STUDY OF V-SHAPED SPECIMEN CONCENTRATION EFFECT UPON STRESS GRADIENT

B Dimova, V Vesselinova-Guteva
unpublished
The paper presents the results of numerical and experimental linear elastic analyses carried out to investigate the stress gradient of notched V-shaped specimens. Specimens with different V-shaped notch geometry subjected to uniaxial tensile loading have been considered. It was shown that the stress fields around the notch-tip are similar to each other regardless the notch shape. The most familiar analytical functions describing the stress field at the notch-tip have been presented. Some of the
more » ... sented. Some of the available approximation formulas are verified with the obtained numerical data. Comparison of results is shown and is discussed. There is a great variety of approximated and analytical solutions [3, 6, 8] for predicting stress distribution in zones adjoining the notch-tip for the most common concentrators. Despite that these solutions can easily be used for analysis of local stress distribution in real constructions (components with concentrators), the use of numerical methods, FEM in particular, is on the rise notwithstanding the complexity of the analyzed geometries. The processing of the large database derived using FEM is often too labor-consuming and slow compared to the compact and quickly accessible results derived through any analytical method. Important parameters, which are used to describe the local stress field in proximity to the notch-tip are: stress concentration factor K t , effective stress concentration factor K f and the relative stress gradient . For constructions subject to cyclic loading, it is well known that a fatigue crack may appear all too early in places with local stress concentration and to accelerate its intensive growth in areas close to the notch-tip. After clarifying the opportunities for forecasting durability upon alternating loads [7, 5] and the proposed relation between  = f(K t /K f) from Neuber [4, 5], a methodology for durability forecasting may be proposed by using the stress gradient. To create such a methodology, it is necessary to know various solutions for its calculation and to determine it for various testing specimens. The relative stress gradient is presented with the following expression (1) 0 x x y max) i (x 1         , where  max is the maximum whereas  y = f(x, d, r, t,...) is the normal stress in the notch-tip and is a function of various parameter that depend on the form of the concentrator, the type of load and the formula used to describe the stress field. The present paper discusses several basic types of solutions-exact, analytical and approximate, which allow calculate the stress gradient. The results obtained from the reviewed solutions are compared to the results from the numerical modeling of the studied specimens with V-shaped concentrators, varying the form of the specimens (bars and plates) and the geometry of the concentrator upon tensile load. The data presented here can attend to calculate the stress intensity factors that determine crack growth in the concentrator and to determine fatigue strength of notched elements.
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