Physics Behind Cutting Brick/Stone With Chisels?

[Mgt3]

TL;DR Summary

What is the physics behind how a cold/masonry chisel splits a brick or concrete?

Can someone please explain the physics of how a cold/masonry chisel used to score a brick cuts the prick along a more or less even line without actually "cutting"?

 

[jrmichler]

The process of cutting a brick starts by light blows to cut a shallow groove. Since bricks are brittle, a groove is a significant stress concentration. Then a harder blow causes peak stress that exceeds the tensile strength along the groove, breaking the brick.

Relevant search terms to learn more:

Stress concentration
Hertzian contact stress
Brittle fracture

The same principle is used to cut glass by first scoring with a cutting tool, then bending it over an edge.

 

[Bystander]

 

[Lnewqban]

TL;DR Summary: What is the physics behind how a cold/masonry chisel splits a brick or concrete?

See also:
https://en.wikipedia.org/wiki/Wedge#Mechanical_advantage

 

[Tom.G]

To completely violate the 'Terms of Use' here, I read somewhere many years ago that:
The water molecules are about the right size to wedge themselves in the micro-cracks in stressed glass.

Details (if any) are lost in the fog of time.

Another common trick is to use Kerosene instead of water.

 

[Baluncore]

Another common trick is to use Kerosene instead of water.

Water is small enough to get in and prevent the glass healing, so it promotes cracking by about 20%. Kerosene, (Paraffin oil), toughens the glass by about 20%, preventing the crack from running.