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Silk has recently attracted considerable interest owing to its versatile properties as a natural fiber, especially in the medical sector. However, the mechanical properties of silk limit its potential applications. In our earlier work, the mechanical performance of silk filaments was enhanced owing to the insertion of cellulose nanofibers (CNFs). Nevertheless, silk filaments must be assembled and twisted to form a continuous yarn. In this study, the mechanical properties of CNF-reinforced silk yarns were evaluated to determine the optimal yarn structure. The evolution of the Young’s modulus, ultimate tensile strength, toughness, and elongation at break was assessed as a function of the twist level in comparison with regular silk. The results demonstrated that the most favorable compromise of the mechanical properties was obtained at 1000 twists per meter.

AbstractA timely review is presented on artificial intelligence (AI) and, more specifically, deep learning, which is a subfield of machine learning (ML), applied to the design and behaviour of modern composite materials systems. The use of composites is increasing due to their high specific strength and stiffness, which make them comparable to metals, and their tunable properties that can be altered to produce lightweight materials with efficient structural configurations. Recent studies are examined and discussed, wherein computational tools have been developed that mimic human brain activity to answer questions and solve challenging problems toward characterizing materials behaviour and improving the performance of materials with less effort and cost. The attractiveness of AI comes from its self-learning capability, the faster computer processing time of large datasets, and the potential to yield highly accurate results. However, as a data-driven method, the quantity and quality of data largely affect the accuracy of ML in addition to the need for well-designed AI algorithms and virtual reality models, hence the need to continue the research efforts in this area.

In this study, we employed corona poling to improve the piezoelectric properties of as-deposited BaTiO3films and conducted a vibration energy harvesting test. Dielectric measurements indicated that the dielectric constant of the as-deposited film increased with temperature, and the frequency dependence of the dielectric constant was minimal at room temperature. Applying an electric field of 1500 kV cm−1resulted in a recoverable energy density of 7.1 J cm−3and an energy storage efficiency of 54%. The corona polarization treatment could align dipoles under high electric fields and prevent dielectric breakdown owing to local defects created by the aerosol deposition (AD) process. The vibration test yielded a harvested energy of 172 nJ and an output voltage of 2.67 V, which is suitable for force sensor applications. Polarization via corona discharge is also feasible without an electrode. Integrating AD with corona poling may benefit new capacitors, sensors, and energy harvesting technologies.

Piezoelectric Internet of Things (IoT) sensors with energy-harvesting capabilities, which can convert mechanical energy into electrical energy, promote battery-less systems. Such sensors can harness the vibration generated by spacecraft and other moving objects, eliminating the need for external power sources or battery replacements, thereby improving the autonomy and reliability of the system. This study investigates the features of a novel piezoelectric vibration energy harvester (PVEH) that comprises a carbon fiber-reinforced polymer (CFRP) electrode. The CFRP electrode provides outstanding electrical conductivity (7190 S/m) and enhances the mechanical characteristics of the energy collector, thereby ensuring a steady electrical energy yield during resonance. The piezoelectric composite consists of potassium sodium niobate (KNN) nanoparticles mixed with epoxy resin. Results show that when the KNN content is about 30 vol%, the piezoelectric properties of d33and d31are 15.21 pC/N and − 5.68 pC/N, respectively. Under an applied displacement of 0.05 mm, the CFRP-reinforced PVEH (C-PVEH) provides an impressive output energy volume density of 89.61 μW/cm3, which is capable of lighting LED bulbs with ease. Notably, this technology shows great application potential for powering wireless communication systems, indicating a remarkable advancement in the field of self-powered IoT sensors. This study provides valuable insights into the potential application of this groundbreaking technology.

Film thickening by aerosol deposition (AD) is effective for the fabrication of self-sustained piezoelectric energy harvesting devices. Here we investigated the properties, microstructure, and residual stresses of BaTiO3films deposited by AD at different film thicknesses. The Young’s modulus measured by the nanoindentation test showed no thickness dependence; however, it increased from approximately 130– 160 GPa with annealing. Ferroelectric hysteresis curves showed that the increase in film thickness facilitated polarization switching. The microstructure of the films showed no significant changes with the film thickness, while the results of X-ray diffraction and finite element analysis of thermal stress showed that the residual stress after annealing depended on the film thickness. The energy harvesting performance of the BaTiO3films deposited by AD may increase owing to the residual stress, rather than the increase in the film thickness.

Energy harvesting using magnetostrictive materials is currently attracting significant attention. The additive manufacturing process can produce such materials with excellent energy-harvesting performance and various required properties, including mechanical properties—by optimizing the lattice structure of the material. This study optimized the manufacturing parameters of a laser powder bed fusion process to produce a magnetostrictive Fe52–Co48alloy. We evaluated the energy-harvesting performance of a Fe52–Co48alloy plate with a honeycomb structure subjected to vibrations and impacts. We compared the results with a fully dense structure and found that the honeycomb structure resulted in a lower resonant frequency. In addition, the honeycomb structure exhibited a power density 4.7 times higher than that of the fully dense structure in a vibration test and 4.9 times higher than that in an impact test. The honeycomb structure is thus an attractive structure for obtaining power efficiently. Furthermore, honeycomb structures and other designs can reduce the weight of a Fe52–Co48alloy plate and improve its sensitivity for use as a particulate-matter sensor.

This work investigates the electromechanical response of piezoelectric macro-fiber composites (MFCs) under tension. Nonlinear three dimensional finite element model incorporating the polarization switching mechanism was used to predict the electromechanical fields near interdigitated electrode (IDEs) in the piezoelectric MFCs. The lead zirconate titanate (PZT) fibers in the MFC are partially poled. The electric field-induced strain was then measured, and test results were presented to validate the predictions.

This paper studies the damage behavior and interlaminar shear properties of hybrid composite laminates subjected to bending at cryogenic temperatures. Cryogenic short beam shear tests were performed on hybrid laminates combining woven glass fiber reinforced polymer (GFRP) composites with polyimide films, and microscopic observations of the specimens were made after the tests. A progressive damage analysis was also conducted to simulate the initiation and growth of damage in the specimens and to determine the interlaminar shear strength based on the maximum shear stress in the failure region. The predicted load-deflection curve and damage pattern show good agreement with the test results, and the numerically determined interlaminar shear strength is higher than the apparent interlaminar shear strength.

The mechanical characteristics of piezoelectric ceramic fibers can be improved by embedding the fibers in a metal matrix. The compressive stress generated during the embedding process, however, limits the polarization of piezoelectric ceramic composites. To study and determine the relationship between the mechanical and piezoelectric properties of piezoelectric ceramics, we analyzed the crystallographic orientation of piezoelectric ceramics embedded in an aluminum matrix via electron backscatter diffraction. The orientation of the crystals before and after the polarization of the piezoelectric fibers, in which residual stresses were generated during embedding, was evaluated. Furthermore, the residual stresses were reduced by heat treatment, and the resultant angle of orientation was evaluated before and after polarization. Results showed that, as the residual stresses were relieved, the orientation of the piezoelectric ceramic crystals changed to reveal increased polarization. Our analysis shows that the crystal orientation of piezoelectric ceramics is impacted by the residual compressive stress that arises from embedding the piezoelectric fiber in the aluminum matrix; it also illustrates the hindering effect of residual stress on the polarization of piezoelectric ceramics.

We present numerical and experimental results on the nonlinear bending behavior due to domain wall motion in functionally graded piezoelectric actuator under alternating current (ac) electric fields. A nonlinear finite element method is employed to analyze the dynamic response of functionally graded piezoelectric actuator. A phenomenological model of domain wall motion is used in computation, and the effects of ac electric field amplitude and frequency, number of layers, and property gradation on the deflection of the cantilever actuators are examined. Experimental results, which verify the model, are presented using a functionally graded bimorph. The numerical results agree very well with the experimental values.

This paper deals with mode III delamination properties of glass fiber reinforced polymer woven laminates at room temperature (293 K), liquid nitrogen temperature (77 K), gas helium temperature (20 K), and liquid helium temperature (4 K). In order to evaluate these properties, the Split Cantilever Beam (SCB) fracture test is performed. The load is applied to a test specimen through a set of identical grips in order to reduce (in some degree) the mode II loading at the free edges. A three-dimensional finite element analysis is used to study the stress and strain state of the specimens and to interpret the experimental measurements. The strain energy release rate is calculated by using the virtual crack closure technique. It is found that the strain energy release rate is dominated by the mode III component. A non-uniform distribution of the strain energy release rate along the delamination front is obtained with mode III component having maximum at the center of the delamination front, while mode II component increases towards the free edges. The strain energy release rate is also determined using the crack closure technique. A finite element analysis is also carried out to calculate the stress intensity factors for the SCB specimens. The fracture surfaces are examined by scanning electron microscopy to identify the fracture mechanisms. The most important conclusion from the present study is that at temperature lowering from 293 to 20 K the mode III fracture toughness increases, further cooling to 4 K produces a toughness decrease.This paper deals with mode III delamination properties of glass fiber reinforced polymer woven laminates at room temperature (293 K), liquid nitrogen temperature (77 K), gas helium temperature (20 K), and liquid helium temperature (4 K). In order to evaluate these properties, the Split Cantilever Beam (SCB) fracture test is performed. The load is applied to a test specimen through a set of identical grips in order to reduce (in some degree) the mode II loading at the free edges. A three-dimensional finite element analysis is used to study the stress and strain state of the specimens and to interpret the experimental measurements. The strain energy release rate is calculated by using the virtual crack closure technique. It is found that the strain energy release rate is dominated by the mode III component. A non-uniform distribution of the strain energy release rate along the delamination front is obtained with mode III component having maximum at the center of the delamination front, while mode II component increases towards the free edges. The strain energy release rate is also determined using the crack closure technique. A finite element analysis is also carried out to calculate the stress intensity factors for the SCB specimens. The fracture surfaces are examined by scanning electron microscopy to identify the fracture mechanisms. The most important conclusion from the present study is that at temperature lowering from 293 to 20 K the mode III fracture toughness increases, further cooling to 4 K produces a toughness decrease.

This paper presents the stress intensity factors for internal and edge cracks in multi-layer glass/epoxy plain weave fabric laminates subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to have occurred in the transverse fiber bundles. Finite element analysis of the limiting case when the cracks extend to the interfaces between two fiber bundles is carried out. Special singular elements containing the exact stress singularity are used to model the singular stress field near the crack tip. Numerical results for the stress intensity factor at cryogenic temperatures are displayed graphically and discussed in detail.

This paper presents the stress intensity factors for internal and edge cracks in multi-layer glass/epoxy plain weave fabric laminates subjected to uniaxial tension load at cryogenic temperatures. Cracks are considered to have occurred in the transverse fiber bundles. Finite element analysis of the limiting case when the cracks extend to the interfaces between two fiber bundles is carried out. Special singular elements containing the exact stress singularity are used to model the singular stress field near the crack tip. Numerical results for the stress intensity factor at cryogenic temperatures are displayed graphically and discussed in detail.

The main results of this paper are as follows. (a) Let π : M→ Nbe a non-trivial Riemannian submersion with totally geodesic fibers of dimension 1 over an Einstein manifold N. If Mis compact and admits a standard Einstein--Weyl structure with constant Einstein--Weyl function, then Nadmits a Kähler structure andMa Sasakian structure. (b) Let $$ \pi:{M^{2n + 1} \to N^{2n}} $$ be a Riemannian submersion with totally geodesic fibers and Nan Einstein manifold of positive scalar curvature $$ \geqslant 4n(n + 1)$$ . If Madmits a standard Sasakian structure, then Madmits an Einstein--Weyl structure with constant Einstein--Weyl function.