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Cellulose acetate (CA) is a semi-synthetic and biodegradable polymer that represents a fair alternative as a structural material for fused filament fabrication (FFF). With very few studies on the subject, the present work aims to broaden and deepen the understanding of FFF of CA with a degree of substitution of 1.7. A fine characterisation of the microstructure and mechanical properties of printed parts and the investigation of the effect of water on this hydrophilic polymer were pursued. Highly dense plasticised CA specimens with a porosity lower than 2% were successfully manufactured. Geometrical discrepancies between the designed and fabricated parts, together with the surface rugosity, inherent from this 3D printing technique, were carefully studied by X-ray microtomography. Ultimately, the printed samples showed no alteration of the intrinsic material's composition, yield strength and tensile modulus, comforting the potential of FFF of CA-based parts for structural applications. In addition to the geometrical imperfections, the plasticising effect of water on CA was quantified as the elastic and yield properties were significantly decreased after water saturation, evidencing the need to account for the two effects when designing, storing and using FFF CA parts. [ABSTRACT FROM AUTHOR]

Polymers are often combined with magnetostrictive materials to enhance their toughness. This study reports a cellulose nanofibril (CNF)-based composite paper containing dispersed CoFe2O4 particles (CNF–CoFe2O4). Besides imparting magnetization and magnetostriction, the incorporation of CoFe2O4 particles decreased the ultimate tensile strength and increased the fracture elongation of the CNF–CoFe2O4 composite paper. CNF was responsible for the tensile properties of CNF–CoFe2O4 composite paper. Consequently, the magnetic and magnetostrictive properties and tensile properties of CNF–CoFe2O4 composite paper can be controlled by changing the mixture ratio of CNF and CoFe2O4 particles. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) green bodies fabricated using robocasting were strengthened by incorporating cellulose nanofiber (CNF) into a SiC slurry and just drying at room temperature. The measured flexural strength of a SiC green body modified via the CNF with a liquid phase weight ratio (water-to-CNF slurry) of 80:20 was 813 ± 37 kPa, 1.5 times larger than the strength of an unmodified green body. The strength was improved due to the increased number of hydrogen-bonding sites between the raw particles and CNF. After annealing at 250 °C, the lowering of the flexural strength indicated the occurrence of the bonding sites via water that was trapped on the CNF. The addition of CNF increased the viscosity and yield stress of the SiC slurry, which remained in the Bingham pseudoplastic behavior regardless of the CNF used. Moreover, this addition showed no effect on the relative densities, microstructures, and crystalline phases of the sintered SiC body. Therefore, the addition of CNF to the SiC slurry aided in handling the green body during processing and showed no detrimental effects on robocasting. [ABSTRACT FROM AUTHOR]

Many structural health monitoring (SHM) techniques have been investigated for damage detection in woven glass fiber reinforced polymer (GFRP) laminates. Recently, the GFRP composites integrated with sensors have received attention because the composite material can transmit information about the structural condition during operation. Magnetostrictive materials are considered as feasible candidates to realize the contactless SHM techniques by exploiting the Villari effect, but the theoretical modeling to correlate a magnetostrictive response with structural conditions is a critical issue. In this study, the analytical procedure considering the mechanics of materials and electromagnetism was proposed to model the magnetic induction by the Villari effect of magnetostrictive GFRP laminates under bending. The magnetostrictive Fe–Co fiber/GFRP composites were then developed, and the four-point bending tests were carried out to evaluate the fabricated composites' stress monitoring capability. The magnetic flux density behavior corresponded to the bending stress fluctuation. The maximum magnetic flux density change was 70.7 mT subjected to the peak bending stress of 158 MPa. The analytical solutions showed reasonable agreement with the experimental results. The applied stress and measured magnetic flux density were correlated by the theoretical models. Thus, these results suggest an important step in realizing the novel contactless SHM technique utilizing magnetostrictive materials. [ABSTRACT FROM AUTHOR]

This paper examines theoretically and experimentally the dynamic electromechanical response of multilayer piezoelectric laminates for fuel injectors at high temperatures. A phenomenological model of depolarization at high temperatures was used, and the temperature dependent piezoelectric coefficients were obtained. The high temperature electromechanical fields of the multilayer piezoelectric actuators under AC electric fields were then calculated by the finite element method. In addition, test data on the electric field induced strain at high temperatures, which verify the model, were presented. [ABSTRACT FROM AUTHOR]

This paper investigates the cyclic fatigue behavior in giant magnetostrictive materials with a crack under magnetic fields. Fatigue tests were performed in three-point bending with single-edge precracked-beam specimens, and the number of cycles to failure under sinusoidal mechanical loads and magnetic fields was obtained. A finite element analysis was also carried out, and the energy release rate was calculated. The effect of magnetic fields on the maximum energy release rate versus number of cycles to failure curve was then discussed. In addition, fracture surfaces were examined by scanning electron microscopy and laser microscopy to correlate with fatigue characteristics. [ABSTRACT FROM AUTHOR]

This paper studies analytically and experimentally the cryogenic static fatigue behavior of cracked piezoelectric ceramics under electric fields. The crack was created normal to the poling direction. Static fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens at room temperature and liquid nitrogen temperature (77 K), and times-to-failure under different mechanical loads and electric fields were obtained. Plane strain finite element analysis using temperature-dependent material properties of piezoelectric ceramics was also performed, and the energy release rate for the permeable crack model was calculated. The effects of electric field and temperature on the energy release rate versus lifetime curve are discussed. [ABSTRACT FROM AUTHOR]

This paper studies the dynamic electromechanical response of S-shaped piezoelectric energy harvesters both numerically and experimentally. The resonant frequency and output voltage of the harvesters excited by bending/torsion vibration were analyzed by three dimensional finite element method. The resonant frequency and output voltage were also measured, and a comparison was made between analysis and experiment. The effects of waviness ratio, proof mass and load resistance on the dynamic electromechanical fields and output power were then discussed in detail. [ABSTRACT FROM AUTHOR]

This paper presents the electromechanical behavior of piezoelectric/carbon nanotube (CNT)-based polymer laminates under three-point bending. The laminate was fabricated using thin lead zirconate titanate (PZT) and multi-walled carbon nanotube (MWNT)-based polycarbonate layers. The three-point bending tests were conducted on the PZT/MWNT-based polycarbonate laminates, and the dependence of the displacement and output voltage due to mechanical loads on the nanotube content and the material dimensions were measured and discussed. The output power was then calculated. This study showed that the piezoelectric/CNT-based polymer laminates can generate power without external load resistance. [ABSTRACT FROM AUTHOR]

This paper investigates theoretically and experimentally the cryogenic fracture behavior of cracked piezoelectric ceramics under electric fields. Fracture tests were performed in three-point bending with the single-edge precracked-beam specimens at room temperature and liquid nitrogen temperature (77 K), and the fracture loads under electric fields were obtained. Plane strain finite element analysis was also carried out using temperature-dependent material properties of the piezoelectric ceramics, and the dependence of the energy release rate on the electric field and temperature was discussed. In addition, possible mechanisms for cryogenic fracture were examined by scanning electron microscopy. [ABSTRACT FROM AUTHOR]

We discuss the mode I energy release rate of a rectangular piezoelectric material with a crack under electromechanical loading at cryogenic temperatures. A crack was created normal or parallel to the poling direction, and electric fields were applied parallel or normal to the poling. A plane strain finite element analysis was carried out, and the effects of electric field and localized polarization switching on the energy release rate were discussed for the piezoelectric ceramics at cryogenic temperatures. [ABSTRACT FROM AUTHOR]

This paper deals with the fatigue behavior of cracked piezoelectric ceramics in cyclic bending under electric fields both numerically and experimentally. Fatigue tests were carried out in three-point bending with the single-edge precracked-beam specimens. The crack was created normal to the poling direction. Number of cycles to failure was measured under different electric fields. A plane strain finite element analysis was also performed, and the effect of polarization switching on the energy release rate was discussed under a high negative electric field. In addition, possible mechanisms for crack growth were discussed by scanning electron microscope examination of the fracture surface of the piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

We characterize the combined Mode I and Mode III delamination fracture behavior of woven glass fiber reinforced polymer (GFRP) composite laminates at cryogenic temperatures. The eight-point bending plate (8PBP) tests were conducted at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K) using a new test fixture. A three-dimensional finite element analysis was also performed to calculate the energy release rate distribution along the delamination front, and the delamination fracture toughnesses were evaluated for various mixed-mode I/III ratios. Furthermore, the microscopic examinations of the fracture surfaces were carried out with scanning electron microscopy (SEM), and the mixed-mode I/III delamination fracture mechanisms in the woven GFRP laminates at cryogenic temperatures were assessed. The fracture properties were then correlated with the observed characteristics. [ABSTRACT FROM AUTHOR]

This paper investigates the application of piezoelectric actuators to control the delamination response in woven fabric composites subjected to Mode I loading. Experiments were conducted on a double cantilever beam (DCB) specimen of woven glass fiber reinforced polymer (GFRP) composite laminates with piezoelectric ceramic actuators bonded on the surfaces, in order to evaluate the dependence of the delamination behavior on the applied electric fields. A finite element analysis of the DCB specimen with surface-bonded actuators was also performed, and a comparison was made between the finite element predictions and the test results. In addition, the effect of the actuator location on the effectiveness of the piezoelectric control was examined numerically. [ABSTRACT FROM AUTHOR]

This study presents the results of the mode I energy release rate of a rectangular piezoelectric material with a single-edge crack under electromechanical loading. A crack was created normal or parallel to the poling direction, and electric fields were applied parallel and antiparallel to the poling. A nonlinear plane strain finite element analysis was carried out, and the effect of localized polarization switching on the energy release rate was discussed for the permeable, impermeable, open, and discharging cracks under a high-negative electric field. The effect of dielectric breakdown on the energy release rate was also examined under a high-positive electric field. [ABSTRACT FROM AUTHOR]

This paper presents the nonlinear electromagneto-mechanical behavior of magnetostrictive/piezoelectric laminated pieces under magnetic fields both numerically and experimentally. The pieces are fabricated using thin Tb0.3Dy0.7Fe2 (Terfenol-D) and Pb(Zr,Ti)O3 (PZT) layers, and the magnetostriction of the pieces is measured. A nonlinear finite element analysis is also employed to evaluate the second-order magnetoelastic constants in Terfenol-D layer bonded to the PZT layer, and the nonlinear displacement, internal stresses and induced voltage for the magnetostrictive/piezoelectric laminated pieces under magnetic fields are discussed. [ABSTRACT FROM AUTHOR]

This article studies the fatigue crack growth in a metastable austenitic stainless steel in cryogenic high magnetic field environments. Fatigue crack growth tests were performed with the compact tension (CT) specimens at liquid helium temperature (4 K) in magnetic fields of 0 and 6 T, and the crack growth rate data were expressed in terms of the J-integral range during fatigue loading. The J-integral range values were evaluated using an elastic-plastic finite element analysis. The measurement of martensite phase in the test specimens and the fractographic examination were also carried out. The high magnetic field effect on the fatigue crack growth rate properties at 4 K is discussed in detail. [ABSTRACT FROM AUTHOR]

This paper studies the scattering of in-plane compressional and shear waves by a diamond shaped inclusion with cracks using the boundary element method. The special case that the shape of the diamond becomes square is also considered. Numerical calculations are carried out for the limited cases of diamond shaped hole and rigid inclusions, and the effects of frequency and inclusion shape on the scattering cross section and dynamic stress intensity factor are shown in graphical form. The results where the elastic properties of the inclusion are the same as those of the matrix are also discussed. [ABSTRACT FROM AUTHOR]

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