The influence of various combinations of residual stress, composition and grain interaction gradients in polycrystalline materials with cubic symmetry on energy‐dispersive X‐ray stress analysis is ...theoretically investigated. For the evaluation of the simulated sin2ψ distributions, two different strategies are compared with regard to their suitability for separating the individual gradients. It is shown that the separation of depth gradients of the strain‐free lattice parameter a0(z) from residual stress gradients σ(z) is only possible if the data analysis is carried out in section planes parallel to the surface. The impact of a surface layer z* that is characterized by a direction‐dependent grain interaction model in contrast to the volume of the material is quantified by comparing a ferritic and an austenitic steel, which feature different elastic anisotropy. It is shown to be of minor influence on the resulting residual stress depth profiles if the data evaluation is restricted to reflections hkl with orientation factors Γhkl close to the model‐independent orientation Γ*. Finally, a method is proposed that allows the thickness of the anisotropic surface layer z* to be estimated on the basis of an optimization procedure.
The influence of various combinations of residual stress, composition and grain interaction gradients in polycrystalline materials with cubic symmetry on X‐ray stress analysis by energy‐dispersive diffraction is discussed on the basis of simulations for ferritic and austenitic steel.
The residual stresses at a circular punched end face in tempered martensitic high-strength steel sheets were investigated using triaxial stress analysis via X-ray diffraction. The maximum principal ...stress and its direction were calculated from the measured nine stress components. The relationship between the directions of the maximum principal stress and hydrogen cracks was verified by generating hydrogen cracks on the punched end face in the same specimen using cathodic hydrogen charging. The direction of the cracks was perpendicular to that of the maximum principal stress. This result indicates that hydrogen embrittlement at the sheared end face is caused by the maximum principal stress. Moreover, the distribution of the residual stresses toward the thickness direction and the relationship between residual stresses and tensile strength of the specimens were investigated. The maximum principal stress on the punch side was lower than that on the dice side. Unlike the maximum principal stresses, the normal stresses did not increase monotonically with the tensile strength of the specimens. Therefore, it was concluded that investigating the maximum principal stress at any area between the dice side and a line located midway from the end face and dice side is crucial for considering the hydrogen embrittlement criteria.
•A pressure based OLED Panel debonding analysis method is proposed.•Simulation model for OLED Panel, including mesh strategy, stress distribution, and interlayer stress extraction method, etc.•The ...new debonding risk index varies non-monotonically with thicknesses, bending radii, and Young’s moduli.
This paper presents a mechanical simulation model and analysis method for OLED panels. The functional layers within the panel are bonded using optically clear adhesives (OCAs), which are pressure-sensitive adhesives (PSAs), resulting in a soft interface bonding problem. It was discovered that the normal tensile debonding strength of OCAs was significantly lower than the shear debonding strength. To address this issue, a three-layer structure simulation model of “hard + soft + hard” is established, which allows for analyzing the screen folding problem of any radius. Additionally, a suitable element mesh generation strategy for multi-layer structure screens is proposed. A debonding risk index based on pressure is introduced by comparing the interlaminar normal and maximum principal stress. The influence of thickness, bending radius, and Young’s modulus on longitudinal stress and debonding risk index is examined. It is observed that the influence of thickness and Young’s modulus on debonding risk is non-monotonic, indicating the presence of an optimal solution. The high debonding risk area is located at the beginning of the folding mechanism and screen bonding. The proposed debonding risk index is not only applicable to OCAs but also to all PSA with similar structures.
Endocrowns: A systematic review Govare, Nicolas; Contrepois, Mathieu
The Journal of prosthetic dentistry,
March 2020, 2020-Mar, 2020-03-00, 20200301, Volume:
123, Issue:
3
Journal Article
Peer reviewed
Open access
The restoration of extensively damaged endodontically treated teeth remains a challenge. The use of post-retained restorations has been questioned because of potential tooth weakening.
The purpose of ...this systematic review was to determine whether endocrowns are a reliable alternative to post-retained restorations for extensively damaged endodontically treated teeth and to determine which preparation design is most appropriate and which materials are best adapted for fabricating endocrowns.
The literature that was analyzed covered endocrowns from 1995 to June 2018. A search was conducted for in vitro and clinical studies in English in 3 research databases (PubMed, Cochrane, and Scopus), and this was complemented by a manual search in the bibliographies of the studies found. Case reports were excluded.
A total of 41 publications consisting of 8 clinical studies and 33 in vitro studies were included in this systematic review. Several analysis parameters were identified: for the clinical studies, survival rate, failure modes, and clinical criteria; for the in vitro studies, fracture resistance, stress distribution, preparation criteria, and materials used.
Endocrowns are a reliable alternative to post-retained restorations for molars and seem promising for premolars. A certain preparation design and a rigorous adhesion protocol must be respected. Among the available materials, lithium disilicate glass-ceramic and nanofilled composite resin stand out.
Abstract Statement of problem The recent development of polymer-based computer-aided design and computer-aided manufactured (CAD/CAM) milling blocks and the limited availability of independent ...studies on these materials make it pertinent to evaluate their properties and identify potential strengths and limitations. Purpose The purpose of this in vitro study was to determine and compare mechanical properties (flexural strength, flexural modulus, modulus of resilience) and compare the margin edge quality of recently introduced polymer-based CAD/CAM materials with some of their commercially available composite resin and ceramic counterparts. Material and methods The materials studied were Lava Ultimate Restorative (LVU; 3M ESPE), Enamic (ENA; Vita Zahnfabrik), Cerasmart (CES; GC Dental Products), IPS Empress CAD (EMP; Ivoclar Vivadent AG), Vitablocs Mark II (VM2; Vita Zahnfabrik), and Paradigm MZ100 Block (MZ1; 3M ESPE). Polished 4×1×13.5 mm bars (n=25) were prepared from standard-sized milling blocks of each tested material. The bars were subjected to a 3-point flexural test on a 10-mm span with a crosshead speed of 0.5 mm/min. In addition, 42 conventional monolithic crowns (7 per material) were milled. Margin edge quality was observed by means of macrophotography and optical microscopy, providing a qualitative visual assessment and a measurement of existing roughness. The results were analyzed by ANOVA followed by the Tukey HSD test (α=.05). Results The mean flexural strength of the tested materials ranged from 105 ±9 MPa (VM2) to 219 ±20 MPa (CES). The mean flexural modulus ranged from 8 ±0.25 GPa (CES) to 32 ±1.9 GPa (EMP). The mean modulus of resilience ranged from 0.21 ±0.02 MPa (VM2) to 3.07 ±0.45 MPa (CES). The qualitative assessment of margin edge roughness revealed visible differences among the tested materials, with mean roughness measurements ranging from 60 ±16 μm (CES) to 190 ±15 μm (EMP). The material factor had a significant effect on the mean flexural strength ( P <.001), flexural modulus ( P <.001), modulus of resilience ( P <.001), and margin edge roughness ( P <.001) of the tested specimens. Conclusions The new-generation polymer-based materials tested in this study exhibited significantly higher flexural strength and modulus of resilience, along with lower flexural modulus values compared with the tested ceramic or hybrid materials. Crowns milled from the new resin-based blocks seemed to exhibit visibly smoother margins compared with the ceramic materials studied.
Abstract The CVD–coated parts are found in a wide range of applications and must meet high quality requirements. The stress state due to temperature changes on diamond and silicon dioxide coated ...parts is studied. For single–layer coatings, the stress state under tensile load is analysed. In addition, the strength of the diamond–coated part under bending stress is also investigated.
Biomechanics investigators are interested in experimentally measuring stresses experienced by dental structures, whole bones, joint replacements, soft tissues, normal limbs, etc. To do so, various ...experimental methods have been used that are based on acoustic, optical, piezo-resistive, or other principles, like digital image correlation, fiber optic sensors, photo-elasticity, strain gages, ultrasound, etc. Several biomechanical review papers have surveyed these research technologies, but they do not mention thermography. Thermography can identify temperature anomalies indicating low- or high-stress areas on a bone, implant, prosthesis, etc., which may need to be repaired, replaced, or redesigned to avoid damage, degradation, or failure. In addition, thermography can accurately predict a structure’s cyclic fatigue strength. Consequently, this article gives an up-to-date survey of the scientific literature on thermography for biomechanical stress analysis. This review (i) describes the basic physics of thermography, thermo-elastic properties of biomaterials, experimental protocols for thermography, advantages, and disadvantages, (ii) surveys published studies on various applications that used thermography for biomechanical stress measurements, and (iii) discusses general findings and future work. This article is intended to inform biomechanics investigators about the potential of thermography for stress analysis.
This study focuses on investigating the fatigue behavior of pressure transducer packages subjected to combined thermal-mechanical and corrosion stresses. To analyze the stress distribution within the ...package, a comprehensive multi-physical finite element model was developed. Experimental testing involved subjecting sample packages to temperature and humidity cycling, along with exposure to NaCl solution. Scanning electron microscopy was utilized to observe any cracks and surface deformations that occurred during the testing period. The results highlighted an increasing measurement deviation with each cycling period, reaching over 14 % after 720 h when exposed to 90 °C and 30 % NaCl solution. The results highlight the adverse influence of corrosion on the thermal stress-induced performance degradation of packaging. To effectively capture and assess the observed trends in the experimental data, an artificial neural network (ANN) model was utilized. The ANN exhibited remarkable predictive abilities, attaining a significantly high coefficient of determination value of 0.997 across diverse conditions.
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This manuscript aims to examine and investigate the bending deflection and stress distribution of sandwich functionally graded nanoplates rested on variable Winkler elastic foundation based on new ...quasi 3D hyperbolic shear theory in conjoint with nonlocal strain gradient theory. The sandwich sigmoidal function graded material (SFGM) is proposed with three different configurations through thickness direction. New 3D hyperbolic shear theory is exploited to satisfy parabolic variation of shear through thickness direction and zero shear at the bottom and top surfaces. Modified continuum nonlocal strain gradient theory is used to include the material and geometrical nanosize length scales. Variable Winkler foundation model is proposed to the first time to include the variable elastic environmental under the nanoplate. The comprehensive model and governing equilibrium equations of SFG nanoplates is derived in detail with principle of virtual work and solved analytically by Galerkin method. The developed model is verified with previous work and parametric studies are presented to illustrate influences of the elastic foundation models, sigmoidal distribution index constant, configuration of sandwich plate, material and length nanoscales, boundary conditions on the static deflection and stress distributions of FG sigmodal nanoplate. The proposed model can be applied in design and analysis of NEMS structure under static load, such as nanocapacitor and nanoswitch.
Boron carbide is characterized by a unique combination of properties that make it a material of choice for a wide range of engineering applications. Boron carbide is used in refractory applications ...due to its high melting point and thermal stability; it is used as abrasive powders and coatings due to its extreme abrasion resistance; it excels in ballistic performance due to its high hardness and low density; and it is commonly used in nuclear applications as neutron radiation absorbent. In addition, boron carbide is a high temperature semiconductor that can potentially be used for novel electronic applications. This paper provides a comprehensive review of the recent advances in understanding of structural and chemical variations in boron carbide and their influence on electronic, optical, vibrational, mechanical, and ballistic properties. Structural instability of boron carbide under high stresses associated with external loading and the nature of the resulting disordered phase are also discussed.
