Threshold Force Research Articles

On critical heat flux and its evaporation momentum and hydrodynamic limits

The upper limit of heat transfer from a heated surface to a surrounding boiling liquid has been the subject of numerous studies ever since Nukiyama (1934) discovered this limit. The underlying physics governing this phenomenon, universally known as the critical heat flux (CHF) limit, has been extensively debated for nearly a century. Two prevailing hypotheses have emerged including hydrodynamic instability and evaporation momentum force thresholds proposed by Kutateladze (1948) and Steinchen and Sefiane (1996), respectively. Zuber (1959) and Kandlikar (2001) developed correlations based on these hypotheses that predict roughly similar CHF values i.e., ∼100 W/cm2 for water at 1 atm on a copper surface. Here, we present experimental and analytical studies conducted on liquids with a wide range of thermophysical properties on planar heater surfaces of different size (to stabilize the flow hydrodynamics) that show the evaporation momentum limit (CHFEM) is roughly 4 times the Zuber's limit (CHFZuber). We show that CHFEM can only be observed when hydrodynamics of liquid and vapor above the surface is stabilized, delineating an ultimate limit governed by a force balance at the surface-fluid interface rather than the instability of liquid and vapor interface away from the surface. We find that CHF/CHFEM varies from 0.2 to 1 for all fluids, saturation temperatures, and heater geometries tested, representing 48 conditions.

Dynamic hardness and formation of Portevin-Le Chatelier bands during impact indentation

The effect of shock indentation on the formation and propagation of the Portevin-Le Chatelier deformation bands in an aluminum-magnesium alloy was studied experimentally using acoustic emission and high-speed video recording methods. Dynamic and nonlinear responses to shock indentation are revealed: the first include high values of dynamic hardness and local strain and loading rates, and the second - threshold and multiple nature of force and acoustic responses. It is shown that the bands of macrolocalized deformation represent a latent bulk type of erosion damage, which reduces the mechanical stability and durability of the alloy. Keywords: contact shock, Portevin-Le Chatelier effect, deformation bands, fracture, aluminum-magnesium alloy.

Динамическая твердость и образование полос Портевена-Ле Шателье при ударном индентировании

The effect of shock indentation on the formation and propagation of the Portevin-Le Chatelier deformation bands in an aluminum-magnesium alloy was studied experimentally using acoustic emission and high-speed video recording methods. Dynamic and nonlinear responses to shock indentation are revealed: the first include high values of dynamic hardness and local strain and loading rates, and the second - threshold and multiple nature of force and acoustic responses. It is shown that the bands of macrolocalized deformation represent a latent volumetric type of erosion damage, which reduces the mechanical stability and durability of the alloy.

Measurement of Force and Intramuscular Pressure Changes Related to Thrust Spinal Manipulation in an In Vivo Animal Model.

Current knowledge regarding biomechanical in vivo deep tissue measures related to spinal manipulation remain somewhat limited. More in vivo animal studies are needed to better understand the effects viscoelastic tissue properties (i.e., dampening) have on applied spinal manipulation forces. This new knowledge may eventually help to determine whether positive clinical outcomes are associated with particular force thresholds reaching superficial and/or deep spinal tissues. A computer-controlled feedback motor and a modified Activator V device with a dynamic load cell attached were used to deliver thrust spinal manipulations at various magnitudes to the L7 spinous process in deeply anesthetized animals. Miniature pressure catheters (Millar SPR-1000) were inserted unilaterally into superficial and deep multifidi muscles. Measurements of applied mechanical forces and superficial/deep multifidi intramuscular pressure changes were recorded during spinal manipulations delivered in vivo. Manipulative forces and net changes in intramuscular pressures reaching deep spinal tissues are greatly diminished by viscoelastic properties of in vivo tissues, which could have possible clinical safety and/or mechanistic implications.

Analytical and numerical study of an eccentric continuous cable bracing system with friction slip mechanism

This study proposes a very simple and low-cost friction mechanism using a pre-stressed cable passing over two fixed pulleys without rotation along with an eccentric continuous cable bracing as a lateral-resistant system for structures subjected to lateral loading such as earthquake. The performance of this mechanism is investigated using analytical solution method and finite element modeling. The purpose of this system is to provide a structure with sufficient stiffness and lateral resistance as well as energy dissipation through frictional slip between the cable and pulleys. The system exhibits two-phase behavior. In case of a small lateral displacement, the system exhibits high stiffness in the linear elastic phase (first phase) and behaves well under normal winds and small earthquakes. In case of large lateral displacement such as a strong earthquake, the system experiences a nonlinear slip phase (second phase) and, accordingly, exhibits a nonlinear behavior with an increase in stiffness and input energy dissipation which protects the structure from displacement. The seismic performance of the proposed system is investigated in terms of three parameters: friction coefficient, initial pre-stressing force, and span length. As the friction coefficient value increases, the lateral resistance of the system rises. In the event of extra rotation of the cable around the pulleys, the coefficient values at static and dynamic friction phases are 5.6 and 5.1 times those in the frictional state, respectively. The rise of the span length and reduction of initial pre-stressing force decrease the system lateral resistance and the initial stiffness of the system, respectively. Upon increasing the initial pre-stressing force up to twice that of the base state, the slip threshold of the system lateral resistance force increases by 33% and as a result, the system remains more at the static friction phase. Also, by reducing the initial pre-stressing to half of its value in the base state, the lateral resistance force corresponding to the slip threshold of system is decreased by 52%; therefore, the slip of the cable on pulleys is initiated earlier. Finally, the cyclic behavior of the steel moment frame with the proposed system is investigated with ATC24 protocol, which increases the stiffness and energy dissipation by 19% compared to the moment frame without the proposed system.

The influence of pin on the low-velocity impact performance of foam sandwich structure

In this study, experimental and computational approaches are used to explore the influence of relative position parameter (ratio of the axial distance between the impactor and the pin to the sum of their radius) and dimensional parameter (ratio of impactor diameter to pin diameter) of pin and impactor on foam core sandwich structure under the low-velocity impact. First, sandwiches with various specifications were subjected to low-velocity impact tests with an energy of 34 J. Then reinforcing effect of the pins and the specimen damage condition were thoroughly evaluated using finite element analysis (FEA). The findings revealed that the enhancement impact was substantial when position parameters were below a value of one and was negligible when position parameters were greater than three. In addition, the deformation and damage patterns of the pins gradually transitioned from crushing to large curvature bending, micro-buckling, and negligible deformation were observed with increasing values of position parameters. To establish the law associating position and dimensional parameters with impact performance (including maximum contact force, resistance to impact damage, perforation threshold energy and dent depth), experiments were designed by the central composite design (CCD) method and simulated through FEA. The analysis of variance revealed that the position parameter have higher significance on the maximum contact force, damage resistance and perforation threshold energy, while the dimensional parameter have higher significance on the dent depth. Finally, a parameter optimization design approach was proposed that increased the sandwich's perforation resistance and damage resistance.

Non-uniform machining allowance planning method of thin-walled parts based on the workpiece deformation constraint

In order to reduce the machining deformation of thin-walled parts during milling, a non-uniform allowance planning method for thin-walled parts based on the workpiece deformation constraint with the idea of adding materials in reverse material removal sequence is proposed in this paper. This method does not require accurate deformation prediction and extensive experiments compared to traditional error compensation methods. It strives to maximize the allowance to enhance the stiffness of the in-process workpiece. First, a cutting force threshold calculation method is proposed according to the finite element method. The cutting force threshold at different positions is calculated by obtaining the local stiffness characteristics at the cutter-contact point under the constraint of allowable deformation. And then, the maximum machining allowance at the cutter-contact point is calculated depending on the cutting force model. Considering that the stiffness of the workpiece is position-dependent and affected by material removal, the stiffness of the workpiece is updated by adding elements in the reverse cutting direction, and the finishing stock is obtained by surface fitting. Experimental results show that compared with the traditional uniform allowance method, the error of the proposed method is reduced by about 83%, which can effectively reduce the deformation and improve the machining accuracy.

Characterization of crude oil charging of Xiaoerbulake dolomite in the Tarim basin: Insights from bitumen distribution

Understanding hydrocarbon charging mechanisms is essential for reservoir quality evaluation. In this study, a systematic investigation of micro-nano scale oil charging characteristics in the Lower Cambrian Xiaoerbulake Formation of the Tarim Basin was performed via mercury intrusion capillary pressure (MICP) on samples of four types of dolomitic lithofacies before and after bitumen removal. Additionally, to determine the pore structure and space that was occupied by the bitumen, a series of observations using both optical and field-emission scanning electron microscopy (FE-SEM), along with micro-computed tomography (micro-CT) were conducted. A combination of these micro-CT and MICP techniques enabled us to determine how bitumen is distributed in micro-nano pore space of the bulk sample. Imaging results show that three types of pores (intergranular pores, intercrystalline pores and intragranular pores) and microfractures are developed within these lithofacies and confirmed that bitumen has occupied pores >20 nm in diameters. Furthermore, a relationship between pore-throat threshold and charging force was established under the reservoir conditions. It was found that the oil charging force and pore-throat threshold are different for each lithofacies with the microbial dolomites demonstrating the highest charging force and smallest pore throat threshold; as a consequence, they are the most favorable lithofacies for the accumulation and migration of oil and gas which should be considered for future exploration efforts in dolomitic reservoirs.

Tracking Mechanical Stress and Cell Migration with Inexpensive Polymer Thin-Film Sensors.

Polydiacetylene (PDA) Langmuir films are well known for their blue to red chromatic transitions in response to a variety of stimuli, including UV light, heat, bio-molecule bindings and mechanical stress. In this work, we detail the ability to tune PDA Langmuir films to exhibit discrete chromatic transitions in response to applied mechanical stress. Normal and shear-induced transitions were quantified using the Surface Forces Apparatus and established to be binary and tunable as a function of film formation conditions. Both monomer alkyl tail length and metal cations were used to manipulate the chromatic transition force threshold to enable discrete force sensing from ~50 to ~500 nN μm-2 for normal loading and ~2 to ~40 nN μm-2 for shear-induced transitions, which are appropriate for biological cells. The utility of PDA thin-film sensors was demonstrated with the slime mold Physarum polycephalum. The fluorescence readout of the films enabled: the area explored by Physarum to be visualized, the forces involved in locomotion to be quantified, and revealed novel puncta formation potentially associated with Physarum sampling its environment.

An experimental model of contusion injury in humans.

Contusion injuries are common in sport, but our knowledge of the responses to injury primarily come from animal studies and research using eccentric exercise. Therefore, the aim of this study was to develop a model of contusion injury in human participants and, additionally, investigate and compare physiological responses to four impact loads. Thirty-two males were exposed to a single impact of either 4.2, 5.2, 6.2 or 7.2kg, dropped from 67 cm, on to the vastus lateralis of one leg. Maximum voluntary and electrically induced quadriceps force, and pressure pain threshold were measured, and blood sampling carried out, prior to and 30min, 24, 48 and 72h post-impact. Magnetic resonance imaging was carried out 24h post-impact to quantify oedema. Despite impact force with 7.2kg (1681.4 ± 235.6 N) not being different to 6.2kg (1690.7 ± 117.6 N), 7.2kg resulted in greater volume of oedema, voluntary force loss, pain and elevations in creatine kinase than the other loads. Although electrically induced force changed over time, post-hoc analysis failed to identify any changes. Interleukin-6 and prostaglandin-E2 did not change over time for any of the loads. Significant correlations were found between oedema volume, pressure pain threshold and maximum voluntary contraction force. This is the first experimental study to investigate traumatic loading of skeletal muscle and the subsequent physiological responses associated with contusion injuries in humans. The absence of immediate elevations in creatine kinase and changes in electrically induced force suggest impact, with forces similar to those experienced in contact sport, does not cause significant, direct damage to skeletal muscle. However, the relationship between oedema volume, changes in pressure pain threshold and maximum voluntary contraction force suggests central inhibition plays a role in contusion-related muscle dysfunction.

Biomechanical evaluation of Back injuries during typical snowboarding backward falls.

To prevent spinal and back injuries in snowboarding, back protector devices (BPDs) have been increasingly used. The biomechanical knowledge for the BPD design and evaluation remains to be explored in snowboarding accident conditions. This study aims to evaluate back-to-snow impact conditions and the associated back injury mechanisms in typical snowboarding backward falls. A previously validated snowboarder multi-body model was first used to evaluate the impact zones on the back and the corresponding impact velocities in a total of 324 snowboarding backward falls. The biomechanical responses during back-to-snow impacts were then evaluated by applying the back-to-snow impact velocity to a full human body finite element model to fall on the snow ground of three levels of stiffness (soft, hard, and icy snow). The mean values of back-to-snow normal and tangential impact velocities were 2.4m/s and 7.3m/s with maximum values up to 4.8m/s and 18.5m/s. The lower spine had the highest normal impact velocity during snowboarding backward falls. The thoracic spine was found more likely to exceed the limits of flexion-extension range of motions than the lumbar spine during back-to-snow impacts, indicating a higher injury risk. On the hard and icy snow, rib cage and vertebral fractures were predicted at the costal cartilage and the posterior elements of the vertebrae. Despite the possible back injuries, the back-to-snow impact force was always lower than the force thresholds of the current BPD testing standard. The current work provides additional biomechanical knowledge for the future design of back protections for snowboarders.

The evaluation of hydrogen embrittlement threshold force using the Small punch test

This study aims at developing a methodology for assessing the hydrogen embrittlement threshold force (Pth) in high strength steels using the Small Punch Test (SPT) technique and the ASTM F1624 standard recommendations. This methodology is based on material specimen stiffness and aims to test steels with hardness lower than 33HRC. In the methodology development phase, non-notched specimens made of four high strength steels (AISI 4137 M − 32HRC and AISI 4130 M − 25, 40, 44HRC), widely used in the oil and gas offshore industry, were tested according to the ASTM F1624 standard. Based on the literature, hold times of 20 min for the first 10 and 40 min for the last 10 steps were adopted. The tests were performed in a cathodic protection environment, consisting of a 3.5 wt% NaCl aqueous solution for hydrogen embrittlement (HE). The threshold force values (Pth-SPT) for the Incremental Small Punch Test (ISPT) were measured based on the specimen stiffness. In order to validate the proposed methodology, the ISPT and the incremental step loading (ISL) techniques were applied to test notched specimens manufactured from AISI 4130 M − 25 HRC and AISI 4137 M − 32HRC. The Pth-SPT values showed a systematic error of -4.0 % and 2.2 %, respectively, in relation to the ISL method, indicating an excellent accuracy. The Pth-SPT values provided by the ISPT under the experimental conditions investigated are adequate and quite promising. These values corroborate that the proposed methodology for the measuring of the Pth-SPT, based on material specimen stiffness, proved to be robust, efficient, and of easy implementation.

Electro-thermo-convection in a high Prandtl number fluid: Flow transition and heat transfer

This paper aims to study the electro-thermo-convection of a high Prandtl number fluid (silicone oil) in a rectangular cavity. A high accuracy numerical solver is undertaken to solve the problem. These numerical simulations are performed for a range of Rayleigh and electric Rayleigh parameters, Ra=0,104∼106 and T=0∼1000, which correspond to regimes from laminar to chaotic flow for different cases. Under the condition of weightlessness Ra=0, a strong mixing between heat and cold liquid caused by the electric field is observed, and there is a flow motion transition from large vortices to plume oscillation with the increased value of T. The large vortices motion has a better effencify on heat transfer enhancement. A dual solution at low and moderate Ra numbers is observed. The beingness of these two solutions is validated by a global linear instability analysis based on the linearized lattice Boltzmann method. With the help of some nonlinear analysis techniques, we find that the presence of the electric field may stabilize the thermal convection system. Furthermore, a full map of the heat transfer rate with respect to electric and thermal driving parameters is provided as a reference for applications. Heat transfer enhancement appears only when the electric field force is dominant. A neutral force curve about Ra−T is presented that can characterize the threshold of electric field force to achieve heat transfer enhancement for thermal convection at different Ra numbers.

Establishment and validation of a rodent model of endometriosis to evaluate the effect of new therapeutic strategies

Objectives: Endometriosis is a common disease that affects about 10% - 15% of women in their reproductive years worldwide with no curative treatment. The most common symptom of endometriosis is debilitating pelvic/abdominal pain. Current therapeutic options have limited insight into the disease mechanism and include drugs and/or surgery, which may be ineffective over the long term with unwanted side effects. We aimed at establishing a translational rodent endometriosis model that can be used to identify novel therapies. The validity of the model was confirmed by investigating the effect of the clinically-used GnRH agonist, leuprolide. Methods: Endometriosis was induced by a surgical procedure in adult non-pregnant female Sprague Dawley rats in the diestrus or estrus stage (cycle determination by vaginal smear). One group of rats received a subcutaneous injection of leuprolide at 1mg/kg, every 4 weeks. Following the treatment period, we performed a direct assessment of the endometriosis-induced abdominal pain using the Von-Frey method and spontaneous pain using the abdominal licking test. Then, the lesions were excised and measured. Results: Abdominal pain threshold was decreased by more than 2 fold in rats with surgically-induced endometriosis compared to sham rats. Leuprolide treatment significantly increased the threshold force required to elicit a behavioral withdrawal response in rats suffering from endometriosis. The observed pelvic floor mechanical hyperalgesia has not been correlated to the growth of endometriosis lesions. The hormonal cycle at the surgery induction influenced the endometriosis lesions growth. Leuprolide significantly inhibited the growth of endometriosis-like lesions. Conclusions: we have established, based on previously reported rodent models, a model of endometriosis-associated pain that responds to clinically active drugs and can, therefore, be used to identify novel therapies and investigate some of the pathophysiological mechanisms involved in endometriosis.

Domain Switching in BaTiO3 Films Induced by an Ultralow Mechanical Force.

Low-energy switching of ferroelectrics has been intensively studied for energy-efficient nanoelectronics. Mechanical force is considered as a low-energy consumption technique for switching the polarization of ferroelectric films due to the flexoelectric effect. Reduced threshold force is always desirable for the considerations of energy saving, easy domain manipulation, and sample surface protection. In this work, the mechanical switching behaviors of BaTiO3/SrRuO3 epitaxial heterostructure grown on Nb:SrTiO3 (001) substrate are reported. Domain switching is found to be induced by an extremely low tip force of 320 nN (estimated pressure ∼0.09 GPa), which is the lowest value ever reported. This low mechanical threshold is attributed to the small compressive strain, the low oxygen vacancy concentration in BaTiO3 film, and the high conductivity of the SrRuO3 electrode. The flexoelectricity under both perpendicular mechanical load (point measurement) and sliding load (scanning measurement) are investigated. The sliding mode shows a much stronger flexoelectric field for its strong trailing field. The mechanical written domains show several advantages in comparison with the electrically written ones: low charge injection, low energy consumption, high density, and improved stability. The ultralow-pressure switching in this work presents opportunities for next-generation low-energy and high-density memory electronics.

The role of liquid rheological properties on the injection process of a spring-driven autoinjector

Accurate injection time prediction is essential in developing spring-driven autoinjector devices since the drug delivery is expected to finish within seconds to bring convenience, reduce the risk for early lift-off, and provide a consistent experience to users. The Carreau model captures the liquid’s shear-dependent viscosity measured in our experiments. Thus, a quasi-steady model, which uses the Carreau model to describe the liquid’s viscosity, is developed to predict the injection time of spring-driven autoinjectors. Analytical relations between the flow rate and the pressure drop in the needle are also obtained. The Carreau number in the spring-driven autoinjector is greater than one and smaller than a critical value; in this region, using the power-law model to describe the liquid viscosity accurately predicts the injection time, which agrees with the current literature findings. Additionally, a force threshold is identified for the friction force between the plunger and the syringe barrel, beyond which the injection time is infinite. Appreciation of this force threshold can help avoid device stalling and reduce the risk of underdosing. Moreover, the role of liquid’s shear-thinning index on the injection time of spring-driven autoinjectors is quantified. Understanding the shear-thinning index allows formulators to experiment with excipients and pH to enhance confidence in drug/device combination product design and integration. Our experimental and theoretical results can help drug product and device developers with integrated product design and improve the patient experience.

Exploration of CO movement characteristics on rutile TiO2(110) surface

The adsorption and two-dimensional movement of CO molecules on the rutile TiO2(110) surface were investigated using atomic force microscopy at 78 K. We found that the stability of the CO molecule was affected around Oad. The CO molecule was unstable under short-range force and became stable, pinning it around Oad. The oxygen-terminated tip apex was used to surmount the force threshold of CO molecules to enable two-dimensional movement on the substrate, which can be achieved by short-range force. The CO adsorption and movement properties can be used for the catalytic design of CO oxide-based metal-semiconductor substrates.

A network-based investigation on the strong contact system of granular materials under isotropic and deviatoric stress states

The contact network is essential in linking the macroscale and microscale behaviors of granular materials. Particles and contacts are equivalent to nodes and links in the framework of the complex network graph, and then the network-based metrics can be applied to assess the network topology of granular materials. In this paper, several series of 3D DEM simulations are carried out, including isotropic compression and deviatoric loading tests for assemblies with different particle size distributions. The topological features, such as cluster size, connectivity, network distance and betweenness centrality, are captured for strong force subnetworks with different force thresholds in granular materials. It is found that the particle size distribution does not influence the general topological characteristics of granular materials, and the percolation is observed in the strong network with a proper force threshold for all granular samples. Chained features are consistently identified for strong networks extracted by around 1.5 times the average contact force at all stress states, and this force threshold also supports a giant cluster spanning the overall granular system. Assemblies under deviatoric states exhibit more identical features in strong network topology than that under isotropic states, giving a hint to understanding the structural uniqueness of granular mechanics.

A deep-learning approach for automatically detecting gait-events based on foot-marker kinematics in children with cerebral palsy-Which markers work best for which gait patterns?

Neuromotor pathologies often cause motor deficits and deviations from typical locomotion, reducing the quality of life. Clinical gait analysis is used to effectively classify these motor deficits to gain deeper insights into resulting walking behaviours. To allow the ensemble averaging of spatio-temporal metrics across individuals during walking, gait events, such as initial contact (IC) or toe-off (TO), are extracted through either manual annotation based on video data, or through force thresholds using force plates. This study developed a deep-learning long short-term memory (LSTM) approach to detect IC and TO automatically based on foot-marker kinematics of 363 cerebral palsy subjects (age: 11.8 ± 3.2). These foot-marker kinematics, including 3D positions and velocities of the markers located on the hallux (HLX), calcaneus (HEE), distal second metatarsal (TOE), and proximal fifth metatarsal (PMT5), were extracted retrospectively from standard barefoot gait analysis sessions. Different input combinations of these four foot-markers were evaluated across three gait subgroups (IC with the heel, midfoot, or forefoot). For the overall group, our approach detected 89.7% of ICs within 16ms of the true event with a 18.5% false alarm rate. For TOs, only 71.6% of events were detected with a 33.8% false alarm rate. While the TOE|HEE marker combination performed well across all subgroups for IC detection, optimal performance for TO detection required different input markers per subgroup with performance differences of 5-10%. Thus, deep-learning LSTM based detection of IC events using the TOE|HEE markers offers an automated alternative to avoid operator-dependent and laborious manual annotation, as well as the limited step coverage and inability to measure assisted walking for force plate-based detection of IC events.

Collision detection for six-DOF serial robots force/position hybrid control based on continuous friction model

In this work, an effective and practical robot collision detection algorithm is proposed, with the aim of addressing the safety problem of industrial robot force/position hybrid control application conditions. First, a robot force/position hybrid control collision detection scheme was designed, and a collision detection model based on dynamics was established. Then, given the problem of large joint friction force identification error caused by the discontinuous joint speed of the robot force control, the continuous friction model was used to identify and address the joint friction problem through the least square method. Finally, experiments were carried out on a light industrial manipulator. According to the different collision directions of the robots during the experiment, a collision detection method was proposed to monitor the torque changes of the position control joints and the force control joints. Experimental results prove that the continuous friction model is more accurate and effective for joint friction compensation than other methods. The proposed method can achieve effective collision detection with force and position control direction thresholds of 8 and 4 N·m, respectively. The practicability and simplicity of the algorithm that can streamline the process of robot collision detection, the simplified model of the collision detection process only detects the torque change in the position control direction, which has a certain engineering reference value.