A Probabilistic Fatigue Damage Model for Describing the Entire Set of Fatigue Test Data of the Same Material

2019 ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Fatigue Test ◽  
Fatigue Damage ◽  
Test Data ◽  
Stress Level ◽  
Damage Model ◽  
Fatigue Tests ◽  
Small Sample ◽  
Test Machine ◽  
Stress Levels ◽  
D Model

Abstract One typical widely-accepted approach for describing the fatigue test data is the P-S-N curve approach. However, the P-S-N curve approach has some issues such as: (1) If there are only a few fatigue test data at a fatigue test stress level, the P-S-N curve approach is not valid due to the small sample size; (2) When the total number of fatigue tests under different stress levels might be larger such as more than 30 even though the number of fatigue tests at the same stress level is small, the P-S-N curve cannot be used to analyze such set of fatigue data; (3) It is difficult to calculate the reliability of a component under a cyclic stress level when the probabilistic distribution function under this stress level is not available in the P-S-N curves. The author has proposed the K-D probabilistic fatigue damage model (K-D model) to overcome those issues. The 6061-T6 10-gauge sheet-type flat fatigue specimen was designed, manufactured, and tested on the Instron 8081 fatigue test machine to verify this K-D model. The fatigue tests were under five different cyclic axial loadings with a total of 195 tests. In this paper, the fatigue test data will be analyzed by the P-S-N curve approach and the K-D model. The systematic comparisons between the P-S-N curve approach and the K-D model have approved and verified that the K-D model can be used to analyze and to describe the fatigue test data under all different fatigue stress levels and can be used to calculate the reliability of a component under any type of cyclic fatigue loading.

A Probabilistic Fatigue Damage Model for Aluminum 6061-T6 10-Gauge Sheet-Type Material

2021 ◽  
Author(s):  
Xiaobin Le
Keyword(s):  
Fatigue Test ◽  
Fatigue Damage ◽  
Cyclic Load ◽  
Damage Model ◽  
Fatigue Tests ◽  
Load Level ◽  
Cyclic Loads ◽  
Test Machine ◽  
Axial Loads ◽  
Fatigue Specimen

Abstract The 6061-T6 10-gauge sheet-type flat fatigue specimen was designed, manufactured, and tested on an Instron 8081 fatigue test machine. The fatigue tests were performed under five different cyclic axial loads with 195 tests. This paper will display how to use these 195 test data under different cyclic axial loads to build a probabilistic fatigue damage model. The model is validated by the results obtained from the traditional P-S-N curve approach. One advantage of this probabilistic fatigue damage model is that it can calculate the reliability of a component under any type of cyclic loads at any cyclic load level.

PROBABILISTIC SPECIMEN PROPERTY-FATIGUE LIFE MAPPING AND P-S-N CURVE FITTING

2013 ◽  
Vol 20 (05) ◽  
pp. 1350020
Author(s):  
LIYANG XIE ◽  
JIANZHONG LIU ◽  
NINGXIANG WU ◽  
WENXUE QIAN
Keyword(s):  
Fatigue Life ◽  
Test Data ◽  
Stress Level ◽  
Curve Fitting ◽  
Cyclic Stress ◽  
Small Sample ◽  
Test Method ◽  
Life Distribution ◽  
Stress Levels ◽  
Curve Fitting Method

Fitting P-S-N curve with small-size sample of fatigue test data is significant in engineering applications. Although several small sample-based P-S-N curve fitting methods have been developed, complexity in mathematics and/or the unrealistic assumption of the methods hinder their application seriously. Based on the principle of probabilistically mapping from the probability distribution of specimen property to that of fatigue life of the specimen, this paper presents a new, easy to apply P-S-N curve fitting method. By collecting the life distribution information dispersed in several small-size samples of fatigue lives tested under different cyclic stress levels, a large-size sample of equivalent fatigue life data can be built based on the mapping mechanism as well as the uniqueness of the relationship between fatigue life standard deviation and cyclic stress level. The basic viewpoint is that the fatigue lives tested at any cyclic stress levels can be equivalently converted to an arbitrary baseline stress level according to the life distribution–stress relationship, and this principle can be applied to determine the P-S-N curves with a limited number of test data. Test results illustrate that the P-S-N curves obtained by such methods with 30, 24 or 20 samples, respectively, are close to those obtained by the conventional test method with 60 or 40 samples.

Fatigue Capacity of Stiffener to Web Frame Connections

2009 ◽  
Author(s):  
Torbjo̸rn Lindemark ◽  
Inge Lotsberg ◽  
Joong-Kyoo Kang ◽  
Kwang-Seok Kim ◽  
Narve Oma
Keyword(s):  
Fatigue Test ◽  
Test Data ◽  
Large Scale ◽  
Fatigue Tests ◽  
Life Assessment ◽  
Shear Stresses ◽  
Test Model ◽  
The Difference ◽  
Marine Engineering ◽  
Plate Connections

Daewoo Shipbuilding & Marine Engineering Co., Ltd. (DSME), StatoilHydro and DNV established a common project to investigate the reason for the difference between calculated fatigue lives and the in-service experience and to assess the fatigue capacity of stiffener web connections subjected mainly to web frame shear stresses. The main objective of the work was to establish fatigue test data and perform numerical analysis of collar plate connections in order to provide improved confidence in analysis methodology for fatigue life assessment. Large scale fatigue tests of different types of connections were carried out to obtain fatigue test data of collar plate connections. Finite element analyses were carried out for comparison with fatigue test data and with measured stresses on the test model. Based on this work recommendations on fatigue design analysis of connections between stiffeners and web frames have been derived. The background for this is presented in this paper.

Fatigue Test Plan to Obtain S-N Curves

2002 ◽  
Author(s):  
Joa˜o Ma´rio Andrade Pinto ◽  
Enrico A. Colosimo ◽  
Tanius Rodrigues Mansur ◽  
Julio Ricardo Barreto Cruz ◽  
Ernani Sales Palma ◽  
...  
Keyword(s):  
Fatigue Test ◽  
Fatigue Tests ◽  
Test Plan ◽  
Practical Application ◽  
Lower Stress ◽  
Precise Data ◽  
Rotating Machine ◽  
Stress Levels ◽  
Optimum Plan ◽  
Sae 8620 Steel

S-N curves of structural materials are obtained through fatigue tests. These tests are often performed using five different stress levels, with fifteen test specimens for each stress level. This kind of test plan provides estimates that are less precise compared to other experimental plans, for example, the ones called optimum plan or compromise plan. The main reason for this drawback is the use of the same number of specimens for all stress levels. It has been observed that less precise results are obtained for lower stress levels because failure occurs less frequently. That is why more specimens should be used for lower stress levels as compared to higher stress levels. As long as the number of specimens to be tested at low stress levels is increased, the total number of failures will also increase, which allows one to develop a more precise data analysis. The objective of this work is to present an alternative experimental plan to obtain S-N curves, which intends to provide accurate estimators. A practical application is done for planning a fatigue test, in a flex-rotating machine, to obtain the S-N curve of SAE 8620 steel.

Cumulative Damage in Composites

1990 ◽  
Vol 112 (3) ◽  
pp. 358-361 ◽  
Author(s):  
H. A. Whitworth
Keyword(s):  
Experimental Data ◽  
Fatigue Damage ◽  
Stress Level ◽  
Present Model ◽  
Damage Model ◽  
Fatigue Loading ◽  
Damage Function ◽  
Epoxy Composites ◽  
Remaining Life ◽  
Cumulative Fatigue Damage

The problem of cumulative fatigue damage in composites is analyzed based upon the development of a phenomenological damage model. In this modeling, a damage function is defined based on the degradation of the residual stiffness and used to predict the remaining life of composite specimens subjected to dual stress level fatigue loading. Available experimental data for graphite/epoxy composites are compared with the predictions of the present model.

Fatigue Performance of Grade R4 and R5 Mooring Chains in Seawater

2014 ◽  
Author(s):  
Jonathan Fernández ◽  
Walther Storesund ◽  
Jesús Navas
Keyword(s):  
Fatigue Test ◽  
Fatigue Damage ◽  
Fatigue Tests ◽  
Design Methods ◽  
Full Scale ◽  
Fatigue Performance ◽  
Test Program ◽  
Gas Industry ◽  
Fatigue Design ◽  
Cumulative Fatigue Damage

With more than 50.000 tons in service to date, the Oil&Gas Industry has the need to understand the tension fatigue performance of grade R5 chains in straight tension, and corroborate the validity of the existing design methods. The chain fatigue design curves in API and DNV are based on fatigue tests obtained in the nineties and early two thousands. However the tests were performed on lower grades such as ORQ, R3 and R4, and small chains, 76 mm diameter being the largest studless chain tested. The industry has moved towards the use of large studless chains, especially in permanent units, where chain diameters above 150 mm are not unusual. This paper gathers information from a full scale fatigue test program on grade R4 and R5 studless chains, performed in seawater and with diameters between 70 mm and 171 mm. The chains being tested are actual production chains supplied for different drilling units and large permanently moored production floating units. The paper analyses the data and determines tension-tension fatigue curves based on API and DNV methods for computation of cumulative fatigue damage, regardless of other damaging mechanisms. Improved fatigue capacity is obtained with respect to the above recommended design methods.

Analysis on High Cycle Fatigue Properties and Fatigue Damage Evolution of TC25 Titanium Alloy

2016 ◽  
Vol 697 ◽  
pp. 658-663
Author(s):  
Rong Guo Zhao ◽  
Ya Feng Liu ◽  
Yong Zhou Jiang ◽  
Xi Yan Luo ◽  
Qi Bang Li ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Fatigue Life ◽  
Strain Hardening ◽  
Fatigue Damage ◽  
Damage Evolution ◽  
High Cycle Fatigue ◽  
Damage Model ◽  
Fatigue Properties ◽  
Test Machine ◽  
Cycle Fatigue

The high cycle fatigue tests for smooth specimens of TC25 titanium alloy under different stress ratios are carried out on a MTS 809 Material Test Machine at a given maximum stress level of 917MPa at ambient temperature, the high cycle fatigue lifetimes for such alloy are measured, and the effects of stress amplitude and mean stress on high cycle fatigue life are analyzed. The initial resistance is measured at the two ends of smooth specimen of TC25 titanium alloy, every a certain cycles, the fatigue test is interrupted, and the current resistance values at various fatigue cycles are measured. The ratio of resistance change is adopted to characterize the fatigue damage evolution in TC25 titanium alloy, and a modified Chaboche damage model is applied to derive the fatigue damage evolution equation. The results show that the theoretical calculated values agree well with the test data, which indicates that the modified Chaboche damage model can precisely describe the accumulated damage in TC25 titanium alloy at high cycle fatigue under unaxial loading. Finally, the high cycle fatigue lifetimes for TC25 titanium alloy specimens at different strain hardening rates are tested at a given stress ratio of 0.1, the effect of strain hardening on fatigue life is investigated based on a microstructure analysis on TC25 titanium alloy, and an expression between fatigue life and strain hardening rate is derived

scholarly journals A 3D progressive damage model for fatigue analysis of woven fabric composites

2018 ◽  
Author(s):  
DC Pham
Keyword(s):  
Fatigue Damage ◽  
Test Data ◽  
Damage Accumulation ◽  
Damage Model ◽  
Peak Load ◽  
Woven Fabrics ◽  
Woven Fabric ◽  
Stress Criterion ◽  
Damage Initiation ◽  
Fatigue Damage Accumulation

A new 3D damage model is developed to predict the progressive failure and accumulated fatigue damage of woven fabric composite materials. Stress-based failure criteria are used to predict the damage initiation in x-tow, y-tow, and matrix constituent. An S-N based damage accumulation model is implemented to characterize the cycle dependent strength of the x- and y- fiber tows and matrix subjected to axial tension, compression, or in-plane share loading. A curve-fit non-linear shear model is also employed based on the static coupon test data of (+45/-45) woven fabric laminates. A static failure progression module is used to predict the damage and failure at the peak load prior to fatigue cycling. Stiffness degradation, fatigue damage accumulation, and failure mode detection are performed during the fatigue marching process. The developed user-defined material model for Abaqus features: 1) description of initial nonlinear shear before the damage initiation; 2) characterization of failure initiation based on a maximum stress criterion; and 3) performance of fatigue damage accumulation using a phenomenological model based on S-N test data. The predictive capabilities of the developed model are demonstrated using tension-tension fatigue of SYNCOGLAS R420 E-glass woven fabrics.

A Probabilistic Approach for Determining the Component’s Dimension Under Fatigue Loadings

2009 ◽  
Author(s):  
Xiaobin Le ◽  
Jahan Rasty
Keyword(s):  
Fatigue Test ◽  
Test Data ◽  
Probabilistic Approach ◽  
Random Variables ◽  
Random Variable ◽  
Design Equation ◽  
Probabilistic Design ◽  
Material Fatigue ◽  
Stress Levels ◽  
Design Scenario

Due to inherent scatters in fatigue test data, the P-S-N curves are normally used to describe material fatigue behaviors. For probabilistic component’s design under fatigue loadings, the component’s dimension should be treated as a random variable because every dimension is certainly with a dimension tolerance. In this design scenario, it is difficult to determine the component’s dimension under fatigue loadings by using the P-S-N curves because stress levels are unknown and random variables. In this paper, a probabilistic approach is presented to build a generic probabilistic design equation which is governed by random variables related to material fatigue behaviors, component conditions and fatigue loadings. The generic probabilistic design equation can be used to determine component’s dimension with a given reliability. One example is presented for explaining the approach in details.

Observations of Fatigue Damage in the Press-Fitted Shaft under Bending Loads

2006 ◽  
Vol 326-328 ◽  
pp. 1071-1074 ◽  
Author(s):  
Dong Hyung Lee ◽  
Seok Jin Kwon ◽  
Jae Boong Choi ◽  
Young Jin Kim
Keyword(s):  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Surface Profile ◽  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Fretting Wear ◽  
Multiple Cracks ◽  
Test Machine ◽  
Edge Region ◽  
Fretting Damage

In this paper, the characterization of fretting damage on press-fitted specimens is proposed by experimental methods. A series of fatigue tests and interrupted fatigue tests on pressfitted specimens were carried out by using a rotate bending fatigue test machine. Macroscopic and microscopic characteristics were observed to identify fretting damage mechanism with a scanning electron microscope (SEM) and profilometer. The mechanism of fretting fatigue damage on pressfitted structure is discussed from experimental results. It is found that small cracks of 30~40m in depth are initiated when the specimen reached about 10% of the total life, and thus almost 90% of the fretting fatigue life of press fits can be considered to be in the crack propagation phase. Most of fatigue cracks are initiated at 1050m inner side of contact edge, and multiple cracks are nucleated and interconnected in the fretted surface. The crack nucleation angle in the near contact edge region is larger than that in the inside of the contact edge region. The fretting wear increased with increasing fatigue cycle. Since the fretting wear is relevant to the evolution of surface profile, the fretting fatigue is observed to be closely related with the fretting wear.

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