Sidewall Adhesion Research Articles

Process applicability and hole wall microstructure evolution mechanism of femtosecond laser spiral drilling

In this work, a 1.5 mm thick GH3044 nickel-based superalloy is processed by femtosecond laser to obtain a micro-hole for the fuel nozzle of an aerospace engine with a large thrust-to-weight ratio. To address the issue of sidewall adhesion during micro-hole machining, a spiral drilling method implemented with a rotating wedge scanning module is used. Combined with a two-step drilling strategy, it achieves flexible removal of adhesion while ensuring machining efficiency and further improving the quality of drilling. The effect of different drilling strategies on the sidewall roughness of micro-holes is investigated. After process optimization, the roughness of the the micro-hole sidewalls is reduced to below Rq 0.4 μm, which is approximately 8% compared to the traditional one-step drilling strategy. Based on the EBSD analysis results, it is observed that the microstructure of the micro-hole sidewalls remains largely unchanged regardless of the drilling strategy employed. The analysis of the micro-hole sidewalls shows the presence of periodic microstructures. When aiming for low roughness, the geometric characteristics of these periodic microstructures can be adjusted by manipulating the laser's single pulse energy. These experimental findings present a new perspective for optimizing the femtosecond laser drilling process and provide theoretical support for future enhancements in the actual fuel injection effect.

Experimental Study on Torsion Resistance of Foundation Ring Land-Based Wind Power Expanded Foundation Scale Model

In this paper, an experimental torsion resistance-loading system for wind power extended foundation scale models is taken as the research object, and four 1:3 scale model specimens of the foundation ring are tested. The transmission mechanism of torque load in the extended foundation was analyzed, and the proportion of each part bearing the torque load was calculated. Test results showed that when the torque load was small, the torque load transmitted from the upper part was mainly borne by the sidewall adhesion force, as well as the top radial reinforcement. In contrast, the torque load was gradually borne by the anchor flange of the foundation ring in the case of a large torque load. At the middle and late stages of torque loading, the top radial reinforcement of the foundation shared about 20% of the torque load, while the bottom flange of the foundation ring shared about 80%. The torque load is most sensitive to changes in the size of the bottom flange but not sensitive to those in the embedded depth of the foundation ring or in the strength of the foundation concrete.

Phonon scattering at kinks in suspended graphene

Recent experiments have shown surprisingly large thermal time constants in suspended graphene ranging from 10 to 100 ns in drums with a diameter ranging from 2 to 7 microns. The large time constants and their scaling with diameter points towards a thermal resistance at the edge of the drum. However, an explanation of the microscopic origin of this resistance is lacking. Here, we show how phonon scattering at a kink in the graphene, e.g. formed by sidewall adhesion at the edge of the suspended membrane, can cause a large thermal time constant. This kink strongly limits the fraction of flexural phonons that cross the suspended graphene edge, which causes a thermal interface resistance at its boundary. Our model predicts thermal time constants that are of the same order of magnitude as experimental data, and shows a similar dependence on the circumference. Furthermore, the model predicts the relative in-plane and out-of-plane phonon contributions to graphene's thermal expansion force, in agreement with experiments. We thus show, that in contrast to conventional thermal (Kapitza) resistance which occurs between two different materials, in 2D materials another type of thermal interface resistance can be geometrically induced in a single material.

Load dependent frictional response of vertically aligned single-walled carbon nanotube films

Here we use microscratch testing to demonstrate how a single-walled carbon nanotube (SWCNT) forest material can exhibit variable adhesion properties with solid surfaces ranging from negligible adhesion at low loading due to the normal alignment of SWCNTs to maximum adhesion at high loading that exploits the extraordinary sidewall adhesion of SWCNTs. This observation, which exhibits no analog in conventional bulk materials, is correlated to loading-induced structural modification of the low-density SWCNT-substrate interface morphology. This observation opens new pathways to use structural modification of low density materials to engineer and control a wide range of adhesion properties with solid surfaces.

Sidewall Adhesion Evolution in Epitaxial Polysilicon as a Function of Impact Kinetic Energy and Stopper Area

This paper investigates the evolution of adhesion forces during dynamic contacts, which simulate realistic shocks. The developed method accounts for the differences in offset, resonance, and quality factor among the devices under test to precisely predict (and monitor) the kinetic impact energy during shocks. The results clearly show that adhesion force grows and stabilizes at an increasing amplitude with the applied impact energy. This dynamic adhesion is also dependent on the contact area, while the native adhesion on the same specimens was independent of it. Finally, a relaxation of the adhesion force with a very long time constant is observed after the end of the tests. [2015-0169]

Suction caisson foundations for offshore wind turbines subjected to wave and earthquake loading: effect of soil–foundation interface

The response of wind turbines founded on suction caissons and subjected to lateral monotonic, cyclic and earthquake loading is studied with due consideration of the role of soil–sidewall adhesion, using non-linear three-dimensional finite-element analyses. In the case of monotonic and slow cyclic lateral loading it is shown that imperfect interface bonding could reduce the moment capacity and may lead to foundation detachment or even uplifting in the case of shallowly embedded caissons. A preliminary comparison of two caisson alternatives has shown that increasing the caisson diameter while maintaining the embedment ratio is more efficient in terms of material resources than increasing the skirt length while keeping the diameter constant. The second part of the study evaluates the response of a soil–foundation–wind turbine interacting system subjected to earthquake shaking. Contrary to an often prevailing impression that seismic effects are insignificant, apparently originating from evaluating the seismic behaviour on the basis of spectral characteristics, it is illustrated that the system kinematics may prove crucial for the response of large wind turbines subjected to simultaneous environmental and seismic loads. Although not instantly catastrophic, the accumulation of foundation rotation could lead to the turbine reaching serviceability limits early during its operation.

A Modified Sidewall Adhesion Model: Hypothesis-Building and Testing Tool for a Surgical Experimental Research

This editorial opinion article is based on our own experience and literature review. The NESA adhesion formation study team members recommend an unique model as a hypothesis building and testing tool in a surgical experimental research.

Effect of fluorocarbon self-assembled monolayer films on sidewall adhesion and friction of surface micromachines with impacting and sliding contact interfaces

A self-assembled monolayer film consisting of fluoro-octyltrichlorosilane (FOTS) was vapor-phase deposited on Si(100) substrates and polycrystalline silicon (polysilicon) surface micromachines. The hydrophobic behavior and structural composition of the FOTS film deposited on Si(100) were investigated by goniometry and X-ray photoelectron spectroscopy, respectively. The effects of contact pressure, relative humidity, temperature, and impact/sliding cycles on the adhesive and friction behavior of uncoated and FOTS-coated polysilicon micromachines (referred to as the Si and FOTS/Si micromachines, respectively) were investigated under controlled loading and environmental conditions. FOTS/Si micromachines demonstrated much lower and stable adhesion than Si micromachines due to the highly hydrophobic and conformal FOTS film. Contrary to Si micromachines, sidewall adhesion of FOTS/Si micromachines demonstrated a weak dependence on relative humidity, temperature, and impact cycles. In addition, FOTS/Si micromachines showed low and stable adhesion and low static friction for significantly more sliding cycles than Si micromachines. The adhesive and static friction characteristics of Si and FOTS/Si micromachines are interpreted in the context of physicochemical surface changes, resulting in the increase of the real area of contact and a hydrophobic-to-hydrophilic transition of the surface chemical characteristics caused by nanoscale surface smoothening and the removal of the organic residue (Si micromachines) or the FOTS film (FOTS/Si micromachines) during repetitive impact and oscillatory sliding of the sidewall surfaces.

Effect of Galvanic Corrosion-Induced Roughness on Sidewall Adhesion in Polycrystalline Silicon Microelectromechanical Systems

A custom microdevice was used to study the effect of hydrofluoric acid processing on the force of adhesion at a silicon sidewall contact interface. Devices exposed to acidic etchant solution for a longer period of time were found to have a significantly higher surface roughness and a lower adhesion force. These results are attributed to an accelerated formation of porous silicon caused by a release etch-induced galvanic couple between the structural silicon and the gold electrical contact pads. Experiments are interpreted in light of galvanic corrosion mechanisms and the effect on the principal components in nanoscale adhesion.

Sidewall Adhesion and Sliding Contact Behavior of Polycrystalline Silicon Microdevices Operated in High Vacuum

The reliability and performance of contact-mode microelectromechanical systems (MEMS) depend strongly on the tribological properties of contact interfaces. Knowledge of the dominant friction and wear mechanisms at submicrometer length scales is therefore of paramount importance to the design of MEMS devices with contact interfaces. The objective of this study was to examine changes in the adhesion behavior and morphology of sliding sidewall surfaces of polycrystalline silicon MEMS devices operated in high vacuum (~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> torr) and under low apparent contact pressures (0.1-18 kPa) and correlate these changes to the operation lifetime. Sidewall adhesion increased with applied contact pressure. Typically, a twofold to fourfold increase in side wall adhesion was measured upon cessation of the device operation (typically, ~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> sliding cycles) due to the increase of the static friction force above the restoring force available by the device. Scanning electron microscopy (SEM) revealed very small amounts of ultrafine wear debris (10-140 nm) on the sidewall surfaces of about half of the tested devices, without discernible changes in the surface topography. Cross-sectional transmission electron microscopy (TEM) showed that sliding did not cause the removal of the silicon oxide film (5-13 nm in average thickness) from the sidewall surfaces. Atomic force microscopy (AFM) indicated that sliding contact was confined at the top of a few elevated ridges on the sidewall surfaces, resulting in nanoscale wear that smoothened locally the surfaces. SEM, TEM, and AFM results of this study show that the tribological properties of contact-mode MEMS devices operating in high vacuum are controlled by only a few nanoscopic contacts, which depend on the local nanotopography of the interacting surfaces.

Evolution of sidewall adhesion in surface micromachines due to repetitive impact loading

A contact-mode surface micromachine consisting of polycrystalline silicon was used to study the effect of repetitive impact loading on the evolution of adhesion at sidewall contact interfaces under different conditions of contact load, ambient pressure, and relative humidity. All micromachines demonstrated an initial run-in phase of low and stable adhesion force, followed by a surface modification phase characterized by the rapid increase of the interfacial adhesion force. The nonlinear increase of the adhesion force with impact cycles was found to be in direct correlation with the micromachine operation lifetime. A criterion of micromachine failure due to excessive interfacial adhesion (stiction) was formulated based on the observed experimental trend. Micromachine lifetime decreased nonlinearly with the increase of the maximum contact pressure. The adhesion force of micromachines operated in vacuum or high-humidity atmosphere increased faster than those operated in dry atmosphere. Despite the significant increase of the adhesion force with impact cycles, high-magnification scanning electron microscopy did not reveal any discernible changes in the surface topography even after 3 × 107 impact cycles. The evolution of the interfacial adhesion force is attributed to the increase of the real area of contact and the work of adhesion due to nanoscale surface smoothening and the removal of adsorbed contaminant layers, respectively. Physical and chemical surface modification is interpreted in the context of results obtained for different maximum contact pressures, ambient pressures, and relative humidity levels.

Tissue levels of cisplatin in previously traumatized tissue without adhesion formation in a rabbit sidewall adhesion and intraperitoneal delivery model

5525 Background: It has been hypothesized that the presence of extensive adhesions after ovarian cancer resection may limit the distribution of intraperitoneal (IP) chemotherapeutics. The objective of this study was to determine if using a hyaluronate/carboxymethylcellulose (HA/CMC) barrier to prevent adhesions during a simulated tumor resection surgery would increase tissue drug levels following subsequent IP chemotherapy. Methods: A sidewall defect/cecal abrasion model was used to induce adhesion formation and simulate tumor resection trauma in 22 rabbits. Seven rabbits received HA/CMC at the end of the surgery. Four weeks after surgery, cisplatin (2.5mg/kg) was administered IP to HA/CMC treated and untreated animals or IV to untreated controls. Animals were sacrificed 24hrs after infusion and tissue samples were collected from inside the defect (with or without adhesions) and outside the defect on the contralateral sidewall. Samples were cryosectioned and analyzed for platinum content by ICP/MS. Results: Platinum tissue levels in the uppermost peritoneal layer (0–1mm) were significantly higher for IP delivery than IV and were the highest for IP delivery when no adhesions were present inside the defect. Platinum levels were significantly higher in the previously traumatized tissue inside the defect than in untraumatized tissue outside the defect. This was consistent for both IP or IV and HA/CMC treated or untreated animals. The benefit of HA/CMC was underscored by the fact that samples under adhesions could not be obtained for that group due to the significant reduction in adhesion formation compared to untreated controls. Conclusions: Recently traumatized tissue without adhesions had the highest platinum levels following IP cisplatin in this model. The previously traumatized tissue had significantly higher platinum levels than untraumatized tissue likely due to both increased peritoneal diffusion and systemic delivery components. [Table: see text] [Table: see text]

An experimental study of sidewall adhesion in microelectromechanical systems

A surface micromachine was designed specifically for studying sidewall adhesion in microelectromechanical systems (MEMS). The dependence of surface adhesion on contact load and ambient conditions was investigated under quasistatic normal loading conditions. Insight was obtained into the relative contributions of van der Waals and capillary forces to the measured adhesion force. Several shortcomings in previous adhesion studies of MEMS were overcome, and measurement of the true adhesion force was achieved under different testing conditions. The present experimental procedure enables the isolation of the van der Waals component of the adhesion force and the determination of the contributions of both contacting and noncontacting asperities to the total adhesion force at the inception of surface separation. The major benefits of the developed experimental methodology and surface micromachine are discussed in the context of adhesion results obtained for different values of apparent contact pressure, ambient pressure, and relative humidity.

An investigation of sidewall adhesion in MEMS

Adhesion or stiction is a key problem in surface micromachining technology, affecting the reliability of most MEMS. To date, the quantitative analysis of the phenomenon has been limited to in-plane adhesion. Since many micromechanisms involve contacts between sidewalls, we have designed a microinstrument to measure sidewall adhesion. Here, we describe the design, modeling, results and problems encountered with this first generation of sidewall adhesion devices.

Costop in the prevention of adhesions

Adhesion formation is a significant source of postoperative morbidity. Current barrier products on the market in the United States are difficult to use during a laparoscopic procedure or over irregular surfaces. The efficacy of a sprayable adhesion prevention barrier, CoStop, was evaluated in three separate rabbit adhesion models. In an initial study, the effect of CoStop and Seprafilm bioresorbable membrane was evaluated in a rabbit uterine horn abrasion model. At necropsy, 67% of the CoStop-treated rabbits and 61% of the Seprafilm-treated animals were adhesion free. In a rabbit sidewall adhesion formation model, 90% of rabbits treated with CoStop were free of adhesions at necropsy, whereas all surgical controls formed adhesions. A comparable level of efficacy was observed in a rabbit re-formation model in which adhesions were generated and lysed 1 week later. After adhesiolysis, all control rabbits re-formed adhesions over 95% of the area. In contrast, 67% of the CoStop- and 38% of the Seprafilm-treated rabbits were adhesion free. Histological evaluation performed on tissues from the studies indicates that the CoStop barrier is biocompatible in all three surgical situations. CoStop-treated animals in all adhesion models showed a significant reduction in the incidence, extent, and severity of adhesion formation.

Evaluation of Polyethylene Glycol/Polylactic Acid Films in the Prevention of Adhesions in the Rabbit Adhesion Formation and Reformation Sidewall Models

Objective: To assess the efficacy of bioresorbable films consisting of various polyethylene glycol 6000 and polylactic acid block copolymers on the formation and reformation of adhesions in rabbit models of adhesion development between the sidewall to the adjacent cecum and bowel. The composition of the different polymers was expressed by the number of monomeric units in the block, namely, ethylene oxide (EO) and lactic acid (LA), respectively. Design: Studies of the efficacy of EO/LA films were conducted in rabbit sidewall adhesion formation studies in the presence and absence of blood and in rabbit adhesion reformation studies. REPEL (Life Medical Sciences, Edison, NJ), a film of EO/LA ratio 3.0 manufactured under commercial conditions, was also tested in these animal models. Setting: University-based laboratory. Animals: New Zealand white rabbits. Intervention(s): Placement of films of various EO/LA ratios at the site of injury to the parietal peritoneum. Main Outcome Measure(s): Adhesion formation and reformation. Result(s): Films of various EO/LA ratios, Seprafilm (Genzyme, Cambridge, MA) and Interceed (Johnson and Johnson Medical, Arlington, TX) placed over an area of excised sidewall at the time of initial injury were highly efficacious in the prevention of adhesion formation. A film of EO/LA ratio 3.7, in contrast with Interceed, was also shown to maintain maximal efficacy in the reduction of adhesion formation in the presence of blood. Further, a film of EO/LA ratio 3.0 produced under commercial conditions, REPEL, was highly efficacious in reducing adhesion development in the rabbit models of adhesion and reformation. Conclusion(s): These studies suggest that bioresorbable EO/LA films reduced adhesion development in rabbit models of adhesion formation and reformation.

Application of the cavitron ultrasonic surgical aspirator (CUSA) for gynecological laparoscopic surgery using the rabbit as an animal model

To study the potential application of the cavitron ultrasonic surgical aspirator (CUSA) in gynecological laparoscopic surgery using a rabbit animal model. Twenty-six rabbits were prospectively randomized into two groups. Laparoscopically directed standard injuries were made on the randomly assigned horn and sidewall in all animals with the CUSA. Contralateral injuries were made with a contact neodymium-yttrium aluminum garnet (Nd:YAG) laser in group 1 and with bipolar cautery in group 2. Adhesion and inflammation scores were assessed for two animals in each group at 24, 48, and 72 hours, and seven animals in each group at 14 days. University animal research facility. Adhesion and inflammation scores were compared between animals in the CUSA versus Nd:YAG study and the CUSA versus bipolar cautery at 14 days. No significant difference in uterine or sidewall adhesion scores was noted between the CUSA versus Nd:YAG or the CUSA versus bipolar cautery. Bipolar cautery produced significantly less inflammation on the uterine horn compared with the CUSA (3.0 +/- 0.2 versus 5.3 +/- 0.7, P = 0.0001), but no difference in sidewall inflammation was noted between the CUSA compared with bipolar cautery. No difference in inflammation was observed between the CUSA and the Nd:YAG laser. The bipolar cautery appears to be preferable to the CUSA for coagulation of uterine lesions, although dissection of the uterus is not possible with bipolar cautery. The CUSA and the Nd:YAG appear to be comparable for uterine horn dissection. Because the CUSA causes similar adhesion formation and tissue inflammation at the sidewall when compared with the Nd:YAG laser and bipolar cautery and may be less likely to damage blood vessels, ureters, or other collagen-rich tissues, the CUSA may represent a promising new surgical tool for laparoscopically directed peritoneal dissection.