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Hydrogels are categorized as soft materials that undergo large deformation when they are subjected to even minor external forces. In this work, the performance of a variety of micro-valves, based on pH-sensitive hydrogel jackets coated on rigid pillars, is studied considering the gel deformation under fluid flow, employing fluid–structure interaction simulations. In this regard, an analytical solution to plane-strain inhomogeneous swelling of a cylindrical jacket is proposed. This is used as a tool to validate the finite element model. Then, a micro-valve consisting of one hydrogel jacket is studied in various inlet pressure and pH values performing fluid–structure interaction simulations. Thereafter, a variety of jacket patterns are investigated in order to identify the effects of the pattern on the micro-valve performance for various fluid stream pressures and pH values. The leakage pressure of the valves is also computed for each of the patterns. Fluid–structure interaction simulation is found to be essential to accurate design of the hydrogel-based microfluidic devices.

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Recently bilayer smart hydrogel beams are widely used in various applications such as sensors, actuators, self-folding structures and switches. Developing a strong tool for designing these bilayer smart hydrogel beams is necessary. In this article, we developed an analytical method to solve the swelling induced bending of bilayer beams made of a pH-sensitive layer attached to an inert elastomer layer. A total deformation gradient tensor, without assuming any intermediary virtual state, is defined to map the initial configuration to the deformed state. An exponential function with four constants is employed to describe the deformation of the pH-sensitive gel layer. The proposed method leads to a system of equations with six unknowns that can be simply solved via numerical techniques. As a case study, this method is implemented to solve the swelling induced bending of several bilayer beams with various parameters. The outcomes of the analytical solution are in excellent agreement with the finite element method results, thus confirming the strength of the presented method.

In this article, a new conceptual design of light-sensitive switches made of a soft bilayer is introduced. The bilayer structure consists of a photothermal-sensitive hydrogel strip attached to another neutral incompressible elastomeric layer. The bilayer is assumed to be initially flat under a uniform light irradiation. Decreasing the light intensity causes the bilayer to bend due to the inhomogeneous swelling of hydrogel layer and results in the switch actuation. To enlighten the actuation mechanism and investigate the influence of various parameters on the switch’s photomechanical response, an analytical method is developed to study the bilayer deformation due to the light-intensity variation under plane-strain condition. Additionally, the finite element analysis of the bilayer is conducted, implementing the relevant constitutive model into a finite element code. The deformation and stress inside the layers are studied both analytically and numerically for several cases. The numerical results verify the accuracy of the presented analytical method in this work. The influence of various material and geometrical parameters including each layer’s modulus, the thickness ratio of the layers, and the aspect ratio of the bilayer is investigated. The analytical method is found to be useful for proper design of the light-sensitive hydrogel-based switches.

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A finite element analysis of crack propagation in an HDPE/CaCo3 composite was carried out using a combination of the extended finite element method (XFEM) and the cohesive zone method (CZM). A unit cell of an entire composite consisting of one particle was chosen as the study zone. The interphase was assumed as a cohesive surface between the matrix and the particle. Variable parameters were the interface adhesion, position of initial crack, volume fraction, and size of the particle. The results showed that, the energy release rate increases when increasing the particle size. Increasing the volume fraction from 5 to 10% has positive effects in decreasing the strain energy release rate; however, the effects of 10 and 15% of volume fraction on the energy release rate are almost the same. Increasing the values of interfacial adhesion strength increases the strength of composite.