Threshold Deformation Research Articles

Optically controllable deformation and phase change in VO2/Si3N4/Au hybrid nanostructures with polarization selectivity

Optically spatial displacement and material modification hold great potential for the appealing applications in nanofabrication and reconfiguration of functional optical devices. Here, we propose and demonstrate a scheme to achieve simultaneous deformation and phase change in vanadium dioxide (VO2)/Si3N4/Au hybrid nanostructures by laser stimuli. Low triggering threshold and significant deformation characteristics of VO2, based on controllable phase transition, are demonstrated in microscale cantilevers. The plasmonic properties of the nanostructure array are further utilized to achieve a polarization-selective dynamic response. The persistence of deformation and dynamical optical modulation are further demonstrated. Such high-precision fabrication methods and non-contact reconfiguration methods are useful for future applications in dynamic optical manipulation.

Modelling the power threshold and optimum thermal deformation of indirectly liquid-nitrogen cryo-cooled Si monochromators.

Maximizing the performance of crystal monochromators is a key aspect in the design of beamline optics for diffraction-limited synchrotron sources. Temperature and deformation of cryo-cooled crystals, illuminated by high-power beams of X-rays, can be estimated with a purely analytical model. The analysis is based on the thermal properties of cryo-cooled silicon crystals and the cooling geometry. Deformation amplitudes can be obtained, quickly and reliably. In this article the concept of threshold power conditions is introduced and defined analytically. The contribution of parameters such as liquid-nitrogen cooling efficiency, thermal contact conductance and interface contact area of the crystal with the cooling base is evaluated. The optimal crystal illumination and the base temperature are inferred, which help minimize the optics deformation. The model has been examined using finite-element analysis studies performed for several beamlines of the Diamond-II upgrade.

Numerical Investigation of Reinforced Concrete Beams with Single and Multi-Longitudinal Hollow Openings

This numerical study was conducted to evaluate the effect of longitudinal hollow openings in reinforced concrete beams. The study was divided into three groups: The first group: was circular holes of different sizes. The second group: different shaped openings (circular, square, rectangular). The third group: the number of openings (one, two, three). Abaqus software was used to analyze the behavior of reinforced concrete beams with hollow openings. The following effects of hollow openings were studied (effect on bending resistance, effect on beam deformations). The results also showed that the presence of hollow openings leads to increased threshold deformations. The results also show that the aperture size has a significant effect on the threshold deformations. Sills with large openings have a greater negative impact on sill deformations compared to sills with small openings. Concrete beams' longitudinal circular hole provides greater load-bearing than rectangular or square slots. Increasing the number of longitudinal holes provides greater load-bearing, but increasing the number reduces the load-bearing. Concrete with longitudinal slots is cheaper and lighter than hollow concrete openings and is used in buildings on a limited budget. Circular slots (10.46% difference) are better than rectangular (18.60% difference) and square (19.76% difference). One hole (10.46% difference) is better than two holes (18.60% difference) and three holes (19.76% difference).

Internal structures and mechanical properties of magnetic gels and suspensions

Abstract We present results of theoretical and computer study of linear chain-like and complicated labyrinth structures in magnetic gels and suspensions as well as effect of these internal structures on macroscopic elastic properties of the composites. Our results show that at a certain threshold deformation, the structures experience a rupture which provokes a fall down of the macroscopic elastic stress, induced by the deformation. This effect is detected for both shear and tensile deformations. The results of calculations are compared with experimental data’s.

3D‐Printed thermoplastic polyurethane/graphene composite with porous segregated structure: Toward ultralow percolation threshold and great strain sensitivity

AbstractLow‐percolation threshold and large deformation capacity are two critical attributes of the strain sensor, which determine its sensitivity and stability respectively. However, endowing these two attributes to the strain sensor simultaneously is still a great challenge in this field. In this work, the strain sensor with the three‐dimensional porous segregated structure constructed by graphene wrapped thermoplastic polyurethane (TPU) particles was fabricated successfully through the selective laser sintering technology. Results demonstrated that the percolation threshold of the composite is only 0.2 wt% and the strain gage factor can reach as high as 668.3, which represents the excellent sensitivity of the strain sensor. Furthermore, after 10 circles of stretching at the 15% strain, resistance‐strain behavior of the strain sensor shows great repeatable, which represents the remarkable stability. Therefore, the highly sensible and stable strain sensor was fabricated successfully, which will provide the guidance for the manufacture of the high‐performance strain sensor.

Mechanical bonding in cold roll-cladding of tri-layered brass/steel/brass composite

Abstract In this paper, brass/steel/brass clad-composite was fabricated using a cold roll-bonding process. Composite sheets were roll-bonded at reduction ratios between 37 and 72% at room temperature from strips of 150 mm in length and 30 mm wide, in one pass without lubrication. The threshold deformation for successful bonding was at a thickness reduction of 48% and peel strengths of the bonds were measured to be approximately 12 N cm-1, and it was found to escalate with an increase in the rolling reduction. The optimum reduction in thickness was ~66% wherein the peel strength was ~33 N cm-1. Various techniques such as optical and electron microscopy were implemented to analyze and investigate the effects of the reduction in thickness and the joining mechanism. The results showed that an increased reduction in thickness in rolling leads to an increase in the joining strength. Furthermore, increasing the brass plate thickness negatively affects the joining strength. A Cu peak on the peeled-off steel surface and the presence of Fe on the peeled-off brass surface strongly suggest that the major bonding between brass and steel was mechanically induced metallurgical bonding.

Mechanical bonding in cold roll-cladding of tri-layered brass/steel/brass composite

Abstract In this paper, brass/steel/brass clad-composite was fabricated using a cold roll-bonding process. Composite sheets were roll-bonded at reduction ratios between 37 and 72% at room temperature from strips of 150 mm in length and 30 mm wide, in one pass without lubrication. The threshold deformation for successful bonding was at a thickness reduction of 48% and peel strengths of the bonds were measured to be approximately 12 N cm-1, and it was found to escalate with an increase in the rolling reduction. The optimum reduction in thickness was ~66% wherein the peel strength was ~33 N cm-1. Various techniques such as optical and electron microscopy were implemented to analyze and investigate the effects of the reduction in thickness and the joining mechanism. The results showed that an increased reduction in thickness in rolling leads to an increase in the joining strength. Furthermore, increasing the brass plate thickness negatively affects the joining strength. A Cu peak on the peeled-off steel surface and the presence of Fe on the peeled-off brass surface strongly suggest that the major bonding between brass and steel was mechanically induced metallurgical bonding.

Parametric Study of Seismic Isolation Properties for Light-Frame Houses

Seismic isolation is a proven technology to protect structures from large earthquakes; however, it has not been extensively implemented in light-frame residential houses in the United States because of perceived high costs, despite the susceptibility of residential houses to earthquake damage. To some extent, the high costs in implementing seismic isolation are associated with the need to accommodate large displacement demands. In this paper, parametric studies of isolation systems with a variety of properties show that a high-friction dish sliding system significantly reduces peak displacement demands compared to conventional low-friction sliding systems at maximum considered earthquake intensity, while limiting isolator restoring force under smaller displacements. Owing to the inherent high strength and stiffness to mass ratios in light-frame structures, nonlinear analyses demonstrate that the story drift ratios in a two-story house with high-friction sliding isolators are below the damage threshold deformation level (<0.2% story drift ratio). A high-friction sliding system with a small restoring stiffness, provided by a large-radius concave sliding surface, is proposed as a cost-effective approach to minimizing the risk of earthquake damage in light-frame residential houses. This approach stands in contrast to typical applications of conventional low-force isolation systems, which are best suited to structures with smaller ratios of strength and stiffness to mass.

Anomalous Refinement of the Austenite Grain upon High-Strain-Rate Hot Deformation of Microalloyed Medium-Carbon Steel

Dynamic recrystallization (DR) of austenite of a medium-carbon steel microalloyed with titanium, niobium, vanadium, and boron has been studied in the course of deformation treatment in the temperature range of 850–1180°C using strain rates of 1–100 s–1. It has been established that the threshold deformation corresponding to the onset of the DR increases in a regular way with increasing strain rate from 1 to 10 s–1 and decreases sharply at 100 s–1. In this case, fine grains (D ≈ 8 μm) are formed, which evidences the occurrence of a specific mechanism of the formation of the austenite structure.

Elastic properties of ferrogels with chain-like structures

The paper deals with theoretical study of shear and tensile elastic properties of ferrogels filled with magnetizable particles, united in linear chains, percolating the sample. It is supposed that a magnetic field is applied along the chains, perpendicular to the shear and parallel to the tension. Our results show that at a certain threshold deformation the chains are ruptured; this break leads to a jump down of the macroscopic stress. This effect is observed for both types of the deformation. The results of calculations are in agreement with experimental data.

Elastic stress in ferrogels with chain aggregates

We propose results of theoretical study of shear and tensile elastic properties of ferrogels filled with magnetizable particles, united in linear chains, percolating the sample. It is supposed that a magnetic field is applied along the chains, perpendicular to the shear and parallel to the tension deformation of the sample. Our results show that at a certain threshold deformation, the chains experience a rupture; this break leads to a fall down of the macroscopic elastic stress. This effect is detected for both types of the deformation. The results of calculations are in agreement with experimental data.

Dynamic Scenarios of the Formation of Martensite with the {110} Habits in the Ni50Mn50 Alloy

Martensitic transformation B2–L10 in the ordered alloy Ni50Mn50, which occurs at comparatively high temperatures (980–920 K), is discussed with the use of dynamic concepts of the wave control of the threshold deformation. The proximity of the observed orientations of martensite-crystal habits (and of twin boundaries) to the planes of the {110} family makes it possible to use the longitudinal waves along the axes 〈001〉 (in the basis of the initial phase) as the driving factors. It is shown that at temperatures of the onset of the transformation there is a satisfactory correspondence between the calculated and experimental data on the tetragonality of martensite and on the volume effect. The opportunity of different dynamic scenarios of the formation of the final phase is noted, namely, of separate crystals; layered structures, in which the crystals of martensite with the identical orientation relationships alternate with the untransformed regions of austenite; and packets of pairwise-twinned crystals. Examples are given of morpho-types corresponding to these scenarios.

Threshold Deformation and Mechanical Properties of Al/Al Laminated-Metal Material with Inner Grooves Fabricated by Hot Rolling

1100 Al/1100 Al laminated-metal material with inner grooves (LMWGs) were fabricated by hot roll bonding. Threshold deformation (the minimum rolling reduction in a single rolling pass that is required for metal bonding) and the mechanical properties of hot-roll-bonded LMWG and cold-roll-bonded LMWG were investigated and compared. The effects of rolling temperature and rolling reduction on the bond strength of the hot-roll-bonded LMWG were also studied. It was observed that the threshold deformation of the hot-roll-bonded LMWG decreased with increasing rolling temperature from 300 to 450 °C. However, the threshold deformations of the LMWGs rolled at 400-450 °C were smaller than those of the LMWGs rolled at room temperature, while the latter were smaller than those of the LMWGs rolled at 300-350 °C. The bond strength, ultimate tensile strength, and yield strength of the hot-roll-bonded LMWG increased with increasing rolling temperature from 300 to 450 °C. The effects of the rolling reduction were slight. When the rolling temperature and rolling reduction were 450 °C and 55%, respectively, the average bond strength reached a maximum value of 89.42 MPa.

Structure Formation of the Nitrogen-Containing Austenitic 04Kh20N6G11M2AFB Steel at Hot Deformation: Part II. Influence of the Phase Composition and Conditions of Hot Deformation on the Process of Dynamic Recrystallization

The impact of δ-ferrite in high-strength corrosion-resistant nitrogen-containing 04Kh20N6G11M2AFB steel on deformation resistance during hot deformation within the temperature range of 900–1200°С and strain rates of 0.1–10 s–1 was investigated. Analysis of diagrams shows that dynamic recrystallization of δ-ferrite steel starts at a lower threshold deformation rate compared with pure austenitic steel. The values of the deformation threshold necessary for the initiation and development of dynamic recrystallization depending on the phase composition of the nitrogen-containing steel were determined. The complex analysis of the structure proved that δ-ferrite contributes to the nucleation and development of dynamic recrystallization at 1200–1000°C (its initiation corresponds to the lowest deformation threshold) and formation of the recrystallized structure in a larger volume as compared with the purely austenitic structure.

Theory of thermo-optic instabilities in dual-core fiber amplifiers.

A coupled-mode theory for nonlinear mode coupling by the thermo-optic effect, originally developed for single-core fiber amplifiers, is applied to the case of dual-core amplifiers. It is shown that a non-phase-matched coupling term, which is usually irrelevant in single-core amplifiers, can strongly affect the mode stability when the coupling length between supermodes exceeds a few centimeters. The phase-mismatched coupling can lead to a strongly reduced instability threshold and static deformation effects for a range of intermediate coupling lengths.

Effect of Cold Rolling Parameters on Bond Strength of Ti Particle Embedded Al Strips

Bond strength of cold roll bonded Al layers with and without Ti particles was studied. The effect of particle’s content that was placed between aluminium sheets and rolling reduction on weld efficiency and bonding was studied. Peel test was used to measure the adhesive strength between the bonded Al strips. The weld efficiency \(\eta\) of the roll bonding process was calculated. The results showed that the weld efficiency in the presence of Ti is lower than that in the absence of Ti. The surface conditions of the peeled surfaces were inspected by scanning electron microscopy. It could be concluded that by enhancing the rolling reduction up to 70%, the bonded area on the interface is increased and bonds with higher strength are produced. However, the addition of Ti particles leads to reduction of the bonded area and bond strength. Also, presence of Ti powders up to 0.5 wt%, lead to the increase of threshold deformation to 45%.

Surface morphology and microstructure evolution of trace titanium and yttrium in W-K-Mo-Ti-Y alloys under transient heat loads

Trace titanium and yttrium (~0.1 wt.%) were doped to the novel W-K-Mo-Ti-Y alloys to investigate their performance under simulated transient heat loads in fusion reactor. The micro-structure, Vickers micro-hardness, cracks formation and surface roughness after transient heat loads were analyzed through X-ray diffraction analysis (XRD), Vickers Micro-hardness device, scanning electron microscopy (SEM) and three dimensional (3D) industrial optical microscope, respectively. It indicated that the transient heat loads would lead to surface cracking and roughening on the loaded surface, as well as a decrease on micro-hardness. Further, trace titanium and yttrium doping in the samples could largely mitigate surface roughening after transient heat loads. Both titanium and yttrium have significant influence on the surface cracking threshold and plastic deformation, indicating the improvement of transient heat loads resistance in this novel alloy.

43. CBCT dose calculation: accuracy assessment of four different methods

Introduction Cone Beam CT (CBCT) images aim at target volume repositioning before treatment fraction. These images may be used for dose calculation in order to dosimetrically quantify anatomical variations that occurs during treatment. The main limits are image quality, Hounsfield numbers (HU) consistency and CBCT reconstruction size. This study aims to assess accuracy of several CBCT dose calculation methods. Methods This study deals with four CBCT (XVI, Elekta) and CT image sets acquired on the same day in context of weekly dose planning of one H&N patient treated with VMAT technique. CT-CBCT sets were used to quantify CBCT dose calculation accuracy by investigating four methods: (i) use of a density to HU relation from phantom CBCT image (phantom HU-D relation), (ii) use of a density to HU relation from patient CBCT image (patient HU-D relation), (iii) density override by three classes threshold (air, soft tissues, bone) and (iv) elastic deformation (Admire, Elekta) between planning CT and CBCT image, by creating a pseudo-CT. After rigid registration, plan characteristics are projected on CBCT images (or pseudo-CT) with Pinnacle v.9.10 (Philips). Dose distribution comparison between CT-based (reference) and CBCT-based calculation was performed by a gamma analysis in 2D and 3D ( γ 2D and γ 3D, criteria: 2%/2 mm, 30% threshold). Then, dose differences were reported in terms of 95% target coverage, parotid glands mean dose (Dmean) and PRV spinal cord maximum dose (D2%). Results On average, γ 3D (percentage of points with gamma The gamma analysis showed location of discrepancy areas: near body contour, regarding shoulders and in presence of heterogeneities ( Fig. 1 ). These differences can be explained by the poor image quality and the HU inconsistency of CBCT images in some areas. The method with pseudo-CT seems to be the best to pass over these issues because densities come from planning CT. Conclusions The four evaluated methods show that dose differences can reach 5% for parotid glands and are lower than 2% for spinal cord and target volumes. The 3D gamma analysis results (2%/2 mm) are higher than 95% for three among four methods. However, additional uncertainties have to be taken into consideration in case of CBCT image delineation and/or calculation on truncated images. This preliminary study shows CBCT dose calculation feasibility to quantify impact of patient anatomical variations during treatment and trigger a new plan based on CT if necessary. The future work is real delivered dose monitoring, based on CBCT image, in perspective of dose guided adaptive radiotherapy.

Early Diagnostics of Damage and Fracture Zones in Composite Materials Using Brittle Strain Gauges and Acoustic Emission

The integrated use of the acoustic emission technique and brittle oxide strain gauges for testing the deformation of damage and fracture zones in samples of polymer composite materials (PCM) at the early phases is considered. For the realization of the proposed technique, integrated parameters were used and software including the cluster analysis and the classification of registered AE pulses was developed, which made it possible to differentiate crack formation signals in the brittle layer of a strain gauge from all the other signals that occur at the early phase of the deformation of PCM samples in the online mode. The use of acoustic emission testing and control video recording for the registration of cracks in a brittle oxide strain gauge with the threshold deformation value of 1000 μm/m provided the precise diagnostics of the forthcoming fracture zone in a sample at the early loading phase under the load level of 10–15% of the limiting one long before the beginning of the active PCM structural degradation phase and made it possible to determine the distribution fields of the highest main deformations in the region of a strain gauge and to perform their quantitative evaluation.

Stress analysis and deformation prediction of sheet metal workpieces based on finite element simulation

After aluminum alloy sheet metal parts machining, the residual stress release will cause a large deformation. To solve this problem, this paper takes a aluminum alloy sheet aerospace workpiece as an example, establishes the theoretical model of elastic deformation and the finite element model, and places quantitative initial stress in each element of machining area, analyses stress release simulation and deformation. Through different initial stress release simulative analysis of deformation of the workpiece, a linear relationship between initial stress and deformation is found; Through simulative analysis of coupling direction-stress release, the superposing relationship between the deformation caused by coupling direction-stress and the deformation caused by single direction stress is found. The research results provide important theoretical support for the stress threshold setting and deformation controlling of the workpieces in the production practice.