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The aim of this study was to explore the value of computed tomography (CT) images based on electronic health (E-health) combined with painless gastrointestinal endoscopy (PGE) in the diagnosis of neurocognitive function in patients with combined anesthesia of propofol and butorphanol tartrate. 126 patients undergoing PGE were selected as the research objects, and all were performed with CT perfusion imaging before and after anesthesia to obtain the cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and time to peak (TTP). The Montreal Cognitive Assessment (MoCA) was adopted to evaluate the cognitive function of patients. The results showed that after anesthesia, the levels of CBF and CBV in the left and right thalami, frontal lobe, and temporal lobe of the patients were lower than those before anesthesia, while TTP and MTT were higher than those before anesthesia ( P < 0.05 ). The MoCA score after anesthesia was lower than that before anesthesia ( P < 0.05 ). After anesthesia, the CBF, CBV, TTP, and MTT values of the left and right frontal lobes and left and right temporal lobes were significantly positively correlated with MoCA ( P < 0.05 ). In conclusion, the brain CT image parameters based on E-health can clearly display the blood perfusion in the lesion area of the patient, which was beneficial to the PGE-assisted judgment of cognitive dysfunction in patients with propofol tartrate and butorphanol tartrate anesthesia. Therefore, CT-assisted PGE examination based on E-health had a certain clinical value in evaluating the neurocognitive function of patients.

The size effect and viscosity effect are both noticeable at the micro-/nano-scale. In the present work, the strain gradient viscoelastic solution of mode-III crack in an infinite quasi-brittle advanced material is proposed based on the strain gradient viscoelasticity theory by using Wiener-Hopf method. The solutions of the gradient-dependent viscoelastic crack problem are obtained directly by using the correspondence principle between the strain gradient viscoelasticity and strain gradient elasticity in Maxwell standard linear solid model. In this model, the stress near the crack tip is time-dependent and size-dependent. Besides, the stress near the crack tip is larger than that which is in gradient elasticity theory. The location and the value of maximum stress change with time,which differs from the case in strain gradient elasticity theory.The time that normalized stress take to stabilize also changes with the changing of with distances from the crack tip. When viscoelasticity is neglected or time tends to infinity, the strain gradient viscoelasticity theory can be reduced to the classical strain gradient elasticity theory.

The emerging skin-integrated devices have been embedded with various functions, whose ideal implementation typically relies on intact bonding to curved substrates. However, the predeformation, which originates from the attachment of a thin film to a curved substrate, attempts to peel the film (i.e., self-debonding). It calls for strong enough interfacial adhesion in applications. On the other hand, too strong adhesion can destroy the surfaces of devices and substrates when the devices are peeled off after service. Therefore, seeking critical conditions becomes essential. Herein, we study the self-debonding of an adhesive thin film on a convex cylindrical surface. Taking Dugdale’s constant-stress law to describe the interfacial traction–separation relationship, we analytically unveil that the self-debonding behaviors are not solely determined by the interfacial energy. Instead, both the interfacial strength and critical interfacial separation are decisive. We thus obtain a phase diagram consisting of two critical conditions correspondingly. Similar results appear in the finite element analysis with the trapezoidal cohesive law, quantitatively showing the evolution of deflection and interfacial detachment force. Furthermore, we find that the circular film, symmetrically adhering to a spherical surface with small deflection, can still share similar self-debonding behavior. Our results provide guidance on how to stick a thin film on a convex cylindrical or spherical surface well with proper interfacial adhesion.

BACKGROUND: Inappropriate macrophages phenotype transition contributes to the development of ulcerative colitis, and the poly (ethylene glycol)-block-poly (d, l-lactic acid) (PEG-PLA) nanoparticles delivery system can be utilized to improve the cryptotanshinone (CTS)-based therapy. METHODS: We used a single emulsification method to prepare CTS-encapsulated nanoparticles (NP(CTS)). The therapeutic efficacy of NP(CTS) was evaluated in dextran sulfate sodium (DSS)-induced colitis mice. Then the proportion of total macrophages and M2-like macrophages were assayed with flow cytometry, and the relative content of pro-inflammatory cytokines in the colon was detected with Western blot. Bone-marrow-derived macrophages (BMDMs) were induced into M1-like macrophages, which were further incubated with NP(CTS) to repolarize into M2 subtype(.) RESULTS: Cryptotanshinone could induce the transition of M1 subtype to M2 subtype as indicated by up-regulated expression of arginase 1 (ARG1), interleukin (IL)-10, and CD206. In vivo, orally administrated NP(CTS) accumulated in the colon-infiltrated macrophages in colitis mice. It further revealed that NP(CTS) significantly alleviated colitis symptoms as indicated by increased body weight and colon length, decreased tumor necrosis factor (TNF)-α, IL-1β, and IL-6 content in the colon, and diminished total macrophage proportion (CD45(+)CD11b(+)F4/80(+)) and up-regulated M2 proportion (CD45(+)CD11b(+)F4/80(+)CD206(hi)). CONCLUSION: Oral administration of NP(CTS) could ameliorate ulcerative colitis with the conversion of M1-like macrophages to M2-like macrophages.

High-density aluminum foam can provide higher stiffness and absorb more energy during the impact Obtaining the constitutive law of such foam requires tri-axial tests with very high pressure, where difficulty may arise because the hydrostatic pressure can reach more than 30 MPa. In this paper, instead of using tri-axial tests, we proposed three easier tests—tension, compression and shear to obtain the parameters of constitutive model (the Deshpande–Fleck model). To verify the constitutive model both statically and dynamically, we carried out additional triaxial tests and direct impact tests, respectively. Based on the derived model, we performed finite element simulation to study the impact response of the present foam. By dimensional analysis, we proposed an empirical equation for a non-dimensional impact time $${\bar{t}}_{\mathrm {d}}$$ , the impact time divided by the time required for plastic wave travelling from the impact surface to the bottom surface, to determine the deformation characteristic of the aluminum foam after impact. For the case with $${\bar{t}}_{\mathrm {d}}\le 1$$ , the deformation tends to exhibit a shock-type characteristic, while for the case with $${\bar{t}}_{\mathrm {d}}>5$$ , the deformation tends to exhibit an upsetting-type characteristic.

How an individual constituent zone behaves during the deformation of a heterostructured metallic material is a fundamental issue for understanding heterostructure deformation, but it remains a challenge to experimentally observe it. Here we report a study on the stress-strain behavior of the nanostructured gradient layer (NGL) in an integrated gradient specimen that consists of a coarse-grained (CG) central layer sandwiched between two NGLs. Constraint from the CG central layer led to the formation of dense and dispersed stable strain bands (SBs) in the NGL, which regained dislocation hardening after initial recovery and grain coarsening. Consequently, the NGL exhibited a transient plateau of flow stress after yielding, and then regained extra strain hardening to achieve excellent uniform elongation. These unique behaviors are dramatically different from those of a freestanding NGL, indicating a fundamentally different deformation principle that is intrinsic to heterostructures, i.e., inter-zone constraint modifies the constitutive behavior of constituent zones.

A lot of research has shown that the strength of nanoparticle composites increases first and then decreases with the decrease of particle size when particle size is at nanoscale, which is the so-called positive-inverse Hall–Petch effects, or called the strengthening-softening characteristic. In this paper, the strengthening-softening behavior of cylindrical nanoparticle composites with periodic distribution of particles is studied. By selecting the representative single cylindrical cell model, the mechanic’s solution is obtained strictly by using the strain gradient viscoelastic theory established previously by the present authors. The results clearly show the strengthening-softening behavior of the nanoparticle composite. In the process of solution, first, the strain gradient elasticity theory is used to strictly solve the problem of the cylindrical cell under uniform external pressure. Then, using the correspondence principle of the strain gradient viscoelastic theory, the solution for the strain gradient viscoelastic theory is obtained through Laplace inversion transformation, and its dependence on the time-space two-scale parameters is analyzed. The results showed a significant positive-inverse Hall–Petch effects.

Indentation scaling relationships intend to guide indentation experiments and help understand the indentation hardness. In the present study, dimensionless functions were obtained by fitting a seri...

Indentation scaling relationships provide normalized guidance for measuring and predicting mechanical properties in indentation experiments. At the nano-scale, the material size-effect is significant, while conventional scaling relationships fail to depict this phenomenon in nanoindentation precisely. In the present research, cross-scale indentation scaling relationships are investigated using a strain gradient theory. The nanoindentation response is found to be sensitive to different material parameters, including the material intrinsic length, yield stress, and work-hardening exponent across size-scales. If the strain gradient effect is ignored, the nanoindentation scaling relationships approach the macroscopic conventional ones. The cross-scale indentation scaling relationships obtained in the form of dimensionless functions in this work provide quantitative references to instrumented indentation tests on multiple size-scales, coinciding well with experimental results. The understanding of nanoindentation hardness is enhanced by the present work.

Gradient structure (GS) possesses a typical trans-scale grain hierarchy with varying internal plastic stability, and the mutual plastic accommodation plays a crucial role in its superior strength-ductility combination. Using the in-situ synchrotron X-ray diffraction (XRD) during tensile loading, we measured lattice strains sequentially from the nanostructured (NS) surface layer to the central coarsegrained (CG) layer to elucidate when and how plastic accommodation occurs and evolves within the GS, along with their roles in plastic deformation and strain hardening. Throughout the tensile deformation, two types of plastic incompatibility occur in the GS. One is an extended elastoplastic transition due to layer-by-layer yielding. The other is strain localization and softening in the NS layer, in contrast with the stable plastic deformation in the CG layer. Plastic accommodation thus occurs concurrently and manifests as both an inter-layer and intra-layer change of stress state throughout tensile deformation. This produces different micromechanical responses between layers. Specifically, the NS layer initially experiences strain hardening followed by an elastoplastic deformation. The hetero-deformation induced hardening, along with forest hardening, facilitates a sustainable tensile strain in the NS layer, comparable to that in the CG layer.

In this paper, a strain gradient viscoelastic theory is proposed strictly, which can be used to describe the cross-scale mechanical behavior of the quasi-brittle advanced materials. We also expect the theory to be applied to the description for the cross-scale mechanical behavior of advanced alloy metals in linear elastic deformation cases. In the micro-/nano-scale, the mechanical properties of advanced materials often show the competitive characteristics of strengthening and softening, such as: the strength and hardness of the thermal barrier coatings with nanoparticles and the nanostructured biological materials (shells), as well as the strength of nanocrystalline alloy metals which show the characteristics of positive-inverse Hall-Petch relationship, etc. In order to characterize these properties, a strain gradient viscoelastic theory is established by strictly deriving the correspondence principle. Through theoretical derivation, the equilibrium equations and complete boundary conditions based on stress and displacement are determined, and the correspondence principle of strain gradient viscoelasticity theory in Laplace phase space is obtained. With the help of the high-order viscoelastic model, the specific form of viscoelastic parameters is presented, and the time curve of material characteristic scale parameters in viscoelastic deformation is obtained. When viscoelasticity is neglected, the strain gradient viscoelasticity theory can be simplified to the classical strain gradient elasticity theory. When the strain gradient effect is neglected, it can be simplified to the classical viscoelastic theory. As an application example of strain gradient viscoelastic theory, the solution to the problem of cross-scale viscoelastic bending of the Bernoulli-Euler beam, is analyzed and presented.

We study the bending stiffness of symmetrically bent circular multilayer van der Waals (vdW) material sheets, which correspond to the nonisometric configuration in bulge tests. Frenkel sinusoidal function is employed to describe the periodic interlayer tractions due to the lattice structure nature and the bending stiffness of sheets is theoretically extracted via an energetic consideration. Our quantitative prediction shows good agreement with recent experimental results, where the bending stiffness of different types of sheets with the comparable thickness could follow a trend opposite to their Young’s moduli. On the basis of our model, we propose that this trend may experience a transition as the thickness decreases. Apart from the apparent effects of Young’s modulus and interlayer shear strength, the interlayer distance is also found to have an important impact on the bending stiffness. In addition, according to our analysis on the size effect, the bending stiffness of such symmetrically bent circular sheets can steadily own a relatively large value, in contrast to the cases of isometric deformations.

Widely used to quantify material wear, the Archard wear law was derived from the asperity flattening model. However, the flattening model is so idealized that it cannot properly represent the real situation with general interlocked asperities, where asperity plowing dominates the wear instead of shearing flattened asperity. Using molecular dynamics simulations, we discussed if Archard law can hold during plowing wear of interlocked interface. Our results indicated Archard law breaks down when fracture dominates the wear. Furthermore, increasing interfacial adhesion or decreasing material ductility changes the dominant wear factor from plasticity to fracture. Finally, we proposed a criterion to determine when Archard wear law will break down and discussed the proposed criterion for real materials.

The stiff film/compliant substrate composite structure with a high modulus ratio finds a wide range of applications in production and in scientific research, and its indentation behavior cannot be described by the traditional theory when the film thickness is reduced from the millimeter scale to the micrometer or nanometer scale. In order to better understand the trans-scale indentation response of the composite structure caused by the reduction in the film thickness, this problem is solved analytically with the strain gradient theory and integral transformation. The gradient effect on the indentation response of the system is assessed in detailed from three aspects: load-displacement relationship, surface topography and distribution of bending moment on the film. In addition, the influences of film thickness, modulus ratio of the film to the substrate, contact radius and Poisson's ratio on the gradient effect are investigated. It is found that the gradient effect on the indentation response of the system, which is not sensitive to the contact radius and Poisson's ratio, is related not only to the film thickness but also to the modulus ratio of the film to the substrate. Based on the above analysis, a dimensionless number (g/l) is proposed to evaluate the gradient effect on the indentation behaviors of the system. And with the help of the dimensionless number, a new simple and accurate method for measuring the material length scale is proposed. Our research provides a theoretical basis for an in-depth understanding of the gradient effects on the indentation response of the stiff film/compliant substrate system and for the measurement of the material length scale.

Based on the assumption of constant-stress (Dugdale) interface bonding, a theoretical model is established in order to characterize the entire peeling response of an elastic film from a rigid substrate. The relationship between the peeling force and the peeling displacement and the relationship between the cohesive zone length and the peeling displacement at different peeling stages are analyzed. Closed-form solutions of the maximum peeling force and the maximum length of cohesive zone are further derived theoretically. It is found that both the maximum peeling force and the maximum length of cohesive zone depend on the interface strength, interface toughness and bending stiffness of the film. Combined with the classical Kendall's model, the cohesive zone length in the steady-state peeling stage is further given. A new method to simultaneously determine the interface strength and interface toughness is proposed, as long as the maximum peeling force, steady-state peeling force and film's bending stiffness are obtained from peeling tests. The results of this paper should be very helpful for interface performance prediction and interface design of film/substrate systems.

The coating thickness-dependent damage and fracture of ceramic coating systems were investigated systematically by using circle plate bending tests based on a scanning electron microscope. Through experimental observations and measurements, results demonstrated that the damage of coating layer appeared because of effects of both radial and circumferential moments for thin coating cases, and because of main circumferential moment effect for thick ones. A circle plate bending damage model for the coating layer was presented to describe coating layer damage evolution and fracture. Via the model, one can effectively predict the failure phenomena of coating layer under the circle plate bending, which were consistent with experimental observations. In addition, modeling results of the relationships between critical external loads and damage zone sizes for coating layer were also consistent with experimental measurements. The damage was found to have a catastrophic characteristic near the failure point based on the mathematic damage model.

Nanomechanical properties of polymer samples were calculated using an adhesive contact model appropriate for AFM indentation problems. A series of Polydimethylsiloxane (PDMS) samples were indented ...

In this paper, we present a new model for the elasto-plastic conformal contact between cylinders. By using finite element simulation, it is observed that the transition of elasto-plastic contact in conformal case is different from the transition in Hertz contact. The plastic contact of conformal case can be physically represented by the plastic-Winkler model. The new model provides an explicit solution for the normal force–displacement relation of elasto-plastic conformal contact. Compared to other elastic contact models of conformal contact, the advantages of our model are: (1) it can be used for high load contact and (2) plasticity is taken into account by using the plastic-Winkler model. Our model, therefore, is capable of dealing with realistic engineering problem with high load and plasticity.

Controlled fracture presents opportunities for the advanced fabrication of thin films. However, programmability analogous to that of Chinese paper cutting is still challenging, where fracture patterns can be created as required without preformed cracks for guidance. Here, we establish a design framework for tearing adhesive thin films from foldable substrates with such programmability. Our analytical model captures the observed crack behavior, demonstrating that the deflection of crack paths can exceed 90^{∘}. Besides, for thick foldable substrates with multiple ridges, we additionally propose a robust method of directional fracture where the cracks are forced to extend along the ridges.

Cohesive zone models have been widely used to model interface crack initiation and propagation both in single-material media and bi-material systems. For single-material media with cohesive elements inserted into interface among segments, in order to ensure that the introduction of interface cohesive zone models does not affect the mechanical properties of single-material media before the softening stage of cohesive zone models, a selection criterion of stiffness of cohesive elements is proposed theoretically firstly based on the properties’ equivalence. Taking the softening stage into account, the mechanical responses of the overall stress-strain relationship of single-material media, for the cases of stable increase of strain and snap-back instability of strain, are both obtained, and the related energy mechanism are investigated. For bi-material systems with cohesive elements at interface between two materials, the thickness-dependent failure characteristics of systems in uniaxial tension are found, which is attributed to the difference of the releasing rate of elastic strain energy in the materials with different thicknesses. Furthermore, as a more complex application of cohesive elements, based on the selection criterion proposed, failure behaviors of the ceramic coating/substrate systems under three-point bending are modeled by finite element method and inserting cohesive elements into the coating segments and the coating/substrate interface simultaneously. The simulation results indicate the transition of dominated failure mode from coating cracking to interface delamination with increasing coating thickness, and show faster damage of thick coating systems, agreeing with experimental results. The effects of interface strength and toughness of cohesive elements on failure are also revealed. These results can provide guidance for the application of cohesive elements, and help us better understand the overall failure behaviors of interface systems.

Indentation hardness is found to be related to indentation depth when indentation test is applied on homogeneous materials under small indentation depth, which shows strong size effect in the indentation. While in contrast, indentation hardness has a very limited relationship with indentation depth when it is large, showing distinct scaling relationships between hardness and material properties. Previous studies on scaling relationships under deep indentation condition of elastic-perfectly plastic homogeneous materials have been carried out systematically by finite element analysis. In this paper, a heterogeneous material, particle-reinforced matrix composite is detailed studied to investigate its scaling relationships under deep indentation with different particle positions and material properties by finite element analysis.

Two-dimensional (2D) materials have received extensive attention due to their excellent physical and chemical properties, whose mechanical properties play critical roles in their applications. In this paper, a new convenient method for measuring the modulus of nanofilm by indentation on hard film/soft substrate system is proposed. In order to verify the correctness of the new method, the graphene oxide (GO) nanofilm deposited on polydimethylsiloxane (PDMS) is tested. The modulus of the GO nanofilm is measured as 60.39 ± 7.82 GPa, which is consistent with the modulus measured by previous researches. Finally, the finite element method (FEM) is used to investigate the effectiveness of the new method and to evaluate its error sensitivity to the indenter size, film radius, and the surface roughness. The results show that this method can accurately measure the modulus of nanofilm through the indentation response of the hard film/soft substrate system. Compared with the free-standing indentation test, the method proposed by us eliminates the disadvantages of boundary adhesion and has the advantages of simple sample preparation, easy operation, and high success rate.

Metal-oxide composites with advanced mechanical properties play an important role in many practical applications, and failure of the metal-oxide interface is directly related to service life of related structures. In order to understand interface failure mechanism, study on atomic-scale separation of metal-oxide interface is significant. In this work, shear behaviors of Ag/MgO (0 0 1) coherent interface and semi-coherent interfaces are studied by employing molecular mechanics method, and some interesting size and defect effects are found. The simulation results show that interface shear stress and displacement appear periodic characteristics with loading. For coherent interface, the interface shear stress and displacement both increase first in each period, then the shear stress drops abruptly after reaching ideal shear strength, and the shear displacement jumps by a unit cell length. The shear strength keeps a constant for all periods. Atomistic simulations of interface systems with different thicknesses show size-independent shear strength and intrinsic interface adhesive energy, but needed loading displacement for the first jump of interface displacement is larger for the thicker systems due to the larger energy consumed by bulk materials. For both 1D and 2D semi-coherent interfaces with dislocations, the shear strength is more than one order of magnitude lower than the ideal shear strength, and the interface displacement changes more continuously with decreased period, which is attributed to different shear mechanism related to dislocation gliding. Comparing 2D semi-coherent interface with 1D case, the shear strength and energy barrier of dislocation motion are both higher due to pinning effect of dislocation intersections.

The Green's function and Eshelby tensors of an infinite linear isotropic second gradient continuum are derived for an inclusion of arbitrary shape. Particularly for spherical, cylindrical and ellipsoidal inclusions, Eshelby tensors and their volume averages are obtained in an analytical form. It is found that the Eshelby tensors are not uniform inside the inclusion even for a spherical inclusion, and their variations depend on the two characteristic lengths of second gradient theory. When size of inclusion is large enough compared to the characteristic lengths, the Eshelby tensor of the second gradient medium is reduced to the classical one, as expected. It is also demonstrated that the existing Green's functions and Eshelby tensors of couple stress theory, Aifantis, Kleinert and Wei–Hutchinson special strain gradient theories could be recovered as special cases. This work paves the way for constructing micromechanical method to predict size effect of composite materials, as shown for the effective modulus of particulate composite derived with the proposed theory.

Staggered structure materials, or “brick and mortar” structure materials, are widely observed in natural biomaterials. In this paper, based on strain gradient theory, a trans-scale shear-lag model is developed to characterize the mechanical properties and their size effects for the staggered bio-structure materials. The analytical expressions of the overall effective modulus, interfacial strengths and deformations of the staggered bio-structure material have been obtained. The results illustrate that the overall effective modulus, interfacial strengths and interfacial deformations have the strong size effects. These effects can be described by a combination parameter, i.e. thickness of organic material layer over the material length scale parameter of strain gradient theory. The overall effective modulus and interfacial strength increase with the decrease of the combination parameter. However, the interfacial deformation considerably decreases with the decrease of the combination parameter value. When the combination parameter value is taken as very large, corresponding to the case of large organic matrix thickness, the results return to the classical ones. The predicted effective moduli of nacre are also compared with experimental results and are in good agreement with experimental results.

A macroscopically nominal flat surface is rough at the nanoscale level and consists of nanoasperities. Therefore, the frictional properties of the macroscale-level rough surface are determined by the mechanical behaviors of nanoasperity contact pairs under shear. In this work, we first used molecular dynamics simulations to study the non-adhesive shear between single contact pairs. Subsequently, to estimate the friction coefficient of rough surfaces, we implemented the frictional behavior of a single contact pair into a Greenwood-Williamson-type statistical model. By employing the present multiscale approach, we used the size, rate, and orientation effects, which originated from nanoscale dislocation plasticity, to determine the dependence of the macroscale friction coefficient on system parameters, such as the surface roughness and separation, loading velocity, and direction. Our model predicts an unconventional dependence of the friction coefficient on the normal contact load, which has been observed in nanoscale frictional tests. Therefore, this model represents one step toward understanding some of the relevant macroscopic phenomena of surface friction at the nanoscale level., 29 pages, 16 figures