Statistical Estimation of Duplex S-N Curves

2015 ◽  
Vol 664 ◽  
pp. 285-294 ◽  
Author(s):  
D.S. Paolino ◽  
A. Tridello ◽  
G. Chiandussi ◽  
Massimo Rossetto
Keyword(s):  
Parameter Estimation ◽  
Fatigue Life ◽  
Fatigue Limit ◽  
Failure Mode ◽  
Failure Modes ◽  
Statistical Parameter ◽  
Experimental Tests ◽  
Unknown Parameters ◽  
Likelihood Principle ◽  
Number Of Cycles

In recent years, experimental tests investigating properties of materials in gigacycle regime have suggested modifications to well-known statistical fatigue life models. Classical fatigue life models based on a single failure mode and by the presence of the fatigue limit, have been integrated by models that can take into account the occurrence of two failure modes (duplex S-N curve).Duplex S-N models involve a number of unknown parameters that must be statistically estimated from experimental data. The present paper proposes a simplified and automated procedure for statistical parameter estimation. The procedure is applied to experimental datasets taken from the literature. Parameter estimation is carried out by applying the Maximum Likelihood Principle and by taking into account the possible presence of runout specimens with unequal number of cycles. The application of the procedure permits to estimate different key material parameters (e.g., the characteristic parameters of transition stress and fatigue limit), as well as to statistically predict the failure mode of each tested specimen.

On the Critical Resolved Shear Stress and its Importance in the Fatigue Performance of Steels and other Metals with Different Crystallographic Structures

2022 ◽  
pp. 37-65
Author(s):  
M. Mlikota
Keyword(s):  
Shear Stress ◽  
Fatigue Life ◽  
Fatigue Limit ◽  
High Fatigue ◽  
Steel Aisi ◽  
Crystallographic Structures ◽  
Face Centered ◽  
Set Up ◽  
Number Of Cycles ◽  
Critical Resolved Shear Stress

This study deals with the numerical estimation of the fatigue life represented in the form of strength-life (S-N, or Wöhler) curves of metals with different crystallographic structures, namely body-centered cubic (BCC) and face-centered cubic (FCC). Their life curves are determined by analyzing the initiation of a short crack under the influence of microstructure and subsequent growth of the long crack, respectively. Micro-models containing microstructures of the materials are set up by using the finite element method (FEM) and are applied in combination with the Tanaka-Mura (TM) equation in order to estimate the number of cycles required for the crack initiation. The long crack growth analysis is conducted using the Paris law. The study shows that the crystallographic structure is not the predominant factor that determines the shape and position of the fatigue life curve in the S-N diagram, but it is rather the material parameter known as the critical resolved shear stress (CRSS). Even though it is an FCC material, the investigated austenitic stainless steel AISI 304 shows an untypically high fatigue limit (208 MPa), which is higher than the fatigue limit of the BCC vanadium-based micro-alloyed forging steel AISI 1141 (152 MPa).

scholarly journals Fatigue Behaviors of Resistance Spot Welds for 980 MPa Grade TRIP Steel

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1086
Author(s):  
Heewon Cho ◽  
Sangwoo Nam ◽  
Insung Hwang ◽  
Je Hoon Oh ◽  
Munjin Kang ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Failure Mode ◽  
Trip Steel ◽  
Failure Modes ◽  
Propagation Speed ◽  
Outer Edge ◽  
Fatigue Load ◽  
Resistance Spot ◽  
Fracture Surfaces ◽  
Pull Out

The fatigue life of the resistance spot weld of 980 MPa grade transformation induced plasticity (TRIP) steel was investigated and failure modes and fracture surfaces according to the fatigue load were analyzed. The fatigue life according to the nugget size was observed by using two electrodes with face diameters of 8 mm and 10 mm. When an electrode face diameter with 10 mm was used, the nugget size was large, and the fatigue life was further increased. After the fatigue test, three types of failure modes were observed, namely pull-out, plug, and heat affected zone (HAZ) failure, depending on the fatigue load. The fracture surfaces in each failure mode were analyzed. In all failure modes, a crack was initiated in the HAZ region, which is the interface between the two materials in all failure modes. In the case of pull-out failure, the crack propagates as if it surrounds the nugget at the outer edge of the nugget. In the case of HAZ failure, the crack propagates in the thickness direction of the material and outward in the nugget shell. Plug failure occurs with pull-out failure and HAZ failure mixed. The propagation patterns of cracks were different for each failure mode. The reason why the failure mode and the fracture surface are different according to the fatigue load is that the propagation speed of the fatigue crack is fast when the fatigue load is relatively large and is slow when the fatigue load is low.

scholarly journals Experimental and Numerical Investigation into Failure Modes of Tension Angle Members Connected by One Leg

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5141
Author(s):  
Edyta Bernatowska ◽  
Lucjan Ślęczka
Keyword(s):  
Numerical Simulations ◽  
Failure Mode ◽  
Failure Modes ◽  
Experimental Testing ◽  
Load Capacity ◽  
Strength Function ◽  
Experimental Tests ◽  
Material Model ◽  
Design Standards ◽  
Element Analysis

This paper presents the results of experimental and numerical tests on angle members connected by one leg with a single row of bolts. This study was designed to determine which failure mode governs the resistance of such joints: net section rupture or block tearing rupture. Experimental tests were insufficient to completely identify the failure modes, and it was necessary to conduct numerical simulations. Finite element analysis of steel element resistance based on rupture required advanced material modelling, taking into account ductile initiation and propagation of fractures. This was realised using the Gurson–Tvergaard–Needleman porous material model, which allows for analysis of the joint across the full scope of its behaviour, from unloaded state to failure. Through experimental testing and numerical simulations, both failure mechanisms (net section and block tearing) were examined, and an approach to identify the failure mode was proposed. The obtained results provided experimental and numerical evidence to validate the strength function used in design standards. Finally, the obtained results of the load capacity were compared with the design procedures given in the Eurocode 3′s current and 2021 proposed editions.

Fatigue Life Estimation in Notched Geometries

2013 ◽  
Author(s):  
Sebastian Cravero ◽  
Hugo Ernst
Keyword(s):  
Fatigue Life ◽  
Experimental Tests ◽  
Crack Size ◽  
Initial Crack ◽  
Life Estimation ◽  
Threaded Connections ◽  
Fatigue Life Estimation ◽  
Initiation Stage ◽  
Study Techniques ◽  
Number Of Cycles

The fatigue failure in components is divided in two stages: an initiation stage that defines the number of cycles that it takes for a crack to appear in the material and a second stage that estimates the number of cycles where the crack grows until it becomes unstable. Usual fatigue life estimation procedures (in crack free components) only consider the initiation stage and assume that the crack propagation period is relatively small compared with the total life. However, in the case of severely notched geometries like threaded connections, the propagation stage can be an important part of the component fatigue life and must be evaluated. A fundamental issue in the calculation of initiation plus propagation fatigue life is the definition of the initial crack size after the initiation stage. In the present study techniques for crack initiation and crack growth are described. Also the procedure to combine the two techniques and define an initial crack size is presented. The study is based on previous work of C. Navarro, et al. [1]. Additionally, validation against experimental tests on notched specimens is provided.

scholarly journals A Probabilistic Fatigue Framework to Enable Location-Specific Lifing for Critical Thermo-mechanical Engineering Applications

2021 ◽  
Author(s):  
Ritwik Bandyopadhyay ◽  
Michael D. Sangid
Keyword(s):  
Fatigue Life ◽  
Failure Mode ◽  
Failure Modes ◽  
Prediction Interval ◽  
Fatigue Crack Initiation ◽  
Strain Range ◽  
Loading Conditions ◽  
The Matrix ◽  
Bayesian Inference Framework ◽  
Increasing Temperature

AbstractThe present paper describes a probabilistic framework to predict the fatigue life and failure mode under various thermo-mechanical loading conditions. Specifically, inclusion- and matrix-driven competing failure modes are examined within nickel-based superalloys. The critical accumulated plastic strain energy density (APSED) is employed as a unified metric to predict fatigue crack initiation in metals, which is favorable due to the usage of a single unknown parameter and its capability to predict failure across loading conditions and failure modes. In this research, we characterize the temperature-dependent variation of the critical APSED using a Bayesian inference framework and predict the competing failure modes in a coarse grain variant of RR1000 with varying strain range and temperature. The critical APSED appears to decrease along a vertically reflected sigmoidal curve with increasing temperature. Further, (a) the prediction of a failure mode, (b) failure mode associated with the minimum life, and (c) the change in the location associated with the matrix-driven failure mode with increasing temperature and decreasing strain range are consistent with the experimentally observed trends in RR1000, as well as other Nickel-based superalloys, documented in the literature. Finally, for each simulated loading condition, the uncertainty in the fatigue life is quantified as a prediction interval computed based on a $$95\%$$ 95 % confidence level of the critical APSED and the computed APSED from simulations. The overall framework provides a promising step towards microstructural-based fatigue life determination of components and enables a location-specific lifing approach.

Multi-Axial Fatigue Life Prediction of a Composite Structural Component

2010 ◽  
Author(s):  
Laura Vergani ◽  
Chiara Colombo
Keyword(s):  
Fatigue Life ◽  
Structural Component ◽  
Life Prediction ◽  
Failure Modes ◽  
Glass Fibers ◽  
Axial Loading ◽  
Experimental Tests ◽  
Fatigue Life Prediction ◽  
The Matrix ◽  
Fibers Orientation

Aim of this work is to test and understand the mechanical behavior of a composite material used to build a structural component, in particular a corner beam of a bus cabin. This component is obtained by means of the pultrusion technique and presents random and longitudinal E-glass fibers as reinforce, while the matrix is a vinyl-ester resin. A series of experimental tests was performed on specimens cut out from this beam. Different fibers orientation with respect to the direction of load application were considered: longitudinal (0°), normal (90°) and inclined (45°), thus both in uni-axial and multi-axial loading conditions. A static and fatigue characterization was carried out to identify the mechanical behaviors and the failure modes in these directions. Obtained fatigue data are then interpolated by fitting parameters required for models of fatigue life prediction.

scholarly journals Application of variable equivalent amplitude for determination of fatigue life of elements subjected to block loading

2021 ◽  
Vol 338 ◽  
pp. 01020
Author(s):  
Justyna Obrał ◽  
Marta Kurek ◽  
Tadeusz Łagoda ◽  
Karolina Głowacka
Keyword(s):  
Fatigue Life ◽  
Experimental Tests ◽  
Mean Value ◽  
Arithmetic Mean ◽  
Time Variable ◽  
Block Loading ◽  
Continuous Basis ◽  
Proposed Model ◽  
Number Of Cycles

This paper contains a proposition of a new method of determining the fatigue life of elements subjected to non-stationary loads. The model was based on the determination of the time-variable equivalent weighted amplitude. This amplitude is derived on a continuous basis as the arithmetic mean of nth root of the amplitudes that occur up to a given time. The analysis of the proposed model was carried out on the basis of selected literature insights based on specimens made of P91 and P92 steels. The experimental tests were performed under block loading with a zero mean value in the conditions of tension-compression with a small number of cycles.

scholarly journals Study on the P-S-N Curve of Sucker Rod Based on Three-Parameter Weibull Distribution

Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 560
Author(s):  
Wenbin Cai ◽  
Wen Li ◽  
Jinze Xu
Keyword(s):  
Fatigue Life ◽  
Weibull Distribution ◽  
Normal Distribution ◽  
Fatigue Limit ◽  
High Strength ◽  
Model Based ◽  
Sucker Rod ◽  
Number Of Cycles ◽  
Log Normal ◽  
Log Normal Distribution

During the oil production process, sucker rods are subjected to cyclic alternating load. After a certain number of cycles, a sucker rod can experience fatigue failure. The number of cycles is called fatigue life (N), and the accurate relationship between maximum stress (S) and fatigue life (N) under a certain reliability (P), namely the P-S-N curve, is an important basis for the reliability analysis and fatigue life prediction of sucker rods. The Basquin model, based on log-normal distribution, is widely used for fitting the P-S-N curves of sucker rods. Due to the limitation of this model, it is difficult to extrapolate the conclusion obtained from a finite fatigue region to the high-cycle or ultra-high-cycle fatigue region, which makes it impossible to estimate the fatigue limit of the sucker rod. Compared to the log-normal distribution, Weibull distribution causes the sucker rod to have a minimum safety life, namely the safety life at 100% survival rate, which complies with the fatigue characteristics of the sucker rod and is more in line with the actual situation. In this study, the fatigue data for ultra-high-strength HL and HY grade sucker rods were obtained through experimental fatigue tests. A new fatigue life model was established and the P-S-N curves of two types of ultra-high strength sucker rods were obtained. For HL- and HY-type ultra-high strength sucker rods, the average error between the fitting result and fatigue test value is 1.25% and 4.39%, respectively. Compared to the S-N curve fitting result obtained from the Basquin model commonly used for sucker rods, the new model based on three-parameter Weibull distribution provides better fitting precision and can estimate fatigue limit more accurately, so this model is more suitable for estimating fatigue life and can better guide the design of ultra-high strength sucker rod strings.

A Procedure to Predict Influence of Acceleration and Damping of Blades Passing Through Critical Speeds on Fatigue Life

2009 ◽  
Author(s):  
J. S. Rao ◽  
Rejin Ratnakar ◽  
S. Suresh ◽  
R. Narayan
Keyword(s):  
Fatigue Life ◽  
Stress Response ◽  
Fatigue Limit ◽  
Fatigue Damage ◽  
Critical Speed ◽  
Turbine Blades ◽  
Peak Stress ◽  
Start Up ◽  
Number Of Cycles ◽  
Peak Value

Turbine Blades suffer fatigue damage when they cross over a critical speed during start up and shut down conditions. The stress response is usually determined from quasi-steady analysis through resonance with an assumed damping. This response above fatigue limit can be divided into several steps to reach the peak value at critical speed and then fall after passing the critical. For a given acceleration of the rotor, one can then determine the number of cycles at each of these stress levels and assess cumulative damage for one crossing. In this paper, the effect of acceleration and damping on the magnitude of peak stress and where it occurs in the vicinity of critical speed is included in determining the damage suffered by a blade while passing through the critical speed.

Combine Nanoprobing Technique with Difference Analysis to Identify Nonvisual Failures

2006 ◽  
Author(s):  
Cha-Ming Shen ◽  
Tsan-Cheng Chuang ◽  
Jie-Fei Chang ◽  
Jin-Hong Chou
Keyword(s):  
Failure Mode ◽  
Failure Modes ◽  
Electrical Characteristic ◽  
The Novel ◽  
Difference Analysis ◽  
Original Idea ◽  
Deductive Method ◽  
Complete Measurement

Abstract This paper presents a novel deductive methodology, which is accomplished by applying difference analysis to nano-probing technique. In order to prove the novel methodology, the specimens with 90nm process and soft failures were chosen for the experiment. The objective is to overcome the difficulty in detecting non-visual, erratic, and complex failure modes. And the original idea of this deductive method is based on the complete measurement of electrical characteristic by nano-probing and difference analysis. The capability to distinguish erratic and invisible defect was proven, even when the compound and complicated failure mode resulted in a puzzling characteristic.

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