Ductile fracture in plane stress

2021 ◽  
pp. 1-15
Author(s):  
Mohammad Torki ◽  
A. Amine Benzerga
Keyword(s):  
Ductile Fracture ◽  
Plane Stress ◽  
Shape Change ◽  
Simple Procedure ◽  
Ductile Failure ◽  
Fracture Initiation ◽  
Fracture Locus ◽  
New Criterion ◽  
Stress Invariant ◽  
Isotropic Theory

Abstract A micromechanics-based ductile fracture initiation theory is developed for high-throughput assessment of ductile failure in plane stress. A key concept is that of inhomogeneous yielding such that microscopic failure occurs in bands with the driving force being a combination of band-resolved normal and shear tractions. The new criterion is similar to the much popularized Mohr—Coulomb model, but the sensitivity of fracture initiation to the third stress invariant constitutes an emergent outcome of the formulation. Salient features of a fracture locus in plane stress are parametrically analyzed. In particular, it is shown that a finite shear ductility cannot be rationalized based on an isotropic theory that proceeds from first principles. Thus, the isotropic formulation is supplemented with an anisotropic model accounting for void rotation and shape change in order to complete the prediction of a fracture locus and compare with experiments. A wide body of experimental data from the literature is explored and a simple procedure for calibrating the theory is outlined. Comparisons with experiments are discussed in some detail.

DUCTILE FAILURE SIMULATION IN SPHERODIZED STEEL USING A CONTINUUM DAMAGE MECHANICS COUPLED FINITE ELEMENT FORMULATION

2010 ◽  
Vol 07 (02) ◽  
pp. 319-348 ◽  
Author(s):  
SACHIN S. GAUTAM ◽  
P. M. DIXIT
Keyword(s):  
Ductile Fracture ◽  
Damage Mechanics ◽  
Ductile Failure ◽  
Fracture Initiation ◽  
Continuum Damage Mechanics ◽  
Critical Value ◽  
Experimental Results ◽  
Element Formulation ◽  
Continuum Damage ◽  
Mechanics Model

Ductile fracture occurs due to microvoid nucleation, growth and, finally, coalescence into microcracks. These microcracks grow in the presence of stresses leading to fracture. In this work, a criterion based on this phenomenon is used to simulate ductile fracture in a class of steel specimens. A critical value of the damage variable, estimated from experimental results, is used as an indicator of fracture initiation. A continuum damage mechanics model is employed to incorporate the damage in the constitutive relation of the material. A damage growth law based on experimental results is used. It is observed that the damage reaches the critical value first at the center in both the cylindrical and prenotched specimens. Thus, the failure begins at the center and then grows radially outward toward the free surface. The analysis is carried out till the damage reaches the critical value across the whole cross-section, at which point the specimen is considered to have failed.

scholarly journals Prediction of Ductile Fracture in Metal Blanking

1999 ◽  
Vol 122 (3) ◽  
pp. 476-483 ◽  
Author(s):  
A. M. Goijaerts ◽  
L. E. Govaert ◽  
F. P. T. Baaijens
Keyword(s):  
Finite Element ◽  
Tensile Test ◽  
Ductile Fracture ◽  
Experimental Error ◽  
Fracture Initiation ◽  
Fracture Model ◽  
Ductile Fracture Model ◽  
Blanking Process ◽  
Ductile Fracture Initiation

This study is focused on the description of ductile fracture initiation, which is needed to predict product shapes in the blanking process. Two approaches are elaborated using a local ductile fracture model. According to literature, characterization of such a model should take place under loading conditions, comparable to the application. Therefore, the first approach incorporates the characterization of a ductile fracture model in a blanking experiment. The second approach is more favorable for industry. In this approach a tensile test is used to characterize the fracture model, instead of a complex and elaborate blanking experiment. Finite element simulations and blanking experiments are performed for five different clearances to validate both approaches. In conclusion it can be stated that for the investigated material, the first approach gives very good results within the experimental error. The second approach, the more favorable one for industry, yields results within 6 percent of the experiments over a wide, industrial range of clearances, when a newly proposed criterion is used. [S1087-1357(00)02202-4]

An Experimental Evaluation of the Effects of Filtercake in Wellbore Strengthening: Filtercake Rupture Resistance and Fracture Sealing Time

2019 ◽  
Vol 142 (4) ◽  
Author(s):  
Mingzheng Yang ◽  
Yuanhang Chen
Keyword(s):  
Drilling Fluid ◽  
Experimental Tests ◽  
Fracture Initiation ◽  
Vital Role ◽  
Fracture Sealing ◽  
Initiation Stage ◽  
Induced Fractures ◽  
Wellbore Strengthening ◽  
New Criterion

Abstract Recent research studies have indicated that filtercakes play a role in preventing fracture initiation, blocking pre-existing narrow fractures, and isolating drilling-induced fractures at the initiation stage. The ability of the filtercakes to effectively strengthen the wellbore expectedly depends on its capability in maintaining its integrity and providing the barrier to isolate pressure and fluid transmission between the wellbore and fractures. In this research, a modified permeability apparatus was used to evaluate the quality of drilling fluid filtercakes. A new criterion defined as filtercake rupture resistance is proposed to characterize the filtercake quality regarding its ability to sustain pressure over an open fracture. Experimental tests were conducted to investigate how filtercake thickness and filtercake yield strength affect the rupture resistance. The mechanism of filtercake in sealing the narrow fractures is explored, and it was observed that solid's plugging/bridging plays the vital role in this mechanism. A thicker and stronger filtercake also contributes to a faster establishment of complete fracture seal. The results of this research can be utilized as a reference that guides the optimization of drilling fluid for continuously strengthening the wellbore.

Anaylsis of Ductile Fracture Initiation in Corroded Plates

2008 ◽  
Author(s):  
Weiwei Yu ◽  
Ge Wang ◽  
Hyun Chung ◽  
Dale G. Karr
Keyword(s):  
Ductile Fracture ◽  
Failure Modes ◽  
Structural Integrity ◽  
Axial Stress ◽  
Fracture Initiation ◽  
Thin Plates ◽  
Ductile Metals ◽  
Fracture Elongation ◽  
Hull Steel ◽  
Plate Geometry

Corrosion of marine structures often compromises structural integrity by reducing fracture elongation and strength, yield and ultimate strength, and fatigue life. When localized or pitting corrosion occurs, strength reduction can be difficult to establish because the effects of uneven surfaces affect the stress fields and failure modes of the structure. We examine in this paper the effects of corrosion on the ductile fracture of steel plating. Defects in material are known to affect the strain-to-failure of ductile metals. Such effects are included in the analyses presented for thin plates subjected to axial stress with local geometric defects caused by corrosion. A strain-to-failure criterion is used for predicting ductile fracture of the plating. Results of fracture strain reduction for particular corrosion states are presented for common ship hull steel. The reduction in strain to failure is shown to be dependent on the size of the elements considered as well as the pitted plate geometry.

Forensic Analyses of Stress-Strain Diagrams to Evaluate Contributions from Microstructure

2018 ◽  
Vol 941 ◽  
pp. 2270-2277 ◽  
Author(s):  
Shigeo Saimoto ◽  
Michael R. Langille ◽  
Marek Niewczas
Keyword(s):  
Work Hardening ◽  
Shape Change ◽  
Constitutive Relations ◽  
Pure Aluminum ◽  
Ductile Failure ◽  
Large Strains ◽  
Strain Diagram ◽  
Annihilation Process ◽  
Stress Strain ◽  
Strength Factor

The conventional characterization of work-hardening is to approximate the stress-strain diagram using the empirical curve-fitting of Hollomon or Voce. The new method uses the Taylor slip analyses to derive a functional form which is optimally fitted to the data. This constitutive relations analysis (CRA) duplicates the data using at least two fit loci. The fit parameters relate to the slip motion within the microstructure and hence its interpretation reveals the possible dynamic shape-change reactions. The fit-process defines a new yield stress which separates the yielding from the deformation mechanisms at large strains that breaks up into two regions separated by intersection parameters. The applications of CRA to nanovoid formation and growth leading to ductile failure, plane stress yield locus prediction using tensile tests and decoding the stress-strain diagram for age-hardened aluminum alloys have been successful. Using super-pure aluminum, this study confirms that CRA is based on crystal plasticity principles and that CRA can predict the correlation of the obstacle strength factor, α, with work-hardening, hence permitting conversion of flow stress at given strains to obstacle density. The derived results show that the inherent annihilation process and the changing strength factor are coordinated to result in a self-consistent constitutive relation.

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