High Contact Force Research Articles

Effect of Adhesive Thickness on Transverse Low-Speed Impact Behavior of Adhesively Bonded Similar and Dissimilar Clamped Plates

This study investigates the effect of adhesive thickness on the transverse low-speed impact behavior of adhesively bonded similar (Al–Al, St–St) and dissimilar (Al–St, St–Al) clamped plates using the three-dimensional explicit finite element method. The contact force and plastic dissipation histories are studied for various impact energies and adhesive thicknesses. The residual plastic strains in both adhesive layer and the two plates increase with increasing impact energy. The central transverse deflections become maximal in Al–Al, moderate in Al–St, St–Al and minimal in St–St bonded plates. The back plates of all configurations deform noticeably. The stiff steel plate results in a shorter contact time, a higher contact force, a lower plastic dissipation energy and the impact energy is absorbed by the adhesive layer rather than by the front and back plates, whereas Al–Al plates dissipate it as much as the adhesive layer. The total contact time gets longer with increasing impact energy. St–St bonded plates experience larger damaged regions in both plates and adhesive layer than those in Al–Al bonded plates. The adhesive thickness has only a minor effect on the magnitude of the contact force and contact time, whereas a stiffer (St) front or back plate affects considerably the contact force and total contact time. Increasing the adhesive thickness decreases apparently residual plastic strains in plates and the adhesive layer, the central transverse deflection. A thick adhesive layer results in a minor increase in the kinetic energy of impactor, a shorter total contact time, a lower plastic dissipation energy and smaller damaged areas on the back faces of the lower plate, along the adhesive–plate interfaces.

10 Micrometer-Scale SPM Local Oxidation Lithography

10 micrometer-scale scanning probe microscopy (SPM) local oxidation lithography was performed on Si. In order to realize large-scale oxidation, an SPM tip with a contact length of 15 microm was prepared by focused-ion-beam (FIB) etching. The oxidation was carried out in contact mode operation with the contact force ranging from 0.1 to 2.1 microN. The applied bias voltage was 50 V, and scanning speed was varied from 10 to 200 microm/s. The scan length was 15 microm for one cycle. The influence of contact force on the large-scale oxidation was investigated. At high contact force, the Si oxide with good size uniformity was obtained even with high scanning speed. The SPM tip with larger contact length may increase the spatial dimensions of the water meniscus between the SPM tip and sample surface, resulting in the larger dimensions of the fabricated oxide. Furthermore, the throughput of large-scale oxidation reached about 10(3) microm2/s by controlling the scanning speed and contact force of the SPM tip. It is suggested that SPM local oxidation can be upscaled by using a SPM tip with large contact length.

An approach to the design of buffer for a buffered impact damper

Presented in this paper is an approach to the optimal design of a buffer for a buffered impact damper. The buffer of a buffered impact damper is modelled as a spring-damper pair. For a buffered impact damper to achieve effective vibration control and at the same time eliminate the inherent disadvantage of the conventional impact damper (i.e. high contact force resulting from impact and high acceleration and noise resulting from high contact force), the design of the buffer is formulated so as to maximize the impulse of impact, thus maximizing the momentum exchange between the damper mass and the primary structure to be controlled, subject to a limit on the maximum impact force. This problem is solved via the production of a design chart. Experiments and numerical simulations demonstrate that the impact damper with the buffer produced from this design approach can not only significantly reduce the contact force and peak value of the acceleration generated by collisions, but also enhance the vibration control effect, which makes it ideal and applicable for general engineering applications. Copyright © 2009 John Wiley & Sons, Ltd.

Low-power electrothermal actuation for microelectromechanical systems

Electrothermal actuation has been used in microelectromechanical systems where low actuation voltage and high contact force are required. Power consumption to operate electrothermal actuators has typically been higher than with electrostatic actuation. A method of designing and processing electrothermal actuators is presented that leads to an order of magnitude reduction in required power while maintaining the low voltage, high force advantages. The substrate was removed beneath the actuator beams, thereby discarding the predominant power loss mechanism and reducing the required actuation power by an order of magnitude. Measured data and theoretical results from electrothermally actuated switches are presented to confirm the method.

Contact Forces in Non-bonded Pavement Materials

We have studied macroscopic stress distributions in horizontal and vertical directions in non-bonded aggregates, as well as the contact forces (local stresses) at the contact areas (microscopic'). A ring chamber was used to study the horizontal and vertical stresses under static vertical loads, whereas contact area stresses were measured using pressure film placed in different parts of the equipment. The pressure films reveal elevated contact forces at some contact areas in response to the applied load, and the grain size range of the particles also influences the stress (contact force) distribution: fine-grained aggregates distribute forces more evenly than coarse-grained aggregates. When an open fraction of aggregates is used, the coarse-grained aggregates have a greater role in supporting loads, as higher contact forces are transmitted across contact areas between large aggregate particles.

Patterning of Polypeptides on a Collagen-Terminated Tissue Surface

Collagen is a ubiquitous component of the extracellular matrix environment, and numerous studies have been devoted toward the development of collagen-based tissue scaffolds. These efforts have been primarily focused on synthetic collagenous materials made from purified collagen. In this article, we present a preliminary study toward the development of a technique that can result in a tissue-derived collagen scaffold. The tissue-derived collagenous matrix was isolated from the retinal Bruch's membrane, and dip pen nanolithography was investigated as a mean to modify the collagenous surface. Characterization experiments of the collagenous surface indicate a fairly hydrophobic surface. Minimal swelling (<7%) of the collagen fibers was observed under elevated humidity conditions with negligible rearrangement of the surface. The hydrophobicity and roughness of the surface can pose a barrier for the deposition of molecules via scanning probe lithography. However, deposition of poly(glutamic acid) and polyarginine onto the surface could be achieved under high contact force and elevated relative humidity conditions (above 55%). Under these conditions, the deposition of the polypeptides occurred through molecular deposition with no observable molecular diffusion. On the other hand, the addition of 0.1% (v/v) Tween-20 surfactant to the inking solution facilitated diffusion of polypeptide inks by increasing the wettability of the collagenous surface. As such, deposition of molecule can be observed under lower contact force at ambient relative humidity (37−40%).

Thermally Actuated Multiport RF MEMS Switches and Their Performance in a Vacuumed Environment

In this paper, unique multiport RF microelectromechanical system switches are proposed as building blocks of redundancy switch matrices. Novel single-pole single-throw (SPST), single-pole double-throw (SPDT), and C-type (transfer) switches are developed, fabricated, and tested. These switches are integrated with thermal actuators that require low actuation voltage and result in high contact force. The RF measurement results reveal an excellent performance with extremely low loss. Up to 20 GHz, the SPST switch has less than 0.3 dB, the SPDT switch has less than 0.5 dB, and the C-type switch has less than 1-dB insertion loss. In addition, the vacuum behavior of these switches is evaluated, which shows a 75% reduced power consumption with an identical RF performance. These switches are excellent candidates for integrating in the form of redundancy switch matrices.

Development of ultrasonic micro hot embossing technology

We succeeded in precise replication of patterns by impressing ultrasonic vibration besides heat and the loading force on the micro hot embossing (MHE). A Ni electroformed mold with micro patterns with seven sizes of entrance from 100 μm 2 to 1.2 mm 2 was used. The experiment was executed on a polycarbonate (PC) sheet while impressing longitudinal wave of ultrasonic vibration at maximum amplitude of 1.8 μm. The effect that bubble defect in the pattern was diminished or completely disappeared was observed by impressing ultrasonic vibration. Moreover, it was clarified that ultrasonic vibration assisted softened PC to move to the center of the pattern area in a mold. We found that the effect of ultrasonic vibration was well pronounced at low contact force. Perhaps very high contact force may be obstructing the progression of ultrasonic vibration.

Contact Forces in Non-bonded Pavement Materials

ABSTRACT We have studied macroscopic stress distributions in horizontal and vertical directions in non-bonded aggregates, as well as the contact forces (local stresses) at the contact areas (“microscopic”). A ring chamber was used to study the horizontal and vertical stresses under static vertical loads, whereas contact area stresses were measured using pressure film placed in different parts of the equipment. The pressure films reveal elevated contact forces at some contact areas in response to the applied load, and the grain size range of the particles also influences the stress (contact force) distribution: fine-grained aggregates distribute forces more evenly than coarse-grained aggregates. When an open fraction of aggregates is used, the coarse-grained aggregates have a greater role in supporting loads, as higher contact forces are transmitted across contact areas between large aggregate particles.

Contact resistance and fretting corrosion of lead-free alloy coated electrical contacts

As lead-free solders replace tin-lead solders in soldering, it is also expected that lead-free solder alloys will be used as contact finish materials for electrical contacts. In this study, the contact resistance and fretting corrosion of tin-silver-copper and tin-copper coatings were investigated and compared with tin-lead eutectic coating. The contact resistance before and after different aging conditions, including mixed flowing gas, steam, and dry heat aging, was examined. Tin-silver-copper and tin-lead alloy coatings have similar performance on contact resistance versus contact normal force after dry heat aging and MFG aging. Severe degradation was found on tin-silver-copper coatings after steam aging. Higher contact force is suggested in the application of tin-silver-copper solder alloy coating than for eutectic tin-lead alloy coatings. Fretting corrosion on tin-silver-copper and tin-copper lead-free alloy coatings was studied and compared with tin-lead coating. Fretting corrosion experiments were conducted and compared at different temperatures and normal forces. In general, tin-silver-copper and tin-copper alloys show equal or better fretting corrosion resistance than tin-lead eutectic alloy at the experimental conditions in this study

Investigation of High-Strength Electroformed Ni for Microprobes

We have developed a microprobe that achieves low contact resistance under low contact force only for gold pads. However, in the case of Al pads, an oxide layer formed on the aluminum pad surface obstructs stable contacting, so higher contact force with a strong probe is required. The present study attempts to enhance the strength of the probe material by improving its mechanical properties. It is said that grain downsizing, functionally alloying, or impurity addition can increase material strength. Our study has adopted impurity addition to the electroforming bath because the process can be controlled. Thus, high-strength electroformed Ni has successfully been obtained. Improved Ni has a high Vickers hardness of Hv600 compared with Hv450 for conventional nickel, and a high Young’s modulus of E=200GPa compared with E=150GPa for conventional nickel.

A parameter study for static and dynamic denting

A parametric study of the factors controlling static and dynamic denting, as well as local stiffness, has been made on simplified panels of different sizes, curvatures, thicknesses and strengths. Analyses have been performed using the finite element method to predict dent resistance and panel stiffness. A parametric approach is used with finite element models of simplified panels. Two sizes of panels with square plan dimensions and a wide range of curvatures are analysed for several combinations of material thickness and strength, all representative of automotive closure panels. Analysis was performed using the implicit finite element code, LS-NIKE, and the explicit dynamic code, LS-DYNA for the static and dynamic cases, respectively. Panel dent resistance and stiffness behaviour are shown to be complex phenomena and strongly interrelated. Factors favouring improved dent resistance include increased yield strength and panel thickness. Panel stiffness also increases with thickness and with higher curvatures but decreases with size and very low curvatures. Conditions for best dynamic and static dent performance are shown to be inherently in conflict ; that is, panels with low stiffness tend to perform well under impact loading but demonstrate inferior static dent performance. Stiffer panels are prone to larger dynamic dents due to higher contact forces but exhibit good static performance through increased resistance to oil canning.

Musculoskeletal Loads in Ergometer Rowing

Rowing ergometers can be found in most gyms and fitness centers, but many people who use them regularly have little or no instruction in rowing technique. It is not known whether nonrowers who regularly practice ergometer rowing are at risk of musculoskeletal problems. This study was done to quantify the differences in kinematics, kinetics, and musculoskeletal loading of competitive rowers and nonrowers during ergometer rowing. An experiment was performed to collect kinematic, external force, and EMG data during er-gometer rowing by 5 university-level competitive rowers and 5 nonrowers. Kinematic and external force data were input to a 3-D whole-body musculo-skeletal model which was used to calculate net joint forces and moments, muscle forces, and joint contact forces. The results showed that competitive rowers and nonrowers are capable of rowing an ergometer with generally similar patterns of kinematics and kinetics; however, there are some potentially important differences in how they use their legs and trunk. The competitive rowers generated higher model quadriceps (vastus) muscle forces and pushed harder against the foot cradle, extending their knees more and their trunks less than the nonrowers during the drive phase. They also had higher contact forces at the knee and higher peak lumbar and knee flexion moments. The ratio of average peak vastus force to average peak erector spinae force in the experienced rowers was 1.52, whereas it was only 1.18 in the nonexperienced rowers.

On the Control of Synchronous Vibration in Rotor/Magnetic Bearing Systems Involving Auxiliary Bearing Contact

During the normal operation of rotor/magnetic bearing systems, contacts with auxiliary bearings or bushes are avoided. However, auxiliary bearings are required under abnormal conditions and in malfunction situations to prevent contact between the rotor and stator laminations. Studies in the open literature deal largely with rotor drop and the requirements of auxiliary bearings design parameters for safe rundown. Rotor drop occurs when the rotor is delevitated and no further means of magnetic bearing control is available. This paper considers the case when full control is still available and rotor/auxiliary bearing contact has been induced by an abnormal operating condition or a temporary fault. It is demonstrated that events leading to contact from a linearly stable rotor orbit can drive the rotor into a nonlinear vibratory motion involving persistent contacts. Furthermore, the phase of the measured vibration response may be changed to such an extent that synchronous controllers designed to minimize rotor vibration amplitudes will worsen the rotor response, resulting in higher contact forces. A modified controller design is proposed and demonstrated to be capable of returning a rotor from a contacting to a noncontacting state.

The effect of molecular weight and temperature on tack properties of model polyisobutylenes

The effect of molecular weight and temperature on the tack of non-crosslinked soft polymers was investigated using blends of low and high molecular weight polyisobutylene as model systems. Molecular weight between entanglements M e was varied systematically by changing the mixing ratio. Video-optical imaging confirms that these model systems exhibit the characteristic debonding features of pressure-sensitive adhesives, including cavitation as well as formation and deformation of fibrils. The initial peak in the stress–strain diagram is a function of both the cohesive strength and ability to wet the probe. It contributes significantly to the work of adhesion at low molecular weight, low temperature and high contact force. Beyond a critical molecular weight, debonding is dominated by fibril deformation. In this regime, the work of adhesion is essentially independent of temperature, molecular weight and the details of the fibrillation pattern (more but thinner fibrils are observed as molecular weight increases). The minimum molecular weight needed for significant fibrillation is around 850 kg/mol (≈3 M e) both at −10°C and 25°C.

Nanometer-Scale Solvent-Assisted Modification of Polymer Surfaces Using the Atomic Force Microscope

We describe the response of poly(methyl methacrylate) surfaces to localized mechanical stimulation by the tip of an atomic force microscope (AFM) in water, methanol, ethanol, and aqueous alcohol solutions. Simply pressing the AFM tip into the surface with no horizontal motion fails to produce visible features in subsequent low contact force images. A single small-area (40 × 40 nm2) high contact force scan has little effect in air but in water or in alcohol−water mixtures produces soft bumps (local volume increase) adjacent to the scanned area. These bumps typically have lateral dimensions of ∼100 nm and rise tens of nanometers above the surrounding surface. Larger, micron-scale scans produce approximately parallel, raised ridges 50−150 nm apart. These structures are stable over time periods of hours or more in air and in solvent. We present evidence that these modifications are due primarily to stress-enhanced solvent uptake in material surrounding the area of tip−polymer contact.

Defining forces that are associated with shoulder dystocia: The use of a mathematic dynamic computer model

Objective: A computer model was modified to study the impact of maternal endogenous and clinician-applied exogenous delivery loads on the contact force between the anterior fetal shoulder and the maternal symphysis pubis. Study Design: Varying endogenous and exogenous loads were applied, and the contact force was determined. Experiments also examined the effect of pelvic orientation and the direction of load application on contact force behind the symphysis pubis. Results: Exogenous loading forces (50-100 N) resulted in anterior shoulder contact forces of 107 to 127 N, with delivery accomplished at 100 N of applied load. Higher contact forces (147-272 N) were noted for endogenously applied loads (100-400 N), with delivery occurring at 400 N of maternal force. Pelvic rotation from lithotomy to McRoberts' positioning resulted in reduced contact forces. Downward lateral flexion of the fetal head led to little difference in contact force but required 30% more exogenous load to achieve delivery. Conclusion: Compared with clinician-applied exogenous force, larger maternally derived endogenous forces are needed to clear the impacted anterior fetal shoulder. This is associated with >2 times more contact force by the obstructing symphysis pubis. McRoberts' positioning reduces shoulder-symphysis pubis contact force. Lateral flexion of the fetal head results in the larger forces that are needed for delivery but has little effect on contact force. Model refinements are needed to examine delivery forces and brachial plexus stretching more specifically. (Am J Obstet Gynecol 2003;188:1068-72.)

Atomic force microscopy imaging and cutting of beaded carbon nanotubes deposited on glass

AbstractWe use contact force mode atomic force microscopy (AFM) to study the structures and to cut carbon nanotubes (CNTs) adsorbed on a glass slide. In addition to regular CNTs, beaded carbon nanotubes (BCNTs) were also observed when preparing products using electric current heating with the pencil technique. Imaging by contact force mode AFM could be achieved at low contact force, whereas cutting could be operated at a higher contact force in conjunction with the y‐scan direction being disabled. Cutting of BCNTs can be done without any translation of the beaded tubes. It is believed that the similar ingredients of the beaded oxides and the glass slide make them bond preferentially by chemical force. Furthermore, the morphologies were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Copyright © 2002 John Wiley &amp; Sons, Ltd.

Mechanical Detachment of Nanometer Particles Strongly Adhering to a Substrate: An Application of Corrosive Tribology

The tip of a scanning probe microscope was used to detach nanometer-scale, single crystal NaCl particles grown on soda lime glass substrates. After imaging a particle at low contact forces, a single line scan at high contact force was used to detach the particle from the substrate. The peak lateral force at detachment is a strong function of particle contact area and humidity. As the relative humidity is raised from low to high values, the strength of the particle-substrate bond decreases dramatically. We interpret these results in terms of detachment by chemically-assisted crack growth along the NaCl-glass interface. Numerical estimates of the electrostatic and dispersive contributions to the work of adhesion are also discussed.

Characteristics of human fingertips in the shearing direction.

The shearing strain of the human fingertip plays an important role in the determination of the optimal grasping force and in the perception of texture. Most research concerned with the mechanical impedance of the human fingertips has treated the orthogonal direction to the tip surface, and little attention has been paid to the tangential direction. This paper describes impedance characteristics of the human fingertips in the tangential directions to the tip surface. In the experiment, step and ramp shearing forces were individually applied to the tips of the thumb, middle finger, and little finger. Dynamics of the fingertips were represented by the Kelvin model. Experimental results show that each fingertip had different properties with respect to the shearing strain versus the applied force, and that the thumb had the strongest shearing stiffness among these three digits. Moreover, the shearing stiffness depended on the direction of the applied force, and the stiffness in the pointing direction was stronger than that in the perpendicular direction. As the contact force in the orthogonal direction to the fingertip surface was increased, the shearing stiffness and viscosity increased without regard to the load speed of the shearing force. Furthermore, it is shown that the average strain rate of the fingertip in the tangential direction to the fingertip surface became slower and converged to a constant value with higher contact forces.