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Composite structures containing lithium-ion polymer (LiPo) batteries are being developed for electrical energy storage in motor vehicles and other applications. This paper presents an experimental and numerical study into the effect of embedding (LiPo) batteries into carbon fibre laminates and sandwich panels on the vibration and acoustic properties. The vibration responses (modal frequencies, damping) were measured experimentally using Laser Doppler vibrometry and calculated numerically using finite element modal analysis. The results reveal that careful placement of LiPo batteries within composite structures is needed to control the vibration properties. Embedding batteries at the nodal points increases the vibration bending damping ratio for modes II and III, with improvements of up to 220% (mode II) and 310% (mode III) for the laminate and sandwich composite, respectively. LiPo batteries also improve the acoustic performance by increasing the coincidence frequency and decreasing the wavenumber amplitude at frequencies above the first vibration bending mode. The results indicate that the judicious placement of embedded LiPo batteries can improve the vibration damping properties of both carbon fibre laminates and sandwich composites. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on the degradation of Piezoelectric Wafer Active Sensors (PWAS) under impact loading. Carbon/epoxy laminates with surface bonded / embedded sensors were subjected to different levels of impact energy, and the performance of PWAS was monitored using impedance analysis. The effect of direct and indirect impact loading on the degradation of piezoelectric sensors was also examined. Using the force history data, a reduction in the flexural stiffness of the embedded specimens was identified. Examining the capacitance, output voltage and electromechanical impedance of PWAS, it was found that the degradation of the sensors under impact loading depends on the level of impact energy, location of the impactor as well as the number of impacts. Identification of the structural damage and sensor's degradation was verified using SEM micrographs. [ABSTRACT FROM AUTHOR]

• Interference fit fasteners under load may separate from the hole that they are inserted into. • Separation causes a non-linear stress effect in the vicinity of the hole. • Accelerating crack growth for high stress cyclic loading. • This effect can be discerned using quantitative fractography. • Ignoring this effect in life predictions may result in unconservative crack growth estimations. Interference fit fasteners are a ubiquitous part of modern airframes, incorporated to increase the fatigue life at critical locations. When inserted into a structure, they have a compound effect of inducing residual stresses and changing the stress concentration. Evidence suggests that this stress state may become non-linear under high tensile loading, as the fastener and hole surface may separate. This paper illustrates the importance of including this separation in fatigue analysis of structures containing interference fit fasteners by showing that separation results in an otherwise unexplained acceleration in crack growth. Test specimens with and without fasteners are subjected to a specifically designed test spectrum, and crack growth rates are measured using quantitative fractography. This investigation reveals a statistically significant acceleration in fatigue crack growth only found in the specimens containing interference fit fasteners. Simulations that model the separation effect predict an acceleration, but classic crack growth equations fall short. Ignoring these separation effects is shown to underpredict the growth of cracks under certain conditions by a factor of two or more. [ABSTRACT FROM AUTHOR]

Abstract: In the current paper, Representative Volume Element (RVE) which is a major tool in modeling heterogeneous media is studied from different aspects. Hierarchical numerical homogenization procedure is performed for characterization of a piezoelectric nanocomposite, composed of a non-piezoelectric polymer reinforced with piezoelectric Boron Nitride Nanotubes (BNNTs). Finite Element Method (FEM) is employed for numerical simulations and the study of influential parameters on the RVE concept. Different key parameters consisting modeling element size, absolute/periodic boundary conditions, volume fraction of nanotubes, aspect ratio of nanotubes, anisotropy class of the nanocomposite, elastic and piezoelectricity contrast between constituent materials are observed within the current research. To this end, sufficient criteria such as convergence of the outputs to a unique value, double checking based on the symmetry/anti-symmetry of coefficient matrix are observed to verify the output results and increase the reliability of the evaluated effective characteristics. [Copyright &y& Elsevier]

Abstract: This paper presents a study on the effect of processing variables on the mechanical properties of clay/epoxy nanocomposites produced in a centrifuge. Several experiments were conducted including different types of clay with varying processing conditions such as centrifuge rotor speed and curing temperature. The effects of these variables on the mechanical properties of nanocomposites were then studied. In order to fully understand the experimental results, a TEM was used to investigate the effect of abovementioned variables on microstructure and intercalation/exfoliation of clay/epoxy nanocomposites. The results from this work could be used to determine the best processing window to obtain appropriate levels of strength, stiffness and energy to failure in clay/epoxy nanocomposites. [Copyright &y& Elsevier]

Operational Modal Analysis (OMA) is a promising candidate for flutter testing and Structural Health Monitoring (SHM) of aircraft wings that are passively excited by wind loads. However, no studies have been published where OMA is tested in transonic flows, which is the dominant condition for large civil aircraft and is characterized by complex and unique aerodynamic phenomena. We use data from the HIRENASD large-scale wind tunnel experiment to automatically extract modal parameters from an ambiently excited wing operated in the transonic regime using two OMA methods: Stochastic Subspace Identification (SSI) and Frequency Domain Decomposition (FDD). The system response is evaluated based on accelerometer measurements. The excitation is investigated from surface pressure measurements. The forcing function is shown to be non-white, non-stationary and contaminated by narrow-banded transonic disturbances. All these properties violate fundamental OMA assumptions about the forcing function. Despite this, all physical modes in the investigated frequency range were successfully identified, and in addition transonic pressure waves were identified as physical modes as well. The SSI method showed superior identification capabilities for the investigated case. The investigation shows that complex transonic flows can interfere with OMA. This can make existing approaches for modal tracking unsuitable for their application to aircraft wings operated in the transonic flight regime. Approaches to separate the true physical modes from the transonic disturbances are discussed. [ABSTRACT FROM AUTHOR]

Due to their low delaminating tendency and high damage tolerance, 3-D braided composites are capable of being utilized in notched components. However, a few studies have investigated the mechanical properties of braided composites with open holes in multi-scale. In this paper, a multi-scale study on the mechanical properties of 3-D 4-directional braided composites with an eccentric circular hole is carried out. The equivalent elastic properties of 3-D 4-directional braided composites are calculated by the homogenization method based on the geometry of the meso unit cells. According to Lekhnitskii's theory, the local stress correction (LSC) method for computing the transverse stress around the eccentric hole is proposed. The models of meso unit cells with different braided angles are established, and the strength of the defect-free composites is predicted by the Tsai-Wu criterion. In the macroscopic view, using the point stress criterion (PSC), the average stress criterion (ASC), and numerical analysis, the strength properties of braided composites with different hole radii, braided angles, and eccentric distances are predicted. This study can be utilized to estimate the stress distributions and strength properties of 3-D braided composites with an eccentric hole and provides theoretical and simulation foundations for the problems of orthotropic materials with holes. • According to Lekhnitskii's theory, the local stress correction (LSC) method for computing the transverse stress around the eccentric hole is proposed. • Using the different damage criteria, the strength properties of braided composites with different hole radii, braided angles, and eccentric distances are predicted. • It is found that the transverse stress calculated by LSC method shows a good agreement with the numerical simulations in Abaqus. • The braided angle, hole radius, and eccentric distance affect the strength of the composites. • The muti-scale method proposed in this paper provides theory and simulation methods for the problems of opening plates in engineering. [ABSTRACT FROM AUTHOR]

This paper presents research findings on the influence of alkaline deacetylation on the thermal stability and fire reaction properties of non-pathogenic Basidiomycota fungi (mycelium) grown in molasses. The relationship between deacetylation conditions, such as incubation time and NaOH concentration, and the thermal and fire reaction properties of mycelium was investigated. The degree of deacetylation was also examined for its influence on the high-temperature thermal stability of mycelium, such as char formation. The findings indicated that the high-temperature thermal stability increased as the degree of deacetylation increased due to the conversion of chitin into chitosan as well as the presence of char-promoting hydroxyl‑terminated polysaccharide moieties. The study further investigated the influence of hollow glass microspheres on the thermal properties and microscale combustion behaviour of unmodified and deacetylated mycelium. This study provides an in-depth analysis of the thermal degradation mechanisms that govern the thermal stability and char-forming ability of unmodified and deacetylated mycelium. Additionally, the link between the thermal stability and fire reaction properties of mycelium and its deacetylated derivatives was established. Finally, the effectiveness of unmodified and deacetylated mycelium mats for fireproofing flammable glass fibre-reinforced epoxy laminates exposed to a simulated moderate-intensity fire was evaluated. [Display omitted] [ABSTRACT FROM AUTHOR]

• The Tachi-Miura Polyhedron (TMP) origami metamaterial with reconfigurable shapes and programmable mechanical properties is developed by a 4D printing method. • The elastic modulus, deformations, force-displacement curves and Poisson's ratios of the TMP origami metamaterials are studied by theoretical models, finite element analysis and experiments. • The TMP origami structures can achieve negative Poisson's ratios and switch between monostable and bistable states. • Due to shape memory effects, deformation shapes and mechanical properties of TMP origami metamaterials can be programmed by controlling temperature and tuning structural parameters. Origami structures have received significant attention in engineering due to their unique design methods and deformation modes along the crease lines. However, the configurations of origami structures are fixed after fabrication, and their mechanical properties are tough to tune and adapt. To overcome this limitation, herein, a 4D printing method is employed to develop Tachi-Miura Polyhedron (TMP) origami metamaterials with reconfigurable shapes and programmable mechanical properties. The elastic modulus, folding/unfolding deformations, force-displacement curves and Poisson's ratios of TMP origami metamaterials under different structure parameters and temperature are studied through theoretical models, finite element analysis (FEA) and experiments. Results reveal that the TMP origami structures can achieve negative Poisson's ratios, and their deformation modes can switch between monostable and bistable states. Due to shape memory effects, deformation shapes and mechanical properties can be programmed by controlling temperature and tuning structural parameters. The 4D Printed origami metamaterials can provide practical solutions in various engineering applications such as self-deployable structures, energy absorption devices and flexible electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

The char yield from mycelium fungi can be improved via alkaline deacetylation wherein chitin polymer segments are converted to chitosan moieties. The influence of alkaline deacetylation conditions (e.g., temperature, incubation time and alkali concentration) on the biochemical composition, microstructural and physicochemical characteristics and thermal properties of mycelium fungi is poorly understood. In this paper, we investigated the influence of different alkaline deacetylation conditions on the degree of deacetylation and thermal properties of non-pathogenic Basidiomycota phylum, mycelium fungi, grown in molasses. Particularly, we determined the relationship between the degree of deacetylation and high-temperature char-forming characteristics of deacetylated mycelium. Further, the effect of an oxidizing agent, KMnO 4 , on the thermal stability and char-forming characteristics of alkaline-treated mycelium was investigated. This paper presents a comprehensive investigation of the relationship between the degree of deacetylation and char yields at high temperatures (e.g., >300°C) as well as an in-depth interrogation of the thermal degradation mechanisms governing the thermal stability of alkaline (and KMnO 4) treated mycelium. Research findings from this study have advanced knowledge of the development and design of bio-derived thermal protection materials for fire-threatened infrastructure. [Display omitted] [ABSTRACT FROM AUTHOR]

The complex architecture of many fibre-reinforced composites makes the generation of finite element meshes a labour-intensive process. The embedded element method, which allows the matrix and fibre reinforcement to be meshed separately, offers a computationally efficient approach to reduce the time and cost of meshing. In this paper we present a new approach of introducing cohesive elements into the matrix domain to enable the prediction of matrix cracking using the embedded element method. To validate this approach, experiments were carried out using a modified Double Cantilever Beam with ply drops, with the results being compared with model predictions. Crack deflection was observed at the ply drop region, due to the differences in stiffness, strength and toughness at the bi-material interface. The new modelling technique yields accurate predictions of the failure process in composites, including fracture loads and crack deflection path. [ABSTRACT FROM AUTHOR]