and osteoblast cells while deterring formation of bacterial biofilms. Selecting surface configurations which favor cell adhesion will lead to decreased infection rates. Progress in identifying appropriate surface configurations is hindered by the lack of quantitative adhesion techniques capable of comparing adhesion of cells and biofilms directly. Recent advancements in adhesion techniques have allowed for quantitatively measured adhesion strengths of both bacterial biofilms and cell monolayers using the laser spallation technique. The quantified stress-based adhesion values allow surface and environmental factors that modulate both bacterial and cell adhesion to implant surfaces to be evaluated. During implantation, blood propagates wound sites completely coating implant surfaces. Quantitatively determining the impact of preconditioning layers that accumulate on the implant surface on cell adhesion is vital to predict implant behavior. Previous work has demonstrated that these preconditioning layers either negatively or neutrally impact bacterial adhesion to titanium implant surfaces. This study focuses on the impact that blood plasma and fibronectin coatings have on the adhesion of osteoblastic (MG 63) cells and fibroblasts to the same titanium surfaces. Adhesion results indicate that preconditioning layers and increased surface roughness positively impact cell adhesion. Incorporating the increased adhesion values for cell adhesion into the Adhesion Index demonstrates that increased surface roughness, coupled with natural wound healing preconditioning of surfaces, yields positive biocompatibility.

Unmanned aerial vehicles (UAVs) are used in many industries thanks to their beneficial characteristics and propellers are one of the most important components of UAVs. Propellers transform rotary motion into linear thrust and they generally provide lift and thrust to the UAV by spinning and creating an airflow, which results in a pressure difference between the top and bottom surfaces of the propeller. During the life cycle of the propellers, they may receive impact loadings as a result of hard landings or bird strikes. Therefore, impact damage can occur in UAV propellers. Due to that reason, the impact resistance of the propellers must be improved. In this study, a composite material is designed to be used in the manufacture of UAV propellers. Polyamide 6 (PA6) is selected as the matrix material thanks to its superior abrasion resistance, outstanding dimensional stability, and high specific tensile strength. In order to improve the impact resistance of the PA6, olefin block copolymer (OBC) and carbon-based reinforcement including carbon nanotube (CNT) are planned to be used. Following the development of the composite formulation, composites are going to be manufactured and tensile tests, Charpy impact, and hardness tests were carried out to determine fundamental mechanical properties. Finally, optical microscopy was used to examine the CNT distribution in the manufactured composites.

Graphene nanoplatelets (GNPs) are widely used as conductive fillers for various polymer nanocomposites. However, the actual performance of these materials is much lower than theoretical predictions due to the natural tendency of GNPs to agglomerate. Contemporary techniques for random dispersion do not offer modulation of the orientation of graphene and thereby limit its capabilities, promoting the usage of higher concentrations that can lead to undesirable effects. Electric field alignment is a promising way to obtain significantly improved directional properties with low concentrations of GNPs. This paper presents the use of real-time AC conductivity measurements to characterize the unidirectional alignment process of GNPs in a thermoset epoxy polymer. Theoretical modeling of the effects of alternating electric field on a single transversely isotropic GNP reveals the key parameters that influence the alignment process, namely, the size of the platelet, viscosity of the epoxy, and the content of GNPs. Considering these parameters, an experimental setup is devised to create an alternating electric field in an aluminum mold separated by epoxy/GNP mixture. Time required for alignment is calculated based on the chain formation and rotation time obtained from the above parameters. Preliminary research shows a two- to threefold increase in electrical conductivity in aligned direction compared to randomly dispersed epoxy/GNP samples. The effects of alignment also reveal an increase in the mechanical strength, resulting in a (10–15%) increase in Young’s modulus in the aligned direction. These significant property improvements also decrease the percolation threshold of randomly dispersed epoxy/GNP sample from 1 to 0.5 wt%. Dielectric spectroscopy of randomly oriented and aligned samples shows a 100% increase in dielectric constant at a frequency of 1000 Hz in the aligned direction.

Structural supercapacitors represent a promising technology that will help in mitigating range anxiety while providing structural integrity to electric vehicles. In most structural supercapacitors, poly (ethylene glycol) (PEG), the ionic component of structural supercapacitor, is responsible for providing percolating channels for ion transfer. The formation of a percolating network of PEG inside epoxy resin is the result of cure-reaction-induced phase separation (CRIPS) that occurs at curing temperature due to spinodal decomposition. Various nanofillers have been explored (organoclay, TiO₂ nanoparticles, and LLZO) that enhance the ionic conductivity while improving the elastic modulus. Out of these, graphene oxide is a promising nanofiller that has high ionic conductivity due to the presence of functional groups on its basal plane and also provides excellent mechanical properties. Hence, it is instructive to understand the effect of graphene oxide on the size of percolating channels, since these will directly affect the overall performance of the structural supercapacitor. This study explores the effect of change in the weight percentage of graphene oxide on phase separation. To this end, graphene oxide content is varied from 0 to 0.7 weight percentage with respect to PEG to study the magnitude of phase separation between PEG and epoxy. Scanning electron microscopy (SEM) images show promising results suggesting a decrease in pore diameter as amount of graphene oxide is increased, which will enhance the mechanical and electrical properties. By varying the amounts of graphene oxide, we are able to achieve an electrolyte that provides optimal multi-functional performance. A detailed study on the effect of graphene oxide in percolating PEG network in tailoring of mechanical and ionic conductivity properties will be carried out in the near future. These results will be presented and discussed.