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High performance composites for structural applications in aviation are sensitive to aging from altering environmental conditions. For instance, the stiffening behavior of glass fiber/polyester composites used by the wind turbine industry has already been demonstrated in previous work of the authors. Now, passenger aircrafts from such composites are increasingly entering into service. It is crucial, thus, to study the exposure of high performance materials to aging-inducing environmental conditions such as varying temperature, humidity, ultraviolet radiation, and assess their impact on mechanical response of such composites. In this work we have applied acoustic emission analysis to study the effects of simulated environmental aging on carbon fiber reinforced composites. Signals collected from three point bending testing of pristine specimens as well from thermally shocked and environmentally aged ones. Signal parameters were afterwards plotted and studied in correlation with the specimens’ mechanical response.

The purpose of this study was to manufacture hybrid composites from fabrics with superior ballistic performance, and to analyze their viscoelastic and mechanical response. Therefore, composites in hybrid lay-up modes were manufactured from Vectran, Kevlar and aluminum fiber-woven fabrics through a vacuum assisted resin transfer molding. The specimens were consequently analyzed using static three-point bending, as well as by dynamic mechanical analysis (DMA). Apart from DMA, time–temperature superposition (TTS) analysis was performed by all available models. It was possible to study the intrinsic viscoelastic behavior of hybrid ballistic laminates, with TTS analysis gained from creep testing. A polynomic mathematical function was proposed to provide a high accuracy for TTS curves, when shifting out of the linearity regimes is required. The usual Williams–Landel–Ferry and Arrhenius models proved not useful in order to describe and model the shift factors of the acquired curves. In terms of static results, the highly nonlinear stress–strain curve of both composites was obvious, whereas the differential mechanism of failure in relation to stress absorption, at each stage of deformation, was studied. SEM fractography revealed that hybrid specimens with Kevlar plies are prone to tensile side failure, whereas the hybrid specimens with Vectran plies exhibited high performance on the tensile side of the specimens in three-point bending, leading to compressive failure owing to the high stress retained at higher strains after the maximum bending strength was reached.

In this work, nanocomposites, based on linear low‐density polyethylene (mLLDPE), produced by metallocene catalyst, were prepared and experimentally investigated by means of thermomechanical-electrical properties and Raman spectroscopy. In particular, scanning electron microscopy (SEM), broadband dielectric spectroscopy (BDS), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile and creep testing have been carried out. Several types of carbonaceous nanomaterials, including carbon nanotubes (CNTs), carbon nanofibers (CNFs) and graphene nano-fillers (GO), which have attracted significant attention for a variety of applications, were employed for the preparation of hybrid and non-hybrid nanocomposites at various loadings. It was found that the simultaneous incorporation of two different nanofiller types into a polymeric matrix, revealed better thermomechanical performance, while in particular the combination of CNTs and GO exhibited a synergistic effect between the nanofillers, supported also by BDS and Raman results. Therefore, the results of the present study offer a new perspective for the potential of mLLDPE/hybrid nanocomposites in targeted applications.

NAVMAT Research project attempts an interdisciplinary approach by integrating Materials Engineering and Informatics under a platform of Knowledge Management. Failure analysis expands into forensics engineering for it aims not only to identify individual and symptomatic reasons of failure but to assess and understand repetitive failure patterns, which could be related to underlying material faults, design mistakes or maintenance omissions. NAVMAT approach utilizes a focused common-cause failure methodology for the naval and marine environment, to begin with. It will eventually support decision making through appropriate Artificial Intelligence and Natural Language Processing methods. The presented work describes the design of a knowledge based system dedicated to effective recording, efficient indexing, easy and accurate retrieval of information, history of maintenance and secure operation concerning failure incidents of marine materials, components and systems in a fleet organisation. Based on materials failure ontology, utilising artificial intelligence algorithms and modern approaches in data handling, NAVMAT aims at the optimisation of naval materials failure management and the support of decision making in Maintenance and Repair Operations (MRO), materials supplies and staff training.

The experimental design of a versatile interrogation-free magnetoelastic resonator suitable for detecting local accumulation of substances/agents potentially harmful to their environment, is presented. The concept uses a thin flexible polycarbonate slab with a Metglas® 2826MB magnetoelastic ribbon attached on its surface, and implements typical damage detection principles. The slab is fixed as a cantilever on one end, with a mobile talk-phone attached to the free end for providing vibration. Owing to the magnetoelastic principle, the vibrating ribbon creates variable magnetic flux, which induces voltage into a low-cost pick-up coil circuit placed in a contact-less manner above the slab. This voltage is recorded by a conventional oscilloscope. No extra interrogation coil or sophisticated hardware are necessary, thus enhancing versatility of the concept while minimizing its complexity and cost. Analysis of the vibration-dependent voltage signal provides specific slab eigenfrequencies, which depend upon (and characterize) its surface loading. The latter may result from environmental/biological/infectious agents or substances accumulating on the resonator’s (suitably coated) surface, which may cause damage/deterioration to fragile or valuable objects placed close to the resonator. Eigenfrequency shifting may, then, allow for detecting such factors and triggering alerts. Tests with small loads on the vibrating slab confirm its potential for surface load detection.

The space environment is extremely hostile to the spacecraft but also to the equipment it carries. The materials which are used to the external side of the spacecraft, the solar panels, the sensors, and the electronics circuits, suffer greatly from their exposure to it. Extreme temperatures, ultraviolet radiation, ionizing radiation from solar proton events and cosmic rays, atomic oxygen in LEO, as well as collisions with micrometeoroids and space debris are factors that degrade the stuff, multiply the mission cost, and increase the risk. Therefore, the state-of-art of material technology is needed. In this study, a set of materials and technologies are presented, which reduce the above-mentioned risks. Extreme temperatures, ultra-vacuum, atomic oxygen, and high-energy radiation including particles as well as energy sources (X- and gamma rays) are potential extreme exposure conditions. Testing and qualification of materials exposed to these extreme conditions is a difficult task, to enable the design and manufacturing of high-endurance reliable components to be used in the world’s most sophisticated satellite and spacecraft components, as well as in future endeavors into the vicinity of the Solar System.

The beginning of the 21st century provided many interesting features in engineering. To begin with, the technology of high performance fiber reinforced composite materials, especially carbon fiber reinforced thermosets, reached their peak in maturity..

This study initially deals with the investigation of the induced strains during hardening stage of a self-setting calcium phosphate bone cement using fiber-Bragg grating (FBG) optical sensors. A complementary Scanning Electron Microscopy (SEM) investigation was also conducted at different time intervals of the hardening period and its findings were related to the FBG recordings. From the obtained results, it is demonstrated that the FBG response is affected by the microstructural changes taking place when the bone cement is immersed into the hardening liquid media. Subsequently, the FBG sensor was used to monitor the absorption process and hygroscopic response of the hardened and dried biocement when exposed to a liquid/humid environment. From the FBG-based calculated hygric strains as a function of moisture concentration, the coefficient of moisture expansion (CME) of the examined bone cement was obtained, exhibiting two distinct linear regions.

Carpal tunnel syndrome (CTS) is a clinical disorder resulting from the compression of the median nerve. The available evidence regarding the association between computer use and CTS is controversial. There is some evidence that computer mouse or keyboard work, or both are associated with the development of CTS. Despite the availability of pressure measurements in the carpal tunnel during computer work (exposure to keyboard or mouse) there are no available data to support a direct effect of the increased intracarpal canal pressure on the median nerve. This study presents an attempt to simulate the direct effects of computer work on the whole carpal area section using finite element analysis. A finite element mesh was produced from computerized tomography scans of the carpal area, involving all tissues present in the carpal tunnel. Two loading scenarios were applied on these models based on biomechanical data measured during computer work. It was found that mouse work can produce large deformation fields on the median nerve region. Also, the high stressing effect of the carpal ligament was verified. Keyboard work produced considerable and heterogeneous elongations along the longitudinal axis of the median nerve. Our study provides evidence that increased intracarpal canal pressures caused by awkward wrist postures imposed during computer work were associated directly with deformation of the median nerve. Despite the limitations of the present study the findings could be considered as a contribution to the understanding of the development of CTS due to exposure to computer work.

Calcium phosphate bone cements have gained significant scientific and commercial attention due to their outstanding biological properties. In this work the cement's paste prepared by mixing a-TCP with sodium phosphate solution and the final hardening occurred after immersion in Ringer's solution. Their internal structure evolution from the hydrolysis of a-TCP to the formation of calcium deficient hydroxyapatite was observed my scanning electron microscopy. Time temperature superposition principle was applied in order to investigate their time- and temperature dependent dynamic response. It was found that time temperature superposition can be applied with success and that the material dynamic stiffness is time-and temperature dependent. Also, a nanostructure of hydroxyapatitic platelets and needles evolves within ten days, after specimen immersion for maturing in a Ringer’s solution. The resulting nanostructure was verified by means of scanning electron microscopy and x-ray diffraction techniques.

The addition of the low-cost mineral filler kaolin to high-density polyethylene (HDPE) creates a composite with both improved stiffness and toughness properties. This study focuses on two aspects of the toughness of these composites: the fracture toughness increment produced by work at the fracture surface and the directionality induced by the injection molding fabrication process. The Essential Work of Fracture (EWF) method gives results which show that a higher volume fraction of kaolin produces more surface work, consistent with earlier work using Compact Tension (CT) tests. The EWF method also demonstrates that a lower volume fraction can produce a higher overall plastic work and apparent toughness. A heat treatment which removes the orientation of the matrix but not that of the particles was applied to study the effect of matrix crystallinity. The results indicate that the matrix supramolecular structure (crystallinity and skin-core effect) is responsible for the directionality of toughness, and that a heat treatment can be used to produce high toughness behavior in both major directions.