Engineering Mechanics

The precision requirements for cyclic plasticity models are often not very high in industrial applications, even though the integrity of many components subjected to cyclic plasticity is critical. Despite its limitations, such as poor prediction of ratcheting behaviour, the Chaboche model remains the most widely used model of cyclic plasticity. This paper presents the calibration of this model for uniaxial and multiaxial cyclic data on 304 stainless steel. The model incorporates a strain memory surface dependence to account for pronounced cyclic hardening. Resulting simulations carried out by calibrated model are used to highlight some of the modelling limitations.

Motivated by the need to model 3D printed electroactive metamaterials, an approach is presented to improve the computational efficiency of the SfePy package for the simulation of structurally complex piezoelectric lattice-like structures. Enhancements to the iterative solver interface allow the use of state-of-the-art iterative solvers and Schur complement-based preconditioners. Their performance is illustrated by a numerical study where the convergence of the iterative solvers is observed for several levels of uniform mesh refinement.

Fractional viscoelasticity introduces a new approach to describe viscoelastic materials using derivatives and integrals of noninteger order. The main disadvantage of this approach is its use in numerical applications because, compared to standard integer-order derivatives, the numerical approximation of the fractional derivative is based on all of the nodal values from the previous time steps while each of these values has a different weight in the computation. For this reason, the usability for large-scale problems is limited because of high memory and computing time requirements. This paper presents several approaches how to deal with this problem by introducing approximation of the fractional derivative which uses only reduced number of previous values.

Wave propagation in 3D printed metals is an area of research that focuses on the behavior of mechanical waves in metallic materials produced by additive technologies, specifically 3D printing. This process is increasingly being used to produce complex geometric structures that can exhibit different properties compared to traditionally manufactured materials. In this context, the focus is on how the structure of the printing material, the microscopic arrangement of particles, porosity, and anisotropy affect the wave behavior. The aim of the research is to understand how different printing parameters (e.g., layer orientation, material composition) affect wave propagation and how this knowledge can be applied for, e.g., defect detection, sound insulation, or structures with optimized mechanical properties. This work focuses on the instrumentation of 3D printed samples with actuators and measurement labels, the creation of an experimental setup and the measurement of initial high frequency mechanical wave propagation experiments.

The paper focuses on microscale viscoelastic properties of Poly-methyl methacrylate (PMMA) measured by a nanoindenter. PMMA serves as a reference homogeneous material suitable for evaluating of theoretical and experimental aspects of the nanoindentation process and computational methods. Viscoelastic constants are calculated with two analytical approaches and compared. Sensitivity to key experimental parameters including maximum load and loading time is assessed.

The company VÚTS, a.s. manufactures KP series indexing gearboxes, which consist of a pair of radial cams and an indexing turret follower fitted with rollers. These indexing cam gearboxes are used to convert the uniform rotary motion of the input camshaft into a unidirectional rotary motion with clearly defined dwell portions of the output shaft. Due to multiple contacts between the rollers and the conjugate cam pair, it is necessary to provide certain reliefs at specific cam areas, both in the profile of the cam pair and the sides of the cams. These reliefs are created to prevent redundant roller/cam connections, thereby avoiding unnecessary impacts in the mechanism, which increase noise during the operation. A test device equipped with the KP series indexing gearbox was designed to evaluate the impact of the size and shape of the reliefs on the working surface and sides of the cams on the operation of the gearbox. The influence of individual parameters of the relief of the conjugate cam pair on the dynamic properties of the indexing gearbox operation was evaluated using the RMS acceleration value in relation to the camshaft revolutions.

The effectiveness of treatment with a fixed orthodontic appliance largely depends on the condition of the bracket slot surface. A high surface roughness increases friction, causes greater wear, hinders tooth movement, and promotes bacterial biofilm retention. In this study, the surface condition of orthodontic bracket slots made of different materials (stainless steel, ceramic, and titanium) was analyzed using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The research evaluated both the quality of the bracket slot surface and its chemical composition. The results show that brackets made of monocrystalline aluminum oxide (sapphire) have the smoothest surface, which helps reduce friction and plaque retention, thus improving treatment. Significant surface irregularities were observed in stainless steel and titanium brackets, potentially affecting archwire sliding in the slot and reducing oral hygiene, which can lower treatment effectiveness and prolong its duration.

To enable high-fidelity and physically relevant simulations of non-spherical suspensions, we aim to design a solver coupling computational fluid dynamics (CFD) with the discrete element method (DEM). The CFD part of the solver is based on the widely used OpenFOAM library. However, to design a robust and computationally efficient DEM for non-spherical particles is still an open problem, as the contact solution is, in this case, nontrivial. In this contribution, we propose an updated formulation of a DEM contact model for non-spherical particles that is (i) based on the concept of overlap volume, (ii) robust, and (iii) for the case of spheres, consistent with the standard Hertz-Mindlin model. The presented model is successfully verified against LIGGGHTS on a DEM benchmark test.

This work examines a simple planar symmetric truss design (modified von Mises truss) which involves two members subjected to deformation by an applied force, with supporting springs at the ends. The analytical numerical model of the truss structure is formulated using first- and second-order theories of deformation, and the ensuing nonlinear model is solved by applying established techniques. The study subsequently correlates the solution using the results derived from the experimental setup. The two approaches are compared, buckling, snap-through effect and error estimation are evaluated.