User talk:Mail2na

Mechanical properties of Graphene
Graphene-two dimensional carbon based material is under a lot of research these days due to its extraordinary mechanical, electronical, and thermal properites. Understanding the mechanical properties such as tensile, shear, compression, and bending properites are very important because it has the crucial role for the potential applications of graphene. Recently, graphen is showed the strongest material under tension test, even stronger than the diamond and carbon nanotube. It is also important to investigate graphene is still the strongest under shear, compression or bending. In this letter, I will describe the anomalous thermal expansion coeffcient which affects the mechanical properties and other mechanical properties available online. In addition, to investige the various properties, such as size, temperature or chirality effect, several different results using different potentials, methods are compared to give researchers better references to compare those each other.

Thermal Expansion Coefficient
There are several studies about the anomalous thermal properties of graphene using several methods, which is the negative thermal expansion coefficient (TEC). DFT simulation shows graphene has the negative TEC in the temperature range of 0~2500K, and Monte carlo (MC) based LCBOPII potential shows that graphene has the negative TEC before 900K and it becomes positive after that. There is also experiment result available using scanning electron microscope (SEM) showing the similar behavior of TEC. It is very important to understand the effect of TEC for the mechanical properties, because it would be the key factor to determine the mechanical properties under the certain temperature range. Comparions with different published data is given in the below figure.

Uniaxial Tension Properties
Since graphene approved to be the strongest material in the world under tension test, it is very important to know and understand the young's modulus and fracture stress variation under diverse conditions such as different temperatures, sizes, and methods. Furthermore, it is also very important to investigate the mechanical properties under various conditions when considering the applications of graphene. Since the experiment has the limitation under diverse conditions, there are several simulation method depending on the accuracy, cost and conditions. Most reliable result would be ab initio method but it is the most expensive method, people prefer using other classical molecular dynamics (MD) or empirical potential based Tight binding (TB) to study further. There are always issues for the simulation for the different conditions on the properties, it is crucial to understand the simulation method and use it properly for the specific conditions.

Shear Test properties
There are several results for the shear modulus for the graphene. The values are ranging between 0.208 and 0.49 under various simulations. Further research through experiments should be done for the comparions and accuracies. In addition, it is also important to know the fracture values under shear or torsion. —Preceding unsigned comment added by 98.212.158.245 (talk) 05:29, 20 November 2009 (UTC)

In the tension test case, we have available experiment data to compare it to the simulation and verify the results. However, for the shear properties case, we do not have the experiment result yet, so it is important to have other similar materials such as graphite and single walled carbon nanotube (SWNT). The table is in the below for the comparisons.

Other mechanical properties
1. Compression test

Since the single layer of graphene is very thin film like mateirlal, it is very weak-easily buckled under compression force. It is shown that [22] the critical compression load for graphene is 3.75 nN for zigzag, and 2.8nN for armchair using molecular dynamics simulation. There are not many published data availble due to its weakness under compression.

2. Bending test

There are two results available for the temperature dependent bending rigidity of graphene. Using molecular dynamics simulation[23], it is proved that bending rigidity decreases as temperature increases due to the effect of the thermal fluctuation. However, using atomistic Monte Carlo simulation[24], the result is opposite - increasing bending rigidity with increasing temperature. The further study should be done to resolve this issue.