Posts Tagged ‘Strength of materials’

No end to new materials with super-strength

October 10, 2013

From the days of the alchemists and then the metallurgists who mixed different materials – often in the molten state – and then to the chemists we have now moved into the age when materials are designed in the lab to have desired properties. The challenge then is to synthesise the desired composition with the atomic structure required and then to devise manufacturing processes for the materials.

“A material called carbyne could be stronger even than graphene or diamond, according to researchers who have calculated its properties”, reports the BBC.

Carbyne is a chain of carbon atoms held together by double or alternating single and triple chemical bonds.

In their paper, Boris Yakobson and colleagues from Rice University in Houston show that carbyne’s tensile strength – the ability to withstand stretching – surpasses that of “any other known material” and is double that of graphene, the flat sheet of carbon atoms that is often held up as a “supermaterial”.

They also calculated that carbyne has twice the tensile stiffness of graphene and carbon nanotubes and nearly three times that of diamond.

It should display a number of other useful properties say the researchers. For example, it could be turned into a magnetic semiconductor (these are materials with electrical conductivity between that of a metal and an insulator like glass) and could be used as a sensor to detect twisting.

Some scientists have reported synthesising small amounts of carbyne in the lab, but it was thought to be extremely unstable. And some chemists have suggested that two strands coming into contact could react explosively.

“Our intention was to put it all together, to construct a complete mechanical picture of carbyne as a material,” said Vasilii Artyukhov, also from Rice University.

“The fact that it has been observed tells us it’s stable under tension, at least, because otherwise it would just fall apart.”

Mingjie Liu , Vasilii I. Artyukhov , Hoonkyung Lee ,Fangbo Xu , and Boris I. Yakobson, Carbyne From First Principles: Chain of C atoms, a Nanorod or a Nanorope,

ACS Nano,  DOI: 10.1021/nn404177r, October 5, 2013

Abstract: We report an extensive study of the properties of carbyne using first-principles calculations. We investigate carbyne’s mechanical response to tension, bending, and torsion deformations. Under tension, carbyne is about twice as stiff as the stiffest known materials and has an unrivaled specific strength of up to 7.5×10^7 N∙m/kg, requiring a force of ~10 nN to break a single atomic chain. Carbyne has a fairly large room-temperature persistence length of about 14 nm. Surprisingly, the torsional stiffness of carbyne can be zero but can be ‘switched on’ by appropriate functional groups at the ends. Further, under appropriate termination, carbyne can be switched into a magnetic-semiconductor state by mechanical twisting. We reconstruct the equivalent continuum-elasticity representation, providing the full set of elastic moduli for carbyne, showing its extreme mechanical performance (e.g. a nominal Young’s modulus of 32.7 TPa with an effective mechanical thickness of 0.772 Å). We also find an interesting coupling between strain and band gap of carbyne, which is strongly increased under tension, from 3.2 to 4.4 eV under a 10% strain. Finally, we study the performance of carbyne as a nanoscale electrical cable, and estimate its chemical stability against self-aggregation, finding an activation barrier of 0.6 eV for the carbyne–carbyne cross-linking reaction and an equilibrium cross-link density for two parallel carbyne chains of 1 cross-link per 17 C atoms (2.2 nm).

Strength in a Manager: The materials analogy

May 8, 2011

No manager operates without stresses of all kinds. He is continuously subjected to physical, mental, psychological and emotional stresses. They may be cyclic or prolonged or sporadic or intermittent. It is his ability to withstand stress and continue operating without breaking down which we can call his strength of character. An individual’s strength is always present and is brought to bear automatically whenever stress is encountered. It cannot be turned “on” or “off” at will or to suit changing circumstances but it is never absent. It is unique to the individual and different individuals will be more or less suitable for the particular stresses encountered. Strength carries no connotations of inherent goodness or badness but whether it is wholly or partially sufficient or suitable depends on the particular individual and the specific stresses experienced.

The materials analogy

The strength of a material is a measure of its ability to withstand stress without failure by fracture or by rupture.

The strength of character of a person is a measure of his ability to withstand the stresses he encounters without failure by “breaking down”.

Napoleon Hill 

“Character is to man what carbon is to steel”

It is remarkable that so many of the terms used in materials science to describe the strength of materials are also applicable to human character. Strong, tough, resilient, brittle, malleable, tempered, hard, stiff, yield, stress, strain, deformation, ductile, elastic, rigid, fracture, fatigued and twisted are all words which have very precise meanings when applied to the properties and behaviour of materials. They are also all words which can be used – with very similar meanings – in describing facets of human character.

Stress in materials science is measured in units of the force applied per unit area of the material. Stress may be tensile (longitudinal pulling) or compressive (longitudinal squeezing) or it may be shear (sideways) or it may be torsion (twisting). The strength of a material is determined by its microstructure and defined as the magnitude of the stress that must be applied for the material to fail by fracture or by rupture.

There seem to be many parallels between the properties of inanimate materials and the components of human character. A person’s strength of character is similarly dependent upon his microstructure and is also a measure of his breaking stress. Toughness in a person, just as in materials, is not synonymous with strength but it is a related characteristic. It represents a person’s ability to absorb a great volume of stress or repeated applications of stress where he may yield to some extent, but does not break. As with a material, his resilience marks his ability to absorb setbacks and to recover his equanimity. He can also be subject to repeated stress cycles or difficult working conditions for prolonged periods leading to fatigue or creep where a gradual onset of small failings can lead to a total failure. Stubbornness in character has great similarity to brittleness in a material. The microstructure of the manager’s character, just like that of a material, can be changed by tempering or hardening or some other strengthening processes. Some managers are strong in tension and resist being pulled along by the latest fashion. Others are strong in compression and can withstand the weight of many trying to squeeze them into a particular shape. Just as material properties make them suitable for particular applications, the different characters of managers make them suitable for particular environments or particular tasks.

Properties of materials are amenable to precise tests and the results of the tests, which can be expressed mathematically, apply universally to all materials having the same composition and microstructure. Human characteristics are subject to much greater variation, are not as easily measurable and cannot be as readily predicted. Tests for the ultimate strength of a material are carried out by stressing a standard piece of the material to the point of destruction and the test pieces themselves are thereafter rendered useless. The strength of human character however, is not amenable to similar testing and does not allow of the same quantitative and mathematical approach. The science of materials though, is illustrative of, and does provide some very valuable insights regarding, human character, but it must be emphasized that it is only an analogy. Analogies serve very well for getting clarity in a new area of study by comparison with a familiar area, but there are many aspects of human character which are quite unlike material properties and the analogy no longer applies. Unlike materials, even conflicting character traits can co-exist in a person and the same trait can be manifested differently in different circumstances or at different times. A material is either brittle or it is ductile, but never both. But human character, for example, may be brittle and uncompromising in regard to integrity but flexible with regard to fallibility, both at the same time. A particular manager may be malleable and yielding with his superior while being hard or inflexible with a subordinate.   A manager may exhibit different, and even diametrically opposite, character traits to the same person but at different times. Strength of character is not an independent trait in itself but is a composite of many different features.

From Chapter 6: Essence of a Manager

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