Critical Force Research Articles

Deformation, shape transformations, and stability of elastic rod loops within spherical confinement

Mechanical insight into the packing of slender objects within confinement is essential for understanding how polymers, filaments, or wires organize and rearrange in limited space. Here we combine theoretical modeling, numerical optimization, and experimental studies to reveal spherical packing behavior of thin elastic rod loops of homogeneous or inhomogeneous stiffness. Across varying loop lengths, a rich array of configurations including circle, saddle, figure-eight, and more intricate patterns are identified. A theoretical framework rooted in the local equilibrium of force and moment is proposed for the rod loop deformation, facilitating the determination of internal and contact forces experienced by the rods during deformation. For the confined homogeneous rod loops, their stable and metastable configurations are well described using proposed Euler rotation curves, which offer a concise and effective approach for configuration prediction. Moreover, formulated analysis on the stability and critical force for homogeneous rod loops on great circles of the spherical confinement are performed. For inhomogeneous rod loops with two segments of differing stiffness, the stiffer segment exhibits less deviation from the great circle, while the softer segment undergoes more pronounced deformation. These findings not only enhance our understanding of buckling and post-buckling phenomena but also offer insights into filament patterning within confining environments.

Oriented External Electric Field Controls the Rupture Forces in Mechanophores.

Controlling the reactivity of molecules under a mechanical pull has generated significant interest in organic and polymer chemistry. Inducing mechano-lability for otherwise rigid molecules has been possible through structural alterations like adjusting the pulling group, ring strain, and electron density of the scissile bond. In this article, we report that an oriented external electric field (OEEF) can significantly assist in mechanochemical transformations. Using a structurally diverse set of ring-opening reactions, 1(a)-4(a), we show that the critical force required for bond-cleavage, Frup, gets appreciably reduced when the OEEF acts in-phase with the bond-polarity direction. The primary condition for utilizing OEEF along with mechanochemistry is the requirement of structural asymmetry along the target bond. Effectively therefore, any polar ring-opening reaction might be manipulated by OEEF. The versatility of the strategy of using OEEF and mechanical force together can also be appreciated by the enhanced rupture force when the direction of the OEEF is flipped. We show that mechanical pulling and electric field can act as entwined twins toward mechano-lability.

Key influence factors in magneto-controlled motion of micro-nano graphite flakes

Magneto-controlling micro-nano materials’ motion is a promising way that enable the noncontact, remote, and nondestructive controlling of their macrostructure as well as functionalities. Here, an optical microscope with an electromagnet was constructed to in-situ monitor the magneto-controlled motion process microscopically. Taking micro-nano graphite flake (MGF) as a model system, we experimentally demonstrate the key factors that influence the magneto-controlling of materials’ motion. First, the product of intensity and gradient of the magnetic field (B∇B) has been confirmed as the dominant driving force and the flipping direction of the MGFs is accordingly determined by the vector direction of B×∇B. Second, quantitatively comparative experiments further revealed that the threshold driving force has an exponential relationship with the structural aspect ratio (b/a) of MGFs. Third, the critical magneto-driving force is found as proportional to the viscosity of the solvent. Accordingly, a dynamic model is developed that describes the flip of the diamagnetic flake under external magnetic field excitation considering the shape factor. It is shown experimentally that the model accurately predicts the flip dynamics of the flake under different magnetic field conditions. In addition, we also discovered the delay effect, multiple cycle acceleration effect, and the fatigue effects due to gas adsorption in magneto-controlled MGFs flipping. These findings can be used to achieve magneto-controlling materials’ macrostructure as well as their functionalities.

Seismic capacity evaluation of reinforced concrete moment-resisting frames with steel damper columns using incremental critical pseudo-multi impulse analysis

Steel damper columns (SDCs) are energy-dissipating members that are suitable for reinforced concrete (RC) moment-resisting frames (MRFs) and those often used for multistory housing. In a previous study, the authors proposed an energy-based prediction procedure for the peak and cumulative response of an RC frame building with SDCs. In this procedure, the accuracy of the equivalent velocity of the maximum momentary input energy (VΔE1*)–peak equivalent displacement (D1*max) relationship is essential for improved prediction. In this article, the seismic capacity curve (VΔE1*–D1*max relationship) of RC MRFs with and without SDCs is evaluated using incremental critical pseudo-multi impulse analysis (ICPMIA). In the ICPMIA, which is based on a study by Takewaki and coauthors, the structure is subjected to various intensities of critical pseudo-multi impulsive lateral force. An ICPMIA of planer four 8- and 16-story RC MRFs with and without SDCs is performed to obtain their structural behaviors under various intensities of pulsive input. Then, the seismic capacity curve obtained from the ICMPIA results are compared with the predicted results based on the simplified equations. The main findings of this article are as follows. (i) The seismic capacity curve of RC MRFs without SDCs strongly depends on the number of impulsive lateral forces (Np). As Np increases, the seismic capacity decreases. The predicted seismic capacity curve severely underestimates that obtained from the ICMPIA in the case of large Np. This trend is notable when the level of pinching behavior in the RC members is severe. (ii) In the case of an RC MRF with SDCs, however, the influence of Np on its seismic capacity curve is small. The predicted seismic capacity curve agrees very well with that obtained from the ICMPIA. The influence of the level of pinching behavior in RC members on the seismic capacity curve is small.

FimH-mannose noncovalent bonds survive minutes to hours under force

The adhesin FimH is expressed by commensal Escherichia coli and is implicated in urinary tract infections, where it mediates adhesion to mannosylated glycoproteins on urinary and intestinal epithelial cells in the presence of a high-shear fluid environment. The FimH-mannose bond exhibits catch behavior in which bond lifetime increases with force, because tensile force induces a transition in FimH from a compact native to an elongated activated conformation with a higher affinity to mannose. However, the lifetime of the activated state of FimH has not been measured under force. Here we apply multiplexed magnetic tweezers to apply a preload force to activate FimH bonds with yeast mannan, then we measure the lifetime of these activated bonds under a wide range of forces above and below the preload force. A higher fraction of FimH-mannan bonds were activated above than below a critical preload force, confirming the FimH catch bond behavior. Once activated, FimH detached from mannose with multi-state kinetics, suggesting the existence of two bound states with a 20-fold difference in dissociation rates. The average lifetime of activated FimH-mannose bonds was 1000 to 10,000 s at forces of 30–70 pN. Structural explanations of the two bound states and the high force resistance provide insights into structural mechanisms for long-lived, force-resistant biomolecular interactions.

Research on the anti-slip performance of arc groove cable clamps

Cable clamps are crucial for connecting component and transmitting prestress in cable structures. The anti-slip performance of the cable clamp is an important factor affecting the stability and safety of the structure. This paper introduces a novel test device to evaluate the anti-slip performance of arc groove cable clamps, and anti-slip performance experiments are performed on four arc groove cable clamps and four straight groove cable clamps. Long-term high strength bolt preload loss tests are conducted to investigate the loss pattern. Furthermore, seventeen parametric finite element models are developed to analyze the effects of groove bending angle, bolt length, cable force, and pressure plate stiffness on the anti-slip performance of arc groove cable clamps. It is found that the arc groove cable clamp exhibits a higher anti-slip bearing capacity, with a friction coefficient equivalent to that of the straight groove cable clamp, both exceeding 0.2. The bolt preload stabilizes at a certain value after 96 h of screwing the bolt, while it stabilizes after 24 h of tensioning the cable. The increase in the bolt length and angel of arc groove, as well as the reduction in the stiffness of the pressure plate, have a positive impact on the anti-slip bearing capacity of the arc groove cable clamp. There is a critical cable force that results in the lowest anti-slip bearing capacity of the arc groove cable clamp. These research results provide valuable insights for the design and engineering application of arc groove cable clamps.

Nanoalignment by critical Casimir torques

The manipulation of microscopic objects requires precise and controllable forces and torques. Recent advances have led to the use of critical Casimir forces as a powerful tool, which can be finely tuned through the temperature of the environment and the chemical properties of the involved objects. For example, these forces have been used to self-organize ensembles of particles and to counteract stiction caused by Casimir-Liftshitz forces. However, until now, the potential of critical Casimir torques has been largely unexplored. Here, we demonstrate that critical Casimir torques can efficiently control the alignment of microscopic objects on nanopatterned substrates. We show experimentally and corroborate with theoretical calculations and Monte Carlo simulations that circular patterns on a substrate can stabilize the position and orientation of microscopic disks. By making the patterns elliptical, such microdisks can be subject to a torque which flips them upright while simultaneously allowing for more accurate control of the microdisk position. More complex patterns can selectively trap 2D-chiral particles and generate particle motion similar to non-equilibrium Brownian ratchets. These findings provide new opportunities for nanotechnological applications requiring precise positioning and orientation of microscopic objects.

Analytical solution for the interfacial stress and energy release rate at failure initiation of the three-point bending test (ISO 14679:1997)

Determining adhesive failure in adhesively bonded joints is still challenging in the field. While the three-point bending test (3PBT) (ISO 14679:1997) has been helpful in identifying critical forces and displacements related to bond strength, it only allows for a qualitative assessment of the bond line. Recently, a new quantitative methodology has been developed to determine critical stress and fracture toughness using the coupled stress–energy criterion and the 3PBT. However, these assessments require a significant effort using semi-analytical or finite element (FE) analysis. Therefore, the present study proposes a reliable set of analytical equations to determine peel and shear stress distributions using a weak interface formulation and 1D Euler–Bernoulli approach. More precisely, a particular numerical method computes the integration constants from these equations. A new method has been proposed for calculating the interfacial stiffness in peel and shear mode, based on the material and geometrical parameters of the geometry. This method differs from the previous approach, where the interfacial stiffness was calibrated from the experimental behavior of the test. The whole approach has been validated through experimental and numerical analysis, including the costly 3D FE analysis. An analytical expression for interfacial energy release is suggested, developed following the works of Fraisse and Schmit on J-integral assessment of sandwich-type overlaps and depending on the applied force and a rotation, which could be experimentally measured. Therefore, this work is significant progress in determining bond strength using a simple mechanical test and equations applicable to various industries.

Compression behavior of lightweight corrugated composite Sandwich panels with smart facesheets reinforced by shape memory alloy wires: an experimental study

AbstractThis paper presents an experimental examination of the compression demeanor of lightweight corrugated core composite (CCC) sandwich panel and corrugated core smart composites (CCSC) sandwich panels subjected to quasi‐static edgewise compression loading. The existence of shape memory alloy (SMA) wires and pre‐strain percentages of SMA are the indicators studied in this article. The fabrication procedure presented and the appraisement of the mechanical properties of the CCC and CCSC sandwich panels are expressed. The core geometry of samples is trapezoid corrugated made of aluminum. The facesheets are four layers of woven glass fiber/ epoxy laminated composite. For evaluation of the efficacy of the presence of SMA wires on mechanical specifications of sandwich panels, three SMA wires with various pre‐strain percentages (0%, 3%, and 6%) are embedded in each composite facesheet. Mechanical properties of all types of CCC and CCSC sandwich panels such as maximum force, critical damage force, specific strength, absorb energy, specific toughness, Young's modulus, and specific stiffness were evaluated. Results showed that the CCC sandwich panel has higher mechanical specifications than the CCSC sandwich panels with 0% and 3% pre‐strain. Also, increasing pre‐strained SMA wires improves all mechanical parameters of CCSC sandwich panels. CCSC sandwich panel with 6% pre‐strain has the highest compression properties than other sandwich panels. Maximum Force, Critical Damage Force, Specific Strength, Absorbed Energy, Specific Toughness, Young's Modulus, and Specific Stiffness of CCSC sandwich panel with 6% pre‐strain are 14.73 kN, 13.6 kN, 9.55 MPa/g, 26.61 kJ, 0.346 MJ/m3g, 4395 MPa and 0.61 kN/mm g, respectively.Highlights Lightweight CCC sandwich panel and CCSC sandwich panel manufactured. Compression behavior of CCC sandwich panel and CCSC sandwich panel evaluated. Pre‐strained SMA wires improves energy absorption of CCSC sandwich panels. Higher specific toughness was obtained with 6% pre‐strain SMA. Presence of SMA wires with no pre‐strain cannot improve the specific strength.

Processing parameter effect, formation mechanism and inhibition method of micro-hole exit defects in rotary ultrasonic pecking drilling of SiCf/SiC composites

High brittleness and anisotropy of ceramic matrix composites lead to great challenges for micro-hole machining. Micro-holes with large depth-to-diameter ratio (10:1) of SiCf/SiC composites were machined by rotary ultrasonic pecking drilling process. Based on the mechanical theory and structural characteristics of SiCf/SiC, a critical thrust force model was established. The effects of processing parameters on machining accuracy and machining quality of micro-hole exits were analyzed and parameters were optimized. The formation mechanism of exit defects includes interfacial debonding, fiber bending and matrix fracture. A method based on the surface morphology to inhibit exit defects by increasing the support stiffness of the material was proposed, under which the exit roundness all reached IT8 level and chipping factors decreased by 53 %–67 %, and only a small amount of chipping and micro-cracks was at the exit. The proactive control of micro-hole exit defects was realized, and a better machining quality was obtained.

Critical hydrodynamic force levels for efficient removal of oral biofilms in simulated interdental spaces

ObjectivesSonic toothbrushes generate hydrodynamic shear forces for oral biofilm removal on tooth surfaces, but the effective thresholds for biofilm removal remain unexplored. This in vitro study aimed to investigate various threshold values for hydrodynamic biofilm removal in vitro.Materials and methodsA specialized test bench was designed with a known water flow field within a gap, ensuring that hydrodynamic shear forces on the wall were solely dependent on the volume flow, which was quantifiable using an integrated flow meter and proven by a computational fluid dynamics simulation. A young 20 h supragingival six-species biofilm was developed on hydroxyapatite disks (∅ 5 mm) and applied into the test bench, subjecting them to ascending force levels ranging from 0 to 135 Pa. The remaining biofilms were quantified using colony forming units (CFU) and subjected to statistical analysis through one-way ANOVA.ResultsVolume flow measures < 0.1 l/s: Error 1% of reading were established with the test bench. Untreated biofilms (0 Pa, no hydrodynamic shear forces) reached 7.7E7 CFU/harvest and differed significantly from all treated biofilm groups. CFU reductions of up to 2.3E6 were detected using 20 Pa, and reductions of two orders of magnitude were reached above wall shear forces of 45 Pa (6.9E5).ConclusionsCritical hydrodynamic force levels of at least 20 Pa appear to be necessary to have a discernible impact on initial biofilm removal.Clinical relevancePure hydrodynamic forces alone are insufficient for adequate biofilm removal. The addition of antiseptics is essential to penetrate and disrupt hydrodynamically loosened biofilm structures effectively.

Wind loads on rooftop solar photovoltaic panels oriented with varying azimuth angles: A comprehensive wind tunnel analysis

Effects of azimuth angles α, tilt angle β, parapet height ratio Hp/Hs, and building corner modification were examined. The modules at the roof corner were subjected to unfavorable wind loads in a normal setting without α. In contrast, the unfavorable loads occurred on modules at the center of panel row close to the approaching flow for a none-zero α. The wind directions associated with the largest most critical C͝fm were 45°, 45°, 30°, and 0° at α = 0°, 15°, 30°, and 45°, respectively. The largest most critical mean and negative peak module force coefficients denoted by C‾fm and C͝fm increased as α increased. The largest most critical C͝fm at α = 45° was 19.1%, 12.5%, and 11.9% larger than those at α = 0°, 15°, and 30°, respectively. The more pronounced flow disturbance at larger α would induce larger RMS values of velocities around modules. The larger RMS values of velocities might induce larger C͝fm on modules at larger α. Both the parapet and corner modification were effective aerodynamic approaches to reduce wind loads. The effect of corner modification on wind loads depended on α. The largest most critical negative C‾fm and C͝fm decreased linearly with Hp/Hs for various α.

Critical force of separation effect behaviors in rotary ultrasonic drilling for SiC

Critical force of separation effect behaviors in rotary ultrasonic drilling for SiC

"What makes blood clots break off?" A Back-of-the-Envelope Computation Toward Explaining Clot Embolization.

One in four deaths worldwide is due to thromboembolic disease; that is, one in four people die from blood clots first forming and then breaking off or embolizing. Once broken off, clots travel downstream, where they occlude vital blood vessels such as those of the brain, heart, or lungs, leading to strokes, heart attacks, or pulmonary embolisms, respectively. Despite clots' obvious importance, much remains to be understood about clotting and clot embolization. In our work, we take a first step toward untangling the mystery behind clot embolization and try to answer the simple question: "What makes blood clots break off?" To this end, we conducted experimentally-informed, back-of-the-envelope computations combining fracture mechanics and phase-field modeling. We also focused on deep venous clots as our model problem. Here, we show that of the three general forces that act on venous blood clots-shear stress, blood pressure, and wall stretch-induced interfacial forces-the latter may be a critical embolization force in occlusive and non-occlusive clots, while blood pressure appears to play a determinant role only for occlusive clots. Contrary to intuition and prior reports, shear stress, even when severely elevated, appears unlikely to cause embolization. This first approach to understanding the source of blood clot bulk fracture may be a critical starting point for understanding blood clot embolization. We hope to inspire future work that will build on ours and overcome the limitations of theseback-of-the-envelope computations.

The rotation stability of the tapered rollers in a novel ring-type lapping process

This work introduces a novel ring-type lapping method for precision machining of tapered rollers. In contrast to the conventional centerless grinding, this method allows for the simultaneous machining of a group of tapered rollers. The stable rotation of the tapered rollers during the lapping process is a prerequisite for achieving a high manufacturing accuracy. Therefore, an investigation is conducted to examine the criteria for achieving a stable rotation of the tapered rollers. First, the equilibrium equation for the tapered rollers in the lapping process was established. The stable rotation region for the tapered rollers was determined according to the stable rotation criteria. The impacts of the included angle of straight groove and the contact force of lapping sleeve on the stable rotation region were examined. The results demonstrated that the tapered roller's stable rotation can only be realized when a specific parameter combination was satisfied. Subsequently, to expand the stable rotation region, the electromagnetic driving force was introduced to enhance the lapping process. An electromagnetic lapping sleeve structure was designed according to the critical electromagnetic force required for the tapered roller's lapping process. Furthermore, the structure of the electromagnetic lapping sleeve was optimized by electromagnetic simulation in order to improve the uniformity of the electromagnetic driving force exerted on each tapered roller. Finally, the rotation movement of the tapered rollers and the critical electromagnetic forces exerted on the tapered rollers were validated on a ring-type tapered roller lapping platform. The results demonstrated that the stable rotation of the bearing rollers in the lapping process can be achieved throughout a wide range of processing parameters. The roundness of the tapered rollers was significantly improved from 0.83 μm to 0.47 μm on the stable rotation condition. This study established a solid foundation for the precision machining of tapered rollers.

Mechanics of single-network hydrogels with network imperfection

Polymer network is a crucial component of hydrogels, and network imperfection is a prominent feature of polymer networks, significantly influencing the performance of hydrogels. Two essential features of network imperfection are unequal chain lengths and dangling chains, both of which have a significant impact on the mechanical properties of single-network (SN) hydrogels. However, a theoretical framework considering network imperfection in SN hydrogels is still lacking. Here, we propose a theoretical model for SN hydrogels with network imperfection to study the damage behavior during deformation, in which we adopt different chain length distributions to accurately depict the real physical characteristics of the polymer network and incorporate the normalized critical chain force for a more precise measurement of network damage. To verify our theory, we discuss the effects of model parameters on the stress-stretch responses of SN hydrogels and predict the results of uniaxial loading-unloading tests of SN hydrogels, which agree well with experimentally measured stress-stretch behaviors. Finally, we implement the constitutive model into ABAQUS as a user subroutine to study the inhomogeneous deformation of hydrogels.

Navigating Ritual Resilience: The Interplay of Change and Continuity in the Shaolin Monastery During the COVID-19 Pandemic

The global upheaval caused by the COVID-19 pandemic introduced considerable perturbations to the religious life and ritual observances within most religious communities around the world. This article delves into the resilience and adaptability of ritual practices within the Shaolin Monastery of China during the five-month COVID-19 quarantine spanning from 23 January to 22 June, 2020. Employing ethnographic methods and grounded in anthropological theory, the study examines the interplay between ritual as a static social fact and as a dynamic, adaptable process, within the context of the Shaolin monastic life. It underlines the intricate interplay between static and dynamic elements in ritual practice, casting light on the Shaolin community’s response to the pandemic. The study discerns dichotomies responsible for the critical forces underlying complex dynamics intrinsic to the Shaolin community’s religious life, namely: religious–secular, isolation–social engagement, discipline–freedom, tradition–innovation, and individual–collective. Tracking the evolutions and consistencies within these dual relationships enabled casting light on the transformative processes that were set in motion and identifying the elements of the religious life that have undergone change and those that have remained constant. This exploration offers a unique glimpse into the mechanisms through which resilience was enacted with the strategies that enabled the community to maintain, adjust and innovate its ritual practices amidst the tribulations presented by the crisis.

Stability of a reinforced concrete column under compression with torsion caused by accidental action

Under emergency situations associated with sudden failures of the load-bearing elements of the structure, torques may additionally occur in the columns due to the specifics of the structural design of the buildings. Thus, the columns may be in a complex stress-strain state. The objective of this study was to develop a semi-analytical design model for analysis of the stability of reinforced concrete columns subjected to compression with torsion as a result of an accidental action. For achieving the objective, authors formulated the initial hypotheses, developed the determining equations for calculating the stability of a reinforced concrete column subjected to compression with torsion. To validate the reliability of the proposed model, it has been compared with the results of modeling in the software complex Ansys. Analysis of the data showed that the largest difference between the results was up to 8.08% for the case P = 0.4·Pcr,e = 126.6 kN. The smallest difference of 3.6% was for the case P = 0.9·Pcr,e = 284.85 kN. It has been shown that as the torque increases, there is a decrease in the value of the critical force causing loss of stability. This is due both to the action of the torsional pair of forces during the distortion of the rod and to the decrease in the mechanical properties of concrete under the combined action of normal and tangential stresses.

Research on Mathematical Modeling of Critical Impact Force and Rollover Velocity of Coach Tripped Rollover Based on Numerical Analysis Method

Research on Mathematical Modeling of Critical Impact Force and Rollover Velocity of Coach Tripped Rollover Based on Numerical Analysis Method

Investigation of ratcheting fatigue behavior and failure mechanism of 1Cr18Ni10Ti pressure pipe under different force amplitudes and internal fluid pressure

This work reports on the development of an improved testing system to examine the effects of force amplitude and internal fluid pressure on ratcheting behavior and failure mechanism of 1Cr18Ni10Ti aero-engine pipe. Experimental results indicate that the ratcheting displacement and its rate during steady stage increase with the increasing force amplitude or internal fluid pressure, exhibiting a reverse tendency to fatigue life. Continuous cyclic softening response until fatigue fracture was observed in all conditions. Furthermore, microstructural evolution was characterized by SEM, EDS, XRD, and EBSD. The critical force amplitude to trigger noticeable dislocation accumulation and transition from austenite to ferrite phase was evaluated to be around 1900 N. The results highlight the decreased high-angle grain boundary (HAGB) and increased dislocation density causing the sample with a higher force amplitude to be more inclined to fracture. The initiation of fatigue crack was accelerated by the accumulation of dislocation within ferrite phase grains. Similar fatigue fracture morphology with ovalization phenomenon was observed in all conditions. To predict the ratcheting fatigue life of aero-engine thin wall pipes, a validated fatigue life estimation model considering steady ratcheting displacement rate based on a finite element analysis (FEA) model was conducted, and all of the fatigue data are contained in a 1.1X scatter band.