asabben97

01-12-2007, 12:46 AM

I am a student doing my masters thesis at the Beth Israel Deaconess

Medical Center in Boston, USA. I have to do some indentation testing on

the outer part of intervertebral discs, the Annulus Fibrosus. It is a

fibrous soft tissue. The samples are composed of single lamellae, which

are between 0.4 and 1 mm thick. The aim is to get the mechanical

properties (Youn's modulus, Poisson's ratio and permeability) from a

stress-relaxation test. Usually, one uses a non-linear elastic biphasic model to

describe the behavior of the Annulus Fibrosus (Ateshian et al., 1997, J

Biomechanics; Perie et al., 2006, Annals of Biomedical Engineering).

The permeability k of the tissue is given by: dsigma/depsilon * d2u/dz2 =

epsilon/k * du/dt, where sigma is the stress, epsilon the stretch, u

the displacement, z the vertical coordinate and t the time. My problem

and question is 1) how to compute the d2u/dz2 term when one does a

stress-relaxation test. I found no explanation in the articles I have read

so far. Because the displacement equals the z coordinate I don't see how

this term is not equal to zero. Would anyone have an idea on how to

solve this? and 2) is the aggregate modulus, HA0, normally determined

under confined compression? or can it also be determined under non-confined

compression?

Thanks in advance.

Alexandre Sabben

Research Assistant

Beth Israel Deaconess Medical Center

Boston, MA, USA

---------------------------------

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Medical Center in Boston, USA. I have to do some indentation testing on

the outer part of intervertebral discs, the Annulus Fibrosus. It is a

fibrous soft tissue. The samples are composed of single lamellae, which

are between 0.4 and 1 mm thick. The aim is to get the mechanical

properties (Youn's modulus, Poisson's ratio and permeability) from a

stress-relaxation test. Usually, one uses a non-linear elastic biphasic model to

describe the behavior of the Annulus Fibrosus (Ateshian et al., 1997, J

Biomechanics; Perie et al., 2006, Annals of Biomedical Engineering).

The permeability k of the tissue is given by: dsigma/depsilon * d2u/dz2 =

epsilon/k * du/dt, where sigma is the stress, epsilon the stretch, u

the displacement, z the vertical coordinate and t the time. My problem

and question is 1) how to compute the d2u/dz2 term when one does a

stress-relaxation test. I found no explanation in the articles I have read

so far. Because the displacement equals the z coordinate I don't see how

this term is not equal to zero. Would anyone have an idea on how to

solve this? and 2) is the aggregate modulus, HA0, normally determined

under confined compression? or can it also be determined under non-confined

compression?

Thanks in advance.

Alexandre Sabben

Research Assistant

Beth Israel Deaconess Medical Center

Boston, MA, USA

---------------------------------

Découvrez une nouvelle façon d'obtenir des réponses à toutes vos questions ! Profitez des connaissances, des opinions et des expériences des internautes sur Yahoo! Questions/Réponses.