Coupled InGaAs Quantum Dots for Electro-Optic Modulation

We investigated the growth of vertically coupled In0.75Ga0.25As quantum dots (QDs) by varying the GaAs spacer thickness (d). Vertically-aligned triple-layer QDs of uniform size and highest accumulated strain are formed with d = 5 nm. The electroluminescence (EL) characteristics for In0.75Ga0.25As QDs show an emission spectrum at optical wavelength (λ) of 1100−1300 nm. The EL spectra exhibit the highest optical gain at λ ~ 1200 nm, and the narrowest FWHM = 151 nm of the sample with d = 5 nm at injection current = 20 mA. Fabry–Perot measurements at λ = 1515 nm of TE and TM polarizations were carried out to investigate the electro-optic modulation for a single-mode ridge waveguide consisting of vertically-coupled triple-layer In0.75Ga0.25As QDs (d = 5 nm). The linear (r) and quadratic (s) electro-optic coefficients are r = 2.99 × 10−11 m/V and s = 4.10 × 10−17 m2/V2 for TE polarization, and r = 1.37 × 10−11 m/V and s = 3.2 × 10−17 m2/V2 for TM polarization, respectively. The results highlight the potential of TE/TM lightwave modulation by InGaAs QDs at photon energy below energy band resonance.

Responses of frozen fine-grained soils due to multiple packets of cyclic stress with variable-amplitude and an empirical prediction model

A suite of stress-controlled cyclic triaxial tests were performed on frozen fine-grained soils to assess the characteristics of the accumulated and cyclic behaviours under packets of cyclic stress with variable-amplitude. The influence of cyclic stress sequences is highlighted, and the results of the variable-amplitude cyclic tests indicate that the applied cyclic stress amplitude sequence is of significant importance regarding the final accumulated deformations. A step change is observed in the accumulated strain when the applied cyclic stress amplitude is beyond that of the previous stress package, while a decreasing level of cyclic stress below the previous loading package results in slight additional strain accumulation. The results of these tests also indicate that the cyclic stiffness is dependent on both the past accumulated strain and the current cyclic stress amplitude. For frozen soil, a higher past accumulated strain and lower cyclic stress levels yield a higher cyclic stiffness. An empirical approach for representing the response of frozen fine-grained soils under multiple packets of cyclic loading are proposed and then verified by the test data. The results show that the proposed empirical model is able to extract and predict the accumulated and cyclic behaviours under multiple packets of cyclic loading.

Strains under Angular Pressing of a Strip from a Cylindrical Billet

The scheme of non-equal channel angular pressing (non-ECAP) of a magnesium billet has been analyzed. The modeling was performed by DEFORM-2D software. A high level of strain is shown to be achieved during non-ECAP. It leads to more homogenous structure refinement of magnesium and plasticity improvement that could favorably affect the subsequent deformation of a Mg-strip by cold rolling. At non-ECAP-process, the upper part of the strip is noted to be hardened more than the lower one. The lower part is supposed to be formed by extensional strain mainly, meanwhile for the upper one, the prime mechanism is likely to be shear strain. Based on hardness measurement of the samples cut from the obtained Mg-strip, conclusions have been made about the influence of the accumulated strain during non-ECAP on the strength properties of the strip.

A Soft Pressure Sensor Array Based on a Conducting Nanomembrane

Although skin-like pressure sensors exhibit high sensitivity with a high performance over a wide area, they have limitations owing to the critical issue of being linear only in a narrow strain range. Various strategies have been proposed to improve the performance of soft pressure sensors, but such a nonlinearity issue still exists and the sensors are only effective within a very narrow strain range. Herein, we fabricated a highly sensitive multi-channel pressure sensor array by using a simple thermal evaporation process of conducting nanomembranes onto a stretchable substrate. A rigid-island structure capable of dissipating accumulated strain energy induced by external mechanical stimuli was adopted for the sensor. The performance of the sensor was precisely controlled by optimizing the thickness of the stretchable substrate and the number of serpentines of an Au membrane. The fabricated sensor exhibited a sensitivity of 0.675 kPa−1 in the broad pressure range of 2.3–50 kPa with linearity (~0.990), and good stability (>300 Cycles). Finally, we successfully demonstrated a mapping of pressure distribution.

Meaningful interpretation of algebraic inequalities to achieve uncertainty and risk reduction

The paper develops an important method related to using algebraic inequalities for uncertainty and risk reduction and enhancing systems performance. The method consists of creating relevant meaning for the variables and different parts of the inequalities and linking them with real physical systems or processes. The paper shows that inequalities based on multivariable sub-additive functions can be interpreted meaningfully and the generated new knowledge used for optimising systems and processes in diverse areas of science and technology. In this respect, an interpretation of the Bergström inequality, which is based on a sub-additive function, has been used to increase the accumulated strain energy in components loaded in tension and bending. The paper also presents an interpretation of the Chebyshev’s sum inequality that can be used to avoid the risk of overestimation of returns from investments and an interpretation of a new algebraic inequality that can be used to construct the most reliable series-parallel system. The meaningful interpretation of other algebraic inequalities yielded a highly counter-intuitive result related to assigning devices of different types to missions composed of identical tasks. In the case where the probabilities of a successful accomplishment of a task, characterising the devices, are unknown, the best strategy for a successful accomplishment of the mission consists of selecting randomly an arrangement including devices of the same type. This strategy is always correct, irrespective of existing uknown interdependencies among the probabilities of successful accomplishment of the tasks characterising the devices.

Specific of the Recrystallization Driving Force Calculation on the early Stages of Thermomechanical Treatment of Aluminum Alloys

The article investigates the effect of the strain rate on the driving force of recrystallization during hot working of the as-cast structure. For the study, we applied previously obtained experimental data of recrystallization kinetics during this stage of thermomechanical treatment. In addition, hot laboratory rolling, followed by saltpeter bath soaking, were performed in order to obtain supplemental data on grain structure size and orientations. Grain structure size was examined by optical microscopy, and its orientation was examined by X-ray texture analysis. The studies demonstrated, that overestimated recrystallization driving force not only results in erroneous kinetics estimation, but also gives excessive number of recrystallization centers and undersized grain structure. Besides, unaccounted effect of recrystallization driving force on grain size leads to distorted predictions of texture composition. In order to avoid this, it was recommended to apply an special exponential accumulated strain dependent coefficient.

Adaptive Affine Homogenization Method for Visco-hyperelastic Composites with Interfacial Damage

Despite intense research on the homogenization methods, it still is a challenging task to predict the nonlinear mechanical responses of visco-hyperelastic particulate-reinforced composites. In this work, we propose the adaptive affine method, a novel mean-field homogenization method designed to ensure the consistency of the accumulated strain state and the concentration tensor, and apply the method to predict the mechanical response of the composite in the large strain regime under uniaxial, cyclic, and bi-axial loadings. Our method is also extended to predict the mechanical response in the presence of interfacial imperfections described by linear cohesive traction-separation laws. The analytic predictions are validated against finite element analyses of representative volume elements. We believe that our adaptive affine method can be extended to model various nonlinear responses of load-bearing composites including the effects of (visco)plasticity and finite deformation.

Analysis of deformation characteristics of Asymmetric Gradient Extrusion in preparing ultra-fine grained bulk materials

A novel method to prepare ultra-fine grained bulk materials, which is named Asymmetric Gradient Extrusion (AGE), is proposed in this article. In AGE, the cross section of extrusion channel is rectangle and two inclined planes are stagger arranged along extrusion direction. To realize repeating extrusion, the thickness of workpiece is restricted to equal the width of channel’s outlet. The deformation characteristics of AGE was first theoretically analyzed by slip line field. Then, these results were verified and supplemented by finite element analysis. The results reveal that deformation characteristics of workpiece in channel is largely related to the two inclined planes. Two independent deformation zones (TIDZ) can be formed with increasing distance between the two inclined planes. In addition, the accumulated strain generated in the TIDZ is complementary in value. Furthermore, the shearing effects of workpiece subjected in one pass extrusion has been improved. A more uniform strain distribution and higher shearing effect can be generated in AGE, which make it as a very promising method to produce ultra-fine grained bulk materials.

Testing the Cross-Sectional Microhardness in Sheets with A 0.08% Carbon Concentration

The research team studied the hardness of cold-rolled sheets of varying thicknesses containing 0.08% carbon. Greater thickness correlated with lower mean hardness. The hardness was found to drop in the middle of a plate and to increase gradually towards the edges. This pattern was observed regardless of the thickness of thin cold-rolled sheet steel. The change in hardness may indicate uneven accumulated strain in the sheets rolled to a desired value. Pre-hardened sheets were analyzed to find whether the hardness was homogeneous through the thickness. The material was hardened by axial tensioning. Analysis showed that at greater accumulated strain, the through-thickness hardness was affected as well. However, the difference was less pronounced at the edge as well as in the middle of sheets. The paper shows graphs of the hardness distribution through thickness.

Evaluation of efficiency of methods for drawing round wire with large diameters

Drawing in monolithic draw dies is the primary and often nonalternative pressure metal treatment (PMT) method used in the wire manufacture for various purposes both in our country and abroad. Its effectiveness largely depends on the wire diameter and properties. Thus, when drawing wire of large diameters (>8.0 mm) from high-carbon steels (high-tensile reinforcing wire, spring wire, etc.), the stability of the process and the probability of metal fraction decreases. The use of classic roller draw dies increases the strain uniformity along the wire cross-section, reduces the force and multiplicity of drawing. However, the «circle-shaped section-circle» roller gauge system used in this process leads to a more complicated process, and most importantly, to a significant increase in production costs. In this paper, a comparative analysis of the drawing efficiency of a round billet with a diameter of 16.00 mm from steel grade 80 into a wire with a diameter of 14.25 mm (strain degree 21%) in one step in the classic monolithic draw die and roller draw dies: three-roller draw die with a spatially closed round gauge and three-roller draw die of radial shear strain. The latter is comparable to the well-known radial-shear rolling. The difference is that the energy is introduced into the deformation zone by applying a front pulling force, and the idler rollers rotate around the wire with a special drive. The authors used finite element modeling in the Deform-3d software package. The deformed state in processes with linear tensile strain was estimated by the distribution of the accumulated strain degree in the billet cross-section, and in processes with torsion – by the change in the curvature of the line applied to the side surface of the billet. The power parameters were determined in Deform-3d in the coordinates: drawing force – time of billet movement. The stress state was determined by the hydrostatic stress on the wire axis and the Cockcroft-Latham fracture criterion. It is established that the wire strain in a monolithic draw die is characterized by a significant strain inhomogeneity across the cross-section, monotonous flow, high energy consumption, and the wire collapsibility, especially of the mid-layers. The use of draw dies with a spatially closed round gauge reduces the drawing force by about 40%, reduces the degree of strain inhomogeneity along the cross-section, and increases the degree of accumulated strain. The radial-shear strain drawing significantly increases the degree of accumulated strain and provides grain grinding, especially in the surface layers of the wire.