The Fused Deposition Modeling (FDM) technology can be successfully used to manufacture biodegradable polymeric scaffolds for tissue reconstruction in case of critical size bone damages. Carbon nanotubes (CNTs) are able to mimic the extracellular matrix and their addition can improve the mechanical and electrical properties of polymers. In this way, the scaffolds are more likely to match the host bone properties and the cell adhesion, differentiation and proliferation can be enhanced. In this paper scaffold-like specimens, manufactured by FDM technology, are tested to evaluate the conductivity increase in PLA/CNT composite compared to pure PLA (polylactid acid).

Active suspension can adapt itself to the rigidity and the damping characteristics based on the vehicle dynamic state and the road condition, making the suspension in the best state of shock absorbing, which can increase the handling stability, the ride comfort and the passing ability of vehicles. As for strikingly rugged roads like off-road conditions, the traditional active suspension can hardly balance the contradiction between the wheel adhesion and the vertical accelerated speed of the body. In this paper, an active suspension in which the position of the vehicle body can be adjusted is proposed. In the proposed suspension, a series of electric cylinders are installed, which can actively adjust the position between the vehicle body and the suspension in order to achieve the purpose of controlling the relative body-wheels position. In this manner, AMESim is used to set up three suspension designs which include suspension supporter adaptation equipment with different locations in the system. Through simulation analysis, the paper has explored the feasibility of the vehicle attitude control of the three suspension designs under off-road conditions. The results proved that the active suspension system with adjustable body position can restrain the body roll or pitch efficiently in which this technology can be applied to the body attitude control when ORVs are at high speed.

Accurately estimating road adhesion coefficient is very important for vehicle stability control system. In this paper, an innovation method to estimate the road adhesion coefficient is proposed. This method can be used in vehicles without additional sensors. And this method is especially suitable to be used in the intelligent vehicle equipped with steer-by-wire (SBW) system. When vehicle steers, releasing the steering wheel suddenly will result in rebound to a certain angle. When the steer wheel turns the same angle on different road whose adhesion coefficients are different, the front wheel rebound angles are different. The friction moment between the road and tire is the main factor to prevent the tire from turning back, and the coefficient of friction is equal to road adhesion coefficient when the vehicle is stationary. In this paper, the detailed dynamical models describing the whole process of the front wheel and tire rebound are established. Furthermore, the Luenberger reduced-order disturbance observer is established to estimate the friction moment, and then the adhesion coefficient is estimated. The SBW system which is usually equipped in intelligent vehicles can control the steer moment and steer angle accurately. When the steer wheel turns to certain angle, the SBW system is able to stop outputting torque quickly and timely, which is important for improving the experiment accuracy. In this paper, the SBW system is used to conduct an experiment on different roads. The experiment results demonstrate the validity of this method.

The suspension is one of the most important systems in a vehicle, which can decrease the vehicle body vibration and maintain good ride performance and driving stability. As for strikingly rugged roads like off-road conditions, the traditional active suspension can hardly balance the contradiction between the wheel adhesion and the vertical accelerated speed of the body. To accelerate to a higher speed while ensuring the ride performance at the same time, high-quality suspension system must be created and applied. As we all know, the active suspension can improve the driving stability and ride performance dramatically. In order to achieve the controllable adjustment of shock absorber damping and vehicle height, and realize the optimization of vehicle suspension performance, a new kind of active suspension which includes magnetorheological damper and servo electric cylinder is proposed. Then, the mathematical model of the proposed active suspension based on “Servo Electric Cylinder-Spring-Magnetorheological damper” is established after being simplified. Finally, the dynamic performances of the passive and active suspension in different modes are simulated by MATLAB based on its mathematical model and dynamic characteristic functions. The results indicate that the proposed active suspension, compared with the passive, can achieve the controlled adjustment of shock absorber damping and vehicle height, and ensure the ride performance.

By analyzing the key safety problems under the front-outside-tire burst steering condition, a vehicle stability control strategy is proposed in this paper, which is based on active front steering and differential braking systems. Taken both the handling stability and safety into account, we divided the whole control strategy into two layers, which are yaw moment control layer and the additional steering angle & tire force distribution layer. To solve the similar linear problem concisely, the LQR control is adopted in the yaw moment control layer. To achieve the goal of providing enough additional lateral force and yaw moment while keeping the burst tire in appropriate condition, the additional steering angle provided by active front steering system and the tire force distribution was adjusted step by step. To test the proposed control strategy performance, we modelling a basic front-outside-tire burst steering condition, in which the tire blows out once the vertical pressure reach the predefined critical value. Through simulation on different adhesion coefficient road, the control strategy proposed in this paper performance quite better compare with the uncontrolled one in aspect of movement, burst tire protection, handling stability.

This paper is a review on mechanical characteristics of natural fibers reinforced elastomers (both thermoplastics and thermosets). Increasing environmental concerns and reduction of petroleum resources attracts researchers attention to new green eco-friendly materials. To solve these environmental related issues, cellulosic fibers are used as reinforcement in composite materials. These days natural fibers are at the center of attention as a replacement for synthetic fibers like glass, carbon, and aramid fibers due to their low cost, satisfactory mechanical properties, high specific strength, renewable resources usage and biodegradability. The hydrophilic property of natural fibers decreases their compatibility with the elastomeric matrix during composite fabrication leading to the poor fiber-matrix adhesion. This causes low mechanical properties which is one of the disadvantages of green composites. Many researches have been done modifying fiber surface to enhance interfacial adhesion between filler particles and elastomeric matrix, as well as their dispersion in the matrix, which can significantly affect mechanical properties of the composites. Different chemical and physical treatments are applied to improve fiber/matrix interlocking.

The current miniaturization of several products requires manufacturing systems and methods able to meet the demanding specifications in terms of precision, efficiency, flexibility and reconfigurability. In particular, the manipulation and assembly of micro-components to obtain such products represent a crucial and challenging phase. For this reason, gripping tools have an essential role. At the micro-scale, the effects of adhesion forces can negatively affect the success and the precision of the manipulation operations, causing unexpected gripping or preventing the release of the components. Therefore, new micro-grippers and suitable release strategies have to be designed and developed to ensure high performance, overcoming the issues typical of the micro-scale. Among the different types of micro-grippers, vacuum micro-grippers represent a suitable tool to manipulate fragile and small components. In this context, this paper discusses different designs of an innovative vacuum micro-gripper integrating a simple and effective release system. The basic working principle is discussed and the related prototype is shown. Finally, a new design enhancement is also introduced to extend its applicability and release capability.

This paper focuses on the design of track-type climbing robots using dry adhesives to generate tractive forces between the robot and climbing surface to maintain equilibrium while in motion. When considering the design of these climbing robots, there are two primary elements of focus: the adhesive mechanisms at the track-surface interface and the distribution of these forces over the full contact surface (the tracks). This paper will present an approach to integrate a generic adhesion model and a track suspension system into a complete model that can be used to design general climbing robot systems utilizing a broad range of dry adhesive technologies.

Vertically-aligned carbon nanotube (VACNT) pads have recently received widespread attention for use as contact surfaces in material handling processes that involve the transfer of bare silicon wafers. Such processes will benefit from the strong friction force interactions and minimal adhesion force offered by these pads, allowing the wafer to be picked up, carried, and quickly placed, without encountering problems which may arise due to excessive adhesive forces. Despite these benefits, practical implementation has been hindered because VACNTs have nonlinear mechanical characteristics which are still not well understood. Consequently, significant attention has been devoted to fully understand and determine the behaviors associated with their nonlinear dynamic mechanical properties. Along this line, several experimental techniques are applied in this paper to further develop a comprehensive understanding of the mechanical behavior of these pads under compressive loading. It is important to note that the samples used in this testing are not standard VACNTs, but have been grown separately from the final substrate on which they are mounted during testing. After growth, the samples are turned upside-down and fixed so that the bottom ends of all VACNTs are planar and present an ultra-flat top surface for contact during manipulation. The tests performed in this research include a low energy impact test and position controlled load-displacement testing with both constant and sinusoidal velocity loading and unloading. Through these testing procedures, the dependencies of the VACNT material properties to compression depth and displacement rate are observed and an attempt is made to incorporate them into a continuous model. For this, the results from the low energy impact testing provide grounds to state the nature of the nonlinear behavior in our VACNTs. By interrogating the available data from each testing technique, a combination of information provided by the theoretical energy balance and the identified coefficients from the Levenberg-Marquardt curve-fitting algorithm is then applied to generate a parametrized phenomenological model of the VACNT pad behavior. The proposed identified model is continuous and reasonably accounts for the overall material behavior as seen in the experimental data. The validity of this model is shown by means of normalized vector correlation of over 99% between the results of the numerical simulations and the existing experimental data. The material behaviors observed in this research qualitatively support those of several earlier investigators who have previously recognized the complex dissipative behavior of VACNTs. The proposed work itself paves the road for developing a useful engineering model of VACNT pad dynamics which will enable their introduction to mechanical applications in industry.

Automotive wings are considered to be aerodynamic devices which have a significant effect on the driving, braking and cornering performances by influencing the flow of fluids around the vehicle without changing the weight of the vehicle. The wings have developed from having a fixed shape to multi-sectional wings in order to amplify the advantages of their aerodynamic effect in specific situations such as cornering and braking. However, the multi-sectional wings based on flaps, ailerons, and slats have to modify their surface or camber using hinged parts. These discrete sections create aerodynamic losses during shape changes. In this paper, a morphing car-spoiler based on a reinforced elastomer capable of continuous self-actuation throughout its surface was applied to a small-scale vehicle without slotted parts or mechanical elements. The designed morphing car-spoiler consists of a woven type Smart Soft Composite (SSC) which was made by weaving Shape Memory Alloy (SMA) wires and glass fibers embedded in a polydimethylsiloxane (PDMS) polymeric soft matrix. The phase transformation from martensite to austenite of the SMA wires creates an axial load in the longitudinal direction resulting in symmetric bending of the spoiler. Using an open-blowing type wind tunnel, tests were conducted on the stand-alone spoiler to verify its aerodynamic effects. Furthermore, to evaluate its performance in practice, the morphing car-spoiler was mounted on a small-scale vehicle and tested in a closed-type wind tunnel. Results show that the morphing car-spoiler generates a downforce which increases the normal tire adhesion and that it is possible to adapt its shape for various situations such as cornering and braking.

This research evaluates simulated walking micro-robots based on orthogonal lateral and vertical actuators, a common restriction on micro-electromechanical system (MEMS) actuation, and subject to small damping effects and certain small-scale external forces operating on robot feet. Dimensional analysis is used to identify scalable trends in a numerical simulation of a simple walking dynamics model in which lateral and vertical motion are treated as dynamically-uncoupled, the limiting case for orthogonal MEMS actuators. The results of this analysis are that the system damping significantly affects walking speed, while small-scale foot-ground interaction forces other than adhesion have significant effects only over large order-of-magnitude variation in robot size. Results are intended to serve as a design tool for walking micro-robots.

In this investigation, use of the LuGre tire friction model for the transient brake force analysis is discussed. In particular, a numerical procedure for estimating parameters for the LuGre tire force model is developed. The parameters of the distributed LuGre model are identified such that the error function of tire forces obtained using the model and experiment can be minimized. Friction parameters used in the LuGre tire force model are estimated using the characteristics curve of the friction coefficient as a function of the slip velocity first, and then the adhesion parameter is estimated using the slope around the zero slip ratio using the least square fitting. Iterative solution procedures are then employed to identify the overall model parameters using the initial estimates provided. It is demonstrated that use of the proposed numerical procedure leads to accurate prediction of the LuGre model parameters for various loading and speed conditions. Furthermore, it is demonstrated that the decrease in the peak of the brake force as the increase in the running speed can be well predicted using the transient distributed LuGre tire force model with model parameters predicated using the proposed procedure.

There is great interest in the application of proximal probe techniques to simultaneously image and measure mechancial properties of surfaces with nanoscale spatial resolution. There have been several innovations in generating time-resolved force interaction between the tip and surface while acquiring a tapping mode AFM image. These tip/sample forces contain information regarding mechanical properties of surfaces in an analogous fashion to a force curve experiment. Here, we demonstrate, via simulation, that the maximum and minimum tapping forces change with respect to the Young’s modulus and adhesiveness of a surface, but the roughness of the surfaces has no effect on the tapping forces. Using these changes in tapping forces, we determine the mechanical changes of a lipid membrane after exposure to a huntingtin exon1 (htt exon1) protein with an expanded polyglutamine (polyQ) domain. Expanded polyQ domains in htt is associated with Huntington’s disease, a genetic neurodegenerative disorder. The htt exon1 protein caused regions of increased surface roughness to appear in the lipid membrane, and these areas were associated with decreased elasticity and adhesion to the AFM probe.

Unless protected by an inert gas atmosphere, micro-scale conjunctions are often separated by molecularly-thin adhered films. Therefore, predicting contact load, friction or adhesion, must consider the contribution of this layer to the overall contact problem. The contribution of an adhered layer can be accounted for using a simplified solution (e.g. an adjustment to the energy of adhesion to account for the liquid film). However, these methods cannot account for layers consisting of multiple species of molecules. The most common approach, which accounts for inter-molecular forces between molecules of various species, is a molecular dynamics simulation. However, this is time consuming, and therefore, often limited for small volumes of fluid and small scale contacts. The current paper proposes an alternative approach, where the pressure and shear between two smooth surfaces separated by an ultra-thin film is predicted using a statistical mechanics based model. This method accounts for the chemical structure of each species of molecules comprising the ultra-thin film, their concentration, intermolecular forces and adsorption to the wall. This approach is very fast, therefore, it can be easily included in a larger scale code predicting the behavior of the entire micro-scale mechanism. It was found that for a specified material of the solid boundary the model can predict the optimal concentration of each species of molecule in the intervening ultra-thin film, to minimize friction or adhesion.

This paper proposes a conceptual design for a microscale experimental device that could be used to investigate oblique, intermittent contact while allowing for tangential slip and adhesion/stiction at the contact interface. The discussion includes a formulation of a reduced-order model of the nonlinear device dynamics. Emphasis is given to a possible contact model that incorporates normal and tangential compliance, friction-like limits on the ratio of tangential to normal contact forces, adhesive interactions, and irreversible energy loss in the normal contact interactions. A preliminary theoretical and numerical analysis is performed on this contact model in order to assess the influence of adhesion and energy loss on the contact phase. The results consider both the case of a normal collision in the absence of coupling between normal and tangential degrees of freedom as well as the general case of an oblique impact with such coupling. The paper argues that there is great value in an experimental validation of such a model for microscale contact, as a growing number of devices either rely on contact directly or must accommodate and design for its possible occurrence. In addition, mention is made of a number of inconsistencies and paradoxes observed in macroscopic models of rigid-body contact with friction that warrant validation or resolution through appropriate experimental designs.

This paper investigates the optimization of electrode geometry in electrostatic adhesives to enhance adhesion forces for use in robotic climbing and gripping applications. Electrostatic adhesion provides an attachment mechanism that is both controllable and effective over a wide range of surfaces including conductive, semi-conductive, and insulating materials. The adhesives function by utilizing a set of high voltage electrodes that generate an electric field. This electric field polarizes the substrate material, thus generating an adhesion force. Optimizing the geometry of these conductive electrodes provides enhanced adhesion forces that increase attachment robustness. To accomplish this, FEA software was used to evaluate the generated electric field for a given electrode configuration. A range of electrode widths and gap sizes were evaluated to find the optimal configuration. These findings were compared with experimental results for different pad geometries over a range of surface types. Experimental results indicate that on smooth surfaces the simulation results are representative of the actual recorded adhesion forces. Rough surfaces provide similar trends but with varying optimal configurations, likely due to the level of electric field dispersion.

Modeling and measurement of stiction or adhesion due to van der Waals force between microstructures and micro-gripper tools are important for contact-based manipulation and assembly of microstructures. Microfabricated structures commonly feature rough tapered curved surfaces due to undercutting and surface alterations inherent in the microfabrication processes. While several theoretical models exist for calculating adhesive forces between microstructures featuring spherical, cylindrical and flat surfaces, a model for estimating adhesive forces between microstructures featuring tapered curved surfaces is lacking in the literature. This paper presents experimentally measured values of adhesion or pull-off force between a rough tapered curved microstructure from a rough plane surface using a custom micro-cantilever beam as a force sensing mechanism. The paper also introduces an approach to estimate adhesive force between a tapered curved surface and a flat surface by considering the tapered curved surface as a frustum of a cone bound between two cylinders and using the van der Waals force model for cylinders. It is shown that the experimentally measured adhesive force values lie within the upper and lower values of the theoretically estimated van der Waals force values for the two cylinders that define the tapered curved surface geometry.

Graphene has attracted great interest due to its exceptional electrical, mechanical, and chemical properties since its discovery in 2004. Since its first realization, the substrate of choice for graphene exfoliation has been Si wafer with approximately 300 nm thick SiO 2 dielectric layer, because it allows 1) direct optical detection of monolayer flakes, and 2) a convenient back gate with dielectric for controlling carrier density in the graphene. However, the amorphous structure of SiO 2 and its associated surface roughness has led to ongoing controversy in determining the structure of SiO 2 -supported graphene. The conductivity of graphene allows scanning tunneling microscopy (STM) to be used to measure its topography, generally allowing its structure to be atomically resolved. In contrast, the insulating SiO 2 must be probed with atomic force microscopy (AFM), and this is often done using ambient tapping-mode AFM. STM measurements of graphene on SiO 2 generally show greater roughness and finer corrugation than is seen in AFM measurements of SiO 2 , and this has been interpreted as evidence for “intrinsic” corrugation of the graphene. However, when the energetics of adhesion and elasticity are considered, the idea of intrinsic structure becomes quite controversial for graphene supported on a substrate. Here we show that UHV non-contact AFM (NC-AFM) measurement of SiO 2 reveals structure unresolved in previous measurements, and shows both greater roughness and smaller lateral feature size than seen for graphene measured by STM. High-resolution measurement of the SiO 2 topography enables an analysis based on the energetics of graphene bending and adhesion, showing that the graphene structure is highly conformal to the SiO 2 beneath it. The topographies reported here contrast the atomically-flat crystalline surfaces used in benchmark NC-AFM measurements. They pose unique challenges for measurement resolution, and highlight the very different physical mechanisms which determine resolution in STM vs. NC-AFM. We discuss these issues and our recent efforts at quantitative modeling of the imaging process, with particular focus on the role of van der Waals forces and their contribution to the image signal.

Usually microorganisms, molecules, or viruses in the fluidic environment are at very low Reynolds numbers because of tiny diameters. At very low Reynolds numbers, viscous forces of molecules and viruses will dominate. Those micro- or nanoparticles will stop moving immediately when flows cease and drag forces disappear, those phenomena were discovered by the fluorescent particle experiment. Of course, molecules and viruses are still subject to Brownian motion and move randomly. In order to increase the adhesion density of micro- and nanoparticles on sensor’s surface, designs of the flow movements in microfluidic channel is proposed. Adhesion density of linker 11-mercaptoundecanoic acid (MUA) and Turnip yellow mosaic virus (TYMV) with specific quantum dots were measured by confocal microscope. Fluorescent intensity and coverage of quantum dots are used to identify the adhesion density quantitatively. Results show that TYMV and MUA layers disperse randomly by dipping method. Fluorescent intensity of quantum dots; i.e. relative to the amount of MUA and TYMV; were 2.67A.U. and 19.13A.U., respectively, in W-type microfluidic devices to contrast just 1.00A.U. and 1.00A.U., respectively, by dipping method. Coverage of MUA and TYMV were 80∼90% and 70∼90%, respectively, in W-type microfluidic channel to contrast just 20∼50% and 0∼10%, respectively, by dipping method.

We have developed a polymer MEMS sensor for measuring mechanical forces generated by single adherent cells. Mechanical forces are known to play a role in cell regulation, and measuring these forces is an important step in understanding cellular mechanotransduction. The sensor consists of four polystyrene microcantilever beams with cell adhesion pads at each end. Finite element analysis was used to guide the design of a compound cantilever to allow measurement of forces in multiple directions. The device was evaluated by measuring forces generated by WS-1 human skin fibroblasts. A single cell was placed on the sensor using a custom micromanipulator. Forces were calculated by optically measuring the deflection of each probe during cell attachment and spreading. Measurements were performed on normal cells and those treated with cytochalasin D to disrupt the actin cytoskeleton. Cytochalasin D treated cells showed a significant decrease in force. This device can be used to evaluate the mechanical response of cells to a variety of chemical, mechanical, and other environmental stimuli.