Search Results (98)

Cell morphology and its mechanical properties are crucial factors in cancer development, affecting migration, invasiveness, and the potential risk of metastasis. However, most studies address these aspects separately, limiting the understanding of how morphological complexity relates to cellular mechanics. This work presents an integrated approach that simultaneously quantifies morphology and viscoelasticity in the human osteosarcoma cell line MG-63. Stress–relaxation experiments and optical imaging of the same cells were performed using a custom-built system that couples Atomic Force Microscopy (AFM) with an inverted optical microscope. Morphometric parameters were extracted from cell contours, while viscoelastic properties were obtained by fitting AFM data to the Fractional Kelvin (FK) and Fractional Zener (FZ) models. Among the morphological descriptors, the Shape Complexity (SC) was proposed. It is derived from the Lobe Contribution Elliptical Fourier Analysis (LOCO-EFA), which captures fine-scale contour features overlooked by conventional metrics. Experimental results show that, in MG-63 cells, higher SC values are associated with greater stiffness, indicating a correlation between cell shape complexity and cell stiffness. Furthermore, loading-rate analysis shows that the FZ model captures strain-rate-dependent stiffening more effectively than the FK model. This methodology provides a first approach to jointly analyzing quantitative morphological parameters and mechanical properties, underlining the importance of combined studies to achieve a comprehensive understanding of cell behavior. Full article

Structural adhesives in aeronautical applications are routinely exposed to complex loading histories that generate time-dependent deformation, making accurate prediction of their viscoelastic response essential for reliable assessment of joint integrity. This work presents an integrated experimental and modeling study of the aerospace-grade epoxy adhesive 3M Scotch-Weld EC-2216 using multi-step creep and stress-relaxation tests performed at room temperature and controlled loading rates, combined with fractional viscoelastic modeling. Unlike traditional single-step characterizations, the multi-step protocol employed here captures the cumulative loading effects and fading-memory dynamics that govern the adhesive’s mechanical response. The experimental data were analyzed using fractional Maxwell, Voigt–Kelvin, and Zener formulations. Statistical evaluation based on the Bayesian Information Criterion (BIC) consistently identified the Fractional Zener Model (FZM) as the most robust representation of the stress-relaxation behavior, effectively capturing both the unrelaxed and relaxed modulus. The results demonstrate that EC-2216 exhibits hierarchical relaxation mechanisms and history-dependent viscoelasticity that cannot be accurately described by classical integer-order models. Overall, the study validates the use of fractional operators to represent the broad and hierarchical relaxation spectra typical of toughened aerospace epoxies and provides a rigorous framework for durability assessment and predictive modeling of adhesively bonded structures. Full article

Monitoring the early-age evolution of cementitious materials is essential for ensuring the quality and reliability of concrete structures. However, most ultrasonic approaches rely on empirical correlations and lack a physics-based mechanism to describe the continuous viscoelastic transition during hydration. This study proposes a fractional-order ultrasonic sensing framework that couples a fractional Zener viscoelastic model with ultrasonic attenuation theory to quantitatively link microstructural evolution and measured acoustic responses. A custom ultrasonic measurement system was developed to capture real-time attenuation during hydration under different water-cement ratios. Results show that the fractional-order model achieves higher accuracy and robustness than classical integer-order and empirical models. The fractional parameter $\beta$ serves as a physically interpretable indicator that reflects the transition from viscous-dominated to elastic-dominated behavior and aligns with known hydration development. The proposed framework provides a compact, physics-informed sensing strategy for early-age characterization of cementitious materials and offers potential for intelligent construction and high-end structural monitoring. Full article

To understand the hot deformation behavior of 7085 aluminum alloy, compression tests were performed under varied conditions (593–743 K/0.001–1 s⁻¹). While the true stress–strain curves predominantly display the features of dynamic recovery, the softening mechanism shifts towards dynamic recrystallization when deforming at higher temperatures and lower strain rates. The validity of the constructed strain-compensated Zener–Hollomon model is confirmed by its exceptional precision in forecasting the flow stress, achieving an R² value of 0.992. The instability areas are concentrated in the high-strain-rate regions, and the optimal deformation processing for 7085 aluminum alloy is 693–743 K/0.01–0.001 s⁻¹. The alloy’s softening mechanism undergoes a transition from solely dynamic recovery to a progressively more significant coordinated role of dynamic recovery and dynamic recrystallization as the temperature rises and the strain rate drops. Full article

The present study proposes a simple and low-cost indirect method for estimating the thickness of plates by measuring the contact time (T_C) generated by the impact of a free-falling sphere. The theoretical model has been developed on Tsai approximation of Zener’s theory, which describes the dynamic interaction between the sphere and the plate taking in account the propagation of flexural waves. The methodology was validated through FEM simulations and through an extensive experimental campaign, where the contact times were measured using a simple electrical circuit. The results show excellent agreements between predicted and actual thicknesses, with relative errors below 3% for λ < 1.5 (where λ is the inelasticity parameter). For very thin plates and highly deformable materials, the above accuracy decreases due to flexibility and plastic deformation. We believe the proposed approach to be particularly promising in non-destructive testing applications within several scenarios, where speed, cost-effectiveness, and safety are essential requirements. Full article

This paper discusses the phenomenon of concrete creep and its impact on bridge structures, with particular emphasis on the mechanical models used to describe it. Classical rheological models, such as the Maxwell and Kelvin–Voigt, along with their generalized and fractional extensions incorporating fractional-order derivatives, are presented. These models differ in their complexity and in the accuracy of fit to laboratory test results. The use of non-classical, fractional-order rheological models (the fractional Kelvin–Voigt model and the fractional Zener model) enables better model fitting. The paper further describes methods for estimating creep effects in bridge design. The most popular is the effective modulus method, which is easy to implement but does not account for the load application history. More accurate approaches (e.g., Trost, Bažant, incremental method according to linear elasticity theory) are based on iterative procedures and require advanced computer implementation. The consequences of creep in bridge structures are highlighted: geometric (changes in elevation) and static (redistribution of internal forces and support reactions, changes in sectional stresses). These effects are particularly important in structures erected in stages, such as bridges built using the balanced cantilever method. The analytical section presents the influence of various creep models on changes in static quantities for a three-span prestressed bridge constructed by the cantilever method. The importance of proper selection of the creep model for the accuracy of engineering calculations and for the correct assessment of the long-term behavior of the structure is emphasized. Full article

For the gluing process of natural fiber-reinforced composite materials like bamboo scrimber, an obvious creep behavior can be found during the working stage, which must be seriously considered in safety and reliability design. In this paper, the compressive creep performance of the bamboo scrimber, a kind of plywood material, was chosen as the research object. Several groups of compressive creep tests were conducted with various stress levels and samples to record the respective processes of creep strain evolution. Furthermore, different types of models were adopted in studying the compressive viscoelastic behavior of the material. The creep growth is sensitive to the stress level of the creep test, according to the results. Furthermore, the conventional Zener model can work well for simulating the compressive creep strain growth behavior of the bamboo scrimber at high stress levels, but obvious errors can sometimes occur when it is applied to analyze this property under low stress levels. At the same time, using MD (memory-dependent) theory to define the Zener model can pertain to the requirement of accuracy in analyzing the compressive creep property under all load conditions and is more practically useful. Full article

The hot deformation behavior of the duplex structured Mg-9Li-5Al-2Sn-1.5Y alloy is investigated via hot compression tests in the temperature range of 200–350 °C and strain rate range of 0.001–1 s⁻¹. The flow behavior of the Mg-9Li-5Al-2Sn-1.5Y alloy is defined by hyperbolic constitutive equation. The Zener–Hollomon parameter Z is used in the hyperbolic-sine-type equation to express the relationships between the peak stress, deformation temperature, and strain rate. Dynamic recovery and dynamic recrystallization are the main characteristics that affect deformation behaviors. The activation energy Q is calculated as 127.89 kJ/mol. Based on the dynamic materials model, the processing maps at strains of 0.6 and 0.8 are constructed, and the optimum processing parameters are determined as the temperature range of 320–350 °C and strain rate range of 0.001–0.007 s⁻¹. Full article

In this article, an ecological composite based on a neat polylactide with 50 and 75% degrees of coffee particles and eggshells as an infill and organic filler, was developed. It has been shown that the content of fillers used reduced the mechanical properties, increasing the possibility of environmental degradation and accelerating the biodegradation process. During the additive production of polylactide with 10% of coffee grounds as a filler, it was possible to reduce the additive manufacturing temperature, which reduced the process time, energy costs, carbon dioxide emissions and the amount of polymer that may affect the environment. The structure of polylactide enriched with hen eggshells is characterized by roan and irregular shapes, which can cause a high tendency to form a concentration of cracks in these areas. Based on the results obtained from the stress relaxation test, the Zener model was used to describe a creep model of the produced ecological composites. The polymer composition of coffee grounds and eggshells shows a tendency to creep faster than pure polylactide and with different degrees of infill. Voids reduce the strength of composite materials, which increases the creep potential of samples with incomplete degrees of infill. Full article

This study investigates the hot deformation behaviour and flow stress prediction of metastable β-Ti-15Mo alloy, a promising material for biomedical applications requiring strength–modulus optimisation and thermomechanical tunability. Isothermal compression tests were performed within the temperature range of 923–1173 K and at strain rates of 0.17, 1.72, and 17.2 ${\mathrm{s}}^{-1}$ to assess the material’s response under industrially relevant hot working conditions. The alloy showed significant sensitivity to temperature and strain rate, with dynamic recovery (DRV) and dynamic recrystallisation (DRX) dominating the softening behaviour depending on the conditions. A strain-compensated Arrhenius-type constitutive model was developed and validated, resulting in an apparent activation energy of approximately 234 kJ/mol. Zener–Hollomon parameter analysis confirmed a transition in deformation mechanisms. Although microstructural and diffraction data suggest possible contributions from nanoscale phase transformations, including ω-phase dissolution at high temperatures, these aspects remain to be fully elucidated. The model offers reliable predictions of flow behaviour and supports optimisation of thermomechanical processing routes for biomedical β-Ti alloys. Full article

This study addresses the challenge of optimizing the viscoelastic performance of acrylonitrile butadiene styrene (ABS) parts manufactured by fused deposition modeling (FDM), where printing parameters strongly influence mechanical properties. The objective was to systematically evaluate the effects of four key factors—infill pattern, build orientation, layer height, and filament color—on storage modulus, damping factor, and glass transition temperature. A combined experimental design approach was employed: Taguchi’s L9 orthogonal array efficiently screened parameter effects, while response surface methodology (RSM) enabled detailed analysis of interaction effects and multiresponse optimization. Results revealed that build orientation and layer height had the greatest impact, increasing instantaneous stiffness ($E_u$) by up to 81%, equilibrium modulus ($E_0$) by 128%, and glass transition temperature ($T_g$) by 1.46%, while decreasing the damping factor (tan $\delta$) by 3.4% between optimized and suboptimal conditions. To complement the statistical optimization, the fractional Zener model (FZM) was applied to characterize the viscoelastic response of two representative samples optimized for either high stiffness or high flexibility. The flexible sample exhibited a higher fractional order ($\alpha =0.24$), indicating enhanced elastic mobility, while the stiff sample showed a higher activation energy ($E_a=0.52$ eV), consistent with restricted molecular motion. This integrated approach provides a robust and generalizable framework for improving material performance in polymer additive manufacturing. Full article

Thermodynamic constraints must be satisfied for the parameters of a constitutive relation, particularly for a model describing an electromagnetic (or any other) material with the intention of giving that model a physical meaning. We present sufficient conditions for the parameters of the constitutive relation of an electromagnetic Zener-type fractional 2D and 3D anisotropic model so that a weak form of the thermodynamic (entropy) inequality is satisfied. Moreover, for such models, we analyze the corresponding thermodynamic constraints for field reconstruction and regularity in the 2D anisotropic case. This is carried out by the use of the matrix version of the Bochner theorem in the most general form, including generalized functions as elements of a matrix, which appear in that theorem. The given numerical results confirm the calculus presented in the paper. Full article

This paper aims to develop a rheological model with fewer parameters that accurately describes the primary and secondary creep behavior of wood materials. The models studied are grounded in Riemann–Liouville fractional calculus theory. A comparison was conducted between the constant-order fractional Zener model and the variable-order fractional Maxwell model, with four parameters each. Using experimental creep data from four-point bending tests on two tropical wood species, along with an optimization algorithm, the variable-order fractional model demonstrated greater effectiveness. The selected fractional derivative order, modeled as a linearly increasing function of time, helped to elucidate the internal mechanisms in the wood structure during creep tests. Analyzing the parameters of this order function enabled an interpretation of their physical meanings, showing a direct link to the material’s mechanical properties. The Sobol indices have demonstrated that the slope of this function is the most influential factor in determining the model’s behavior. Furthermore, to enhance descriptive performance, this model was adjusted by incorporating stress non-linearity to account for the effects of the variation in constant loading level in wood. Consequently, this new formulation of rheological models, based on variable-order fractional derivatives, not only allows for a satisfactory simulation of the primary and secondary creep of wood but also provides deeper insights into the mechanisms driving the viscoelastic behavior of this material. Full article

The motivation of this research was to analyze the dynamic properties, mainly the loss modulus, of vulcanized immiscible blends of natural rubber (NR) and styrene-butadiene rubber (SBR) in the glass transition zone, where the SBR phase is in a glassy state and the NR phase is in a rubbery state. The blends were cured at 433 and 443 K and studied around the glass transition using a dynamic mechanical analyzer. The dependence of the loss modulus on temperature was described by considering the phase separation, and the frequency dependence was also included to provide a deeper insight into the dynamic properties. This was achieved by integrating the mechanical model proposed by Zener, which considers a single relaxation time related to temperature using both the Arrhenius and Vogel–Fulcher–Tammann (VFT) relations. The best correlation with the data was obtained using the Arrhenius relationship. The activation energy of the NR phase increases with the NR content in the blend, while in the SBR phase, it varies slightly. The trends obtained are related to curative migration from the SBR to the NR phase, increasing the crosslink density at NR domain boundaries. These insights are valuable for optimizing the performance of these elastomeric blends in practical applications. Full article

As a representative third-generation Al-Li alloy, 2A97 alloy has attracted significant attention for applications in aeronautics and astronautics, but its poor hot workability and complex thermal deformation behavior, which make for difficult optimization, significantly limit its widespread industrial utilization. In this study, the thermal deformation behavior of 2A97 Al-Li alloy was systematically investigated via thermal compression tests conducted over a temperature range of 260–460 °C and strain rates ranging from 0.001 s⁻¹ to 1 s⁻¹. The effects of deformation parameters on the alloy’s microstructural evolution were examined using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Based on the dynamic materials model, a constitutive equation was established by analyzing the stress–strain data under various thermal deformation conditions. Furthermore, a thermal processing map was compiled to analyze the effects of the temperature and strain rate on the power dissipation efficiency and flow instability factor. The thermal deformation mechanisms were identified through combined analysis of the thermal processing map and microstructural features. Results indicate that the fraction of low-angle grain boundaries increases with a rising lnZ value (Zener–Hollomon parameter) during the thermal compression process. Dynamic recrystallization is the main deformation mechanism of 2A97 Al-Li alloy in the stable region, whereas the alloy exhibits flow localization in the unstable region. According to the thermal processing map, the optimal hot working windows for the 2A97 Al-Li alloy were determined to be (1) 360–460 °C at strain rates of 0.05 s⁻¹–1 s⁻¹, and (2) 340–420 °C at strain rates of 0.001 s⁻¹–0.005 s⁻¹. These conditions offer favorable combinations of microstructure and deformation stability, providing critical guidance for the thermo-mechanical processing of 2A97 alloy. Full article