Dent Profile Research Articles

La Educación superior durante la pandemia de COVID-19 en Brasil: factores que influyeron en la participación de los estudiantes

In early 2020, when the coronavirus pandemic began to affect every area of society, the situation in Brazil was no different from that of other countries. Covid-19 brought the implementa- tion of social isolation measures and led to readjustments in living and working conditions. In turn, this led to readjustments in the conditions of employees and users of public services who wished to access those services. In education, it also created new social inequalities resulting from teachers and students’ lack of access to the technologies, tools and programmes they needed. Other issues detected were health and financial problems due to unemployment as well as a lack of policies aimed at reducing the number of working hours. In view of this, the Federal University of Pernambuco (UFPE), the Federal University of Paraíba (UFPB) and the University of Pernambuco (UPE), all of which are located in the northeast of Brazil, carried out an inter-institutional study of factors that influenced the participation of undergraduate students in online classes during the period of social isolation. The aim of this article is to present the partial results from this study in relation to stu- dent profile and the infrastructure available to those students to aid their participation in the online classes taught on their respective degree programmes.

Full Scale Dent Rebound Testing of X65 Steel Linepipe

Dents in buried pipelines can be formed due to a number of causes: third party machinery strikes, rock strikes during backfilling, pipe resting on rock, and amongst others. Dents in pipelines would not only affect short and/or long-term integrity, but would also have a potential impact on the pass capacity of in-line inspection and cleaning tools when the size of the dent is large enough. Rebound for an originally constrained dent can decrease the dent depth and improve the pass capacity of in-line inspection and cleaning tools. In order to estimate the rebound capacity of dents especially in spiral weld pipelines, a full-scale dent rebound testing program of X65 steel pipeline was designed and performed. The full scale testing was conducted on the parent material and the spiral welds. Hemispherical and pyramidal indenters were used to generate dents to different depths. Strains around the denting area during formation of the dent and changes in depths due to rebounding after removing indenter were measured. Following each rebound test, the dent profile was portrayed with a 3D laser scanner and the maximum equivalent strain was then calculated. With the information obtained from the above measurements, detailed analyses were performed and a numerical model was developed. In this paper, the approach used for the study is described first. The results and findings are then presented. The effectiveness of the developed numerical model for dent integrity management is demonstrated.

Assessment of dents for gas pipelines

The analytical solution of the stress-strain state for pipe with dent based on the method of equivalent loads is developed. The shape of the dent is given in an analytic smooth function for which a semi-analytical solution is found. As a basic, a harmonic dent is considered, the displacements of which are easily calculated, therefore, forces and moments can be easily found. A solution for a single dent is obtained based on expansion in Fourier series. A comparison of analytical and numerical results for the axial force and pressure load is given. Influence of the dent profile to stress concentration factor is discussed.

A Basic Numerical Peening Indentation Model with Geometric Indenter Based on Dynamic Impact Analysis

As shot peening is widely used to improve the crack resistance of various metals, it isimportant to have an accurate method to calculate the compressive residual stress produced by thisprocess. To this end, this paper presents a finite element (FE) model that includes an indenterdesigned from a dent profile. The results of compressive residual stress obtained by using thisindenter model and a normal shot impact model are compared. The indentation FE solution with anunmodified indenter is close to that obtained using the rigid shot (RS) impact model. The solutionfor the indentation FE model with a modified indenter closely matches that for an elasticdeformable shot (EDS) impact model. These results confirm the effectiveness of the indentation FEmodel based on the dent profile. This model can replace the present impact FE models to calculatethe compressive residual stress produced by shot peening.

A 2-D Axisymmetric Indentation Model for Peening Residual Stress in Metallic Material and its Experimental Verification

Various impact analysis models have been used for analytical prediction of peeningresidual stress. In this paper, a new approach based on finite element (FE) analysis was proposed topredict the peening residual stress through single indentation analysis using the dent profilegenerated on a shot-peened surface. Three analysis models (rigid, elastic, and plastic shots) werecompared each other, and the dent obtained in the plastic shot impact analysis model showed a dentprofile almost identical to that of the experimentally obtained dent. A rigid indenter modelconstructed using the dent profile obtained by dynamic impact analysis, and it integrated into thesingle indentation analysis model. The FE surface residual stress obtained in the center of the dentof the indentation analysis model was found to be almost identical to the surface residual stressmeasured by X-ray diffraction (XRD), thus verifying the validity of the proposed single basicindentation FE model based on impact analysis.

Possibility of Shear Fracture in Low-Velocity Impact of Al-6061 Projectiles on Al-6061Plates

Experiments on low-velocity impacts of hollow cylindrical Al-6061 projectiles on thin Al-6061 plates are modelled using smooth particle hydrodynamics technique using Johnson-Cook and Bao-Wierzbicki damage models. At 65 m/s, the projectile dents the target plate while at 85 m/s, the target is perforated. The dent profile is adequately represented in the simulations except that the central dent is underestimated by ∼10%. The numerical procedure allows for a well-defined demarcation of shear and tensile damage by the degree of triaxiality and the simulations at 85 m/s show that the tensile damage exists over a greater spread in the target plate and has a magnitude an order greater than the shear damage. Hence, the tensile damage and thus JC damage model would adequately describe the low-velocity impact of Al-6061 projectiles on thin Al-6061 plates.

Parametric study on single shot peening by dimensional analysis method incorporated with finite element method

Shot peening is a widely used surface treatment method by generating compressive residual stress near the surface of metallic materials to increase fatigue life and resistance to corrosion fatigue, cracking, etc. Compressive residual stress and dent profile are important factors to evaluate the effectiveness of shot peening process. In this paper, the influence of dimensionless parameters on maximum compressive residual stress and maximum depth of the dent were investigated. Firstly, dimensionless relations of processing parameters that affect the maximum compressive residual stress and the maximum depth of the dent were deduced by dimensional analysis method. Secondly, the influence of each dimensionless parameter on dimensionless variables was investigated by the finite element method. Furthermore, related empirical formulas were given for each dimensionless parameter based on the simulation results. Finally, comparison was made and good agreement was found between the simulation results and the empirical formula, which shows that a useful approach is provided in this paper for analyzing the influence of each individual parameter.

Process Design for Preventing the Gate Oxide Thinning in the Integration of Dual Gate Oxide Transistor

In this study, a method is proposed to alleviate a gate oxide (GOX) thinning problem at the edge of shallow trench isolation (STI), when STI is adopted in the dual gate oxide process (DGOX). It is well known that the DGOX process is usually used for realizing both low and high voltage operating parts in one chip. However, it is found that severe GOX thinning occurs from 320 Å (in active area) to 79 Å (at STI top edge) and a dent profile exists at the top edge of STI, when conventional DGOX and STI processes are adopted. In order to solve these problems, a new DGOX process is used in this study. The GOX thinning is prevented mainly by a combination of a thick sidewall oxide with SiN pullback. Therefore, good subthreshold characteristics without a so-called double hump are obtained by the prevention of GOX thinning and a deep dent profile.

Spall initiation and propagation due to debris denting

An analytical model has been developed to investigate the effects of dent on spall initiation and propagation in lubricated contacts. The model is based on the damage mechanics concept that the fatigue spall initiation and propagation is due to the accumulated plastic strain process rather than the stress intensity at the tip of the crack. The contact surface layer was divided into small metal matrix (cell) and for each cell a damage law was applied to determine whether the cell is undergoing damage or not. In this model, spall will be formed when a cell is damaged. A dent profile from finite element analysis for a spherical debris denting the contact surface was used in a point EHL model. The pressure and traction profiles were then used to obtain the internal stresses and accumulated plastic strain for each cell. A damage variable was calculated for each cell based on the accumulated plastic strain. When the damage in a cell reaches a certain level, the cell is damaged and is assumed to fall off the contact surface layer, hence, spall is generated. The spall will further modify the contact surface resulting in new pressure and traction profiles. The accumulated plastic strain and damage are calculated again based on which new spalls may be generated. The entire procedure is repeated which allows the spall to propagate. Spall size and growth rate versus cycle number are presented. The results indicate that spall will always initiate at the dent edge.