Transition of Crack Propagation Path Under Varied Levels of Load in Bimodal Grain Size Al-Mg Alloy

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Leila Ladani ◽  
Steven Nelson
Keyword(s):  
Grain Size ◽  
Crack Propagation ◽  
Crack Nucleation ◽  
Crack Propagation Rate ◽  
Propagation Path ◽  
Ultrafine Grain ◽  
Coarse Grain ◽  
Fatigue Crack Nucleation ◽  
Coarse Grains ◽  
Bimodal Grain Size

Mechanical fatigue crack nucleation and propagation is modeled in bimodal grain size aluminum alloy. A multiscale modeling approach in conjunction with a continuum based damage modeling technique, successive initiation, is used to determine microstructural site of crack nucleation and its propagation through different regions of the materials. Analyses conducted for material with different coarse grain volume ratios under different load amplitudes showed that damage initiates at the interface of coarse grains and the ultrafine grain matrix. It propagates initially through coarse grains with higher initial damage rate. Once the coarse grains lose their load bearing capacity, the load is transferred to the ultrafine matrix and it fails rather quickly. Comparison between different large grain volume ratios shows that the small distance between large grains at high coarse grain volume ratios facilitates crack bridging between coarse grains and results in very high crack propagation rate in coarse grains which eventually results in catastrophic failure of the whole structure.

scholarly journals Crack Propagation Behavior of a Ni-Based Single-Crystal Superalloy during In Situ SEM Tensile Test at 1000 °C

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1047
Author(s):  
Wenxiang Jiang ◽  
Xiaoyi Ren ◽  
Jinghao Zhao ◽  
Jianli Zhou ◽  
Jinyao Ma ◽  
...  
Keyword(s):  
Crack Propagation ◽  
Tensile Test ◽  
Single Crystal ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Single Crystal Superalloy ◽  
Propagation Path ◽  
Propagation Behavior ◽  
Crack Propagation Behavior

An in situ scanning electron microscope (SEM) tensile test for Ni-based single-crystal superalloy was carried out at 1000 °C. The stress displacement was obtained, and the yield strength and tensile strength of the superalloy were 699 MPa and 826 MPa, respectively. The crack propagation process, consisting of Model I crack and crystallographic shearing crack, was determined. More interestingly, the crack propagation path and rate affected by eutectics was directly observed and counted. Results show that the coalescence of the primary crack and second microcrack at the interface of a γ/γ′ matrix and eutectics would make the crack propagation rate increase from 0.3 μm/s to 0.4 μm/s. On the other hand, crack deflection decreased the rate to 0.05 μm/s. Moreover, movement of dislocations in front of the crack was also analyzed to explain the different crack propagation behavior in the superalloy.

scholarly journals Elucidating the Effect of Bimodal Grain Size Distribution on Plasticity and Fracture Behavior of Polycrystalline Materials

2020 ◽  
Vol 11 (04) ◽  
pp. 2050007
Author(s):  
Fabrice Barbe ◽  
Ivano Benedetti ◽  
Vincenzo Gulizzi ◽  
Mathieu Calvat ◽  
Clément Keller
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Tensile Properties ◽  
Fracture Behavior ◽  
316L Stainless Steel ◽  
Scale Model ◽  
Coarse Grain ◽  
Polycrystalline Materials ◽  
Element Modeling ◽  
Bimodal Grain Size

The refinement of grains in a polycrystalline material leads to an increase in strength but as a counterpart to a decrease in elongation to fracture. Different routes are proposed in the literature to try to overpass this strength-ductility dilemma, based on the combination of grains with highly contrasted sizes. In the simplest concept, coarse grains are used to provide relaxation locations for the highly stressed fine grains. In this work, a model bimodal polycrystalline system with a single coarse grain embedded in a matrix of fine grains is considered. Numerical full-field micro-mechanical analyses are performed to characterize the impact of this coarse grain on the stress-strain constitutive behavior of the polycrystal: the effect on plasticity is assessed by means of crystal plasticity finite element modeling [B. Flipon, C. Keller, L. Garcia de la Cruz, E. Hug and F. Barbe, Tensile properties of spark plasma sintered AISI 316L stainless steel with unimodal and bimodal grain size distributions, Mater. Sci. Eng. A 729 (2018) 248–256] while the effect on intergranular fracture behavior is studied by using boundary element modeling [I. Benedetti and V. Gulizzi, A grain-scale model for high-cycle fatigue degradation in polycrystalline materials, Int. J. Fract. 116 (2018) 90–105]. The analysis of the computational results, compared to the experimentally characterized tensile properties of a bimodal 316L stainless steel, suggests that the elasto-plastic interactions taking place prior to micro-cracking may play an important role in the mechanics of fracture of this steel.

Stress corrosion property of 304 stainless steel and Q345 steel laser-MAG hybrid welded joints

2019 ◽  
Vol 34 (01n03) ◽  
pp. 2040057
Author(s):  
Hang Lv ◽  
Guoqing Gou ◽  
Zhenghong Fu ◽  
Wei Gao
Keyword(s):  
Stainless Steel ◽  
Crack Propagation ◽  
Stress Corrosion ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Corrosion Property ◽  
304 Stainless Steel ◽  
Propagation Path ◽  
Crack Propagation Path ◽  
Immersion Testing

The stress corrosion cracking (SCC) property of laser-MAG hybrid welded 304 stainless steel and Q345 steel was evaluated through cycle-immersion testing in 3.5 wt.% NaCl solution. The average SCC crack propagation rate of different zones under different initial stress intensity factors was calculated, and the SCC fracture and crack propagation path were observed. The microstructure and mechanical properties of the weld joint have also been examined. The result indicates that the fusion zone (FZ) is extremely prone to SCC. The average SCC crack propagation rate in FZ is [Formula: see text] mm/h, while no obvious SCC was found in the base metal (BM) and heat-affected zone (HAZ). The steel BM and HAZ may also suffer SCC, but not as fast as in FZ. Grooves caused by SCC were found on the fracture surface with a large amount of corrosion products accumulated close to the interface between the pre-crack section and SCC section. Crystallized-sugar-shaped pattern was found on the SCC zone of FZ. Crack jumping, deflection and crack closure occurred in the crack propagation path. Martensite on the FZ was considered to be the major reason that the FZ has a higher SCC propagation rate.

scholarly journals Improvement of structural efficiency in metals by the control of topological arrangements in ultrafine and coarse grains

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Abdallah Shokry ◽  
Aylin Ahadi ◽  
Per Ståhle ◽  
Dmytro Orlov
Keyword(s):  
Plastic Instability ◽  
Ultrafine Grain ◽  
Coarse Grain ◽  
Random Structure ◽  
Heterogeneous Structure ◽  
Efficient Design ◽  
Structural Efficiency ◽  
Coarse Grains ◽  
Dimensional Finite Element ◽  
Scale Levels

AbstractImprovement of structural efficiency in various materials is critically important for sustainable society development and the efficient use of natural resources. Recently, a lot of attention in science and engineering has been attracted to heterogeneous-structure materials because of high structural efficiency. However, strategies for the efficient design of heterogenous structures are still in their infancy therefore demanding extensive exploration. In this work, two-dimensional finite-element models for pure nickel with bimodal distributions of grain sizes having ‘harmonic’ and ‘random’ spatial topological arrangements of coarse and ultrafine-grain areas are developed. The bimodal random-structure material shows heterogeneities in stress–strain distributions at all scale levels developing immediately upon loading, which leads to developing concentrations of strain and premature global plastic instability. The bimodal harmonic-structure material demonstrates strength and ductility significantly exceeding those in the bimodal random-structure as well as expectations from a rule of mixtures. The strain hardening rates also significantly exceed those in homogeneous materials while being primarily controlled by coarse-grain phase at the early, by ultrafine-grain at the later and by their compatible straining at the intermediate stages of loading. The study emphasises the importance of topological ultrafine-/coarse-grain distributions, and the continuity of the ultrafine-grain skeleton in particular.

Effect of centrifugal load on crack path in thin-rimmed and webbed gears

2015 ◽  
Author(s):  
F. Curà ◽  
A. Mura ◽  
C. Rosso
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Root Zone ◽  
Crack Nucleation ◽  
Numerical Models ◽  
Propagation Path ◽  
Initiation Point ◽  
Centrifugal Load ◽  
Bending Load ◽  
Uncertainty Zone

Thin rimmed and webbed gears are used in particular applications to reduce systems weight. This kind of gears need an accurate and fail safe design. As a matter of fact, a possible failure, due to bending fatigue, consists in crack nucleation and consequent growth, in particular in the tooth root zone. These cracks may propagate through the tooth or through the rim. Crack propagation direction is basically influenced by the wheel geometry parameters, above all the rim thickness. Studies available in literature emphasize three ranges for the backup ratio values, involving different behaviors. These ranges are related to the crack propagation paths; respectively through the tooth, through the rim and in an unforeseeable way. This last uncertainty zone depends on other parameters, related to both geometry and loading conditions. In this work the effect of wheel speed related to the bending load has been investigated. The investigation has been carried out by means of numerical models involving both 2D finite element and extended finite element models (XFEM). Results shows that both crack initiation point and crack propagation path are strongly influenced by centrifugal load; this effect is mainly evident in the uncertainty zone of the backup ratio.

Effect of Heat Imput on Microstructure and Toughness of High Strength Bridge Steel

2011 ◽  
Vol 194-196 ◽  
pp. 255-258
Author(s):  
Kun Ning Jia
Keyword(s):  
Grain Size ◽  
Crack Propagation ◽  
Heat Affected Zone ◽  
High Strength ◽  
Thermal Simulation ◽  
Granular Bainite ◽  
Coarse Grain ◽  
Bridge Steel ◽  
Lath Bainite

The coarse grain heat affected zone(CGHAZ) at different parameters t8/5 of high-strength bridge steel Q460q were simulated with thermal simulation machine. the microstructure of CGHAZ and the effect of granular bainite on the toughness were analyzed in this paper.The results show that: When t8/5<60s, lath bainite and granular bainite intertwine, and the quantity of strip M-A constituents in granular bainite decreased, so toughness is higher.When t8/5>60s, the quantity of eutectoid ferrite and granular bainite increased, coarse M-A constituent resulting in the grain size of effective crack propagation becoming coarser and toughness decreased significantly.

The Material Discontinuous Zone Influence on the Behavior of Crack Propagation in the Matrix Material

2013 ◽  
Vol 345 ◽  
pp. 263-267
Author(s):  
Zhi Jia Sun ◽  
You Tang Li
Keyword(s):  
Crack Propagation ◽  
Deflection Angle ◽  
Matrix Material ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Propagation Path ◽  
Propagation Behavior ◽  
The Matrix ◽  
The Deflection Angle ◽  
Simulation Results

A numerical method to simulate the crack propagation is presented in this paper. The FEM is used to estimate the influence of the material discontinuous zone on the propagation behavior of the crack placed in close to it in the matrix. The crack propagation paths in the matrix with different material discontinuous zone are simulated. The simulation results show that the crack propagation path will deviate toward the material discontinuous zone when the crack grows in closed to it and the property of the material discontinuous zone influences the deflection angle and the crack propagation rate.

Effects of Grain Size on Fatigue Crack Propagation in Copper Film

2010 ◽  
Vol 452-453 ◽  
pp. 289-292
Author(s):  
Kenichi Shimizu ◽  
Tashiyuki Torii
Keyword(s):  
Grain Size ◽  
Fatigue Crack ◽  
Crack Propagation ◽  
Crack Opening Displacement ◽  
Fatigue Crack Propagation ◽  
Fatigue Cracks ◽  
Crack Opening ◽  
Crack Propagation Rate ◽  
Propagation Rate ◽  
Opening Displacement

Using a fatigue testing method by which fatigue cracks can be initiated and propagated in a film adhered to cover a circular through-hole in a base plate subjected to cyclic loads, annealed copper films of 100m thickness with different crystal grain sizes were fatigued. The fatigue crack propagation in the film with large grains was often decelerated, so the crack propagation rate of the film with the large grain was lower than that of the film with the small grain. When the crack propagation was decelerated, the crack opening displacement obtained from the film with large grain size was smaller than that obtained from the film with small grain size. The relationship between the fatigue crack propagation rate and the stress intensity factor estimated from the crack opening displacement was identical for the cracks in the film with the large grain and the small grain.

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