Understanding Material Breakage: Fractures, Fatigue, and More

[anime9999]

Hi and thank you in advance.

I want to understand how do fractures/breaks/fatigues occur in general.

I remember a proverb saying that when a farmer breaks a rock after 100 hits using his axe, it is not the 100th hit that breaks the rock, but it is all of the 100 hits.

How material break? what happens when you hit a metal with something and it doesn't break? where does the energy go? does every hit means a degradation in the structure (although not visible)?

For example, if I gently hit my tooth with a spoon, do I still impact the structure of my tooth (although my tooth doesn't break?)

I hope you understand my question.
Thank you and best regards.

 

[Bandit127]

You should look up fatigue. Find an article with an S-N curve if you can.

 

[AppleBite]

What you are describing is an entire academic field called Fracture Mechanics, covered by many engineering courses. The field is vast, and the process of fracture will depend on the material, loading and test conditions, etc.

Start with this link, and there are also numerous books and papers on the subject depending on what materials you are interested in:

http://en.wikipedia.org/wiki/Fracture_mechanics

 

[anime9999]

Thank you. I will look up fatigue and fracture mechanics.
I see this is indeed a very complex subject.

 

[alphy]

I can provide some insights into understanding material breakage, fractures, and fatigue. Material breakage occurs when the applied stress on a material exceeds its strength, causing it to fail. This can happen through various mechanisms such as fractures, fatigue, and plastic deformation.

Fractures occur when the material experiences an external force that exceeds its strength, causing it to crack or break. This can happen due to a single large force or repeated smaller forces over time.

Fatigue, on the other hand, is the weakening of a material due to repeated loading and unloading cycles. This can happen even when the forces applied are below the material's strength, as the cumulative effect of the repeated cycles can cause microcracks to form and grow, eventually leading to failure.

In your example of the farmer breaking a rock with his axe, it is not just the 100th hit that causes the rock to break. Each hit weakens the rock, causing microcracks to form and grow until it can no longer withstand the applied force.

When hitting a metal with something, the energy from the impact is transferred to the material. If the force is below the material's strength, it will deform elastically and return to its original shape. However, if the force is above the material's strength, it will deform plastically, causing permanent damage and potentially leading to failure.

In the case of your tooth and spoon example, hitting your tooth with a spoon may not cause visible damage, but it can still impact the structure of your tooth at a microscopic level. The repeated impacts over time can lead to fatigue and weaken the tooth, making it more prone to fractures or breaks in the future.

I hope this helps to answer your question and provide a better understanding of material breakage. It is important to consider the strength and fatigue properties of materials when designing and using them in various applications to prevent failures and ensure their longevity. Thank you for your question and best regards.