A plasticity model for sand-structure interfaces

The predictive capacity of numerical analyses in geotechnical engineering depends strongly on the efficiency of constitutive models used for modeling of interfaces behavior.Interfaces are considered as thin layers of the soil adjacent to structures boundary whose major role is transferring loads from structures to soil masses.An interface model within the bounding surface plasticity framework and the critical state soil mechanics is presented.To this aim,general formulation of the interface model according to the bounding surface plasticity theory is described first.Similar to granular soils,it has been shown that the mechanical behavior of sand-structure interfaces is highly affected by the interface state that is the combined influences of density and applied normal stress.Therefore,several ingredients of the model are directly related to the interface state.As a result of this feature,the model is enabled to distinguish interfaces in dense state from those in loose state and to provide realistic predictions over wide ranges of density and normal stress values.In evaluation of the model,a reasonable correspondence between the model predictions and the experimental data of various research teams is found.

Improved shape hardening function for bounding surface model for cohesive soils

A shape hardening function is developed that improves the predictive capabilities of the generalized bounding surface model for cohesive soils, especially when applied to overconsolidated specimens. This improvement is realized without any changes to the simple elliptical shape of the bounding surface, and actually reduces the number of parameters associated with the model by one.

Atomistic simulations of the surface severe plastic deformation-induced grain refinement in polycrystalline magnesium:The effect of processing parameters

Magnesium(Mg)based alloys are promising candidates for many applications,but their untreated surfaces usually have low strength and hardness.In this study,a single point diamond turning(SPDT)technique was applied to refine the grain size and improve the mechanical properties of the surface layers of Mg-Li alloys.By refining grains in the topmost layer to the nanometer scale(~60 nm),the surface hardness was found to be enhanced by approximately 60%.The atomic plastic deformation process during the SPDT was then studied by the real-time atomistic molecular dynamics(MD)simulations.A series of MD simulations with different combinations of parameters,including rake angle,cutting speed and cutting depth,were conducted to understand their influences on the microstructural evolution and associated plastic deformation mechanisms on the surface layer of the workpieces.The MD simulation results suggest that using increased rake angle,cutting speed and cutting depth can help to achieve better grain refinement.These simulation results,which provide atomic-level details of the deformation mechanism,can assist the parameter design for the SPDT techniques to achieve the high-performance heterogeneous nanostructured materials.

Microstructure homogeneity regulation of 7050 aluminum forgings by surface cumulative plastic deformation

To regulate the microstructure homogeneity of large aluminum structural forgings for aircraft,the surface cumulative plastic deformation was proposed.The microstructure of 7050 aluminum forgings after the surface cumulative plastic deformation was investigated by electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),and X-ray diffraction(XRD).The results showed that the microstructure evolution of 7050 aluminum forgings was more sensitive to the deformation temperature than the strain rate.The dislocation density continued to increase with the decrease of the deformation temperature and the increase of the strain rate.Dislocation density and stored energy were accumulated by the surface cumulative plastic deformation.Besides,a static recrystallization(SRX)model of 7050 aluminum forgings was established.The SRX volume fraction calculated by this model was in good agreement with the experimental results,which indicated that the model could accurately describe the SRX behavior of 7050 aluminum forgings during the surface cumulative plastic deformation.

On the homogenization of metal matrix composites using strain gradient plasticity

The homogenized response of metal matrix composites（MMC） is studied using strain gradient plasticity.The material model employed is a rate independent formulation of energetic strain gradient plasticity at the micro scale and conventional rate independent plasticity at the macro scale. Free energy inside the micro structure is included due to the elastic strains and plastic strain gradients. A unit cell containing a circular elastic fiber is analyzed under macroscopic simple shear in addition to transverse and longitudinal loading. The analyses are carried out under generalized plane strain condition. Micro-macro homogenization is performed observing the Hill-Mandel energy condition,and overall loading is considered such that the homogenized higher order terms vanish. The results highlight the intrinsic size-effects as well as the effect of fiber volume fraction on the overall response curves, plastic strain distributions and homogenized yield surfaces under different loading conditions. It is concluded that composites with smaller reinforcement size have larger initial yield surfaces and furthermore,they exhibit more kinematic hardening.

Analysis of meso-inhomogeneous deformation on a metal material surface under low-cycle fatigue

A polycrystalline Voronoi aggregation with a free surface is applied as the representative volume element（RVE）of the nickel-based GH4169 superalloy.Considering the plastic deformation mechanism at the grain level and the Bauschinger effect,a crystal plasticity model reflecting the nonlinear kinematic hardening of crystal slipping system is applied.The microscopic inhomogeneous deformation during cyclic loading is calculated through numerical simulation of crystal plasticity.The deformation inhomogeneity on the free surface of the RVE under cyclic loading is described respectively by using the following parameters：standard deviation of the longitudinal strain in macro tensile direction,statistical average of first principal strains,and standard deviation of longitudinal displacement.The relationship between the fatigue cycle number and the evolution of inhomogeneous deformation of the material’s free surface is investigated.This research finds that：（1）The inhomogeneous deformation of the material free surface is significantly higher than that of the RVE inside;（2）the increases of the characterization parameters of inhomogeneous deformation on the free surface with cycles reflect the local maximum deformation of the RVE growing during cyclic loading;（3）these parameters can be used as criteria to assess and predict the low-cycle fatigue life rationally.

Plasticityimprovement of a Zr-based bulk metallic glass by micro-arc oxidation

Mciro-arc oxidation（MAO）was used to coat porous films on the surface of a Zr-based bulk metallic glass sample.The compressive test results indicated that,compared with the as-cast sample,the MAO treated one exhibited higher deformation capacity,associated with multiple shear bands with higher density on the side surface and well-developed vein patterns with smaller size on the fractured surface.The pore in the MAOed film and the matrix/coating interface initiated the shear bands and impeded the rapid propagation of shear bands,thus favoring the enhanced plasticity of the MAO treated sample.The obtained results demonstrated that MAO can be considered as an effective method to finely tune the mechanical performance of monolithic bulk metallic glasses.

Biomaterial types,properties,medical applications,and other factors:a recent review

Biomaterial research has been going on for several years,and many companies are heavily investing in new product development.However,it is a contentious field of science.Biomaterial science is a field that combines materials science and medicine.The replacement or restoration of damaged tissues or organs enhances the patient’s quality of life.The deciding aspect is whether or not the body will accept a biomaterial.A biomaterial used for an implant must possess certain qualities to survive a long time.When a biomaterial is used for an implant,it must have specific properties to be long-lasting.A variety of materials are used in biomedical applications.They are widely used today and can be used individually or in combination.This review will aid researchers in the selection and assessment of biomaterials.Before using a biomaterial,its mechanical and physical properties should be considered.Recent biomaterials have a structure that closely resembles that of tissue.Antiinfective biomaterials and surfaces are being developed using advanced antifouling,bactericidal,and antibiofilm technologies.This review tries to cover critical features of biomaterials needed for tissue engineering,such as bioactivity,self-assembly,structural hierarchy,applications,heart valves,skin repair,bio-design,essential ideas in biomaterials,bioactive biomaterials,bioresorbable biomaterials,biomaterials in medical practice,biomedical function for design,biomaterial properties such as biocompatibility,heat response,non-toxicity,mechanical properties,physical properties,wear,and corrosion,as well as biomaterial properties such surfaces that are antibacterial,nanostructured materials,and biofilm disrupting compounds,are all being investigated.It is technically possible to stop the spread of implant infection.