scholarly journals A New Methodology for Predicting Brittle Fracture of Plastically Deformable Materials: Application to a Cold Shell Nosing Process

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1593
Author(s):  
Jae Gun Eom ◽  
Sang Woon Byun ◽  
Seung Won Jeong ◽  
Wan Jin Chung ◽  
Man Soo Joun
Keyword(s):  
Brittle Fracture ◽  
Bauschinger Effect ◽  
Effective Strain ◽  
Critical Value ◽  
Quantitative Agreement ◽  
Maximum Principal Stress ◽  
Traditional Theory ◽  
Brittle Fractures ◽  
Deformable Materials ◽  
Damage Criteria

The traditional theory of ductile fracture has limitations for predicting crack generation during a cold shell nosing process. Various damage criteria are employed to explain fracture and failure in the nose part of a cold shell. In this study, differences in microstructure among fractured materials and analysis of their surfaces indicated the occurrence of brittle fractures. The degree of “plastic deformation-induced embrittlement” (PDIE) of plastically deformable materials affects the likelihood of brittle fractures; PDIE can also decrease the strength in tension due to the Bauschinger effect. Two indicators of brittle fracture are presented, i.e., the critical value of PDIE and the allowable tensile strength (which in turn depends on the degree of PDIE or embrittlement-effective strain). When the maximum principal stress is greater than the latter and the PDIE is greater than the former, our method determines the likelihood of brittle fracture. This approach was applied to an actual cold shell nosing process, and the predictions were in good quantitative agreement with the experimental results.

Modelling of the Ductile Damage Behaviour of a Beta Solidifying Gamma Titanium Aluminide Alloy during Hot-Working

2014 ◽  
Vol 783-786 ◽  
pp. 556-561 ◽  
Author(s):  
Dilek Halici ◽  
Daniel Prodinger ◽  
Cecilia Poletti ◽  
Daniel Huber ◽  
Martin Stockinger ◽  
...  
Keyword(s):  
Titanium Aluminide ◽  
Titanium Aluminides ◽  
Hydrostatic Stress ◽  
Effective Strain ◽  
Maximum Principal Stress ◽  
Ductile Damage ◽  
Hot Workability ◽  
Gamma Titanium Aluminide ◽  
Gamma Titanium ◽  
Damage Criteria

Gamma titanium aluminides are innovative materials for high temperature and light weight applications [1]. On the other hand, their hot workability can be limited by failure during hot deformation processes. The prediction of ductile damage in metallic materials can be performed by macromechanical ductile damage criteria [2-4]. If the calculated damage D parameter exceeds a critical value Dc, the material fails. Some macromechanical ductile damage criteria are shown in Table 1, with σ as effective stress, ε as effective strain, σmax as maximum principal stress, σm as hydrostatic stress (mean stress) and εf as equivalent fracture strain. The damage responds to strain localization and thus, to multiaxial stress concentration that increases fracture probability.

scholarly journals Brittle Fracture Theory Describes the Onset of Frictional Motion

2019 ◽  
Vol 10 (1) ◽  
pp. 253-273 ◽  
Author(s):  
Ilya Svetlizky ◽  
Elsa Bayart ◽  
Jay Fineberg
Keyword(s):  
Friction Coefficient ◽  
Brittle Fracture ◽  
Static Friction ◽  
Quantitative Agreement ◽  
Interface Fracture ◽  
Earthquake Dynamics ◽  
Rupture Dynamics ◽  
Static Friction Coefficient ◽  
Fracture Theory ◽  
Macroscopic Motion

Contacting bodies subjected to sufficiently large applied shear will undergo frictional sliding. The onset of this motion is mediated by dynamically propagating fronts, akin to earthquakes, that rupture the discrete contacts that form the interface separating the bodies. Macroscopic motion commences only after these ruptures have traversed the entire interface. Comparison of measured rupture dynamics with the detailed predictions of fracture mechanics reveals that the propagation dynamics, dissipative properties, radiation, and arrest of these “laboratory earthquakes” are in excellent quantitative agreement with the predictions of the theory of brittle fracture. Thus, interface fracture replaces the idea of a characteristic static friction coefficient as a description of the onset of friction. This fracture-based description of friction additionally provides a fundamental description of earthquake dynamics and arrest.

Prediction of the Absence of Brittle Failure Risk for Ferritic Steel Piping Components in the Brittle-Ductile Region

2011 ◽  
Author(s):  
S. Marie ◽  
J. Schwab ◽  
S. Vidard
Keyword(s):  
Brittle Fracture ◽  
Fracture Risk ◽  
Brittle Failure ◽  
Risk Evaluation ◽  
Critical Stress ◽  
Ferritic Steel ◽  
Loading Condition ◽  
Maximum Principal Stress ◽  
Fracture Transition ◽  
Secondary Loop

This paper deals with the brittle fracture risk evaluation for a C-Mn piping component in the upper shelf of the brittle to ductile fracture transition temperature range, with the main objective to validate a predictive criteria, able to demonstrate the complete absence of brittle fracture risk. The criteria is based one a critical stress and the volume around the crack were the maximum principal stress exceed this critical stress. The model is calibrated on notched tensile specimens and CT specimens. A four-points bending pipe test has then been designed using this criterion to insure that no brittle fracture will occurs at a temperature that all CT specimens failed by cleavage. The material is a French secondary loop Tu42C ferritic steel and the pipe dimensions for the test are the same than the size of the principal secondary loop pipes. The results of the pipe test confirm the prediction with the model and the interpretation lead to define an equivalence between the loading conditions (based on the J parameter) of the pipe and the loading condition of a CT specimen.

scholarly journals A New Fracture Analysis Technique for Charpy Impact Test Using Image Processing

2021 ◽  
Vol 59 (1) ◽  
pp. 61-66
Author(s):  
Tae Chang Park ◽  
Beom Suk Kim ◽  
Ji Hee Son ◽  
Yeong Koo Yeo
Keyword(s):  
Image Processing ◽  
Brittle Fracture ◽  
Ductile Fracture ◽  
Impact Test ◽  
Charpy Impact ◽  
Charpy Impact Test ◽  
Fracture Analysis ◽  
Binary Image ◽  
Fracture Area ◽  
Brittle Fractures

The Charpy impact test is used to identify the transition between ductility and brittleness. The percentages of ductile and brittle fractures in steel can be evaluated based on each fracture area, which is presently determined by an analyzer with the naked eye. This method may lead to subjective judgement, and difficulty accurately quantifying the percentage. To resolve this problem, a new analysis method based on image processing is proposed in this study. A program that can automatically calculate the percentage of the ductile and brittle fractures has been developed. The analysis is performed after converting an RGB fracture image into a binary image using image processing techniques. The final binary image consists of 0 and 1 pixels. The parts with the pixel values of 1 correspond to the brittle fracture areas, and the pixel values of 0 represent the ductile fracture areas. As a result, by counting the number of 0 pixels in the entire area, it is possible to automatically calculate the percentage of ductile fracture. Using the proposed automatic fracture analysis program, it is possible to selectively distinguish only the brittle fracture from the entire fracture area, and to accurately and quantitatively calculate the percentages of ductile and brittle fractures.

Limits to elastic response. Yielding and failure

2020 ◽  
pp. 357-368
Author(s):  
Lallit Anand ◽  
Sanjay Govindjee
Keyword(s):  
Shear Stress ◽  
Tensile Stress ◽  
Critical Value ◽  
Maximum Principal Stress ◽  
The Body ◽  
Elastic Response ◽  
Elastic Behaviour ◽  
Pressure Independent ◽  
Yield Conditions ◽  
Is Failure

This chapter presents conditions for determining the limits of elastic behaviour for isotropic materials. The stress invariants of equivalent pressure, equivalent shear stress, and equivalent tensile stress are defined. These are then used to define common yield conditions, viz. the pressure-independent Mises and Tresca yield conditions, as well as the pressure-dependent Coulomb-Mohr and the Drucker-Prager yield conditions. Rankine’s failure criterion for brittle materials in tension, that is failure in a brittle material will initiate when the maximum principal stress at a point in the body reaches a critical value, is also discussed.

scholarly journals Prediction of Crack Formation for Cross Wedge Rolling of Harrow Tooth Preform

Materials ◽  
2019 ◽  
Vol 12 (14) ◽  
pp. 2287 ◽  
Author(s):  
Zbigniew Pater ◽  
Janusz Tomczak ◽  
Tomasz Bulzak ◽  
Jarosław Bartnicki ◽  
Arkadiusz Tofil
Keyword(s):  
Crack Formation ◽  
Experimental Testing ◽  
Critical Value ◽  
Cross Wedge Rolling ◽  
Laboratory Conditions ◽  
University Of Technology ◽  
Material Fracture ◽  
Damage Criteria

The article presents the issue of material fracture during the process of cross-wedge rolling (CWR). The object of the research was the process of forming a harrow tooth preform. In the conducted analysis nine damage criteria were applied. The critical value of damage was determined with a new calibrating test, basing on rotational compression of a sample in a channel. The results of calculations were compared to the results of experimental testing performed in laboratory conditions in Lublin University of Technology. On the basis of the obtained results an assessment of the applied damage criteria and their applicability in the analysis of CWR processes was conducted.

scholarly journals Determination of the critical value of damage in a channel-die rotational compression test

2019 ◽  
Vol 13 (6) ◽  
pp. 993-1002
Author(s):  
Z. Pater ◽  
J. Tomczak ◽  
T. Bulzak ◽  
Ł. Wójcik ◽  
P. Walczuk
Keyword(s):  
Finite Element Method ◽  
Critical Value ◽  
Material Damage ◽  
The Finite Element Method ◽  
Axial Zone ◽  
Compression Process ◽  
Skew Rolling ◽  
Damage Criteria ◽  
Critical Damage

AbstractThis article describes the problems involved in modelling material cracking in skew rolling processes. The use of the popular damage criteria is impossible because of the lack of a calibration test that would make it possible to determine the critical value of material damage under conditions similar to those found in skew rolling. To fill this gap, a test called channel-die rotational compression was proposed. It consisted of rolling a disk-shaped specimen in a cavity created by two channels of cooperating tools (flat dies), which had heights smaller than the diameter of the specimen. When the rolling path was sufficiently long, a crack formed in the axial zone of the specimen. In this test, modelling using the finite element method made it possible to determine the critical values of material damage. As an illustration, the test was used to determine the critical damage value when conducting a rotational compression process on 50HS steel (1.5026) specimens formed in the temperature range of 950–1200 °C. The analysis was conducted using the Cockcroft–Latham damage criterion.

Effect of Friction on Billet Deformation during Multi-Axial Compressions

2010 ◽  
Vol 143-144 ◽  
pp. 879-883
Author(s):  
Feng Jian Shi ◽  
Si Zhen Ye ◽  
Lei Gang Wang ◽  
Sheng Lu
Keyword(s):  
Finite Element Method ◽  
Principal Stress ◽  
Effective Strain ◽  
Longitudinal Axis ◽  
Maximum Principal Stress ◽  
Rigid Plastic ◽  
Stress Increase ◽  
Maximum Compression ◽  
Compression Load ◽  
Strain Inhomogeneity

The effect of friction on compression load, effective strain, damage value and maximum principal stress were analyzed by rigid-plastic finite element method during multi-axial compressions (MAC). The results show that with the number of compressions, the maximum compression load increases gradually, the effective strain distributes ringwise and the maximum effective strain is in the center and the minimum at the surface. The damage is inclined to appear at the barreled shape perpendicular to the longitudinal axis. With the increase of friction coefficient, the maximum compression load, strain inhomogeneity, damage value and maximum principal stress increase under the condition of same number of compression. These results indicate that the friction is adverse during MAC. Appropriate measures should be adopted to decrease the effect of frictional force.

Stress Concentrations for Filled and Unfilled Closely Spaced Cylindrical Defects

1985 ◽  
Vol 107 (4) ◽  
pp. 271-276 ◽  
Author(s):  
T. Ihara ◽  
M. C. Shaw
Keyword(s):  
Brittle Fracture ◽  
Tensile Stress ◽  
Young’S Modulus ◽  
Fracture Stress ◽  
Brittle Materials ◽  
Critical Value ◽  
Stress Concentrations ◽  
High Quality ◽  
Close Spacing ◽  
The Matrix

All real materials contain defects which significantly reduce the fracture stress of brittle materials. It has been proposed by Griffith [3] that brittle fracture occurs when the maximum intensified tensile stress on the surface of a defect reaches a critical value. It has recently been found [1] that for many brittle materials of high quality, the nature and density of the defects are such that they may be modelled by isolated cylindrical voids. This study considers the stress intensification consequences of the close spacing of cylindrical defects that are filled with a material having a Young’s modulus different than that of the matrix.

Brittle Fracture Assessments of Offshore PSVs

2014 ◽  
Author(s):  
Kannan Subramanian ◽  
Jorge Penso ◽  
Harbi Pordal ◽  
Graham McVinnie ◽  
Greg Garic
Keyword(s):  
Brittle Fracture ◽  
Stress Analysis ◽  
Stress Ratio ◽  
Operating Conditions ◽  
Ratio Method ◽  
Conservative Approach ◽  
Relief Valve ◽  
Valve Body ◽  
Fracture Assessment ◽  
Brittle Fractures

Pressure safety relief valve needs to be designed and operated to assure metal temperatures are not lower than the Minimum Allowable Temperature (MAT) to prevent brittle fractures. Design and fitness for service codes include general procedures to prevent brittle fractures. Design procedures in the codes are very conservative whereas fitness for service codes in some cases lack details. In the absence of a detailed brittle fracture assessment procedure for valves subject to significant low temperatures as a result of either Joule-Thompson effect or auto-refrigeration, an approach involving pressure based stress ratio method of ASME/API 579, Part 3 has been adopted and implemented. The initial and very conservative approach involved a worst case combination of the upstream pressure while calculating the stress ratio and a comparison of the newly established MAT with the downstream temperature. This conservative approach resulted in the disqualification of numerous PSVs studied in this work. Valve replacement and associated lost production time leads to high costs. A sophisticated and appropriately conservative brittle fracture assessment approach involving the use of computational fluid dynamics (CFD) followed by finite element method analysis (FEA) based stress analysis was adopted based on the concepts defined in ASME/API 579 and is presented in this paper. Predictive CFD analysis establishes more realistic temperatures and pressures in relation to the actual operating conditions. The CFD predicted pressure and temperature field is used to determine the stresses in the valve body using FEA methods. The stress analysis is followed by an intermediate brittle fracture assessment based on the procedures described in API 579 Part 3 using the actual PSV body metal temperatures and stresses established using the stress analysis. A discussion on the allowable stresses and stress components to be used in this intermediate assessment is also presented. If the PSVs cannot be qualified with this intermediate brittle fracture assessment, fracture mechanics evaluations are carried out to establish the limiting flaw sizes for the valves. In addition, the flaw tolerances of the valves are also established using reference flaw approach described in API 579, Part 9.

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