Notch Stress Analysis Research Articles

Notch stress analysis and fatigue strength assessment of tube flange welded joints under torsional loading

Notch stress analysis and fatigue strength assessment of tube flange welded joints under torsional loading

Numerical study of the influence of weld geometry variations on fatigue life using the notch stress analysis

Idealized geometry is typically used in standards for the fatigue life assessment of welded joints. In the presence of stochastic geometrical variations along the weld, the choice of the idealized geometry is however ambiguous. In the notch stress (NS) method with a fictitious notch radius rref = 1 mm, the FAT 225 curve is derived for welds with relatively good quality in toe profiles. In the NS method with rref = ractual + 1 mm, a lower FAT 200 curve is recommended. Both approaches neglect the stochastic variability in toe radius, toe angle and leg length along the weld. The aim of this paper is two-fold. First, a numerical comparison between both approaches in terms of their predicted fatigue life is performed for a non-load carrying fillet cruciform joints. The results show that the NS method with rref = 1 mm and FAT 225 is substantially more conservative. Second, these methods are enhanced by replacing the deterministic stress concentration factor by a probability distribution computed using Monte Carlo simulation. It is shown that NS with rref = 1 mm and FAT 225 does not predict any substantial influence of the stochastic variability in process parameters since the actual toe radius is not included in the analysis. However, the NS method with rref = ractual + 1 mm and FAT 200 predicts a decrease in fatigue life when uncertainties in geometrical parameters is included. This numerical study paves the way for an experimental validation of the predicted influence of stochastic variability of geometrical parameters based on the stochastic notch stress analysis.

Multi-body simulation with notch stress analysis of an axle assembly

The optimization of mining vehicle rear axle weld joints is a complex procedure. The designs for low-cycle fatigue with peak loads were analyzed using computational models and rig testing. On-road evaluation of high-cycle fatigue was performed with the entire vehicle. The iterative analysis is used in design optimization to minimize design cycle time. In sophisticated fatigue calculations with all affecting factors, FEM is utilized. In fatigue failures using road load data, the present deterministic method yields up to 80% correlations. Some critical failure spots were most likely missed owing to operational variations caused by the randomness and multiaxiality of load transfer in link mechanisms with non-linear elements. The fabricated rear axle housing joints are optimized by comparing damage state estimates using stochastic type and multiaxial equivalent loads obtained using Multibody Simulation. The damage state analysis as MBS input stimulus in FE weld models and bolted designs were compared.

A novel semi-analytical method for notch stress and fatigue strength analysis of tube-flange welded joints

This paper presents a semi-analytic method to rapidly estimate the notch stress and fatigue strength for tube-flange welded joints. Considering the stress singularity effect at the weld toe, the parameters related to geometry and opening angle are simplified as singular intensity factors. The equivalent singular intensity factors can be fitted by the stress distribution rather than the peak stress at the corner. On this basis, the modified notch stress formulas for tube-flange welded joint (TFWJ) under pure bending or torsion load were fitted and verified. Meanwhile, the simple relationships between singular intensity factor, notch stress intensity factor, strain energy density and peak stress were further deduced, separately. The comparison results show that the fatigue assessment parameters calculated by the traditional approaches and the proposed method are in good agreement. Finally, four groups of fatigue data of TFWJs were summarized to verify the simplified assessment formulas.

Notch stress analysis and fatigue strength assessment of tube-flange welded joints under torsion loading

A simple method named singularity length method (SLM) with a key parameter singularity length ‘as’ is proposed to estimate the shear stress distribution at the V-notch corner. For tube-flange welded joints (TFWJs) with 135° weld toe notches, the singularity length ‘as’ is observed to be determined by different geometries and is summarized into concise formulas. A rapid calculation method of the mode III notch stress intensity factor (NSIF K3) without any FEA process is presented based on the SLM. Good agreement is showed between the fine meshed FE, the coarse meshed FE for the strain energy density (SED) and the proposed method. Six fatigue tests data of TFWJs is collected to conduct fatigue strength assessments based on the nominal shear stress and the rapidly-calculated NSIF K3. The results shows the NSIF K3 can be well applied as a fatigue parameter.

Influence of Nonsymmetric Steel Sandwich Panel Joints on Response and Fatigue Strength of Passenger Ship Deck Structures

Present paper investigates the factors contributing to the stress response of steel sandwich panel deck joints when applied into the hull girder of modern passenger vessel. The emphasis is put on the fatigue analysis, which is the critical design criterion in application of these structures to ships. Two types of joints are considered, i.e., a symmetrical and a nonsymmetrical prismatic joint with respect to the geometrical midplane of the sandwich panel. Stiffness properties are derived for the joints in order to enable the modeling of sandwich structures as part of the hull girder finite element model. The influence of sandwich joints to hull girder response is studied. Notch stress analysis is used for the fatigue strength estimation. The applicability of notch stress method for steel sandwich panels is validated with experiments. The investigation shows that the fatigue strength of steel sandwich panels does not depend only on local stress concentration factors at details, but also on the global stiffness of the structural hull girder system, the sandwich panels, and thus the joint response must be taken into account.

Allowable stresses in high-frequency mechanical impact (HFMI)-treated joints subjected to variable amplitude loading

The effectiveness of high-frequency mechanical impact (HFMI) is considered to rely on the existence of compressive residual stresses. To determine when residual stress relaxation occurs, and what the resulting influence on fatigue improvement is, local stress-strain response in as-welded and HFMI-treated weld toes was modelled under different peak stress conditions. Then, effective notch stress analysis was used to correlate these results with available experimental observations. The simulations showed that high stress ratios and compressive peak stresses were critical with respect to residual stress relaxation, as expected. A compressive peak stress of 0.6f y (nominal yield strength) resulted in full residual stress relaxation. The relative fatigue damage calculations and the notch stress analysis indicated, however, that fatigue improvement could be expected even after significant residual stress relaxation. Based on this and previously observed benefit for high stress ratios, an increase in maximum allowable stresses for HFMI-treated welded steel joints is suggested. The maximum stress ratio is proposed to be increased from R = 0.52 to R = 0.7, and the maximum stress range to limit compressive stresses is proposed to be increased from ΔS max = 0.9f y to ΔS max = 1.2f y , which corresponds to S min = −0.6f y for stress ratio R = −1.

Finite element based fatigue assessment of corrugated steel web beams in highway bridges

This paper presents a finite element analysis and its related experimental test of corrugated steel web beams subjected to fatigue loading. A particular focus in this study was set on the fatigue failure arising from web-to-flange welded joints of corrugated steel web beams. Using ANSYS and FE-SAFE software packages, a detailed three-dimensional finite element model which explicitly includes the geometry of the web-to-flange welds along the corrugated web was developed to simulate the test corrugated web beams. The finite element model is verified by comparing with related fatigue experimental test results. The effective notch stress approach was also applied to analyse the web-to-flange welded joint replicating the local critical region in the corrugated web beam. The fatigue strength of the web-to-flange welded joint was evaluated and compared numerically by considering the stress distribution at potential fatigue crack initiation location. The fatigue life of the corrugated steel web beam was assessed numerically by incorporating material S-N relation and employing fracture mechanics approach. The comparison with fatigue test results show that it is possible to expect the fatigue crack failure arising at the weld root or weld toe corresponding to the sections with reference angle using the effective notch stress analysis. The range of these predictions was evaluated by comparing with fatigue test results with good accuracy and can be considered between AASHTO fatigue categories B and B’. The parametric notch stress analysis incorporating the influences of corrugation angle was performed and demonstrates it is possible to expect the fatigue crack failure arising at the weld root or weld toe. Finally, a practical solution for possible fatigue life enhancement of such structure is suggested by decreasing corrugation angle or smoothing the intersection geometry of the corrugated web together with moderate increase of the flange thickness.

Investigations on different fatigue design concepts using the example of a welded crossbeam connection from the underframe of a steel railcar body

For thin-walled steel structures, welded joints often turn out to be the weak spots under cyclic loading. For the dimensioning of welded safety components in vehicle construction, strength concepts are necessary that are well-defined and well-reviewed, in terms of their predictive accuracy. Within the scope of the research results presented here, the applicabilities of the nominal, structural and notch stress approaches have been examined on the basis of different arc welded and cyclic loaded steel structures, taken from the railway sector. In detail, this is a crossbeam connection from the underframe of a railcar body. Different sheet thicknesses in the range 2.7 mm–4 mm in combination with a misalignment lead to an increase of load in the region of the weld seams. Several different components and specimens with critical regions of failure have been tested under cyclic loading with constant amplitude. With the help of strain gauges, the (technical) crack initiation has been determined. A short review of the possibility of obtaining information about the crack initiation by ultrasonic-burst-phase-thermography is also given. The specimens were the basis for the application and evaluation of the different concepts for the assessment of fatigue life. The numerical determination of the nominal, structural and notch stresses has been performed with finite-element models. For a local approach, according to the notch stress analysis, a submodelling technique has been used. The FE-models have been compared with the experimental data by means of optical 3D deformation analysis and strain measurements with strain gauges. Existing weld seam and specimen tolerances have been included through the use of parametric models. Finally the experimental and computational results have allowed the derivation of structural and notch S– N curves for the crack initiation and the rupture of the specimen.

Fatigue strength analysis of a welded railway vehicle structure by different methods

The endurance limit approach with maximum amplitude loading (constant loading amplitude) and the cumulative damage approach with variable amplitude loading are both established methods for the fatigue assessment of the bogie frame of a rolling stock. These methods are presented for the vertical main loading of a bogie frame for a light rail vehicle. Assessments are carried out for the normative load requirements according to the relevant standard EN 13749 [1] and also for a vertical force range spectrum deriving from a multiple body system simulation of this railway vehicle. The multiple body system simulation supplies more realistic loads depending on the actual railway application conditions. These different fatigue assessments allow a comparison of the normative load requirements with realistic load assumptions. In general the stress analysis is based on the nominal stress approach. Additionally, for the area subject to the maximum stress, a notch stress analysis is carried out. The comparison of stress analyses for some selected stress points shows the potential and the advantages of the fatigue assessment with the real loading assumptions and with different evaluation methods.

Statistics of Weld Geometry for Laser-Hybrid Welded Joints and its Application within Notch Stress Approach

During the past few decades the shipbuilding industry has shown an increasing interest in laser welding. In particular, laser-hybrid welding offers special advantages over arc welding such as low levels of welding distortion because of the different welding processes used. In the present study, the influence of weld geometry on notch stresses in butt-welded joints was studied experimentally and numerically using a notch stress approach. The results of hybrid-welded joints were compared to those of laser- and arc-welded joints. In the case of laser-based joints the weld height, weld width and notch depth are the dominant geometrical parameters. The flank angle of the weld has a minor influence, unlike in an arc-welded joint, because of the difference in the weld bead size. The weld dimensions showed a large statistical variation, and this resulted in significant differences in the stress concentration factor values between the critical and mean weld geometries. The analysis of fatigue test results indicated that the statistical variation of the weld dimensions should be included in the notch stress analysis in order to improve the accuracy of fatigue strength prediction.

Round robin study on structural hot-spot and effective notch stress analysis

Within the Network of Excellence MARSTRUCT a round robin was carried out in which three different structural details were assessed by calculating structural hot-spot stresses or in one case the effective notch stresses. The first structural detail deals with the stress increase at thickness steps in plate structures. For two different cases the structural hot-spot stress is determined with different types of models. The second structural detail is the penetration of a longitudinal through a bulkhead with four different hot-spots. The third structural detail deals with the assessment of root failure of single-sided fillet welds. The welded joint of the end connection of a rectangular hollow section member is taken as an example. The relevant stress here is the effective notch stress in the fictitiously rounded notch root. In the paper, the different modelling techniques applied are described. The results are compared with each other and sources of scatter are identified. Finally, recommendations regarding appropriate modelling are derived from the results.

Estimation of the fatigue strength of light alloy welds by an equivalent notch stress analysis

In this work the well known local approach to predict the fatigue strength of sharply notched components, based on the analytic expressions of the local stress field as proposed in literature, is applied to welded joints in aluminium alloys in a simplified form oriented to practical applications. A particular value of the general expression of the local stress field parameter is taken into account, which the fatigue strength depends on. Then a simple model is proposed by the authors in order to estimate such a parameter, based on the calculation of a geometric (or structural) contribution to the local stress field, depending on the overall joint geometry, and a local contribution evaluated by considering a specimen with lateral V-notches characterised by the same weld toe profile and a depth proportional to the weld throat thickness. Doing so, the estimation of the fatigue strength of a welded joint can be reduced to the estimation of the fatigue strength of the equivalent V-notch subjected to a remote stress equal to the structural stress (that can be regarded as a ‘hot spot’ stress). Finally a simple fatigue strength diagram, in the form recently proposed by Atzori and Lazzarin and calibrated on experimental fatigue test results, is proposed, so that one can estimate the fatigue strength of a welded joint, in terms of structural stress at a given number of cycles, as a function of the equivalent V-notch depth. By considering this diagram, the scale effect and the effectiveness of the methods to improve the fatigue strength by smoothing the weld toe radius are also taken into account.

Notch-Stress Analysis by FE Submodeling

This paper presents experiences in detailed finite element analyses of pressure vessel components with respect to load-carrying capacity and fatigue strength. The application of the submodeling technique for shell-to-solid models is discussed.

Notched bend tests on WC-Co hardmetals

Notched bend tests have been performed on a range of WC-Co hardmetals. The notch stress concentration factors were derived from conventional notch stress analysis and by a finite-element method. The introduction of the notch suppressed the initiation of failures from macroscopic defects such as pores and inclusions. The strength values obtained were thus representative of the underlying hardmetal microstructure.

Economy and convergence of notch stress analysis using boundary and finite element methods

AbstractThe BEM is shown to be superior to FEM with respect to economy (man hour and data processing) and convergence (with increasing number of boundary nodes) in the elasic notch stress analysis of compact components.

On the Relationship between Notch Stress Analysis and Crack Fracture Mechanics

On the Relationship between Notch Stress Analysis and Crack Fracture Mechanics

Energy Variations in Notch Stress Analysis

Technical Briefs Energy Variations in Notch Stress Analysis D. M. Parks D. M. Parks Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. 02139 Search for other works by this author on: This Site PubMed Google Scholar Author and Article Information D. M. Parks Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Mass. 02139 J. Appl. Mech. Dec 1979, 46(4): 952-954 (3 pages) https://doi.org/10.1115/1.3424688 Published Online: December 1, 1979 Article history Received: April 1, 1979 Revised: June 1, 1979 Online: July 12, 2010

The determination of the fracture parameters for polymers in impact

AbstractA method of analysis is given by which the critical strain energy release rate Gc for impact tests may be deduced for both Charpy and Izod tests from normal energy measurements. Suitable calibration factors are determined and the method is applied to a range of polymers. Very close agreement is achieved between the Charpy and Izod results except for highly ductile materials for which it was necessary to use a fully plastic analysis. The method is extended to blunt notches and it is shown that the use of a strain energy per unit volume to yielding, together with a blunt notch stress analysis, gives a good description of the results.

Prediction of the Low Cycle Fatigue Life of Pressure Vessels

The bases for ASME Boiler and Pressure Vessel Code, Section III, fatigue evaluation procedures, the fracture mechanics approach to fatigue life analysis, and the notch stress analysis method are reviewed. Fatigue life predictions are compared with the results of materials, model, and full size pressure vessel tests performed for PVRC and AEC. These tests were made in response to the research objectives established by ASME Special Committee to Review Code Stress Basis in 1958. A proposed design procedure based on the notch stress analysis method and experimental results is presented.