scholarly journals On the micromechanism of inclusion driven ductile fracture and its implications on fracture toughness

2020 ◽  
Author(s):  
Yu Liu ◽  
Xinzhu Zheng ◽  
shmuel osovski ◽  
Ankit Srivastava
Keyword(s):  
Fracture Toughness ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Small Scale ◽  
Crack Advance ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Material Parameters

The objective is to identify the micromechanism(s) of ductile crack advance, and isolatethe key microstructural and material parameters that a?ect these micromechanisms andfracture toughness of ductile structural materials. Three dimensional, ?nite element, ?nitedeformation, small scale yielding calculations of mode I crack growth are carried out forductile material matrix containing two populations of void nucleating particles using anelasto-viscoplastic constitutive framework for progressively cavitating solid. The larger par-ticles or inclusions that result in void nucleation at an early stage are modeled discretelywhile smaller particles that require large strains to nucleate voids are homogeneously dis-tributed. The size, spacing and volume fraction of inclusions introduce microstructure-basedlength-scales. In the calculations, ductile crack growth is computed and fracture toughness ischaracterized. Several features of crack growth behavior and dependence of fracture tough-ness on microstructural and material parameters observed in experiments, naturally emergein our calculations. The extent to which the microstructural and material parameters a?ectthe micromechanisms of ductile crack advance and, hence, the macroscopic fracture tough-ness of the material is discussed. The results presented provide guidelines for microstructuralengineering to increase ductile fracture toughness, for example, the results show that for amaterial with small inclusions, increasing the mean inclusion spacing has a greater e?ect onfracture toughness than for a material with large inclusions.

Influence of Weld Residual Stresses on Ductile Crack Behavior in AISI Type 316LN Stainless Steel Weld Joint

2018 ◽  
Author(s):  
Sai Deepak Namburu ◽  
Lakshmana Rao Chebolu ◽  
A. Krishnan Subramanian ◽  
Raghu Prakash ◽  
Sasikala Gomathy
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Crack Growth ◽  
Weld Joint ◽  
Volume Fraction ◽  
Growth Behavior ◽  
Welding Residual Stress ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth

Welding residual stress is one of the main concerns in the process of fabrication and operation because of failures in welded steel joints due to its potential effect on structural integrity. This work focuses on the effect of welding residual stress on the ductile crack growth behavior in AISI 316LN welded CT specimens. Two-dimensional plane strain model has been used to simulate the CT specimen. X-ray diffraction technique is used to obtain residual stress value at the SS 316LN weld joint. The GTN model has been employed to estimate the ductile crack growth behavior in the CT-specimen. Results show that residual stresses influence the ductile crack growth behavior. The effect of residual stress has also been investigated for cases with different initial void volume fraction, crack lengths.

scholarly journals Influence of matrix characteristics on fracture toughness of high volume fraction Al2O3/Al–AlN composites

2000 ◽  
Vol 15 (5) ◽  
pp. 1145-1153 ◽  
Author(s):  
N. Nagendra ◽  
V. Jayaram
Keyword(s):  
Heat Treatment ◽  
Fracture Toughness ◽  
Steady State ◽  
Crack Growth ◽  
Volume Fraction ◽  
Void Nucleation ◽  
Matrix Composition ◽  
Al Alloy ◽  
Constraint Factor ◽  
The Matrix

The role of matrix microstructure on the fracture of Al-alloy composites with 60 vol% alumina particulates was studied. The matrix composition and microstructure were systematically varied by changing the infiltration temperature and heat treatment. Characterization was carried out by a combination of metallography, hardness measurements, and fracture studies conducted on compact tension specimens to study the fracture toughness and crack growth in the composites. The composites showed a rise in crack resistance with crack extension (R curves) due to bridges of intact matrix ligaments formed in the crack wake. The steady-state or plateau toughness reached upon stable crack growth was observed to be more sensitive to the process temperature rather than to the heat treatment. Fracture in the composites was predominantly by particle fracture, extensive deformation, and void nucleation in the matrix. Void nucleation occurred in the matrix in the as-solutionized and peak-aged conditions and preferentially near the interface in the underaged and overaged conditions. Micromechanical models based on crack bridging by intact ductile ligaments were modified by a plastic constraint factor from estimates of the plastic zone formed under indentations, and are shown to be adequate in predicting the steady-state toughness of the composite.

Effect of Constraint on the Initiation of Ductile Fracture in Shear Loading

2004 ◽  
Vol 261-263 ◽  
pp. 183-188 ◽  
Author(s):  
Majid R. Ayatollahi ◽  
David John Smith ◽  
M.J. Pavier
Keyword(s):  
Fracture Toughness ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Void Growth ◽  
Crack Tip ◽  
Shear Loading ◽  
Mode Ii ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Void Growth And Coalescence

Research studies for mode I cracks have shown that fracture toughness or the critical value of J for fracture initiation, Jcrit is not merely a material property but depends also on the geometry and loading configurations. The geometry dependency of fracture toughness can be attributed to the effect of the crack tip constraint. In this paper, the constraint effect is studies for the initiation stage in mode II ductile crack growth. Two major mechanisms of ductile fracture: 'void growth and coalescence' and 'shear band localization and de-cohesion' are considered. A boundary layer model is simulated using the finite element method and the effect of far-filed T-stress on the relevant stress parameters near the crack tip is studied. It is shown that the initiation of the ductile crack growth in mode II is influenced significantly by T for the mechanism of void growth and coalescence and is insensitive to T for the mechanism of shear localisation and de-cohesion.

Ductile Crack Extension Analysis for X80 Bending Deformation Using Damage-Based Model

2014 ◽  
Author(s):  
Satoshi Igi ◽  
Mitsuru Ohata ◽  
Takahiro Sakimoto ◽  
Kenji Oi ◽  
Joe Kondo
Keyword(s):  
Plastic Strain ◽  
Simulation Model ◽  
Crack Growth ◽  
Crack Extension ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Notch Tip

This paper presents experimental and analytical results focusing on the strain limit of X80 linepipe. Ductile crack growth behavior from a girth weld notch is simulated by FE analysis based on a proposed damage model and is compared with the experimental results. The simulation model for ductile crack growth accompanied by penetration through the wall thickness consists of two criteria. One is a criterion for ductile crack initiation from the notch-tip, which is described by the plastic strain at the notch tip, because the onset of ductile cracking can be expressed by constant plastic strain independent of the shape and size of the components and the loading mode. The other is a damage-based criterion for simulating ductile crack extension associated with damage evolution influenced by plastic strain in accordance with the stress triaxiality ahead of the extending crack tip. The proposed simulation model is applicable to prediction of ductile crack growth behaviors from a circumferentially-notched girth welded pipe with high internal pressure, which is subjected to tensile loading or bending (post-buckling) deformation.

On the Crack Quasi-Static Growth

2019 ◽  
Vol 827 ◽  
pp. 312-317
Author(s):  
Vitalijs Pavelko
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Plastic Material ◽  
Small Scale ◽  
Invariant Equation ◽  
Practical Applications ◽  
Wide Range ◽  
Scale Yielding ◽  
Elastic Plastic Material ◽  
Principal Assumption

The theoretical model of quasi-static crack growth in the elastic-plastic material under load variation in a wide range. Small-scale yielding is principal assumption and main restriction of proposed theory. The model of crack growth provides for continues and interrelated both the crack propagation and plastic deformation development. The nonlinear first-order differential equation describes the quasi-static process of crack growth. In dimensionless form this equation invariant in respect to geometrical configuration and material. The critical size of the plastic zone is proposed as the characteristics of material resistance which is directly connected with the fracture toughness, but more convenient in practical applications of invariant equation. The demonstration of solution is performed for the double cantilever beam that widely used as the standard (DCB) sample for measurement of the mode-I interlaminar fracture toughness. he short analysis of some properties of solution of the invariant equation and its application is done.

Effect of Annealing on Fracture Mechanism of Biodegradable Poly(lactic acid)

2004 ◽  
Vol 261-263 ◽  
pp. 105-110 ◽  
Author(s):  
Sang Dae Park ◽  
Mitsugu Todo ◽  
Kazuo Arakawa
Keyword(s):  
Fracture Toughness ◽  
Lactic Acid ◽  
Crack Growth ◽  
Fracture Mechanism ◽  
Poly Lactic Acid ◽  
Crack Growth Behavior ◽  
Annealing Conditions ◽  
Macroscopic Fracture ◽  
Biodegradable Poly ◽  
Static Fracture

Effect of annealing on the fracture behavior of poly(lactic acid) (PLA) was investigated. Fracture toughness of PLA samples prepared under different annealing conditions was measured under static and dynamic loadings. Microstructure and crack growth behavior were characterized by polarizing microscopy (POM). Crystallinity was determined by DSC analysis. Fracture surface morphology was also studied by scanning electron microscopy. It was shown that the static fracture toughness increased with increase of crystallinity, while the dynamic toughness increased as crystallinity increased. POM exhibited that craze formation played an important role in the fracture mechanism of amorphous samples. Macroscopic fracture toughness and microscopic crack growth mechanism were correlated on the basis of these experimental results, and effect of annealing on the toughness and mechanism were discussed.

Effects of Gaseous Hydrogen on Fatigue Crack Growth Behavior of Low Carbon Steel

2009 ◽  
Author(s):  
Dongsun Lee ◽  
Hide-aki Nishikawa ◽  
Yasuji Oda ◽  
Hiroshi Noguchi
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Strain Range ◽  
Hydrogen Gas ◽  
Crack Growth Behavior ◽  
Low Carbon ◽  
Nitrogen Gas

In order to investigate the effects of hydrogen on the fatigue crack growth behavior of low carbon steel JIS S10C, bending fatigue tests were carried out using a specimen with a small blind artificial hole in a low pressure pure hydrogen gas atmosphere. The results show that the fatigue crack growth rate in hydrogen gas is higher than that in nitrogen gas, moreover, the degree of acceleration is greater in the high strain range. In fractography, intergranular facets mixed with ductile fracture and quasi-cleavage fracture with brittle striations appear in a hydrogen gas environment, while only ductile fracture mainly appears in nitrogen gas. In the low growth rate range, many intergranular facets are seen on the ductile fracture surface, and in the higher growth rate range, quasi-cleavage facets increase as the growth rate increases. The growth rate of a small crack in nitrogen gas can be expressed by dl/dN ∝ Δεpnl in the wide range of applied total strain range Δεt. The same type equation is also satisfied in hydrogen gas, but in the narrow range roughly from Δεt = 0.25% to Δεt = 0.37%. The fracture surface in this range shows only intergranular facets and a ductile morphology, but no quasi-cleavage fracture. Although the crack growth mechanism in hydrogen is different from that in nitrogen, observation of the mechanism of intergranular facet formation shows a similarity to the mechanism in nitrogen in which the slip-off mechanism of crack growth is valid. The formation of intergranular facets is also closely related to the slip behavior influenced by hydrogen. This means that there exists a high possibility for the application of the small crack growth law inhydrogen to not only S10C, but also to other carbon steels in which the intergranular facet appears.

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