scholarly journals Sliding-induced adhesion of stiff polymer microfibre arrays. II. Microscale behaviour

2008 ◽  
Vol 5 (25) ◽  
pp. 845-853 ◽  
Author(s):  
Bryan Schubert ◽  
Jongho Lee ◽  
Carmel Majidi ◽  
Ronald S Fearing
Keyword(s):  
Shear Force ◽  
Strong Dependence ◽  
Adhesive Force ◽  
Shear Forces ◽  
Spherical Probe ◽  
Adhesive Pads ◽  
Normal Adhesion ◽  
Fibre Angle ◽  
First Time ◽  
Adhesion Effect

The adhesive pads of geckos provide control of normal adhesive force by controlling the applied shear force. This frictional adhesion effect is one of the key principles used for rapid detachment in animals running up vertical surfaces. We developed polypropylene microfibre arrays composed of vertical, 0.3 μm radius fibres with elastic modulus of 1 GPa which show this effect for the first time using a stiff polymer. In the absence of shear forces, these fibres show minimal normal adhesion. However, sliding parallel to the substrate with a spherical probe produces a frictional adhesion effect which is not seen in the flat control. A cantilever model for the fibres and the spherical probe indicates a strong dependence on the initial fibre angle. A novel feature of the microfibre arrays is that adhesion improves with use. Repeated shearing of fibres temporarily increases maximum shear and pull-off forces.

scholarly journals Shear-sensitive adhesion enables size-independent adhesive performance in stick insects

2019 ◽  
Vol 286 (1913) ◽  
pp. 20191327 ◽  
Author(s):  
David Labonte ◽  
Marie-Yon Struecker ◽  
Aleksandra V. Birn-Jeffery ◽  
Walter Federle
Keyword(s):  
Body Weight ◽  
Adhesive Force ◽  
Whole Body ◽  
Small Animals ◽  
Shear Forces ◽  
Stick Insects ◽  
Adhesive Pads ◽  
The Difference ◽  
Large Animals ◽  
Adhesive Performance

The ability to climb with adhesive pads conveys significant advantages and is widespread in the animal kingdom. The physics of adhesion predict that attachment is more challenging for large animals, whereas detachment is harder for small animals, due to the difference in surface-to-volume ratios. Here, we use stick insects to show that this problem is solved at both ends of the scale by linking adhesion to the applied shear force. Adhesive forces of individual insect pads, measured with perpendicular pull-offs, increased approximately in proportion to a linear pad dimension across instars. In sharp contrast, whole-body force measurements suggested area scaling of adhesion. This discrepancy is explained by the presence of shear forces during whole-body measurements, as confirmed in experiments with pads sheared prior to detachment. When we applied shear forces proportional to either pad area or body weight, pad adhesion also scaled approximately with area or mass, respectively, providing a mechanism that can compensate for the size-related loss of adhesive performance predicted by isometry. We demonstrate that the adhesion-enhancing effect of shear forces is linked to pad sliding, which increased the maximum adhesive force per area sustainable by the pads. As shear forces in natural conditions are expected to scale with mass, sliding is more frequent and extensive in large animals, thus ensuring that large animals can attach safely, while small animals can still detach their pads effortlessly. Our results therefore help to explain how nature’s climbers maintain a dynamic attachment performance across seven orders of magnitude in body weight.

scholarly journals Shear-sensitive adhesion enables size-independent adhesive performance in stick insects

2019 ◽  
Author(s):  
David Labonte ◽  
Marie-Yon Struecker ◽  
Aleksandra Birn-Jeffery ◽  
Walter Federle
Keyword(s):  
Body Weight ◽  
Adhesive Force ◽  
Whole Body ◽  
Small Animals ◽  
Shear Forces ◽  
Stick Insects ◽  
Adhesive Pads ◽  
The Difference ◽  
Large Animals ◽  
Adhesive Performance

The ability to climb with adhesive pads conveys significant advantages, and is hence widespread in the animal kingdom. The physics of adhesion predict that attachment is more challenging for large animals, whereas detachment is harder for small animals, due to the difference in surface-to-volume ratios. Here, we use stick insects to show that this problem is solved at both ends of the scale by linking adhesion to the applied shear force. Adhesive forces of individual insect pads, measured with perpendicular pull-offs, increased approximately in proportion to a linear pad dimension across instars. In sharp contrast, whole-body force measurements suggested area-scaling of adhesion. This discrepancy is explained by the presence of shear forces during whole-body measurements, as confirmed in experiments with pads sheared prior to detachment. When we applied shear forces proportional to either pad area or body weight, pad adhesion also scaled approximately with area or mass, respectively, providing a mechanism that can compensate for the size-related loss of adhesive performance predicted by isometry. We demonstrate that the adhesion-enhancing effect of shear forces is linked to pad sliding, which increased the maximum adhesive force per area sustainable by the pads. As shear forces in natural conditions are expected to scale with mass, sliding is more frequent and extensive in large animals, thus ensuring that large animals can attach safely, while small animals can still detach their pads effortlessly. Our results therefore help to explain how nature’s climbers maintain a dynamic attachment performance across seven orders of magnitude in body weight.

The Effect of Ball Pad Metallurgy and Ball Composition on Solder Ball Integrity of Plastic Ball Grid Array Packages

1998 ◽  
Author(s):  
C.H. Zhong ◽  
Sung Yi
Keyword(s):  
Failure Mode ◽  
Barrier Layer ◽  
Shear Force ◽  
Solder Ball ◽  
Ball Grid Array ◽  
Reliability Test ◽  
Shear Forces ◽  
Ball Shear ◽  
Plastic Ball ◽  
Plastic Ball Grid Array

Abstract Ball shear forces of plastic ball grid array (PBGA) packages are found to decrease after reliability test. Packages with different ball pad metallurgy form different intermetallic compounds (IMC) thus ball shear forces and failure modes are different. The characteristic and dynamic process of IMC formed are decided by ball pad metallurgy which includes Ni barrier layer and Au layer thickness. Solder ball composition also affects IMC formation dynamic process. There is basically no difference in ball shear force and failure mode for packages with different under ball pad metallurgy before reliability test. However shear force decreased and failure mode changed after reliability test, especially when packages exposed to high temperature. Major difference in ball shear force and failure mode was found for ball pad metallurgy of Ni barrier layer including Ni-P, pure Ni and Ni-Co. Solder ball composition was found to affect the IMC formation rate.

Study of Structure and Properties of New Rolling-Cut Shear

2010 ◽  
Vol 146-147 ◽  
pp. 991-995
Author(s):  
Zhi Bing Chu ◽  
Qing Xue Huang ◽  
Zhi Yuan Zhang ◽  
Dan Li
Keyword(s):  
Theoretical Analysis ◽  
Shear Force ◽  
Motion Path ◽  
Negative Bias ◽  
Horizontal Force ◽  
Structure And Properties ◽  
Force Component ◽  
Shear Forces ◽  
Maximum Shear Force ◽  
Force Components

Based on rolling-cut shear simulation, using a kind of single-shaft and double eccentricity rolling-cut shear, which adopts a new structure of asymmetric feature and negative bias, as the calculating model by establishing motion path equation of spatial shear mechanism, comparing with the steel shear forces, link forces and horizontal link force components with or without asymmetric feature, the asymmetric formulation is deduced. Such asymmetric crank structure can decrease horizontal force component between the linkages during rolling-cut process, increase the effective drive force on links while it comes to the maximum shear force, and decrease the extrusion of blade arc on steel edge as well. Theoretical analysis and steel-shearing quality at site indicate that asymmetric and negative bias is an important and efficient way to prolong the lifetime of blade, decrease blade wear, improve shearing quality, and maintain the constant clearance between blades.

Effect of Bottom Boundary on VIV for Energy Harnessing at 8×103

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
K. Raghavan ◽  
Michael M. Bernitsas ◽  
D. E. Maroulis
Keyword(s):  
Strong Dependence ◽  
Clean Energy ◽  
Reynolds Numbers ◽  
Strong Impact ◽  
University Of Michigan ◽  
Vortex Induced Vibration ◽  
Bottom Boundary ◽  
The University ◽  
Energy Harnessing ◽  
First Time

The concept of extracting energy from ocean/river currents using vortex induced vibration was introduced at the OMAE2006 Conference. The vortex induced vibration aquatic clean energy (VIVACE) converter, implementing this concept, was designed and model tested; VIV amplitudes of two diameters were achieved for Reynolds numbers around 105 even for currents as slow as 1.6 kn. To harness energy using VIV, high damping was added. VIV amplitude of 1.3 diameters was maintained while extracting energy at a rate of PVIVACE=0.22×0.5×pU3DL at 1.6 kn. Strong dependence of VIV on Reynolds number was proven for the first time due to the range of Reynolds numbers achieved at the Low-Turbulence Free Surface Water (LTFSW) Channel of the University of Michigan. In this paper, proximity of VIVACE cylinders in VIV to a bottom boundary is studied in consideration of its impact on VIV, potential loss of harnessable energy, and effect on soft sediments. VIV tests are performed in the LTFSW Channel spanning the following ranges of parameters: Re∊[8×103–1.5×105], m∗∊[1.0–3.14], U∊[0.35–1.15 m/s], L/D∊[6–36], closest distance to bottom boundary (G/D)∊[4−0.1], and m∗ζ∊[0.14–0.26]. Test results show strong impact for gap to diameter ratio of G/D<3 on VIV, amplitude of VIV, range of synchronization, onset of synchronization, frequency of oscillation, hysteresis at the onset of synchronization, and hysteresis at the end of synchronization.

Effectiveness of various materials in reducing plantar shear forces. A pilot study

2000 ◽  
Vol 90 (7) ◽  
pp. 346-353 ◽  
Author(s):  
M Curryer ◽  
ED Lemaire
Keyword(s):  
Diabetes Mellitus ◽  
Pilot Study ◽  
Diabetic Foot ◽  
Shear Force ◽  
Foot Ulcers ◽  
Shear Forces ◽  
Patients With Diabetes ◽  
Force Data ◽  
Precipitating Factor ◽  
Better Than

Vertical plantar forces are known to be a major precipitating factor in the development of foot pathology. It is also postulated that shear forces are important in the pathogenesis of foot ulcers in patients with diabetes mellitus. Various materials are used in insoles designed to reduce forces on the foot. While many foam materials have been tested for their ability to dissipate vertical forces, few studies have tested the effect of these materials on shear forces. This study assessed the effectiveness of five different materials in reducing plantar shear forces and compared two new gel materials with three of the more conventional foam materials. Four subjects were tested while walking over a force platform with one of the five materials taped to the surface. Peak force, impulse, and resultant shear force data were analyzed. The gel materials were significantly better than the foam materials at reducing shear forces. Thus the use of gel materials in insoles may be indicated for the reduction of plantar shear forces on the diabetic foot.

Dependence of the Sn0/2+ charge state on the Fermi level in semi-insulating CdTe

2007 ◽  
Vol 22 (11) ◽  
pp. 3249-3254 ◽  
Author(s):  
V. Babentsov ◽  
J. Franc ◽  
H. Elhadidy ◽  
A. Fauler ◽  
M. Fiederle ◽  
...  
Keyword(s):  
Fermi Level ◽  
Charge State ◽  
Strong Dependence ◽  
High Resistivity ◽  
Level Variation ◽  
Radiative Transitions ◽  
Deep Traps ◽  
First Time ◽  
Positively Charged

We explored the growth and characteristics of CdTe doped with Sn to heighten our understanding of the role of deep levels on electrical compensation and trapping. We demonstrated, for the first time, the strong dependence of the SnCd charge state on the Fermi-level variation (2–3kT) in high-resistivity CdTe. The concentration of deep traps for electrons was determined by the number of doubly positively charged Sn2+ atoms. Thermoelectric-effect spectroscopy and photovoltage measurements revealed the conversion of the SnCd defect from the electron SnCd2+ trap to the hole SnCd0 trap. The results agree well with the existence of a negative U-center in the SnCd0/2+ defect. We also showed that the neutral Sn defect is responsible for the near midgap C-band → bound hole radiative transitions band with a maximum at 0.76 eV.

A Shear-Force Sensitive Silicon Sensor

1999 ◽  
Author(s):  
Lin Wang ◽  
David J. Beebe
Keyword(s):  
Shear Force ◽  
Elevation Angle ◽  
Applied Force ◽  
Strain Gauges ◽  
Shear Forces ◽  
Shear Sensitivity ◽  
Repeatability Standard Deviation ◽  
Microfabrication Technology ◽  
High Repeatability ◽  
Silicon Sensor

Abstract A shear-force sensitive silicon sensor is developed using microfabrication technology. Four ion implanted piezoresistive resistors are embedded in a silicon diaphragm and used as independent strain gauges. An epoxy mesa is added on top of the diaphragm to transmit force from the load to the diaphgram. Both the shear and normal components of an applied force can be resolved by measuring the resistance variations of the four resistors. The sensor is tested when a 0-3 N variant force is applied at elevation angles of 0° (normal), 30°, 45° and 60°. At each elevation angle, the sensor rotates from 0° to 360° at an increment of 30°. Good linearity (R &gt; 0.98) and high repeatability (standard deviation &lt; 8 %) are observed. Both normal and shear sensitivities are measured. The shear sensitivity is characterized in terms of both magnitude and direction of the applied force. The results show that the sensor has a high sensing ability to both normal and shear forces (compared to commercial load cell). In this paper, the sensor design, fabrication and testing are described. The sensor characterization and shear sensing ability are discussed.

scholarly journals Determination of the Shear Force at the Balance between Bacterial Attachment and Detachment in Weak-Adherence Systems, Using a Flow Displacement Chamber

2007 ◽  
Vol 74 (3) ◽  
pp. 916-919 ◽  
Author(s):  
M. Reza Nejadnik ◽  
Henny C. van der Mei ◽  
Henk J. Busscher ◽  
Willem Norde
Keyword(s):  
Bacterial Adhesion ◽  
Biofilm Formation ◽  
Shear Force ◽  
Polymer Brush ◽  
Bacterial Attachment ◽  
Adhesion Forces ◽  
Shear Forces ◽  
Flow Displacement

ABSTRACT We introduce a procedure for determining shear forces at the balance between attachment and detachment of bacteria under flow. This procedure can be applied to derive adhesion forces in weak-adherence systems, such as polymer brush coatings, which are currently at the center of attention for their control of bacterial adhesion and biofilm formation.

Tension Induces Changes in Lipid Lateral Diffusion in Model Fluid-Phase Membranes

2009 ◽  
Author(s):  
Hari S. Muddana ◽  
Ramachandra R. Gullapalli ◽  
Peter J. Butler
Keyword(s):  
Shear Stress ◽  
Membrane Fluidity ◽  
Shear Force ◽  
Transmembrane Proteins ◽  
Lateral Diffusion ◽  
Fluid Phase ◽  
Receptor Activation ◽  
Shear Forces ◽  
Model Fluid ◽  
G Protein Coupled

Shear stress due to blood flow on endothelial cells elicits numerous responses including G-protein coupled receptor activation and integrin-mediated signaling. Shear-induced change in membrane fluidity has been suggested to be one of the earliest mechanosensing mechanism involved in these processes [1, 2]. Alternatively, it has been suggested that shear forces are transduced through glycocalyx directly to transmembrane proteins and cytoskeleton [3], with very little shear force sensed by the membrane. It is not yet clear whether physiological tensions can alter membrane fluidity significantly.

Sign in / Sign up

Export Citation Format

Share Document