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Name: Alhassan
Status: student
Grade: 9-12
Country: United Kingdom
Date: Winter 2013-14


Question:
What distinguishes fracture from cleavage?



Replies:
Hi Alhassan,

Thanks for the question. In material science, cleavage is the breaking apart of a crystal into smaller crystals. Crystals will usually break along certain directions. In simple cases, the directions of cleavage can be predicted by assuming like charges repel.

Fracture is the breaking apart of a material (which could be crystalline or amorphous, like glass) due to an applied force or repetitive stress. The fracture of aluminum in aircraft frames is due to the repetitive stress of pressurization and depressurization cycles. This type of fracture has been responsible for fatalities, but can be detected using radiography.

I hope this helps. Thanks Jeff Grell


HI Alhassen,

Neither of these terms has a rigid engineering definition, but the best way I can describe the difference is that a fracture is a random failure of a crystalline material. Cleavage is the intentional fracturing of a crystalline material, into two parts, usually using a directed and controlled impact, and often the with the impact directed to align with the direction of a material's crystal plane.

As an example, smashing a diamond with a hammer will randomly fracture it, but you can split a diamond in two more or less equal parts by cleaving it along a suitable crystal plane using a chisel and a light hammer tap.

Regards, Bob Wilson


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