Solid State Phenomena Vol. 381

Abstract: 4D (four-dimensional) printing is an innovative manufacturing tool for creating smart, shape-morphing materials extending the capabilities of additive manufacturing (3D printing) to minimise complex manufacturing and part assembly, whilst potentially reducing the energy consumption required in part creation. The purpose of this study is to investigate the feasibility of 4D printing of fibrous constructs utilising discontinuous carbon and glass fibre reinforcements in multilayer architectures. As the final step of 4D printing process, the shape transformation is achieved by controlling the gradient of in-plane thermal shrinkage through the thickness at the single-layer level. A critical understanding of how printing conditions govern the development of anisotropic molecular chain alignment is essential for achieving targeted morphing behaviour. It has been observed that several key factors influence the morphing mechanism, including the alignment of molecules through the nozzle, flow speed changes during deposition, extrusion temperature and post-print cooling rate. Anisotropic molecular chain alignment arises from rapid cooling near the polymer's glass transition temperature, resulting in the locking of aligned molecular chains, and consequently generating shrinkage strain, within the printed multilayer composite. It was observed that asymmetric cooling and complex thermal boundary conditions, coupled with the influence of fibre reinforcement on thermal conductivity and local cooling dynamics, play a significant role in determining the degree of anisotropy. This research demonstrates how multilayer fibre-reinforced composites can be strategically engineered to enable programmable shape-morphing behaviours without relying on dual-material or multi-directional printing; thus, opening new applications for 4D printing of fibre-reinforced components.

Abstract: This work presents a simulation-driven approach for designing patterned flexible sensors based on laser-induced porous carbon composites. By implementing a large-deformation electromechanical coupling model into ABAQUS via a user subroutine, we efficiently predicted strain-dependent conductivity. High-throughput simulations were conducted to evaluate serpentine structures with varying geometric parameters. Key performance indicators—linearity, sensitivity, and directional selectivity—were assessed, and Pareto-optimal solutions were identified to enable multi-objective optimization. Compared to experimental trials, this method reduces design time by over 90%. The proposed framework offers a rapid and generalizable strategy for optimizing high-performance flexible sensors with anisotropic electromechanical properties.

Abstract: This study investigated the charging and discharging characteristics of charge-accumulating textile fabrics, especially those made of composite fibers, by measuring the voltage half-life, which is the time required for voltage to decrease to half of maximum value. Results demonstrated that composite textile fabrics exhibit significantly different electrostatic properties compared to conventional textiles such as cotton and polyester. A non-contact electrostatic measurement method was employed using corona discharge to apply positively charged ions to the material. It is shown that this method makes it possible to simultaneously measure the time-dependent surface voltage and charge accumulation during charging processes, as well as the surface voltage decay during the discharging processes.

Abstract: Fiber-reinforced composites are widely used in lightweight design for their exceptional specific strength. However, their inherent multiscale property variations require systematic consideration during structural optimization. This study develops a cross-scale analysis framework and fatigue life prediction model that explicitly accounts for the propagation of mechanical property variations from microscale constituent properties to macroscopic performance, utilizing representative volume element (RVE) modeling. Application of the framework to a carbon fiber composite battery box verifies its predictive capability, with results quantitatively revealing the mechanisms by which property variations affect structural durability. These findings establish a fundamental methodology for evaluating the operational performance of automotive composite structures.

Abstract: Replacing mild steel with composite laminates in automotive structures alters vibration characteristics, posing risks like resonance and structural damage. This study employs finite element (FE) analysis to investigate the influence of fiber configurations on the modal parameters of laminates. For unidirectional laminates (UDLs), natural frequencies exhibit symmetry with extrema at 45° fiber orientation angle (FOA). In multidirectional laminates (MDLs), modal responses depend critically on the position, proportion, and type of FOAs. A modal control method is integrated within the forward design under frequency constraints. A case study of an automotive rear floor demonstrates the method’s ability to achieve efficient frequency tuning without modifying the structural geometry, thereby outperforming conventional methods in cost and flexibility.

Abstract: The mode I interlaminar fracture toughness, G_IC, of unidirectional fiber-reinforced polymer matrix composite laminates was determined using the double cantilever beam (DCB) specimens. To ensure real-time correspondence with the growing crack length, load and displacement, the Digital Image Correlation (DIC) technology, a non-contact optical measurement technique, was selected for the fracture toughness tests in this paper. In addition, fracture toughness calculation programs were used to accelerate data processing.The results indicated that the DIC technology was reliable compared with the traditional technology (magnifying glass). The G_IC values obtained from all the three calculation methods (CC, MBT and MCC method) differed by no more than 3%. The SEM analysis showed that the crack propagation occurred along the fiber-matrix interface, resulting in plastic cracking and microcracks in the matrix. The observed intact fiber bundles indicated the matrix-dominated cracking in crack propagation, with localized fiber fracture at high stress and a small amount of fiber bridging during separation.

Abstract: This paper investigates the influence of finite element mesh parameters on the accuracy of modeling the penetration of a steel plate by a bullet in the ExplicitDynamics ANSYS WB computational module. The best results were obtained for the 3rd type of mesh, which included 180 finite elements in the contact zone. For the plate made of impact-resistant S-7 steel, the maximum stresses for the 2nd type of mesh at the attempted penetration reached 1 572,7 MPa, but no penetration was observed. For the S-7 steel plates, penetration was observed only when using the third type of mesh, which confirms the importance of density in the contact zone for an adequate description of dynamic processes. The analysis showed that the Sweep method with density is optimal for modeling steel plate penetration due to the balance of calculation performance and accuracy of the results.

Abstract: An exact analytical solution is presented for the problem of plane transverse bending of a segment of a narrow multilayer circular arch subjected to a normal uniformly distributed load on its longitudinal surfaces. The solution is constructed using the superposition principle based on the general solutions obtained by the authors for the bending problems of multilayer cantilevers with a circular axis under the action of loads on the free end and a uniformly distributed normal load on the longitudinal surfaces. Methods for modelling different types of end restraints for multilayer arches are considered: rigid, hinged, and combined. Using the example of a five-layer arch with varying restraints at the end, the influence of transverse shear deformations on the deflection and normal stresses is analyzed. The obtained relations allow determining the stress-strain state of multilayer arches with an arbitrary number of homogeneous (orthotropic, isotropic) layers, taking into account transverse shear and compression deformations, and can be used to construct other important solutions to arch deformation problems and develop more universal methods for calculating such structural elements.

Abstract: The article is devoted to the determination of the main physical and mechanical characteristics of compressed concrete at different strain rates of its. A method for predicting the main strength and deformation characteristics of compressed concrete in the widest range of its loading rates is proposed: from instantaneous dynamic to long-term with the maximum possible development of creep deformations. This method is based on the well-known law of conservation of potential energy of material deformation (up to its destruction) and the general patterns of change of the known integral characteristic of concrete - the factor of elasticity-plasticity. The functional interdependence of the levels of strength and deformability of compressed concrete for its different strain rates was established.