This article presents a comprehensive analysis of the mechanical and structural characteristics of multilayer GaN/AlN/GaN/AlN and AlN/GaN/AlN heterostructures formed by chloride-hydride epitaxy on hybrid SiC/Si(111) and single-crystal Al2O3 substrates. Nanoindentation was used to measure the mechanical properties. Atomic force microscopy was employed to analyze the surface morphology. It was found that the morphological and mechanical properties significantly depend on the substrate type. GaN/AlN/GaN/AlN heterostructures on an Al2O3 substrate are characterized by the formation of deep etch pits up to 1500 nm deep, whereas on SiC/Si(111) substrates these structures are devoid of obvious defects and are distinguished by a uniform distribution of irregularities close to normal. Moreover, the AlN/GaN/AlN heterostructures on both substrates exhibit a hilly surface relief with a comparable degree of smoothness. Nanoindentation data revealed differences in the mechanical characteristics. On SiC/Si(111) substrates, the mechanical properties remain stable throughout the entire indentation depth, with an elastic modulus of up to 320 GPa for the GaN/AlN/GaN/AlN structure and up to 340 GPa for AlN/GaN/AlN. At the same time, Al2O3 substrates exhibit higher elastic modulus values: up to 397 GPa for GaN/AlN/GaN/AlN and up to 428 GPa for AlN/GaN/AlN, and also exhibit a strain hardening effect. An analysis of the mechanisms of property formation showed that the porous structure of the SiC/Si(111) substrate promotes stress relaxation but increases the dispersion of mechanical characteristics, while the monolithic Al2O3 substrate provides higher quality of surface layers but forms a gradient of mechanical stresses across the thickness of the heterostructure.
The focus of this study is the development of a nonlinear dual-phase lag (DPL) comprehensive bioheat transfer model, which attempts to capture the behavior of biological tissues under laser irradiation. The model treats thermal conductivity (the tissue’s ability to conduct heat) and volumetric blood flow as functions of temperature. The model also considers laser irradiation as internal heating, which gives rise to a set of coupled thermal relations. By integrating temperature-dependent thermal conductivity and blood perfusion within a dual-phase-lag framework, the model achieves more accurate and realistic predictions of thermal behavior than conventional linear approaches. An implicit finite difference approach with Newton-Raphson is utilized, which is expected to achieve fast convergence and stability. The temperature dependence of thermal conductivity was implemented, and this influences the redistribution of heat as well as the maximum temperature. The results indicate that nonlinear factors (α, β) and blood perfusion are essential in regulating heat distribution and tissue damage progression, while relaxation durations (τq, τT) considerably influence thermal wave dynamics. Compared to the linear model, the difference is much more pronounced. The results replicate a multitude of published experimental observations and show the adaptability of the model under a variety of numerical approaches. Therefore, the model provides a strong theoretical basis for future work involving the accuracy and potential risks involved with laser-assisted thermal therapies.
This study investigates the thermal buckling behavior of Functionally Graded Material (FGM) plates subjected to a general three-dimensional (3D) non-uniform temperature field, which varies both in the plane and through the thickness. Such a complex thermal load scenario is critical for realistic design but poses significant analytical challenges. To address this, an advanced semi-analytical solution framework is developed by synthetically combining the state-space method (SSM) and the differential quadrature method (DQM). The SSM elegantly handles the continuous variation of material properties and temperature along the thickness direction, reducing the 3D problem to a state-space formulation. The DQM then efficiently discretizes the in-plane differential operators and boundary conditions. This coupled SSM-DQM approach accurately transforms the thermo-elastic buckling problem into a standard eigenvalue problem. The proposed method is first validated against existing solutions for degenerate cases. A comprehensive parametric study then reveals the profound influence of the 3D temperature gradient profile, material gradient index, and plate aspect ratio on the critical buckling temperature. Results demonstrate that simplified temperature assumptions can lead to substantial errors, underscoring the necessity of employing a full 3D thermal load model for the safe design of advanced FGM structures in extreme thermal environments.
This work considers the implications of gravity, voids, initial tension, and magnetic field‑dependent the interaction and reflection regarding an SV-wave striking a free interface. An SV-wave and two damped P-waves are reflected during its interaction with the free surface the medium is modeled as elastically semi-infinite, under the given configuration of condition accounting incorporating initial stress and A uniform magnetic field. collectively modify the propagation dynamics of SV-waves. We developed a comprehensive theoretical framework that accounts for voids within the medium, as well as external influences from rotation, gravity, and initial tension. These results hold potential significance for advancing seismic wave studies. Furthermore, for a zero-order viscoelastic or the case where voids and rotation are omitted from the model, the outcomes align closely with established data for fibre-reinforced composites. Furthermore, by disregarding the non-homogeneity and strengthened elastic properties, the findings reduce to the well-known isotropic and homogeneous medium. It has been noted that the surface waves are unable to travel through a rapidly spinning medium or in a strong initial magnetic field. For specific materials, numerical simulations are provided together with graphical illustrations.
This study investigates the effects of double porosity structure and thermoelastic coupling on wave propagation in plate structures. A Kirchhoff thin‑plate model incorporating double porosity and thermoelasticity is developed for flexural wave analysis. By introducing two pore‑volume‑fraction fields and a temperature field, the governing equations are derived to account for the multi‑field coupling among thermal, elastic, and double porosity responses. Using harmonic wave solutions, a characteristic equation describing the frequency‑dependent dispersion of flexural waves is obtained, which takes the form of a tenth‑degree polynomial in the complex wavenumber, thereby elucidating the mechanisms of wave dispersion and attenuation. Theoretical analysis demonstrates that, compared with classical elastic plates and single‑phase thermoelastic plates, the multi‑field coupling in double porosity thermoelastic plates excites a greater number of wave modes. Five distinct modes are identified: the first is a macropore‑dominated pore wave; the second is a micropore‑dominated pore wave. Both pore‑wave modes exhibit cut‑off frequencies beyond which pronounced dispersion occurs. The third mode is a thermally coupled wave, whose dispersion and attenuation are comparable and intensify simultaneously with increasing frequency. The remaining two modes correspond to a coupled flexural traveling wave and a flexural standing wave. Although their variation trends generally align with those in classical thin plates, their phase speeds are lower than the classical predictions due to the combined effects of porosity and thermoelastic coupling. This work provides a theoretical basis for understanding wave propagation in porous thermoelastic plate‑like structures.
