Rounded Notches Research Articles

Clarification of creep damage condition and rupture time prediction method for round notch bar specimens on Modified 9Cr-1Mo Steel under creep loading

Clarification of creep damage condition and rupture time prediction method for round notch bar specimens on Modified 9Cr-1Mo Steel under creep loading

Creep damage process and rupture property of 2.25Cr steel round notch bar specimen

Creep damage process and rupture property of 2.25Cr steel round notch bar specimen

A modified plate model for an efficient analytical treatment of stress concentrations at notches

AbstractIn the present work, a modified plate model is proposed lying in‐between the established Kirchhoff‐Love and first‐order shear deformation plate theories. The resulting system of partial differential equations can be solved using a complex potential approach which allows for tackling complex geometries such as sharp or rounded notches. Using the proposed model, the singular stress field in the vicinity of a sharp notch can be obtained explicitly and the influence of the notch opening‐angle on the singular behaviour is investigated. It is shown that resulting bending moments and transverse shear forces match with asymptotic solutions according to first‐order shear deformation plate theory and are in very good agreement with numerical results.

Bending fatigue strength design method for machine components with complex geometries

The purpose of this study is to devise a bending fatigue strength evaluation method that can be widely used for any machine component under the consideration that bending fatigue breakage depends on the initiation of a surface fatigue crack, namely, the conditions for the initiation of a fatigue crack can be used as the criteria for bending fatigue strength design. The specially designed and manufactured three-point bending specimens with crowned round notches are used in bending fatigue experiments. The obtained bending fatigue strengths are expressed as the maximum actual stress at the critical point, which increases with decreasing notch radius. Considering the effects of the stress distribution on the bending fatigue strength, we present a method for estimating the tension fatigue strength of a smooth specimen, which is shape-independent fatigue strength and can be applied to bending fatigue strength design for machine components with complex geometries.

Acceleration of nickel diffusion by high tensile stress in cold-worked type 316 stainless steel at 450°C

ABSTRACTThe effect of tensile stress on diffusion was studied by the diffusion couple method. A diffusion couple was prepared by electroless plating a nickel thin layer on the round notch surface of a compact tension-type specimen of 20% cold-worked Type 316 stainless steel. The couple was diffused at 450°C for 4003 h under the maximum tensile stress of 553 MPa in the load direction. A rapid diffusion coefficient of nickel in the Type 316 stainless steel was observed at the high tensile stress zone that was 6.5 times faster than that at the low-stress zone.

Energy-based low cycle fatigue indicator prediction of non-load-carrying cruciform welded joints

A new uniform analytical formulation is proposed to predict the low cycle fatigue assessment indicator of non-loading cruciform welded joints under tensile cyclic loading considering the effects of plasticity and mechanical heterogeneity of the welded materials and geometry configurations. Particularly, weld toe of the joints is dealt with a notch rounding in order to avoid the notch tip singularity in accordance with generalized Neuber concept of Fictitious Notch Rounding (FNR). The relationship between elastic and plastic energy concentration factor of weld toe is firstly determined by the combination of notch stress and strain distribution with the increases of nominal loading, then the main parameters affecting the energy concentration factor are investigated by separating elastic and plastic stages. Stress and strain field intensities are finally expressed in terms of total energy values, which are linked to the nominal energy ones. The energy prediction function which takes into account the material and geometry factors is capable of providing a closed form analytical expression about the state of energy both under small and large-scale yielding for industrial facilities by the comparison against finite element analysis results.

Periodic System of Closely Located Holes in an Elastic Plane Under the Conditions of Antiplane Deformation

We construct a singular integral equation of an antiplane periodic problem of the theory of elasticity for an isotropic plane weakened by smooth curvilinear holes. A numerical solution of the problem is obtained in the case of closely located holes with rounded V-shaped vertices made in the elastic plane under the conditions of uniform shear at infinity. On this basis, we determine the stress concentration factors at the rounded vertices of a bilateral V-shaped semiinfinite notch. By using the well-known relation between the stress intensity and stress concentration factors for sharp and rounded V-shaped notches, we perform the limit transition to a bilateral sharp V-shaped notch. The dependence of the stress intensity factor at the sharp vertices of a bilateral V-notch on its apex angle is determined.

Neuber fictitious notch rounding approach reformulated for orthotropic materials

In this short contribution, the fictitious notch rounding concept is applied to U-shaped notches in orthotropic bodies. Using the normal stress criterion, the fictitious notch radius is determined in closed form. It is found that the fictitious radius strictly depends on the actual notch radius, the microstructural support length and the elastic properties of the material, the latter playing a crucial role.

Creep Damage Assessment of Various Shape of Round Bar Notch Specimens Mod.9Cr-1Mo Steel

Creep Damage Assessment of Various Shape of Round Bar Notch Specimens Mod.9Cr-1Mo Steel

Relationship Between Creep Damage and Stress States of Round Bar Notch Specimens

Relationship Between Creep Damage and Stress States of Round Bar Notch Specimens

A study of fatigue notch sensibility on titanium alloy TiAl6V4 parts manufactured by selective laser melting

Titanium Ti6Al4V alloy is a light alloy characterized by having excellent mechanical properties and corrosion resistance combined with low specific weight, commonly used in biomedical applications, automotive and aerospace components. Current work analyses the fatigue behavior of titanium alloy TiAl6V4 parts, manufactured by selective laser melting (SLM), intending to characterize fatigue strength from low to high life range, under constant amplitude strain control. Fatigue tests were carried out at room temperature, using round dog bone specimens where laser powder deposition occurred in layers perpendicular to the sample axle. All specimens were subjected to stress release treatment. A second batch of specimens was tested in order to investigate the notch sensibility of the material. All tests were performed under displacement control. The material was characterized in terms of the tensile mechanical properties, cycle curve, Basquin and Coffin equations. The analysis of the results showed a strain-softening behavior that increased with applied strain, and non-linear response in and plastic regime. In addition, this alloy exhibited a low transition life, about 250 reversals, which can be attributed to the combination of high strength and relatively low ductility. The material revealed a notch sensibility factor, that was quantified for the round notch with a stress concentration factor Kt=1.7 (with respect to the effective cross section), increasing with fatigue life, from one for low cycle fatigue tending to 1.42 for high cycle fatigue (Nf of about one million cycles). SEM analysis showed that fatigue crack initiated from the surface and propagated through the cross section, occurring in many cases multi-nucleation.

On the use of the peak stress method to assess the linear elastic and the fatigue notch factors of notched components under tension

AbstractA simple method is proposed, which allows the theoretical stress concentration factor at a rounded notch tip to be assessed from the fictitious stress value arising at the tip of the corresponding pointed V‐notch. Such a stress value suffices to be determined by a finite element analysis carried out using a mesh pattern with a constant average element size, d, strictly related to the actual root radius, ρ, and the opening angle, 2α, of the radiused notch. The relevant expression linking d to ρ and 2α is obtained in closed form and the accuracy of the proposed method is discussed versus the results of a number of finite element analyses carried out on notched plates under tension.Eventually, the possibility of using the peak stress directly as a strength parameter is explored, and an example related to the fatigue strength of welded joints is provided to support this idea.

A novel test method for the fatigue characterization of metal powder bed fused alloys

This research addresses the conflicting factors of high costs of fatigue testing and large number of influencing factors that need to be investigated for PBF material and process qualification. Metal powders are remarkably expensive, the PBF production process requires expensive systems and fatigue testing requires multiple specimens (depending the required degree of confidence) to characterize a single material/process combination. In this paper a novel fatigue test method aimed at the peculiar needs of PBF technology is initially presented and fatigue data obtained on Direct Metal Laser Sintering Ti6Al4V are validated against standard rotating bending test results. Then, the link between microstructure and directional fatigue behavior is demonstrated using the present methodology and SLM Inconel 718: namely, the stress direction parallel to build direction is the most severe. Finally, the new test method is applied to the investigation of the fatigue notch sensitivity of DMLS Ti6Al4V in relation to the notch fabrication process. Round notches in specimens with opposite fabrication orientations (i.e. up-skin vs down-skin) resulted in two notch fatigue factors and the up-skin notch has a better fatigue strength than the down-skin notch.

CrMoV鍛鋼環状切欠き試験片のクリープ破断強度

CrMoV鍛鋼環状切欠き試験片のクリープ破断強度

直径1mm丸棒引張型ミニチュア試験片を用いたCrMoV鍛鋼のクリープ損傷評価

Creep damage assessment of high temperature components in aged thermal power plants is necessary to maintain reliable operation. Although an accurate creep damage assessment result is obtained by a destructive assessment method in which creep tests are performed, it is difficult to cut a standard size specimen from actual components. Therefore, development of testing and damage assessment methods by using a miniature specimen are expected. In this study, creep tests of a CrMoV forging steel were conducted by using a solid bar tensile type miniature creep specimen with 1mm diameter at 600℃. It was demonstrated that equivalent creep deformation and rupture properties to those obtained from the standard size specimen are obtained by the miniature specimen under stress level below 200MPa. Creep damage materials were produced by interrupting creep tests performed by using a standard sized smooth bar specimen and two types of round notch bar specimen with radiuses at notch root of 0.5mm(R0.5) and 2.0mm(R2.0). Uniaxial tensile creep tests were performed by using the miniature creep specimens taken from the plain specimens and the notch roots of the notch specimens. Although accurate creep damage assessment results were obtained from the creep tests with the miniature creep specimens taken from the plain specimens, it should be noted that the results may give under estimation for higher creep damaged condition. Creep damage assessment results based on the creep tests with miniature specimens also gave under estimation for the creep damaged material of R0.5 due to lower axial creep strain accumulation under multiaxial stress states before interrupting the creep tests. On the other hand, accurate creep damage assessment results were obtained for the creep damage materials of R2.0 indicating that creep tests with the miniature specimens may be applicable to creep damage assessment of components under certain range of stress multiaxiality.

Life property of a round notch bar specimen on CrMoV forging steel under creep-fatigue loading

Life property of a round notch bar specimen on CrMoV forging steel under creep-fatigue loading

A review of the notch rounding approach under in plane mixed mode loading

The fictitious notch rounding approach is widely used for the fatigue assessment of welded joints and for this reason in the present paper a review of the concept applied to inclined lateral V-notches with root hole subjected to in-plane mixed mode loading has been carried out. This is the basis for future applications to welded structures in presence of mixed mode loading.The analytical framework of the method is herein recalled and the fictitious notch radius is determined as a function of the real notch radius, the microstructural support length and the notch opening angle. In order to reduce the complexity of the task, we adopt a method based on the normal stress failure criterion. The method provides the values of the microstructural support factor as a function of the mode mixity parameter and the notch-opening angle. Moreover, the support factor is assumed independent of the microstructural support length. Finite element simulations for various notch shape and configurations are compared to experimental data from pointed V-notches made of polymethylmethacrylate. The model prediction showed good agreement with the experimental results. These results are very promising for the application to welded structures.

Distribution of Stresses Near V-Notches in an Orthotropic Plane Under Symmetric Loads

The solution of a plane problem of elasticity theory for an orthotropic plane with semiinfinite rounded V-notch under the action of symmetric loads is obtained by the method of singular integral equations. By using this solution, we deduce the relations between the stress intensity factor at the sharp tip of the V-notch and the normal stresses at the tip of the corresponding rounded notch. For bounded bodies with V-notches, the indicated solution is obtained as an asymptotic relation for small radii of rounding of their tips. The presented relation can be used in the limit transitions in order to find the stress intensity factor at the tips of sharp V-notches according to the solutions for the corresponding rounded stress concentrators.

Influence of the Anisotropy of Materials on the Distribution of Stresses Near Parabolic Notches

We consider the problems of distribution of stresses in an infinite anisotropic plane containing a parabolic notch for three main types of deformation in the case where the asymptotics of the stress field is specified at infinity (including stress intensity factors at the tip of the corresponding semiinfinite crack). The solutions of these problems are obtained with the help of the limit transition from the known analytic solutions obtained for an elliptic hole in the anisotropic plane for three types of loading at infinity (symmetric tension, transverse and longitudinal shear). These results generalize the well-known data on the distribution of stresses near narrow rounded notches in the isotropic plane and reflect the influence of anisotropy of the material on the stress concentration.

Effects of plate stiffness on the fatigue resistance and failure location of pipe-to-plate welded joints under bending

A series of tests have been carried out using specimens made of a tube, having a thickness of t=10mm, joined to a plate by fillet welding. Two different kinds of specimen were employed, differing in the plate geometry (stiffness). Both kinds of specimen were tested under bending (prevalent load) and shear loading in as welded conditions.Different initiation regions for the fatigue cracks were found and significantly different fatigue resistances were obtained for the two geometries in terms of the nominal stress approach (or in terms of applied load vs cycles to failure). Two local methods for the fatigue life assessment were then applied to independently analyse the experimental results: the fictitious notch rounding approach proposed by Radaj, which is also recommended by some international standards and the more recently proposed peak stress method, which is based on the NSIF concept.It is shown that the nominal stress method, which is by far the simplest method among those recommended in standards for analysing the joint under study, fails to explain the observed different endurances. On the other side, the methods based on local stresses account for the different joint stiffness and provide a reduced scatter in the results. However, even if local approaches, accounts for differences in the structural behaviour of the joint, the knowledge of the actual geometry of the weld need to be accounted for, in order to be able to identify the fatigue crack initiation region.For a design purpose, a safe prediction of the fatigue endurance of the joint can be obtained by all the analysed methods, if the corresponding recommended design curve is used.