Symmetric Bending Research Articles

Analysis of Symmetrical Three-Point Bending and Springback Process of Pipes

This study presents a theoretical analysis of the single-pressure straightening process for large-scale pipes, addressing the challenges of inadequate straightening precision and low efficiency associated with the current practice, which heavily relies on operator expertise. The straightening process of pipes through pressure is fundamentally a symmetrical three-point bending elastic–plastic deformation process. With the assumption of small deformations, the symmetric three-point bending of the pipe can be divided into two distinct deformation stages: fully elastic and elastic–plastic. For each stage, calculation models are developed, yielding the deflection formulae for any point on the pipe before and after unloading under varying punch strokes. The accuracy and reliability of the theoretical models are confirmed through finite element analysis and physical simulation experiments on smaller pipes. These models enhance the accuracy of single-pressure straightening and lay the groundwork for online material performance parameter identification based on load–stroke curves during the initial straightening phase. Both theoretical analysis and experimental outcomes demonstrate that the relationship between the maximum deflection after springback and the punch stroke are nearly linear, offering a practical method for developing intelligent control systems for pressure straightening.

Fracture mechanics properties of human cranial bone

The mechanical properties of the human skull have been examined and established previously in the literature, for example, the transversal isotropy of cranial bone and properties including the Elastic modulus and Poisson's ratio. However, despite the existing data, there are still mechanical properties which remain to be determined for the human skull. The present study aims to characterise the fracture properties of human cranial bone within the Linear Elastic Fracture Mechanics (LEFM) framework. Unembalmed human (2 female and 3 male) cortical cranial bone samples were harvested from the frontal, and left and right parietal bones and were tested in Mode I (N = 124), Mode II (N = 31) and Mixed-Mode I-II (N = 47) loading conditions. For Mode I, samples were tested using Single Edge Notched Beams (SENB) under symmetric 3-point bending, while for Mixed-Mode I-II samples were tested under asymmetric 3-point bending. For Mode II, 4-point bend tests were carried out. All samples fractured in a brittle fashion. From these tests, reference values of stress intensity factor (KI and KII) and the strain energy release rate (JI, GI, GII, GI-II) for the frontal, left and right parietal bones were calculated. It was determined that the fracture toughness of the frontal, and left and right parietal bones are not statistically different from each other and that they exhibit symmetry about the sagittal plane. It was also demonstrated that, as is the case for other human bones and for the age range tested here, the fracture toughness of human cranial bone is lower for females (KIfemale 2.48 (±2.16) MPa∗m0.5, KImale 4.75 (±2.58) MPa∗m0.5, GIfemale 1.07 (±3.01) kJ/m2, GImale 1.85 (±1.93) kJ/m2, JIfemale 1.57 (1.89) kJ/m2 and JImale 4.03 (±3.32) kJ/m2) and varies with age. More experimental work should be carried out to confirm the extrapolation of these conclusions to the other fracture modes tested here.Although these results are influenced by the age range and the age gap within the group of donors, the primary data presented here is valuable to those wishing to predict crack evolution and propagation in the human cranial bone and may prove useful in developing failure criterion or simulations of skull fracture using Finite Element Analysis.

Mixed FEM implementation of three-point bending of the beam with an edge crack within strain gradient elasticity theory

This paper considers the problem of symmetrical three-point bending of a prismatic beam with an edge crack. The solution is obtained by the mixed finite element method within the simplified Toupin–Mindlin strain gradient elasticity theory. A mixed variational formulation of the boundary value problem for displacements–strains–stresses and their gradients is applied, simplifying the choice of approximating functions. The concept of energy balance is adopted to calculate the energy release rate with a virtual increase in crack length. The increment of the potential energy of an elastic body is determined by accounting for the strain and stress gradient contribution. Numerical calculations were performed using a quasi-uniform triangular mesh of the cross-type. The mesh refinement was applied in the vicinity of the crack tip, at the concentrated support, and the point of application of the transverse force, and uniform mesh partitioning was utilized in the rest of the beam. The fine-mesh analysis was carried out on the successively condensed meshes in the stress concentration domain for different values of the length scale parameter. The crack opening displacements and the distribution of strains and Cauchy stresses for various values of the length scale parameter are presented. An increase in this parameter increases the stiffness of the crack, which leads to a decrease in the crack opening displacements and a smooth closure of its faces at the crack tip. In addition, accounting for the scale parameter reduces the calculated values of strains and stresses near the crack tip. Based on the energy balance criterion, local fracture parameters such as the release rate of elastic energy at the crack tip and the stress intensity factor are determined for different values of the mesh step. The numerical calculations indicate the convergence of the obtained approximations. The main feature of solutions, which includes the strain gradient contribution, is the decrease in the values of the calculated parameters associated with the fracture energy compared to the classical elasticity theory.

Spectroscopic Investigation of Pearl Samples from Online Platforms and E-Marketplaces

P urchasing pearls from online platforms and e-marketplaces has been around for years, where buyers could join in the thrill of the show of opening pearls from oysters or mollusks. In exchange for those materials that claim to be pearls, buyers must pay a high price per piece. In this study, the spectroscopic properties of twenty-seven samples purchased from online platforms and e-marketplaces were revealed. The FTIR spectra show the characteristic peaks of aragonite at 1483, 716, 712, and 699 cm-1, while exhibiting the vaterite peaks at 882 and 879 cm-1. Correspondingly, Raman spectra indicate the ν1 symmetrical and ν4 in-plane bending modes of the carbonate at 1083, 701, and 704 cm-1. Thus, it clarified that all the samples are pearls. The SrO/MnO ratio acquired by energy dispersive X-ray spectroscopy (EDXRF) at an average of 0.44 suggested that the samples are freshwater pearls. Apart from the white pearl, the cause of the color of the sample is separated into two factors. The natural color, which is presented in cream and peach, is caused by polyene pigments. In contrast, vivid colors such as blue, violet, purple, and pink are shown as evidence of dyes. The UV-Vis reflectance spectra also present a different absorption between natural and dyed pearls.

Passing-through I-plates-to-SHS moment resisting joints subjected to symmetric bending moments

When using hollow structural section (HSS) members in multi-storey buildings, beam-to-column moment resisting connections’ design raises critical questions to tackle. With conventional welded and bolted joints’ response being generally very flexible, the design resistance becomes governed by a deformation criterion rather than a strength criterion. This underscores the necessity for smart reinforcement techniques. A widespread solution is the diaphragm approach, in which the stiffeners usually protrude over the tubular column. The solution of plates passing through the HSS column is another stiffening option which was studied recently for CHS, yet, SHS columns have not been subject to comparable scrutiny. The objective of this paper is to study experimentally, numerically, and analytically the mechanical behaviour of I-beam-to-SHS column moment resisting joints using passing through I-plates under symmetric bending moments. The testing of two full-scale specimens corroborates previous findings with CHS columns in the elastic regime. However, significant deviations were observed in the post-peak response, revealing new insights into the behaviour of SHS columns. Failure was due to progressive buckling of passing through plates and yielding of tube-wall in transverse compression. A finite element model using solid and contact elements is developed and validated against experimental data. This model underscores how loads are redistributed between the tube wall and passing plates. A simplified version of the FE model is used to perform a thorough parametric numerical analysis on 101 configurations expanding upon the experimental test database by varying geometrical parameters such as passing plate thickness, tube, and beam dimensions. Finally, an analytical model integrating the different components of the joint is proposed to evaluate the initial rotational stiffness and the bending resistance.

Nonlinear Analysis of Plane Frames Using a Co-Rotating Timoshenko Beam Element

The present work describes a co-rotating shear flexible beam element without shear locking and integrating Euler-Bernoulli's and Timoshenko's beam theories. The co-rotational kinematics is based on the separation of the motion in deformational and rigid body components. The deformation of the beam element is composed by three natural modes of deformation: the extension mode, the symmetric bending mode, and the anti-symmetric bending mode. The respective generalized stresses from these natural modes are self-balanced, allowing the achievement of a consistent tangent stiffness matrix. In this paper, it is detailed and deduced all the algebraic steps for the deduction of the elastic stiffness matrix, the geometric stiffness matrix, and the co-rotation stiffness matrix. Some examples are presented and the numerical results demonstrate that the beam element here presented is able to handle large rotations.

Biomechanical Study of Symmetric Bending and Lifting Behavior in Weightlifter with Lumbar L4-L5 Disc Herniation and Physiological Straightening Using Finite Element Simulation.

Physiological curvature changes of the lumbar spine and disc herniation can cause abnormal biomechanical responses of the lumbar spine. Finite element (FE) studies on special weightlifter models are limited, yet understanding stress in damaged lumbar spines is crucial for preventing and rehabilitating lumbar diseases. This study analyzes the biomechanical responses of a weightlifter with lumbar straightening and L4-L5 disc herniation during symmetric bending and lifting to optimize training and rehabilitation. Based on the weightlifter's computed tomography (CT) data, an FE lumbar spine model (L1-L5) was established. The model included normal intervertebral discs (IVDs), vertebral endplates, ligaments, and a degenerated L4-L5 disc. The bending angle was set to 45°, and weights of 15 kg, 20 kg, and 25 kg were used. The flexion moment for lifting these weights was theoretically calculated. The model was tilted at 45° in Abaqus 2021 (Dassault Systèmes Simulia Corp., Johnston, RI, USA), with L5 constrained in all six degrees of freedom. A vertical load equivalent to the weightlifter's body mass and the calculated flexion moments were applied to L1 to simulate the weightlifter's bending and lifting behavior. Biomechanical responses within the lumbar spine were then analyzed. The displacement and range of motion (ROM) of the lumbar spine were similar under all three loading conditions. The flexion degree increased with the load, while extension remained unchanged. Right-side movement and bending showed minimal change, with slightly more right rotation. Stress distribution trends were similar across loads, primarily concentrated in the vertebral body, increasing with load. Maximum stress occurred at the anterior inferior margin of L5, with significant stress at the posterior joints, ligaments, and spinous processes. The posterior L5 and margins of L1 and L5 experienced high stress. The degenerated L4-L5 IVD showed stress concentration on its edges, with significant stress also on L3-L4 IVD. Stress distribution in the lumbar spine was uneven. Our findings highlight the impact on spinal biomechanics and suggest reducing anisotropic loading and being cautious of loaded flexion positions affecting posterior joints, IVDs, and vertebrae. This study offers valuable insights for the rehabilitation and treatment of similar patients.

Wavelength-dependent photoisomerization of trans-4,4′-azopyridine: Nonadiabatic dynamics simulation

The trans–cis photoisomerization processes of 4,4′-azopyridine upon S1 and S2 excitations have been investigated by nonadiabatic dynamics simulations based on multi-reference CASSCF calculations. 119 sampling trajectories were simulated starting from the trans form excited to the S1 (S2) state and the cis-isomer quantum yield is evaluated to be (3 ± 2)% ((18 ± 4)%), which is qualitatively in agreement with the recent experimental results in ethanol. We found that rotation around the central N-N bond accompanied by the N-N-C symmetrical bending vibrations is the main mechanism in photoisomerization of the target molecule excited to the S1 and S2 states. Upon S1 excitation, S1-S0 transition occurs earlier along the C-N-N-C torsional coordinate, leading to a low cis-isomer quantum yield. Upon S2 excitation, half of the simulated trajectories are trapped in a potential well on the S2 state, from which the twisted conical intersections are more easily reached in the internal conversion, resulting in a higher cis-isomer quantum yield.

Time-Resolved X-ray Emission Spectroscopy and Resonant Inelastic X-ray Scattering Spectroscopy of Laser Irradiated Carbon.

The existence of liquid carbon as an intermediate phase preceding the formation of novel carbon materials has been a point of contention for several decades. Experimental observation of such a liquid state requires nonthermal melting of solid carbon materials at various laser fluences and pulse properties. Reflectivity experiments performed in the mid-1980s reached opposing conclusions regarding the metallic or insulating properties of the purported liquid state. Time-resolved X-ray absorption studies showed shortening of C-C bonds and increasing diffraction densities, thought to evidence a liquid or glassy carbon state, respectively. Nevertheless, none of these experiments provided information on the electronic structure of the proposed liquid state. Herein, we report the results of time-resolved resonant inelastic X-ray scattering (RIXS) and time-resolved X-ray emission spectroscopy (XES) studies on amorphous carbon (a-C) and ultrananocrystalline diamond (UNCD) as a function of delay time between the irradiating pulse and X-ray probe. For both a-C and UNCD, we attribute decreases in RIXS or XES signals to transition blocking, relaxation, and finally, ablation. Increased signal at 20 ps following the irradiation of the UNCD is attributed to the probable formation of nanoscale structures in the ablation plume. Differences in the amount of signal observed between a-C and UNCD are explained by the difference in sample thickness and, specifically, incomplete melting of the UNCD film. Comparisons to spectral simulations based on MD trajectories at extreme conditions indicate that the carbon state in our experiments is crystalline. Normal mode analysis confirmed that symmetrical bending or stretching of the C-C bonds in the diamond lattice results in XES spectra with small intensity differences. Overall, we observed no evidence of melting to a liquid state, as determined by the lack of changes in the spectral properties for up to 100 ps delays following the melting pulses.

High-resolution FTIR spectroscopy and analysis of the K a = 0 ← 1 subbands of the fundamentals ν 3 and ν 6 of the dimer (HF)2

We report new far-infrared spectra of (HF)2 obtained by high resolution long-path Fourier Transform-Infrared (FTIR) spectroscopy. The origins of the two tunneling components of the K a = 0 ← 1 subband of the in-plane symmetric bending fundamental ν 3 were found to be at 450.4546 cm − 1 (Γ t : A + ← B +) and at 451.4583 cm − 1 (B + ← A +), and of the K a = 0 ← 1 subband of the out-of-plane bending fundamental ν 6 at 382.0802 cm − 1 (A + ← A +) and at 383.2245 cm − 1 (B + ← B +). The K a = 0 term values with respect to the ground state Γ t = A + term are 486.9442 cm − 1 for the A + and 486.8834 cm − 1 for the B + tunneling levels of ν 3. They are 417.5053 cm − 1 for the A − and 419.7140 cm − 1 for the B − vibration-tunneling sublevels of ν 6. The results are discussed in relation to full-dimensional quantum dynamics and predictions based on recent ab initio calculations and our empirically refined potential energy hypersurfaces. Graphical abstract

Emergence of Perovskite and Hashemite-type phases in chromium doped (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides: Formation, Rietveld refinement and Raman spectra

Perovskite- and Hashemite-type oxides are relevant due to their applications as oxidizing agent, photocatalyst, nutrient, fuel cells, gas sensors, batteries materials. An attempt has been made here to synthesize (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ(x = 0 – 1.0) and characterized with regards to structure and Raman vibrations. It depicts (a) pure cubic (Ba0.90Sr0.10)FeO3-δ phase, (b) cubic+orthorhombic, and (c) single orthorhombic (Ba0.90Sr0.10)CrO4 phase for x = 0–0.10, 0.20 – 0.80, and 1.0, respectively. It exhibits (i) decrease of cubic lattice parameter (ac)as 4.020 – 3.926 Å, (ii) expansion of orthorhombic unit cell, (iii) complete appearance of chromium in 6+ state for x = 1.0, and (iv) decrease of bond length and angle both with chromium. The bond lengths corresponding to Ba/Sr-O ∼ 2.84 Å, Fe-O ∼2.04 Å and Ba/Sr-O1 ∼ 3.227 Å, Ba/Sr-O2 ∼ 2.893 Å, Ba/Sr-O3 ∼2.859 Å have been derived for cubic (x = 0) as well as orthorhombic structure (x = 1.0), respectively. The bond angles e.g., Cr-O1-Cr ∼ 129°, Cr-O2-Cr ∼ 104.3° and Cr-O3-Cr ∼ 83.3° have been found for x = 1.0. Moreover, the bond Cr-O1 is compressed and Cr-O2 is more stretched than Cr-O3 bond. The morphology has also been changed to bigger size (nm) and shows different nature with chromium content. Raman spectra for Hashemite-type (Ba0.90Sr0.10)CrO4 reveal bands at ∼350, 360, 401, 425, 861, 886 and 904 cm−1 and arise due to symmetric (υ1, υ2) and antisymmetric (υ3, υ4) bending/ stretching mode. The present findings suggest potential applications of (Ba0.90Sr0.10)(Fe1-xCrx)O3±δ oxides.

Sperm Incubation in Biggers-Whitten-Whittingham Medium Induces Capacitation-Related Changes in the Lizard Sceloporus torquatus.

Sperm capacitation involves biochemical and physiological changes that enable sperm to fertilize the oocyte. It can be induced in vitro under controlled conditions that simulate the environment of the oviduct. While extensively studied in mammals, its approach in lizards remains absent. Understanding the mechanisms that ensure reproduction is essential for advancing the implementation of assisted reproductive technologies in this group. We aimed to perform a sperm analysis to determine if capacitation-related changes were induced after incubation with capacitating media. Fifteen males of Sceloporus torquatus were collected during the early stage of the reproductive season. The sperm were isolated from the seminal plasma and then diluted up to a volume of 150 μL using BWW medium to incubate with 5% CO2 at 30 °C for a maximum duration of 3 h. A fraction was retrieved hourly for ongoing sperm assessment. The sperm analysis included assessments of its motility, viability, the capacitation status using the chlortetracycline (CTC) assay, and the acrosome integrity with the lectin binding assay to detect changes during incubation. We found that total motility was maintained up to 2 h post incubation, after which it decreased. However, sperm viability remained constant. From that moment on, we observed a transition to a deeper and less symmetrical flagellar bending in many spermatozoa. The CTC assay indicated a reduction in the percentage of sperm showing the full (F) pattern and an increase in those exhibiting the capacitated (B) and reactive (RA) patterns, accompanied by an elevation in the percentage of damaged acrosomes as revealed by the lectin binding assay. In mammals, these changes are often associated with sperm capacitation. Our observations support the notion that this process may also occur in saurian. While sperm analysis is a valuable method for assessing certain functional changes, additional approaches are required to validate this process.

Development and Characterization of a Remanufactured Motorcycle Clutch Hub from End-of-Life Aluminium Alloy

This study aims to employ reverse engineering in the development of the Yamaha CY 80 motorcycle clutch hub using end-of-life (EOL) aluminium alloy obtained from automotive vehicle scraps. The remanufactured motorcycle clutch hub underwent characterization and transient thermal analysis by integrating the geometric and structural features of the clutch hub. The EOL aluminium was thoroughly washed with a sodium hydroxide (NaOH) solution, cleaned with running water, and dried under sunlight to remove impurities trapped on the metal surfaces. The EOL aluminium alloy was melted in a gas furnace, and the molten metal was cast into the clutch hub using a permanent mold designed with the geometric features and characteristics of the Yamaha CY 80 motorcycle clutch hub. The EOL aluminium alloy was characterized using Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). The remanufactured CAD model of the Yamaha CY 80 motorcycle clutch hub was subjected to transient thermal analysis using ANSYS Workbench to predict the thermal behavior of the clutch hub during operation. The FTIR spectra exhibited the following distinctive bands: Al-O stretching modes in octahedral and tetrahedral structures, as well as symmetric bending of Al-O-H, with wavenumbers between 340 and 3131 cm-1 for -OH bonds and between 2109 and 1688 cm-1 for H-O-H bonds. The SEM-EDS micrographs indicated that the two main elements were bromine and silicon. Results from the transient thermal analysis indicated that the minimum and maximum temperatures were 40.109 °C and 250.09 °C within a time frame of 240 seconds. The maximum total heat flux was 30,271,000 W/m2. The compressive yield strength and tensile yield strength obtained in this study were 280 MPa, while the ultimate tensile strength was measured at 310 MPa. The alternating stress levels ranged from 62.05 MPa to 275.8 MPa. This study established that the material is susceptible to fatigue failure, as the alternating stress levels were below the material’s yield strength of 280 MPa.

Microwave dielectric properties, Raman spectra and sintering behavior of novel low loss La7Nb3W4O30 ceramics with rhombohedral structure

This study introduced a novel low-loss tungstate ceramic, La7Nb3W4O30 (LNWO), synthesized using the solid-state techniques. The structural analysis of the La7Nb3W4O30 ceramic material, utilizing X-ray diffraction (XRD) patterns and followed by detailed structural refinement, validated its rhombohedral structure. Transmission electron microscopy (TEM) was utilized to confirm the ordered layer arrangement characteristic of the rhombohedral structure. The internal structure was characterized by scanning electron microscopy (SEM), with the sample's relative density reaching 97.5 %. The correlation between the full width at half maximum (FWHM) of the Raman matrix at 901 cm−1 corresponding to the symmetric bending mode vibrations of WO5 and the Q × f value was discussed. Furthermore, the main factors affecting the dielectric constant, including density, bond valence, secondary phases, and variations in porosity, were analyzed. Encouragingly, the ceramic showed significant microwave dielectric properties when it was sintered at 1425 °C (εr = 23.68, Q × f = 26,687 GHz (f = 7.2 GHz), τf = −35.2 ppm/°C).

The tunneling splittings of the ground state and some excited vibrational states for the inversion motion in H3C− anion and H3Si[rad] radical

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling in the H3C− anion and H3Si radical is analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. We used the following two vibrational coordinates for the H3X structure (X = C, Si): the distance of the X atom from the plane of a regular triangle formed by three hydrogen atoms (1) and a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms (2). The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H3C− at the CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, CCSD(T)/aug-cc-pV5Z, CCSD(T)/CBS(TQ5), CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/t-aug-cc-pVTZ, and CCSD(T)/q-aug-cc-pVTZ levels of theory, based on recommendations from recently published work [M.C. Bowman, B. Zhang, W.J. Morgan, H.F. Schaefer III, Mol.Phys., 117 (2019) 1069–1077]. The same 2D PES for the H3Si radical was calculated at the CCSD(T)/aug-cc-pVDZ CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, and CCSD(T)/CBS(D,T,Q) as well as at the CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVQZ levels of theory. The tunneling splittings for the D3C− anion and D3Si radical were calculated as well. The results of calculations demonstrate good agreement with available experimental data on umbrella vibration frequencies and inversion splittings for the title molecules.

Effect of warp yarn paths on the symmetrical cyclic bending fatigue properties of 3D woven composites

AbstractIn this study, the symmetric cyclic bending fatigue properties of three‐dimensional (3D) woven composites under the condition of R = −1 were investigated. Three types of 3D preform structures with different warp yarn paths were designed, and a bending fatigue testing fixture suitable for 3D woven composites under R = −1 conditions was developed. In addition, the bending fatigue properties, damage mechanisms, and failure modes of three composites were studied. The results showed that the warp yarn paths were responsible for the differences in quasi‐static bending properties. The bending fatigue properties were related to the warp yarn paths and applied stress. Satin woven (SW) structure had the highest bending fatigue failure strain value, followed by the twill woven (TW) structure, and the plain woven (PW) structure had the lowest. The bending fatigue limits of PW, TW, and SW structures were 40% (136 N), 40% (210.5 N), and 16% (119.4 N) stress levels, respectively. The bending fatigue failure mode of 3D woven composites was softening failure under the condition R = −1.Highlights The warp yarn paths significantly affects the quasi‐static bending properties. A symmetrical cyclic bending fatigue testing fixture was developed. The symmetrical cyclic bending fatigue life of 3D woven composites was obtained. SW composites have the highest bending fatigue failure strain value. The symmetrical cyclic bending fatigue failure modes were softening failures.

A miniature piezoelectric actuator with fast movement and nanometer resolution

To accomplish fast movement and high positioning capability, a miniature self-moving piezoelectric actuator (MSPA) is developed with two groups of polyphenylene sulfide (PPS) transducers operating in the symmetric bending (SB) or counter symmetric bending (CSB) vibration. Each group includes the inner and outer legs, whose vibrations are orthogonal and horizontal to the ground, respectively; this interestingly imitates the stepping and swing functions of the forelimbs and hindlimbs of the gorilla in the ‘running on all fours’ gait. To examine the validity, first, by utilizing the model on the basis of Krimhertz transmission theory, the resonant frequency of the CSB vibration was structurally tuned to approach that of the SB vibration. Then, a MSPA prototype with the size of 30 × 45 × 49 mm and the weight of 25.2 g was fabricated to assess the moving, carrying, and positioning performance. In a tethered manner, the MSPA yielded the maximal speed of 562 mm/s (18.73 body length per second), the maximal payload of 485 g (19.25 times of its own weight), and the towing force of 0.5 N (corresponding to the towing force density of 19.8 N/kg). Moreover, it achieved the turning movements (whose directions, angular speeds, and steering radii are changeable) and in-situ rotations, climbed the slope of 12.5°, and moved on the curved floor. In an untethered manner, the MSPA produced the minimal step displacement of 31.9 nm. These results demonstrate that the MPSA possesses the large speed and the nanometer resolution owing to the bionic operating principle and the employment of PPS, and provides a new approach to design lightweight piezoelectric actuators.

Проблема оценки выносливости элементов корпуса низколетящих орбитальных объектов

The paper analyzes the issue of calculating the endurance of the body of lowflying orbital objects from cyclic temperature alternating deformation beyond the limits of Hooke's law. The practical absence of direct calculation methods is stated. An indirect calculation is proposed on the basis of available experimental data on mechanical tests of samples with the «stress» parameter and an algorithm for transition from actual deformations to equivalent stresses. The calculation method is based on the use of the existing experimental fatigue curve under a symmetrical bending cycle, the results of static tensile tests at extreme cycle temperatures, and a generalization of known information about the patterns of changes in the endurance parameters of the material under consideration in relation to the conditions of cyclic temperature alternating deformation. The adequacy of the methodology is verified using the example of depressurization of the housing of the Zarya orbital module of the international space station, made of AMg6 alloy after ≈120,000 cycles of alternating temperature loading. The difference between the calculated and actual endurance of the AMg6 alloy is within the natural range of 20 % during fatigue testing.

Anomalous electron channeling in PZT thin films

The study of the surface of lead zirconate-titanate (PZT) thin films using a scanning electron microscope (SEM) identified the patterns of electron channeling on the surface of the perovskite phase crystals. However, the observation conditions were completely uncommon and contradicted model representations. Thus, there was enough evidence to believe that the observed patterns of electron channeling were an anomaly. It was necessary to conduct an additional detailed study of the perovskite crystal in a PZT thin film in order to clarify which conditions could cause this anomaly. In particular, the method of electron backscatter diffraction (EBSD) in SEM was used to study the crystallographic specific features of the crystal. The method is based on the collection and automatic processing of electron diffraction patterns which calculate a corresponding crystallographic orientation for each point on the scanned crystal surface. As a result, the study revealed the unusual features of the crystallographic structure of perovskite in a PZT thin film that provided an opportunity for the manifestation of anomalous electron channeling. The research showed that the crystal lattice of perovskite experienced an axially symmetric monotone bend, which determined the round shape of the crystal. The study demonstrated the possibility of producing ferroelectric crystals with a curved crystallographic surface. In order to describe the growth of round perovskite crystals from the amorphous phase in PZT thin films, the author provided a dislocation model where the continuous bending of the perovskite crystal lattice could be explained by the accommodationof mechanical stresses with a decrease in the phase volume of the film material. In addition, it was shown that the bands observed in the electron channeling patterns corresponded to crystallographic planes, while any distortions of the pattern indicated a local deformation of the lattice in a highly symmetrical uniformly curved perovskite crystal in a PZT thin film

Dynamic test study of twelve elastic constants of larch timber

The elastic modulus, shear modulus, and Poisson’s ratio of timber are the elastic constants characterizing its material properties. In this paper, the transient excitation method was used to dynamically measure the 10 elastic constants of the falling larch wood under the condition of the free board and cantilever board, that is, 3 elastic moduli E, 3 shear moduli G, and 4 Poisson’s ratios μ. The other two Poisson’s ratios μ were derived using the principle of orthogonality. At the same time, the elastic modulus, shear modulus, and Poisson’s ratio under static conditions were tested and verified by symmetrical four-point bending, asymmetrical four-point bending, and tensile methods. This study is expected to have good application value and practical significance for timber as an engineering structural material, which is widely used in architecture, decoration, furniture, transportation, musical instruments, and in other fields.