How can materials become stronger through the introduction of weak bonds?

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In summary, the strength of materials is determined by a combination of factors, including atomic bond strength, density, melting temperature, and interatomic distance. While it is commonly believed that a material is only as strong as its weakest bond, there are many examples of materials becoming stronger through the introduction of weak bonds or defects. Ultimately, material strength is determined at a higher level and can be improved through various mechanisms such as impeding dislocation motion or interrupting crack propagation.
  • #1
garfield1729
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what is it that makes materials strong ?

density ? melted ? chemistry reactions ? strong nuclear force ? all of that ?


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garfield1729
 
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  • #2
force of attraction between the molecules I guess. Everything else is dependent on it.
 
  • #3
What makes materials strong is any impediment to what makes them fail. Seriously. In metals, for example, failure often occurs by crystal planes slipping past each other via dislocation motion. Anything that impedes dislocation motion (like precipitate obstacles or other dislocations) will strengthen the metal. Brittle materials like ceramics, in contrast, often fail by crack propagation, which calls for different strengthening mechanisms.

A related question is what makes materials stiff (strength is resistance to permanent deformation, stiffness is resistance to elastic, or recoverable, deformation). Stiffness is strongly coupled to the interatomic bond strength. So is density and melting temperature, and the element-to-element trend for these three material properties is similar.
 
  • #4
garfield1729 said:
what is it that makes materials strong ?

density ? melted ? chemistry reactions ? strong nuclear force ? all of that ?
Basically, the atomic bonds. A material is a strong as the weakest bond.

Density is a function of atomic mass, most of which resides in the nucleus, and the atomic (ionic) radii or interatomic distance. One can find low density but very strong materials.

Strength decreases with temperature.


See this thread - https://www.physicsforums.com/showthread.php?t=68286

and http://www.isotruss.org/hsratio.htm [Broken]
 
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  • #5
Basically, the atomic bonds. A material is a strong as the weakest bond.

I'm going to go ahead and disagree with this. There are many examples of materials becoming stronger through the deliberate introduction of weak or unsatisfied bonds. One example is in metals, where additional dislocations and grain boundaries (1-D and 2-D defects, respectively, consisting of distorted and broken bonds) strengthen the material. Another example is ceramics, where voids (no bonds at all!) are used to interrupt crack propagation and again strengthen the material.

The statement isn't even true in a general sense: covalent and ionic bonds are generally stronger than metallic bonds, but metals are generally stronger than covalent and ionic crystals in tension!
 
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  • #6
Mapes said:
Basically, the atomic bonds. A material is a strong as the weakest bond.

I'm going to go ahead and disagree with this. There are many examples of materials becoming stronger through the deliberate introduction of weak or unsatisfied bonds. One example is in metals, where additional dislocations and grain boundaries (1-D and 2-D defects, respectively, consisting of distorted and broken bonds) strengthen the material. Another example is ceramics, where voids (no bonds at all!) are used to interrupt crack propagation and again strengthen the material.

The statement isn't even true in a general sense: covalent and ionic bonds are generally stronger than metallic bonds, but metals are generally stronger than covalent and ionic crystals in tension!

I'll agree with your disagreement. Material strength is determined at a higher level than atomic bond strength. There are some excellent books by J. E. Gordon "Structures" and "The New Science of Strong Materials" that go into this in a lightly mathematical, very conversational way. He recounts an episode where a new graduate makes what he claims is a very strong material, because the bonds comprising it were stronger. Actual testing shows it had "... the strength of wet cheese."
 

1. What is the definition of strength in materials?

Strength in materials refers to the ability of a material to withstand an applied force without breaking or deforming. It is a measure of the resistance to failure under a given load.

2. What factors contribute to the strength of a material?

The strength of a material is influenced by its composition, microstructure, and external factors such as temperature and applied force. The atomic bonds within the material also play a crucial role in determining its strength.

3. How is the strength of a material measured?

The strength of a material can be measured using several techniques such as tensile testing, compression testing, and impact testing. These tests involve applying a force to the material and measuring its response to determine its strength.

4. What makes some materials stronger than others?

The strength of a material depends on its chemical and physical properties, such as the type of atomic bonds, crystal structure, and grain size. Materials with stronger atomic bonds and more organized crystal structures tend to be stronger than those with weaker bonds and less organized structures.

5. Can the strength of a material be improved?

Yes, the strength of a material can be improved through various methods, such as alloying, heat treatment, and cold working. These processes can change the microstructure and atomic bonds of the material, making it stronger and more resistant to failure.

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