Tensile Strength and Tensile Strain

In summary, the discussion revolves around the comparison of tensile strength and tensile stress of bioabsorbable copolymers and the human acetabular labrum. The properties of the copolymer need to closely match those of the labrum for it to effectively repair tears. The concept of modulus is also brought up, with the understanding that any two values of stress, strain, and modulus can determine the third. The goal is to find a copolymer with similar tensile properties to the labrum for successful tissue regeneration.
  • #1
EpiGen
16
0
Are these two things the same? I'm looking at bioabsorbable copolymers with similar properties to the human acetabular labrum, but I can only find tensile strength values for the copolymers and tensile stress at break for the labrum.

I've looked at the definitions of each it sounds like the values would be very similar - is this true?

Edit: Title should read 'Tensile Strength and Tensile Stress"
 
Last edited:
Engineering news on Phys.org
  • #2
Well, the title of your post contains "tensile strain", but your post talks about "tensile stress". Just so you know, stress and strain are different concepts. They are somewhat related, but not the same concept.

However, in response to your post, I'm not sure about what the acetabular labrum is. From what I gathered, it's a ring of cartilage that stops the femur from pulling out of the socket of the hip joint. Cartilage seems to me to be a fairly non-ductile material, so I would think that the tensile stress at break (I'm interpreting this as fracture) would be close to the ultimate tensile strength. For the copolymer, I'm assuming the "tensile strength" is referring to the ultimate tensile strength. I would think the two would be fairly similar. I would like some confirmation on this from other smart people on the forums though ;-)
 
  • #3
Your source of data for the copolymer will probably have another column in the table labelled modulus, or bulk modulus or youngs modulus or some such.

Knowledge of this this will help us help you relate stress and strain. So if it is not obvious just post all the data you have on the copolymer (and the cartilege).
 
  • #4
Studiot said:
Your source of data for the copolymer will probably have another column in the table labelled modulus, or bulk modulus or youngs modulus or some such.

Knowledge of this this will help us help you relate stress and strain. So if it is not obvious just post all the data you have on the copolymer (and the cartilege).

So if I know the strain, could I just divide the modulus by the value and the result would be stress?
 
  • #5
Like tim, I am not well up on anatomy so you will need to help us to help you.

Both he and I asked some questions, designed to elicit the information needed for this.

Please answer them rather than asking further questions. It should be obvious, from my last post, that there is more than one type of modulus. It will be necessary to to assess the structural situation to suggest the most appropriate formula and modulus to use.
 
  • #6
Studiot said:
Like tim, I am not well up on anatomy so you will need to help us to help you.

Both he and I asked some questions, designed to elicit the information needed for this.

Please answer them rather than asking further questions. It should be obvious, from my last post, that there is more than one type of modulus. It will be necessary to to assess the structural situation to suggest the most appropriate formula and modulus to use.

The project I am working on is to find a bioabsorbable copolymer that we can use to repair acetabular labrum tears (acetabular labrum is what forms the seal around your hip joints, and keeps synovial fluid inside.) When someone tears their acetabular labrum they often describe a 'clicking' in their joint as the synovial fluid inside is free to move around (there's a damaged seal.) This often results in the femoral head scraping against the inside of the socket, which is very painful.

Once I find a copolymer with similar properties in tensile strength and tensile modulus to the acetabular labrum, we will get a piece of kevlar (a material can be tolerated inside the body) and attach micropores (bubbles) of the copolymer on each side (2-3 pore-layers thick.) The idea is that new tissue will grow into the space between the spheres, and as the copolymer is absorbed by the body more and new tissue can move into seal the tear (the body basically regenerates itself.)

The main thing is that the properties of the copolymer have to have same tensile strength, tensile modulus and strain to the acetabular labrum for this idea to work (an exact match isn't going to be possible, but very close should work.)
 
  • #7
That sounds like a worthwhile objective indeed.

In general, modulus = Stress divided by strain

Picking any two of these fixes or determines the third.

In the abscence of further information I would hazard a guess as follows.

From Tim's description of the labrum thingy it is like an O ring. So to pull the lump on the end of the femur pulling through will need to stretch the ring. This will cause an increase in tension in the ring.

So long as your copolymer has a tensile stength equal to or greater than that of the cartilege it will perform the same function. A close match of modulus will ensure that the amount of stretch (= strain) is the same for both materials. You do not need to know any further detail to state this.

How does all that sound?
 
  • #8
Studiot said:
That sounds like a worthwhile objective indeed.

In general, modulus = Stress divided by strain

Picking any two of these fixes or determines the third.

In the abscence of further information I would hazard a guess as follows.

From Tim's description of the labrum thingy it is like an O ring. So to pull the lump on the end of the femur pulling through will need to stretch the ring. This will cause an increase in tension in the ring.

So long as your copolymer has a tensile stength equal to or greater than that of the cartilege it will perform the same function. A close match of modulus will ensure that the amount of stretch (= strain) is the same for both materials. You do not need to know any further detail to state this.

How does all that sound?

Sounds good! Thanks for your help
 
  • #9
Just keep in mind that tissue typically exhibits non-Linear elastic behavior, so it's not really a matter of getting the same modulus, as much as a matter of getting a similar curve (if it's important for your project that is ;) )
 
  • #10
Just keep in mind that tissue typically exhibits non-Linear elastic behavior

Good point, but polymers too typically exhibit non linear behaviour.
Also I think in this particular application (cartilege substitution) the mechanical range is quite restricted so a linear approximation will probably suffice. I don't see the ring being pulled out like an elastic band.

go well
 

What is Tensile Strength?

Tensile strength is the maximum amount of stress that a material can withstand before breaking or deforming permanently. It is typically measured in units of force per cross-sectional area, such as pounds per square inch (psi) or megapascals (MPa).

What is Tensile Strain?

Tensile strain is the measure of the deformation or elongation that a material undergoes when subjected to tension or pulling forces. It is expressed as a ratio of the change in length to the original length of the material.

What factors affect Tensile Strength?

Some factors that can affect tensile strength include the type of material, the manufacturing process, the temperature and environmental conditions, and any pre-existing defects or damage in the material.

How is Tensile Strength measured?

Tensile strength is typically measured using a tensile testing machine, which applies an increasing amount of force to a sample of the material until it breaks. The maximum force the material can withstand is then recorded as its tensile strength.

What is the difference between Tensile Strength and Tensile Strain?

Tensile strength and tensile strain are related but different properties. Tensile strength measures the maximum stress that a material can withstand, while tensile strain measures the amount of deformation that occurs under a given amount of stress. In other words, tensile strength tells us how strong a material is, while tensile strain tells us how much it can stretch without breaking.

Similar threads

  • Mechanical Engineering
Replies
1
Views
903
Replies
1
Views
982
  • Mechanical Engineering
Replies
1
Views
2K
  • Mechanical Engineering
Replies
11
Views
2K
  • Mechanical Engineering
Replies
7
Views
3K
  • Mechanical Engineering
Replies
1
Views
938
Replies
2
Views
1K
  • Mechanical Engineering
Replies
3
Views
2K
Replies
4
Views
1K
  • Mechanical Engineering
Replies
2
Views
1K
Back
Top