Fatigue Life Analysis and Tensile Overload Effects with High Strength Steel Notched Specimens

1983 ◽  
Vol 22 ◽  
Author(s):  
J. H. Underwood
Keyword(s):  
Fatigue Life ◽  
Cyclic Loading ◽  
Fatigue Cracking ◽  
High Strength ◽  
Pressure Vessels ◽  
Life Testing ◽  
Stress Concentrations ◽  
Notched Specimens ◽  
Life Analysis ◽  
Fatigue Life Analysis

Pressure vessels often have notches or other stress concentrations present. Considering further that pressure vessels are nearly always subjected to some cyclic loading, fatigue cracking at notches is an important problem. The objective here is to describe some fatigue life testing and analysis which was performed with notched specimens in order to determine the effects of notch overload on fatigue life of pressure vessels.

Fatigue Life of Welded Joints of High-Strength Structural Steel S960QL

2016 ◽  
Vol 250 ◽  
pp. 169-174 ◽  
Author(s):  
Tomasz Slezak ◽  
Lucjan Sniezek
Keyword(s):  
Fatigue Life ◽  
Structural Steel ◽  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fatigue Cracking ◽  
High Strength ◽  
Propagation Rate ◽  
Total Strain Amplitude ◽  
Fatigue Life Analysis

The article presents the results of research on low cycle fatigue strength of welded joints of structural steel S960QL. Two types of butt welds were analysed: I-joints and V-joints. The tests were performed under load controlled using the total strain amplitude εac. Fatigue life analysis was conducted based on the Manson-Coffin-Basquin equation, which made it possible to determine fatigue parameters. High concordance was found of the adopted description model with experimental results. Studies have shown differences in the fatigue life of the various joints analysed, wherein I-joints showed about 20-50% higher fatigue life. Fractographic tests of fatigue fractures in joints revealed the details of fatigue cracking and differences in the propagation rate of fatigue cracks.

Microstructural, surface and fatigue analysis of stress peened leaf springs

2015 ◽  
Vol 6 (5) ◽  
pp. 589-604 ◽  
Author(s):  
Georgios Savaidis ◽  
Stylianos Karditsas ◽  
Alexander Savaidis ◽  
Roselita Fragoudakis
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Fatigue Life ◽  
Manufacturing Process ◽  
Treatment Process ◽  
High Strength ◽  
Content Type ◽  
Leaf Springs ◽  
Life Analysis ◽  
Fatigue Life Analysis

Purpose – The purpose of this paper is to investigate the fatigue and failure of commercial vehicle serial stress-peened leaf springs, emphasizing the technological impact of the material, the thermal treatment and the stress-peening process on the microstructure, the mechanical properties and the fatigue life. Theoretical fatigue analysis determines the influence of each individual technological parameter. Design engineers can assess the effectiveness of each manufacturing process step qualitatively and quantitatively, and derive conclusions regarding its improvement in terms of mechanical properties and fatigue life. Design/methodology/approach – Two different batches of 51CrV4 were examined to account for potential batch influences. Both specimen batches were subjected to the same heat treatment and stress-peening process. Investigations of their microstructure, hardness and residual stress state on the surface’ areas show the effect of the manufacturing process on the mechanical properties. Wöhler curves have been experimentally determined for the design of high-performance leaf springs. Theoretical fatigue analyses reveal the influence of every above mentioned technological factor on the fatigue life of the specimens. Therewith, the effectiveness and potential for further improvement of the manufacturing process steps are assessed. Findings – Microstructural analysis and hardness measurements quantify the decarburization and the degradation of the specimens’ surface properties. The stress-peening process causes significant compressive residual stresses which improve the fatigue life. On the other hand, it also leads to pronounced surface roughness, which reduces the fatigue life. The theoretical fatigue life analysis assesses the mutual effect of these two parameters. Both parameters cancel each other out in regards to the final effect on fatigue life. The sensitivity of the material and the potential for further improvement of both heat treatment and stress peening is appointed. Research limitations/implications – All quantitative values given here are strictly valid for the present leaf spring batches and should not be widely applied. The results of the present study indicate the sensitivity of high-strength spring steel used here to the various technological factors resulting from the heat treatment and the stress-peening process. In addition, it can be concluded that further research is necessary to improve the two processes (heat treatment process and the stress peening) under serial production conditions. Practical implications – The microstructure investigations in conjunction with the hardness measurements reveal the significant decrease of the mechanical properties of the highly stressed (failure-critical) tensile surface. Therewith, the potential for improvement of the heat treatment process, e.g. in more neutral and controlled atmosphere, can be derived. In addition, significant potential for improvement of the serially applied stress-peening process is revealed. Originality/value – The paper shows a systematic procedure to assess every individual manufacturing factor affecting the microstructure, the surface properties and finally, the fatigue life of leaf springs. An essential result is the quantification of the surface decarburization and its influence on the mechanical properties. The methodology proposed and applied within the theoretical fatigue life analysis to quantify the effect of technological factors on the fatigue life of leaf springs can be extended to any engineering component made of high-strength steel.

Some Notes on the Influence of Manufacturing on the Fatigue Life of Welded Aluminum Marine Structures

2004 ◽  
Vol 20 (03) ◽  
pp. 164-175
Author(s):  
J. Kecsmar ◽  
R. A. Shenoi
Keyword(s):  
Fatigue Life ◽  
High Speed ◽  
Fatigue Cracking ◽  
High Strength ◽  
Stress Concentrations ◽  
Alloy Matrix ◽  
Workshop Practice ◽  
Weld Porosity ◽  
The Cost ◽  
Fatigue Life Reduction

Designers are constantly looking for ways to reduce the structure weight to lower the overall displacement and hence the cost of fast ferries and other high-speed vessels. The easiest option for the designer is to choose a lightweight material. Aluminum has become the adopted choice of material for high-speed vessels owing to its high strength to weight characteristics. Unlike steel, aluminum is more prone to fatigue cracking and has no fatigue limit. In order to minimize weight, the designer will make use of finite element methods to optimize the scantlings and perform fatigue checks against established codes. This can lead to a structure that has the empirical margins of safety reduced owing to the accuracy of mathematical modeling. However, what is often overlooked is the effect the manufacturing process has on the fatigue life of the fabricated structure. This aspect is excluded from the designer's fatigue calculations, which assist in reducing the scantlings. Currently, there is no guidance for fatigue life reduction for the designer that establishes good and bad workshop practice, other than experience, or the implications of basic shipyard fabrication. It is shown that whereas strain-hardened alloys improve mechanical strength, they reduce ductility. This has consequences when forming the hull plate by potentially introducing crack like flaws into the alloy matrix if the plater overrolls the plate. If there is misalignment or there is too much gap between the plates, the weld will create localized stress concentrations. If the welder has poor joint preparation or gas shielding, porosity can be introduced into the weld. Porosity has a significant effect on the fatigue life of the weldment. This paper brings together a collection of data on such issues that the designer needs to be aware of to prevent an unwanted fatigue failure in the fabrication process.

Study on Fatigue Life of Pressure Vessels Based on Random Load

2012 ◽  
Vol 569 ◽  
pp. 400-404
Author(s):  
Guang Zhong Hu ◽  
Zhong Bin Liu ◽  
Liu Kang ◽  
Tao Quan Wang
Keyword(s):  
Fatigue Life ◽  
Design Theory ◽  
Pressure Fluctuations ◽  
Pressure Vessels ◽  
Stochastic Dynamic ◽  
Load Spectrum ◽  
Random Load ◽  
Life Analysis ◽  
Fatigue Life Analysis ◽  
Coupling Characteristics

The paper discusses the fatigue design theory of pressure vessels. For pressure vessel loads absorbed (pressure, temperature, earthquake, wind, snow, etc.) have significant stochastic dynamic characteristics and coupling characteristics, fatigue life analysis of pressure vessels based on random load history is proposed. Discusses in detail the random load spectrum rain flow counting process, the linear damage theory and fatigue life analysis. The new structure reactor of synthesis system fatigue life is calculated, the results show that the fatigue life and the design life of equipment vary widely, the need to improve pressure fluctuations of the synthesis of system.

Hydrogen-enhanced fatigue life analysis of Cr–Mo steel high-pressure vessels

2017 ◽  
Vol 42 (16) ◽  
pp. 12005-12014 ◽  
Author(s):  
Zhengli Hua ◽  
Xin Zhang ◽  
Jinyang Zheng ◽  
Chaohua Gu ◽  
Tiancheng Cui ◽  
...  
Keyword(s):  
High Pressure ◽  
Fatigue Life ◽  
Pressure Vessels ◽  
Life Analysis ◽  
Fatigue Life Analysis
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