Applied Mechanics

This paper presents the mechanical characterisation of sandwich composites. Different specimen configurations have been tested with a three-point bending load and their mechanical behavior has been discussed. In addition, the acoustic emission technique was used to detect the onset of damage mechanisms and to monitor their evolution. The proposed analysis is based on processing recorded acoustic emission bursts. An unsupervised classification approach, combining the k-means algorithm with Principal Component Analysis (PCA), is used to group the detected acoustic events. The cluster analysis of the acquired data allows for correlation with the damage mechanisms occurring in sandwich composites. In addition to the advantages of multivariate data analysis, the results highlight the influence of sensor placement on the analysis of damage mechanisms is investigated. A suitable sensor configuration is proposed to improve the detection of acoustic emission activity. The originality of this work lies in the combined mechanical–AE interpretation that provides new insight into the damage behaviour of both a synthetic and a bio-based sandwich material. The comparative analysis of these two types of materials, coupled with a dedicated evaluation of sensor placement effects on defect detection, offers a contribution not previously reported in the literature.

Degradable solute transport in porous media significantly influences various ecological, geological, and industrial processes. In this paper, a mathematical model for solute transport in porous media with varying hydrodynamic dispersion is examined, integrating balance and kinetic equations alongside initial and boundary conditions. The model is enhanced by include variable hydrodynamic dispersion. Numerical approaches are utilized to address the problem, and a solution algorithm founded on the finite difference method is introduced. Computer simulations are conducted to examine the impact of different model parameters on solute transport, and the findings are evaluated. Numerical tests were performed for constant dispersion and three representative spatially variable forms—exponential, linear, and parabolic—for same other model parameters. Simulations show that neglecting diffusion/dispersion significantly delays the transport of material and underestimates both aqueous concentrations and adsorbed reserves. The results demonstrate that accounting for variable hydrodynamic dispersion significantly enhances the accuracy of solute transport predictions. The exponential form of dispersion produces stronger spreading effects, while the linear and parabolic forms show moderate variations. These findings underline the importance of incorporating scale-dependent dispersion in modeling contaminant migration in porous media.

Additive Manufacturing (AM) using Fused Layer Modelling (FLM) often results in polymer components with limited and highly anisotropic mechanical properties, exhibiting structural weaknesses in the layer direction (Z-direction) due to low interlaminar adhesion. The main objective of this work was to investigate and quantify these mechanical limitations and to develop strategies for their mitigation. Specifically, this study aimed to (1) characterize the anisotropic behavior of unreinforced Polycarbonate (PC) components, (2) evaluate the effect of continuous, unidirectional (UD) carbon fiber tape reinforcement on mechanical performance, and (3) validate experimental findings through Finite Element Method (FEM) simulations to support predictive modeling of reinforced FLM structures. Methods involved experimental tensile and 3-point bending tests on specimens printed in all three spatial directions (X, Y, Z), validated against FEM simulations in ANSYS Composite PrepPost (ACP) using an orthotropic material model and the Hashin failure criterion. Results showed unreinforced samples had a pronounced anisotropy, with tensile strength reduced by over 70% in the Z direction. UD tape integration nearly eliminated this orthotropic behavior and led to strength gains of over 400% in tensile and flexural strength in the Z-direction. The FEM simulations showed very good agreement regarding initial stiffness and failure load. Targeted UD tape reinforcement effectively compensates for the weaknesses of FLM structures, although the quality of the tape–matrix bond and process reproducibility remain decisive factors for the reliability of the composite system, underscoring the necessity for targeted process optimization.