# Traceless compression ?

1. May 23, 2010

### savasagduk

Hi I'm a beginner in solid state physics. My question is :

What does it mean "Traceless Compression" ?

In matris terms "traceless" means product of diagonal elements is zero .

is this the same thing ?
Thank you for any help .

2. May 25, 2010

### Patrus89

I cannot find an online reference to this, but I have never heard of another definition for "Traceless". Compression or Shear, traceless is traceless in a matrix.

3. May 25, 2010

### tiny-tim

"Traceless" means the sum of the diagonal elements is zero.

4. May 25, 2010

### Patrus89

I missed that, sorry. Still, traceless compression is the same use of traceless as in shear or any other matrix, correct?

5. May 26, 2010

### tiny-tim

I assume so.

6. May 26, 2010

### Gokul43201

Staff Emeritus
I've never heard that term. For the stress tensor to be traceless, at least one of the uniaxial stress components needs to be tensile, while another one needs to be compressive.

If you do find a reference that explains this term, please post it here.

7. May 26, 2010

### tiny-tim

Hi Gokul!
Isn't that exactly what happens when you squeeze most things? Compression in the direction you squeeze it, and tension in perpendicular directions?

8. May 26, 2010

### Gokul43201

Staff Emeritus
Yes, squeeze or stretch, you essentially conserve volume if you're in the elastic regime. But I've never heard that term before, and wonder when you call something a traceless compression as opposed to say, a traceless tension.