Epoxy-layered silicates nanocomposites based on diglycidyl ether of bisphenol A and an anhydride-curing agent have been successfully synthesised. A manufacturing process using hand lay-up, vacuum ...bagging, and hot pressing techniques was developed to produce glass fibre-reinforced laminates with this nanocomposite matrix. Transmission electron microscopy indicated that silicate layers dispersed in the epoxy matrix present a long-range order with an interlamellar spacing of about 9
nm. X-ray diffraction analysis confirmed this nanostructure both in the nanocomposites and in the fibre-reinforced composite based on the same matrix. Scanning electron micrographs of the laminate with a nanocomposite matrix showed that nanolayers are apparently sticking at the surface of the glass fibre, improving possibly in this manner the interfacial properties of the fibres. Flexural testing of the laminates showed that the nanolayers improve the modulus and the strength, respectively, by 6% and 27%. Dynamic mechanical analyses of the epoxy and nanocomposite plates and their corresponding laminates showed a systematic glass transition temperature decrease of the nanocomposite based materials. This explains probably the larger water uptake observed at 50
°C in the plate and the laminate based on a nanocomposite matrix as compared with those based on the pristine epoxy.
High-velocity (up to 25m/s) impact tests were performed on pig kidneys to characterize failure behavior at deformation rates associated with traumatic injury. Cylindrical tissue samples (n=45) and ...whole perfused organs (n=34) were impacted using both falling weights and a high-velocity pneumatic projectile impactor. Impact energy was incrementally increased until visible rupture occurred. The strain energy density failure threshold fell between 25 and 60kJ/m3 for excised porcine tissue samples, and between 15 and 30kJ/m3 for whole, perfused organs. The relationship between localized failure in whole organ impacts and tissue level failure thresholds observed in cylindrical tissue samples was explored using a detailed finite element model of the human kidney. The model showed good correlation between experimentally observed injury patterns and predicted strain energy density distributions within the renal parenchyma. Finally, to facilitate interpretation of the porcine renal impact results with regard to human trauma, quasi-static compression test results of freshly excised human kidney cortex samples (n=30) were compared against similar tests on pig kidneys. Human tissues failed at Lagrange strain levels similar to porcine tissue (63±6.3%), but at 52% lower Lagrange stress (116±28kPa), and 35% lower strain energy density (17.1±4.4kJ/m3). Thus conservative interpretation of porcine test results is recommended.
An existing model for interlaminar normal stress distribution in singly curved and moderately thick laminates neglects to model the influence of interlaminar shear. This work completes the previous ...model and validates improvement of accuracy. The new model and a FEM model based upon solid finite elements are used to predict the critical delamination loads observed in experiments which are also described.
Dispersion of nano-sized, silicate-based filler in epoxy resin is expected to yield improved materials properties in several areas. Various mechanical properties, specifically improved fracture ...toughness, as well as improved flame-retardant effects are of interest. The final objective of the research is investigating whether a nano-modified epoxy matrix yields improved delamination resistance in a fiber-reinforced laminate compared to a laminate with neat epoxy as matrix material. As a first step towards this goal, the fracture toughness of nano-modified epoxy resin is compared with that of the neat resin. Fracture toughness improvement up to about 50% and energy release rates increased by about 20% are observed for addition of 10
wt.% of organosilicate clay.
Active fibre composite elements (AFCs) based on piezoelectric fibres are used as acoustic emission (AE) sensors on composites (unidirectional glass-fibre and carbon-fibre reinforced epoxy) and ...polymer (polymethyl-methacrylate, PMMA) plates. AFCs are mounted reversibly or permanently bounded to the plates. Their performances are compared with that of commercial AE sensors. The sensitivity of both sensors is characterised using signal attenuation curves and polar diagrams. The data indicate a large anisotropy behaviour of the AFCs in comparison with conventional AE sensors, leading to higher sensitivity of AFCs along the direction of the piezoelectric fibres. The emission of simulated AE by AFCs and AE sensors is also studied. Transient electric impulses applied to the AFC yield short vibrations transmitted to the testing object, that can be sensed by other AFCs or AE sensors. Permanently bonded AFCs show promising sensing and emitting properties for possible acousto-ultrasonic applications in composite laminates.
Active fiber composite (AFC) composed of lead zirconate titanate (PZT) fibers with interdigitated electrodes (IDEs) has been integrated into orthotropic glass fiber reinforced plastic (GFRP) ...laminates to characterize the performance of AFC as a smart material component in laminated materials. Monotonic cyclic tensile loading was performed on integrated specimens at different strain levels. The AFC output was monitored to determine the effect of applied strain level on the AFC performance. It was found that the AFC sensitivity degraded beyond strains of 0.20% and approached a minimum at 0.50% strain. The degradation in the AFC performance appears to be attributed to the dominating effect of PZT fiber fragmentation during testing, as opposed to depolarization. Acoustic emission (AE) monitoring was used to detect damage in laminates during testing and was correlated with crack evidence from microscopy observations during testing to characterize damage evolution in response to strain levels.
The paper presents a new model for interlaminar normal stress distribution in moderately thick and singly curved laminates. It requires in-plane strain information which must also map the kinematical ...effects caused by the curved laminate shape. The number of free parameters of the exact solutions for each layer is reduced and determined by a finite-element procedure which is also explained. The results of the mechanical model are compared with FEM results for unidirectional and cross-ply laminates. The new model can be developed for element-level post processing in a FEM program with simple finite structural elements.
Active fiber composites (AFC) composed of lead zirconate titanate (PZT) fibers embedded in an epoxy matrix and sandwiched between two interdigitated electrodes provide a thin and flexible smart ...material device which can act as a sensor or actuator. The thin profiles of AFC make them ideal for integration in glass or carbon fiber composite laminates. However, due to the low tensile limit of the PZT fibers, AFC can fail at strains below the tensile limit of many composites. This makes their use as a component in an active laminate design somewhat undesirable. In the current work, tensile testing of smart laminates composed of AFC integrated in glass fiber laminates was conducted to assess the effectiveness of different packaging strategies for improving AFC sensor performance at high strains relative to the tensile limit of the AFC. AFC were encased in carbon fiber, silicon, and pre-stressed carbon fiber to improve the tensile limit of the AFC when integrated in glass fiber laminates. By laminating AFC with pre-stressed carbon fiber, the tensile limit and strain sensor ability of the AFC were significantly improved. Acoustic emission monitoring was used and the results show that PZT fiber breakage was reduced due to the pre-stressed packaging process.
Nano-sized, functionalized organo-silicate fillers dispersed in the epoxy matrix are one approach that is investigated for improving the delamination resistance of fiber-reinforced composites. The ...variety of nano-silicate fillers available on the market, of processing conditions and the related characterization effort make it desirable to have a simple, easily analyzed screening method for both, nano-modified resins and laminates. An impact test using hail simulation equipment and visual assessment on glass-fiber laminates with nano-modified epoxy matrix yields rough indications of the effect of nano-modification on the fracture behavior of the specimens that correlate with more sophisticated macroscopic and microscopic characterization.
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