Bending Method Research Articles

The effect of in-situ formed layered hBN on the machinability and mechanical properties of SPS sintered SiC

In this study, the relationship between machinability, mechanical properties and microstructure of hBN-SiC composites was investigated. Manufacturing of the composites started with the calcination of raw materials at 850 °C for 16 h under a nitrogen atmosphere prior to mixing with 5 wt% of Al 2 O 3 :Y 2 O 3 sintering additives and then powder mixtures were spark plasma sintered at 1850 °C for 17 min by applying 50 MPa pressure. Characterizations of the samples were carried out with FTIR, XRD, SEM and TEM methods. The physical and mechanical properties of the samples were determined with density measurement, Vickers hardness, Young's modulus, three-point bending, fracture toughness and drill test methods. The amount of in-situ formed hBN phase within the sintered composites was calculated by using the Rietveld method. The physical, mechanical and machinability properties of the composite were evaluated according to the calculated amount of hBN. The highest drilling speed during the test was obtained as 34.24 mm/min for the sample containing 29 wt% of hBN. Increasing the drill load from 19.61 N to 49.03 N resulted in 4.33 times increase in the drilling rate. TEM and STEM studies which were carried out for the microstructural investigations showed the internal defects as delamination bands within hBN phase formed during sintering. In addition to these analyses, novel precession electron diffraction method in TEM was utilized for orientation mapping to investigate any possible orientation relationship between SiC and in-situ synthesized hBN phase.

The three-point off-axis bending method for determining in-plane shear properties in wood

Several methods to determine in-plane shear properties of anisotropic materials (i.e. fiber reinforced composite materials and natural wood) based on flexural loading have been proposed. One of those methods is the off-axis bending test that considers unidirectional composite materials subject to three-point bending (3-PB) loading. As a result of the anisotropic behaviour, unidirectional off-axis laminates subjected to flexure present a bending–twisting coupling that may cause, in the case of three-point bending loading, a lift-off of the specimen on the fixture supports. Such specimen lift-off has been considered one of the critical features to be considered on the mentioned experimental method. Besides, geometrical parameters and material elastic constants (i.e. longitudinal, transversal, and shear elastic moduli) influence the validity to use this method for characterizing in-plane shear properties. On that sense, an analytical approach for studying the material conditions for which the application of the off-axis 3-PB test is adequate to characterize natural wood is presented in this work. The condition of small displacements and the condition of lift-off between the specimen and the fixture supports have been taken into account. Some theoretical ideas regarding stress and displacement fields are also presented. The in-plane shear characterization has been performed on two natural wood species: Norway spruce (Picea abies) and beech (Fagus sylvatica). Test conditions for the off-axis 3-PB experimental bending test, in order to ensure its applicability, are presented.

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The results of a study of the semimetal films deformation produced by dome bending of the substrate are presented. Deformation control was carried out by means of X-ray diffraction analysis. It is shown that the dome bending method can be used to study films under planar deformation in a film-substrate system with different thermal expansion coefficients. The maximum in-plane deformation for bismuth films of 1 mkm thickness order was found. It was shown that the deformation created by the dome bending of the substrate in combination with the use of substrates with different temperature expansion makes it possible to obtain a relative in-plane deformation of bismuth films up to 0.8% at 300 K.

Деформация тонких пленок полуметаллов методом купольного изгиба подложки

The results of a study of the semimetal films deformation produced by dome bending of the substrate are presented. Deformation control was carried out by means of X-ray diffraction analysis. It is shown that the dome bending method can be used to study films under planar deformation in a film-substrate system with different thermal expansion coefficients. The maximum in-plane deformation for bismuth films of 1 mkm thickness order was found. It was shown that the deformation created by the dome bending of the substrate in combination with the use of substrates with different temperature expansion makes it possible to obtain a relative in-plane deformation of bismuth films up to 0.8% at 300 K.

Прочность оптических волокон с органическими покрытиями после воздействия аммиака

A study of the effect of ammonia vapor and solution on optical fibers in acrylate, polyimide and carbon/polyimide coatings was carried out to determine the degree of degradation of the mechanical characteristics of optical fibers in an alkaline environment. The ultimate strength of the optical fibers was measured by the two-point bending method, and the coating condition after interaction with ammonia was monitored with an optical microscope. A decrease in the tensile strength was recorded for all the examined types of protective-strengthening coatings starting from the first hour of exposure. It was determined that after 7 days of exposure to gaseous and aqueous ammonia the structure of quartz glass is completely destroyed.

Design of a robotic system for battery dismantling from tablets

Due to the rapid increase in sales of mobile electronic devices, the number of batteries ending up in waste electric and electronic equipment (WEEE) is also rapidly increasing. According to the EU legislation, all batteries need to be removed from WEEE, which is currently done manually for tablets, posing potential safety risks for workers and resulting in high processing costs due to the labour intensity of the required dismantling operations. Therefore, a robotic dismantling system is developed in this research to automatically remove both the back covers and batteries from a mixed waste stream of tablets of different models and brands. At the outset of the design process, a total of 47 randomly collected tablets were analyzed to define the location of the battery and the required manual dismantling time. Thereafter, a robotic bending method was tested for removing the back cover. Once the battery is exposed, two different methods are tested: using a heat gun to loosen the glue that fixes the battery to the rest of the tablet and a robotic scraping method with a spatula to mechanically extract the battery. Whereas the required time for only the heating showed to be more than 120s, the results with the bending and scraping tool show that the proposed robotic dismantling system is capable of removing the back cover and battery for 63% of the tested tablets in less than 90s. However, to increase the economic viability and robustness of the proposed method to be able to cope with the high variety in tablet model designs, future work is required to develop algorithms to recognize product models to enable to define and retrieve product specific toolpaths for dismantling.

СРАВНИТЕЛЬНЫЙ АНАЛИЗ СХЕМ ОПРЕДЕЛЕНИЯ ДИНАМИЧЕСКОЙ ПРОЧНОСТИ СЛОИСТЫХ КОМПОЗИТОВ ПРИ МЕЖСЛОЙНОМ СДВИГЕ

To determine the mechanical characteristics under conditions of intense dynamic impacts of polymer composite materials during interlayer shear, three experimental schemes were proposed and tested: dynamic three-point bending of a short beam, dynamic compression of specimens-plates with notches, and dynamic extrusion of the middle part of specimens in the form of parallelepipeds. To create shock loads and record the response of the samples, the technique of measuring rods is used. The calculation of forces and displacements is carried out according to the Kolsky formulas according to the data of tensometric measurements. Using numerical simulation, one of the fundamental assumptions and conditions for the applicability of the Kolsky method for determining the characteristics of materials in an experiment on dynamic bending of a short beam, namely, the condition of dynamic equilibrium of the sample during loading, was verified. Approbation of the schemes was carried out on samples of a layered composite material with a polymer matrix reinforced with carbon fiber. A comparative analysis of the data obtained using three different test schemes is given. It is noted that the data obtained by the extrusion method are in good agreement with the data determined during dynamic compression of notched specimens. The strength characteristic, determined by the short beam bending method, turned out to be noticeably higher. It has been found that the interlaminar shear strength values determined in the dynamic range are, on average, 25% lower than the static characteristic. Of the three schemes, the most preferable is the scheme for extrusion of the middle part of the parallelepiped specimen, since, unlike beam bending, it allows you to vary and control the loading conditions, and, unlike testing notched specimens, it is symmetrical, which eliminates the appearance of bending moments in the specimen.

Deformation of Thin Films of Semimetals by the Dome Bending Method of the Substrate

Deformation of Thin Films of Semimetals by the Dome Bending Method of the Substrate

Порівняльна оцінка міцностних характеристик композитів світлової полімеризації для реставрації зубів за методом трьохточкового згину

Purpose: to carry out a comparative analysis of the strength characteristics of composites of swiil polymerization for the restoration of teeth using the threepoint bending method. Results. It was determined that in terms of bending strength, dental composites were arranged in the following order: Tetric N-Ceram (164.44 MPa) < Charisma Classic (141.19 MPa) < Filtek Z250 (129.38 MPa) < Latelux (60.75 MPa). According to the Tukey criterion, the bending strength of the Latelux composite is statistically significantly different from other materials (p < 0.01). At the same time, between the fracture load of composites Tetric N-Ceram and Charisma Classic (p > 0.2), Charisma Classic and Filtek Z250 (p > 0.09), Tetric N-Ceram and Filtek Z250 (p > 0.8) this difference is not significant. Conclusion. In terms of bending strength parameters and elastic modulus, the studied materials meet modern requirements for the strength of hybrid materials, and the Tetric N-Ceram composite has the best performance. Key words: polymer composites, strength, acoustic emission method.

Investigation on the Mixed Mode Fracture Toughness of Freshwater Ice Using the Semi-Circular Bend Method

Investigation on the Mixed Mode Fracture Toughness of Freshwater Ice Using the Semi-Circular Bend Method

Research on Dynamic and Static Test Methods for Evaluating the Poisson’s Ratio of Oriented Strand Board

In this article, dynamic method and static method of testing Poisson’s ratio of OSB (Oriented Strand Board) were proposed. Through modal and static numerical analyses, the position where the transverse stress is equal to zero was determined. The binary linear regression method was applied to express the gluing position of the strain gauge as a relational expression that depended on the length-width ratio and width-thickness ratio of the cantilever plate. Then the longitudinal and transverse Poisson’s ratios of OSB were measured by the given dynamic and static methods. In addition, the test results of OSB Poisson’s ratio were analyzed with the probability distribution of random variables. The results showed that using the proposed dynamic method and static method, the test results for longitudinal and transverse Poisson’s ratios of OSB were quite consistent, despite the gluing position of the strain gauges being different. And these OSB Poisson’s ratios were accorded with that obtained by the axial tensile method and the four-point bending method. OSB longitudinal and transverse Poisson’s ratios followed Weibull distribution.

Experimental and modelling of temperature-dependent mechanical properties of CNT/polymer nanocomposites

Polymer-matrix composites (PMC) reinforced with nanofillers are in constant demand in various industrial applications. Among nano reinforcements, carbon nanotubes (CNT), show a unique combination of physical properties. Often, PMC/CNT composites perform under harsh operating and environmental conditions ranging from aggressive chemical attacks to high temperatures. Material characterization is critical for correct implementation in multifunctional systems. In this study, we have developed two Representative Volume Elements based on the formation of agglomeration above 2 wt% percentage of CNTs. Using finite element analysis (FEA) we studied the mechanical properties of the nanocomposites as a function of temperature. The viscoelastic properties of different percentages of nanofillers (i.e., 0.5, 1, 2, 4, 5 wt%) were derived. Experimental validation was performed with the samples containing the percentages of nanofillers. The samples were tested using Dynamic Mechanical Analysis (DMA) equipment employing the three-point bending method at a fixed frequency. The data shows that the nanofillers drastically influenced the storage, loss modulus and loss factor with a small addition of carbon nanotubes. The viscoelastic properties are presented from temperatures ranging from 40 ℃ to 120 ℃. Finally, a good agreement between the numerical and experimental approaches was found.

Strength and life estimation for assigning the useful life of wheelpairs of high-speed flat wagons

Aim. The most vital unit of railway rolling stock is a wheelpair, as a broken wheel or axle may have catastrophic consequences. Therefore, before the production of a highspeed flat wagon designed for operation at speeds of up to 140 km/h, which is unique for the 1520 mm gauge space, could commence, it was required to research the applicability of the standard wheelpair for high-speed movement. Ensuring the safe operation of a wheelpair involves compliance with the requirements that are to be confirmed by means of assessment of strength and durability parameters [1]. Product conformity assessment may be based on the requirements of standards, whose voluntary fulfilment ensures compliance with [1], or other documents. Methods. The paper describes the computational and experimental methods used for confirming the strength and estimating the life (durability) of wheelpair elements in the probabilistic setting. As experimental data, the authors used the results of full-scale bench testing of wheelpairs for fatigue using the method of rotational bending as it best approximates the loading conditions in operation. The results confirmed the endurance limits of the axle and wheel as parts of an assembled wheelpair. Using design analysis, the authors examined the stress-strain state of the wheelpair caused by installation and operational loads in various running modes. Results. The conducted studies confirmed the wheelpair’s compliance with the requirements of [1–3] in terms of safety factors of fatigue strength and endurance, which eliminates the possibility of hazardous situations in the course of high-speed flat wagon operation. The time to fatigue crack nucleation in wheelpair components was evaluated using the fatigue resistance figures of the parts and equivalent amplitudes of dynamic stress caused by operational loads. It appears that this assessment allows establishing – with the assumed probability of destruction – the assigned useful life of a wheelpair axle at 32 years, which corresponds to the assigned useful life of the flat wagon according to the combined criterion. Corresponding standards and regulations required for developing the container-carrying flat wagon are being updated and a new State Standard is being developed. Conclusion. The conducted conformity assessment established that the flat wagon wheelpair meets the safety requirements of [1] and ensures the absence of unacceptable risks associated with harm to life and health of people, animals and plants, the environment and property of individuals and companies in the course of flat wagon operation.

Mechanical characterization of TiO2 nanowires flexible scaffold by nano-indentation/scratch

Mechanical properties of nanowires (NWs) flexible scaffold biomaterials with open pores and channels are important factors to cell reorganize in growth for tissue regeneration engineering. However, accurate test the mechanical properties of the NWs scaffold is still a challenge because of their flexible property and porous structure. Herein, we measured the mechanical characterizes of TiO2 nanowires (TiO2NWs) flexible scaffold by multi-loads, multi-displacements mixed verification method in nano-indentation/scratch. The results showed that the hardness and Young's modulus of the TiO2NWs flexible scaffold had a certain change rules with a change of the indentation load from 5 μN to 400 μN. Meanwhile, the tangential force of the TiO2NWs flexible scaffold had significantly tensile fracture characteristic under nano-scratch. The multi-loads, multi-displacements mixed verification method by nano-indentation/scratch could be widely applied to measure the mechanical properties of all 3D NWs flexible scaffold nanostructure conveniently and accurately, which is helpful to cover the shortage of bending method for only measure the mechanical properties of 1D nanostructures.

Microstructure evolution and fracture behavior of heat treated enamel coating: Experiment and finite element analysis

The enamel coating (CaO-BaO-MgO-SiO 2 -Al 2 O 3 ) is prepared and performed isothermal oxidation at 900 °C. With the increase of oxidation time, the microstructure and phase evolution of enamel coating are analyzed. Meanwhile, the fracture toughness of heat treated enamel coatings are characterized using the micro-cantilever bending method. The experimental result indicates that the heat treatment can promote the precipitation of oval crystal particles from the enamel itself. With increase of crystallinity, the fracture toughness of heat treated enamel coatings increases from 2.35 to 4.20 MPa·m 1/2 . In addition, finite element method (FEM) with inserting global cohesive elements is adopted to estimate the fracture of micro-cantilever for enamel including elliptical crystals. Both load-displacement curves and failure modes from FEM analyses agree well with those from experiments. Meanwhile, the fracture mechanisms including crack deflection, crack bridging, intergranular and transgranular fracture of the enamel can be revealed. • With the increase of oxidation time, the microstructure evolution and phase of enamel coating are analyzed. • The crystallization of SiO 2 -Al 2 O 3 -CaO-BaO-MgO based enamel coating can improve its fracture toughness. • Finite element method (FEM) with inserting global cohesive elements can simulate the authentic fracture process of enamel coating including crystals. And, this method aids in understanding the fracture behavior of glass-ceramic coating.

Optimization of Machining Parameters for Improving Accuracy of Dimension and Shape of Bent Part in Rotary Draw Bending

This study dealt with the rotary draw bending method most used for tube bending and investigates how applied bending such as normal bending, using mandrels or pressing with booster have an effect on machining accuracy, focusing on dimensional defects due to springback and flat deformation to the transverse plane. The study used particle swarm optimization (PSO) algorithms to investigate the optimal machining conditions for improving the accuracy of dimension and shape of a bent part. The following findings were obtained: The springback during applied machining using a mandrel, or using a mandrel and booster together, is almost the same as during normal processing; The flattening near the center of the bend in applied processing using a mandrel, or a mandrel and booster together, decreases more than with normal processing at mandrel protrusion L ≥ 4 mm, and the maximum can be suppressed to approximately 0.15%; When the sum of the springback and the flattening is taken as the objective function and the minimum value is obtained, the optimal solution is around L = 7 mm.

A New Technique for Curved Rod Bending Tests Based on Digital Image Correlation

BackgroundThe study of the deformation of curved rods subjected to bending and its associated stress state is a complex task that has not been treated in depth in the literature, which makes difficult to obtain constitutive models or Finite Element Models (FEM) in which it is necessary to know all the components of the stress and strain tensors.ObjectivesThis study focuses on a new calculation methodology to obtain stress and strain tensors of curved rods under bending.MethodsThe stress and strain tensors have been determined based on the theory of continuum mechanics and differential geometry of curves (moving bases), in a general methodology and valid for large strains, curved geometries and variable cross-sections along the specimen. This has been applied to the human rib and, in addition, a new experimental method for bending of curved specimens based on Digital Image Correlation (DIC) is presented.ResultsBoth the test method and the proposed calculations applied to the human rib show results according to expectations, allowing to know the rib curvature changes along the test, the stresses and strains along the rib and the components of both stress and strain in all directions, in order to build the stress and strain tensors. In addition, the results of stress, strain and young’s modulus correspond to those of previous literature in tensile testing of human rib cortical bone.ConclusionsThe proposed calculations allow the construction of the strain and stress tensors of a curved specimen subjected to bending, which is of great importance for the development of constitutive models. Moreover, since with this method it is possible to calculate both tensors along the entire length of the specimen and in all directions, it is possible to apply this method in finite element models. Finally, the new test methodology allows to know the stress and strain in curved specimens such as the human rib, from bending tests.

Experimental Study on Single Corner Cold Bending Mechanical Response of Laminated of PVB Interlayer Tempered Glass Panes and the Coupling Effect with Load.

The cold bending method is a type of curved glass curtain wall construction method that has been used in practical engineering for a short time. It has the advantages of simple operation, high efficiency and low cost. However, the mechanical response and properties of glass panes caused by cold bending have not been solved effectively. To study the mechanical response and the properties of cold formed laminated tempered glass panes after applying with a wind load, cold bending and load tests of 9 laminated tempered glass panes were conducted by the orthogonal experimental design method. The effects of cold bending curvature, glass pane thickness and interlayer thickness were considered. In this paper, the response law of cold bending stress to the curvature and the relationship among the influencing factors were analyzed. The variation process of stress, the deflection of cold-formed glass panes under uniform load and the characteristics affected by cold-formed stress and deformation were studied. The results show that the cold bending stress is distributed in a saddle shape, and the curvature has the greatest influence on the cold bending stress, followed by the thickness of the glass panes. The influence of the interlayer thickness is small. The maximum stress appears near the corner of the short side direction adjacent to the cold bending corner. The cold bending stress increases linearly with increasing cold bending curvature. The cold bending stress and deformation have little effect on the change process of the later stage load effect.

Shear-strain-mediated photoluminescence manipulation in two-dimensional transition metal dichalcogenides

In two-dimensional transition metal dichalcogenides, normal strain can modulate electronic band structures, yet leaving the optical selection rules intact. In contrast, a shear strain can perturb the spin-valley locked band structures and possibly induce mixing of the spin subbands which in turn can transfer oscillator strength between spin-allowed bright and spin-forbidden dark excitons. Here, we report a novel scheme to manipulate photoluminescence (PL) in a monolayer WSe2-MoSe2 lateral heterostructures, controlled by an external bending method in which strong out-of-plane shear strain (OSS) of up to 5.6% accompanies weak in-plane normal strain up to 0.72%. The spectra revealed a striking dependence on the bending direction that is stagnant in the negative (compressive) strain region and then rapidly changes with increasing positive (tensile) strain. The dependency of the PL signal under tensile bending was represented not only by the large energy shift (40 meV) of the lowest excited states of both the WSe2 and MoSe2 monolayers, but also by the tendency to violate the optical selection rules that brightens (darkens) the excitons of the WSe2 (MoSe2) side. The analyses on the observed energy shifts and PL intensity changes confirm the different origins in compressive bending compared with tensile bending. The well-established band-anticrossing is identified to be affecting only the compressive deformation region. The spectral changes in the tensile region, on the other hand, originates mainly from the generation of an off-diagonal perturbation to a spin-specific Hamiltonian induced by OSS. The degree of spin-state mixing, which correlates precisely with the spin-flip coefficient of the theoretical model, is further represented by the OSS matrix elements, the spin splitting energy, and the shear deformation potential.

Ray velocity derivatives in anisotropic elastic media – Part I: general anisotropy

SUMMARY We present an original, generic and efficient approach for computing the first and second partial derivatives of ray (group) velocities along seismic ray paths in general anisotropic (triclinic) elastic media. As the ray velocities deliver the ray element traveltimes, this set of partial derivatives constructs the so-called kinematic and dynamic sensitivity kernels which are used in different key seismic modelling and inversion methods, such as two-point ray bending methods and seismic tomography. The second derivatives are useful in the solution of the above-mentioned kinematic problems, and they are essential for evaluating the dynamic properties along the rays (amplitudes and phases). The traveltime is delivered through an integral over a given Lagrangian defined at each point along the ray. In our approach, we use an arclength-related Lagrangian representing a reciprocal of the ray velocity magnitude. Although this magnitude cannot be explicitly expressed in terms of the medium properties and the ray direction components, its derivatives can still be formulated analytically using the corresponding arclength-related Hamiltonian that can be explicitly expressed in terms of the medium properties and the slowness vector components; this requires first to obtain (invert for) the slowness vector components, given the ray direction components. Computation of the slowness vector and the ray velocity derivatives is considerably simplified by using an auxiliary scaled-time-related Hamiltonian obtained directly from the Christoffel equation and connected to the arclength-related Hamiltonian by a simple scale factor. This study consists of two parts. In Part I, we consider general anisotropic (triclinic) media, and provide the derivatives (gradients and Hessians) of the ray velocity, with respect to (1) the spatial location and direction vectors and (2) the elastic model parameters. The derivatives are obtained for both quasi-compressional and quasi-shear waves, where other types of media, characterized with higher symmetries, can be considered particular cases. In Part II, we apply the theory of Part I explicitly to polar anisotropic media (transverse isotropy with tilted axis of symmetry, TTI), and obtain the explicit ray velocity derivatives for the coupled qP and qSV waves and for SH waves. The derivatives for polar anisotropy are simplified (as compared to general anisotropy), obviously yielding more effective computations. The ray velocity derivatives are tested by checking consistency between the proposed analytical formulae and the corresponding numerical ones.