Hasil untuk "Materials of engineering and construction. Mechanics of materials"

Oliver Santos-Lopes, Dimitrios S. Tzeranis, Vasileios Vavourakis

Stiffness is a pivotal property of the insoluble matrix surrounding cells, and a known regulator of multiple cell phenotypes. Yet, no universal metric to quantify the stiffness perceived by cells in 3D matrices exists. This manuscript presents a direct metric and efficient in silico method to quantify cell-perceived stiffness within lattice-like microporous biomaterials, focusing on freeze-dried porous collagen-based scaffolds (PCS) and 3D-printed scaffolds. Simulations show that cells inside microporous biomaterials perceived variable matrix stiffness due to the stochastic nature of cell-matrix adhesion and lattice loading. In PCS, cells sense a softer matrix with increased contractility, opposing the stress-stiffening response observed in most biological specimens. Furthermore, cell-perceived stiffness in PCS is significantly affected by neighbouring cell contractility, suggesting cell–cell communication through matrix stiffness alterations. These force-dependent effects, arising from the large deformations of PCS struts, may influence cell mechanoresponsive pathways and explain reported downregulation of wound contraction during skin regeneration in PCS. In contrast, cells in 3D-printed scaffolds perceive stiffness three orders of magnitude higher, which is insensitive to cell contractility. The methodology offers novel insights on the mechanical environment perceived by cells within microporous biomaterials, supporting biomaterial design, comparison, interpretation of complex cell-biomaterial interactions observed in vitro or in vivo.

Mohammad Hadi Khanbabaee Saatloo, Amir Abdollah-Zadeh, Rajab Ali Seraj

Introduction and Objectives: The properties of coatings deposited by cold spray depend on the parameters of the process. The aim of this research is to investigate the effect of gas pressure and stand-off distance of cold spray process of zinc on a low carbon steel substrate.Materials and Methods: In this research, zinc powder was sprayed at pressures of 20 and 30 bar and stand-off distances of 20 and 30 mm. The microstructure of the coatings was investigated using optical and scanning electron microscope and the micro-hardness of the coatings was measured. Then, the selected coating and steel substrate were subjected to polarization corrosion test.Results: The results showed that increasing the gas pressure from 20 to 30 bar decreased the porosity and increased the micro-hardness due to further deformation. Also, for a constant pressure, the stand-off distance of 20 mm has the lowest porosity and the highest micro-hardness due to the higher temperature of the particles when impact the substrate. The results obtained from the polarization test show that the coating has a sacrificial nature compared to the substrate and reduces the corrosion current density by 48% and corrosion rate by 33% compared to the substrate.Conclusion: In this study, the effect of gas pressure and stand-off distance of cold spray process of zinc on low carbon steel substrate was investigated. The results showed that increasing the gas pressure from 20 to 30 bar and reducing the stand-off distance from 30 to 20 mm improved porosity and increased coatings micro-hardness. The results of this study can be used to optimize the parameters of the cold spraying of zinc for use in various industries such as automotive, power plants and marine infrastructure.

D.A. Abdoh

Tausif E Elahi, Azmayeen Rafat Shahriar, Mohammad Shariful Islam

S. Muguda, M. Wyndham

Changming Li, Yubing Fu, Haifeng Cheng et al.

Tiancheng Li, Haiyang Chen, Yubo Huang et al.

In the present (CoCrNi)92Mo2Al6 medium entropy alloy (MEA), a dual heterogeneous structure is achieved by regulating the degree of recrystallization of the FCC matrix and σ phase precipitation through incomplete annealing. Compared to the alloys with single-phase FCC structure or uniform precipitation structure, this dual heterostructured MEA has superior mechanical properties by possessing the hetero-deformation-induced (HDI) hardening, precipitation strengthening and twinning-induced plasticity (TWIP) mechanism. Our research contributes to the understanding of the micromechanical behavior of heterogeneous materials and also provides a solution to the problem that precipitation increases strength at the expense of plasticity.

Natalie N. Neal, Kailash Arole, Huaixuan Cao et al.

Abstract Structural color arises from light scattering rather than organic pigments and can be found in Nature, such as in bird feathers and butterfly wings. Synthetic materials can mimic Nature by leveraging materials with contrasting optical characteristics by controlling each materials’ spatial arrangement in a heterostructure. Two-dimensional MXene nanosheets are particularly interesting due to their unique optical properties, but MXenes have not been used directly as a structural colorant because it is challenging to control the spatial placement of MXenes at the nanometer level. Here, we report the emergence of structural color in layer-by-layer (LbL) assemblies of Ti3C2Tz MXene nanosheets and polyelectrolyte heterostructures with controlled block thicknesses. The block thickness and spatial placement of MXene are controlled by the assembly’s salt concentration and number of layer pairs. This work demonstrates that optical characteristics of MXene/polyelectrolyte heterostructures depend on MXene content and placement, while deepening the understanding of MXenes within structural color films.

Jéssica Peixoto Rodrigues, Jéssica Regina da Costa Silva, Bruno Antônio Ferreira et al.

Abstract The development of wound dressings from biomaterials has been the subject of research due to their unique structural and functional characteristics. Proteins from animal origin, such as collagen and chitosan, act as promising materials for applications in injuries and chronic wounds, functioning as a repairing agent. This study aims to evaluate in vitro effects of scaffolds with different formulations containing bioactive compounds such as collagen, chitosan, N-acetylcysteine (NAC) and ε-poly-lysine (ε-PL). We manufactured a scaffold made of a collagen hydrogel bioconjugated with chitosan by crosslinking and addition of NAC and ε-PL. Cell viability was verified by resazurin and live/dead assays and the ultrastructure of biomaterials was evaluated by SEM. Antimicrobial sensitivity was assessed by antibiogram. The healing potential of the biomaterial was evaluated in vivo, in a model of healing of excisional wounds in mice. On the 7th day after the injury, the wounds and surrounding skin were processed for evaluation of biochemical and histological parameters associated with the inflammatory process. The results showed great cell viability and increase in porosity after crosslinking while antimicrobial action was observed in scaffolds containing NAC and ε-PL. Chitosan scaffolds bioconjugated with NAC/ε-PL showed improvement in tissue healing, with reduced lesion size and reduced inflammation. It is concluded that scaffolds crosslinked with chitosan-NAC-ε-PL have the desirable characteristics for tissue repair at low cost and could be considered promising biomaterials in the practice of regenerative medicine. Graphical Abstract

W. Chen, Y. Wen

To inquire about the properties of concrete reinforced with polyvinyl alcohol (PVA) fiber (various fiber lengths and dosages), different experimental tests including mechanical property, cracking resistance, and chloride resistance were investigated. The overall performance of PVA fiber-reinforced concrete (FRC) was innovatively analyzed integrating mechanical indicators and crack resistance parameters. Furthermore, nuclear magnetic resonance (NMR) and scanning electron microscope (SEM) were selected to analyze the causes and mechanisms underlying the alterations in the performance of PVA-FRC. The experimental results demonstrate that the flexural strength, the crack resistance characteristic and chloride ion penetration resistance of PVA-FRC are significantly improved compared to ordinary concrete. Increasing fiber length plays a key role in flexural strength, compared with fiber dosage. Considering both mechanical properties and durability, PVA-FRC containing 0.25% volume fraction of 12 mm PVA fibers (F12-0.25) demonstrated optimal performance.

Suhua Jiang, Fukai Zhu, Yang Lin et al.

Owing to residual tumor tissues around the treatment margins, it is difficult to totally ablate large tumors, eliminate disseminated and metastatic nodules as well as prevent the tumor recurrence simultaneously by conventional photothermal therapy (PTT). In this work, PTT combined reactive oxygen species oxidative therapy (ROT) was conducted via mesoporous polydopamine nanosphere with nanoceria doping (MPDA-Ce). After surface anchoring with Arg-Gly-Asp (RGD) molecules, the dispersive stability and tumor targeting of this innovative nanoplatform were substantially boosted. In vitro studies revealed that the unique nanotherapeutics had satisfactory photothermal conversion efficiency (η = 51.41%), continuous nanoceria release in cytoplasm of tumor cells after acid microenvironment (pH = 5.5) induced biodegradation. Significantly, hyperthermia amplified the abundant reactive oxygen species generation under 808 nm laser irradiation that potent ROT was realized with only 27.1% cells alive. Strikingly, Indocyanine green (ICG) loaded MPDA-Ce with RGD modification shows robust tumor targeting capability in breast carcinoma bearing Balb/C mice under fluorescent imaging in the second near-infrared window. The combined treatments resulted in complete tumor cells eradication under 808 nm laser illumination both in vitro and in vivo. This work highlights the promising application of MPDA-Ce as a powerful nanoplatform for ROT and PTT combined treatment in clinical.

HUANG ZhenRong, ZHANG Juan

In order to study the influence of pitting defect on the contact stress of face gear, a face gear of helicopter transmission system was taken as the research object, the defect shape was assumed to be spherical and the solid model was built by UG and Catia software. Using the finite element loading tooth contact analysis method（LTCA）, the contact stress distribution and variations of maximum contact stress value and its position are obtained when the defect is in different position on the tooth surface. The results show that the introduction of pitting defect can increase the maximum contact stress of tooth surface by 21%. When the defect is close to the contact trace line and tooth tip, the maximum contact stress is greater than that of other positions. The maximum contact stress occurs near the middle or upper part of the defect, its position is on the right of the defect while the defect is outside the contact trace line, and it is the opposite when the defect is inside the contact trace line. The maximum contact stress near the defect increases with the increase of defect radius gradually. The influence of defect depth on contact stress is small.

Dongqing Zhang, Kai Zhao, Daoxiu Li et al.

In this work, novel TiC particles doped by trace amounts of B, referred to as TiCB, were introduced to an Al-Mn alloy with the Al-TCB master alloy. The effects of the TiCB particles on the solidification microstructure, extrusion behavior, and mechanical properties of the Al-Mn alloy were systematically studied. The results showed that TiCB particles could significantly refine α-Al grains by providing heterogeneous nucleation substrates and hindering the growth of α-grains. For example, when the amount of added TiCB particles was 0.5 wt%, average α-Al grain size could be refined to a minimum of 40.2 μm from 410.1 μm when no particles were added. After hot extrusion, TiCB particles and fractured α-Al(Fe, Mn)Si formed streamlines along the extrusion direction. More importantly, TiCB particles could inhibit the dynamic recrystallization process during hot extrusion and retain numerous geometrically necessary dislocations. Consequently, the mechanical properties of the Al-Mn alloy at room temperature (25 °C) and elevated temperature (350 °C) were significantly improved after adding TiCB particles. When the amount of added TiCB particles was 1.5 wt%, the ultimate tensile strengths at 25 °C and 350 °C were increased by 25.6% and 32.4%. This work sheds light on the grain refinement and strengthening of non-heat-treatable wrought Al-Mn alloys.

Nataf, Frédéric, Tournier, Pierre-Henri

Scalability of parallel solvers for problems with high heterogeneities relies on adaptive coarse spaces built from generalized eigenvalue problems in the subdomains. The corresponding theory is powerful and flexible but the development of an efficient parallel implementation is challenging. We report here on recent advances in adaptive coarse spaces and on their open source implementations in domain specific languages such as FreeFem, focusing on a new domain decomposition for saddle point formulations with some numerical tests.

Hongwei Cheng, Hwan‐Ching Tai

Aliakbar Gholampour, Togay Ozbakkaloglu, Osman Gencel et al.

V A Ilyichev, N S Nikiforova, A V Konnov

Abstract The article is devoted to the application of the technological soil mechanics principles in the design and construction of underground structures, also in problematic soils – loose water-saturated sands. The definition of technological soil mechanics is given. The relevance of the research topic is justified. A quantitative assessment of the stress strain behavior (SSB) of the soil mass containing the support systems of deep pits, depending on the technology and sequence of work during underground construction, was made. The possibility of the SSB of ground mass managing during underground construction in order to select the most economical options for design and technological solutions is proved. Recommendations for SSB management of underground parts of buildings and structures, as well as the surrounding soil mass, based on the technological soil mechanics application are formulated.

Narine Pirumyan, Mihran Stakyan, Gagik Galstyan

A mathematical model has been proposed for processing data from tests of building materials and obtaining optimal links between the characteristics of the bearing capacity and technological parameters of building materials for the use of these connections in refined design and construction procedures for building structures. To improve the accuracy of the results obtained, a three-level optimization principle was applied using the least squares method and a computational algorithm was compiled that allows us to develop an additional computational subroutine expanding the capabilities of the corresponding standard computer programs.

YANG Fan, LIU XiaoNing, LIU Bing et al.

In order to increase the burst pressure of copper pipe,save the copper material under the premise of guaranteeing safety,overpressure enhancement of TP2 copper tube was tested at room temperature,the relationship between the burst pressure of copper tube and the pretreatment pressures was studied,the changes of TP2 material tensile strength was analyzed. Based on28 groups burst test of TP2 copper tubes under different pretreatment pressure at room temperature,studies have shown that: 1)If the enhancement pretreatment pressure of TP2 copper tube is equal to the yield pressure,the thermal effect of copper tubes brazing should be improved,copper tube burst pressure and TP2 material tensile strength should be strengthened to a certain extent. 2) Compared with non overpressure enhancement at room temperature,for the burst pressure and the tensile strength of TP2 copper tube used appropriate pressure pretreatment,the means of copper tube burst pressure and the TP2 material tensile strength are increased significantly,the standard deviation and coefficient of variation are decreased significantly,and the precision is improved obvious. For the burst pressure and the tensile strength of TP2 copper tube,the fluctuation range of the average,standard deviation and coefficient of variation are smaller,and the stability is become well.

Seun Samuel Owoeye, Davies Oladayo Folorunso

This paper investigates the corrosion behaviour of Zn-27Al based hybrid composites reinforced with quarry dust (QD) and silicon carbide particles (SiCp). The Zn-27Al hybrid composites containing 8 wt% and 10 wt% SiCp-QD particles reinforcement with varied weight percentage of 0, 25, 50, 75 and 100% quarry dust respectively were synthesized using stir casting technique. The corrosion behaviour of the composites was investigated in 0.3M H2SO4 and 3.5 wt% NaCl solution at 25ºC using electrochemical methods in accordance with ASTM G59-97(2014) standard. The results show that for 8 wt% reinforcement, the hybrid composites A2 and A3 (corresponding to 50% SiCp: 50% QD and 25% SiCp: 75% QD respectively) having corrosion rate of 0.006 mmpy displayed superior corrosion resistance. For 10 wt% reinforcement, hybrid grades B1 (75% SiCp: 25% QD), B2 (50% SiCp: 50% QD) and B3 (25% SiCp: 75% QD) has superior corrosion rate of 0.0172, 0.0126 and 0.0135 mmpy respectively while B4 (corresponding to 100% QD) shows the most superior corrosion rate of 0.00315 mmpy when compared with the monolithic alloy having corrosion rate of 0.213 mmpy all in marine environment (3.5 wt% NaCl solution). However, except for composite grade A2 with 0.055 mmpy corrosion rate and B4 (corresponding to 100% QD) with superior corrosion rate of 0.0143 mmpy in 0.3M H2SO4 medium, all other composite grades performed poorly in the acidic medium.