Design of ‘Tolerant and Hard’ Superhydrophobicity to Freeze Physical Deformation

While the development of mechanically durable and abrasion tolerant superhydrophobicity on a rigid interface itself remains a highly challenging task, the design of superhydrophobic coating that can restrict both the...

The Effect of Transverse Shear in Symmetric and Asymmetric End Notch Flexure Tests–Analytical and Numerical Modeling

This paper focuses on the effects of transverse shear and root rotations in both symmetric and asymmetrical end-notched flexure (AENF) interlaminar fracture toughness tests. A theoretical model is developed, whereas the test specimen is subdivided into four regions joined by a rigid interface. The differential equations for the deflection and rotations of each region are solved within both the Euler–Bernoulli simple beam theory (SBT) and the more refined Timoshenko beam theory (TBT). A concise analytical equation is derived for the AENF deflection profile, compliance, and transverse shearing forces as a function of the specimen geometry, stacking sequence, delamination length, and fixture span. Modeling results are compared with numerical finite element analyses, obtaining a very good agreement. Performed analyses suggest that even in the case of symmetrical and unidirectional laminates considered as pure mode II fracture, a complex compression/tension and bending moment state is present, as well as a slight contribution of anti-planar shear at the vicinity of the crack tip.

Experimental Testing and Analytical Modeling of Asymmetric End-Notched Flexure Tests on Glass-Fiber Metal Laminates

An experimental campaign on glass-fiber/aluminum laminated specimens was conducted to assess the interlaminar fracture toughness of the metal/composite interface. Asymmetric end-notched flexure tests were conducted on specimens with different fiber orientation angles. The tests were also modeled by using two different analytical solutions: a rigid interface model and an elastic interface model. Experimental results and theoretical predictions for the specimen compliance and energy release rate are compared and discussed.

Mass transfer around bubbles flowing in cylindrical microchannels

This work focuses on the mass transfer around unconfined bubbles in cylindrical microchannels when they are arranged in a train. We characterise how the mass transfer, quantified by the Sherwood number, $Sh$, is affected by the channel and bubble sizes, distance between bubbles, diffusivity, mean flow velocity, deformation of the bubble, the presence of surfactants in the limit of rigid interface and off-centred positions of the bubbles. We analyse the influence of the dimensionless numbers and especially the distance between bubbles and the Péclet number, $Pe$, which we vary over eight decades, identifying five different mass transfer regimes. We show different concentration patterns and the dependence of the Sherwood numbers. These regimes can be classified by either the importance of the diffusion along the streamlines or the interaction between bubbles. For small $Pe$ the diffusion along the streamlines is not negligible as compared to convection, whereas for large $Pe$ convection dominates in the streamlines direction and, thus, crosswind diffusion becomes crucial in governing the mass transfer through boundary layers or the remaining wake behind the bubbles. Interaction of bubbles occurs for very small $Pe$ where the mass transfer is purely diffusive, or for very large $Pe$ where long wakes eventually reach the following bubble. We also observe that the bubble deformability mainly affects the $Sh$ in the regime for very large $Pe$ in which bubbles interaction matters, and also that the rigid interface affects the boundary layer and the remaining wake. The effect of off-centred position of the bubble, determined by the transverse force balance, is also limited to large $Pe$. The boundary layers on rigid bubble surfaces are thicker than those on stress-free bubble surfaces, and thus the mass transfer is weaker. For centred bubbles, the influence of inertia on the mass transfer is negligible. Finally, we discuss the implication of our results on the dissolution of bubbles.

Custom-Fit Three-Dimensional-Printed BiPAP Mask to Improve Compliance in Patients Requiring Long-Term Noninvasive Ventilatory Support

Noninvasive ventilator support using bi-level positive airway pressure/continuous positive airway pressure (BiPAP/CPAP) is commonly utilized for chronic medical conditions like sleep apnea and neuromuscular disorders like amyotrophic lateral sclerosis (ALS) that lead to weakness of respiratory muscles. Generic masks come in standard sizes and are often perceived by patients as being uncomfortable, ill-fitting, and leaky. A significant number of patients are unable to tolerate the masks and eventually stop using their devices. The goal of this project is to develop custom-fit masks to increase comfort, decrease air leakage, and thereby improve patient compliance. A single-patient case study of a patient with variant ALS was performed to evaluate the custom-fit masks. His high nose bridge and overbite of lower jaw caused poor fit with generic masks, and he was noncompliant with his machine. Using desktop Stereolithography three-dimensional (3D) printing and magnetic resonance imaging (MRI) data, a generic mask was extended with a rigid interface such that it was complementary to the patient's unique facial contours. Patient or clinicians interactively select a desired mask shape using a newly developed computer program. Subsequently, a compliant silicone layer was applied to the rigid interface. Ten different custom-fit mask designs were made using computer-aided design software. Patient evaluated the comfort, extent of leakage, and satisfaction of each mask via a questionnaire. All custom-fit masks were rated higher than the standard mask except for two. Our results suggest that modifying generic masks with a 3D-printed custom-fit interface is a promising strategy to improve compliance with BiPAP/CPAP machines.

Mixed Electrical Conditions on Interface Inclusion in a Piezoelectric Bimaterial under Antiplane Mechanical and Inplane Electric Loadings

An absolutely rigid interface inclusion in a bimaterial piezoelectric space under the action of antiplane mechanical and in-plane electric loadings is analyzed. One zone of the inclusion is electrically insulated while the other part is electrically permeable. This problem is important for engineering application, but it has not been solved earlier in an analytical way. Presenting all electromechanical quantities via sectionally analytic vector functions, the combined Dirichlet-Riemann boundary value problem is formulated. An exact analytical solution of this problem is obtained. Closed form analytical expressions for electromechanical quantities at the interface are derived. Some of these values are also presented graphically along the corresponding parts of the material interface. Singular points of the shear strain and the electric displacement are found and the corresponding intensity factors are determined as well.

Elastodynamic image forces on screw dislocations in the presence of phase boundaries

The elastodynamic image forces acting on straight screw dislocations in the presence of planar phase boundaries are derived. Two separate dislocations are studied: (i) the injected, non-moving screw dislocation and (ii) the injected (or pre-existing), generally non-uniformly moving screw dislocation. The image forces are derived for both the case of a rigid surface and of a planar interface between two homogeneous, isotropic phases. The case of a rigid interface is shown to be solvable employing Head's image dislocation construction. The case of the elastodynamic image force due to an interface is solved by deriving the reflected wave's contribution to the global solution across the interface. This entails obtaining the fundamental solution (Green's function) for a point unit force via Cagniard's method, and then applying the convolution theorem for a screw dislocation modelled as a force distribution. Complete, explicit formulae are provided when available. It is shown that the elastodynamic image forces are generally affected by retardation effects, and that those acting on the moving dislocations display a dynamic magnification that exceed the attraction (or repulsion) predicted in classical elastostatic calculations.

Testing and Analysis of Micro-Vibrations Generated by Control Moment Gyroscope in Different Installation Boundary

The micro-vibrations caused by CMG (Control Moment Gyroscope) can seriously degrade the pointing accuracy and imaging quality of spacecraft. To test the micro-vibrations generated by CMG and obtain the corresponding frequency spectrum characteristics is the key to design the vibration restraining and analyze the vibration transfer properties. In order to simulate the actual installation boundary of CMG on spacecraft, a flexible interface is designed to compare with the rigid interface in traditional testing methods. The results show that: due to the existence of coupling effect between the CMG structure and the flexible interface, the traditional rigid interface is unable to predict the disturbance emitted by CMG in the installation boundary of spacecraft accurately. To study the micro-vibrations produced by CMG in the installation boundary of flexible interface is of great significance.