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>

Experimental Setup for the Determination of Mechanical Solder Materials Properties at Elevated Temperatures

2010 ◽  
Vol 638-642 ◽  
pp. 3793-3798
Author(s):  
Wolfgang H. Müller ◽  
Holger Worrack ◽  
Jens Sterthaus
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
Elevated Temperatures ◽  
Young's Modulus ◽  
Linear Optimization ◽  
Strain Curve ◽  
Stress And Strain ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Non Linear

The fabrication of microelectronic and micromechanical devices leads to the use of only very small amounts of matter, which can behave quite differently than the corresponding bulk. Clearly, the materials will age and it is important to gather information on the (changing) material characteristics. In particular, Young’s modulus, yield stress, and hardness are of great interest. Moreover, a complete stress-strain curve is desirable for a detailed material characterization and simulation of a component, e.g., by Finite Elements (FE). However, since the amount of matter is so small and it is the intention to describe its behavior as realistic as possible, miniature tests are used for measuring the mechanical properties. In this paper two miniature tests are presented for this purpose, a mini-uniaxial-tension-test and a nanoindenter experiment. In the tensile test the axial load is prescribed and the corresponding extension of the specimen length is recorded, both of which determines the stress-strain- curve directly. The stress-strain curves are analyzed by assuming a non-linear relationship between stress and strain of the Ramberg-Osgood type and by fitting the corresponding parameters to the experimental data (obtained for various microelectronic solders) by means of a non-linear optimization routine. For a detailed analysis of very local mechanical properties nanoindentation is used, resulting primarily in load vs. indentation-depth data. According to the procedure of Oliver and Pharr this data can be used to obtain hardness and Young’s modulus but not a complete stress-strain curve, at least not directly. In order to obtain such a stress-strain-curve, the nanoindentation experiment is combined with FE and the coefficients involved in the corresponding constitutive equations for stress and strain are obtained by means of the inverse method. The stress-strain curves from nanoindentation and tensile tests are compared for two mate-rials (aluminum and steel). Differences are explained in terms of the locality of the measurement. Finally, material properties at elevated temperature are of particular interest in order to characterize the materials even more completely. We describe the setup for hot stage nanoindentation tests in context with first results for selected materials.

An Experimental Investigation of Elastic-Plastic Pulse Propagation in Aluminum Rods

1967 ◽  
Vol 34 (1) ◽  
pp. 91-99 ◽  
Author(s):  
S. R. Bodner ◽  
R. J. Clifton
Keyword(s):  
Room Temperature ◽  
Elevated Temperatures ◽  
Strain Curve ◽  
Static Stress ◽  
Stress Strain Curve ◽  
Proportional Limit ◽  
Stress Strain ◽  
Elastic Plastic ◽  
Time Profiles ◽  
The Impact

Experiments are reported involving elastic-plastic pulses due to explosive loading at one end of long, annealed, commercially pure, aluminum rods at room temperature and at elevated temperatures up to 750 deg F. The stress waves were detected by a condenser microphone at the far end of the rod and, in some cases, by strain gages at a cross section distant from the impact end. The essential features of the recorded velocity-time profiles and strain-time profiles are found to be in agreement with the predictions of rate independent elastic-plastic theory which takes a Bauschinger effect into account. At room temperature, the reference dynamic stress-strain curve does not differ appreciably from the quasi-static stress-strain curve whereas at elevated temperatures there appears to be a marked difference between the dynamic and quasi-static stress-strain curves. The experiments also serve to determine the dynamic proportional limit which is found to be fairly insensitive to temperature. Since the maximum plastic strains are small at cross sections remote from the impact end, the measurements, and consequently the conclusions, are limited to small strains beyond the proportional limit.

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.

Experimental Study on the Mechanical Properties of Shape Memory Alloy

2015 ◽  
Vol 775 ◽  
pp. 204-208
Author(s):  
Cheng Xu ◽  
Qi Rong Zhu
Keyword(s):  
Mechanical Properties ◽  
Shape Memory Alloy ◽  
Shape Memory ◽  
Strain Curve ◽  
Small Scale ◽  
Sample Material ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Alloy Material ◽  
Force Range

In this paper, the technology, equipment and method used to m easure the mechanical properties of micro-scale new-style intelligent shape memory alloy material were studied. First, two groups of small-scale shape memory alloy samples were made and the suitable micro load device was designed according to samples’ size and force range. Then the strain of the samples were observed with the video microscopy and calculated. Comparing with the corresponding force, the stress-strain curves of the two groups of samples were obtained respectively. After fitting these two curves, the stress-strain curve of the sample material was obtained. Finally, the basic mechanical properties of this shape memory alloy materials were discussed.

Creep Analysis for Pressurized Components Under Creep Conditions Based on Isochronous Stress-Strain Curve and Elastic-Perfectly Plastic Material Model

2018 ◽  
Author(s):  
Qi-Wei Xia ◽  
Jian-Guo Gong ◽  
Fu-Zhen Xuan
Keyword(s):  
Elevated Temperatures ◽  
Plastic Material ◽  
Strain Curve ◽  
Inelastic Strain ◽  
Material Model ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Perfectly Plastic ◽  
Creep Analysis ◽  
Elastic Perfectly Plastic

This work is to address the creep analysis for components at elevated temperatures based on isochronous stress-strain curve and the elastic-perfectly plastic material model through numerical analyses. Numerical results presented that the creep deformation is very sensitive to the target inelastic strain chosen for analysis. A small inelastic strain, corresponding to a small yield stress, can cause very conservative result for the case studied. Moreover, the target inelastic strain, corresponding to the minimum inelastic strain along with the given path, is different from each other for various internal pressures.

Engineering Analysis of the Warm Prestressing (WPS) Effect: Influence of Stress-Strain Curve, Specimen Size and WPS Level

2006 ◽  
Author(s):  
Jiri Novak
Keyword(s):  
Strain Curve ◽  
Theoretical Models ◽  
Small Scale ◽  
Strain Hardening Exponent ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Warm Prestressing ◽  
Universal Dependence ◽  
Scale Yielding

Under WPS effect is understood ratio of stress intensity factor at fracture after WPS (Kfr) and the “usual” fracture toughness KIc. Theoretical models of WPS effects were derived for Small Scale Yielding (SSY) conditions. For comparison of experimental results with theory, classical Chell model was chosen: real Kfrexper is compared with predicted KfrChell. For characterization of pre-stress level in case of small specimens, it is convenient to use elastoplastic quantity KJWPS corrected to the equivalent KJWPS in SSY conditions; this quantity is denoted by symbol KJWPS(SSY). For material with certain stress-strain curve σ = f(ε), universal dependence of Kfrexper/KfrChell on KJWPS(SSY) was obtained, which describes behaviour of specimens of different sizes. If another stress-strain curve has the same shape (i.e. if σ = const.f(ε)), KIcfrexper/KfrChell lies (up to the accuracy of experiments) on the universal dependence curve Kfrexper/KfrChell vs. KJWPS(SSY)/σy, where KJWPS(SSY)/σy is a quantity proportional to the square root of the plastified zone size in SSY conditions. Different stress-strain curve shapes lead to smaller or greater Kfrexper/KfrChell. Stress-strain curves cannot be generally expressed by power law hardening, but the Curry-Smith model derived with the use of Ramberg-Osgood law qualitatively predicts the increase or decrease of Kfr in dependence on the strain hardening exponent.

A modified version of MATLAB application window for predicting the weld bead profile and stress–strain plot of AA5052 CMT weldment using ER4043

SIMULATION ◽  
2021 ◽  
pp. 003754972110315
Author(s):  
B Girinath ◽  
N Siva Shanmugam
Keyword(s):  
Strain Curve ◽  
Weld Bead ◽  
Welding Parameters ◽  
Bead Geometry ◽  
Hybrid Technique ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Weld Bead Geometry ◽  
Inference System ◽  
Engineering Stress

The present study deals with the extended version of our previous research work. In this article, for predicting the entire weld bead geometry and engineering stress–strain curve of the cold metal transfer (CMT) weldment, a MATLAB based application window (second version) is developed with certain modifications. In the first version, for predicting the entire weld bead geometry, apart from weld bead characteristics, x and y coordinates (24 from each) of the extracted points are considered. Finally, in the first version, 53 output values (five for weld bead characteristics and 48 for x and y coordinates) are predicted using both multiple regression analysis (MRA) and adaptive neuro fuzzy inference system (ANFIS) technique to get an idea related to the complete weld bead geometry without performing the actual welding process. The obtained weld bead shapes using both the techniques are compared with the experimentally obtained bead shapes. Based on the results obtained from the first version and the knowledge acquired from literature, the complete shape of weld bead obtained using ANFIS is in good agreement with the experimentally obtained weld bead shape. This motivated us to adopt a hybrid technique known as ANFIS (combined artificial neural network and fuzzy features) alone in this paper for predicting the weld bead shape and engineering stress–strain curve of the welded joint. In the present study, an attempt is made to evaluate the accuracy of the prediction when the number of trials is reduced to half and increasing the number of data points from the macrograph to twice. Complete weld bead geometry and the engineering stress–strain curves were predicted against the input welding parameters (welding current and welding speed), fed by the user in the MATLAB application window. Finally, the entire weld bead geometries were predicted by both the first and the second version are compared and validated with the experimentally obtained weld bead shapes. The similar procedure was followed for predicting the engineering stress–strain curve to compare with experimental outcomes.

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