Flow Curve Determination at Large Plastic Strain Levels to Accurately Constitutive Equations of AHSS in Forming Simulation

2011 ◽  
Author(s):  
X. Lemoine ◽  
S. Sriram ◽  
R. Kergen
Keyword(s):  
Plastic Strain ◽  
Constitutive Equations ◽  
Flow Curve ◽  
Large Plastic Strain ◽  
Forming Simulation ◽  
Curve Determination

151 Apparatus for Providing Large Plastic Strain on Material and its Application

2009 ◽  
Vol 2009.58 (0) ◽  
pp. 31-32
Author(s):  
Minoru YAMASHITA ◽  
Joji SATO ◽  
Toshio HATTORI
Keyword(s):  
Plastic Strain ◽  
Large Plastic Strain

Analysis of the Hydraulic Bulge Test with FEA Concerning the Accuracy of the Determined Flow Curves

2009 ◽  
Vol 410-411 ◽  
pp. 439-447 ◽  
Author(s):  
Alper Güner ◽  
Alexander Brosius ◽  
A. Erman Tekkaya
Keyword(s):  
Flow Curve ◽  
Material Flow ◽  
High Strength ◽  
Bulge Test ◽  
Flow Curves ◽  
Element Analysis ◽  
Hydraulic Bulge ◽  
The Finite Element Analysis ◽  
Curve Determination ◽  
Set Up

This work covers the finite element analysis of geometric and process parameters in hydraulic bulge tests in terms of the accuracy of the evaluated flow curve. The important parameters are identified and varied to cover the whole range of possible uses. The effects of these parameters are analyzed for three representative materials: aluminium, mid-strength steel, and high-strength steel. The flow curves of the materials for each set of parameters are calculated by using the results of the simulations and the membrane theory. It is seen that even with simulation results, it is not always possible to obtain the input flow curve, especially towards the end of the test. The dimensions of the sheet and the tooling affect the plastic strain development and geometry of the bulge, leading to errors in computed flow curves. In order to observe the effect of the material flow from the flange on the determined yield stresses, the function and position of the drawbeads are also examined. These parameters, together with the method used to calculate the radius of the bulge, determine the accuracy of the calculated flow curve. Guidelines for an accurate flow curve determination regarding the test set-up and calculation methods are given.

Fitness-For-Service Assessment of the Pipelines with Localized Geometric Imperfections such as Buckles and Wrinkles

2008 ◽  
Vol 385-387 ◽  
pp. 173-176
Author(s):  
Zheng Mao Yang ◽  
Shashi Bhushan Kumar ◽  
Jens P. Tronskar
Keyword(s):  
Plastic Strain ◽  
Fracture Resistance ◽  
Assessment Procedure ◽  
Test Results ◽  
Single Edge ◽  
Large Plastic Strain ◽  
Failure Assessment ◽  
Critical Flaw ◽  
Edge Notch ◽  
Girth Welds

In this paper, FFS assessment procedure for the buckle damaged pipeline with cracks in the girth welds is presented. For FFS assessment the tensile and J R-curve data from a pre-strained pipeline material, API 5L X65 were obtained in the laboratory to study the influences of the large plastic strain on the material properties and the fracture resistance of the pipeline girth welds. Tensile and single edge notch bend specimens in as-received, 10% pre-strained and 20% prestrained conditions were tested. The test results show significant increase in yield and tensile strength in the pre-strained specimens. Generally, the elongation and fracture resistance decreased after pre-straining. In FFS material specific failure assessment diagrams (FADs) generated based on the stress-strain curves obtained from testing were used. The critical flaw sizes of the pipeline girth welds were calculated, and the influence of the large plastic strain on the FFS results was discussed.

Influence of Localized Geometric Imperfections i.e. Buckles and Wrinkles on the Integrity of Pipelines

2008 ◽  
Author(s):  
Zhengmao Yang ◽  
Kumar Shashi ◽  
Jens P. Tronskar
Keyword(s):  
Stress Concentration ◽  
Plastic Strain ◽  
Material Properties ◽  
Fracture Resistance ◽  
Axial Strain ◽  
Compressive Strain ◽  
Mechanical Damage ◽  
Local Deformation ◽  
Local Geometry ◽  
Large Plastic Strain

Pipelines are relied upon to transport hazardous liquids and gasses over long distances. A major threat to the integrity of pipelines is mechanical damage, caused by outside natural forces. According to the AGA report [1], 39% of offshore and 37.7% land based natural gas pipeline failures were caused by outside force. During the installation of offshore pipelines the pipe wall at the 6 o’clock position sees large compressive strain and local buckling may occur. Dents may also occur by impact onto hard objects such as the rollers on the stinger or rocks on the seabed and by anchor impact etc. These kinds of imperfections change the local geometry of the pipe, and therefore, a stress concentration and local bending stress will be induced. The stress concentration factor can be up to 10 depending on the geometry of the imperfection. As a result, the local stresses will be much higher than the design stresses for the pipeline in operation subject to internal pressure and axial strain, and fracture and fatigue capacity of the pipelines with these imperfections will decrease dramatically. Because of the large local deformation, the materials in the deformed pipe region have undergone large local plastic strains i.e. 10–20% plastic deformation. The material properties of the pipe with large plastic strain will be drastically changed, and therefore the fracture resistance of the pipe is expected to be decreased, especially when the damage is located at the seam or girth welds. To assess the criticality of such damage which often can be associated with strain induced flaws in the heavily deformed parent metal and welds, ‘fitness-for-service’ assessment is required. The objective is to determine the severity of the flaws in the deformed pipe and to make the repair/replacement decision. At present there are no definitive assessment guidelines that consider these aspects and how to incorporate the behaviour and fracture capacity of the heavily deformed material. In this paper, a numerical model of typical local imperfections i.e. buckles and wrinkles was established from the in-situ geometry measurements. The local stress distributions of the pipes were analyzed. Based on this stress analyses, the stress concentration around the local imperfections in operation were obtained and the fracture capacity and fatigue life of the pipeline was assessed. The tensile and J R-curve data for deformed pipeline materials were obtained by the DNV Energy laboratory to study the influences of the large plastic strain on the material properties, and the fracture resistance and fatigue crack growth of the pipe. Based on the numerical analysis and test results, a fracture combined fatigue assessment was performed to decide on the mitigation and remediation strategies for the pipeline.

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