Clamping Stress Research Articles

Planar clamping anchorage for CFRP plate: Experimental research, friction-adhesion synergistic mechanism and theoretical model

Carbon fiber-reinforced polymer (CFRP) is an anisotropic material, which poses great challenge to its anchorage. In this paper, the performance of a planar clamping anchorage (PCA) for single-layer CFRP plate cable was investigated through the static tensile test. Influencing parameters included interface treatment form, clamping stress, and anchor length. Two interfacial treatment forms were considered: pure friction and friction-adhesion action. Furthermore, the bearing capacity calculation method of friction-adhesion coupling anchor was developed based on the analysis of the process of adhesion and friction. The results indicate that friction-adhesion coupling action significantly improved the anchor bearing capacity compared to pure friction, and the rate of increase in ultimate load displayed a decreasing trend as the clamping stress increased. Additionally, the error between the theoretical and experimental values of anchor bearing capacity for specimens with friction-adhesion coupling anchor was generally within approximately ±10 %.

Comparison and Experimental Study of Cotton Stalk Extraction via Nip Roller Based on Nip Motion Trajectory Equation

In the field of straw recycling, a cotton straw-harvesting mechanism is an important piece of agricultural equipment. The mechanistic analysis method of the harvesting mechanism is a major focus of research and development in this field. Currently, in the mechanistic analysis of the cotton straw recycling mechanism, the kinematic and mechanical analysis of the recycling mechanism is generally the main focus. There is not a lot of research based on the quantitative analysis between different recycling mechanisms. In this study, a clamped cotton straw pulling mechanism is optimized and designed, and two different pulling structures are designed. In addition, a two-dimensional modeling and analysis method is used to establish the two-dimensional equations of motion of the two pulling mechanisms, analyze the leakage and breakage rates of the two clamping structures, predict the final pulling effect, and verify the results of the field tests. According to the analysis, the belt-clamping side has more uniform clamping stress and a larger clamping contact area than the chain-clamping side, and the tangential stress on cotton straw is smaller. Based on the field-test verification, the band-clamping side had a higher pulling net rate by an average of 19.32% and a lower missed pulling rate by an average of 6.01% than the chain-clamping side. Therefore, it was determined that the main reason for the lower pulling net rate of the chain-gripped side than that of the belt-gripped side was the higher pulling breakage rate, and the secondary reason was the high leakage pulling rate. Thus, the feasibility and accuracy of the analytical method of this study are verified.

Micropatterned Fluororubber-Based Dry Adhesive for Pan-Semiconductor Production Line with Complicated Operating Conditions.

The efficient and safe manipulation of precision materials (such as thin and fragile wafers and glass substrates for flat panel displays) under complicated operating conditions with vacuum, high temperature, and low preload stress is an essential task for pan-semiconductor production lines. However, current manipulation approaches such as suction-based gripping (invalid under vacuum conditions) and mechanical clamping (stress concentration at the contact interfaces) are challenged to satisfy such complex requirements. Herein, fluororubber (FKM) is employed as an adhesive material to overcome such challenges due to its outstanding thermostability, availability under vacuum environments, and high adhesion at low contacting preloads. However, the adhesion of the FKM film decreases significantly with increasing temperature (decrease by 84.83% at 245 °C). Consequently, a micropatterned FKM-based dry adhesive (MFA) fabricated by laser etching is developed. The experimental results reveal that MFAs are efficient in restraining adhesion attenuation at high temperatures (minimum 15% decrease at 245 °C). The numerical analysis and in situ observations reveal the mechanism of the MFAs in restraining adhesion attenuation. The contamination-free and high adhesion at low contacting preload of MFAs can be of great interest in pan-semiconductor production lines that require complicated operating conditions on temperature, vacuum, and interface stress.

Numerical Analysis of Double Riveted Lap Joints

In a previous work, the fatigue behaviour of different hot riveted joints under fatigue loadings were experimentally calculated. In particular, the experimental data showed a Wöhler curve slope close to five against the slope of three proposed by Eurocode 3. However, two series of shear splice riveted joints showed, at two million cycles, a stress range very close to the value suggested by Eurocode for shear splices that use non-preloaded high-strength bolts. In order to clarify the fatigue behaviour of riveted joints at high- and medium-fatigue regimes, this paper presents a preliminary three-dimensional non-linear FE analysis of a double-riveted lap joint previously analysed experimentally. Different friction coefficients and rivet clamping stress have been taken Into account, as well as the elastoplastic behaviours of the main plate subjected to tensile loadings. The numerical analysis shows that the friction force tends to reduce the range of stresses at the net section during fatigue loadings, and the force distribution or the stress concentration on the rivets is always critical for the external rivet, which is also the case regarding the non-linear behaviour of the material.

Numerical Study on Slender Circular Reinforced Concrete Column Clamped with Steel Sheet

Various methods to enhance the performance of circular reinforced concrete column have been widely investigated. However, most researches used internal strengthening method such as intensifying steel reinforcement. Others utilized carbon fiber reinforced polymer (CFRP), glass fiber and aramid to retrofit either reinforcement or concrete surface. Few studies incorporated steel to cover concrete surface but neglecting clamp pressure between steel and concrete surface. This study proposes a steel sheet strap strengthening method by initial clamping stress on steel sheets as an external confining technique through experimental works and in-depth numerical analysis. The experimental investigation includes nine steel sheet strengthened reinforced concrete specimens of 20 MPa subjected to axial concentric and axial eccentric. Retrofitting devices will be fabricated from BJ37 steel. Steel sheet straps in each specimen will be subjected to varying initial clamp pressure by fastening bolts. Applied load, lateral displacement and vertical and horizontal deformation will be measured by the instrumentation. Experimental works will observe failure mode, force displacement, stress and ductility. Section analysis based on experimental results will define compatibility equations for numerical stage. Strengthening model from experimental stage will also be analyzed in numerical study with inhouse software 3DNLFEA. F-D curve and moment-curvature loading behavior and ductility will be obtained from numerical analysis. It is believed that the proposed strengthening mechanism with its geometrical and stress variations could enhance the section, member and structural ductility of circular reinforced column against vertical and lateral load. Furthermore, the developed analytical model could well predict the behavior of the proposed clamp mechanism for practical applications.

Effect of aircraft rivet installation process and production variables on residual stress, clamping force and fatigue behaviour of thin sheet riveted lap joints

This paper presents research on the effect of riveting process parameters on residual stresses, clamping stresses and clamping force in thin sheet riveted joints, as well as the fractographic observations of riveted lap joints. The following variables were considered in the study: riveting force, sheet thickness, sheet material and rivet material, rivet hole tolerance and rivet diameter tolerance. The research was carried out for 2024-T3 aluminium alloy sheets with a thickness of 1.6 mm and 1 mm and universal head MS20470-AD (2117-T4 aluminium alloy) rivets with shank diameters of 3.96 mm and 3.18 mm. The results obtained from finite element (FE) analyses were linked with observations of the fatigue crack initiation site, crack path and fretting phenomenon in real three-row riveted lap joints. The results show that the crack initiation site depends on the zone of compressive residual hoop stress in the sheets and the clamping force. The location of the crack path can be related to the location of the largest favourable residual normal stress in the sheets (acting in the direction of the joint loading), the value of the clamping force and the range of the residual clamping stress zone. Large fretting wear regions on the contact surface of sheets for joints with more severely squeezed rivets are associated with a larger zone and a higher value of clamping stresses, which during fatigue loading through friction intensify the harmful phenomenon of fretting.

Influence of electroacupuncture of"Zusanli"(ST36)on mast cells/TRPV1 signaling pathway in visceral hypersensitivity rats with functional dyspepsia

To explore the interventional mechanism of electroacupuncture (EA) of "Zusanli"(ST36)based on the involvement of mast cells/ transient receptor potential vanilloid type1 (TRPV1) signaling pathway in relieving visceral hypersensitivity in functional dyspepsia (FD) rats. Sixty SD rats (half male and half female, 10 days in age) were randomly divided into normal control, model, medication (ketotifen) and EA groups, with 15 rats in each group. The FD model was established by gavage of iodoacetamide combined with tail clamping (stress stimulation). Rats of the medication group received intraperitoneal injection of ketotifen (1 mg·kg-1·d-1) for 14 d, and those of the EA group received EA of ST36 for 20 min, once a day for 14 d. An air-balloon was inserted into the rat's stomach for recording changes of the intragastric pressure (mL/mm Hg) via a pressure transducer. The visceral hypersensitivity was assessed using abdominal withdrawal reflex (AWR) score and the number and degranulation of mast cells of gastric mucosa were observed using toluidine blue staining. The expression levels of TRPV1 and proteinase activated receptor 2 (PAR2) in the stomach were observed using immunofluorescence histochemistry and Western blot, separately, and the contents of SP and CGRP in the stomach detected using ELISA. When the intragastric pressure was at 50, 60 and 70 mm Hg, the gastric compliance was significantly decreased (P<0.01), and the levels of visceral sensitivity increased in the model group （P<0.01）。 TRPV1 immunofluorescence tensity, expression of PAR2 and TRPV1 proteins, and contents of SP and CGRP in the stomach were considerably up-regulated in the model group compared with the normal control group (P<0.01). In comparison with the model group, under intragastric pressure of 50，60 and 70 mm Hg, the gastric compliance was obviously increased, and the visceral hypersensitivity decreased in the EA group （P<0.01,P<0.05）. TRPV1 immunofluorescence intensity, expression levels of PAR2 and TRPV1 proteins, and the contents of SP and CGRP in the stomach were considerably down-regulated in both medication and EA groups compared with the model group (P<0.01, P<0.05). The therapeutic effect of EA was significantly superior to that of medication in up-regulating the gastric compliance （at 70 mm Hg）, and down-regulating the contents of SP and CGRP (P<0.05). No significant differences were found between the EA and medication groups in up-regulating gastric compliance at intragastric pressure of 50 and 60 mm Hg, and in down-regulating the visceral sensitivity, TRPV1 fluorescence intensity, and expression of PAR2 and TRPV1 proteins (P>0.05). Toluidine blue staining showed an apparent increase of mast cell number with obvious degranulation in the gastric mucosa of rats in the model group, which was milder in the EA and medication groups. EA of ST36 can suppress visceral hypersensitivity and increase the gastric compliance in FD rats, which may be related with its effects in inhibiting the activation of gastric mast cells, and down-regulating the expression of gastric PAR2 and TRPV1 proteins and SP and CGRP contents.

Finite element analysis of the clamping stress of photovoltaic silicon brick in diamond wire sawing

The clamping of photovoltaic silicon brick will produce clamping stress. During sawing, the coupling stress concentration and release of the clamping stress, the sawing stress and the thermal stress of silicon brick will cause macroscopic cracks in the silicon brick, causing its breakage and scrapping. The clamping scheme has an important influence on the clamping stress distribution in the silicon brick. In this paper, a three-dimensional finite element model of clamping photovoltaic multi-crystalline silicon brick is established, the influence of cylinder joint shape, number and distribution on clamping stress was studied, and the influence of resin plate structure on clamping stress was analyzed. The results show that the maximum clamping stress of silicon brick can be reduced from the current general clamping scheme of 0.88 MPa–0.25 MPa by using improved clamping scheme, a decrease of about 72%. The results of this paper provide ideas and theoretical reference for understanding the influence of clamping scheme on the clamping stress of silicon brick, reducing the clamping stress of silicon brick and internal hidden cracks.

Electroacupuncture Regulates TRPV1 through PAR2/PKC Pathway to Alleviate Visceral Hypersensitivity in FD Rats.

Visceral hypersensitivity (VH) is the predominant pathogenesis of functional dyspepsia (FD). Duodenal hypersensitivity along with nausea further reduces the comfort level in gastric balloon dilatation and inhibits gastric receptive relaxation. The potential mechanism behind electroacupuncture- (EA-) mediated alleviation of VH has not been elucidated. In an FD rat model with tail clamping stress, iodine acetamide (IA) induced VH. The rats were treated with EA with or without PAR2 antagonist FSLLRY-NH2, and the body weight, gastric sensitivity, compliance, and gastrointestinal motility were determined. Mast cells and activated degranulation were stained with toluidine blue (TB) staining and visualized under a transmission electron microscope (TEM). Immunofluorescence was used to detect the expression of PAR2, PKC, and TRPV1 in the duodenum and dorsal root ganglion (DRG) and that of CGRP, SP in DRG, and c-fos in the spinal cord. EA alone and EA + antagonist enhanced the gastrointestinal motility but diminished the expression of TRPV1, CGRP, SP, and c-fos-downstream of PAR2/PKC pathway and alleviated VH in FD rats. However, there was no obvious superposition effect between the antagonists and EA + antagonists. The effect of EA alone was better than that of antagonists and EA + antagonists 2 alone. EA-induced amelioration of VH in FD rats was mediated by TRPV1 regulation through PAR2/PKC pathway. This protective mechanism involved several pathways and included several targets.

Experimental and simulation investigations of the effect of hybrid GO-thermoplastic polyimide sizing on the temperature-dependent tensile behavior of short carbon fiber/polyetherimide composites

Sizing treatment of fibers is crucial to the interfacial properties and thus the mechanical properties and temperature dependent reinforcing efficiency of short fiber reinforced polymer composites. In this work, polyetherimide (PEI) composites were prepared using highly efficient injection molding technique by introducing three kinds of short carbon fibers (SCFs) treated with graphene oxide (GO), thermoplastic polyimide (TPI) and GO-TPI hybrid sizing, respectively. The effects of sizing agent on the temperature-dependent (−60 °C, 20 °C and 100 °C) tensile behavior of SCF/PEI composites were systematically investigated. The results indicate that the tensile strength of SCF/PEI composites increases with decreasing the temperature due to the higher interfacial clamping stress at low temperature. In particular, it is observed that the hybrid GO-TPI sizing leads to the optimum reinforcement effectiveness, attributing to the blocking effect of GO and the miscibility of TPI and PEI. Single fiber push-in test was conducted and corresponding numerical simulation was made to reveal the effect of GO-TPI sizing on the interfacial properties of SCF/PEI. In addition, the finite element modeling of single carbon fiber composite fragmentation with different sizing treatments was developed to clarify the temperature-dependent mechanical behavior of PEI composites based on the three types of coated SCFs.

Electrocaloric Performance of Multilayer Ceramic Chips: Effect of Geometric Structure Induced Internal Stress

Driven by an ever-growing demand for environmentally benign cooling systems, the past decade has witnessed the booming development in the field of electrocaloric (EC) cooling technology, which is considered as a promising solid-state cooling approach. Multilayer ceramic chip capacitors (MLCCs) represent the optimum structure for EC cooling elements because of large breakdown strengths, low driving voltages, and high macroscopic volumes of active EC materials. However, fundamental relationships between the geometric parameters of MLCCs and the EC coefficient are less understood. In this study, 0.92Pb(Mg1/3Nb2/3)O3-0.08PbTiO3 (PMN-PT) MLCCs with controlled configurations, such as active/inactive layer thickness, number of layers, and active volume ratio, were fabricated, and their EC performance was evaluated. The electric properties of the MLCCs are confirmed to be closely related to the geometric structure, which influences not only the heat flow but also the internal stress, resulting in the variability of EC performance and reliability/breakdown strength. The internal stress arises due to the residual thermal stress originating from the densification-related shrinkage, thermal expansion mismatch during the sintering, and clamping stress arising from the inactive area due to the large strain from the active area under a high electric field. The geometric structure-based stress distribution and the magnitude of stress on the active layers in MLCCs were determined by finite element modeling (FEM) and correlated with the experimental EC coefficients. The results reveal that a low inactive volume percentage is beneficial toward increasing the breakdown field and enhancement of EC performance because of reduced clamping stress on active EC material.

A Novel Approach to Reduce Optical Aberrations by using Deformable Bushes at Opto-Mechanical Interfaces

There is a continuous need to enhance the aperture size of telescopes by astronomers to explore the space much deeper by getting better resolutions and high image quality. Supporting large optics and maintaining high dynamic stability involves more number of constraints. This renders optical surface more distorted and results in poor image quality, since the image quality deteriorates with increase in RMS surface error. A new approach is proposed to introduce deformable bushes at the interfaces. These are tuned to deform under specific clamping force and thus arrests all Degrees of Freedom (DOF). This limits the clamping force exerted by an axial DOF ([Formula: see text]) to an insignificant value. This approach helps to arrest [Formula: see text] without imposing clamping stress on the opto-mechanical mount and brings down optical aberrations and enhances dynamic stability of the mounting system. This due to the fact that all clamping forces are taken by deformable bushes and the stress is not transferred to mount and thus does not contribute to non-uniformity of the optical surface. The non-uniformity of the optical surfaces influenced by clamping forces is simulated by Finite Element (FE) techniques. The use of deformable bush approach in minimizing optical aberrations and stability enhanced by additional constraints to opto-mechanical mounts are demonstrated by simulations.

Fatigue life extension of existing welded structures via high frequency mechanical impact (HFMI) treatment

High Frequency Mechanical Impact (HFMI) is one of the post-weld treatment methods. In this study, comparative axial fatigue tests were conducted on as-welded and HFMI-treated welded transverse attachment details. The test results demonstrated the efficiency of HFMI-treatment in fatigue life extension of cracked welded structures, providing that the existing crack size is less than 1.2 mm. Cracks were created in some specimens through fatigue testing before HFMI-treatment, while other specimens were not subjected to any fatigue loading prior to treatment. Many of the treated specimens ran-out after 10 million cycles of loading when tested at a stress range of 150 MPa. Therefore, the stress range was increased to 180 MPa or 210 MPa. No remarkable difference was found between the fatigue strength of the crack-free and the cracked treated specimens. It was found that the induced compressive residual stress can exceed the material yield limit, and reach a depth larger than 1.5 mm in most of the cases. The induced compressive residual stress, the local material hardening, the increase in weld toe radius, the change in crack orientation and the shallowness of the crack size were the causatives of the obtained long fatigue lives of the HFMI-treated specimens. Besides, linear elastic fracture mechanics calculations were conducted to predict the fatigue lives of as-welded and HFMI-treated details. The results were in agreement with the experiment. Moreover, the calculations showed that the initial crack size, the clamping stress and the induced compressive residual stress were the main factors behind the scatter in fatigue lives.

The effect of clamping stress on the measured surface figure of optical glass BK7

This work probes the effect of clamping stress induced by pad block’s support surface (PBSS) shape error in measured surface figure of optical glass BK7. Under given PBSS topography measured by three coordinate machine, the clamping stress loaded on the workpiece and its effect on workpiece’s surface deformation was simulated by finite element method. Furthermore, the surface figure residual error (SFRE) in simulation was in good agreement with experimental results despite the measurement repeatability error.

Shear in sand-lightweight and conventional high strength concrete through the push-off test

abstract: Shear design models in reinforced concrete structures depend on stress transfer through cracks. Such mechanism is influenced by the displacement and roughness of the opposite faces generated during cracking. Shear is reduced when an aggregate particle is fractured leading to a smoother crack as found in lightweight and high strength concrete. This study evaluated the ultimate shear strength of sand-lightweight and conventional high strength concrete as well as the differences in their behavior. Results from Pereira and Soares with 29 push-off test specimens were used. Transverse clamping stress ranged from 4.79 to 12.71 MPa while fcm was 30 and 50 MPa. The experimental results showed significant differences in the concrete studied. A tri-linear model was proposed to calculate the ultimate shear strength. An overall mean value of τu, exp/τu, cal was 0.96.

Finite Element Analysis of the Axial Mechanical Properties of Piezoelectric Actuator with Tubular Interdigitated Electrodes

We theoretically investigate a new type of piezoelectric actuator with tubular interdigitated electrodes. A partial model is adopted due to the axial symmetry of the actuator, which is divided into non-overlapping opposing electrode pairs on the center plane of the branch electrode. We present a finite element model of actuator and analyze its static-dynamic properties by using the commercially available finite element software ABAQUS. The length-to-diameter ratio of the tubular actuator can be as larger as necessary, so we are more concerned with the axial mechanical properties of the actuator. Thus we studied the influence of the electrode’s shape and structure size on the clamping stress and free strain of the partial models. We also analyzed an ordinary piezoelectric model of the same size. We demonstrated that the partial model displayed significantly improved axial performance over the ordinary one. The axial stress of the partial model can reach 2.75 times that of the ordinary one, and the axial free strain can reach 1.55 times that of the ordinary one. According to the results of the static analysis, appropriate electrodes and structural parameters were selected to establish a tubular actuator model, with which modal and harmonic response analysis were performed. A modal analysis was used to obtain the frequencies and the shapes of the axial vibration. Each pair of electrodes is shunted to a sinusoidal varying voltage. Using the results of the harmonic response analysis, we obtained the actuator’s axial resonance curve.

Fracture mechanics analysis of the effect of clamping stress on the fatigue life of riveted built-up railroad girders under variable amplitude loading

A linear-elastic Fracture Mechanics approach is used to estimate the fatigue life of riveted connections present in railroad bridge built-up steel girders under variable amplitude loading. Special care has been taken to analyze the effect of thermal clamping stresses on fatigue life. The analysis is developed using the variable amplitude stresses generated due to a traversing heavy axle train on a simply supported girder. Stress intensity factors for quarter elliptical corner crack emanating from a through-thickness (rivet) hole under remote tension were used. Thermal clamping stress, typically generated during the installation process, was quantified through a finite element simulation. Superposition principle was utilized to account for localized clamping stress present on the base material along with remote tension. Fatigue life estimations calculated using a linear-elastic Fracture Mechanics approach with and without considering clamping stress are compared. Finally, crack growth proved to be different under the effect of localized clamping stresses when compared to a crack growth emanating from a hole with no clamping stress.

One-step mask patterning of micro lead zirconate titanate arrays by electrohydrodynamic atomization

In this paper, the lead zirconate titanate microarrays were fabricated with a one-step mask patterning route via electrohydrodynamic atomization. The composite ink consisting of PZT microparticles dispersed in PZT sol was prepared for the fabrication process. The sintered composite PZT cells demonstrated the perovskite structures and the coexistence of the rhombohedral and morphotropic phase boundary, as shown from the XRD and XPS results. It was found that the discrete PZT cell showed an increase of the remanent polarization, coupled with the piezoelectric coefficient (d33) of ~110 p.m./V at remanence, which was approximately 1.5 times larger than that of the continuous films. These results could be ascribed to the increased mobility of the domain wall and the reduced clamping stress. The simplicity of the fabrication routes and the fast producing capability of electrohydrodynamic atomization shows great potentiality of producing microarrays for PZT based microelectronic devices.

Dynamic Rupture Simulations of the M6.4 and M7.1 July 2019 Ridgecrest, California, Earthquakes

AbstractThe largest earthquakes of the 2019 Ridgecrest, California, sequence were a M6.4 left‐lateral rupture followed 34 hr later by a M7.1 on a perpendicular right‐lateral fault. We use dynamic rupture modeling to address the questions of why the first earthquake did not propagate through the right‐lateral fault in one larger event, whether stress changes from the M6.4 were necessary for the M7.1 to occur, and how the Ridgecrest earthquakes affected the nearby Garlock Fault. We find that dynamic clamping and shear stress reduction confined surface rupture in the M6.4 to the left‐lateral fault. We also find that stress changes from the M6.4 were not necessary to allow a M7.1 on the right‐lateral fault but that they affected the slip and likely accelerated the timing of the M7.1. Lastly, we find that the Ridgecrest earthquakes may have brought the central Garlock Fault closer to failure.

Characterization of Thermally Induced Runaway in Pouch Cells for Propagation

Thermal runaway of lithium-ion batteries is particularly dangerous in systems where runaway can propagate through many cells. To understand thermal runaway propagation in these systems, it is important to understand the differences between failure characteristics of the initial cell that fails due to an abuse event and subsequent cells that fail due to thermal runaway propagation. This work compares thermal runaway events for single cells failed using a heater with cells failed due to propagation in an array. Most of the tests were conducted in an inert environment within a pressure vessel. Cell clamping stress, vessel gas pressure and temperature data show that runaway in cells within an array traverses the cells more slowly and releases gas at a slower rate than singly failed cells. For heater-initiated cell failure, post-experiment cell teardowns suggest that thermal runaway originates at a single point and creates a gas flow stream that causes heavy damage and exits from one side of the cell. Teardowns of cells which failed due to array propagation show more uniform damage and gas release from a larger area.