Papers by Keyword: Differential Method

Abstract: Despite the significant advantages of the Ring-Core method over the hole-drilling method, the Ring-Core method is still less common. Recent developments at our department showed the full potential of the method when using the adequate calibration coefficients. In this paper the differential method, a quick and easy method for uniform residual stress evaluation is described and the influence of its relaxation coefficients on the specimen’s dimensions is obtained.

Abstract: There is a strong need for reliable residual stress measurements. On the one hand, residual stresses can be beneficial, when they are adapted to external loads. On the other hand, they can be detrimental, when they are unknown. Thus, their occurrence can lead to an uneconomical oversizing of components or in their failure, as well. Apart from diffraction methods, mechanical methods are well recognized in order to determine unknown residual stress states. Depending on the applied method, specific boundary conditions have to be taken into account. In the case of mechanical methods like the hole-drilling and the ring-core method, the characteristics of the geometry of the component should be in accordance with an ideal and thick plate. The reason behind is the need for a calibration data set to transform strains into stresses. The calibration is usually carried out numerically. For the sake of simplicity, the geometry of the component is an ideal thick plate and the hole is introduced in its center. However, in most cases, this is not identical with the geometry of the component under investigation. Hence, an application tool was designed that enables the parametric design of a Finite Element Model, the determination of calibration coefficients, the evaluation of the experiment and the visualization of the results for geometries of practical importance. So far, the application tool can represent plates variable in their geometries and in positioning of the point of measurement. The option for other geometries are also possible e.g. a turbine blade.

Abstract: To improve the surface behavior of metal structures, like wear-and heat resistance or hardness, often thermally sprayed ceramic coatings are applied. A modern technology to realize dense layers is the High Velocity Oxygen Fuel (HVOF) technique. The deposition process and necessary pretreatments can cause high residual stresses within the coating and the substrate. While tensile stresses in the brittle coating may cause cracks, compressive stress states can even improve the materials behavior. To guarantee high product quality, it is necessary to know exactly the occurring residual stresses in the metal-ceramic hybrid system. A very common measurement technique is the incremental hole drilling (IHD) method. To determine the residual stresses out of IHD measurements the differential method (DM) or integral method (IM) can be used. To investigate the influence of interfacial layers, nonlinear stresses, cracking, anisotropy, variation of coating thickness and calculation formalisms several FEM models have been build, while case sensitive calibration was used for the coated systems.

Abstract: The hole-drilling method (HDM) and ring core method (RCM) are limited to low residual stresses under 60% of the yield stress. This issue will experimentally analyze the method of adaptive calculation function, presented by the author on the ICRS9. With a four-point-bending test machine, a defined stress can be triggered between the middle bending. In this defined loading area, the strains in two load cases with the HDM and the RCM configuration were measured. With these measured strains the residual stress calculation will be analysed.

Abstract: Due to its large length/thickness ratio, the casing structure can be treated as plates andshells,thus the classical plates and shell theories can be applied. A general MATLAB program wasdesigned to solve the deflection problems of the isotropic casing with simple support usingdifferential method. To test its precision,two different load conditions as well as two materials wereused and their results was made comparison with that of finite element method and Navier solution.The results were in good agreement with each other and the method was efficient in solving thedeflection problems of a casing structure

Abstract: The incremental hole-drilling method is the method of choice to determine residual stress depth distributions with limited costs and minor destruction of the investigated component. With a spatial resolution of commonly two millimeters in diameter and one millimeter in depth especially the effects of frequently used surface treatments like e.g. shot peening or deep rolling can be reliably detected if the in depth residual stress gradients are relatively smooth. Nevertheless up to now the quantitative accuracy of the method is poor for residual stress analyses close to the materials surface up to depths of approximately 0.2 mm and in the case of steep in-depth residual stress gradients or oscillating residual stress depth distributions. In this paper, residual stress depth distributions of a broad range introduced by mechanical surface-treatments in flat specimens were analyzed with the hole-drilling method and compared with the results measured by X-ray diffraction as the reference. It comes out, that arbitrary residual stress depth distributions can be successfully determined with a modified differential evaluation formalism. For this purpose, often neglected well known weak points of the hole-drilling method were considered and improved, e.g. hole geometry, numerical calibration and data conditioning. Especially, the proposed strategy of data conditioning results in an almost user-independent evaluation formalism.

Abstract: Two commonly used mechanical methods for the determination of residual stresses are the hole-drilling method and the ring-core method, which can be regarded as semi-destructive. The most restricting limitation for the general applicability of both methods, according to the current state of science and technology, is the fact that the scope for relatively low residual stress under 60% of the yield stress is limited.This is a result of the notch effect of the hole or ring core, which leads to a plastification around and on the bottom of the hole and ring shaped groove already at stresses well below the yield stress of the material. The elastic evaluation of the resulting plastic strains leads consequently to an overestimation of the delineated residual stresses. In this paper the influence of elastic-plastic material properties no the specific calibration function for the hole-drilling method using the differential method is studied, and the method of adaptive calibration functions is presented.

Abstract: Parameter Identification is the key technology in measurement-based load modeling. In order to identify parameters in power system ,the differential method which is based on the multiple curves fitting and interpolated method are compared in the paper. Numerical results illustrate that the differential method can improve the accuracy for load modeling parameter identifications.

Abstract: Through analyzing several common errors that have impact on the kinematic accuracy of globoidal cam mechanism, finally a mathematical model of globoidal cam impinged with error was established. By using the differential method, the motion accuracy influence coefficients of the globoid cam mechanism were obtained. The change rule of kinematic accuracy influence coefficient with the change of globoidal cam rotation angle was analysed with practical cases. The analysis result shows: different error factors lead to different influence coefficient; Radius error of the index disc roll has the greatest impact on motion precision, while shaft angle error almost has no influence on the movement precision; The meshing position of the globoidal cam mechanism affects the kinematic accuracy volatile; Moreover, each motion accuracy influence coefficient has a certain relationship with the structure factors of globoidal cam.

Abstract: A novel photoelectric sensor based on differential method and position sensitive detector for refractive index (RI) measurement is proposed. In the paper, we systematically proposed an electro-optical measurement principle, built a mathematical model, and designed the structure of sensing probe; through detail calculation, key parameters of the refractometer are determined, simulation results showed that resolution reaches order of 10^-6, preliminary experiment also verified the feasibility of the design.