Notch Sensitivity Factor Research Articles

Notch Fatigue Property of 7050-T7451 Aluminum Alloy under Bending Resonance Environment

Based on the electromagnetic shaker table, the resonant fatigue testing system and the corresponding conventional fatigue testing system were designed respectively. The fatigue life (S-N) curves of smooth and notched 7050-T7451 aluminum alloy specimens were measured in the range of 105-107 cycles, and the notch fatigue property of 7050-T7451 aluminum alloy under bending resonance environment was studied. The results indicate that the fracture mechanism under bending resonant fatigue environment is roughly the same as that under bending conventional fatigue loading. All the S-N curves obtained through resonant and conventional fatigue tests show a continuously downward trend, and there are no obvious fatigue limits. Notch fatigue property under bending resonance environment presents “stage characteristics”, which increases first and then decreases with the increase of cycles. There is a critical cycle number Nc at 8×105 cycles, corresponding to the maximum fatigue notch factor Kf-max (or the maximum notch sensitivity factor qmax). There are two critical cycles N1 and N2. When N1<N<N2, the notch fatigue property of the material and the corresponding structures under resonance environment requires more consideration than conventional fatigue loading.

Deformation and failure of pseudo-ductile quasi-isotropic all-carbon hybrid FRPS with an open hole under tension

An experimental study has been carried out to investigate the elastic and pseudo-ductile deformation processes of carbon fibre reinforced plastics, containing low elongation (LE) and high elongation (HE) layers of standard thickness. The behaviour of unidirectional homogeneous LE- and HE-laminates, hybrid [HE/LE/HE] and quasi-isotropic composites, with sublaminates sequence [0/45/90/-45]s and [0/60/-60]s were studied up to complete tensile failure. Tests carried out on standard prismatic specimens and specimens with a central hole. A clip-on extensometer and digital image correlation (DIC) were used to distinguish the stable elastic deformation, the microdamage accumulation in the LE-layers, and the delamination of LE and HE layers. For notched specimens, acoustic emission signals revealed the accumulation of scattered microdamage and the localisation of the pseudo-ductility around the hole. The quasi-isotropic hybrid laminates were almost notch insensitive, with the notch sensitivity factors in the open hole tension test for pseudo-yield and ultimate stress below 1.15.

A novel thread connection structure of slimehole drilling tool in ultra-deep natural gas well.

The thread connection's root fillet radius of 0.038″ size is the greatest weakness of the API NC type joints and thread. During the slimehole drilling, especially in the deep and ultra-deep gas well, its stress concentration factor and notch sensitivity factor are very high A novel thread connection design (TM) of a drilling tool is proposed to decrease the fatigue failure of the slimehole drilling tool in the deep and the ultra-deep gas well in the Tarim oilfield China. The novelty in the TM thread structure is, reducing the threads per inch, extending the distance from the last engaged thread to the external shoulder of the pin and adding three threads to the conventional connection. The novel thread connection will improve the slimehole drilling tool's anti-fatigue life due to its improved elasticity and rigidity. Furthermore, the TM can transfer the maximum stress at the connection root to the loaded surface, which can effectively lower the fatigue notch's sensitivity coefficient. In this paper, the finite element method (FEM) is applied to carry out the detailed comparative analysis of the TM with existing thread connection NC38, TX60 and TH90. The TM has the lowest stress concentration factor and fatigue notch sensitivity coefficient, so its anti-fatigue life is the highest. In addition, TM is manufactured and is tested at Tarim oilfield in China.

Influence on nonhomogeneous microstructure formation and its role on tensile and fatigue performance of duplex stainless steel by a solid-state welding process

Material and Property analysis of Duplex Stainless Steel due to microstructures formed on the surface. Because of the implication of various solid-state welding processes used to join two or more DSS structures. Many studies and experiments have been done using various methodologies like girth friction welding, friction stir welding, etc. to search for further possibilities. This review article is an analysis of research performed to study the effect of solid-state welding on DSS and its importance. This study shall help various researchers to analyze the importance of DSS and problems generated during its welding. Basquin constants were evaluated. The fatigue strength, notch sensitivity factor, fatigue notch factor were also evaluated for the dissimilar joints. Fatigue strength is correlated with microstructure, microhardness. The tensile properties of the joints were also evaluated.

Investigation of Fatigue Strength and Life Prediction for Automotive Safety Components of V-Notched and Un-notched Specimen Part I: Utilization of Waste Materials into Raw Materials

This paper deals with a design of industrial cast-parts and mainly focuses on fatigue life influenced by organic and inorganic particles at different stress levels over a wide range spectrum, which is evaluated and compared. The fracture mechanisms and fatigue strength of V-notch and un-notch specimens are described. The notch factor and notch sensitivity factors have been studied. Porosity is the main factor for crack growth, and it reduces with the addition of waste particles. This combination receives a lot of attention due to its low cost and environmental safety. The micro-/macro-cracks and fracture surface are revealed using SEM and OM analysis.

A fatigue life prediction method from magnetic pole material to simulation part

Due to the higher reliability needs of the large moving component motor-generator rotor, the assessment of the service life has drawn more and more attention. After finite element analysis of the rotor, the simulation part which can represent the magnetic pole with the most dangerous position of the rotor was designed to investigate the S–N curves. Compared with the conventional specimen, considering the main influencing factors of fatigue life for simulation part, the comprehensive factor was proposed to establish the fatigue life relationship between magnetic pole material and simulation part. It was found that the calculation method of fatigue notch factor based on the notch sensitivity factor is relatively simple and practical, and there is no significant effect of surface roughness on high and low cycle fatigues for low roughness ( R a is about 1 µm), and the dimension factor changes linearly with the scale factor. Based on those results, a fatigue life prediction method was proposed and validated, and the predicted results were in good agreement with the experimental data. This study will provide a reasonable reference to determine the fatigue life prediction of large moving components.

Validation of Notch Sensitivity Factors

An end-to-end example of the application of the procedures of verification, validation, and uncertainty quantification (VVUQ) is presented with reference to mathematical models formulated for the prediction of fatigue failure in the high cycle range. A validation metric based on the log likelihood function is defined. It is shown that the functional forms of the notch sensitivity factors proposed by Neuber and Peterson cannot be validated but a revised form can be. Calibration and validation are based on published records of fatigue tests performed on notch-free and notched test coupons fabricated from aluminum alloy and alloy steel sheets.

Effect of organic and inorganic reinforced particulates for fatigue behaviour of Al–Si7–Mg0.3 hybrid composite: V-notched and un-notched specimen experiments with microstructural constituents

The design of industrial cast parts Al–7Si–0.3Mg alloy is widely used as structural components of aircraft and automotive safety components. The investigation mainly focuses on fatigue life influenced by organic and inorganic particles with different weight fractions measured at different stress levels over a wide range spectrum of three different materials which are evaluated and compared. The notch and un-notch specimens of these materials are described fatigue strength and crack mechanism using high cycle fatigue. According to Basquin constants, fatigue notch factor and notch sensitivity factor were studied. The A356/7.5% rice husk ash-7.5% fly ash hybrid composite increases fatigue strength of 30% and lower the fatigue notch factor to 25% compared to the matrix alloy. Porosity is the main factor for estimation of fatigue life. The micro-/macro-cracks and fracture surface are revealed under the SEM and optical microscope analysis.

Bending fatigue design of case-hardened gears based on test specimens

Different design methods against bending fatigue are reported in ISO 6336 standard. The standard suggests primarily the method based on reference test gears and provides the relevant fatigue curves. Additionally, the standard suggests the use of specimens (instead of gears) to generate the reference fatigue curves, but it also advices that specimen-based methods can be used when gears are not available and that specimens are particularly useful for comparing fatigue performances of gear materials relative to one another. The purpose of the present paper is to evaluate the accuracy of the specimen-based methods mentioned in the ISO standard when applied to design gears against bending fatigue. Experimental data were generated by means of pulsator fatigue tests on case-hardened gears used in off-highway vehicles. Afterwards, experimental results were compared with theoretical estimations according to the approaches based on reference test gears (as suggested by the ISO standard) and test specimens. Concerning the latter approach, the relevant fatigue design curves were generated by testing smooth as well as notched specimens made of the same case-hardened gear steel. It was found that the specimens-based methods are as accurate as the reference gears-based method, provided that the material notch sensitivity factor is properly calibrated on the experimental results obtained from specimens.

Fatigue Behaviour of Friction Stir Welded AZ31B Magnesium Alloy Joints

Friction stir welding (FSW) is a relatively better joining technique particularly for magnesium and aluminum alloys that are difficult to weld by fusion welding techniques. Fusion welding of these alloys is not preferable due to hot cracking, formation of porosity, etc. However solid state welding techniques, such as, friction sitr welding are found to offer solution to the above problems. Many research papers available in open literature focusing tensile properties, microstructural characteristics, and corrosion behaviour of friction stir welded AZ31B magnesium alloys but fatigue behaviour of these welds are not yet investigated. Hence, in this investigation, an attempt has been made to evaluate fatigue behaviour of friction stir welded rolled plates of AZ31B magnesium alloys.Fatigue experiment was conducted using servo hydraulic controlled fatigue testing machine. Fatigue strength, fatigue notch factor and notch sensitivity factor were evaluated. It is found that the fatigue strength of AZ31B welded joints is 46 MPa at 2x106 cycles which is approximately 34 % lower than that of the base metal fatigue strength.

The effects of notch size and material microstructure on the notch sensitivity factor for notched components

Nickel base superalloys are used in hot sections of gas turbine engines due to its high strength and good creep, fatigue, and corrosion resistance at high temperature. In this paper, a new probabilistic approach based on weakest-link theory that accounts for the effects of the microstructure, notch size and notch acuity is described and applied to nickel base superalloy to determine the fatigue notch factor, notch sensitivity index and the probability of forming microstructurally small crack from the notch root. The simulation results obtained from this framework are compared with experimental results and results obtained using existing classical methods for notched polycrystalline nickel base superalloys for the different notch root radii and acuities considered.

A Finite Fracture Mechanics Model for the Prediction of the Notched Response and Large Damage Capability of Composite Laminates

A new model based on Finite Fracture Mechanics (FFMs) has been proposed to predict the open-hole tensile strength of composite laminates [1]. Failure is predicted when bothstress-based and energy-based criteria are satisfied. This model is based on an analytical solution, and no empirical adjusting parameters are required, but only two material properties: the unnotched strength and the fracture toughness. In the present work, an extension of the proposed FFMs model to predict the notched response of composite laminates with notch geometries other than a circular opening [2] is presented and applied to the prediction of size effects on the tensile and compressive notched strength of composite laminates. The present model is also used to assess the notch sensitivity and brittleness of composite laminates by means of versatile design charts and by the identification of a dimensionless parameter designated as notch sensitivity factor. A further extension of the FFMs model is proposed, which takes into account the crack resistance curve of the laminate in the model's formulation, and it is used to predict the large damage capability of a non-crimp fabric thin-ply laminate [3].

Prediction of notch sensitivity effects in fatigue and in environmentally assisted cracking

AbstractSemi‐empirical notch sensitivity factors q have been used for a long time to quantify notch effects in fatigue design. Recently, this old concept has been mechanically modelled using sound stress analysis techniques, which properly consider the notch tip stress gradient influence on the fatigue behaviour of mechanically short cracks. This mechanical model properly calculates q values from the basic fatigue properties of the material, its fatigue limit and crack propagation threshold, considering all the characteristics of the notch geometry and of the loading, without the need for any adjustable parameter. This model's predictions have been validated by proper tests, and a criterion to accept tolerable short cracks has been proposed based on it. In this work, this criterion is extended to model notch sensitivity effects in environmentally assisted cracking conditions.

Fatigue behaviour of notched ADI castings

This work aims at studying the capability of mechanical stress analysis software (ANSYS 12·0) as a non-destructive tool to characterise and quantify the fatigue strength of notched austempered ductile iron (ADI) castings with different radii (from 1 to 3 mm). Castings were made of ductile iron with a chemical composition of 3·55C–2·18Si–0·35Mn–0·022P–0·008S–0·045Mg. The samples were heat treated by austenitising at 900°C for 1 h and then rapidly quenched into two different salt baths at 350 and 400°C for 1 h each. Because the properties of the samples austempered at 350°C were matched with the ASTM standard for ADI alloy grade 2 (1050-700-07), the fatigue strength of the samples austempered at 350°C was first predicted using a mechanical stress analysis software (ANSYS 12·0). To verify these theoretical results obtained by ANSYS 12·0, experimental fatigue tests using rotating bending fatigue machine at high stress regime were performed on the samples austempered at 350°C. The fatigue samples were machined with different radii of 1, 1·5 and 2 mm. The results showed that the predicted fatigue strength by ANSYS 12·0 is very close to the experimental one. In addition, both austempering temperatures of 350 and 400°C showed relatively similar notch sensitivity factor q, and its value decreased with increasing notch radius.

Notch Sensitivity of Poly(Acrylonitrile-Butadiene-Styrene)/Poly(Methyl Methacrylate)/Ethylene Methacrylate Co-Polymer (EMA) Composites

Polymer blends of poly (acrylonitrile-butadiene-styrene)/poly (methyl methacrylate) with ethylene methacrylate copolymer (EMA) were injection molded, and the notch sensitivity of the bends were examined by Izod impact and tensile tests. Investigations revealed that the toughness of ABS/PMMA composites were greatly improved and appeared a linear increase with the addition of EMA. However, the blends also show strong notch sensitivity due to the EMA component but the EMA content seems not a factor responsible for it. Tensile tests of the blends revealed that notches in any depth have great detrimental effects on the elongation at break of the materials, which is not consistent with the calculated notch sensitivity factor (kS) data.

Study on the Notch Strength and Notch Sensitivity of Composite Modified Double-Base Propellants

To obtain the notch strength of the composite modified double base (CMDB) propellant, three-point bending tests on the single-edge U-notched thin plate specimens and uniaxial tensile tests on standard tensile specimens were carried out at 20°C. Experimental data include three parts in different range of the stress concentration factor Kt of specimens. The stress concentration factor Kt of the specimens have a distinct effect on the notch strength in a specific range. When Kt is less than the notch sensitivity factor KbN which is approximately equal to 1.35, the notch strength of CMDB propellant is approximately equal to its fracture strength and independent of the stress concentration factor of test specimens. When Kt is upper than 2.41, the notch strength change to be steady to a proper value which associate with the fracture toughness of the propellant . This shows that the CMDB propellant is insensitive to notch. The tensile test data is used to predict the value of the notch strength and notch sensitivity factor,and the prediction fit well with the test results of the notched specimens in a specific range.

Does notch sensibility exist in environmentally assisted cracking (EAC)?

Empirical notch sensitivity factors q have been used for a long time to account for notch effects in fatigue design. This old concept has been recently modeled using sound mechanical principles to properly quantify the influence of the stress gradient around the notch tip on the fatigue behavior of mechanically short cracks. This model can be used to calculate q values from the basic fatigue resistances of the material, its fatigue limit and its crack propagation threshold, considering all the characteristics of the notch geometry and of the loading. This model predictions have been validated by proper tests, and based on this experimental evidence a criterion to accept tolerable short cracks has been proposed. In this work the mechanical principles that support this criterion are extended to account for notch effects in environmentally assisted cracking problems.

Is notch sensitivity a stress analysis problem?

Semi–empirical notch sensitivity factors q have been widely used to properly account for notch effects in fatigue design for a long time. However, the intrinsically empirical nature of this old concept can be avoided by modeling it using sound mechanical concepts that properly consider the influence of notch tip stress gradients on the growth behavior of mechanically short cracks. Moreover, this model requires only wellestablished mechanical properties, as it has no need for data-fitting or similar ill-defined empirical parameters. In this way, the q value can now be calculated considering the characteristics of the notch geometry and of the loading, as well as the basic mechanical properties of the material, such as its fatigue limit and crack propagation threshold, if the problem is fatigue, or its equivalent resistances to crack initiation and to crack propagation under corrosion conditions, if the problem is environmentally assisted or stress corrosion cracking. Predictions based on this purely mechanical model have been validated by proper tests both in the fatigue and in the SCC cases, indicating that notch sensitivity can indeed be treated as a stress analysis problem.

Notch Sensitivity Factor Determination With Artificial Neural Network For Shafts Under The Bending Stress

Notch, hole, tap and a variety of geometric shapes such as curves or discontinuities can be found with various reasons in the design of Machine Element. Stress is caused by sudden changes in section aggregating. Stress concentration can occur with the reason of material features of size or direction of forces application. This type of stress concentration in the material brings out the effect of notch. Notch impact can lead to distortions and breakage of materials. In this study, the notch sensitivity factor values have been modelled Artificial Neural Networks (ANN) for shafts that is under the influence of bending stress, and the accuracy of the model has been verified by using Statistica software. The model has been developed using Pythia. With this software, the user can be obtained the accurate value by inputing shaft dimension and the applied force without the need for notch sensitivity factor tables and any calculations.

Fatigue Life Prediction Using Simplified Endurance Function Model

A methodology is proposed to apply an endurance function model with a genetic algorithm to estimate the fatigue life of notched or smooth components. The endurance function model is based on stress tensor invariants and deviatoric stress invariants. In the proposed methodology, FEA is used to simplify the application of the endurance function model. Experimental results from published literature are considered for the case studies to evaluate the proposed methodology. The results show that the proposed methodology simplified the application of the endurance function model, particularly by reducing the need for notch sensitivity factors, and the stress invariants can be calculated directly from the stresses at the critical point. The comparison with experimental results shows that, with proper calibration, the model can predict fatigue life accurately.