Archives of Civil and Mechanical Engineering最新文献

Spinal dura mater provides essential structural protection for the spinal cord and helps maintain cerebrospinal fluid pressure, yet its mechanical characterization remains challenging because of its thinness and anisotropy. This study investigated the uniaxial tensile behavior of spinal dura mater and examined how speckle-paint application, the strain-measurement method (Digital Image Correlation (DIC)-derived strain vs. crosshead displacement), preconditioning, and donor demographics affect measured mechanical parameters. Samples were harvested postmortem from seven donors and assigned to three groups: painted & not preconditioned, unpainted & preconditioned, and unpainted & not preconditioned. A 3D-printed adapter was used to standardize sample geometry. Tests were conducted at a crosshead displacement rate of 5 mm·min⁻¹ (strain rate of 0.0042 s⁻¹), with some specimens undergoing cyclic preloading. Speckle paint increased stiffness but did not affect failure stress or stretch. DIC-derived elastic moduli were higher than those from crosshead displacement. After correcting for paint- and method-induced effects, the mean elastic moduli in the longitudinal and circumferential directions were ~ 283 MPa and ~ 16 MPa, respectively. Both orientations exhibited a failure stretch of ~ 1.10–1.12. The apparent Poisson function (Hencky form) ranged from 1.57 to 4.84 (longitudinal) and 2.91 to 6.29 (circumferential), indicating volumetric changes that challenge near-incompressibility assumptions. These findings emphasize the importance of standardized protocols and data normalization when investigating soft tissue mechanics. The higher DIC-based moduli arise primarily from local, gauge-region strain measurement and stiffening induced by the acrylic speckle coating, while the elevated apparent Poisson’s ratios likely reflect fluid redistribution and collagen-fiber reorientation under tensile loading in this highly anisotropic tissue.

Interest in random fields (RFs) with rotated anisotropy has been growing, yet the identification of the anisotropy rotation angle has been mostly limited to rocks and soils with visible anisotropic structures. This paper presents a method for simultaneously determining the principal values of the scale of fluctuation (SOFs) and the anisotropy rotation angle based on limited CPTu soundings. The proposed method extends the approach of Ching et al. (2018, Geosci. Front., 9, 1597–1608) by including the identification of the rotation angle. The findings demonstrate that accurate and precise identification of the rotation angle is possible and that the identified values can be significant in some cases. Furthermore, it is shown that assuming an incorrect anisotropy rotation angle (e.g., commonly assumed α = 0°) can lead to two major problems: (1) loss of convergence when identifying SOF values (resulting in large coefficients of variation for the major SOF) when the difference between the true and assumed angles is large; and (2) incorrect identification of SOF values (with the error up to 80% or more) even when the difference is small (and convergence is not lost). Therefore, the proposed extended method, which reduces the error to approximately 10%, may be necessary for the accurate identification of RF parameters, even for soils with small anisotropy rotations, which are often neglected. Although small anisotropy rotations have little direct impact on probabilistic outcomes when the principal SOFs are correctly identified, they still influence the identification procedure itself, and therefore can have a significant indirect effect on the resulting probabilistic analyses.

In deep-buried tunnel construction, the instability issues caused by excavation under high-stress conditions have been challenging. In this study, a series of true triaxial single-sided unloading tests were performed on jointed sandstone specimens with different joint inclinations to explore the fracture behavior of jointed rock at different burial depths under excavation unloading. The results show that the specimen under Loading Path I (unloading first and then loading) exhibits an unloading rebound phenomenon and a distinct yielding stage, reflecting a ductile failure. The specimen under Loading Path II (loading first and then unloading) shows a higher brittleness and greater susceptibility to failure, without an obvious yield stage. In the specimen under Loading Path I, the macroscopic failure forms a V-shaped notch due to buckling tensile cracks, whereas the failure of specimen under Loading Path II resembles the rockburst phenomenon with far-field tensile cracks. Additionally, the increased burial depth increases the yield and peak stresses of specimen and suppresses large-scale cracks but intensifies the crack propagation in specimen upon unloading, resulting in a more severe failure. The joint inclination affects the crack propagation and fragmentation characteristics of specimen, with the greatest influence occurring at 30°–45°. At joint inclinations of 0°–30°, the failure of specimen is dominated by shear cracks initiated from joint tips. At joint inclinations of 45°–60°, the failure of specimen involves mixed tensile-shear cracks, while at the joint inclination of 90°, the tensile cracks parallel to the joint dominate.

The deformation behavior of 2205 duplex stainless steel was analyzed using in situ electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) to investigate phase-specific strain accommodation mechanisms. Results indicate that the slip deformation in the austenite and ferrite phases correlates with their mechanical property differences. In austenite, Σ3 boundaries enclosing twins demonstrated effective deformation compatibility. As strain increased, the slip systems activated remained consistent with those predicted by the maximum Schmid factor. In contrast, ferrite exhibited cross-slip behavior due to the simultaneous activation of {110} and {112} slip systems, deviating from the Schmid law. The evolution of low-angle grain boundaries (LAGBs) was a dominant deformation feature in ferrite, with the density of LAGBs increasing during tensile deformation. Additionally, preferential rotation of grain subdomains led to misorientation accumulation near original high-angle grain boundaries (HAGBs) and triple junctions, forming new HAGBs. These findings reveal coordinated deformation mechanisms involving grain rotation and slip interactions between the two phases.

Although intensively researched in the last decade, additive manufacturing techniques are still subject to certain shortcomings, such as internal porosity or anisotropy of properties. In this work, we investigate the effects of postprocessing via hot isostatic pressing (HIP) on the properties of the titanium alloy Ti6Al4V produced via two various additive manufacturing methods: laser powder bed fusion (LPBF) and cold spray (CS). The LPBF produced a microstructure composed of a mixture of hcp-structured α(Ti) and α’(Ti), whereas α(Ti) and bcc-structured β(Ti) were recognized in the CS-ed materials. The subsequent HIP treatment did not cause reformation of the LPBF microstructure. This process had a significant effect on the densification of the CS-ed samples. To study the anisotropy of the material properties, the tensile and compressive strengths of the materials were determined in the planes parallel and perpendicular to the building (LPBF) and spraying (CS) directions. The LPBF materials exhibited significantly better mechanical properties stemming from the typical α/α’ martensitic microstructure, whereas the CS-ed materials presented a high number of pores and smooth and textured regions composed of recrystallized grains and grains with a high number of dislocations, respectively. The HIP treatment led to a reduction in porosity, causing a significant increase in the mechanical properties (UTS by 132%) and a reduction in the UTS anisotropy in the CS-ed materials.

This work’s primary objective is to create and demonstrate a low-cost computational technique and an easy-to-implement formulation for estimating buckling capacity of multiple parallel nano-scale elements elastically connected by a Kerr-type foundation subjected to axial load. To accomplish this goal, the system of governing equilibrium equations of the considered multi-bonded structure, which includes n coupled linear differential equations of order 8th, is extracted using the calculus of variations approach and after eliminating the deformation of the inner shear spring layers. A set of explicit and parametric formulas for predicting the stability strength of the system under-investigation, focusing on the double-bond system, is ultimately obtained after the resulting system of equations is solved using trigonometric functions for simply-supported boundary conditions. The attained closed-form formulations require a minimal computational cost, which greatly decrease the central processing unit time, and the extracted expressions, along with their correctness and precision, can be used to achieve the critical loads associated with both in-phase and out-of-phase buckling mode deflections. An exhaustive parametric study is conducted to precisely examine the sensitivity of endurable buckling loads of double-bonded nano-scale elements after the accuracy of the extracted closed-form solution formulations is evaluated. This study considers the effects of various parameters, including the non-locality parameter, the shear layer stiffness constant, the stiffness of Winkler-type elastic medium, including the top and bottom layers, mode number, and axial load ratio, taking into account the effects of applying compressive and/or tensile axial force.

This study focused on the high-temperature behavior of pure liquid Mg on three dissimilar types of cast iron substrates (Fe-C alloys with different morphologies, quantities, and distributions of the graphite phase). The experiments were performed using the sessile drop method under isothermal conditions at 715 °C in two different flowing gas atmospheres: (i) pure Ar and (ii) a mixture of Ar and 5 wt% H₂. The tests were conducted using non-contact heating of a couple of dissimilar materials combined with capillary purification of Mg drops from a native oxide film directly at the test temperature in an experimental chamber by squeezing the drops from a graphite capillary placed above cast iron substrates. The high-temperature behavior of Mg/substrate couples was recorded with a high-speed CCD camera, and collected images were used for measurements of the contact angle values (θ) formed between the liquid Mg and selected substrates. The solidified Mg/substrate couples were subjected to detailed microstructural observations by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The obtained results showed significant differences in the wetting behavior of Mg depending on the type of cast iron and the test atmosphere. In all cases, non-wetting behavior (θ > 90°) was observed in pure Ar, while the addition of hydrogen led to a reduction in contact angle values, especially for spheroidal graphite iron (SGI), where values decreased below 90°, commonly accepted as wetting behavior. In contrast, lamellar graphite iron (LGI) remained non-wettable under both atmospheres used in this study, although a decrease in contact angle (Δθ ~ 27°) was determined in the hydrogen-containing atmosphere, as compared to pure Ar. Compact graphite iron (CGI) also exhibited non-wetting behavior in both atmospheres; however, the values of contact angle were close to 90° in the Ar + 5 wt% H₂ atmosphere. The SEM/EDS analysis of cross-sectioned solidified Mg/cast iron substrates revealed slight morphological differences. For SGI and CGI, localized interface areas containing Mg, O, and occasionally Si were observed, particularly after testing in the Ar + 5 wt% H₂ atmosphere. These areas were generally thin and discontinuous, and no evidence of new phases was found. The presence of isolated Mg crystallites on the LGI surface was attributed to mechanical deposition or condensation of Mg during cooling.

This study investigates the mechanical and microstructural behavior of ambient-cured geopolymer mortars synthesized with ground granulated blast furnace slag (GBFS) and Class F fly ash (FA) as binder materials. Sodium hydroxide (NaOH) solutions at molarities of 4 M, 6 M, and 8 M were used as alkali activators, while GBFS was partially replaced with FA at ratios ranging from 0% to 25% by weight. The fresh and hardened properties of the mortars were evaluated through flow table tests, flexural and compressive strength measurements, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and mercury intrusion porosimetry (MIP). Results indicated that higher activator molarity significantly enhanced both the flexural and compressive strengths, while increased FA content improved workability but adversely affected strength. Microstructural analyses revealed that greater FA replacement led to more microcracks and higher porosity, contributing to reduced mechanical performance. The formation of C-A-S-H and N-A-S-H gels was observed to be critical for strength development. The findings suggest that optimizing activator molarity and binder composition is essential for achieving durable, environmentally friendly geopolymer mortars under ambient curing conditions. Unlike most existing studies relying on elevated-temperature curing, this study offers a detailed analysis of ambient-cured systems using only industrial by-products, thus providing a novel framework for low-energy geopolymer mortar production suitable for real-world applications.

This study explores the influence of SiC weight fraction and Field-Assisted Sintering Technology/Spark Plasma Sintering (FAST/SPS) parameters on the microstructure and thermal performance of Al–SiC composites. Composites containing 70 wt% and 90 wt% SiC were consolidated at temperatures ranging from 600 °C to 2150 °C, under compaction pressures of 80–100 MPa and heating rates between 25 and 100 °C/min. X-ray diffraction revealed the presence of Al, SiC, Al₂O₃, and secondary phases such as Al₄C₃ and Si. The highest relative density (98.65%) was achieved in the 90 wt% SiC sample sintered at 2100 °C under 100 MPa. Microstructure analysis showed a heterogeneous microstructure with residual porosity. Thermal characterization indicated that increasing density improved thermal conductivity and specific heat capacity, while the coefficient of thermal expansion (CTE) decreased with increasing SiC content. The results demonstrate that precise control of FAST/SPS parameters enables optimization of densification and thermal properties in Al–SiC composites for potential use in high-performance structural applications.

This study investigates the three-dimensional thermoelastic response of a functionally graded viscoelastic cylindrical panel embedded with piezoelectric layers subjected to asymmetric thermal loading. Utilizing the Boltzmann integral model to capture the viscoelastic behavior and a power-law distribution for the relaxation modulus in the radial direction, the governing equations are formulated based on full three-dimensional elasticity theory. The piezoelectric effects and the functional gradation of materials are rigorously incorporated. A combination of Laplace transform, Fourier series expansion, and state-space method is employed for analytically solving the simply-supported boundary condition, while a semi-analytical differential quadrature method (DQM) is used for more complex boundary conditions. The accuracy of the proposed method is validated through comparison with existing literature and analytical results. Parametric studies explore the effects of support conditions, time constants, opening angles, piezoelectric layer thicknesses, and other key factors on the structural response, providing insights into the design of smart FG cylindrical systems.