scholarly journals Determining the endurance limit of AISI 4340 steels in terms of different statistical approaches

2021 ◽  
Vol 15 (58) ◽  
pp. 344-364
Author(s):  
Salim Çalışkan ◽  
Rıza Gürbüz
Keyword(s):  
Fatigue Limit ◽  
Curve Fitting ◽  
Endurance Limit ◽  
Load Path ◽  
Confidence Levels ◽  
Safe Life ◽  
In The Beginning ◽  
Fail Safe ◽  
Damage Tolerant ◽  
Aisi 4340

In engineering applications, fatigue phenomenon is a key issue and needs to be analyzed in the beginning of design phase in case of any component exposed to alternating loading on operation otherwise catastrophic fatigue failure may cause. Component can be designed with safe-life, fail-safe, and damage tolerant approach based on whether redundant load path and damage sensitive. Before starting analyzing the structure, material allowable data needs to be presented in a reliable way to predict fatigue life of components. SN curves with presented confidence levels are the robust approach to make a prediction on safe life of a structure in terms of fatigue. In this point, there are so many approaches to determine fatigue limit of materials and issue shall be handled by statistical manner. In literature, different staircase and curve fitting methods were presented to estimate endurance limit of materials and some reliability manuscript published. In this paper, fatigue limit of AISI 4340 steel will be investigated through most convinced staircase and curve fitting approaches and their reliability will be queried.

The Influence of Surface Residual Stress on Fatigue Limit of Titanium

1960 ◽  
Vol 82 (1) ◽  
pp. 76-78 ◽  
Author(s):  
E. C. Reed ◽  
J. A. Viens
Keyword(s):  
Residual Stress ◽  
Titanium Alloy ◽  
Fatigue Limit ◽  
Experimental Error ◽  
Endurance Limit ◽  
Simple Equation ◽  
Surface Residual Stress ◽  
A Value ◽  
Effect Of Surface

Investigation of the effect of surface residual stress on the endurance limit of 6Al 4V titanium alloy shows that this effect is equal within experimental error to the residual stress divided by a constant. Results can be expressed by a simple equation. A value for the constant has been derived.

Properties of PH 13-8 Mo Steel for Fatigue Application in Helicopters

2010 ◽  
Vol 654-656 ◽  
pp. 2507-2510
Author(s):  
Sunny Lok Hin Chan ◽  
Ung Hing Tiong ◽  
Graham Clark
Keyword(s):  
Fatigue Limit ◽  
High Strength ◽  
Fatigue Properties ◽  
Management Problem ◽  
Operational Environment ◽  
Corrosion Properties ◽  
R Ratio ◽  
Number Of Cycles ◽  
Damage Tolerant ◽  
Simple Stress

While many fixed-wing aircraft have adopted damage-tolerant design in recent years, helicopter design is still based predominantly on a safe life approach, in which relatively simple Stress Life (S-N) data underpins the tools used for life prediction. Due to their unique loading, helicopter structures experience a high number of loading cycles as compared to fixed-wing aircraft, and this presents a more challenging fatigue life management problem. To minimise the fatigue damage, the helicopter community tends to design components such that most of the loading experienced falls below the fatigue limit of the selected material. These materials are usually of high strength and have good fatigue properties, although the large number of cycles experienced by some components raises the possibility of fatigue in the “gigacycle” regime where the fatigue limit drops to a new, lower level. This paper discusses the suitability of a high-quality PH 13-8 Mo steel for critical helicopter usage, using a simulated application in Australian service to evaluate its fatigue performance particularly at high R ratio and other properties such as density, corrosion properties and cost in terms of the operational environment experienced in Australian helicopter operations.

scholarly journals An empirical study on stress-based fail-safe topology optimization and multiple load path design

2021 ◽  
Author(s):  
Micah Kranz ◽  
Julian K. Lüdeker ◽  
Benedikt Kriegesmann
Keyword(s):  
Topology Optimization ◽  
Computational Cost ◽  
Element Model ◽  
Maximum Length ◽  
Length Scale ◽  
Structural Members ◽  
Load Path ◽  
Evaluation Scheme ◽  
Fail Safe ◽  
Safe Approach

AbstractExplicitly considering fail-safety within design optimization is computationally very expensive, since every possible failure has to be considered. This requires solving one finite element model per failure and iteration. In topology optimization, one cannot identify potentially failing structural members at the beginning of the optimization. Hence, a generic failure shape is applied to every possible location inside the design domain. In the current paper, the maximum stress is considered as optimization objective to be minimized, since failure is typically driven by the occurring stresses and thus of more practical relevance than the compliance. Due to the local nature of stresses, it is presumed that the optimization is more sensitive to the choice of the failure shape than compliance-based optimization. Therefore, various failure shapes, sizes and different numbers of failure cases are investigated and compared on the basis of a general load-path-based evaluation scheme. Instead of explicitly considering fail-safety, redundant structures are obtained at much less computational cost by controlling the maximum length scale. A common and easy to implement maximum length scale approach is employed and fail-safe properties are determined and compared against the explicit fail-safe approach.

Evaluation of Fatigue Endurance Foran Ultra Lightweight Inline Skate Frame

2013 ◽  
Vol 739 ◽  
pp. 431-436
Author(s):  
Ho Kyung Kim
Keyword(s):  
Stress Analysis ◽  
Tensile Properties ◽  
Fatigue Limit ◽  
Endurance Limit ◽  
Fem Analysis ◽  
Fatigue Tests ◽  
Von Mises Stress ◽  
Al 7075 ◽  
Von Mises ◽  
Fatigue Endurance

In order to evaluate the fatigue endurance for an ultra lightweight inline skate frame, FEM analyses was performed. The tensile properties and an S-N curve were determined through tensile and fatigue tests on a modified Al-7075+Sc alloy. The yield and ultimate tensile strengths were 553.3 MPa and 705.5 MPa, respectively. The fatigue endurance limit of this alloy was 201.2 MPa. To evaluate the fatigue endurance of the inline skate frame, the S-N data were compared with the stress analysis results through FEM analyses of the frame. The maximum von Mises stress of the frame was determined to be 106 MPa through FEM analysis of the frame, assuming that the skater weight is 75 kg. Conclusively, on the basis of the fatigue limit, the inline skate frame has a safety factor of approximately 2.0.

Fail‐Safe vs. Safe‐Life Philosophy in V/STOL Design

1969 ◽  
Vol 14 (4) ◽  
pp. 2-9 ◽  
Author(s):  
Fred H. Immen
Keyword(s):  
Structural Features ◽  
Tilt Rotor ◽  
Safe Life ◽  
Design Engineers ◽  
Rational Combination ◽  
Life Philosophy ◽  
Fail Safe ◽  
Rotary Wing ◽  
Life Design ◽  
Rigid Wing

V/STOL aircraft combine the technological features of rigid‐wing and rotary‐wing aircraft, incorporating many of the structural features of helicopters. A review indicates that structures analysts of conventional aircraft have concentrated on fail‐safe design; while helicopter design engineers have generally been content to rely on component safe‐life design. The two philosophies are examined and an approach to the rational marriage of helicopter and airplane fatigue technologies is suggested, in order to provide an integrated, economically feasible, statistically rational combination of fail‐safe and safe‐life methodology for tilt‐wing and tilt‐rotor V/STOL aircraft.

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