A New Method of Creep Ruptures Data Extrapolation Based on the Work
For structural and machine components in service at high temperature and pressure, such as those used in power generating and petrochemical plants, as well as aero-engines and metallurgical machineries, creep life assessment is a major concern because of safety and economic reasons. In this paper, a new model for creep life prediction is proposed based on energy processes. The work of making the material failure of applied loads is used to describe the creep processes respectively. By mathematical technique, the expression of the model is, where is Larson-Miller constant, and is also material constant at certain condition. This function Moreover, owing to its simple expression, it is very easy to use this model to predict the creep life. To check the validity of the new model proposed in this paper, the 250000h creep rupture strength estimates for 2.25Cr1.0Mo steel under stress control at 743~793K have been performed. The results are in a good agreement with the experimental data.
Creep life predictions in nickel-based superalloys
Abstract Creep life prediction techniques such as the Larson-Miller parameter, life trend diagrams, the Monkman-Grant relationship and the Dobes-Milicka relationship are critically reviewed. Problems associated with the scatter in creep life data and the inability of these relationships to accommodate for service-induced material degeneration are discussed. These effects are rationalized in terms of the erratic tertiary creep behaviour of complex engineering alloys. A new creep design relationship based on the sum of the primary creep life tp plus the secondary creep life ts, normalized by the sum of the primary creep strain ϵp plus the secondary creep strain ϵs, varying as a function of secondary creep rate ϵ has been proposed. The relationship is described by t p +t s ϵ p +ϵ s ϵ M =K where M and K are constants. The equation is accurate over a wide range of stresses (350–700 MPa) and temperatures (760–890°C) in IN-738LC. The method systematically reveals the creep degeneration effects with increasing service life. The relationship appears to be independent of any changes in the predominant deformation mechanism.
Assessment of fractures in endodontically treated teeth restored with and without root canal posts using high-resolution cone beam computed tomography
Background Root fractures are a diagnostic challenge for dentists in endodontic treatment. This study aimed to determine the relationship between the characteristics of tooth fractures and the presence of root canal posts in endodontically treated teeth using high-resolution cone beam computed tomography (CBCT). Material and Methods Fifty high-resolution CBCT scans of endodontically treated teeth with a diagnosis of fracture were obtained, of which 30 were from women and 20 were from men. These scans were acquired with three Veraviewepocs 3D units and one 3D Accuitomo 170 unit, with a 40 × 40-mm field of view and 125 μm voxel size. The variables assessed included the type of fracture, extent of fracture, type of retention, post length, cause of endodontic failure, location of the lesion, and time required to detect the fracture (difficulty score). For data analysis, the chi-squared test, Student’s t-test, and multiple linear regression (α <0.05) were used. Results No association was found between the type of fracture and type of retention or between the type of fracture and its extent (P>0.05). On the other hand, the type of fracture significantly influenced the time required for its detection. Additionally, the most difficult plane for detecting the fracture and the difficulty score were associated, with statistically significant results. Conclusions The type of fracture in endodontically treated teeth was not associated with the type of post used for restoration. All of the CBCT systems used to detect tooth fracture showed the same efficiency. Key words:Cone-Beam CT, Tooth Fracture, Root Canal Post.