Small Size Scale Research Articles

Grain size-dependent tensile behaviour in a metastable beta titanium alloy

The present study investigates the effect of beta grain size on the stability of the beta phase in terms of trigger stress and the resultant mechanical properties of metastable beta titanium alloy. The trigger stress has a complex U-shaped relation concerning the beta grain size, which could be due to alternant mechanisms from interface friction and elastic energy. Nevertheless, the residual stress/strain could affect the trigger stress in the small grain size scale. More interestingly, dominant deformation modes are altered by a change of grain size with predominant stress-induced martensite (SIM) at small grain size and prime dislocation at large grain size, leading to grain size-dependent tensile behaviour of a metastable beta titanium alloy.

A cascaded combination method for defect detection of metal gear end-face

Defect detection plays an important role in implementing zero-defect manufacturing (ZDM) and improving the sustainability of manufacturing systems. The remarkable diversity of gear types, the inhomogeneity of end-face structure, as well as the small size and multi-scale of defects, are the common problems confronted during the metal gear end-face defect detection, which leads to poor performance of existing detection methods in terms of detection rate and accuracy. To address the problems above, this study proposes a cascaded combination method SR-ResNetYOLO to automatically detect the defects by region extraction and multi-scale fusion of sampled features under 16X. To obtain more effective features, this study proposes the visual-saliency-based method to extract the machined area image, eliminating the interference between the invalid features of non-machined areas and edge burrs and reducing thereby the image complexity. Subsequently, establish a 16X down-sampled feature extraction backbone network (ResNet-21), to efficiently obtain the high-resolution features of the defects by using the machined area images as input. With the multi-scale fusion module, the min-scale feature map, output by the ResNet-21, fuses at the medium- and large-scales. Finally, the three-fused-scale feature maps are classified and located by the location and classification module. The proposed method achieves satisfactory performance in terms of the mAP and recall rate, which are respectively 96.66% and 97.07%, and the average computation time of the detection for per image is 0.12 s, which can effectively detect small size and multiple scale defects of metal gear end-face.

An exact method for job sequencing in a mixed-model assembly line considering feeding lines based on the Benders decomposition approach

ABSTRACT The study proposes an exact method based on the Benders decomposition approach to solve the sequencing problem of the mixed-model assembly line considering feeding lines. A mathematical model is presented and linearized that is capable of solving the small-size scales of the problem. Since the problem is well known as a strongly NP-hard problem, appropriate methods can improve the effectiveness of the outcomes of the model. Therefore, we introduce a Benders decomposition method, which can solve the proposed problem on the medium and large scales. Moreover, a proper accelerator is presented to enhance the performance of the proposed method and to reduce computational time. The outcomes show that the proposed method can provide solutions with a maximum of 4.47% deviation from the optimal for small-scale instances. The result indicates the success of this exact method in solving the problem with different dimensions. In addition, comparing results emphasized that the accelerator used can reduce iterations up to 24% to provide the final solution.

Pressure-Gradient Current at High Latitude from Swarm Measurements

The pressure-gradient current is among the weaker ionospheric current systems arising from plasma pressure variations. It is also called diamagnetic current because it produces a magnetic field which is oriented oppositely to the ambient magnetic field, causing its reduction. The magnetic reduction can be revealed in measurements made by low-Earth orbiting satellites flying close to ionospheric plasma regions where rapid changes in density occur. Using geomagnetic field, plasma density and electron temperature measurements recorded on board ESA Swarm A satellite from April 2014 to March 2018, we reconstruct the flow patterns of the pressure-gradient current at high-latitude ionosphere in both hemispheres, and investigate their dependence on magnetic local time, geomagnetic activity, season and solar forcing drivers. Although being small in amplitude these currents appear to be a ubiquitous phenomenon at ionospheric high latitudes characterized by well defined flow patterns, which can cause artifacts in the main field models. Our findings can be used to correct magnetic field measurements for diamagnetic current effect, to improve modern magnetic field models, as well as to understand the impact of ionospheric irregularities on ionospheric dynamics at small-scale sizes of a few tens of kilometers.

Small-scale size effects on the shearing behavior and sliding stiffness reduction-displacement curves of rock-plastic gouge simulant under low normal stresses

Assessment of the influence of laboratory specimen size (and scale effects) is critical to be obtained in the study of geological structures. The present work examines the influence of the small-scale size of specimens (in the range of a few tens of millimeters) on the behavior of analogue discontinuities with highly plastic clay filling material using a custom-built apparatus. The results showed that the displacement required to reach the peak friction increased with the specimen size, while the shearing stiffness showed an opposite trend. A slight increasing tendency of peak friction with increasing specimen size was also observed, but it needs further testing to be assertive. The weakening behavior in the gouge layer increased at larger normal stresses leading to significant post-peak softening, which was intensified as the gouge layer size increased. Application of pre-consolidation to the gouge layer intensified the weakening behavior. The degree of non-linearity in the stress-displacement curves and rigidity of the specimens were also quantified, and a hyperbolic-type model was implemented to measure the shear stress mobilization rate based on the stress-displacement curves. The data were further integrated with that from previously published works on experiments at smaller and larger scales to enhance the findings from this work on scale effects on the mechanical behavior of geological structures.

A damage model for granite subjected to quasi‐static contact loading

AbstractAn anisotropic damage model is employed in order to simulate the fracture pattern of Bohus granite under quasi‐static (Q‐S) spherical indentation loading. The chosen damage description is added to the previously employed Drucker–Prager (DP) plasticity model with variable dilation angle. The resulting constitutive model is implemented to simulate the behavior of Bohus granite under indentation up to the load capacity of the material. The initial fragmentation, corresponding to the first small load‐drop in the force–penetration curve, is likely due to the high radial tensile stress state at or close to the contact boundary. Both predicted fracture pattern and force–penetration results from the numerical simulation are compared to experimental data and a good agreement is found. The variability in tensile strength of the material is included in the chosen damage model by taking advantage of Weibull statistics. In this work, it is suggested that indentation test results by themselves may be used to calibrate the statistical distribution of tensile strength at small size scales such as in indentation applications.

Experimental Study on Failure Mechanical Properties of Two Kinds of Seafloor Massive Sulfides

Remarkable hydrostatic pressures have a significant effect on the failure mechanical properties of seafloor minerals, which also affects the selection and development of mining excavation tools. In this paper, a Brazilian splitting test and triaxial compression test were adopted to investigate the strength and deformation behavior of two kinds of seafloor massive sulfides (SMS) samples at a small-scale size. Based on the mineralogical characterization of the studied samples, the mechanical properties were preliminarily correlated with their internal structures and mineral compositions. Results indicate that there is a significant difference in the triaxial compression deformation properties between the two kinds of SMS samples and the geotechnical data are controlled by mineral type and composition, including porosity. In general, the triaxial compression process of the two kinds of samples included initial compaction, elastic stage, yield stage, failure stage and residual stage, and shows strain softening characteristics after the peak. With the increase in confining pressure, the strain-softening behavior of the white sample is mitigated and gradually changes into strain-hardening. The peak strength and peak strain of the two samples increased linearly with the increase in confining pressure within the confining pressure range of these tests, and the failure pattern of the specimens also changed from a typical brittle failure to a ductile failure. The results of this study provide data to support further understanding of different kinds of SMS, and are of great significance in the design of efficient SMS exploitation equipment.

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Tiny yet tough: Maximizing the toughness of fiber-reinforced soft composites in the absence of a fiber-fracture mechanism

Humidity-controlled direct ink writing for micro-additive manufacturing with water-based inks

Direct-ink-writing type additive manufacturing with water-based inks such as hydrogels or polymer solutions is broadly utilized for bioprinting applications. However, the resolution of this implementation is limited due to the rapid ink drying experienced at small size scales leading to nozzle clogging and low fidelity prints. To address this issue, a humidity-controlled direct-ink-writing (HCDIW) approach is presented, where the microenvironment around the printing nozzle is controlled through introduction of aerosolized water. Using this approach, the nozzle microenvironment can be varied between undersaturated yet high relative humidity (ambient to 100% RH) to oversaturated conditions where condensing droplets are deposited on the already printed ink filaments. The influence of the aerosolized water and the resultant micro-environment on the printing process was studied using water dissolved sodium carboxymethyl cellulose (NaCMC) ink, specifically focusing on nozzle clogging, printed filament geometry, surface quality and layer by layer stacking. These studies showed that the ink drying induced nozzle clogging issues can be mitigated through increased relative humidity at the nozzle exit and is virtually eliminated for ~100 μm nozzles in oversaturated conditions. The decelerated ink drying under the effect of aerosolized water leads to reduced solute advection and skin formation. This in turn improves surface roughness while reducing adverse effects such as coffee-ring and void formation during additive manufacturing of micro-scale structures. Furthermore, layer-to-layer fusion and associated side-surface quality were improved specifically in undersaturated conditions. Reduction of deposited ink filament concentration in oversaturated conditions leads to excessive spreading of the deposited inks leading to geometric distortions. These results indicate that the humidity control approach can significantly improve the resolution of the direct-ink-writing approaches, enabling processing of water-based inks at micro-scales.

Vibration Actuator System with Small-Scale Size Capable of Visual Inspection of Large Complex Iron Structures

Deterioration of social infrastructure equipment has become a major problem in countries around the world. In the present study, a novel vibration actuator system capable of movement on an iron structure having complicated surfaces, such as steps, is proposed. A vibration actuator capable of reciprocating movement with a small-scale size was prototyped and tested. In consideration of mobility, the size of the vibration actuator is designed to be smaller than 50 mm and the total mass is lighter than 20 g. The experimental result demonstrates that the maximum efficiency of the vibration actuator was 28.1%, and the maximum pulling power was 1.8 N. Furthermore, a vibration actuator system in which two vibration actuators and a wheel having a magnetic force connected by a flexible silicone rubber material was prototyped. This actuator system can move over a step of 48 mm in the horizontal plane and 25 mm in the vertical plane without control. Finally, a machine test was conducted on the frame surface moving, which is difficult even for robots. This actuator system can move at an average speed of 12.1 mm/s within the frame.

Size, shape and orientation of macro-sized substrate protrusions affect the toe and foot adhesion of geckos.

Geckos are excellent climbers using compliant, hierarchically arranged adhesive toes to negotiate diverse terrains varying in roughness at multiple size scales. Here, we complement advancements at smaller size scales with measurements at the macro scale. We studied the attachment of a single toe and whole foot of geckos on macroscale rough substrates by pulling them along, across and off smooth rods and spheres mimicking different geometric protrusions of substrates. When we pulled a single toe along rods, the force increased with the rod diameter, whereas the attachment force of dragging toes across rods increased from about 60% on small diameter rods relative to a flat surface to ∼100% on larger diameter rods, but showed no further increase as rod diameter doubled. Toe force also increased as the pulling changed from along-rod loading to across-rod loading. When toes were pulled off spheres, the force increased with increasing sphere diameter as observed for along-rod pulling. For feet with separated toes, attachment on spheres was stronger than that on rods with the same diameter. Attachment force of a foot decreased as rod and sphere size increased but remained sufficient to support the body weight of geckos. These results provide a bridge to the macroscale roughness seen in nature by revealing the importance of the dimension, shape and orientation of macroscale substrate features for compliant toe and foot function of geckos. Our data not only enhance our understanding of geckos' environmental adaptive adhesion but can also provide inspiration for novel robot feet in development.

Dynamic and static isogeometric analysis for laminated Timoshenko curved microbeams

An effective computational approach that can simultaneously deal with several complexities in geometries, material properties, and size effects is of non-trivial yet important tasks for the design and optimization of device components in micro- and nano-electromechanical systems. This study is devoted to the development of such an effective computational approach, which is formed by integrating the modified couple stress theory into isogeometric analysis framework. The proposed approach is applied to mechanical problems of laminated Timoshenko curved microbeams, i.e., anazlying static bending, natural frequency and transient response. The developed method enables to describe and examine nontrivial features in both material and geometrical properties of laminated curved microbeams. Geometries of curved microbeams and displacement approximation are accurately described by the non-uniform rational B-spline basis functions. For laminated composites, the material coupling is taken into account with the use of equivalent elastic modulus; and the deepness term is properly included in laminate stiffness parameters. In addition, the small-scale size effects are captured with the use of modified couple stress theory. The accuracy and performance of proposed method are demonstrated through several numerical examples, in which the static bending, free vibration and transient response of laminated curved microbeams are considered under effects of some factors such as aspect ratios, lay-ups, boundary conditions and size dependence.

Flexural wave and vibration properties of nanotubes conveying fluid

The flexural wave and vibration properties of carbon nanotubes (CNTs) conveying fluid are studied by considering van der Waals (vdW) interactions between the nanotube surface and the fluid. Based on the modified model, the exact dispersion and eigenvalue relations are derived, and the corresponding wave and dynamic properties are calculated and discussed in details. The results show that the wave and vibration properties of the fluid‐conveying nanotubes with allowance for the nanotube‐fluid vdW interactions are significantly different from those predicted based on the conventional models. These properties can provide a better understanding on the relationships between the flexural waves/vibrations and the flow velocities of the fluid‐conveying components at small size scale level and to design stable nanotube‐based nanofluidic channels. In addition, the dynamic properties calculated herein by the exact dispersion and eigen equations can also serve as benchmark solutions for verifying results obtained by other approximate approaches.

Investigating the fatigue behaviour of small scale and real size HFMI-treated components of high strength steels

The present study reports on results of a completed research project, which investigated amongst others the fatigue strength of weldments made of structural steels S355J2+N, S690QL and S960QL and treated with the post-weld treatment process High Frequency Mechanical Impact (HFMI). Reference tests on as-welded (AW) specimens, which were manufactured from the same material batches, were carried out in order to enable a direct comparison. Main goal of the present tests series was, apart from the revalidation of the higher efficiency of HFMI on high strength steels, to investigate possible scale effects, when the post-weld treatment method is applied on real size structural components. Therefore, usual fatigue test specimens and real size structural beams HEA 260 were tested. The welded structural detail of transverse stiffeners was investigated in all cases. All results are evaluated with the nominal stress approach and they are presented in S-N curves along with the respective FAT classes, which are proposed by the design guidelines of Eurocode and the recommendations of International Institute of Welding (IIW). Beach mark tests were carried out on HFMI-treated small scale fatigue test specimens, in order to investigate the influence of HFMI on the fatigue crack growth behaviour (FCG). In all cases, a significant increase in fatigue strength was achieved by the application of HFMI with the fatigue life extension being more significant for the high strength steels. No scaling effect was documented regarding the application of the method on the structural beams having similar plate thicknesses as the small scale specimens but more complex geometries and significantly longer weldments. Finally, the evaluation of the beach mark tests and their comparison with reference curves found in literature did not allow a clear assessment of the HFMI influence on the fatigue crack propagation (FCP).

Ultrasonic Nondestructive Testing Method for Mechanical Properties of Metallic Nanomaterials

For metallic nanomaterials, the small size scale of nanoparticles leads to a significant increase in their surface area, resulting in a series of new mechanical properties. In order to detect the mechanical properties of metal nanomaterials, a new ultrasonic nondestructive testing method is proposed. Using defocusing measurement and time discrimination method, the surface wave velocity of metal nanomaterials at different positions and angles was measured, and the mechanical properties at corresponding positions and angles were obtained. The experimental results show that the new ultrasonic nondestructive testing method can accurately characterize the mechanical properties of metal nanomaterials without causing damage to the tested objects.

How does transition to secondary school influence home, school and community play?

AimThis study gathered views of 10 to 12-years-old pupils about their play experiences before and after transition to secondary school, comparing access to their right to play.MethodA multiple-case study design was used to gather views of six Year 6 primary pupils and six Year 7 secondary pupils living in the same community in the United Kingdom (UK). Six workshops, including a focus group, were conducted with each year group.FindingsQualitative data from both focus groups were analysed thematically, individually and across year groups. Findings indicated that temporal, spatial and psychological factors affected both Year 6 and Year 7 pupils’ play access. Year 6 pupils were more satisfied with their play opportunities and reported more time to play.LimitationsThe small-scale size of this study limits drawing conclusions. Data were collected in the summer term and therefore the weather and point in the school year may have been influential.ConclusionsFindings suggested that, for the pupils involved, play opportunities appeared to decrease upon transition to secondary school. It is therefore important that barriers to play across age groups are considered and addressed, to ensure that all children can realise their right to play. Educational psychologists (EPs) can raise awareness of the benefits of play and the potential impact of limited play opportunities for older children.

Size effect characteristics of structural surfaces by improved projective covering method

Accurate characteristic of structural surfaces roughness at the relevant scale is very important to understand mechanical properties of rock mass discontinuities. So, a systematic investigation has been carried out to understand the effect of scale on the structural surface roughness by fractal dimension method. Firstly, considering the shortcoming of the projective covering method (PCM), we improved this method based on stochastic approach. Secondly, to investigate the size effect of the structural surface roughness, we selected six sampling windows, respectively, from the central and four corners part of structural planes (2 m × 2 m). The sampling windows range from 62.5 mm × 62.5 mm to 2000 mm × 2000 mm. And then, we calculated fractal parameters of the different size surfaces using improved projective covering method (IPCM) at the same resolution. Thirdly, we discussed a new method of determining reasonable size of structural surfaces by the parameter Delta D_{max }^{SD}. This parameter is difference of the maximum fractal dimension of the same size structural surface in different regions. The results show that: (1) The size effect of structure surfaces is different with different morphological surface. Generally, as the size increases, the roughness of structure surfaces increases and then decreases. There is positive size effect in small scale and negative size effect in large scale. (2) For a given structural surface, when the same size surfaces are selected from different locations of the structural planes, and the size effect characteristics are also different. (3) As the size of structure surfaces increases, the parameter Delta D_{max }^{SD} gradually decreases and tends to almost constant. The result of this study is a useful supplement to the comprehensive understanding of the size effect of structural surfaces roughness.

Magnetic field causes the strong and weak nuclear forces and is the GUT force

The Scalar Theory of Everything (STOE) suggests the four fundamental forces are emergent properties of the magnetic field of permanent magnets. The STOE postulates the fractal (self--similar) principle that suggests small size scales are similar to our everyday size scale. Thus, the assembly of permanent magnets into a sphere is similar to a nucleon. The magnetic force from the sphere varies as the inverse cube of the distance from the center of the sphere (nucleon) which is approximately exponential, it has short range attractive field, it is an assembly of gluons (short photons), it explains the one proton to one electron atomic structure despite the large difference in mass, it suggests a size limit to the nucleon, it reminds of strong and weak forces, and it suggests a structure of the nucleus has protons on an outside shell. The STOE has the feature of the other sense of a ``Theory of Everything'' - that of a ``Grand Unified Theory'' (GUT).

A Feature-Enhanced Anchor-Free Network for UAV Vehicle Detection

Vehicle detection based on unmanned aerial vehicle (UAV) images is a challenging task. One reason is that the objects are small size, low-resolution, and large scale variations, resulting in weak feature representation. Another reason is the imbalance between positive and negative examples. In this paper, we propose a novel architecture for UAV vehicle detection to solve above problems. In detail, we use anchor-free mechanism to eliminate predefined anchors, which can reduce complicated computation and relieve the imbalance between positive and negative samples. Meanwhile, to enhance the features for vehicles, we design a multi-scale semantic enhancement block (MSEB) and an effective 49-layer backbone which is based on the DetNet59. The proposed network offers appropriate receptive fields that match the small-sized vehicles, and involves precise localization information provided by the contexts with high resolution. The MSEB strengthens discriminative feature representation at various scales, without reducing the spatial resolution of prediction layers. Experiments show that the proposed method achieves the state-of-the-art performance. Particularly, the main part of vehicles, much smaller ones, the accuracy is about 2% higher than other existing methods.

Higher modes of buckling in shear deformable nanobeams

The size-dependent buckling instability of shear deformable nanobeams rested on a two-parameter elastic foundation is studied through the stress-driven nonlocal theory of elasticity and the kinematic assumptions of the Timoshenko beam theory. The small-scale size effects are taken into account by nonlocal constitutive relationships, which define the strains at each point as integral convolutions in terms of the stresses in all the points and a kernel. In this manner, the nonlocal elasticity formulation is well-posed and does not include inconsistencies usually arising using other nonlocal models. The size-dependent governing differential equations in terms of the transverse displacement and the cross-sectional rotation are decoupled, and closed form solutions are presented for the displacement functions. Proper boundary conditions are imposed and the buckling problem is reduced to finding roots of a determinant of a matrix, whose elements are given explicitly for different classical edge conditions. The closed form treatment of the problem avoids the numerical instabilities usually occurring within numerical techniques, and allows to find also higher buckling loads and shape modes. Several nanobeams rested on the Winkler or Pasternak elastic foundations and characterized by different boundary conditions, shear deformability, and nonlocality are considered and the critical loads and shape modes are presented, including those for the higher modes of buckling. Excellent agreements are found with the available approximate numerical results in the literature and novel insightful findings are presented and discussed, which are in accordance with experimental observations.