Comparison of Ring Expansion vs Flat Tensile Testing for Determining Linepipe Yield Strength

1996 ◽  
Author(s):  
Wahib E. Saikaly ◽  
William D. Bailey ◽  
Laurie E. Collins
Keyword(s):  
Standard Deviation ◽  
Yield Strength ◽  
Yield Stress ◽  
Tensile Testing ◽  
Accurate Determination ◽  
Tensile Tests ◽  
Ring Expansion ◽  
Tensile Specimen ◽  
Ring Test ◽  
Ring Testing

Ring expansion testing has been compared to conventional tensile testing as a means to evaluate the circumferential yield strength of pipe products. It was found that ring expansion testing provides a more accurate determination of hoop yield stress than tensile testing of flattened pipe samples. In addition, ring testing was found to be more sensitive to the metallurgical condition of the steel. Tests were conducted on ERW and Spiral pipes. Different grades and diameter to thickness (D/t) ratios were evaluated. In comparison to tensile testing on flattened specimens, ring expansion tests gave: a) higher yield strength; and b) reduced standard deviation in test data. The difference in yield strength measured by ring and tensile tests increased with increasing grade and lower D/t. The higher yield strength measured in the ring test is a result of reducing the Bauschinger effect associated with flattening tensile samples. The reduced standard deviation is due to the elimination of flatness and machining variations that occur on a flattened tensile specimen. It was concluded that ring testing provides a true measure of pipe circumferential yield stress.

The Effect of Sample Flattening on Yield Strength Measurement in Line Pipe

2010 ◽  
Author(s):  
Dave G. Crone ◽  
Laurie E. Collins ◽  
Yankui Bian ◽  
Paul Weber
Keyword(s):  
Tensile Strength ◽  
Yield Strength ◽  
Tensile Testing ◽  
Measurement Techniques ◽  
Base Material ◽  
Ring Expansion ◽  
Tensile Specimen ◽  
Forming Process ◽  
Line Pipe ◽  
Ongoing Research

Tensile testing is a key part of the qualification process of Line Pipe. When qualifying pipe products various items are considered when tensile testing; Yield Strength (YS), Ultimate Tensile Strength (UTS), Percent Elongation (%EL), and the Yield Strength to Tensile Strength Ratio (Y/T) are all important. Of these, the YS is the most critical and yet the most sensitive to both preparation and measurement techniques. During the pipe forming process, the base material is plastically formed into a curved shape, and then welded into the final product. The Transverse to Pipe Axis (TPA) tensile specimen removed for testing is curved and must be flattened prior to testing. The flattening process is varied in many facilities and the standards to which testing is conducted are not specific enough to ensure uniformity of procedures. ASTM acknowledges flattening processes and the degree of flatness “may affect test results”, though no guidance is given. This paper will provide an overview of ongoing research efforts, concerning the measurement of the Yield Strength of TPA tensile specimens and its relationship to curvature and flattening methods, prior to testing. By comparing flattened strap tests, to round bar and ring expansion tests, it is shown that the flattened strap test provides a conservative estimate of the actual YS of the pipe.

Tensile testing low density multilayers: Aluminum/titanium

1998 ◽  
Vol 13 (10) ◽  
pp. 2902-2909 ◽  
Author(s):  
D. Josell ◽  
D. van Heerden ◽  
D. Read ◽  
J. Bonevich ◽  
D. Shechtman
Keyword(s):  
Thin Films ◽  
Yield Stress ◽  
Tensile Testing ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Low Density ◽  
Multilayer Thin Films ◽  
Bilayer Thickness ◽  
Relationship Of ◽  
The Relationship

Yield stresses, ultimate tensile strengths, and specific strengths of aluminum/titanium multilayer thin films are determined from the results of uniaxial tensile tests. The plasticity in the stress-strain curves, the nature of the fracture surfaces, and the relationship of the yield stress and the bilayer thickness are discussed. Properties are compared with those of other multilayer materials published in the literature.

scholarly journals Effect of Zr Addition and Aging Treatment on the Tensile Properties of Al-Si-Cu-Mg Cast Alloys

2020 ◽  
Author(s):  
Jacobo Hernandez-Sandoval ◽  
Mohamed H. Abdelaziz ◽  
Agnes M. Samue ◽  
Herbert W. Doty ◽  
Fawzy H. Samuel
Keyword(s):  
Yield Strength ◽  
Tensile Properties ◽  
Tensile Testing ◽  
Quality Index ◽  
Prolonged Exposure ◽  
Aging Treatment ◽  
Tensile Tests ◽  
Heat Treated ◽  
Cast Alloys ◽  
Noticeable Reduction

The present study focused on the tensile properties at ambient and high temperatures of alloy 354 without and with the addition of zirconium. Tensile tests were performed on alloy samples submitted to various aging treatments, with the aim of understanding the effects of the addition made on the tensile properties of the alloy. Zirconium reacts only with Ti, Si, and Al in the alloys examined to form the phases (Al,Si)2(Zr,Ti) and (Al,Si)3(Zr,Ti). Testing at 25°C reveals that the minimum and maximum quality index values, 259 and 459 MPa, are observed for the as-cast and solution heat-treated conditions, respectively. The yield strength shows a maximum of 345 MPa and a minimum of 80 MPa within the whole range of aging treatments applied. The ultimate tensile and yield strength values obtained at room temperature for T5-treated samples stabilized at 250°C for 200 h are comparable to those of T6-treated samples stabilized under the same conditions, and higher in the case of elevated-temperature (250°C) tensile testing. Coarsening of the strengthening precipitates following such prolonged exposure at 250°C led to noticeable reduction in the strength values, particularly the yield strength, and a remarkable increase in the ductility values.

High Strain Rate Tensile Testing

2004 ◽  
pp. 251-263
Keyword(s):  
High Strain Rate ◽  
Strain Rate ◽  
Tensile Testing ◽  
High Strain ◽  
Split Hopkinson Pressure Bar ◽  
Tensile Tests ◽  
Ring Test ◽  
Hopkinson Pressure Bar ◽  
Strain Rate Effects ◽  
Pressure Bar

Abstract High strain rate tensile testing is necessary to understand the response of materials to dynamic loading. The behavior of materials under high strain rate tensile loads may differ considerably from that observed in conventional tensile tests. This chapter discusses the processes involved in determining strain rate effects in tension by conventional tensile tests, expanding ring test, flat plate impact tests, split-Hopkinson pressure bar test, and rotating wheel test, along with their applications, advantages, and disadvantages.

Measurement of Mechanical Properties on Line Pipe: Comparison of Different Methodologies

2014 ◽  
Author(s):  
Steven Cooreman ◽  
Dennis Van Hoecke ◽  
Martin Liebeherr ◽  
Philippe Thibaux ◽  
Mary Yamaguti Enderlin
Keyword(s):  
Mechanical Properties ◽  
Yield Strength ◽  
Tensile Tests ◽  
Ring Expansion ◽  
Isotropic Hardening ◽  
Forming Process ◽  
Element Analysis ◽  
Line Pipe ◽  
Expansion Test ◽  
Round Bar

Line pipe manufacturers always have to verify the mechanical properties on pipe to make sure that the pipe meets the requirements specified by the standard and/or customer. This involves measurement of mechanical properties along the hoop direction. The most accurate way to do so is by performing a ring expansion test, which, however, requires dedicated tools. The two other methodologies consist of standard tensile tests on either non-flattened round bar samples or so called ‘flattened tensile samples’. Round bar samples have the disadvantage that only part of the pipe’s wall thickness is considered. Furthermore they can only be used in case of larger OD/t ratios. Tests on flattened samples, on the other hand, require a flattening operation, which induces additional plastic deformation. However, this flattening operation is not standardized. Moreover, it was observed that the mechanical properties — especially the yield strength — resulting from tensile tests on flattened samples largely depend on test parameters such as residual deflection, extensometer position, flattening procedure, etc. Most manufacturers prefer to test flattened samples, because sample preparation is straightforward and cheap. Moreover it only requires a standard tensile bench. An extensive FEA (Finite Element Analysis) study was launched to investigate the influence of those parameters on the measured yield strength. The applied FEA methodology consists of three steps. First the complete pipe forming process is modeled (in a simplified way). Next a pipe sample is flattened. Finally a tensile sample is cut from the flattened pipe sample and loaded in tension. The mechanical material behaviour is described by a combined kinematic-isotropic hardening model, which allows taking into account the Bauschinger effect. The results are also compared to simulations of ring expansion tests and tests on round bar samples. Next a dedicated experimental test campaign was performed to verify the results of FEA. Results of ring expansion tests are compared to results obtained on round bar samples and flattened tensile samples. The results of this study have shown that the applied methodology significantly affects the measured yield strength. Moreover tests on insufficiently flattened samples could considerably underestimate the actual yield strength on pipe. Finally some guidelines are provided to improve the reproducibility of the measured yield strength when using flattened samples.

Best Practices for Yield Stress Determination Using the Flattened Strap Tensile Test

2014 ◽  
Author(s):  
L. E. Collins ◽  
M. Rashid
Keyword(s):  
Best Practices ◽  
Tensile Properties ◽  
Yield Stress ◽  
Tensile Testing ◽  
Best Practice ◽  
Tensile Specimen ◽  
Flat Plates ◽  
Step Method ◽  
Line Pipe ◽  
Flattening Process

The tensile properties of line pipe are usually determined using a flattened strap tensile sample which is obtained by cutting a long transverse sample from the pipe and then flattening it prior to machining the final tensile coupon. Although, several documents have been published to standardize this test, variability in the reported yield stress for the same material tested by different labs continues to be an issue particularly in high strength line pipe (X70 and X80). Pipe properties are influenced by the pipe forming operations which introduce plastic strain into the steel. As well, the flattening of the tensile blank reverses the deformation and leads to Bauchinger effects which further alter the tensile properties of the material. There is no standard available for the flattening process and pipe manufacturers and operators continue to seek a best practice for the process. In addition, other factors such as placement of extensometer on a flattenend tensile specimen during the tensile testing have been considered a source of variation in the results. Several projects were conducted to identify the source of variability and to standardize the flattening and testing process among the Evraz QA Labs. These initiatives included: a round robin tensile testing program in which tensile tests were performed on flat plates and subsequently on flattened strap specimens produced from a sister plate; examination of a 2-step flattening procedure against a 1-step method, and investigation of the extensometer placement (ID, OD or side mounted) on the recorded stress-strain behaviour. The flattening process was found to be the main source of variability of yield stress. No real trend was observed resulting from extensometer position. Other testing practices such as specimen gripping, zeroing the load and positioning at the start of the test, and the dimensional variability within the reduced section of a specimen were also found to contribute to yield stress variability. Best practices for determination of yield stress using flattened strap tensile samples are discussed.

Regularities and properties of instrumented indentation diagrams obtained by ball-shaped indenter

2020 ◽  
Vol 86 (5) ◽  
pp. 43-51
Author(s):  
V. M. Matyunin ◽  
A. Yu. Marchenkov ◽  
N. Abusaif ◽  
P. V. Volkov ◽  
D. A. Zhgut
Keyword(s):  
Yield Strength ◽  
Ultimate Strength ◽  
Elastoplastic Deformation ◽  
Elastic Limit ◽  
Tensile Tests ◽  
Indentation Load ◽  
International Standards ◽  
Instrumented Indentation ◽  
Indentation Methods ◽  
Special Points

The history of appearance and the current state of instrumented indentation are briefly described. It is noted that the materials instrumented indentation methods using a pyramid and ball indenters are actively developing and are currently regulated by several Russian and international standards. These standards provide formulas for calculating the Young’s modulus and hardness at maximum indentation load. Instrumented indentation diagrams «load F – displacement α» of a ball indenter for metallic materials were investigated. The special points on the instrumented indentation diagrams «F – α» loading curves in the area of elastic into elastoplastic deformation transition, and in the area of stable elastoplastic deformation are revealed. A loading curve area with the load above which the dF/dα begins to decrease is analyzed. A technique is proposed for converting «F – α» diagrams to «unrestored Brinell hardness HBt – relative unrestored indent depth t/R» diagrams. The elastic and elastoplastic areas of «HBt – t/R» diagrams are described by equations obtained analytically and experimentally. The materials strain hardening parameters during ball indentation in the area of elastoplastic and plastic deformation are proposed. The similarity of «HBt – t/R» indentation diagram with the «stress σ – strain δ» tensile diagrams containing common zones and points is shown. Methods have been developed for determining hardness at the elastic limit, hardness at the yield strength, and hardness at the ultimate strength by instrumented indentation with the equations for their calculation. Experiments on structural materials with different mechanical properties were carried out by instrumented indentation. The values of hardness at the elastic limit, hardness at the yield strength and hardness at the ultimate strength are determined. It is concluded that the correlations between the elastic limit and hardness at the elastic limit, yield strength and hardness at the yield strength, ultimate tensile strength and hardness at the ultimate strength is more justified, since the listed mechanical characteristics are determined by the common special points of indentation diagrams and tensile tests diagrams.

scholarly journals Mechanical properties, deformation and fracture mechanisms of bimodal Cu under tensile test

2021 ◽  
Vol 60 (1) ◽  
pp. 15-24
Author(s):  
Silu Liu ◽  
Yonghao Zhao
Keyword(s):  
Yield Strength ◽  
Grain Refinement ◽  
Volume Fraction ◽  
Shear Fracture ◽  
High Strength ◽  
Tensile Specimen ◽  
Deformation Mechanisms ◽  
Fracture Mechanisms ◽  
Fracture Angle ◽  
Area Reduction

Abstract Metals with a bimodal grain size distribution have been found to have both high strength and good ductility. However, the coordinated deformation mechanisms underneath the ultrafine-grains (UFGs) and coarse grains (CGs) still remain undiscovered yet. In present work, a bimodal Cu with 80% volume fraction of recrystallized micro-grains was prepared by the annealing of equal-channel angular pressing (ECAP) processed ultrafine grained Cu at 473 K for 40 min. The bimodal Cu has an optimal strength-ductility combination (yield strength of 220 MPa and ductility of 34%), a larger shear fracture angle of 83∘ and a larger area reduction of 78% compared with the as-ECAPed UFG Cu (yield strength of 410 MPa, ductility of 16%, shear fracture angle of 70∘, area reduction of 69%). Grain refinement of recrystallized micro-grains and detwinning of annealing growth twins were observed in the fractured bimodal Cu tensile specimen. The underlying deformation mechanisms for grain refinement and detwinning were analyzed and discussed.

Quantitative Analysis of Pre-Strain Effect on Mechanical Properties of the Austenitic Stainless Steel

2014 ◽  
Author(s):  
Zhiwei Chen ◽  
Caifu Qian ◽  
Guoyi Yang ◽  
Xiang Li
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Tensile Strength ◽  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Yield Strength ◽  
Tensile Testing ◽  
Control Mode ◽  
Strain Effect ◽  
Strain Control

The test of austenitic stainless steel specimens with strain control mode of pre-strain was carried out. The range of pre-strain is 4%, 5%, 6%, 7%, 8%, 9% and 10% on austenitic stainless steel specimens, then tensile testing of these samples was done and their mechanical properties after pre-strain were gotten. The results show that the pre-strain has little effect on tensile strength, and enhances the yield strength more obviously. According to the experimental data, we get a relational expression of S30408 between the value of yield strength and pre-strain. We can obtain several expressions about different kinds of austenitic stainless steel by this way. It is convenient for designers to get the yield strength of austenitic stainless steel after pre-strain by the value of pre-strain and the above expression.

Modeling of elastic-plastic deformation of the ring parts as applied to the analysis of the results of testing the material of the fuel-element cladding

2021 ◽  
Vol 87 (7) ◽  
pp. 67-75
Author(s):  
V. M. Markochev
Keyword(s):  
Yield Strength ◽  
Fuel Element ◽  
Yield Stress ◽  
Test Procedure ◽  
Analytical Formula ◽  
Residual Deformation ◽  
Pure Bending ◽  
Fuel Element Cladding ◽  
Current Form ◽  
Actual Yield

An analytical formula for a smooth description of the tension diagram of EK-181 steel and a method for rearranging the diagram when changing the direction of deformation are proposed for the first time. The process of straightening a quarter of an annular sample and further stretching is numerically modeled. It is shown that the conditional yield strength of the material of the straightened sample is 7.5% less than the actual conditional yield strength of steel. It is shown that the test for pure bending of a cantilever sample in the form of a semicircle with the processing of the bending diagram (by analogy with GOST 3565–80 for torsion) provides an estimate of the conditional yield strength which is 32% higher than the actual yield strength. The possibility of numerical reconstruction of the tension diagram from the diagram of pure bending of a cantilevered semi-ring sample is proved. It is shown that this procedure really gives the value of the conditional yield strength of steel EK-181 with a tolerance for the residual deformation of 0.2%. The analysis of the test procedure for the rings of fuel element cladding and the proposed algorithm for determination of the conditional yield stress of the ring material is carried out. Attention is drawn to the arbitrariness of the choice of the designed load on the two-stage diagram of the diametrical tension of the ring and to the lack of scientific substantiation of the possibility of determining the yield stress on the second part of the diagram. It is shown that this method in the current form contradicts GOST for tensile testing due to the absence of a base with a uniform stress state on the ring. Therefore, the considered method is not recommended for determining the values of the conditional yield strength suitable for strength calculations.

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