Fatigue Limit Diagram Research Articles

Fatigue reliability analysis of bogie frames considering parameter uncertainty

With the increasing service life of bogie frames, the risk of fatigue failure becomes significant, making fatigue reliability analysis crucial for ensuring operational safety. However, accurately analyzing fatigue reliability presents a significant challenge with uncertain factors such as load fluctuations, unstable material shaping, and dimensional manufacturing deviations. To address this, this paper establishes a comprehensive active learning reliability framework based on surrogate models, enabling high-fidelity modeling and precise fatigue reliability analysis of welded frames under parameter uncertainty. The material utilization method was developed using APDL for secondary development to efficiently evaluate frame fatigue failure indicators. The effectiveness of this method was validated by combining the improved Goodman-Smith fatigue limit diagram and test bench fatigue tests, which helped identify the locations on the frame most prone to fatigue fractures. An Atom Search Optimization-BP Neural Network surrogate model was established with the objective of maximum material utilization, and the fatigue reliability of the bogie frame was obtained by combining the active learning function and the Monte Carlo method. The results show that the uncertainty design parameters greatly impact the fatigue reliability of critical welded structures. The proposed method improves the accuracy and efficiency of the fatigue reliability analysis of the bogie frame.

Fatigue Limit Diagram for Ferritic Stainless Steels Subjected to Excess Deformation under Fixed Maximum Stress Conditions

Fatigue Limit Diagram for Ferritic Stainless Steels Subjected to Excess Deformation under Fixed Maximum Stress Conditions

A method for modifying octagonal Goodman–Smith fatigue limit diagram

PurposeIn order to extend the application of the original octagonal Goodman–Smith fatigue limit diagram, which is commonly used for the evaluation of structure fatigue stress in engineering, a modification of it is proposed for the structure made of S355 steel (commonly used in high-speed electric multiple units (EMUs) bogie frame).Design/methodology/approachThe modification is made based on Deutscher Verband für Schweißen und verwandte Verfahren e. V. (DVS) 1612 standard and the γ-P-S-N curve, with consideration of the fatigue evaluation requirements of different survival rates and confidence levels. The verification of the modification is performed for three welded joints and for the comparison with the experimental data.FindingsThe results indicate that the design survival rate, the design safety margin and the fatigue stress evaluation of welded joint types are all improved by using the modified diagram.Originality/valueThere are relatively few studies on modifying octagonal Goodman–Smith fatigue limit diagram. In this paper, a modified diagram is proposed and applied in order to ensure the safety and durability of key welded structures of rail vehicles.

An improved Goodman-Smith fatigue limit diagram for railway vehicle base metals and welded structures

In this paper, an improved method of Goodman-Smith (GS) fatigue limit diagrams for metallic materials of railway vehicles is proposed. Firstly, this method is based on the three traditional GS curves described in the TB/T 3548–2019 standard, coupled with the S-N curve model from the British BS7608 standard, resulting in improved GS curves applicable to different structural configurations. Within this framework, the survival probability p is introduced as a controllable parameter into the improved GS diagrams, and based on this, the conversion equations of yield strength under different cyclic characteristics applicable to different structures are given for the base metal and the welded structure, which are diametrically opposed in terms of the influence of stress ratios, respectively. Finally, fatigue simulation tests were conducted on the bogie frame to verify and validate the improved GS diagrams. It was found that, while meeting the required criteria, the safety margin at the same survival probability reduced to 0.58 times of the original maximum position. Additionally, the coordinates of the inflection points of the improved GS diagrams for different bogie frame structures and their corresponding design criteria were provided.

A New General Fatigue Limit Diagram and Its Application of Predicting Die Fatigue Life during Cold Forging.

Traditional fatigue fracture theory and practice focus principally on structural design. It is thus too conservative and inappropriate when used to predict the high-cycle fatigue life of dies used for metal forming, especially cold forging. We propose a novel mean stress correction model and diagram to predict the high-cycle fatigue lives of cold forging dies, which focuses on the upper part of the equivalent fatigue strength curve. Considering the features of die materials characterized by high yield strength and low ductility, a straight line is assumed for the tensile yield line. To the contrary, a general curve is used to represent the fatigue strength. They are interpolated, based on the distance ratio, when finding an appropriate equivalent fatigue strength curve at the mean stress and stress amplitude between the line and curve. The approach is applied to a well-defined literature example to verify its validity and shed light on the characteristics of die fatigue life. The approach is also applied to practical forging and useful qualitative results are obtained.

Research on Strength Test Technology and Fatigue Evaluation Method of Bogie Frame and Body Bolster

Bogie frame and body bolster are of vital importance to the reliable operation of the rolling stocks. There are two kinds of test methods for bogie frame and body bolster. One is separate test, and the other is joint test. To effectively detect the strength performance of bogie frame and body bolster as well as to improve the test efficiency, we adopted the method of joint test, and designed the test plan according to the standard. The strength test of bogie frame and body bolster is carried out where load analysis is studied and applied. The structural performance of bogie frame and body bolster is evaluated by means of Goodman fatigue limit diagram.

Dependence of fatigue limit on stress ratio and influence of cyclic stress on shear strength for an adhesive lap joint

ABSTRACT The improvement in adhesion technology for joining different types of materials has led to expectations of weight reduction in cars and commercial vehicles. Various levels of stress and stress ratios are loaded onto the joints of such transport vehicles. Therefore, the fatigue shear strength of an adhesive lap joint is important. This study is related to the fatigue properties of structural adhesive joints. Lap-joint specimens using epoxy adhesive were prepared, and fatigue tests with four different stress ratios were conducted. Subsequently, the fatigue limit diagram was plotted, and the effect of stress ratio on the fatigue limit was investigated. Moreover, the strength of the specimens subjected to various cyclic stress levels was investigated systemically. With cyclic shear stress, the influence of the shear stress amplitude on the resistance to fatigue failure was more significant than that of the number of cycles. The specimens that endured the fatigue tests maintained approximately the same shear strength as that of the as-received specimens. The findings of this study can provide important guidance for the design of a car body.

Safety Evaluation for Pure Titanium by Lock-in Infrared Thermography

The lock-in infrared thermography has been applied to an estimation of fatigue limits at several stress ratios, i.e., R=-1, 0.05, and 0.5, for commercially pure titanium (CP-Ti JIS grade 2) at room temperature. In the present study, frequencies were1 Hz and 4 Hz at R=-1, and 7 Hz at R=0.05 and 0.5. Tests at R=-1 showed a negligible frequency dependency of a fatigue limit of 250 MPa. Other tests at R=0.05 and 0.5 showed respective fatigue limits of 123 MPa and 48 MPa. Tensile tests were performed to obtain a tensile strength and a proof stress. A fatigue limit diagram of the sample was plotted using the above values, showing a violation of the mod. Goodman line and the Soderberg line. Next, the diagram was revised using a stress starting plastic deformation shown by creep tests. It revealed a safety area of the new diagram is 35% smaller than that of the conventional safety standards.

Evaluating the fatigue limit of metals having surface compressive residual stress and exhibiting shakedown

AbstractThe objective of the study described in this article is to evaluate the effect of shakedown of surface compressive residual stresses introduced by shot peening on fatigue limit of stainless steel. First, the tension‐compression fatigue tests were conducted on ASTM CA6NM specimens under controlled load and displacement conditions to acquire a fatigue limit diagram under various compressive mean stress. The results showed that shakedown of negative mean stress occurs under controlled displacement. We then carried out in‐plane–bending fatigue tests under controlled load conditions on welded ASTM 309 stainless steel specimens with surface compressive residual stress introduced by ultrasonic shot peening. The results provide a fatigue limit of 415 MPa, which agrees with the value of 404 MPa calculated based on a modified Goodman line considering shakedown. Therefore, it is suggested that the surface layer is restricted by the internal bulk that creates controlled displacement conditions and the shakedown of surface compressive residual stress occurs.

Strength Evaluation of a Bogie Frame by Different Methods

Some crucial loads that current strength design specifications have not taken into account are also considered when assessing the strength of a bogie frame. Calculation methods of these loads come from load analysis. Finite element simulation and fatigue test rig have been used to assess static strength and fatigue strength of a bogie frame. In addition to the two methods, actual running test is also used to assess bogie frame fatigue strength. In finite element simulation method, endurance limit and modified Goodman fatigue limit diagram are two important tools to judge whether fatigue strength of a bogie frame meets requirement. In actual running test method, Miner linear cumulative damage rule is used to assess bogie frame fatigue strength.

Fatigue Strength Analysis of Bogie Frame In Consideration of Parameter Uncertainty

In this paper, a fatigue strength analysis approach based on Goodman-Smith fatigue limit diagram （GSFLD） and reliability theory is proposed to solve the problem that the traditional fatigue strength analysis of bogie frame is too conservative, considering the parameter uncertainty in engineering practice. Firstly, according to UIC615-4, EN13749 standard and GSFLD, the fatigue strength of the frame is calculated. The experimental results are compared with the simulation data to determine the location of the higher fatigue strength as the control point for the strength evaluation. Secondly, the parametric model of the frame is established by APDL language, and the D-optimal experiment design of uncertainty parameters is carried out. The polynomial response surface function with the mean stress and stress amplitude of the control point as the objective is established. The control points under the influence of uncertainty parameters are obtained by importance sampling method. Finally, the functional expression of GSFLD without considering the safety factor is derived, and the fatigue strength reliability of control point is calculated. The results of this study not only reveal the influence of parameter uncertainty on fatigue strength, but also demonstrate a need of developing new evaluation methods to accommodate fatigue analysis.

Fatigue Strength Analysis and Fatigue Damage Evaluation of Roller Chain

This paper deals with the roller chain commonly used for transmission of mechanical power on many kinds of industrial machinery, including conveyors, cars, motorcycles, bicycles, and so forth. It consists of a series of four components called a pin, a bush, a plate, and a roller, which are driven by a sprocket. To clarify the fatigue damage, in this paper, the finite element method (FEM) is applied to those components under three different types of states, that is, the press-fitting state, the static tensile state, and the sprocket-engaging state. By comparing those states, the stress amplitude and the average stress of each component are calculated and plotted on the fatigue limit diagram. The effect of the plastic zone on the fatigue strength is also discussed. The results show that the fatigue crack initiation may start around the middle inner surface of the bush. As am example, the FEM results show that the fatigue crack of the inner plate may start from a certain point at the hole edge. The results agree with the actual fractured position in roller chains used in industry.

Study on Fatigue Design Method of an Engine Component Produced by Flake Graphite Cast Iron for Different Loading Modes and Mean Stresses

In order to improve reliability of an automotive engine, a fatigue design method was studied based on the fatigue mechanisms in flake graphite cast iron. In the present study, fatigue test specimens were cut from an actual engine component. The material used showed nonlinear behavior in stress–strain relationship from lower stress level during tensile testing. Rotating bending fatigue testing and axial load fatigue testing were performed. Fatigue crack initiation and propagation behavior were observed during the fatigue tests by a replication technique. Fatigue cracking initiated from the tip of flake graphite in early stage of the total fatigue life when the applied stress was higher than the fatigue limit. On the other hand, fatigue cracking was not observed in the specimen tested with applied stress below the fatigue limit. The threshold stress intensity factor obtained with a small surface crack was lower than that obtained with a through-thickness crack. Fatigue limits under various loading conditions such as bending loading and axial loading were predicted well based on fracture mechanics using the $$ \sqrt {\text{area}} $$ parameter. Threshold stress intensity factor for a small surface crack and the maximum graphite size assumed as an initial crack were used for the prediction. Axial load fatigue tests with different stress ratios were performed. The fatigue limit diagram obtained by the fatigue tests did not follow the modified Goodman relation. On the other hand, fatigue limits prediction based on fracture mechanics approach showed good agreement with fatigue limit obtained with fatigue tests in a wider range of mean stresses σmean varying from − 150 to 50 MPa, in negative stress ratio. In case of σmean higher than 50 MPa, in a positive stress ratio, a smaller effect of stress ratio in the fatigue limit diagram was observed. It was considered that this phenomenon could be explained by the lower effect on the crack closure in a small surface crack initiated from the tip of graphite flake and also influence of local plastic behavior of the matrix around the tip of graphite flake. It can be summarized that the fracture mechanics approach is an effective way to predict fatigue limits of an engine component produced by flake cast iron in different loading conditions and in wider range of mean stress conditions.

Effect of surface compressive residual stress introduced by surface treatment on fatigue properties of metallic material

This study considers shakedown in evaluating the fatigue limit of metals with compressive residual stress at the surface. We begin by applying tension-compression fatigue tests to ASTM CA6NM under conditions of controlled load and displacement to obtain fatigue limit diagram in compressive mean stress. The results imply that shakedown occurs under the condition of controlled displacement, therefore, shakedown should be considered when evaluating the fatigue limit of metals with compressive residual stress at the surface.

Estimation of fatigue limit diagram for various materials using infrared thermography

Estimation of fatigue limit diagram for various materials using infrared thermography

Establishment of simple evaluation method of fatigue limit diagram

Establishment of simple evaluation method of fatigue limit diagram

GS0210-269 ハイテンスポット溶接部の疲労強度 : 2. 切欠き部の疲労限度線図

The spot weld of high tensile steel does not improve as base metal strength. The previous study has investigated that a stress Intensity Factor mixed mode (mode I and mode II) can evaluate the fatigue strength. However, influence of residual stress is still not obvious which is important for the design of fatigue or spot weld conditions. Therefore, this study accomplish to clarify the fatigue limit diagram of notched specimen to evaluate fatigue strength of spot weld toe. Then, it become obvious that the compressive residual stress make extensive improvement of the fatigue strength.

熱延高張力鋼板におけるシャー切断面の疲労強度に関する研究

For application of the high-strength steel plate to automobile chassis parts, it is important to reserve the fatigue reliability. In the manufacturing of automotive parts from a steel sheet, the shear cutting process with a die is commonly used. Although the process is economic, it has a drawback that fatigue cracks may initiate from the shearing edges. Therefore, in terms of the reliability of parts, it is necessary to evaluate the influence of shearing edges on the fatigue strength. In this paper, fatigue experiments are conducted on the specimen of high-strength steel sheet with the shearing edge and the influence factors such as the residual stress and surface roughness are examined. As a result, the experiments elucidate that the residual stress has a major influence. The fatigue limit of the shearing edge can be estimated using the residual stress re-distributed by fatigue and fatigue limit diagram, and a method for predicting the S-N curve of shear cutting surface is proposed on the basis of the estimation.

Fatigue Strength Simulation of Boom System Structure of Pump Truck

The motion equation of boom system of pump truck carrying concrete flow is set up based on the coupled vibration theory of cantilevered pipe and the finite element theory. Dynamic stress history of boom system with parameters of dip angle α=0°is simulated combining MATLAB simulation analyses with ANSYS finite element model. The feasibility of this method is verified through field experiment. Stress histories are simulated by adjusting parameter of dip angle as follows: α=20°,52°and 80°.Great stress points are painted on the Goodman Fatigue Limit Diagram measured by experiment. And then fatigue strength assessment of boom system is done. The research method can be used for the design calculation of similar products.

Evaluation of local fatigue strength in spot weld by small specimen

ABSTRACTIt has been reported that high strength steel sheet cannot improve fatigue strength of components with a spot weld. The purpose of this study is to discuss the dominant factors on the fatigue strength of spot weld in order to clarify the reasons. A new fatigue testing technique is developed for a small specimen with a total length of less than 3 mm, and the local fatigue strength of heat‐affected zone (HAZ), which is the crack initiation site in the joint, in a mild steel sheet (270MPa‐grade) and a high strength steel sheet (590MPa‐grade) are evaluated by this technique. The fatigue strength of HAZ is almost equal in both steels although the tensile strength of the 590MPa steel is higher than that of the mild steel. The stress in the tensile‐shear spot‐welded joint under cyclic loading and the residual stress by the spot‐welding are evaluated by finite element analyses. The residual stress is tensile in both steels. However, the plastic deformation takes place in the joint of the mild steel and this releases the residual stress. On the other hand, the stress in the 590MPa steel is elastic and the residual stress decreases the allowable alternating stress. The stress under the condition of the experimental fatigue limit of the joint considering the residual stress coincides well with the fatigue limit diagram of HAZ, which means that the fatigue limit of the joint is determined by the fatigue limit of HAZ and the residual stress.