An Experimental Study on Fatigue Life Variance, Residual Stress Variance, and Their Correlation of Face-Turned and Ground Ti 6Al-4V Samples

2002 ◽  
Vol 124 (4) ◽  
pp. 809-819 ◽  
Author(s):  
Xiaoping Yang ◽  
C. Richard Liu ◽  
A. F. Grandt
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Manufacturing Processes ◽  
Machining Processes ◽  
Stress Variation ◽  
Bending Fatigue ◽  
New Process ◽  
The Impact ◽  
The Relationship ◽  
Stress Variance

It is well known that there is a large variance associated with fatigue life. However, in literature little is found on the relationship between manufacturing processes and fatigue variance of the manufactured components. In this research, the influence of machining processes on the fatigue variance of the machined Ti 6Al-4V samples is studied experimentally. The impact is evaluated by comparing the safety ratios of face-turned samples with those of ground samples. The safety ratio is defined as the average fatigue life over the fatigue life with a reliability of 95%. In the computation, it is assumed that fatigue life follows Weibull distribution. Two sets of faced samples and two sets of ground samples are tested for bending fatigue. The test is under constant amplitude in high cycle fatigue regime under room temperature. The results show that the safety ratios of face-turned samples are significantly smaller than are those of ground samples. Consequently, it is suggested that fatigue life variance be considered as a new process capability. This capability serves as a basis in choosing manufacturing processes for making fatigue critical products such as aircraft. Another finding is the positive correlation between the residual stress variation and fatigue life variation. This correlation suggests that a better understanding and prediction of residual stress lead to a better prediction of fatigue life.

Fatigue Life Variance Prediction Incorporating Residual Stress Scatter Induced by Super-Finishing Grinding Process

2009 ◽  
Vol 416 ◽  
pp. 45-50
Author(s):  
Guang Hui Lu ◽  
Xue Ping Zhang ◽  
Er Wei Gao
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Diffraction Method ◽  
Machining Process ◽  
Stress Distributions ◽  
X Ray Diffraction ◽  
Machining Processes ◽  
Surface Residual Stress ◽  
Bearing Rings ◽  
The Impact

It is well known that there is a lager deviation in the fatigue life of machined components even under nominally identical loading conditions. Understanding and controlling fatigue life variance are essential to enhance reliability. However, few research focus on the impact of machining processes on the fatigue life variance of machined components. In this study, surface residual stress distributions of bearing rings randomly selected from a production line by super-finishing grinding, are measured by X-ray diffraction method in cutting and feed direction, and its scatter is analyzed by statistical tools. Based on the variance prediction theories, build a simplified fatigue life variance prediction model incorporating the resultant residual stresses scatter induced by machining process. Based on the Basquin equation, the model is validated by experimental data published in literature. The predicted fatigue life agrees well with the experimental average fatigue life. Statistical analysis shows that the predicted variances of fatigue life are equal to those estimated from experimental fatigue life.

Investigating Machining Impact on Fatigue Variance: A Machining Quality Perspective

2004 ◽  
Vol 127 (3) ◽  
pp. 492-502 ◽  
Author(s):  
Xiaoping Yang ◽  
C. Richard Liu
Keyword(s):  
Fatigue Life ◽  
Data Center ◽  
Room Temperature ◽  
Fatigue Tests ◽  
Machining Processes ◽  
Case Scenario ◽  
Bending Fatigue ◽  
Machining Quality ◽  
Four Point Bending ◽  
The Impact

Fatigue life of nominally identical structures under nominally identical loading conditions can scatter widely. This study has investigated the impact of machining processes on such scatters. After Ti 6Al-4V samples were surface ground and face turned, they were subject to constant amplitude four-point bending fatigue tests under room temperature. The best-case scenario of process capability ratios of fatigue for these samples were evaluated with assumed tolerances of fatigue life. Based on these ratios, the numbers of nonconforming parts were estimated. Under the machining conditions from the Machining Data Handbook (Machining Data Center, Cincinnati, 1980), up to 39% of samples due to one process are expected to be nonconforming, whereas only up to 0.6% of samples due to the other process are expected to be nonconforming. The ramifications in terms of cost for machining quality control due to the different capability ratios have been discussed. The current findings indicate an urgent need to further the study of this issue in a scientific manner.

Investigating Machining Impact on Fatigue Variance: A Machining Quality Perspective

2006 ◽  
Author(s):  
Xiaoping Yang ◽  
C. Richard Liu
Keyword(s):  
Fatigue Life ◽  
Room Temperature ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Machining Processes ◽  
Case Scenario ◽  
Bending Fatigue ◽  
Machining Quality ◽  
Four Point Bending ◽  
The Impact

Fatigue life of nominally identical structures under nominally identical loading conditions can scatter widely. This study has investigated the impact of machining processes on such scatters. After Ti 6Al-4V samples were surface ground and face turned, they were subject to constant amplitude four-point bending fatigue tests under room temperature. The best case scenario of process capability ratios of fatigue for these samples were evaluated with assumed tolerances of fatigue life. Based on these ratios, the numbers of nonconforming parts were estimated. Under the machining conditions from a handbook, up to 39% of samples due to one process are expected to be nonconforming while only up to 0.6% of samples due to the other process are expected to be nonconforming. The ramifications in terms of cost for machining quality control due to the different capability ratios have been discussed. The current findings indicate an urgent need to further the study of this issue in a scientific manner.

scholarly journals Bending Fatigue Behaviors Analysis and Fatigue Life Prediction of 20Cr2Ni4 Gear Steel with Different Stress Concentrations near Non-metallic Inclusions

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3443 ◽  
Author(s):  
Zhiguo Xing ◽  
Zhiyuan Wang ◽  
Haidou Wang ◽  
Debin Shan
Keyword(s):  
Fatigue Life ◽  
Quantitative Analysis ◽  
Steel Production ◽  
The State ◽  
Heavy Duty ◽  
Stress Concentrations ◽  
Bending Fatigue ◽  
Gear Steel ◽  
Gear Steels ◽  
The Relationship

To investigate the relationship between inclusions and bending fatigue behaviors in 20Cr2Ni4 steel under different stress concentrations. This paper designs a new experimental method to prefabricate different size stress concentrations near the inclusions, and then conducts a new type of bending fatigue test to study the inclusions and their surrounding stress distributions in 20Cr2Ni4 steel. A microhardness tester was combined with laser etching equipment to realize the prefabrication of different stress concentrations at arbitrary positions around any inclusion on the gear steel surface. This method provides an experimental basis for the quantitative analysis of the relationship between stress distribution and fatigue life around the inclusions of heavy-duty gear steels. We also predict the bending fatigue lives of heavy-duty gear steels with different types of inclusions, stress states, and spatial distributions. Then, based on the prefabricated notch parameters and the state of inclusions in the steel, a mathematical model of quantitative analysis is proposed, which can accurately predict the fatigue limit of heavy-duty gear steel. The research results can be applied to the actual use of heavy-duty gears and to the accurate life estimation based on the state of gear stress, thereby providing a quantitative reference model for subsequent gear steel production and gear part processing.

The Effect of Morphology and Distribution of Sulfides on Mechanical Properties and Fatigue Life of Non-Quenched and Tempered Steel

2008 ◽  
Vol 51 ◽  
pp. 11-20
Author(s):  
Ming Tu Ma ◽  
Guo Zhong Li ◽  
Zhi Gang Li ◽  
Hong Zhou Lu
Keyword(s):  
Mechanical Properties ◽  
Fatigue Life ◽  
Fatigue Fracture ◽  
Rolling Direction ◽  
Impact Fracture ◽  
Fatigue Properties ◽  
Bending Fatigue ◽  
Quenched And Tempered Steel ◽  
The Impact ◽  
Tempered Steel

The effect of morphology and distribution of sulfides on tensile, impact and bending fatigue properties of non-quenched and tempered steel 49MnVS3 has been investigated in this paper. Microscopic structure and morphology of sulfides are observed, and impact fracture and fatigue fracture have been analyzed by SEM. The results show that the morphology of sulfides is mostly strip and distributes in ferrite, which affects mechanical properties and fatigue life. The length direction of sulfide strip is parallel to the rolling direction of steel. When the length of sulfide is short relatively and is approximate to the shape of particles. The impact properties and bending fatigue performance of 49MnVS3 are higher. Under those conditions, there are more ductile characteristics in their impact fracture and the fatigue fracture. The reasons for the effect of sulfide morphology on the mechanical and fatigue properties are explained.

scholarly journals Exploring the Links between Party and Appointment: Canadian Federal Judicial Appointments from 1989 to 2003

2010 ◽  
Vol 43 (3) ◽  
pp. 633-659 ◽  
Author(s):  
Lori Hausegger ◽  
Troy Riddell ◽  
Matthew Hennigar ◽  
Emmanuelle Richez
Keyword(s):  
Group Representation ◽  
Comparative Perspective ◽  
Political Connections ◽  
Judicial Selection ◽  
Judicial Appointments ◽  
New Process ◽  
The Impact ◽  
The Relationship

Abstract. Studies of federal judicial appointments made before 1988 discovered significant partisan ties between judicial appointees and the governments appointing them. In 1988, in response to criticism of these “patronage appointments,” the Mulroney government introduced screening committees to the process. This article explores the impact of these committees. Using information gained from surveys of legal elites, we trace the minor and major political connections of federal judicial appointees from 1989 to 2003 in order to determine whether patronage has continued despite the reform to the process. We discover that political connections continued to play an important role in who was selected for a judicial appointment. However, these connections were not quite as common as those found before 1988, and the new process does appear to have prevented the politically motivated appointment of completely unqualified candidates. Interestingly, our findings also suggest that the impact of patronage varies by region and interacts with other, newer influences, in particular, concerns for group representation on the bench. The paper concludes by briefly discussing these results in the context of the relationship between judicial selection and politics with a comparative perspective.Résumé. Les études sur les nominations judiciaires fédérales réalisées avant 1988 ont découvert des liens partisans étroits entre les juges nommés à la cour et les gouvernements les nommant. En 1988, en réponse aux critiques sur le favoritisme entourant les nominations, le gouvernement Mulroney a introduit des comités d'évaluation dans le processus. Cet article explore l'impact de ces comités. En utilisant de l'information recueillie lors de sondages menés auprès de la communauté légale, nous retraçons les connexions politiques mineures et majeures des attributaires judiciaires fédéraux de 1989 à 2003 en vue de déterminer si le favoritisme a persisté malgré la réforme du système. Nous découvrons que les connexions politiques continuent à jouer un rôle important dans la sélection des juges. Toutefois, ces connexions ne sont pas aussi importantes que celles qu'on a identifiées avant 1988 et le nouveau processus semble avoir réussi à prévenir les nominations partisanes de candidats entièrement non qualifiés. Les résultats de notre recherche suggèrent également que l'effet du favoritisme varie par région et dépend aussi d'autres facteurs plus nouveaux, en particulier le souci de représentation de certains groupes au sein de la magistrature. L'article conclut en discutant brièvement ces résultats dans le contexte de la relation entre la sélection judiciaire et la politique dans une perspective comparative.

A Study on the Development of Mach Peening for Prolonging Fatigue Life of Machine Structural Alloy Steel

2008 ◽  
Vol 580-582 ◽  
pp. 621-624
Author(s):  
Bok Kyu Lim
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Fatigue Strength ◽  
Alloy Steel ◽  
Compressive Residual Stress ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Light Weight ◽  
Structural Alloy ◽  
Bending Fatigue

The light weight components, crucial in automobiles and machinery, is require hight strength. Mach peening process is one of many of techniques utilized for improving fatigue properties. From the results of rotary bending fatigue tests, the fatigue strength increases up to 129% in mach peening specimen compared with un-peening. A layer of highly compressed residual stress is obtained by mach peening. The compressive residual stress, induced by mach peening, seems to be an important factor for increasing the fatigue strength.

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