Parallel Force Research Articles

Deformation and load transfer analysis of staggered composite-steel lap joints subjected to progressive damage

In bolted composite connections design, staggered arrangements might offer a good area usage especially for structural elements with a small width. In this research, experimental and numerical works were employed to study the composite-steel double lapped joints with staggered bolts arrangement under static loads. Staggered bolt arrangement was studied with different bolt diameters and numbers. The predictions of developed models were compared to the experimental results and a good correlation was evaluated. The experimental study shows that the side distance in the staggered bolted joint has a significant influence on the maximum load due to the out-of-plane rotation. Simulation of the experimental work shows that this out-of-plane rotation produces a horizontal force on the direction causing early failure for the joint. A parametric study was performed to investigate the effect of bolt numbers and diameters. It was found that the number of bolts has a more significant effect on increasing joint failure load than the bolt diameter. In all cases, the first bolt from the composite plate side has the maximum force, therefore, the first damage happened under this bolt.Considering the axial applied load direction as a reference direction, high perpendicular to parallel forces ratio was evaluated on the bolts of the staggered joint. It is recommended to consider this force during the design of the laminate. Furthermore, the staggered bolt arrangement was found to cause a significant out-of-plane bending which is recommended to be taken into consideration.

COMPARING METHODS FOR 3D INVERSE DYNAMICS ANALYSIS OF SQUAT LIFTING USING A FULL BODY LINKED SEGMENT MODEL

Objective: The main objective of this study was to assess the accuracy of bottom-up solution for three-dimensional (3D) inverse dynamics analysis of squat lifting using a 3D full body linked segment model. Least squares solution was used in this study as reference for assessment of the accuracy of bottom-up solution. Findings of this study may clarify how much the bottom-up solution can be reliable for calculating the joint kinetics in 3D inverse dynamics problems. Methods: Ten healthy males volunteered to perform squat lifting of a box with a load of one-tenth of their body weights. The joint moments were calculated using 110 reflective passive markers (46 anatomical markers and 64 tracking markers) and a 3D full body linked segment model. Ground reaction forces and kinematics data were recorded using a Vicon system with two parallel Kistler force plates. Three-dimensional Newton–Euler equations of motion with bottom-up and least squares solutions were applied to calculate joint moments. The peak and mean values of the joint moments were determined to check the quantitative differences as well as the time-to-peak value of the moment curves was determined to check the temporal differences between the two inverse dynamics solutions. Results: Significant differences (all [Formula: see text]-values [Formula: see text]) between the two inverse dynamics solutions were detected for the peak values of the hip (right and left sides) and L5–S1 joint moments in the lateral anatomical direction as well significant differences (all [Formula: see text]-values [Formula: see text]) were detected for the peak and mean values of the L5–S1 joint moment in all anatomical directions. Moreover, small differences (all RMSEs [Formula: see text]%) were detected between the two inverse dynamic solutions for the calculated lower body joint moments. Conclusions: The findings of this study clarified the disadvantages of the straightforward solutions and demonstrated that the bottom-up solution may not be accurate for more distal measures from the force plate (for hip and S1–L5) but it may be accurate for more proximal joints (ankle and knee) in 3D inverse dynamics analysis.

Anisotropic ultimate strength and microscopic fracture patterns during tensile testing in the dentin-enamel junction region.

The dentin-enamel junction (DEJ), which is the interface between the outer tooth enamel and the underlying dentin, has unique biomechanical properties that allow the two different materials to function together without fracture. The aim of this study was to investigate the anisotropic ultimate tensile strength of the DEJ. Twenty dumbbell-shaped samples were prepared from 10 extracted human molar teeth for tensile strength testing. The maximum tensile forces at fracture were measured in the direction parallel (10 samples) and perpendicular (10 samples) to the DEJ. The mean tensile strength of the samples was significantly higher under parallel forces (30.9±3.3 MPa) than under perpendicular forces (20.6±4.8 MPa; p<0.05). Our findings confirm the structural anisotropy of the DEJ.

Study of Arrhenius activation energy on the thermo-bioconvection nanofluid flow over a Riga plate

This article deals with a study of Arrhenius activation energy on thermo-bioconvection nanofluid propagates through a Riga plate. The Riga plate is filled with nanofluid and microorganisms suspended in the base fluid. The fluid is electrically conducting with a varying, parallel Lorentz force, which changes exponentially along the vertical direction, due to the lower electrical conductivity of the base fluid and the arrangements of the electric and magnetic fields at the lower plate. We consider only the electromagnetic body force over a Riga plate. The governing equations are formulated including the activation energy and viscous dissipation effects. Numerical results are obtained through the use of shooting method and are depicted graphically. It is noticed from the results that the magnetic field and the bioconvection Rayleigh number weaken the velocity profile. The bioconvection Schmidt and the Peclet number decrease the microorganism profile. The concentration profile is enhanced due to the increment in activation energy and the Brownian motion tends to increase the temperature profile. The latter is suppressed by an increment of the Prandtl number.

A heavy load miniature six-component force sensing mechanism with hybrid branches

The heavy-load force sensing mechanisms with small size and wide range have always been a challenge. To tackle this challenge, we propose a parallel six-component force sensing mechanism with sensitive measuring branches and high load-bearing branches based on the design idea of hybrid branch. Based on the virtual work principle and the geometric compatibility condition, the stiffness model and force mapping relationship of the mechanism are deduced, which provide the theoretical basis for the mechanism. Further, the comparison between the numerical calculation and the simulation values of the force sensing mechanism shows that the mathematical model is in good agreement with the finite element model. Finally, a calibration testing platform is built to analyze the measuring performances of the force sensing mechanism. By using the least square method to analyze the experimental data, the calibration matrix is obtained and the maximum nonlinear error is 1.65%.

Effect of Various Surface Treatments on Ti-Base Coping Retention.

Mechanical surface roughening of the titanium-abutment base is necessary to increase the pull-off bond strength of the lithium disilicate abutment material. Additional chemical surface treatment may further increase the bond strength, but the effects are product specific.

A genetic-fuzzy control method for regenerative braking in electric vehicle

In order to improve the recovery ratio of the regenerative braking energy in electric vehicles, the influence factors on braking energy feedback in electric vehicles were analysed. Then, a parallel braking force distribution model was established, and a fuzzy controller on braking force distribution was designed, in which the inputs were vehicle speed, braking strength, battery SOC, and output was regenerative braking ratio. On the other hand, the implementation of genetic algorithm in optimisation process was studied. Furthermore, the genetic algorithm was used to optimise the fuzzy control rules, and new fuzzy distribution rules of electro-hydraulic braking force were obtained. The experimental results showed that the recoverable energy ratio was increased by 2.7% with the comparison of the optimised distribution rules and the original rules. So, the genetic-fuzzy control method is effective for regenerative braking in electric vehicles.

A genetic-fuzzy control method for regenerative braking in electric vehicle

In order to improve the recovery ratio of the regenerative braking energy in electric vehicles, the influence factors on braking energy feedback in electric vehicles were analysed. Then, a parallel braking force distribution model was established, and a fuzzy controller on braking force distribution was designed, in which the inputs were vehicle speed, braking strength, battery SOC, and output was regenerative braking ratio. On the other hand, the implementation of genetic algorithm in optimisation process was studied. Furthermore, the genetic algorithm was used to optimise the fuzzy control rules, and new fuzzy distribution rules of electro-hydraulic braking force were obtained. The experimental results showed that the recoverable energy ratio was increased by 2.7% with the comparison of the optimised distribution rules and the original rules. So, the genetic-fuzzy control method is effective for regenerative braking in electric vehicles.

Monte Carlo simulation on the adsorption of polymer chains on polymer brushes

&lt;sec&gt; The adsorption of polymer on surface is a hot topic in physical, chemical and biological communities, which is influenced by many factors, such as the topological structure and the flexibility of the polymer, the attractive interaction between the polymer and the surface, the detailed structure of the surface, etc. The adsorption of polymers on solid surfaces is extensively studied, while the adsorption behaviors of polymers on soft surfaces are still unclear.&lt;/sec&gt;&lt;sec&gt; In this work, the static and dynamical characters of the adsorption of a free polymer chain on polymer brushes are studied by using Monte Carlo simulation. The brush is formed by grafted polymers with length &lt;i&gt;N&lt;/i&gt;&lt;sub&gt;b&lt;/sub&gt; and distance &lt;i&gt;d&lt;/i&gt;. Results indicate that, with increasing the adsorption energy (&lt;i&gt;ε&lt;/i&gt;) between the free polymer and the brush, the free polymer shows a phase transition from a desorbed state to an adsorbed state. Based on the dependence of the number of the adsorption segment of the free polymer (&lt;i&gt;m&lt;/i&gt;&lt;sub&gt;ad&lt;/sub&gt;) on the adsorption energy &lt;i&gt;ε&lt;/i&gt;, we defined the critical adsorption point (&lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;) where the phase transition occurs. &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt; is nearly independent of the length of the free polymer, but it increases with decreasing the length of the grafted polymer or increasing the distance between the grafted polymers. When &lt;i&gt;ε&lt;/i&gt; &lt; &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;, the free polymer is desorbed and its size is the same as that in free space. When &lt;i&gt;ε&lt;/i&gt; ≈ &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;, the free polymer is sucked into the brush and meanwhile the size is compressed. While when &lt;i&gt;ε&lt;/i&gt; &lt;inline-formula&gt;&lt;tex-math id="Z-20200813163453"&gt;\begin{document}$\gg $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20200411_Z-20200813163453.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20200411_Z-20200813163453.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;, the free polymer is strongly adsorbed on the surface of the brush and forms a quasi two-dimensional conformation, and meanwhile the whole adsorption process contains two stages: the adsorption process of the free polymer and the diffusion process of the brush. Moreover, with the increase of &lt;i&gt;ε&lt;/i&gt;, the diffusion of the free polymer shows an obvious transition from the normal model to the sub-diffusion model near &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt;. The transition of the diffusion model maybe useful for separation of polymers with different attractive polymer-brush interactions. For example, one may construct a brush surface and use it as a polymer separation device. Under weak driving force parallel to the surface, polymers with polymer-brush interaction &lt;i&gt;ε&lt;/i&gt; &lt; &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt; can move quickly, while polymers with &lt;i&gt;ε&lt;/i&gt; &gt; &lt;i&gt;ε&lt;/i&gt;&lt;sub&gt;C&lt;/sub&gt; will move slowly or be trapped on the brush.&lt;/sec&gt;

Rolling and no-slip bouncing in cylinders

The purpose of this paper is to compare a classical non-holonomic system---a sphere rolling against the inner surface of a vertical cylinder under gravity---and a class of discrete dynamical systems known as no-slip billiards in similar configurations. A well-known notable feature of the non-holonomic system is that the rolling sphere does not fall; its height function is bounded and oscillates harmonically up and down. The central issue of the present work is whether similar bounded behavior can be observed in the no-slip billiard counterpart. Our main results are as follows: for circular cylinders in dimension $3$, the no-slip billiard has the bounded orbits property, and very closely approximates rolling motion, for a class of initial conditions which we call transversal rolling impact. When this condition does not hold, trajectories undergo vertical oscillations superimposed to an overall downward acceleration. Considering cylinders with different cross-section shapes, we show that no-slip billiards between two parallel hyperplanes in Euclidean space of arbitrary dimension are always bounded even under a constant force parallel to the plates; for general cylinders, when the orbit of the transverse system (a concept that depends on a factorization of the motion into transversal and longitudinal components) has period two---a very common occurrence in planar no-slip billiards---the motion in the longitudinal direction, under no forces, is generically not bounded. This is shown using a formula for a longitudinal linear drift that we prove in arbitrary dimensions. While the systems for which we can prove the existence of bounded orbits have relatively simple transverse dynamics, we also briefly explore numerically a no-slip billiard system, namely the stadium cylinder billiard, that can exhibit chaotic transversal dynamics.

Towards the crystal structure of thymine: An intermolecular force field development and parallel global cluster optimizations.

A new ab initio potential for the thymine dimer has been developed by using a combination of density functional theory and symmetry-adapted perturbation theory (DFT-SAPT). It has been shown that DFT-SAPT is in very good agreement with the reference CCSD(T) calculations performed for the hydrogen-bonded and stacked thymine dimers. Parallel global cluster optimizations have been carried out employing the new force field from the dimer to n = 50. It has been observed that the resulting cluster structures tend to form the building blocks of the crystal structure of thymine. This study therefore highlights the importance of dimer potentials to gain insights about the crystal structures.

A composite rupture model for the great 1950 Assam earthquake across the cusp of the East Himalayan Syntaxis

Although the M=w8.7, 1950 Assam earthquake endures as the largest continental earthquake ever recorded, its exact source and mechanism remain contentious. In this paper, we jointly analyze the spatial distributions of reappraised aftershocks and landslides, and provide new field evidence for its hitherto unknown surface rupture extent along the Mishmi and Abor Hills. Within both mountain fronts, relocated aftershocks and fresh landslide scars spread over an area of ≈330 km by 100 km. The former are more abundant in the Abor Hills while the later mostly affect the front of the Mishmi Hills. We found steep seismic scarps cutting across fluvial deposits and bounding recently uplifted terraces, some of which less than two thousand years or even a couple centuries old, at several sites along both mountain fronts. They likely attest to a minimum 200 km-long 1950 surface rupture on both the Mishmi and Main Himalayan Frontal Thrusts (MT and MFT, respectively), crossing the East Himalayan Syntaxis. At two key sites (Wakro and Pasighat), co-seismic surface throw appears to have been over twice as large on the MT as on the MFT (7.6 ± 0.2 m vs. >2.6 ± 0.1 m), in keeping with the relative, average mountain heights (3200 m vs. 1400 m), mapped landslide scar numbers (182 vs. 96), and average thrust dips (25–28° vs. 13–15°) consistent with relocated aftershocks depths. Corresponding average slip amounts at depth would have been ≈17 and ≈11 m on the MT and MFT, respectively, while surface slip at Wakro might have reached ≈34 m. Note that this amount of superficial slip would be out of reach using classic paleo-seismological trenching to reconstruct paleo-earthquake history. Most of the 1950 first arrivals fit with a composite focal mechanism co-involving the two shallow-dipping thrust planes. Their intersection lies roughly beneath the Dibang Valley, implying forced slip parallel to GPS vectors across the East Himalayan Syntaxis. Successive, near-identical, terrace uplifts at Wakro suggest near-characteristic slip during the last two surface rupturing earthquakes, while terrace boulder ages may be taken to imply bi-millennial return time for 1950-size events. As in Nepal, East-Himalayan mega-quakes are not blind and release most of the elastic, interseismic shortening that accumulates across the range.

Nucleolin mediates the binding of cancer cells to L-selectin under conditions of lymphodynamic shear stress.

Head and neck squamous cell carcinoma (HNSCC) cells bind to lymphocytes via L-selectin in a shear-dependent manner. This interaction takes place exclusively under low-shear stress conditions, such as those found within the lymph node parenchyma. This represents a novel functional role for L-selectin-selectin ligand interactions. Our previous work has characterized as-of-yet unidentified L-selectin ligands expressed by HNSCC cells that are specifically active under conditions of low shear stress consistent with lymph flow. Using an affinity purification approach, we now show that nucleolin expressed on the surface of HNSCC cells is an active ligand for L-selectin. Parallel plate chamber flow-based experiments and atomic force microscopy (AFM) experiments show that nucleolin is the main functional ligand under these low-force conditions. Furthermore, AFM shows a clear relationship between work of deadhesion and physiological loading rates. Our results reveal nucleolin as the first major ligand reported for L-selectin that operates under low-shear stress conditions.

Detection of self-generated nanowaves on the interface of an evaporating sessile water droplet.

Evaporating sessile droplets have been known to exhibit oscillations on the air-liquid interface. These are generally over millimeter scales. Using a novel approach, we are able to measure surface height changes of 500 nm amplitude using optical trapping of a set of microscopic particles at the interface, particularly when the vertical thickness of the droplet reduces to less than 50 μm. We find that at the later stages of the droplet evaporation, particularly when the convection currents become large, the top air-water interface starts to spontaneously oscillate vertically as a function of time in consistency with predictions. We also detect travelling wave trains moving in the azimuthal direction of the drop surface which are consistent with hydrothermal waves at a different combination of Reynolds, Prandtl and Evaporation numbers than previously observed. This is the first time that wave-trains have been observed in water, being extremely challenging to detect both interferometrically and with infra-red cameras. We also find that such waves apply a force parallel to the interface along the propagation direction.

How Mosul fell: the role of coup-proofing in the 2014 partial collapse of the Iraqi security forces

The Islamic State’s capture of the Iraqi city of Mosul in June 2014 was a seismic event. How can this be explained? This article answers this question by turning to the literature on anti-coup d’etat measures and its side effects. It argues that, to prevent a military coup, Prime Minister of Iraq Nouri al-Maliki engaged in extensive ‘coup-proofing’ methods such as purging rivals, ethnic staking, creating a parallel security force, and increasing intra-government surveillance. These measures were highly effective in preventing a possible military putsch but did greatly reduce the Iraqi troops’ capacity and willingness to fight. Ethnic stacking in particular resulted in mass troop desertions when the Islamic State advanced in 2014. In advancing this argument, this article not only helps us better understand the dramatic fall of Mosul, but may also assist states to strengthen other international assistance programmes for governments fighting domestic insurgencies.

Scaled and Dynamic Optimizations of Nudged Elastic Bands.

We present a modified nudged elastic band routine that can reduce the number of force calls by more than 50% for bands with nonuniform convergence. The method, which we call "dyNEB", dynamically and selectively optimizes images on the basis of the perpendicular PES-derived forces and parallel spring forces acting on that region of the band. The convergence criteria are scaled to focus on the region of interest, i.e., the saddle point, while maintaining continuity of the band and avoiding truncation. We show that this method works well for solid state reaction barriers-nonelectrochemical in general and electrochemical in particular-and that the number of force calls can be significantly reduced without loss of resolution at the saddle point.

Study of up–down poloidal density asymmetry of high- impurities with the new impurity version of XGCa

Addition of multispecies impurity ions to the total-f gyrokinetic particle-in-cell code XGCa is reported, including a cross-verification of neoclassical physics against the NEO code. This new version of the neoclassical gyrokinetic code XGCa is used to benchmark and confirm the previous reduced-equation-based prediction that high- $Z$ impurity particles in the Pfirsch–Schlüter regime can exhibit a significant level of up–down poloidal asymmetry, through the large parallel friction force, and thus influence the radial plasma transport significantly. The study is performed in a plasma with weak toroidal rotation. In comparison, when the impurity particles are in the plateau regime, the up–down poloidal asymmetry becomes weak, with the parallel friction force becoming weaker than the parallel viscous force. It is also found that the linearization of the perturbed distribution function, based on the small poloidal asymmetry assumption, can become invalid. Using the numerical data from XGCa, each term in the parallel fluid force-balance equation have been analysed to find that both the main ions and the electrons respond to the poloidal potential variation adiabatically when the high- $Z$ tungsten possesses large poloidal variation.

Validation of simple superelement model of warping transfer in moment connections of portal frames

ABSTRACTA simple beam element‐based modelling technique has been developed to allow the analytic definition of a stiffness matrix to describe the behavior of corner region between two doubly symmetric thin‐walled I beams connected through moment connection. The stiffness matrix describes the relation between „out‐of‐plane” type deformations of connected beam ends and related internal forces including shear force parallel to the flanges, torsion, weak axis bending and warping of flanges. The model allows to simulate the warping and distortion of the beams within the connection region. The resulting stiffness matrix is compatible with the thin walled beam theory with 7DOF beam elements. A parametric study has been performed to validate the model with shell element‐based simulation, using Abaqus and ConSteel software, concentrating on the direct out‐of‐plane behavior of portal frames. In the validation process first and second order analysis results and results of linear buckling analysis have been analyzed. The correctness of the shell element‐based simulation has been proved by full‐scale laboratory test. The test result has shown excellent agreement with the numerical simulation and with the proposed model.

Steady state cyclic behaviour of a half-plane contact in partial slip subject to varying normal load, moment, shear load, and moderate differential bulk tension

A new solution for a general half-plane contact in the steady state is presented. The contacting bodies are subject to a set of constant loads – normal force, shear force and bulk tension parallel with the interface – together with an oscillatory set of the same quantities. Partial slip conditions are expected to ensue for a range of these quantities. In addition, the line of action of the normal load component does not necessarily need to pass the centre-line of the contact, thereby introducing a moment and asymmetry in the contact extent. This advancement enables a mapping to be formalised between the normal and tangential problem. An exact and easy to apply recipe is defined.

Nature of the excited state in lead iodide perovskite materials: Time-dependent charge density response and the role of the monovalent cation

Charge density response is responsible for the excited-state properties of lead iodide perovskites and is related to both the light absorption properties as well as subsequent electronic and lattice relaxation in the system, important for the working conditions of the material in solar cell applications. Here we investigate the nature of the excited state and its relation to pathways for electronic and lattice relaxations by performing time-dependent density-functional theory (TDDFT). Charge density response upon photoexcitation close to the band edge and deeper into the absorption spectra are investigated for three lead perovskite compounds with different $A$-site monovalent cations ${\mathrm{CsPbI}}_{3},\mathrm{C}{\mathrm{H}}_{2}{(\mathrm{N}{\mathrm{H}}_{2})}_{2}\mathrm{Pb}{\mathrm{I}}_{3}\phantom{\rule{4pt}{0ex}}\phantom{\rule{0.28em}{0ex}}(\mathrm{FAPb}{\mathrm{I}}_{3})$, and $\mathrm{C}{\mathrm{H}}_{3}\mathrm{N}{\mathrm{H}}_{3}\mathrm{Pb}{\mathrm{I}}_{3}(\mathrm{MAPb}{\mathrm{I}}_{3})$. The carrier cooling mechanism is analyzed and shows that the initial force acting on the nuclei follows the symmetry of the ground-state electronic structure upon photoexcitation with a force parallel to the polarization of the incoming light. This effect is investigated for the three different compounds and shows an initial force for induced ionic movement that depends on both the underlying symmetry of the inorganic lattice as well as on the type and orientation of the organic cation. The excess energy after thermalization under blue-light illumination is large enough for overcoming the activation energy for iodide migration and can thus trigger vacancy formation. Iodide vacancies are seen to be dipole-field compensated by the organic cation, with a shielding of the local field, and thus form an explanation for the defect tolerance found in these systems under photovoltaic operation. A partial charge transfer from the inorganic cage to the monovalent organic cation is predicted with TDDFT calculations for blue- and UV-light illumination with a population of antibinding orbitals in the N--H bond in both ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}$ (MA) and ${\mathrm{CH}}_{2}{({\mathrm{NH}}_{2})}_{2}$ (FA), where the implication for this is discussed in terms of the intrinsic photostability of organic cation containing lead perovskites. The results show the importance of a fundamental understanding of the excited-state properties of perovskite material to reveal the underlying mechanism for the defect tolerance and thus high photovoltaic performance when using organic dipolar cations as well as a rationale for using mixed halide perovskites to decrease the halide migration, effect of vacancy formation, and stability issues under blue- and UV-light illumination.