Non-Conventional Deformations: Materials and Actuation.

This paper reviews materials and structures displaying non-conventional deformations as a response to different actuations (e.g., electricity, heat and mechanical loading). Due to the various kinds of actuation and targeted irregular deformation modes, the approaches in the literature show great diversity. Methods are systematized and tabulated based on the nature of actuation. Electrically and mechanically actuated shape changing concepts are discussed individually for their significance, while systems actuated by heat, pressure, light and chemicals are condensed in a shared section presenting examples and main research trends. Besides scientific research results, this paper features examples of real-world applicability of shape changing materials, highlighting their industrial value.

The Effect of Multilevel Carbon Reinforcements on the Fire Performance, Conductivity, and Mechanical Properties of Epoxy Composites.

We studied the effect of a multilevel presence of carbon-based reinforcements-a combination of conventional load-bearing unidirectional carbon fiber (CF) with multiwalled carbon nanotubes (CNT) and conductive CNT-containing nonwoven carbon nanofabric (CNF(CNT))-on the fire performance, thermal conductivity, and mechanical properties of reference and flame-retarded epoxy resin (EP) composites. The inclusion of carbon fibers and flame retardant reduced the peak heat release rate (pHRR) of the epoxy resins. The extent to which the nanoreinforcements reduced the pHRR depended on their influence on thermal conductivity. Specifically, high thermal conductivity is advantageous at the early stages of degradation, but after ignition it may lead to more intensive degradation and a higher pHRR; especially in the reference samples without flame retardant. The lowest pHRR (130 kW/m²) and self-extinguishing V-0 UL-94 rating was achieved in the flame-retarded composite containing all three levels of carbon reinforcement (EP + CNF(CNT) + CNT + CF FR). The plasticizing effect of the liquid flame retardant impaired both the tensile and flexural properties; however, it significantly enhanced the impact resistance of the epoxy resin and its composites.

Toughening of Epoxy Resin: The Effect of Water Jet Milling on Worn Tire Rubber Particles.

In this work a cycloaliphatic amine-cured epoxy (EP) resin was modified by micron-scale rubber particles (RP). Nominal RP, in sizes of 200 and 600 µm respectively, were produced using worn truck tires and ultra-high-pressure water jet cutting. The RP were dispersed into the EP resin using different mixing techniques (mechanical, magnetic, and ultrasonic stirring) prior to the introduction of the amine hardener. The dispersion of the RP was studied using optical light microscopy. A longer mixing time reduced the mean size of the particles in the EP compounds. Static (tensile and flexural), dynamic (unnotched Charpy impact), and fracture mechanical (fracture toughness and strain-energy release rate) properties were determined. The incorporation of the RP decreased the stiffness and strength values of the modified EPs. In contrast, the irregular and rough surface of the RP resulted in improved toughness. The fracture toughness and strain-energy release rate were enhanced up to 18% owing to the incorporation of 1% by weight (wt%) RP. This was traced to the effects of crack pinning and crack deflection. Considerably higher improvement (i.e., up to 130%) was found for the unnotched Charpy impact energy. This was attributed to multiple cracking associated with RP-bridging prior to final fracture.

Self-Sensing Polymer Composite: White-Light-Illuminated Reinforcing Fibreglass Bundle for Deformation Monitoring.

The goal of our research was to develop a continuous glass fibre-reinforced epoxy matrix self-sensing composite. A fibre bundle arbitrarily chosen from the reinforcing glass fabric in the composite was prepared to guide white light. The power of the light transmitted by the fibres changes as a result of tensile loading. In our research, we show that a selected fibre bundle even without any special preparation can be used as a sensor to detect deformation even before the composite structure is damaged (before fibre breaking).

Analysis of the Light Transmission Ability of Reinforcing Glass Fibers Used in Polymer Composites.

This goal of our research was to show that E-glass fiber bundles used for reinforcing composites can be enabled to transmit light in a common resin without any special preparation (without removing the sizing). The power of the transmitted light was measured and the attenuation coefficient, which characterizes the fiber bundle, was determined. Although the attenuation coefficient depends on temperature and the wavelength of the light, it is independent of the power of incident light, the quality of coupling, and the length of the specimen. The refractive index of commercially available transparent resins was measured and it was proved that a resin with a refractive index lower than that of the fiber can be used to make a composite whose fibers are capable of transmitting light. The effects of temperature, compression of the fibers, and the shape of fiber ends on the power of transmitted light were examined. The measurement of emitted light can provide information about the health of the fibers. This can be the basis of a simple health monitoring system in the case of general-purpose composite structures.

Biodegradable foam plastics based on castor oil.

In this work, a simple but effective approach was proposed for preparing biodegradable plastic foams with a high content of castor oil. First of all, castor oil reacted with maleic anhydride to produce maleated castor oil (MACO) without the aid of any catalyst. Then plastic foams were synthesized through free radical initiated copolymerization between MACO and diluent monomer styrene. With changes in MACO/St ratio and species of curing initiator, mechanical properties of MACO foams can be easily adjusted. In this way, biofoams with comparable compressive stress at 25% strain as commercial polyurethane (PU) foams were prepared, while the content of castor oil can be as high as 61 wt %. The soil burial tests further proved that the castor oil based foams kept the biodegradability of renewable resources despite the fact that some petrol-based components were introduced.

Biomechanical evaluation of press-fit femoral fixation technique in ACL reconstruction.

In this experimental study, the authors evaluated the biomechanical properties of the femoral press-fit graft fixation technique in ACL reconstruction. 20 fresh frozen distal femurs, patellae and patellar ligaments were used from 10 cadaver specimens. Three bone-patellar tendon grafts of 10 mm width were prepared from each sample; altogether 60 bone-patellar tendon grafts were prepared for the experiment. Three 9 mm wide tunnels were drilled in each distal femur at different angles (0, 15, 30, 45, and 60 degrees). This means that 60 tunnels were drilled into the 20 femurs, 12 at each angle. The trapezoid bone blocks were impacted into the holes. The primary stability and stiffness of this press-fit fixation method were measured with a Zwick 020 computer-controlled testing device using maximum-failure tensile-strength tests. The ultimate tensile strength was the greatest at 45 degrees (534+/-20 N, range 507-554), with 118+/-10 N/mm (range 99-126) stiffness, followed by 485+/-35 N (range 416-510) with 122+/-13 N/mm (range 104-136) stiffness at 30 degrees, 353+/-18 N (range 320-371) with 113+/-13 N/mm (range 83-124) stiffness at 15 degrees, and 312+/-30 N (range 261-343) with 89+/-14 N/mm (ranged:68-103) stiffness at 0 degrees. In the cases of 0, 15, 30 and 45 degrees the bone blocks were pulled out of the drilled holes, but at 60 degrees rupture of the patellar tendon or breakage of the bone block occurred more frequently. It can be seen that the ultimate tensile strength increased with the angle between the loading direction and the bone block. When compared to data in the literature, these data showed similar and satisfying biomechanical properties of femoral press-fit fixation. Because of the known advantages of an implantation-free fixation technique, the femoral press-fit fixation technique can be a good alternative in ACL surgery. These results provide the basis for future studies involving the postoperative healing process of this femoral press-fit fixation technique in porcine knees.