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Structural health monitoring (SHM) is a technology aimed to monitor the soundness of the structures. Applications for aircraft structures are largely investigated. The goal is to utilize the information acquired during the monitoring to save maintenance costs, improve flight safety, and design lighter structures. Different issues, like load monitoring and impact detection, are investigated by SHM research. The most largely investigated issue is damage detection, i.e., developing a system that utilizes sensors to detect the damage in the structure. Damage detection can be performed with two sensors: dynamic and static. Dynamic sensors work by transmission of waves through the structures. Defects are identified by deviation and reflection of the waves by damages. The SHM approach described in this work is based on static sensors, like strain gages or fiber optics. The strain fields under load in pristine and damaged conditions are compared; the evaluation of the change in the strain field identifies damages. Two different algorithms for damage detection have been developed and patented in Leonardo Aircraft and are described in this work; they are based on the reverse finite element model (FEM) and neural network. The issues related to the strain field measurement are also briefly described. [ABSTRACT FROM AUTHOR]

A numerical procedure to simulate the curing process of polymer‐based composites is proposed. This model is applied to a carbon‐epoxy composite at a micromechanical level to predict residual stress at the end of the process and the evolution of the most important process parameters. A finite element model is written in the Ansys APDL environment and comprises two moduli that must be solved consecutively: the thermal–kinetical and structural modules. At each timestep, first thermal/kinetics problem is solved, then the temperature and degree of conversion profile results are used to calculate the viscoelastic properties, allowing the calculation of residual stress. [ABSTRACT FROM AUTHOR]

This article proposes a numerical routine to predict the residual stresses developing in an epoxy component during its curing. The scaling of viscoelastic properties with the temperature and the degree of conversion is modeled, adopting a mathematical formulation that considers the concurrent effects of curing and structural relaxation on the epoxy's viscoelastic relaxation time. The procedure comprises two moduli: at first, the thermal–kinetical problem is solved using the thermal module of Ansys and a homemade routine written in APDL, then the results in terms of temperature and the degree of conversion profiles are used to evaluate the viscoelastic functions, and the structural problem is solved in the mechanical module of Ansys, allowing the residual stresses calculation. The results show that the residual stresses mainly arise during cooling and scale with the logarithm of the Biot number. [ABSTRACT FROM AUTHOR]

This paper analyzes the effect of crosslinking reactions on a thermoset polymer's viscoelastic properties. In particular, a numerical model to predict the evolution of epoxy's mechanical properties during the curing process is proposed and implemented in an Ansys APDL environment. A linear viscoelastic behavior is assumed, and the scaling of viscoelastic properties in terms of the temperature and degree of conversion is modeled using a modified version of the TNM (Tool–Narayanaswamy–Mohynian) model. The effects of the degree of conversion and structural relaxation on epoxy's relaxation times are simultaneously examined for the first time. This formulation is based on the thermo-rheological and chemo-rheological simplicities hypothesis and can predict the evolution of epoxy's relaxation phenomena. The thermal–kinetic reactions of curing are implemented in a homemade routine written in APDL language, and the structural module of Ansys is used to predict the polymer's creep and stress relaxation curves at different temperatures and degrees of conversion. [ABSTRACT FROM AUTHOR]

Graphene hybrid-filler polymer composites have emerged as prominent materials that revolutionize heavy industries. This review paper encapsulates an in-depth analysis of different influential factors, such as filler/graphene type, aspect ratios, dispersion methods, filler-matrix compatibility, fiber orientation, synergistic effects, different processing techniques, and post-curing conditions, which affect the processing and properties of graphene hybrid polymer composites, as well as their resultant applications. Additionally, it discusses the substantial role of graphene reinforcement with other fillers, such as carbon nanotubes, silica, nano-clays, and metal oxides, to produce functionalized hybrid polymer composites with synergistically enhanced tailored properties, offering solutions for heavy industries, including aerospace, automotive, electronics, and energy harvesting. This review concludes with some suggestions and an outlook on the future of these composite materials by emphasizing the need for continued research to fully optimize their potential. [ABSTRACT FROM AUTHOR]

The intermolecular forces are of great importance to scientists in a wide field of disciplines as the progress of interactions between molecules determines the bulk properties of substances. It is a matter of fact that the approximation of thermodynamic and transport properties of polymers requires a realistic intermolecular potential associated with the topological constraints of the matter, namely the specific one‐to‐one secondary interactions between molecular groups. The out‐of‐equilibrium volume relaxation in glassy polymers remains confined to the phenomenological observation of bulk properties. The Lennard‐Jones (LJ)‐type potentials and the Tait equation are compared in this communication. It is shown that the subtle relaxation responses observed in glassy polymers can be suitably described using both the local (LJ) interactions and the phenomenological Tait equation for bulk behavior. The approach is based on the oversimplified assumption that the volume relaxation phenomena are the isotropic manifestation of random relaxations of local directional interactions of secondary bonds. The results appear surprisingly appealing, given the straightforward approach. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has significant potential to create sustainable, lightweight, multifunctional material systems in a single step. Fused filament fabrication (FFF) is the most commonly used AM technology, which involves the deposition of thermoplastic polymer filament layers. Phase inversion is one method that can be used to produce filaments for FFF. In this process, a polymer solution is prepared and then extruded into a coagulation bath. By applying a unidirectional casting direction to the composite solution, the orientation of the reinforcements can be optimized to achieve superior mechanical performance. The objective of this study is to demonstrate the potential of the phase inversion technique, combined with the controlled alignment of reinforcements within a polymeric matrix, to improve the mechanical properties of the resulting composite films. The results may prove promising for the development of unidirectional reinforcing filaments commonly used in FFF processes. [ABSTRACT FROM AUTHOR]

This study compares thermal conductivity results of vertically orientated carbon fiber and graphene, polydimethylsiloxane (V‐CFG/PDMS) composites with randomly orientated R‐CFG/PDMS composites and pure PDMS to highlight the impact of aligned structure on thermal conductive properties. The results reveal that, at 25 wt.% filler loading R‐CFG/PDMS composites exhibit a thermal conductivity of 2.68 W m−1 K−1, while V‐CFG/PDMS achieves maximum thermal conductivity of 4.02 W m−1 K−1. This excellent performance of V‐CF/G PDMS can be attributed to the synergistic effects arising from the combination of carbon fiber and graphene. [ABSTRACT FROM AUTHOR]

This study investigates the hydrothermal synthesis of (Co, Zr) co‐doped iron oxide nanoparticles, varying the synthesis for 4 and 6 h at 150 °C. X‐ray diffraction (XRD) analysis discloses crystalline sizes from 16 to 24 nm. Magnetic characterization through vibrating sample magnetometer (VSM) indicates ferromagnetic behavior, as shown by magnetic hysteresis (MH) loops, with a maximal magnetic saturation of approximately 40 emu g−1 achieved in samples subjected to a 6‐h reaction time. This highlights the critical influence of the 6‐h duration in optimizing the magnetic properties of the synthesized nanoparticles. [ABSTRACT FROM AUTHOR]

Wood ash is the powdery residue remaining after wood combustion. Today, only some of the wood ashes are recycled, while most are disposed of in landfills. Increasing recycled wood ash can limit environmental damage and save transportation costs and waste disposal. This paper presents including 10% of wood ashes as a filler material for geopolymers. The ashes, coming from a local Italian restaurant, are sieved between 65 and 79 µm and are incorporated into a metakaolin‐based geopolymer matrix, cured at room temperature (25 °C). Ionic conductivity, pH, and Infrared Spectroscopy analysis, conducted after 7, 14, 28, and 56 days of curing time, reveal the occurrence of the geopolymerization process. Furthermore, the mechanical strength results allow the comparison of these materials with Portland cement, one of the most common polluting competitors. [ABSTRACT FROM AUTHOR]

Poly(meta-phenylene isophtalamide) (PMIA) was processed via electrospinning to provide nanofibrous membranes with randomly and aligned fibers. Mechanical performance of such membranes was evaluated, applying a normalization procedure that takes into account the peculiar morphology of such complex substrate where voids can sum up to almost 80% of the sample volume. Random and aligned fibers membranes are applied onto wood panels to test their fire resistance in cone calorimetry when coated in polyaramidic thin nanofiber mats. Tests highlighted that random fibers provide a better fire protection, increasing Time to Ignition and decreasing the Fire Performance Index. Another important parameter affecting the performance is the adhesive system used to apply the nanofibers onto wood that is able to significantly modify the fire performance of the polyaramidic-coated wood panels., INTRODUCTION Wood is an obvious green and sustainable material: it comes from renewable resources, is biodegradable and in the last years, the environmental concerns and the interesting properties possessed by [...]

This paper presents a study of the electrical and mechanical properties of polystyrene (PS)/carbon nanotube (CNT) composites prepared using the doctor blade technique. The nanocomposite films of PS/CNT were prepared by casting a composite solution of PS/CNT in tetrahydrofuran (THF) on a glass substrate using a doctor blade and drying in an oven. The nanocomposite films were then characterized using a tensile test and the four-point probe method to evaluate their mechanical properties and electrical conductivity. The experimental results were used to analyze the unpredicted behavior of the nanocomposite films. The experimental results showed that the electrical conductivity of the nanocomposite films became almost insensitive or unmeasurable with increasing CNT content for very dilute PS–THF solutions. In contrast, at higher PS concentrations, film conductivity increased to a given CNT threshold and then decreased. Based on PS–THF viscosity–concentration data, a discussion is elaborated that partially justifies the experimental results. [ABSTRACT FROM AUTHOR]

This paper discusses the theoretical and experimental correlations between fatigue and static strength statistical distributions. We use a two-parameter residual strength model that obeys the qualitative strength-life equal rank assumption (SLERA) for guidance. The modeling approach consists of recovering the model's parameters by best fitting the constant amplitude (CA) fatigue data at a given stress ratio, R, and the experimental Weibull parameters of the static strength distribution function. An extensive set of fatigue life and residual strength data for AS4 carbon/epoxy 3k/E7K8 Plain Weave Fabric with [45/−45/90/45/−45/45/−45/0/45/−45]S layups, obtained at different stress ratios, R, have been analyzed. The modeling approach consists of recovering the model's parameters from pure tension or compression fatigue data at R = 0.1 and R = 5, respectively. Once the parameters are fixed, the model's capabilities, potential, and limits are discussed by comparing its predictions with residual strength and fatigue life data obtained at stress ratios with mixed tension/compression loadings, namely R = −0,2 and R = −1. Moreover, from a preliminary analysis, the theoretical extension of the model's capabilities to variable amplitude loadings is conceptualized. The application of Miner's rule is also discussed and compared with a new damage rule to analyze the fatigue responses under variable amplitude loadings. [ABSTRACT FROM AUTHOR]