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Stimuli‐responsive hydrogels are representatives of smart materials with enormous swelling capability. The prediction of discrete hydrogel swelling states by artificial neural network based on the processing parameters has been realized in our previous work. In the current study, we explore ways to enhance the prediction capabilities by integrating physical information of the swelling curves to the model: Instead of predicting discrete swelling states, we predict the mathematical parameters of the continuous swelling curve. We therefore assume that the swelling behavior of hydrogels is consistent with a sigmoidal tanh function, based on their physical properties. After predicting the parameters of the sigmoidal function with the trained model, we analyze the prediction accuracy in comparison to the initial discrete prediction. Moreover, the new approach then allows us to physically interpret the different material properties, which denote sensitivity, maximum achievable differential swelling, and the position of the reference point for derivation of a material model. [ABSTRACT FROM AUTHOR]

Shaft misalignments are one of the main causes of damage to couplings in machines. If they are not detected in time, they can lead to machine downtimes. When assembling a machine, however, it is not always possible to align the shafts perfectly. Elastic couplings are able to compensate for such misalignments up to a certain degree. To detect the present radial misalignment, the concept of a sensor‐integrating jaw coupling, developed to determine the transmitted torque, is used. In the teeth of the gear rim, boreholes are drilled and dielectric elastomer sensors (DES) are inserted. If the teeth deform during use of the coupling the DES will deform as well, leading to a change in capacitance, which can be detected. If the two shafts, which the coupling connects, are perfectly aligned to each other, each of the loaded teeth will deform uniformly. However, if there is a radial or angular misalignment, the deformation is different for each tooth, which can be determined with the help of the DES. To demonstrate this effect, a finite element model of the sensor‐integrating jaw coupling with misalignments is created, and numerical simulations are conducted. In this model, the hyper‐viscoelastic material behavior of (i) the gear rim of the jaw coupling and (ii) the DES is taken into account. From the mechanical simulation, the deformed state of the DES is obtained, which is used to compute the capacitance of the sensor. With the results of the numerical simulations, a symbolic regression is performed. The result is an analytical formula that makes the accurate detection of the present radial misalignment possible. The developed framework can later be easily programmed on a microcontroller which is integrated in the sensor‐integrating jaw coupling. [ABSTRACT FROM AUTHOR]

In the paper, the spark plasma sintering (SPS) process for metal particles has been simulated based on experimental data and using the finite element method in the thermo-electro-mechanical formulation with taking into account the temperature influence on parameters of materials (nickel and copper). A comparison of obtained results with experimental data made it possible to create a computational model of the SPS process, the model being convenient to evaluate the influence of creep and plasticity parameters on the size of the interparticle neck forming in SPS. It was found that the creep effect significantly dominated over the plasticity influence on the process of forming the sintering neck at high temperatures. In this case, the variation of creep parameters in simulation also actively affects the formation of the neck.

As an important category of smart materials, stimuli-responsive hydrogels are highly concerned due to their extensive application possibilities and their outstanding biocompatibilities. The ability of responsive hydrogels about significant volume change by external stimuli inspires the design of electronic devices, for example, as sensors and actuators. The modeling of the hydrogel behavior enables the optimization of corresponding applications. In the present research, on the basis of the experimentally determined material parameters, a chemo-poromechanical model was implemented in COMSOL Multiphysics® to investigate the constricted swelling of hydrogels. The swelling kinetics affected by the diffusion coefficient is discussed in detail with numerical simulations. [ABSTRACT FROM AUTHOR]

In the present contribution, the FE2 scheme for beam elements is extended to thermomechanically coupled problems. Beam elements have the advantage of drastically reducing the number of degrees of freedom compared to solid elements. However, the major challenge in modeling structures with beam elements lies in developing sophisticated non‐linear beam material models. This drawback resides in the fact that these elements require effective cross‐sectional properties involving material and geometric properties. The FE2 method, combined with a homogenization scheme based on the Hill‐Mandel condition, solves this problem. Within this scheme, homogenization of a representative volume element (RVE) on the mesoscopic scale provides effective cross‐sectional properties for the macroscopic scale. This homogenization procedure allows the consideration of non‐linear material formulations and cross‐sectional deformation within the analysis of a beam structure. The applicability of such a FE2 scheme for purely mechanical problems was already shown. In the present contribution, an extension to thermomechanically coupled problems is provided. In the proposed setting, the macroscopic scale is represented by beam elements with displacement, rotation, and temperature degrees of freedom. Solid elements with displacements and temperature degrees of freedom describe the behavior of the RVE. Hence, the proposed extension solves both scales in a monolithic approach. The assumption of a steady state problem at both scales allows a focus on a consistent scale transition and a discussion about the choice of suitable boundary conditions under the assumption of beam kinematics. [ABSTRACT FROM AUTHOR]

Hydrogels are an outstanding material for sensor and actuator applications, for example, chemosensors and microfluidics, and have been extensively studied in both, experiments as well as in modeling within the last years. The theoretical investigations of hydrogels are key factors for the development of new hydrogel-based concepts in research and engineering. The recent approaches in modeling of the light-sensitive behavior of hydrogels are often complicated and very detailed. Commonly, they are based on the Helmholtz free energy function within a continuum-mechanical framework. In contrast, the Stimulus Expansion Model (SEM) is a simple and very effective approach to embed the swelling properties of a hydrogel into a continuum mechanical framework. Originally, the SEM was applied to chemical stimulation processes based on available experimental swelling curves. The current work provides an extension of the SEM for photo-thermo-sensitive hydrogels. The present approach considers (i) the attenuation of light by applying Lambert-Beer's law as well as (ii) the energy transfer of light into heat. In this study, PNIPAm hydrogels with incorporated light-absorbing particles of copper-chlorophyllin are investigated. To demonstrate the capabilities of the presented approach, the effect of the variation of (i) light power, (ii) particle volume fraction, and (iii) ambient temperatures on the swelling behavior is analyzed. The obtained results show an excellent correlation with experimental results from literature. Concluding, the extended Stimulus Expansion Model provides further opportunities to design and simulate photo-thermo-sensitive hydrogels for engineering applications. [ABSTRACT FROM AUTHOR]

The present research deals with a three‐dimensional (3D) Finite Element Method (FEM) bifurcation analysis based on the global mechanical potential that can be used to find the parameters at which a crack pattern changes. In our case we want to analyze at which point the star‐shaped shrinkage cracks in an aqueous colloidal suspension filled in a glass cylinder change from four to three or two cracks growing. The driving force for the crack growth is shrinkage caused by diffusion controlled drying. The 3D crack front geometry is described efficiently by using a Fourier series approach. Based on steady‐state crack growth, the Fourier coefficients are determined in a first step using an optimization algorithm. As a result, the time dependent crack growth can be determined. In a second step, the bifurcation point is determined by an eigenvalue analysis of the second order derivatives of the potential energy of the system. If the lowest eigenvalue reaches zero the fundamental solution becomes unstable and a transition will occur. Our analysis shows that the transition from four to two cracks is preferred over the transition from four to three cracks. [ABSTRACT FROM AUTHOR]