Variations in the implant thread shape and occlusal load behavior may result in significant changes in the biological and mechanical properties of dental implants and surrounding bone tissue. Most ...previous studies consider a single implant thread design, an isotropic bone structure, and a static occlusal load. However, the effects of different thread designs, bone material properties, and loading conditions are important concerns in clinical practice. Accordingly, the present study performs Finite Element Analysis (FEA) simulations to investigate the static, quasi-static and dynamic response of the implant and implanted bone material under various thread designs and occlusal loading directions (buccal-lingual, mesiodistal and apical). The simulations focus specifically on the von Mises stress, displacement, shear stress, compressive stress, and tensile stress within the implant and the surrounding bone. The results show that the thread design and occlusal loading rate have a significant effect on the stress distribution and deformation of the implant and bone structure during clinical applications. Overall, the results provide a useful insight into the design of enhanced dental implants for an improved load transfer efficiency and success rate.
Intervertebral disc degeneration (IDD) is closely related to changes in the intervertebral disc (IVD) composition and the resulting viscoelastic properties. IDD is a severe condition because it ...decreases the disc's ability to resist mechanical loads. Our research aims to understand IDD at the cellular level, specifically the changes in the viscoelastic properties of the nucleus pulposus (NP), which are poorly understood. This study employed a system integrating nanoindentation with Raman spectrometry to correlate biomechanics with subtle changes in the biochemical makeup of the NP. The characterization was, in turn, correlated with the degenerative severity of IVD as assessed using magnetic resonance imaging (MRI) of different patients with spinal stenosis, degenerative spondylolisthesis, and degenerative scoliosis. It is shown that there is an increase in the crosslinking ratio in collagen, a reduction in proteoglycan, and a build‐up of minerals upon the rise in the severity level of the disc damage in the NP. Assessment of mechanical characteristics reveals that the increasing disc degeneration makes the NP lose its elasticity, becoming more viscous. This shows that the tissue undergoes abnormalities in weight‐bearing ability, which contributes to spinal instability. The correlation of the individual discs shows that grades III and IV have similarities in the changes of Amide I and III toward the storage modulus. In contrast, grades IV and V correlate with mineralization toward the storage modulus. Reduction of proteoglycan has the highest impact on the changes of the storage modulus in all grades of IDD. Connecting compositional alterations to IVD micromechanics at various degrees of degeneration expands our understanding of tissue behavior and provides critical insight into clinical diagnostics, treatment, and tissue engineering.
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•Comparison of oxidation behavior of IN718 made by SLM and conventional method.•Revealing previously unobtained information about early stages of IN718 oxidation.•Systematic in-situ ...study of microstructure and chemical evolution with temperature.•Finding three stages in oxidation process from in-situ analysis.•Proposing a sequence for the formation of probable oxides at different temperatures.
This work reveals the initial stages of Inconel 718 (IN718) oxidation manufactured by selective laser melting (SLM). In-situ and ex-situ investigations were conducted on SLM-IN718 and a commercially obtained Inconel 718 sample (Comm-IN718) to compare their oxidation behavior. In-situ and ex-situ testing was performed using a unique synchronized system integrating precise thermal control with Raman spectroscopy, optical microscopy and scanning probe techniques. X-Ray diffractometry (XRD) and Scanning Electron Microscopy (SEM) were used for microstructure analyses before and after heating. Raman spectroscopy indicated that, in both samples, there is a threshold temperature for oxidation at around 300 °C. The highest rate of oxidation was observed up to 550 °C as different oxides form. After 550 °C, there was no noticeable formation of new compounds up to 650 °C. Extended heating at 650 °C resulted in further changes in the Comm-IN718 sample, however the SLM-IN718 sample was unchanged by longer heating times. XRD of cooled samples did not detect any oxides because of the structurally disordered nature of the oxides. After being cooled, Comm-IN718 showed undesirable oxides like iron oxides in an inhomogeneous crystalline oxide layer. For SLM-IN718 the continuous unbroken oxide layer on the cooled SLM-IN718 sample imparted more effective protection of the alloy.
The present paper concerns the application of the upper bound theorem based on the work function to analyze metal forming processes. An advantage of this theorem formulation is that it provides a ...unified method for finding solutions for any yield criterion. In particular, any available kinematically admissible velocity field used in conjunction with the von Mises yield criterion can be utilized with no modification. On the other hand, an explicit function representing the work function associated with a given yield criterion cannot readily be expressed except for some particular cases. The approach proposed in the present paper is to assume a work function instead of a yield criterion. The paper is restricted to the work functions represented by first-order homogeneous functions. Moreover, the material is supposed to be isotropic and incompressible. The strength differential effect is neglected. Illustrative examples reveal the effect of the yield criterion on the limit load for axisymmetric extrusion and ring compression processes. These solutions utilize kinematically admissible velocity fields available in the literature.
This paper presents a semi-analytic solution for the continued quasi-static compression of a thin rigid/plastic layer between two rigid, parallel rough plates. The constitutive equations of isotropic ...material postulate that the shear yield stress depends on the equivalent strain rate, the equivalent strain, and other internal variables. No restriction is imposed on this dependence. The general solution is valid for any finite number of internal variables. This solution reduces to several simple differential equations and one transcendental equation in Lagrangian coordinates. The solution is based on the standard assumptions in formulating the boundary value problem for simpler material models. More straightforward particular cases of the constitutive equations that are important for applications are considered separately. The solution reduces to a single differential equation in the most straightforward cases. A transcendental equation should be solved to find the initial condition of this differential equation. The friction factor’s effect on the solution’s qualitative behavior is discussed in detail. A numerical example illustrates the solution for an uncoupled material model. An applied aspect of this research is that its results can be used to analyze the plane-strain compression of thin metal strips, an essential metal-forming process.
A semi-analytical solution for an elastic/plastic sphere subject to thermo-mechanical loading is given. Material properties are temperature dependent. The solution is valid for any isotropic ...pressure-independent yield criterion. Even though the general solution in both elastic and plastic regions is rather simple, the solution of the boundary value is cumbersome. The solution is facilitated by using the dimensionless temperature as an independent variable instead of the radial coordinate. A detailed analysis of the solution of the boundary value problem is provided assuming that the pressure and temperature at the inner radius slowly increase whereas the pressure and temperature at the outer radius are kept constant. In particular, qualitative features of the solution are emphasized. Some of these features are useful for the design of spherical vessels subject to thermos-mechanical loading.
Doping enhances diamond like carbon (DLC) coatings for extreme high-temperature applications. However, understanding the enhancement mechanism is elusive. This study employs a novel system ...integrating Raman spectroscopy and depth-sensing indentation with a heating chamber to monitor chemical structural, and mechanical properties of doped and un-doped hydrogenated DLC films, with temperature. This in-situ investigation represents extreme working conditions, revealing how doping enhances DLC films thermal stability. It is shown that the thermal stability of the a-C:H:Si films could be maximized by increasing the Si content. The film with the highest Si content was stable until 650 ̊C while the films with lower Si or No–Si content graphitized at lower temperatures. This study presents hardness measurement under high-temperature conditions that were not available before. In-situ observations reveal how Si doping correlates with stability of mechanical properties at elevated temperatures. The correlation of the mechanical properties with WG reveals that the mechanism of thermal stability is that Si doping makes the film resistant to graphitization by promoting sp3 hybridization. Furthermore, our in-situ approach makes it possible to conduct characterization that emulates real service conditions, and therefore, our results show great potential of the industrial application of DLC coatings in extreme thermal conditions.
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•In-situ thermal stability analysis of the a-C:H:Si films with temperature rise.•Thermal stability of a-C:H:Si films is greatly enhanced by increasing Si content.•The film with the highest Si content was stable until at least 650 ̊C.•The films with lower Si or no Si content graphitized at much lower temperatures.•Hardness of the films is measured under high-temperature conditions.
The accuracy of the defect assessment methods strongly depends on the accuracy of limit load solutions. Usually, many parameters classify welded structures. Therefore, parametric analysis of such ...structures may be time-consuming. The upper bound theorem supplies an efficient method for reducing lengthy calculations. The mathematical features of this theorem allow for accurate estimations of the limit load to be found using rather simple kinematically admissible velocity fields. In the case of highly undermatched welded joints, the known singular velocity behavior near the bi-material interface can be taken into account to choose a kinematically admissible velocity field satisfying some features of the real velocity field. The present article provides such a solution for V-bevel butt welds containing a crack of quite an arbitrary shape. The welded joint is subject to tension. The solution consists of two steps. The first step determines the limit load of the specimen with no crack. This step requires the numerical minimization of a function of one variable. The second step accounts for the crack, assuming that the solution for the uncracked specimen is known. This step is purely analytical. The accuracy of the solution is confirmed by comparison with a solution for a particular geometry of the weld found using Riemann's method. The effect of the weld geometry on the limit load is revealed.
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•Determine complex hierarchy of oxide structures in the oxidation of IN718 at 650 °C.•Provide valuable insights into the formation of passivation layers.•Reveal complex 3D passivating ...layers forming on the alloy.•Passivation layer being composed of a Cr2O3 sublayer and a NiFexCr(2−x)O4 layer.•Estimation of x in NiFexCr(2−x)O4 for different heating times by the Raman maps.
This research presents a detailed structure and time evolution for forming the passivation layer during oxidation of Selective Laser Melted (SLM-IN718) and commercially cast (Comm-IN718) Inconel 718 at 650 °C. It reveals that this layer has a complex 3D structure, with a top layer of Fe-Ni Chromite spinels (NiFexCr(2−x)O4) and a sublayer of Cr2O3. Raman maps and statistical analysis estimate x in NiFexCr(2−x)O4 for different heating times. The heating process initially forms iron-rich NiFexCr(2−x)O4 with x≈2, decreasing to ≈1 after 72 h of heating for both Comm- and SLM-IN718. Interestingly, a slightly different result was observed for the heat-treated SLM sample (HTSLM-IN718), where x increased again to 1.2 and 1.4 after 72 h. Secondary Ion Mass Spectrometry (SIMS) results reveal the depth hierarchy of the passivation layer profile, with the chromite layer covering a thicker Cr2O3 layer forming above the niobium-rich intermetallic layer above the alloy. Passivation layers are critical to the endurance of superalloys during extreme thermal cycling conditions. Therefore, by precisely determining the complex stoichiometry and hierarchy of the layer, this study can guide the development of durable superalloys with improved resistance to extreme thermal cycling conditions.
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