Effects of Hydroforming Process on Fatigue Life of Reinforced S-Shaped Bellows

2019 ◽  
Vol 795 ◽  
pp. 296-303
Author(s):  
Zhe Yuan ◽  
Shi Hui Huo ◽  
Jian Ting Ren
Keyword(s):  
Plastic Deformation ◽  
Fatigue Life ◽  
Plastic Strain ◽  
Wall Thickness ◽  
Mechanical Characteristics ◽  
Forming Process ◽  
Weak Part ◽  
Metal Bellows ◽  
Hydroforming Process ◽  
Fatigue Life Analysis

Reinforced s-shaped bellows, which can withstand high pressure, is a kind of typical reinforced metal bellows. The reinforced s-shaped bellows mainly uses the hydroforming process, and the forming process is a severe plastic deformation process. The hydroforming process and its effects on the fatigue life of reinforced s-shaped bellows were discussed in the present study. Different levels of plastic strain and wall thickness thinning were detected in the hydroforming process. The maximum plastic strain can reached 32%, while the maximum wall thickness thinning ratio is 20%, which occurs on the wave peak. Mechanical characteristics of reinforced s-shaped bellows were discussed considering the effects of hydroforming process. The maximum stress appears on the upper and lower ends, which is the weak part of the structure. Fatigue life of the reinforced s-shaped bellows was analyzed based on the modified Manson-Coffin method. Mechanical properties of related materials, which can be more accurate consideration the effects of hydroforming process, were tested under the pre-plastic deformation. Fatigue life analysis of reinforced s-shaped bellows was carried out and the effects of hydroforming process were discussed. The hydroforming process will lead to a decline in fatigue life, which needs to be considered well in the structural design and analysis. Keywords: Reinforced s-shaped bellows, Hydroforming process, Fatigue life, Mechanical characteristics.

Strain-based fatigue life analysis of pipelines with external defects under cyclic internal pressure

2020 ◽  
pp. 030932472095756
Author(s):  
Hojjat Gholami ◽  
Shahram Shahrooi ◽  
Mohammad shishehsaz
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Plastic Strain ◽  
Internal Pressure ◽  
Oil And Gas ◽  
Isotropic Hardening ◽  
Element Simulation ◽  
Life Analysis ◽  
Fatigue Life Analysis ◽  
Pipe Geometry

Gouge and dent are common mechanical defects in oil and gas pipelines. These defects with plastic strain cause stress concentration in the pipelines. Plastic strain is dependent on initial deformation and spring-back behavior of materials. Therefore, they reduce the fatigue life of pipelines. In this paper, the strain-base fatigue life analysis is investigated in pipelines with smooth dent or combination smooth dent and gouge defects under cyclic internal pressure. For this purpose, elastic-plastic multilinear isotropic hardening finite element simulation was used to investigate the effects of various factors, such as residual stress of dent, amplitude internal pressure, pipe geometry, gouge geometry, and smooth dent geometry on stress concentration factor (SCF). Finally, a new method is proposed for predicting the fatigue life of pipelines with uniform dent and uniform dent and gouge combination defects. The model is presented based on the Smith-Watson-Topper (SWT) criterion. A set of fatigue life test specimens with various pipe materials, size and geometry were prepared and tested. The specimens carried a smooth dent, as well as a combination of smooth dent and gouge defects, results of which were collected to validate those obtained based on the proposed model. The results of the predicted tests using the developed formula showed a good correlation to practical experiments.

Plastic Deformation in Microtomed Sections

1971 ◽  
Vol 29 ◽  
pp. 458-459
Author(s):  
J. Temple Black
Keyword(s):  
Plastic Deformation ◽  
Plastic Strain ◽  
Applied Stress ◽  
Elastic Strain ◽  
High Strain ◽  
Tool Material ◽  
Cutting Edge ◽  
Material Structure ◽  
Geometrical Constraints

The output of the ultramicrotomy process with its high strain levels is dependent upon the input, ie., the nature of the material being machined. Apart from the geometrical constraints offered by the rake and clearance faces of the tool, each material is free to deform in whatever manner necessary to satisfy its material structure and interatomic constraints. Noncrystalline materials appear to survive the process undamaged when observed in the TEM. As has been demonstrated however microtomed plastics do in fact suffer damage to the top and bottom surfaces of the section regardless of the sharpness of the cutting edge or the tool material. The energy required to seperate the section from the block is not easily propogated through the section because the material is amorphous in nature and has no preferred crystalline planes upon which defects can move large distances to relieve the applied stress. Thus, the cutting stresses are supported elastically in the internal or bulk and plastically in the surfaces. The elastic strain can be recovered while the plastic strain is not reversible and will remain in the section after cutting is complete.

scholarly journals Influence of turning tool wear on the surface integrity and anti-fatigue behavior of Ti1023

2021 ◽  
Vol 13 (4) ◽  
pp. 168781402110112
Author(s):  
Li Xun ◽  
Wang Ziming ◽  
Yang Shenliang ◽  
Guo Zhiyuan ◽  
Zhou Yongxin ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Plastic Deformation ◽  
Titanium Alloy ◽  
Fatigue Life ◽  
Tool Wear ◽  
Surface Integrity ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Machined Surface ◽  
Deformation Layer

Titanium alloy Ti1023 is a typical difficult-to-cut material. Tool wear is easy to occur in machining Ti1023, which has a significant negative effect on surface integrity. Turning is one of the common methods to machine Ti1023 parts and machined surface integrity has a direct influence on the fatigue life of parts. To control surface integrity and improve anti-fatigue behavior of Ti1023 parts, it has an important significance to study the influence of tool wear on the surface integrity and fatigue life of Ti1023 in turning. Therefore, the effect of tool wear on the surface roughness, microhardness, residual stress, and plastic deformation layer of Ti1023 workpieces by turning and low-cycle fatigue tests were studied. Meanwhile, the influence mechanism of surface integrity on anti-fatigue behavior also was analyzed. The experimental results show that the change of surface roughness caused by worn tools has the most influence on anti-fatigue behavior when the tool wear VB is from 0.05 to 0.25 mm. On the other hand, the plastic deformation layer on the machined surface could properly improve the anti-fatigue behavior of specimens that were proved in the experiments. However, the higher surface roughness and significant surface defects on surface machined utilizing the worn tool with VB = 0.30 mm, which leads the anti-fatigue behavior of specimens to decrease sharply. Therefore, to ensure the anti-fatigue behavior of parts, the value of turning tool wear VB must be rigorously controlled under 0.30 mm during finishing machining of titanium alloy Ti1023.

scholarly journals An Optimum Fatigue Design of Polymer Composite Compressed Natural Gas Tank Using Hybrid Finite Element-Response Surface Methods

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 483
Author(s):  
Kazem Reza Kashyzadeh ◽  
Seyed Saeid Rahimian Koloor ◽  
Mostafa Omidi Bidgoli ◽  
Michal Petrů ◽  
Alireza Amiri Asfarjani
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Natural Gas ◽  
Response Surface ◽  
Polymer Composite ◽  
Wall Thickness ◽  
Composite Shell ◽  
Compressed Natural Gas ◽  
Fiber Angle ◽  
Composite Tank

The main purpose of this research is to design a high-fatigue performance hoop wrapped compressed natural gas (CNG) composite cylinder. To this end, an optimization algorithm was presented as a combination of finite element simulation (FES) and response surface analysis (RSA). The geometrical model was prepared as a variable wall-thickness following the experimental measurements. Next, transient dynamic analysis was performed subjected to the refueling process, including the minimum and maximum internal pressures of 20 and 200 bar, respectively. The time histories of stress tensor components were extracted in the critical region. Furthermore, RSA was utilized to investigate the interaction effects of various polymer composite shell manufacturing process parameters (thickness and fiber angle) on the fatigue life of polymer composite CNG pressure tank (type-4). In the optimization procedure, four parameters including wall-thickness of the composite shell in three different sections of the CNG tank and fiber angle were considered as input variables. In addition, the maximum principal stress of the component was considered as the objective function. Eventually, the fatigue life of the polymer composite tank was calculated using stress-based failure criterion. The results indicated that the proposed new design (applying optimal parameters) leads to improve the fatigue life of the polymer composite tank with polyethylene liner about 2.4 times in comparison with the initial design.

Effect of Residual Stress or Plastic Deformation History on Fatigue Life Simulation of Pipeline Dents

2018 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Rick Wang
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Fatigue Life ◽  
Residual Stresses ◽  
Three Dimensional ◽  
Strain History ◽  
Deformation History ◽  
Stress Strain ◽  
Element Analysis ◽  
Fea Model

Mechanical dents often occur in transmission pipelines, and are recognized as one of major threats to pipeline integrity because of the potential fatigue failure due to cyclic pressures. With matured in-line-inspection (ILI) technology, mechanical dents can be identified from the ILI runs. Based on ILI measured dent profiles, finite element analysis (FEA) is commonly used to simulate stresses and strains in a dent, and to predict fatigue life of the dented pipeline. However, the dent profile defined by ILI data is a purely geometric shape without residual stresses nor plastic deformation history, and is different from its actual dent that contains residual stresses/strains due to dent creation and re-rounding. As a result, the FEA results of an ILI dent may not represent those of the actual dent, and may lead to inaccurate or incorrect results. To investigate the effect of residual stress or plastic deformation history on mechanics responses and fatigue life of an actual dent, three dent models are considered in this paper: (a) a true dent with residual stresses and dent formation history, (b) a purely geometric dent having the true dent profile with all stress/strain history removed from it, and (c) a purely geometric dent having an ILI defined dent profile with all stress/strain history removed from it. Using a three-dimensional FEA model, those three dents are simulated in the elastic-plastic conditions. The FEA results showed that the two geometric dents determine significantly different stresses and strains in comparison to those in the true dent, and overpredict the fatigue life or burst pressure of the true dent. On this basis, suggestions are made on how to use the ILI data to predict the dent fatigue life.

Micromechanics Method to Evaluate Fatigue Life of Ni-Based Superalloys during Morphological Evolution

2008 ◽  
Vol 385-387 ◽  
pp. 221-224
Author(s):  
Wen Ping Wu ◽  
Ya Fang Guo ◽  
Yue Sheng Wang
Keyword(s):  
Fatigue Life ◽  
Plastic Strain ◽  
Life Prediction ◽  
Morphological Evolution ◽  
Mean Field ◽  
Prediction Method ◽  
Field Method ◽  
External Stress ◽  
Equivalent Inclusion ◽  
Evolution Of Precipitates

A quantitative life prediction method has been proposed to evaluate fatigue life during morphological evolution of precipitates in Ni-based superalloys. The method is essentially based on Eshelby’s equivalent inclusion theory and Mori-Tanaka’s mean field method. The shape stability and life prediction are discussed when the external stress and matrix plastic strain are applied. The calculated results show that the fatigue life is closely related with microstructures evolution of precipitates. The magnitude and sign of the external stress and matrix plastic strain have an important effect on fatigue life of Ni-based superalloys during the morphological evolution of precipitates.

Sign in / Sign up

Export Citation Format

Share Document