Consideration of Yield Discontinuity in the Elastic-Plastic Fracture Analysis of Circumferentially Flawed Pipes

2017 ◽  
Author(s):  
Longjie Wang ◽  
Elvin Eren ◽  
Bin Wang ◽  
Guiyi Wu
Keyword(s):  
Driving Force ◽  
Large Scale ◽  
Strain Curve ◽  
Tensile Tests ◽  
Image Correlation ◽  
Uniaxial Tensile ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Stress Plateau ◽  
Crack Driving Force

This study examined the fracture behaviour of pipes containing surface flaws oriented circumferentially and made from a material that exhibits yield discontinuity (known as Lüders plateau) with the view of making recommendations for the assessment of pipes subject to high level of plasticity. Starting with the fundamental and first principles, uniaxial tensile tests were carried out with the use of digital image correlation (DIC) to observe the formation and propagation of Lüders bands quantitatively. Finite element (FE) analyses were then carried out to simulate the Lüders banding phenomenon in uniaxial tensile specimens and consequently cracked pipes. Different material models were adopted in FE analyses, including the stress-strain curve with a flat stress plateau neglecting upper yield stress, and the so-called ‘up-down-up’ (UPU) stress-strain curve for refining crack driving force predictions. The numerical analysis of tensile tests demonstrated that UPU stress-strain model satisfactorily simulated the main macroscopic features of Lüders band observed in the experiment. FE analysis of flawed pipes using both flat and UPU stress-strain curves produced a similar trend in the crack tip opening displacement (CTOD)-strain trajectory as that obtained from large-scale testing. It was seen that the shape of the UPU stress-strain curve, particularly the magnitude of softening, considerably affects the magnitude of crack driving force in the flawed pipe. However, the strain localisation associated with Lüders banding was not observed in the circumferentially flawed pipe in the case of using the flat stress-strain curve. The CTOD crack driving force obtained from simulations was lower than the CTOD obtained from experiments in the Lüders plateau regime, even with the consideration of ductile tearing. Finally, as a result of this study, recommendations on the optimum choice of material parameters were made for more accurate predictions of crack driving force in the presence of yield discontinuity.

Mechanical properties of UN-5100 envelope material for stratospheric airship

2020 ◽  
pp. 1-17
Author(s):  
W.-c. Xie ◽  
X.-l. Wang ◽  
D.-p. Duan ◽  
J.-w. Tang ◽  
Y. Wei
Keyword(s):  
Mechanical Properties ◽  
Significant Role ◽  
Strain Curve ◽  
Image Correlation ◽  
Membrane Structures ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Biaxial Tensile ◽  
Envelope Material ◽  
Biaxial Tensile Testing

ABSTRACT Stratospheric airships are promising aircraft, usually designed as a non-rigid airship. As an essential part of the non-rigid airship, the envelope plays a significant role in maintaining its shape and bearing the external force load. Generally, the envelope material of a flexible airship consists of plain-weave fabric, composed of warp and weft fibre yarn. At present, biaxial tensile experiments are the primary method used to study the stress–strain characteristics of such flexible airship materials. In this work, biaxial tensile testing of UN-5100 material was carried out. The strain on the material under unusual stress and the stress ratio were obtained using Digital Image Correlation (DIC) technology. Also, the stress–strain curve was corrected by polynomial fitting. The slope of the stress–strain curve at different points, the Membrane Structures Association of Japan (MSAJ) standard and the Radial Basis Function (RBF) model were compared to identify the stress–strain characteristics of the materials. Some conclusions on the mechanical properties of the flexible airship material can be drawn and will play a significant role in the design of such envelopes.

Further Investigation of the Hydrostatic Bulge Test in a Plasticity Laboratory

2009 ◽  
Vol 37 (2) ◽  
pp. 159-174
Author(s):  
O. Ifedi ◽  
Q. M. Li ◽  
Y. B. Lu
Keyword(s):  
Tensile Test ◽  
Effective Stress ◽  
Strain Curve ◽  
Plasticity Theory ◽  
Loading Path ◽  
Uniaxial Tensile ◽  
Bulge Test ◽  
Uniaxial Tensile Test ◽  
Stress Strain Curve ◽  
Stress Strain

In plasticity theory, the effective stress–strain curve of a metal is independent of the loading path. The simplest loading path to obtain the effective stress–strain curve is a uniaxial tensile test. In order to demonstrate in a plasticity laboratory that the stress–strain curve is independent of the loading path, the hydrostatic bulge test has been used to provide a balanced biaxial tensile stress state. In our plasticity laboratory we compared several different theories for the hydrostatic bulge test for the determination of the effective stress–strain curve for two representative metals, brass and aluminium alloy. Finite element analysis (FEA) was performed based on the uniaxial tension test data. It was shown that the effective stress–strain curve obtained from the biaxial tensile test (hydrostatic bulge test) had a good correlation with that obtained in the uniaxial tensile test and agreed well with the analytical and FEA results. This paper may be used to support an experimental and numerical laboratory in teaching the concepts of effective stress and strain in plasticity theory.

Deformational characteristics of thermally treated sandstone from an underground coalmine fire region, India

2021 ◽  
Author(s):  
Adarsh Tripathi ◽  
Noopur Gupta ◽  
Ashok Kumar Singh ◽  
Nachiketa Rai ◽  
Anindya Pain
Keyword(s):  
Large Scale ◽  
Elevated Temperatures ◽  
Strain Curve ◽  
Small Scale ◽  
Carbonaceous Shale ◽  
Deformation Pattern ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Thermomechanical Behaviour ◽  
Thermally Treated

<p>The Jharia region of lower Gondwana in India is one of the largest Underground Coalmine Fires (UCF) affected coalfield in the world. The UCF induced small scale as well as large-scale surface fracturing often creates the life-threatening conditions to coal miners and local surroundings. So, there is a need to understand the thermomechanical behaviour of coal measures rocks to predict the land disturbances in thermo-environmental conditions. It will provide an insight into the UCF induced subsidence mechanism and its preventive measures. The Jharia coal field predominantly consists of sandstone (75-80% by volume) and rest is composed of coal, shale and carbonaceous shale. The present study focuses on thermo-mechanical behaviour of Barakar sandstone (BS) under elevated temperatures. The cores of BS sample were prepared according to the ISRM standards. Further, samples were grouped and thermally treated in temperature range of 25°C, 100°C, 150°C, 300°C, 400°C, 500°C, 600 °C, 700°C and 800°C at a heating rate of 5°C/min for 24 hours in furnace.  Then, these thermally treated BS samples were subjected to laboratory test for stress-strain characteristics. In the process of deformational characteristics evaluation, effect of mineralogical changes and mode of fracture pattern were also studied at the mentioned elevated temperature. Based on the obtained results, the deformational behaviour of thermally treated BS specimens can be grouped into three zones, viz., zone 1 (25-300°C), zone 2 (300-500°C) and zone 3 (500-800°C). In zone 1, the characteristics of the stress-strain curve is similar to those under air dried sandstone specimen. However, small increment in stiffness were observed upto 300°C. The stress-strain curves in this zone shows dominantly brittle fracturing. The increment in stiffness may be related to evaporation of pore water that increases the cohesion between the mineral grains resulting higher stiffness value. In zone 2, the deformation pattern again shows brittle fracturing with continuous decrement in stiffness. The reduction in stiffness may be related to thermally induced porosity and increased microcrack density. In zone 3, the stress strain curve is observed to be concave upward. It indicates the pseudo-ductile behaviour of the thermally treated BS specimens. The observed results suggest a typical behaviour of deformation pattern under UCF induced rock fracturing which may be useful in predicting the land subsidence in UCF affected areas. Present research outcome may be used to design the support measures to reduce the associated hazards.</p>

scholarly journals Mechanical Properties of Compact Bone Defined by the Stress-Strain Curve Measured Using Uniaxial Tensile Test: A Concise Review and Practical Guide

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4224
Author(s):  
Che-Yu Lin ◽  
Jiunn-Horng Kang
Keyword(s):  
Mechanical Properties ◽  
Tissue Engineering ◽  
Tensile Test ◽  
Bone Tissue Engineering ◽  
Strain Curve ◽  
Compact Bone ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Stress Strain Curve ◽  
Stress Strain

Mechanical properties are crucial parameters for scaffold design for bone tissue engineering; therefore, it is important to understand the definitions of the mechanical properties of bones and relevant analysis methods, such that tissue engineers can use this information to properly design the mechanical properties of scaffolds for bone tissue engineering. The main purpose of this article is to provide a review and practical guide to understand and analyze the mechanical properties of compact bone that can be defined and extracted from the stress–strain curve measured using uniaxial tensile test until failure. The typical stress–strain curve of compact bone measured using uniaxial tensile test until failure is a bilinear, monotonically increasing curve. The associated mechanical properties can be obtained by analyzing this bilinear stress–strain curve. In this article, a computer programming code for analyzing the bilinear stress–strain curve of compact bone for quantifying the associated mechanical properties is provided, such that the readers can use this computer code to perform the analysis directly. In addition to being applied to compact bone, the information provided by this article can also be applied to quantify the mechanical properties of any material having a bilinear stress–strain curve, such as a whole bone, some metals and biomaterials. The information provided by this article can be applied by tissue engineers, such that they can have a reference to properly design the mechanical properties of scaffolds for bone tissue engineering. The information can also be applied by researchers in biomechanics and orthopedics to compare the mechanical properties of bones in different physiological or pathological conditions.

Strain-Rate Effects on Constitutive Behavior of Sn3.8-Ag0.7-Cu Lead-Free Solder

2009 ◽  
Author(s):  
Kok Ee Tan ◽  
John H. L. Pang
Keyword(s):  
Strain Rate ◽  
Yield Stress ◽  
Strain Curve ◽  
Tensile Tests ◽  
Lead Free ◽  
Indentation Hardness ◽  
Strain Rates ◽  
Test Results ◽  
Stress Strain Curve ◽  
Stress Strain

In this paper, the strain-rate dependent mechanical properties and stress-strain curve behavior of Sn3.8Ag0.7Cu (SAC387) solder is presented for a range of strain-rates at room temperature. The apparent elastic modulus, yield stress properties and stress-strain curve equation of the solder material is needed to facilitate finite element modeling work. Tensile tests on dog-bone shaped bulk solder specimens were conducted using a non-contact video extensometer system. Constant strain-rate uni-axial tensile tests were conducted over the strain-rates of 0.001, 0.01, 0.1 and 1 (s−1) at 25°C. The effects of strain-rate on the stress-strain behavior for lead-free Sn3.8Ag0.7Cu solder are presented. The tensile yield stress results were compared to equivalent yield stress values derived from nano-indentation hardness test results. Constitutive models based on the Ramberg-Osgood model and the Cowper-Symond model were fitted for the tensile test results to describe the elastic-plastic behavior of solder deformation behavior.

scholarly journals A study of the Cu0.95Al0.05 alloy: stress-strain curve and microstructure

2018 ◽  
Vol 20 (2) ◽  
Author(s):  
Emilio Medrano ◽  
Mauro Quiroga ◽  
Felipe A. Reyes
Keyword(s):  
Room Temperature ◽  
Single Phase ◽  
Strain Curve ◽  
Tensile Tests ◽  
Optical Microscope ◽  
Metal Alloys ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Electrolytic Copper ◽  
Mechanical Traction

After fabricating five metallographic specimens of the Cu0.95Al0.05 alloy from electrolytic copper and aluminum, these ones were both microstructurally characterized by using a metallographic optical microscope at room temperature and subjected to mechanical traction in order to chart the stress-strain curve. From the characterization, it has been found out that the Cu0.95Al0.05 microstructure is composed of a single phase, and from the tensile tests, it has been obtained its rupture point, 249.361 MPa. The obtained results were explained in the framework of the theory of metals and metal alloys.

Procedure for the Determination of True Stress-Strain Curves From Tensile Tests With Rectangular Cross-Section Specimens

2004 ◽  
Vol 126 (1) ◽  
pp. 70-76 ◽  
Author(s):  
I. Scheider ◽  
W. Brocks ◽  
A. Cornec
Keyword(s):  
Finite Element ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Strain Curve ◽  
Tensile Tests ◽  
Tensile Specimen ◽  
True Stress ◽  
Image Correlation ◽  
Stress Strain ◽  
Three Dimensional Finite Element

The problem of determining true stress-strain curves from flat tensile specimens beyond the onset of necking has been investigated based on finite element analyses under consideration of experimental accessible data using digital image correlation (DIC). The displacement field on the specimen surface is determined by in-situ deformation field measurement. A three-dimensional finite element study with different stress-strain-curves has been carried out to develop a formula, with which it is possible to calculate the true stress subject to the strain in the necking region. The method has been used to evaluate the true stress-strain curve with a so-called micro flat tensile specimen, which is normally used to determine the material properties in the material gradient around thin weldments.

scholarly journals Study on The Mechanical Properties of Steel - Basalt Fiber Composite Reinforcement (SBFCBs)

2020 ◽  
Vol 165 ◽  
pp. 05028
Author(s):  
Lei Zhao ◽  
Shengjiang Sun ◽  
Wei Qi
Keyword(s):  
Elastic Modulus ◽  
Fiber Composite ◽  
Low Cost ◽  
Basalt Fiber ◽  
Strain Curve ◽  
Tensile Tests ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Failure Patterns ◽  
Steel Bars

Steel bar and Basalt Fiber are combined to obtain a new structural material with high strength, high elastic modulus, high toughness, corrosion resistance, low cost and other excellent comprehensive performance: Steel Basalt Fiber Composite Bars (SBFCBs). In this paper, three different types of composite bars were tested by monotonic tensile tests, and the failure patterns of steel bars were introduced in the process of stretching, and the yield strength, ultimate strength, elastic modulus and stress-strain curves of steel bars were obtained. Test results showed that the stress-strain curve of SBFCBs was obviously double-folded, and SBFCBs exhibited stable post-yielding stiffness after the reinforcement yielded. The stress-strain curve model of SBFCBs under uniaxial tension was derived according to the material’s compounding rule. By sorting the experimental data and comparing it with theoretical values, we could prove the accuracy of the model.

Determination of constitutive relation from miniature tensile test with digital image correlation

2020 ◽  
Vol 55 (3-4) ◽  
pp. 99-108 ◽  
Author(s):  
Yunlu Zhang ◽  
Sreekar Karnati ◽  
Tan Pan ◽  
Frank Liou
Keyword(s):  
Digital Image Correlation ◽  
Tensile Test ◽  
Constitutive Relation ◽  
Digital Image ◽  
Strain Curve ◽  
True Stress ◽  
Image Correlation ◽  
Stress Strain Curve ◽  
Stress Strain

The determination of constitutive relation from the miniature tensile test is of high interest in multiple areas. Here, a convenient experimental method is proposed to determine the true stress–strain curve from the miniature tensile test. The instantaneous cross-sectional area is estimated by only one camera in aid of digital image correlation technique. This method was applied on commercial pure titanium and aluminum 6061 alloys, and the results indicate that the extracted true stress–strain curves are not scale-dependent. The derived mechanical properties from miniature specimens match well with the results of standard specimens. The correctness of the true stress–strain curve was evaluated by the finite element analysis method. The results suggest that the derived true stress–strain curve is capable to represent the constitutive behavior of the tested materials.

Subultimate Prestrain and Aging in Mild Steel

1965 ◽  
Vol 87 (2) ◽  
pp. 319-324 ◽  
Author(s):  
D. K. Felbeck ◽  
W. G. Gibbons ◽  
W. G. Ovens
Keyword(s):  
Mild Steel ◽  
High Speed ◽  
Strain Curve ◽  
Local Stress ◽  
Tensile Tests ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Limited Region ◽  
Small Increments ◽  
Necessary And Sufficient

Room-temperature tensile straining of mild steel followed by aging at 350 F causes return of the upper yield and a raising of the stress-strain curve. Tensile tests on a special rimmed steel of low Mn/C ratio show not only the expected raising of the stress-strain curve, but raising by an additional amount when several small increments of strain are each followed by aging at moderate temperatures. Longitudinal tensile prestrain by rolling gives substantially the same results. Tests of specimens prestrained in a limited region by impact or in slow tension and aged indicate that embrittlement of the whole specimen may result. The combined theories of Griffith and Orowan, plus an extension of the Ludwik triaxiality concept, can provide a consistent description of the local stress and average stress (energy) criteria that are necessary and sufficient for high-speed low-energy fracture to occur.

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