In this work, the mechanical behaviour of an AZ31 wrought magnesium alloy due to tensile, compressive and four-point bending tests was analysed. Several specimens of this material were taken in different directions from a rolled plate. Tensile and compression tests allowed to characterise the mechanical properties of the material in the rolling and cross rolling directions. To take the effect of the anisotropy induced by the rolling procedure itself into account, the bending tests were carried out using specimens with four different orientations. Six strain gages per specimen allowed to observe the evolution of the strain with the bending moment during the tests. All bending specimens were bent until a total compressive deformation of 2.5%. It was observed that the corresponding tensile strain was significant lower and slightly different for each orientation of the specimens. In addition, a characteristic non-uniform distribution of deformation twinning was observed. The induced residual stresses after bending were characterised by X-ray diffraction (XRD) and incremental hole-drilling (IHD). Due to the different mechanical behaviour in tension and compression, an asymmetric residual stress distribution after bending could be observed. The neutral axis was, in all cases, shifted towards the tensile side. This observation agrees with the strain measurements during bending tests. In addition, an example of the influence of the asymmetric deformation behaviour during fatigue was given.
A novel cellulose-based bio-battery made of electrospun fibers activated by biological fluids has been developed.
ABSTRACT--The same shot-peening treatment was applied to five steels with different mechanical properties. The induced residual stress profiles were analyzed using X-ray diffraction and incremental hole drilling (IHD). The results of both techniques showed that IHD can still be successfully used for measuring shot-peening residual stresses, even if these exceed the yield strength of the bulk material. Expected errors due to the plasticity effect are reduced by the strain hardening of the surface. For an assessment of the reliability of IHD data, strain-hardening variation was quantified by microhardness measurements to estimate the yield strength of the plastified layer. All the main calculation methods for IHD were applied. The results were compared and discussed with respect to the characteristics of each method.KEY WORDS--Residual stresses, incremental hole drilling, shot peening, plasticity effect, X-ray diffractionResidual stresses are present in most mechanical components due to production processes or service loading. Because residual stresses can have either beneficial or detrimental effects, the exact knowledge and control of residual stress state and in-depth distribution are of high practical relevance.The incremental hole-drilling (IHD) technique and the Xray diffraction (XRD) sin2O method find broad acceptance among the quantitative in-depth residual stress measurement methods. A comparison of studies that apply both methods simultaneously, however, leads to quite inconsistent findings. In some cases, a relatively good agreement between the results of both measurement techniques is reported. L2 On the other hand, comparable results are often found only in the interior of the samples; 3-6 the near-surface regions and strong stress gradients seem to be problematic for the holedrilling method. For that reason, residual stress distributions obtained by the IHD method are frequently completed by additional XRD measurements on the surface. 7-1~ In Ref. 11, however, the IHD method was found to be unsuitable for accessing residual stress gradients in the case of a deep-rolled aluminum alloy. A systematic comparison of both methods was carried out in a recent survey. ]2 Observed discrepancies are often attributed to the basic shortcoming of the hole-drilling method, which is its limitation to residual stresses up to 60 percent of the material's yield strength. ~ 2-~5 Higher residual stresses lead to local plastic deformations caused by the stress concentration of the drilled hole itself, which depends on the stress state. For the equibiaxial stress state, the stress concentration factor of a through hole is 2, compared with even higher values of other stress states. As with drilling-induced plastic deformations, this so-called plasticity effect can strongly affect the residual stress evaluation, which assumes linearelastic material behavior. An estimation of the related error (overestimation of residual stresses) is difficult, since the local yield strength of the interesting near-surface layers can differ si...
Este artigo expõe as principais características metodológicas e os resultados apresentados pelos estudos de prevalência do Transtorno do Déficit de Atenção e Hiperatividade (TDAH) através de artigos publicados no período de 2003 a 2014. Realizou-se uma busca em uma das principais bases de dados da área da saúde, o PubMed/MEDLINE que resultou em 23 artigos. Investigou-se as estimativas de prevalência; o processo de amostragem; o tipo de estudo; os critérios diagnósticos; e, as principais variáveis exploradas. O processo de mineração foi realizado pelos programas: EXCEL; NVIVO-10, SPSS 20; e MENDELEY. Resultados: Observou-se a média central de 11.26% entre as estimativas de prevalência encontradas; 99% dos estudos foram transversais; e o processo de amostragem mais utilizado foi o probabilístico por conveniência em 26.08% dos estudos. Os resultados alcançados apoiam a premissa de que os critérios metodológicos e diagnósticos ampliam a variabilidade das estimativas de prevalência a nível global.
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