Macroscopic Mechanics Research Articles

Mechanisms of deformation, damage and life behavior of inconel 617 alloy during creep-fatigue interaction at 700 °C

The continuous fatigue tests and creep-fatigue tests with the imposition of strain hold at the peak strain were conducted at 700 °C on Inconel 617 alloy. The strain amplitude of 0.25 %, 0.30 %, 0.35 %, 0.40 %, and hold time of 60 s, 600 s and 1800 s were used. The cyclic deformation behavior and dynamic strain aging (DSA) were discussed. The strain localization, dislocation substructure and precipitation behavior were carefully characterized, which provided physical information to understand the cyclic deformation behavior. The dominant damage mechanism and damage interaction, responsible for the cracking behavior were identified based on the fracture surface observation and secondary cracks morphology. The cyclic life saturation effect was comprehensively elucidated from the perspective of macroscopic mechanical response and microscopic deformation mechanism.

Research on the Thermal Aging Mechanism of Polyvinyl Alcohol Hydrogel.

Polyvinyl alcohol (PVA) hydrogels find applications in various fields, including machinery and tissue engineering, owing to their exceptional mechanical properties. However, the mechanical properties of PVA hydrogels are subject to alteration due to environmental factors such as temperature, affecting their prolonged utilization. To enhance their lifespan, it is crucial to investigate their aging mechanisms. Using physically cross-linked PVA hydrogels, this study involved high-temperature accelerated aging tests at 60 °C for 80 d and their performance was analyzed through macroscopic mechanics, microscopic morphology, and microanalysis tests. The findings revealed three aging stages, namely, a reduction in free water, a reduction in bound water, and the depletion of bound water, corresponding to volume shrinkage, decreased elongation, and a "tough-brittle" transition. The microscopic aging mechanism was influenced by intermolecular chain spacing, intermolecular hydrogen bonds, and the plasticizing effect of water. In particular, the loss of bound water predominantly affected the lifespan of PVA hydrogel structural components. These findings provide a reference for assessing and improving the lifespan of PVA hydrogels.

Mineral and cross-linking in collagen fibrils: The mechanical behavior of bone tissue at the nano-scale

The mineralized collagen fibril is the main building block of hard tissues and it directly affects the macroscopic mechanics of biological tissues such as bone. The mechanical behavior of the fibril itself is determined by its structure: the content of collagen molecules, minerals, and cross-links, and the mechanical interactions and properties of these components. Advanced glycation end products (AGEs) form cross-links between tropocollagen molecules within the collagen fibril and are one important factor that is believed to have a major influence on the tissue. For instance, it has been shown that brittleness in bone correlates with increased AGEs densities. However, the underlying nano-scale mechanisms within the mineralized collagen fibril remain unknown. Here, we study the effect of mineral and AGEs cross-linking on fibril deformation and fracture behavior by performing destructive tensile tests using coarse-grained molecular dynamics simulations. Our results demonstrate that after exceeding a critical content of mineral, it induces stiffening of the collagen fibril at high strain levels. We show that mineral morphology and location affect collagen fibril mechanics: The mineral content at which this stiffening occurs depends on the mineral’s location and morphology. Further, both, increasing AGEs density and mineral content lead to stiffening and increased peak stresses. At low mineral contents, the mechanical response of the fibril is dominated by the AGEs, while at high mineral contents, the mineral itself determines fibril mechanics.

Experimental and mechanistic investigation on the plastic anisotropic deformation behavior of α-phase titanium alloy Ti-2Al-2.5Zr

Ti-2Al-2.5Zr is widely used in piping and structural support applications, however, the rolling forming process results in anisotropic deformation during service. This behavior has implications for the manufacturing processes and structural safety assessments in engineering applications. In this study, the plastic anisotropic deformation behavior of a rolled Ti-2Al-2.5Zr plate was investigated using uniaxial tensile tests along the transverse, normal, and 45° directions. Acoustic emission, electron backscatter diffraction, and scanning electron microscopy methods were used to investigate dislocation slip and twinning mechanisms. The results indicated that different microscopic deformation mechanisms caused the significant macroscopic anisotropy of Ti-2Al-2.5Zr. The primary mechanisms involved were prismatic <a> slip, pyramidal <c+a> slip, and {10-12} extension twinning. The stress direction determined the influence of each of these mechanisms during the yielding and plastic deformation phases. Application of the visco-plastic self-consistent model established the relationship between the macroscopic mechanical responses and microscopic deformation mechanisms. It was revealed that Ti-2Al-2.5Zr achieved its optimum strength when the initial texture aligned most of the grain c-axis at angles ranging from 30° to 50° relative to the deformation direction. This finding provides a direction for the texture design of Ti-2Al-2.5Zr in engineering materials.

Quantum control and Berry phase of electron spins in rotating levitated diamonds in high vacuum

Levitated diamond particles in high vacuum with internal spin qubits have been proposed for exploring macroscopic quantum mechanics, quantum gravity, and precision measurements. The coupling between spins and particle rotation can be utilized to study quantum geometric phase, create gyroscopes and rotational matter-wave interferometers. However, previous efforts in levitated diamonds struggled with vacuum level or spin state readouts. To address these gaps, we fabricate an integrated surface ion trap with multiple stabilization electrodes. This facilitates on-chip levitation and, for the first time, optically detected magnetic resonance measurements of a nanodiamond levitated in high vacuum. The internal temperature of our levitated nanodiamond remains moderate at pressures below 10−5 Torr. We have driven a nanodiamond to rotate up to 20 MHz (1.2 × 109 rpm), surpassing typical nitrogen-vacancy (NV) center electron spin dephasing rates. Using these NV spins, we observe the effect of the Berry phase arising from particle rotation. In addition, we demonstrate quantum control of spins in a rotating nanodiamond. These results mark an important development in interfacing mechanical rotation with spin qubits, expanding our capacity to study quantum phenomena.

Comparative assessment of liver tissue: from microstructural and mesoscale vascular architecture to macroscopic mechanics

Comparative assessment of liver tissue: from microstructural and mesoscale vascular architecture to macroscopic mechanics

Impact characterization of coral aggregate reinforced concrete beam: A 3D numerical study

Coral aggregate concrete (CAC), an innovative construction material, utilizes abundant marine resources, including coral aggregates and seawater. In the realm of reef engineering, CAC is widely used in structural elements such as reinforced beams and columns. This paper presents a three-dimensional (3D) mesoscale model to assess the impact behavior of coral aggregate reinforced concrete beams (CARCB), incorporating the heterogeneity characteristics of CAC and the explicit simulation of reinforcement components. The 3D mesoscale modelling approach developed in this paper was validated by previous experimental data of CARCB, and used for extensive parametric studies evaluating effects such as concrete strength grade, reinforcement ratio, and impact velocity on the static and dynamic bending behaviors of CARCB. Finally, based on the mesoscopic cracking process and damage patterns of CARCB under static and dynamic loads, this study illustrates the corresponding macroscopic mechanical behaviors and failure mechanisms. Results indicate that the predominant forms of flexural failure in CARCBs are tensile cracking in the mid-span region and diagonal shear cracking. Results demonstrate that the predominant forms of flexural failure in CARCBs are tensile cracking in the mid-span region and diagonal shear cracking. Specifically, local bending failures and symmetrical diagonal shear cracks were evident in the CARCBs subjected to dynamic loads, closely resembling those in ordinary concrete beams. With increasing concrete strength grades (C30 to C60) and reinforcement ratios (0.9 %–1.7 %), a significant reduction in the mid-span ultimate deflection of CARCB is observed, indicating enhanced impact resistance. Additionally, as the impact velocity increases from 1 m/s to 50 m/s, the mid-span ultimate deflection of CARCB is magnified by a factor of approximately 200, indicating intensified dynamic damage to CARCB with increasing impact velocities.

Preliminary study on the mechanical behavior of clay in one-dimensional compression with DEM simulations

The mechanical behavior and physical properties of clay are closely associated with its microstructure. Current research on the macroscopic mechanics and physical properties of clay is comprehensive and systematic. However, the microstructural variations underlying these characteristics have been predominantly examined under mercury intrusion porosimetry and scanning electron microscopy, while quantitative and systematic studies are notably limited. This research employs the discrete element method (DEM) simulation to investigate the microscopic responses of clay, simulating one-dimensional compression tests on two clay types: card-house and book-house structures. The analysis of pore size and morphology was conducted using virtual mercury intrusion porosimetry and the pore segmentation method. The clay microstructure was quantitatively characterized by parameters such as pore aspect ratio, orientation distribution, and cumulative pore volume curve. The findings demonstrate that DEM effectively replicates the fundamental mechanical behavior of clay, revealing and explaining the evolution pattern of clay pore structure during one-dimensional compression in terms of platelet alignment adjustment. This macroscopic compression is characterized by variations in pore size distribution, orientation, and aspect ratio.

A damage constitutive model of layered slate under the action of triaxial compression and water environment erosion

Based on the macroscopic structure control theory, The slate with a significant bedding plane is a composite rock mass composed of rock blocks containing microscopic defects, joint surface closure elements, and shear deformation elements. Considering the coupling damage effect of water erosion and triaxial compressive load on bedding structure plane, the transversely isotropic damage constitutive model of slate under triaxial compressive load is derived with the dip angle of bedding and confining pressure as the variable. Firstly, based on the statistical theory of continuous damage mechanics and the maximum tensile strain criterion, the transversely isotropic deformation constitutive model of rock block with micro-defects is given; Secondly, based on the phenomenological theory of closed deformation and shear-slip deformation mechanism of layered structural plane under the coupling action of water erosion and triaxial compression load, the calculation formula of axial deformation of layered structural plane under the coupling action is given; Finally, to verify the accuracy of the established constitutive model, triaxial compression tests are carried out to study the influence of dip angle and confining pressure on the macroscopic mechanical properties and mechanism of slate. The results show that: the established triaxial compression damage constitutive model of bedding slate can accurately describe the stress–strain relationship of bedding slate after water environment erosion. With the increase of bedding dip angle, the strength and deformation capacity of the bedding slate first decreases and then increases, showing a U-shaped distribution as a whole. There are three main types of failure: tension shear composite failure, shear slip failure, and splitting tension failure.

A High-Finesse Suspended Interferometric Sensor for Macroscopic Quantum Mechanics with Femtometre Sensitivity.

We present an interferometric sensor for investigating macroscopic quantum mechanics on a table-top scale. The sensor consists of a pair of suspended optical cavities with finesse over 350,000 comprising 10 g fused silica mirrors. The interferometer is suspended by a four-stage, light, in-vacuum suspension with three common stages, which allows for us to suppress common-mode motion at low frequency. The seismic noise is further suppressed by an active isolation scheme, which reduces the input motion to the suspension point by up to an order of magnitude starting from 0.7 Hz. In the current room-temperature operation, we achieve a peak sensitivity of 0.5 fm/Hz in the acoustic frequency band, limited by a combination of readout noise and suspension thermal noise. Additional improvements of the readout electronics and suspension parameters will enable us to reach the quantum radiation pressure noise. Such a sensor can eventually be utilized for demonstrating macroscopic entanglement and for testing semi-classical and quantum gravity models.

NMR-based analysis of fractal characteristics of the pore structure of fully aeolian sand concrete under carbonation-dry-wet cycles

The evolution law of the pore structure of concrete is important for the study of concrete durability. To study the quantitative relationship between pore structure and macroscopic mechanics of aeolian sand concrete(ASC) under carbonation-dry-wet cycle(DWCs), the fractal characteristics of ASC under carbonation DWCs were analyzed by means of nuclear magnetic resonance(NMR) technology. The results showed that the carbonization product CaCO3 filled the pores and the compressive strength of ASC increased as the carbonization time increasing. When the DWCs was 0 times, the compressive strength of C1 and C2 groups increased by 9% and 13.6%, respectively, compared with C0. The compressive strength of C0 and C1 groups reached the maximum value when the DWCs was 40 times, while the C2 group reached the maximum value when the DWCs was 20 times. Compared with C0, the compressive strength of C1 and C2 increased by only 4% and 6%, respectively, after 100 DWCs. The fractal dimension Dmax reflected the proportion of harmless and multiple harmful pores in the damaged ASC. The fractal dimension Dmax was proportional to the proportion of harmless pores, and the correlation coefficient was 0.9303. The fractal dimension Dmax was inversely proportional to the proportion of harmful pores, and the correlation coefficient was 0.9565. The macroscopic mechanical properties were mainly affected by harmless pores and harmful pores, while the influence of less harmful pores and harmful pores was weak. This study will provide a theoretical justification for the use of ASC in practical engineering.

Discrete element simulation study on effects of grain preferred orientation on micro-cracking and macro-mechanical behavior of crystalline rocks

Abstract Grain-preferred orientation significantly influences the brittle fracture mechanism and failure mode of crystalline rocks. However, current grain-based models (GBMs) based on particle flow code (PFC) software are mostly proposed on the basis of the Voronoi tessellation method for grain boundary generation, which is difficult to simulate the heterogeneity of microstructure such as shape and orientation of rock minerals. To study the effect of grain-preferred orientation on macroscopic mechanical properties and microscopic characteristics of crystalline rocks, a novel grain-based microstructure transformation method (MTM) is proposed. Based on the MTM, a GBM with a target aspect ratio and crystal orientation is obtained by transforming the Voronoi crystal geometry through a planar coordinate mapping. Specifically, embedded FISH language is used to control random mineral seed size and distribution pattern to generate Tyson polygons. A polygon geometry that satisfies the rock texture is obtained as a grain boundary by spatially transforming the vertex of the Tyson polygon. The transformed complex geometry is taken as the crystal structure of the GBM, and the Lac du Bonnet granite models with different aspect ratios and crystal orientations were developed in PFC2D. Finally, a series of unconfined compressive strength tests are performed in PFC2D to verify the proposed modeling methods for the geometric variation of the crystals and to study the effects of the preferred orientation of the grains on the macroscopic mechanical properties and microscopic fracture mechanisms of the crystalline rocks from different perspectives.

Study of the Effect of Drying and Wetting Cycles and Water Content on the Shear Characteristics of Tailing Sands

Abstract The mechanical characteristics of tailing sands have an important impact on the safety and stability of the tailing dams. Fully understanding the effect of drying and wetting cycles (DWC) and water content on the characteristics of tailing sands is urgently needed. In this study, direct shear tests were first carried out to analyze the effect of DWC and water content on the macroscopic mechanical characteristics of tailing sands. Then, the mesoscopic mechanical behavior of tailing sands with different water contents under the action of DWC was studied by using PFC2D particle flow software. The results showed that the effect of DWC on the shear properties of tailing sands is more pronounced than water content. The cohesive force and the internal friction angle increase first and then decrease with the increasing water content. With the increasing number of DWC, the cohesive force and the internal friction angle all decreased to varying degrees. The results of the mesoscopic mechanical analysis indicated that after experiencing the DWC, the force chain of the sample gradually thickens to form a coarse force chain network area, and the number of cracks inside the sample is significantly larger than that of the sample that has not experienced the DWC. The results of this study are of great significance for understanding the macroscopic and mesoscopic shear failure mechanism of tailing sands under the effects of DWCs and water content.

Numerical simulation study of high-speed lip seal considering eccentricity

PurposeThis paper aims to focus on the high-speed rotary lip seal in aircraft engines, combining its service parameters, its own structure and application conditions, to study the influence of different eccentric forms, eccentricity, rotational speed and other factors on the performance of the rotary lip seal.Design/methodology/approachA numerical simulation model for high-speed eccentric rotary lip seals has been developed based on the theory of elastic hydrodynamic lubrication. This model comprehensively considers the coupling of multiple physical fields, including interface hydrodynamics, macroscopic solid mechanics and surface microscopic contact mechanics, under the operating conditions of rotary lip seals. The model takes into account eccentricity and uses the hazardous cross-sectional method to quantitatively predict sealing performance parameters, such as leakage rate and friction force.FindingsEccentricity has a large impact on lip seal performance; lips are more susceptible to wear failure under static eccentricity and to leakage failure under dynamic eccentricity.Originality/valueThis study provides a new idea for the design of rotary lip seal considering eccentricity, which is of guiding significance for the engineering application of rotary lip seal.

Identification of different lithofacies laminations in oil shale and their mechanical properties

Lamination can greatly enhance the anisotropy and heterogeneity of shale and plays a significant role in influencing hydraulic fracturing. The structure and mechanical difference of different lithofacies lamination are the basis to reveal the fracture propagation mechanism. In this paper, research focused on three continental oil shale with different lithofacies in Qikou sag, Bohai Bay basin, including Quartz-Feldspar dominated shale, Carbonate dominated shale and mixed-mineral shale. Scanning electron microscopy and mineral analysis are used to identify quartz-feldspar lamination and mixture lamination in Quartz-Feldspar dominated shales, as well as carbonate lamination and mixture lamination in Carbonate dominated shales. The distinct laminations with different characteristics were precisely located using FIB, which served as the guiding tool for the indentation experiment. The micromechanical properties of laminations with different lithofacies in oil shale samples are examined using the nanoindentation technique, highlighting their distinct differences. The findings demonstrate that the micromechanical properties of quartz-feldspar lamination in Quartz-Feldspar dominated shales exhibit superior strength, while the mechanical difference between laminations in Quartz-Feldspar dominated shales are significantly larger. The quartz-feldspar lamination exhibits the highest resistance when subjected to indentation force. The mechanical properties of mixture lamination in Quartz-Feldspar dominated shales and Carbonate dominated shales are comparable due to their similar mineral composition. Moreover, in conjunction with macroscopic rock mechanics experiments, it has been verified that the lamination structure facilitates the initiation and propagation of macroscopic fractures under stress loading.

Influence of basalt fiber on pore structure, mechanical performance and damage evolution of cemented tailings backfill

To study the influence of the addition of basalt fibers on the mechanical properties, pore structure, and damage evolution characteristics of the cemented tailings backfill (CTB), the uniaxial compression tests, nuclear magnetic resonance tests and scanning electron microscopy analysis were conducted on the CTB with four different content and lengths of basalt fibers. Test results show the following. (1) An increase in the content of basalt fibers will lead to an increase in the proportion of micropores and secondary pores in the CTB, while a decrease in the proportion of macropores. The influence of basalt fiber length on pore structure is not as significant as the content. (2) With the increase of basalt fiber content and length, the peak stress and peak strain of the CTB increase, but the elastic modulus decreases. Basalt fiber can significantly improve the ductility and bearing time of the CTB, with a length of 12 mm and a content of 1.5 % having the best effect. The length of basalt fibers affects macroscopic mechanics more than content. (3) The CTB without fiber have fewer cracks and faster crack propagation speed, while the CTB with fiber have more cracks and slower crack propagation speed. Basalt fibers mainly play a bridging role between hydration products, delaying the failure process of the sample. (4) A damage constitutive model was constructed. The rationality and reliability of the model were verified, and the damage evolution law of CTB was analyzed. The content and length of basalt fibers have a positive impact on damage evolution.

Internal Elastic Strains of AZ31B Plate during Unloading at Twinning-Active Region

Magnesium alloys, being the lightest structural metals, have garnered significant attention in various fields. The characterization of inelastic behavior has been extensively investigated by researchers due to its impact on structural component performance. However, the occurrence of twinning in the absence of any applied driving force during unloading has lacked reasonable explanations. Moreover, the influence of deformation mechanisms other than twinning on inelastic behavior remains unclear. In this study, uniaxial tension and compression tests were conducted on hot-rolled magnesium alloy plates, and neutron diffraction experiments were employed to characterize the evolution of macroscopic mechanical response and microscopic mechanisms. Additionally, a twinning and detwinning (TDT) model based on the elastic visco-plastic self-consistent (EVPSC) model has been proposed, incorporating back stress to describe the deformation behavior during stress relaxation. This approach provides a comprehensive understanding of the inelastic behavior of magnesium alloys from multiple perspectives and captures the influence of microscale mechanisms. A thorough understanding of the inelastic behavior of magnesium alloys and a reasonable explanation for the occurrence of twinning under zero-stress conditions offer valuable insights for the precise design of magnesium alloy structures.

Micromechanical homogenization of a hydrogel-filled electrospun scaffold for tissue-engineered epicardial patching of the infarcted heart: a feasibility study

AbstractFor tissue engineering applications, accurate prediction of the effective mechanical properties of tissue scaffolds is critical. Open and closed cell modelling, mean-field homogenization theory, and finite element (FE) methods are theories and techniques currently used in conventional homogenization methods to estimate the equivalent mechanical properties of tissue-engineering scaffolds. This study aimed at developing a formulation to link the microscopic structure and macroscopic mechanics of a fibrous electrospun scaffold filled with a hydrogel for use as an epicardial patch for local support of the infarcted heart. The macroscopic elastic modulus of the scaffold was predicted to be 0.287 MPa with the FE method and 0.290 MPa with the closed-cell model for the realistic fibre structure of the scaffold, and 0.108 MPa and 0.540 MPa with mean-field homogenization for randomly oriented and completely aligned fibres. The homogenized constitutive description of the scaffold was implemented for an epicardial patch in a FE model of a human cardiac left ventricle to assess the effects of patching on myocardial mechanics and ventricular function in the presence of an infarct. Epicardial patching was predicted to reduce maximum myocardial stress in the infarcted LV from 19 kPa (no patch) to 9.5 kPa (patch) and to marginally improve the ventricular ejection fraction from 40% (no patch) to 43% (patch). This study demonstrates the feasibility of homogenization techniques to represent complex multiscale structural features in a simplified but meaningful and effective manner.

The macroscopic mechanical characteristics and microscopic evolution mechanism of plastic concrete

Plastic concrete has been extensively used in the underground anti-seepage engineering. Due to its complexity, there are notably discrepant between the uniaxial and triaxial mechanical behavior of plastic concrete, and the mechanism investigation on its mechanical performance remains an ongoing endeavor. In this paper, to understand the mechanical performance mechanism of plastic concrete, uniaxial tests and triaxial tests were employed to evaluate the macroscopic mechanical characteristics of plastic concrete. Moreover, the Scanning electron microscopy(SEM) and X-Ray diffraction(XRD) were utilized to probe the microstructure and composition of plastic concrete. The result of macroscopic tests showed that plastic concrete acts like strain-hardening materials and presents typical shear failure with obvious banded shear surface in higher confining pressure. The higher cement dosage and the lower bentonite content or w/c ratio increased the strength and peak strain. The E/f28 increased firstly followed by decreased with the increment of cement dosage and w/c ratio, while it increased with the addition of bentonite. As increasing the confining pressure, the strength and volume shrink deformation were enhanced while the modulus increased then decreased followed by increasing. The result of micro-test showed that the porosity of microstructure increased with the addition of bentonite and the voids of ITZ were packed up with the cementitious productions. It is suggested that the evolution of mechanical properties and microstructural features of plastic concrete are mainly driven by the synergistic effect of plasticization and solidification. The plasticization effect increased the microstructure porosity and weakened the mechanical properties of plastic concrete, while the solidification effect enhanced the bonding performance of particles in ITZ region and improved the shear strength of plastic concrete.

Study on the mechanical properties and microstructure of a rich-watered grouting material

The effective method of mine gas control and efficient development is gas extraction technology. The sealing effect of grouting material on borehole directly affects the efficiency of gas extraction. The new type of rich-watered sealing material with suitable mechanical strength and significant plastic characteristics was developed based on the addition of accelererant, alkali activator, expansion agent and reinforcing agent to Portland cement for mining. The effect of reinforcing agent on the mechanical properties of materials under different w/c ratios was tested by RMT. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and other test methods, the microstructure evolution of grouting materials and its influence mechanism on macroscopic mechanics were revealed. The results show that the crystal structures of hydration products AFt, Ca(OH)2 and C-A-H regulate the development of mechanical strength of materials. The uniaxial compressive strength of rich-watered grouting materials can reach 3.5–5.6 MPa and the residual strength is greater than 3 MPa in the range of rich-watered ratio of 0.9–1.3. The new rich-watered grouting material developed has significant plastic deformation characteristics under high rich-watered ratio conditions, which can greatly adapt to borehole deformation and reduce the gap width of slurry-coal interface, and can meet the technical requirements of long-term sealing of gas extraction boreholes.