Understanding the effect of grain size distribution on the stability of nanocrystalline materials: An analytical approach

Materialia ◽  
2020 ◽  
Vol 9 ◽  
pp. 100579 ◽  
Author(s):  
Srikant Gollapudi ◽  
Ajay K Soni
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Nanocrystalline Materials ◽  
Analytical Approach ◽  
The Stability

scholarly journals The Influence of Grain Size Distribution on the Hydraulic Gradient for Initiating Backward Erosion

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2644 ◽  
Author(s):  
Willem-Jan Dirkx ◽  
Rens Beek ◽  
Marc Bierkens
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Laboratory Experiments ◽  
Hydraulic Gradient ◽  
Concentrated Flow ◽  
Pipe Formation ◽  
Novel Method ◽  
Flow Through ◽  
The Stability

Backward erosion by piping is one of the processes that threaten the stability of river embankments in the Netherlands. During high river stages, groundwater flow velocities underneath the embankment increase as a result of the steepened hydraulic gradient. If a single outflow point exists or forms, the concentrated flow can entrain soil particles, leading to the formation of a subsurface pipe. The processes controlling this phenomenon are still relatively unknown due to their limited occurrence and because piping is a subsurface phenomenon. To study the initiation of piping, we performed laboratory experiments in which we induced water flow through a porous medium with a vertically orientated outflow point. In these experiments, we explicitly considered grain size variations, thus adding to the existing database of experiments. Our experiments showed that the vertical velocity needed for the initiation of particle transport can be described well by Stokes’ law using the median grain size. We combine this with a novel method to relate bulk hydraulic conductivity to the grain size distribution. This shows that knowledge of the grain size distribution and the location of the outflow point are sufficient to estimate the hydraulic gradient needed to initiate pipe formation in the experiment box.

Grain Size Distribution Effect on Mechanical Behavior of Nanocrystalline Materials

2004 ◽  
Vol 821 ◽  
Author(s):  
A.V. Sergueeva ◽  
N.A. Mara ◽  
A.K. Mukherjee
Keyword(s):  
Grain Size ◽  
Mechanical Behavior ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Nanocrystalline Materials ◽  
Tensile Deformation ◽  
Size Structure ◽  
Niti Alloy ◽  
Distribution Effect ◽  
The Matrix

AbstractGrain size distribution effect on the mechanical behavior of NiTi and Vitroperm alloys were investigated. Yielding at significantly lower stresses than found in equiaxed counterparts, along with well defined strain hardening was observed in these nanocrystalline materials with large grains embedded in the matrix during tensile deformation at temperatures of 0.4Tm. At higher temperature the effect of grain size distribution on yield stress was not revealed while plasticity was increased in 50% in NiTi alloy with bimodal grain size structure.

The Inverse Hall-Petch Effect—Fact or Artifact?

2000 ◽  
Vol 634 ◽  
Author(s):  
Carl C. Koch ◽  
J. Narayan
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Computer Simulations ◽  
Nanocrystalline Materials ◽  
Grain Sizes ◽  
Average Grain Size

ABSTRACTThis paper critically reviews the data in the literature which gives softening—the inverse Hall-Petch effect—at the finest nanoscale grain sizes. The difficulties with obtaining artifactfree samples of nanocrystalline materials will be discussed along with the problems of measurement of the average grain size distribution. Computer simulations which predict the inverse Hall-Petch effect are also noted as well as the models which have been proposed for the effect. It is concluded that while only a few of the experiments which have reported the inverse Hall-Petch effect are free from obvious or possible artifacts, these few along with the predictions of computer simulations suggest it is real. However, it seems that it should only be observed for grain sizes less than about 10 nm.

Grain sorting effects on the formation of tidal sand waves

2009 ◽  
Vol 629 ◽  
pp. 311-342 ◽  
Author(s):  
TOMAS VAN OYEN ◽  
PAOLO BLONDEAUX
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Fine Fraction ◽  
Sand Wave ◽  
Flat Bottom ◽  
Sand Waves ◽  
Sand Mixture ◽  
Sea Bed ◽  
The Stability

A model is developed to investigate the process which leads to the formation of sand waves in shallow tidal seas characterized by a heterogeneous sea bed composition. The main goal of the analysis is the evaluation of the effects that a graded sediment has on the formation of the bottom forms and the investigation of the sorting process induced by the growth of the bottom forms. The analysis is based on the study of the stability of the flat bed configuration, i.e. small amplitude perturbations are added to the flat bottom and a linear analysis of their time development is made. For an oscillatory tidal current dominated by one tidal constituent, the results show that the graded sediment can stabilize or destabilize the flat bottom configuration with respect to the uniform sediment case, depending on the standard deviation σ* of the grain size distribution and on the ratio between the horizontal tidal excursion and the water depth. For moderate values of , i.e. values just larger than the critical value for which the sediment is moved and sand waves appear, the presence of a sand mixture stabilizes the flat bed. On the other hand, for large values of , the mixture has a destabilizing effect. In both cases the effect that a sand mixture has on the stability of the flat bed configuration is relatively small. Moreover, for moderate values of , the fine fraction of the mixture tends to pile up at the crests of the bottom forms while the coarse fraction moves towards the troughs. For large values of , the grain size distribution depends on the value of σ*. The results are physically interpreted and provide a possible explanation of the apparently conflicting field observations of the grain size distribution along the sand wave profile, carried out in the North Sea.

The Role of the Nd/Zn Ratio on the Stability of Mg-Zn-Nd Clusters and the Evolution of Texture in Two Mg-Zn-Nd Alloys during Annealing

2016 ◽  
Vol 879 ◽  
pp. 542-547
Author(s):  
Mehdi Sanjari ◽  
Amir Rezaei Farkoosh ◽  
Abu S.H. Kabir ◽  
Jing Su ◽  
In Ho Jung ◽  
...  
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Early Stage ◽  
Texture Evolution ◽  
Reduction Rate ◽  
Grain Coarsening ◽  
Weight Percentage ◽  
Basal Pole ◽  
The Stability

Texture evolution in two magnesium alloys, Mg-4%Zn-1%Nd and Mg-1%Zn-1%Nd (weight percentage), was studied after rolling and the subsequent isothermal annealing. The finish rolling was completed in a single pass with a thickness reduction rate of ~30% at 100 °C and a rolling speed of 1000 m/min. After cooling to room temperature, the rolled samples were annealed at 350 °C for different annealing times. Upon annealing, the maximum intensity of the basal pole texture decreases as recrystallization progresses. In the Mg-1Zn-1Nd alloy (with a high Nd/Zn ratio), texture weakening is maintained even after complete recrystallization and grain coarsening, while in the Mg-4Zn-1Nd alloy, texture strengthening occurs after grain coarsening, and a single peak replaces the double split basal peaks. In the Mg-1Zn-1Nd alloy, grain coarsening is accompanied by a bimodal grain size distribution, whereas in the Mg-4Zn-1Nd alloy, the grain coarsening leads to a uniform grain size distribution. TEM investigations show the formation of the Zn and Nd rich clusters at early stage of annealing in both alloys. During recrystallization, these clusters were dissolved in the Mg-4Zn-1Nd alloy, but they are more stable in the Mg-1Zn-1Nd alloy. In our opinion, the formation of these stable clusters is one of the main factors for texture weakening of the Mg-Zn-RE alloys.

A Model for Predicting the Failure Behavior of Bimodal Nanocrystalline Materials

2014 ◽  
Vol 1081 ◽  
pp. 132-137
Author(s):  
Song Feng Tian ◽  
Hong Jian Yu ◽  
Ying Guang Liu ◽  
Rong Yuan Ju ◽  
Xiao Dong Mi ◽  
...  
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Grain Size Distribution ◽  
Nanocrystalline Materials ◽  
Volume Fraction ◽  
High Strength ◽  
Failure Behavior ◽  
Failure Properties ◽  
Bimodal Grain Size ◽  
Bimodal Grain Size Distribution

Giving a bimodal grain size distribution in nanocrystalline materials can effectively achieve both high strength and high ductility. Here we propose a theoretical model to study the failure behavior of nc materials with bimodal grain size distribution. The dependence of failure properties on grain size distribution were calculated. Numerical results show the strength and ductility of bimodal nanocrystalline materials are sensitive to grain size and the volume fraction of coarse grains.

Deformation and Coble Creep of Nanocrystalline Materials

2002 ◽  
Vol 740 ◽  
Author(s):  
C.S. Pande ◽  
R. A. Masumura
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Yield Stress ◽  
Grain Size Distribution ◽  
Nanocrystalline Materials ◽  
Threshold Stress ◽  
Experimental Results ◽  
Model Based ◽  
Dislocation Interactions ◽  
Coble Creep

ABSTRACTModeling of strengthening by nanocrystalline materials need consideration of dislocation interactions and sliding due to Coble creep, both of which may be acting simultaneously. Such a mechanism is considered in this paper. It is shown that a model based on using Coble creep (with a threshold stress) for finer grains and conventional Hall-Petch strengthening for larger grains, appears to be most successful in explaining experimental results provided care is taken to incorporate into the analysis the effect of grain size distribution occurring in most specimens. A generalized expression relating yield stress to grain size is also proposed.

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