Acta Mechanica Sinica最新文献

The current artificial bone is unable to accurately replicate the inhomogeneity and anisotropy of human cancellous bone. To address this issue, we proposed a personalized approach based on clinical CT images to design mechanical equivalent porous structures for artificial femoral heads. Firstly, supported by Micro and clinical CT scans of 21 bone specimens, the anisotropic mechanical parameters of human cancellous bone in the femoral head were characterized using clinical CT values (Hounsfield unit). After that, the equivalent porous structure of cancellous bone was designed based on the gyroid surface, the influence of its degree of anisotropy and volume fraction on the macroscopic mechanical parameters was investigated by finite element analysis. Furthermore, a mapping relationship between CT values and the porous structure was established by jointly solving the mechanical parameters of the porous structure and human cancellous bone, allowing the design of personalized gradient porous structures based on clinical CT images. Finally, to verify the mechanical equivalence, implant press-in tests were conducted on 3D-printed artificial femoral heads and human femoral heads, the influence of the porous structure’s cell size in bone-implant interaction problems was also explored. Results showed that the minimum deviations of press-in stiffness (<15%) and peak load (<5%) both occurred when the cell size was 20% to 30% of the implant diameter. In conclusion, the designed porous structure can replicate the human cancellous bone-implant interaction at a high level, indicating its effectiveness in optimizing the mechanical performance of 3D-printed artificial femoral head.

It is a challenge to determine the dominant topological characteristics of mechanical properties of adhesive interfaces. In this paper, we used graph theory and molecular dynamics simulation to investigate the influence of topological characteristics on the strength and toughness of highly cross-linked polymer interface systems. Based on the microstructure of the adhesive system, we extracted the dominant topological characteristics, including the connectivity degree (D) that determines the yield strength, and the average node-path (P) and the simple cycles proportions (R) that determine the deformability and load-bearing capacity during the void propagation respectively, which co-determine the toughness. The influence of the wall-effect on the dominant topological characteristics was also analyzed. The results showed that the interfacial yield strength increases with the increase of D, while the toughness increases with the increase of P and R. The wall-effect has a significant influence on D, P, and R. The strong wall-effect causes the enrichment of amino groups near the wall and insufficient cross-linking away from the wall, leading to the lower D and R, i.e., the lower yield strength and load-bearing capacity during the void propagation. With the attenuation of the wall-effect, the D increases gradually, while the P and the R first increase and then decrease, showing an optimized wall-effect for the toughness of the adhesive interface. This paper reveals the dominant topological characteristics of adhesive interfacial strength and toughness, providing a new way to modulate the mechanical properties of polymer adhesive interface systems.

This study investigates surface erosion wear caused by collision and friction between propellers and sand particles during the flight of propeller transport aircraft in harsh environments like deserts and plateaus, which are characterized by strong sand and wind conditions. Firstly, the erosion behavior of individual propeller blades is analyzed under various sand particle parameters using the commercial software FLUENT. Subsequently, dynamic simulations of the entire blade are conducted by the sliding mesh method to examine erosion patterns under different operational conditions, including rotation speed and climb angle. Finally, the impact of erosion on the aerodynamic characteristics of the propeller is obtained based on simulation results. This study delves into the erosion patterns observed in large aircraft propellers operating within sandy and dusty environments, as well as the consequential impact of propeller surface wear on aerodynamic performance. By elucidating these phenomena, this research provides valuable insights that can inform future endeavors aimed at optimizing propeller design.

Organisms have evolved a strain limiting mechanism, reflected as a non-linear elastic constitutive, to prevent large deformations from threatening soft tissue integrity. Compared with linear elastic substrates, the wrinkle of films on non-linear elastic substrates has received less attention. In this article, a unique wrinkle evolution of the film-substrate system with a J-shaped non-linear stress-strain relation is reported. The result shows that a concave hexagonal array pattern is formed with the shrinkage strain of the film-substrate systems developing. As the interconnection of hexagonal arrays, a unit cell ridge network appears with properties such as chirality and helix. The subparagraph maze pattern formed with high compression is mainly composed of special single-cell ridge networks such as spiral single cores, chiral double cores, and combined multi-cores. This evolutionary model is highly consistent with the results of experiments, and it also predicts wrinkle morphology that has not yet been reported. These findings can serve as a novel explanation for the surface wrinkle of biological soft tissue, as well as provide references for the preparation of artificial biomaterials and programmable soft matter.

This article presents a detailed theoretical hybrid analysis of the magnetism and the thermal radiative heat transfer in the presence of heat generation affecting the behavior of the dispersed gold nanoparticles (AuNPs) through the blood vessels of the human body. The rheology of gold-blood nanofluid is treated as magnetohydrodynamic (MHD) flow with ferromagnetic properties. The AuNPs take different shapes as bricks, cylinders, and platelets which are considered in changing the nanofluid flow behavior. Physiologically, the blood is circulated under the kinetics of the peristaltic action. The mixed properties of the slip flow, the gravity, the space porosity, the transverse ferromagnetic field, the thermal radiation, the nanoparticles shape factors, the peristaltic amplitude ratio, and the concentration of the AuNPs are interacted and analyzed for the gold-blood circulation in the inclined tube. The appropriate model for the thermal conductivity of the nanofluid is chosen to be the effective Hamilton-Crosser model. The undertaken nanofluid can be treated as incompressible non-Newtonian ferromagnetic fluid. The solutions of the partial differential governing equations of the MHD nanofluid flow are executed by the strategy of perturbation approach under the assumption of long wavelength and low Reynolds number. Graphs for the streamwise velocity distributions, temperature distributions, pressure gradients, pressure drops, and streamlines are presented under the influences of the pertinent properties. The practical implementation of this research finds application in treating cancer through a technique known as photothermal therapy (PTT). The results indicate the control role of the magnetism, the heat generation, the shape factors of the AuNPs, and its concentration on the enhancement of the thermal properties and the streamwise velocity of the nanofluid. The results reveal a marked enhancement in the temperature profiles of the nanofluid, prominently influenced by both the intensified heat source and the heightened volume fractions of the nanoparticles. Furthermore, the platelet shape is regarded as most advantageous for heat conduction owing to its highest effective thermal conductivity. AuNPs proved strong efficiency in delivering and targeting the drug to reach the affected area with tumors. These results offer valuable insights into evaluating the effectiveness of PTT in addressing diverse cancer conditions and regulating their progression.

The symplectic approach was utilized to derive solutions to the orthotropic micropolar plane stress problem. The Hamiltonian canonical equation was first obtained by applying Legendre’s transformation and the Hamiltonian mixed energy variational principle. Then, by using the method of separation of variables, the eigenproblem of the corresponding homogeneous Hamiltonian canonical equation was derived. Subsequently, the corresponding eigensolutions for three kinds of homogeneous boundary conditions were derived. According to the adjoint symplectic orthogonality of the eigensolutions and expansion theorems, the solutions to this plane stress problem were expressed as a series expansion of these eigensolutions. The numerical results for the orthotropic micropolar plane stress problem under various boundary conditions were presented and validated using the finite element method, which confirmed the convergence and accuracy of the proposed approach. We also investigated the relationship between the size-dependent behaviour and material parameters using the proposed approach. Furthermore, this approach was applied to analyze lattice structures under an equivalent micropolar continuum approximation.

The reduced elastic modulus E_r and indentation hardness H_IT of various brittle solids including ceramics, semiconductors, glasses, single crystals, and laser material were evaluated using nanoindentation. Various analysis procedures were compared such as Oliver & Pharr and nominal hardness-based methods, which require area function of the indenter, and other methods based on energy, displacement, contact depth, and contact stiffness, which do not require calibration of the indenter. Elastic recovery of the imprint by the Knoop indenter was also utilized to evaluate elastic moduli of brittle solids. Expressions relating H_IT/E_r and dimensionless nanoindentation variables (e.g., the ratio of elastic work over total work and the ratio of permanent displacement over maximum displacement) are found to be nonlinear rather than linear for brittle solids. The plastic hardness H_p of brittle solids (except traditional glasses) extracted based on E_r is found to be proportional to (E_{mathrm{r}}sqrt {H_{text{IT}}}).

A simplified calculation of the specimen’s stress-strain curve is generally conducted using the two-wave method by the split Hopkinson pressure bar (SHPB), which aligns the onset of the transmitted and reflected waves. However, this approach neglects the travel time of elastic waves within the specimen. Considering the travel time of elastic waves, this study quantitatively investigates the error characteristics and patterns of stress, strain, and strain rate in the specimen under different conditions using the theoretical two-wave method, and compares the results with those obtained using the onset-aligned two-wave method. The study reveals that the stress-time curves derived from the theoretical two-wave method are lower than the actual stress curves, whereas those obtained from the onset-aligned two-wave method are consistently higher than the actual stress curves, with the stress deviation approximating a constant value when the dimensionless time exceeds 2.0. The starting point of the stress-strain curves obtained by the theoretical two-wave method is not zero but a point on the strain axis, whereas the onset-aligned two-wave method always starts at zero. However, the slopes of the stress-strain curves obtained by both methods differ from the actual Young’s modulus of the material, and functional relationships between the slopes and the actual Young’s modulus are provided. This research offers theoretical guidance for the refined design of SHPB experiments and the accurate processing of data.

Numerical simulation plays an important role in the dynamic analysis of multibody system. With the rapid development of computer science, the numerical solution technology has been further developed. Recently, data-driven method has become a very popular computing method. However, due to lack of necessary mechanism information of the traditional pure data-driven methods based on neural network, its numerical accuracy cannot be guaranteed for strong nonlinear system. Therefore, this work proposes a mechanism-data hybrid-driven strategy for solving nonlinear multibody system based on physics-informed neural network to overcome the limitation of traditional data-driven methods. The strategy proposed in this paper introduces scaling coefficients to introduce the dynamic model of multibody system into neural network, ensuring that the training results of neural network conform to the mechanics principle of the system, thereby ensuring the good reliability of the data-driven method. Finally, the stability, generalization ability and numerical accuracy of the proposed method are discussed and analyzed using three typical multibody systems, and the constrained default situations can be controlled within the range of 10⁻²–10⁻⁴.

The present study investigates the influences of aorta geometry on hemodynamics and material transport. Based on the observation of the human aorta, two geometric parameters are examined for a model aorta, saying the angle spanned by the main aortic arc and the diameter of the descending aorta. Direct numerical simulations are conducted for nine model aortas with different combinations of aorta arc and outlet diameter. Results reveal that the outlet diameter has a significant impact on aorta hemodynamics. A smaller outlet diameter compared to the inlet leads to accelerated blood flow in the descending segment, affecting flow morphology including the vortex structures, and increasing peak pressure gradient and wall shear stress. However, it reduces the oscillatory shear index, indicating a more organized flow. Analyses show faster particle transport and reduced accumulative residence time for smaller outlet diameters. The arc angle has less significant effects on these properties, except for delaying the time to reach the maximum pressure gradient during ejection. The research results may suggest that the diameter of the aortic outlet has a greater impact on the flow structures, while the arc angle has a relatively less effect. These findings provide insights into the relation between hemodynamics and aorta geometry, with potential clinical implications.