Numerical analysis of WaveOne Gold and 2Shape endodontic files during root canal treatment

This study aims to develop and analyse a finite element model of the endodontic nickel-titanium (NiTi) instrument during the root canal treatment (RCT). The 3D model of the tooth and the endodontic instrument has been created using computer-aided design software. The nonlinear explicit dynamic analysis in the CAE package (ANSYS) has been used to analyse the mechanical behaviour of endodontic instruments such as total deformation, equivalent elastic strain, and equivalent stress during canal preparation. The mechanical behaviour of three commercially available endodontic NiTi alloy instruments such as WaveOne Gold (WOG), 2Shape 1 (TS1) and 2Shape 2 (TS2) endodontic files was evaluated using FEA. Consequently, the effect of deformation, equivalent stress and equivalent elastic strain on endodontic files during cleaning and shaping are investigated and compared. The results show that the total deformation and equivalent elastic strain are maximum in the TS1 endodontic file in comparison to TS2 and WOG files. Graphical abstract [Formula: see text]

Strain and interface energy of ellipsoidal inclusions subjected to volumetric eigenstrains: shape factors

Thermodynamic modeling of the development of non-spherical inclusions as precipitates in alloys is an important topic in computational materials science. The precipitates may have markedly different properties compared to the matrix. Both the elastic contrast and the misfit eigenstrain may yield a remarkable generation of elastic strain energy which immediately influences the kinetics of the developing precipitates. The relevant thermodynamic framework has been mostly based on spherical precipitates. However, the shapes of actual particles are often not spherical. The energetics of such precipitates can be met by adapting the spherical energy terms with shape factors. The well-established Eshelby framework is used to evaluate the elastic strain energy of inclusions with ellipsoidal shapes (described by the axes a, b, and c) that are subjected to a volumetric transformation strain. The outcome of the study is two shape factors, one for the elastic strain energy and the other for the interface energy. Both quantities are provided in the form of easy-to-use diagrams. Furthermore, threshold elastic contrasts yielding strain energy shape factors with the value 1.0 for any ellipsoidal shape are studied.

Effect of Fibre Reinforcement on Creep in Early Age Concrete

This research analyses the strain behaviour of fibre-reinforced concrete (FRC) in the event of a creep episode. The analysis of creep experienced by FRC specimens during the test reflects better performance than that predicted by the EHE-08 standard. The authors propose a formulation for the evaluation of creep strain undergone by FRC. During the research, the evolution of the modulus of elasticity of FRC after a creep episode is analysed. After the test campaign, it can be concluded that FRC loaded at an earlier age stiffens after a creep episode. After the creep test is completed, the delayed elastic strain undergone by FRC is analysed and it is observed that FRC loaded at an earlier age undergoes less deformation. The authors propose a formulation for the evaluation of the delayed elastic strain undergone by FRC after a creep episode.

Evolution of bone tissue based on angiogenesis as a crucial factor: New mathematical attempt

In this paper, we present a novel theoretical model of bone evolution. The model takes into account growth of the blood vessels network as a real issue during the process. The stimulation of this growth is controlled by the signals from overloaded dying cells. A system of integro-differential equations describes changes in the density of blood vessels, bone cells and Young modulus, all of which define how the bone tissue evolves over time. The model considers several biomechanical signals such as changes in the density of elastic strain energy and nutrients. Two examples of changing bone tissue were examined to test the model: bone healing around a tooth implant and formation of osteophytes during osteoarthritis. In both cases, the effects of mechanical loading in the bone tissue evolution which are in agreement with the medical observations can be observed.

Mechanism of Hydraulic Fracturing Cutting Hard Basic Roof to Prevent Rockburst

Rockburst is globally regarded as one of the most severe and complicated mining dynamic disasters to predict or control. Generally, the occurrence mechanism of rockbursts can be considered as a process of the elastic strain energy accumulation, emancipation, transmission, and occurrence. Tracing to the source, the reasons for large accumulation of elastic strain energy in coal and rock mass are the high stress of the roof layer that loads on the coal and rock masses around the mining space coupling effect with the natural horizontal tectonic stress. In this study, using the minimum energy theory and elasticity theory, the analytical formula for calculating elastic strain energy of the roof cantilever beam structure acting on the coal body load in front of the working face is deduced. Accordingly, we achieved a method of using hydraulic fracturing to improve the roof structure. In detail, we use a high-pressure jet to cut the cantilever roof structure, which can make a prelocated fracture surface, and then utilize the packers to make sure that the injected high-pressure fracturing fluid is propagating along the prelocated fracture surface and can cut off the cantilever roof structure eventually to prevent rockbursts in advance. Due to the rockburst occurrence mechanism and the quantitatively elastic strain energy analytical formula, a preconditioning water jet cutting induced fracture surface to create orientation-controllable hydraulic fracture strategy is proposed to guard against the high hazard caused by the massive elastic strain energy, which accumulated in the coal body in front of the working face and coal pillar.

Nonlinear Elasto-Visco-Plastic Creep Behavior and New Creep Damage Model of Dolomitic Limestone Subjected to Cyclic Incremental Loading and Unloading

For many rock engineering projects, the stress of surrounding rocks is constantly increasing and decreasing during excavating progress and the long-term operation stage. Herein, the triaxial creep behavior of dolomitic limestone subjected to cyclic incremental loading and unloading was probed using an advanced rock mechanics testing system (i.e., MTS815.04). Then, the instantaneous elastic strain, instantaneous plastic strain, visco-elastic strain, and visco-plastic strain components were separated from the total strain curve, and evolutions of these different types of strain with deviatoric stress increment were analyzed. Furthermore, a damage variable considering the proportion of irrecoverable plastic strain to the total strain was introduced, and a new nonlinear multi-element creep model was established by connecting the newly proposed damage viscous body in series with the Hookean substance, St. Venant body, and Kelvin element. The parameters of this new model were analyzed. The findings are listed as follows: (1) When the deviatoric stress is not more than 75% of the compressive strength, only instantaneous deformation, transient creep, and steady-state creep deformation occur, rock deformation is mainly characterized by the instantaneous strain, whereas the irrecoverable instantaneous plastic strain accounts for 38.02–60.27% of the total instantaneous strain; (2) Greater deviatoric stress corresponds to more obvious creep deformation. The visco-elastic strain increases linearly with the increase of deviatoric stress, especially the irrecoverable visco-plastic strain increases exponentially with deviatoric stress increment, and finally leads to accelerated creep and delayed failure of the sample; (3) Based on the experimental data, the proposed nonlinear creep model is verified to describe the full creep stage perfectly, particularly the tertiary creep stage. These results could deepen our understanding of the elasto-visco-plastic deformation behavior of dolomitic limestone and have theoretical and practical significance for the safe excavation and long-term stability of underground rock engineering.

Polarized Raman spectroscopy of GaP nanowires under 5% elastic strain

Optical porperties of highly-strained gallium phosphide nanowires were investigated via polarized Raman spectroscopy. 5% elastic strain was created in individual nanowire lying on nickel substrate by the means of atomic force microscopy. Micro-Raman mapping along the nanowire cross section in parallel and perpendicular polarization was carried out. Strain-induced effects on transverse optical mode position and shape were analyzed. The pronounced splitting of the mode due to high level of strain was observed. It was found that in parallel polarization the mode shape is sensitive to the position of the pumping spot which can be attributed to enhanced light-nanowire coupling effects.

Study on Energy Evolution and Damage Constitutive Model of Siltstone

In order to study the energy evolution characteristics and damage constitutive relationship of siltstone, the conventional triaxial compression tests of siltstone under different confining pressures are performed, and the evolution laws of input energy, elastic strain energy and dissipative energy of siltstone with axial strain and confining pressure are analyzed. According to the test results, the judgment criterion of the rock damage threshold is improved, and an improved three-shear energy yield criterion is proposed., The damage constitutive equation of siltstone is established based on the damage mechanics theory through the principle of minimum energy consumption and by considering the residual strength of rock, and lastly, the rationality of the model is verified by experimental data. The results reveal that (1) both the input energy and dissipative energy gradually increase with the increase of axial strain, and the elastic strain energy first increases and then decreases with the increase of axial strain, and reaches its maximum at the peak. (2) The input energy and dissipation energy increase exponentially with the increase of the confining pressure, and the elastic strain energy increases linearly with the increase of confining pressure. (3) According to the linear relationship between the sum of shear strain energy and hydrostatic pressure, an improved three-shear energy yield criterion is established. (4) The model curve can better describe the strain softening stage and the residual strength characteristics of siltstone. The relative standard deviation between the model results and the test results is only 4.35%, which verifies the rationality and feasibility of the statistical damage constitutive model that is established in this paper.