Value Of Stress Concentration Factor Research Articles

NUMERICAL STUDY OF GRADUAL CHANGE IN SHAFT DIAMETER AND RELIEF GROOVE RADIUS ON STRESS CONCENTRATION FACTOR

The purpose of this work is to investigate the effect of relief groove radius and the taper in gradual diameter change of shaft on stress concentration factors. Finite element analysis was used to conduct theoretical research in order to reduce the maximum value of stress in stepped shafts. In comparison based on a straight shaft without relief groove, the results show the decrease of taper angle has a significant effect in decrease the values of stress concentration factors. On the other hand, the increase of location of relief grooves from shaft shoulder tends to increase the stress concentration factors values, especially at high taper angle.

Probability of maximum values of stress concentration factors in tubular DKT-joints reinforced with FRP under axial loads

In the paper, the most suitable probability distributions for SCFmax in DKT-Joints stiffened with FRP under axial loading conditions are studied. To this end, 1296 models were generated and then analyzed in the ANSYS to provide five reliable samples. Created FE models were validated using previous laboratory and FE data. Afterward, to predict the appropriate probability distribution models, 12 different kinds of distributions were utilized to check the fit distribution curve to the samples. Next, the accuracy and reliability of the distribution curves were assessed with the help of goodness-of-fit tests, such as the Kolmogorov-Smirnov (KS) and the Chi-squared (CS). The results of the analysis reveal that the Birnbaum-Saunders distribution is the best option. Furthermore, based on the probability graphs, it was concluded that the developed distribution is suitable enough for the given data sets.

Stress Concentration Factors of Concrete-Filled Double-Skin Tubular K-Joints

Tubular joints are important connecting parts of a welded steel tube structure. The S-N curves based on the hot spot stress (HSS) method are often used to evaluate the fatigue life of tubular joints in practical engineering. The stress concentration factor (SCF) is a key parameter to calculate HSS. In this paper, stress concentration tests of hollow-section and concrete-filled double-skin tubular (CFDST) K-joints were carried out, respectively, and then finite element models of K-joints considering the weld were established. The developed models were validated with the experimental results. The influence of key geometrical parameters, such as the diameter ratio of brace to chord β, the diameter to thickness ratio of chord γ, the wall thickness ratio of brace to chord τ, brace angle θ, and hollow section ratio ζ on the distribution and key position of SCFs along the weld toe, was discussed. Parametric studies were conducted to obtain the calculating equations for the SCF values of CFDST K-joints. The results demonstrate that infill concrete can effectively reduce SCFs along the weld on the chord. When the hollow section ratio was reduced to 0.317, the SCF was reduced by 77.2%. Notably, the SCF reduction rate was sensitive to γ and θ, with a decrease observed as γ increased. The hollow section ratio ζ had a less pronounced effect on SCF distribution patterns, but as ζ decreased, the chord’s stiffness improved, suggesting a potential approach to enhance joint performance. The distribution of SCFs is similar for joints of the same type but different geometric configurations. The innovatively integrated hollow section ratio in the CFDST design equation significantly simplifies and enhances the precision of SCF calculations for CFDST K-joints.

Evaluation of Dynamic and Energy parameters of a Tower Crane with a Frequency-Controlled Drive

The purpose of the study is to evaluate the energy parameters of tower cranes when using a frequency-controlled drive mechanism. The relevance of the study lies in the fact that existing tower cranes quickly become obsolete. However, there is an alternative to buying new cranes – the modernization of existing ones with the improvement of their parameters and the scientific justification for increasing the efficiency of work. The following methods are used for research: method of equivalent power and the methods of metal fatigue theory. The main scientific novelty is the approach to assessing the possible increase in the service life of crane elements when using a frequency drive based on the theory of fatigue. Also presented are examples of equivalent power calculations for the working cycles of the turning mechanism with various forms of speed change in acceleration and deceleration modes. Numerical estimates are given for increasing the service life of the main types of welded joints with different values of stress concentration factors. Showing ways to further improve the efficiency of tower cranes and their mechanisms due to more optimal transients. The proposed approaches can be used when choosing the type of drive for the designed crane or to evaluate the economic efficiency of replacing the drive.

Stress concentration factor based design curves for cylinder-cylinder connections in pressure vessels

The results of the parametric analysis of the cylinder-cylinder intersections in pressure vessels, performed in both elastic and plastic regions, are discussed in this study. Besides, the outcomes that contribute to the development of classical solutions in the literature are addressed as design curves depending on stress concentration factors (SCF). To begin with, the maximum stresses for cylinder-cylinder connections were calculated by finite element analysis and SCF values were obtained. In these calculations, external local loads acting on the nozzle centre and internal pressure are the main variables for loading conditions. Following that, different parametric approaches and loading conditions are presented to develop design curves for cylinder/cylinder connections by changing the main geometric parameters, such as cylinder and nozzle radii, and their thicknesses. A new approach is presented using these new curves thus allowing industrial designers to calculate maximum nozzle stresses without the need to undertake a thorough finite element analysis.

Statistical evaluation of tubular joint SCFs from test data and finite element analyses

Stress concentration factors (SCF) derived from both FEA and measurements from laboratory experiments are associated with uncertainties. To understand these uncertainties, SCF values can be determined from a series of tests or possibly also several SCF-values estimated from converged finite element analysis. The challenge is to determine a recommended value for the SCF based on these tests or analysis, ensuring that the resulting SCF along with the SN-curve meets the code required 2.3% exceedance probability. In this paper, structural reliability analysis (SRA) methods are employed to model the combined uncertainty of the parameters representing the SN-curve and the measured SCFs from experimental test joints. Based on this analysis, the SCF that, when paired with the design SN-curve, provides the minimum fatigue life is established. From this analysis, a method to provide characteristic values of the SCF is suggested. Finally, FEA of the same detail, with and without modelling the weld, using both first and second-order elements are performed. From these analyses the SCF is estimated using linear extrapolation and direct extraction. Based on these findings and their comparison to the characteristic SCF, a suggested method to extract SCFs from FEA is provided.

An Artificial Neural Network Model for the Stress Concentration Factors in KT-Joints Subjected to Axial Compressive Load

Stress concentration factor (SCF) is usually used to estimate the fatigue life of an offshore joint. Historically, parametric equations were used to estimate SCF based on a statistical analysis of experimental and finite element analysis (FEA) results, to reduce cost and time. These equations give the SCF at the saddle/crown position for simple joints and basic load cases. However, for modified or defective joints, the location of the maximum SCF can change. In such circumstances, the single-point SCF equation cannot be used to estimate the maximum value of SCF, as its location may have changed from saddle/crown. To our knowledge, there are no general expressions to estimate SCF around the brace axis accurately. As artificial neural networks (ANN) can approximate the trend of complex phenomena better than conventional data fitting, a mathematical model based on ANN is proposed to estimate SCF based on the weights and biases of trained ANN. Nine hundred thirty-seven finite element simulations were performed to generate SCF data for training the ANN. This ANN was used to model an empirical equation for SCF. The proposed empirical model can estimate SCF around the brace axis with less than 5% error. The current study provides a roadmap to using FEA and ANN for empirical modeling of SCF in tubular joints, and this approach can be applied to any joint type, with or without design modification or damage. Once a database of similar equations is available, it can be utilized for quickly estimating SCF instead of costly experimentation and FEA. Optimization of the ANN can further improve the accuracy of the developed mathematical model.

Determination of Stress Concentration Factor for a Rectangular Bar with Fillet Under Axial Loading: An Artificial Neural Networks Approach

Using computer techniques, stress concentration factors from the graphs can be converted into numerical values. Stress concentration factor values were collected in a database and an Artificial Neural Network (ANN) model can be developed for improving and extending the database. ANN model provides accuracy in obtaining the stress concentration factor values.

Determination of Stress Concentration Factor for a Stepped Bar Under Bending Loading: An Artificial Neural Networks Approach

Even today, charts and formulas derived from experimental determinations are used to obtain the stress concentration factor.Stress concentration factors from charts can be converted into numerical values using computational techniques. Stress concentration factor values were collected in a database and an Artificial Neural Network (ANN) model can be developed for improving the database. ANN model provides accuracy in obtaining the stress concentration factors. Using the static stress concentration factor for a stepped bar under a bending load we can quantify the impact of notches in fatigue.

On the Verification of Finite Element Determinations of Stress Concentration Factors for Handbooks

Abstract Here we offer an approach for being reasonably sure that finite element determinations of stress concentration factors are accurate enough to be included in engineering handbooks. The approach has two contributors. The first consists of analyzing a stress concentration on a sequence of systematically refined meshes until the error estimates of ASME have that sufficient accuracy has been achieved. The second consists of constructing a test problem with an exact and somewhat higher value of its stress concentration factor, then analyzing this test problem with the same sequence of meshes and showing that, in fact, sufficient accuracy has been achieved. In combination, these two means of verification are applied to a series of U-notches in a plate under tension. Together they show that it is reasonable to regard finite element values of stress concentration factors on the finest meshes as being accurate to three significant figures. Given this level of accuracy, it is then also reasonable to use the approach to verify other existing stress concentration factors and resolve any discrepancies between them, as well as to verify new stress concentration factors.

Stress distribution in an infinite plate with discontinuities like elliptical or circular hole by boundary force method

This paper deals with the boundary force method to determine the stress distribution in an infinite plate subjected to uni-axial tension having elliptical or circular hole. The elasticity solution for a point force in an infinite plate is used as the fundamental solution. The boundary conditions are satisfied in terms of the resultant forces. Stress distribution obtained by boundary force method is validated against the results from analytical equations. Traction free boundary condition is weakly satisfied. Hoop stress closely follow the results from analytical equations (AE). Accurate values of stress concentration factor are computed using boundary force method for different values of ratio of semimajor axis to semiminor axis.

Influence of Different Dapped-End Reinforcement Configurations on Structural Behavior of RC Dapped-End Beam

Severe damage or collapse of reinforced concrete dapped-end beams (RC-DEBs) may occur during the service life. The collapse of the Concorde overpass structure in Laval, Quebec, Canada, in 2006 revealed the causes of collapse, i.e., insufficient shear strength (no stirrups), misplacement of hanger reinforcement, etc. In addition, the inspection report of RC half-joint bridges in England until 2018 expressed that damages or failures of half-joint structures can be attributed to the poor condition of structures or non-compliant reinforcement detailing. These conditions exhibited how important it is to understand the proper detailing of dapped-end reinforcement. To date, some studies have performed investigations on the effect of inadequate dapped-end reinforcement on the structural behavior of DEBs. However, the results of the research to date were not yet complete enough to disclose the role of each group of dapped-end reinforcement in resisting the working load. Therefore, this study was carried out to investigate the main role of each group of dapped-end reinforcement separately on the structural performance of RC-DEBs. Eight large-scaled RC-DEBs (with sizes of 1800 mm length, 120 mm width and 250 mm height) were prepared, cast and cured. All DEB specimens were tested under the three-point loading up to failure. To localize the effect of shear failure, the shear span-depth ratio (av⁄d) of 1.43 was set. Test results exhibited that arrangement of a specific group of dapped-end reinforcement separately affects the structural performance of DEBs significantly. The diagonal reinforcement (DR) group was found to be more effective than the vertical hanger reinforcement (HR) group. The failure load capacity of the DR group (DEB-18) achieved 0.29 times that of the control beam (DEB-3). Meantime, the nib flexure reinforcement (NFR) group demonstrated the most important role in the structural performance of DEBs compared to other dapped-end reinforcement groups. The failure load capacity of the NFR group (DEB-39) reached 0.62 times that of the control beam, while rupture deflection of the NFR group also exhibited the highest value than other groups, i.e., 0.62 times that of the control beam. In addition, analysis results of rosette strain gages (RSGs) data indicated that regions near to re-entrant corner and its vicinity experienced the highest stress concentration factor (SCF) compared to other places of the beams. These regions were more susceptible to experiencing the first crack, progressive crack, damage or failure first than other regions of DEBs. The greater the value of SCF, the greater the probability of collapse occurring in the related structural elements, which is also followed by a lower failure load capacity. DEB-1 (without dapped-end reinforcement) has the highest SCF (205.68), and the lowest failure load capacity (12.58 kN), whilst DEB-3 (with the complete dapped-end reinforcement) has the lowest SCF (79.62), but the highest failure load capacity (105.26 kN). Obviously, DEB-3 can withstand the working load properly. Its adequate dapped-end reinforcement is able to accommodate and distribute the high stress flows in the dapped-end region properly, which causes the SCF value to decrease.

A numerical study on tensile stress concentration in semi-ellipsoidal corrosion pits

Pitting corrosion is a common cause of concern for steel structures in an offshore environment. As geometric stressconcentrating features, corrosion pits can potentially act as fatigue crack initiation sites. The severity of a pit can be analyzed based on its geometric characteristics, and the loading and boundary conditions of the component. In this study, the stress distribution in and around a semi-ellipsoidal pit in a plate subjected to (remote) uniaxial tension is investigated using finite element analysis. The investigated characteristics include the width, length and depth of semi-ellipsoidal pits (2b, 2c and a, respectively); the remote load acts parallel to the pit length. A parametric study was conducted with a focus on normalized parameters b/c, a/t and a/2c, and their effect on the stress concentration factor (SCF). The considered value ranges for b/c, a/t and a/2c were 0.1 to 1, 0.01 to 0.2 and 0.125 to 1.5, respectively. Within the range of values for each parameter, SCF did not vary significantly with changes in a/t and increases for increasing a/2c and b/c values. The maximum value of SCF is obtained for the sharpest pit with a circular mouth (a/2c = 1.5 and b/c = 1).

Modelling on stress redistribution around broken fibers for fiber reinforced plastic with poor fiber distribution uniformity

AbstractIn order to calculate stress redistribution after a fiber breaking for unidirectional fiber reinforced plastic (FRP) with practically poor fiber distribution uniformity, a new and efficient FE model is developed with high computation efficiency. Based on the proposed FE model, the stress concentration factor (SCF) of intact fibers around a broken fiber is investigated for unidirectional FRP. It is observed that the SCF depends heavily on the local fiber volume ratio (FVR), and a modified analytical SCF model is proposed which takes into account the variation of local FVR. It is proved that the modified analytical SCF model can provide SCF values with much better accuracy for FRP with poor fiber distribution uniformity. The modified analytical SCF model would be very useful for accurate prediction of progressive fiber breaking in FRP.

Stress Concentration Factor in vessels with circular crosshole: Continuous parameters analysis

In this paper, a parametric study of the Stress Concentration Factor (SCF) has been carried out in cylindrical pressure vessels with circular holes. A three-dimensional finite element analysis has been carried out performing a variation of dimensionless parameters (thickness ratio, size ratio and aspect ratio) exploring a wider range than other investigations. It is observed that the maximum value of the SCF increases as the hole size ratio and the aspect ratio increase, although the location of the maximum SCF is located from the internal area of the vessel to the external part depending on the geometric configuration, defining thus three differentiated zones. Additionally, in the final part of the document, a fit model is defined to determine the value of the maximum SCF for different continuous values of the defined dimensionless parameters. This model allows to quickly calculate or locate from a contour map the maximum value of SCF for a specific geometry of pressure vessel.

Experimental study of hot spot stress for three-planar tubular Y-joint: I. Basic loads

Various tubular joints of offshore wind turbines (OWTs) have seen rapid development in the past decades. However, experimental studies on multiplanar tubular joints have mainly been underexplored. This study designed and constructed a multiplanar loading experimental system for multiplanar tubular joints. A model test was performed using this system to investigate the hot spot stress (HSS) of a three-planar tubular Y-joint, which is critical for the fatigue design of a tripod substructure. The HSS distribution along the weld seams under the 12 basic load cases was obtained from the test analysis. The geometric stresses at the key positions of the chord and brace sides were obtained and analysed. The peak values of stress concentration factor (SCF) were obtained and compared with those calculated using the method recommended by the codes. An indirect method that explicitly considers the interaction between multiple braces was proposed and verified to calculate the SCF distribution of multiplanar tubular joints.

Effects of Size Parameters of Stepwise Corrosion Pit on Stress Concentration of Steel and Its Computation Model Establishment

Stepwise corrosion pit (SCP) nucleated in late corrosion period can make corroded steel surface more irregular, and lead to the severe stress concentration, even failure of steel member, so the stress concentration caused by SCP needed to be carefully investigated and studied. In this work, a non-contact 3D scanner was employed to measure the profile measurements of corroded steel specimens produced from an artificially accelerated corrosion test. The corrosion pitting parameters of SCP were surveyed and used for statistical analysis. And then the effects of pitting parameters on stress concentration were systematically analyzed by means of the finite element simulation. The results showed that the stress concentration caused by SCP was the most obvious on the corroded steel surface compared with any other type of corrosion pit, and the stress concentration factor (SCF) relied on all of the pitting parameters of SCP, of which the weights were varied depending on the type of SCP (such as bilateral stepwise pit (BSP), partial bilateral stepwise pit (PSP) and unilateral stepwise pit (USP)). For all kinds of SCP, each pitting parameter had a different influence on SCF, and the corresponding weight was also different. So, a calculation model (written as SCP-SCF) was established to calculate SCF by using the least square method, based on the relationships between SCF and pitting parameters of SCP. By contrast, it was found that the error between the theoretical value of SCF calculated by the SCP-SCF method and the true value obtained by the FEM with the actual corroded surface was within 5%.

Influence of Stress Concentration Factor due to Scallop Form on the Wrang Plate Stucture

The presence of opening in construction is unavoidable for the purpose of reducing stress. A small opening at the construction serves as access to continue the installed construction that runs through the web or girder. However, the presence of the hole also creates an unavoidable problem, the concentration of stress in the area around the hole that will gradually reduce the strength of the ship's construction. Stress concentration occurs due to changes in geometry, causing the flow of stress initially uniformly driven and following the existing geometry. This analysis aims to determine the value of stress concentration factors on the wrang plate due to variations in the shape of scallops. The research method is performed numerically using finite element analysis to find variations in the model with the lowest stress concentration factor. This variation consists of 3 different scallops models with 2 load, drag and press conditions. The values of stress concentration factors are grouped into 3 modes according to mechanical fractures in press loading conditions. Based on the analysis of panel models with compressed loads, it can be seen that model III has the smallest stress concentration factor value in case modes I and III but for mode II the value of the smallest stress concentration factor in model II.

Concentration of stresses near the hole in contact with rigid cylinder in composite plate, taking into account lateral clearances

Problems. When designing bolted joints (BJ), it is necessary, in particular, to carry out their verification calculations for strength. At the same time, it is desirable to use express analysis: calculations by simple formulas of sufficient accuracy. For BJ of plates made of layered polymer composite materials (PCM), the problem has not yet been solved.
 The aim of the study. The task is to test the accuracy of three known formulas for quick calculation of the value of the stress concentration factor (SCF) in zone of contact of bolt-hole with a rigid cylinder (bolt). The study was carried out on contrasting examples of materials and schemes of reinforcement of plates made of PСM, taking into account possible clearance between bolt and hole in the real range: from zero to 1% of diameter.
 Methodology of implementation. Numerical calculations were made using the finite element method (contact problem) for the BJ of plates made of layered PCM. 3D orthotropy of each monolayer was provided. Three simple formulas of express analysis were tested. The results are summarized in the tables and many illustrations are given.
 Research results. Numerical estimates of depending of the SCF in zone of the surface of the bolt-hole from considered factors are obtained. The factors are the material characteristics, the schemes of reinforcement of plates made of layered PСM and the values of the clearance between bolt and hole in the plates, as well as the accuracy of the considered formulas.
 Conclusions. Changing the material and the scheme of reinforcement of plate made of layered PСM leads to a significant change in the values ​​of maximum stresses and SCF in zone of the bolt-loaded hole in the weakened by hole cross section of a plate. Considered formulas of the express analysis have insufficient accuracy for consideration of contrast properties of materials and schemes of reinforcement of a plate. Changing size of clearance between bolt and hole in the range from zero to 1% of the diameter leads to relatively small changes in SCF: up to 10% maximum. Additional research is needed.

Probabilistic analysis of the SCFs in tubular T/Y-joints reinforced with FRP under axial, in-plane bending, and out-of-plane bending loads

The stress concentration factor (SCF) is one of the most important parameters in the fatigue reliability analysis of tubular offshore structures. This parameter exhibits remarkable scatter which calls for more emphasis in accurately computing the SCFs for determining the fatigue life. As per the authors’ knowledge, no study has been conducted on the probability distribution of SCFs in tubular joints with FRP. Therefore, in this study, results of performing 288 FE analyses on 96 T/Y-joints with FRP have been used to propose a probability distribution model for SCFs in the FRP-reinforced joints subjected to axial, IPB, and OPB loads. According to the T/Y-connection FE models which were validated with several experimental tests, a set of SCF sample databases was generated. 11 various probability density functions (PDFs) were fitted to the relative frequency histograms of the SCF samples. For determining the parameters of every distribution, the maximum likelihood method was applied. Evaluating the goodness-of-fit according to the Chi-squared and Kolmogorov-Smirnov tests indicated that the Weibull distribution is the best one for the maximum SCF values in tubular T/Y-connections retrofitted with FRP under axial load. Also, the Gamma distribution was set as the governing probability function for T/Y-joints with FRP under IPB and OPB loads. In the final step, five fully defined PDFs were proposed for the maximum weld SCFs of in T/Y-joints with FRP under three different types of loadings.