I want to compare two steel grades regarding the toughness (i.e. their ability to absorb energy until failure).
I need to ask two questions on that issue.
1. Considering that impact and fracture toughness involve the theory or LEFM and EPFM respectively, which is the theory behind the modulus of toughness (i.e. the area under the stress-strain curve)
2. In case a material e.g. grade A, has higher modulus of toughness than grade B, is it necessary that it has also higher impact or fracture toughness?
Hello My friend.
About number 1: I never think about the theory behind modulus of toughness. But, thinking here, if we observe the units involved, stress is, basicly J/m3. Strain is dimensionless. When you integrate it, you obtain energy per volume (this is the modulus of toughness).
About number 2: This energy per volume is the modulus of toughness. But fracture toughness is different of the toughness obtained from stress-strain curve area. Fracture toughness is the capacity of the material resist rupture, after crack. Here we are talking about materials with similar crack. Then, I suppose higher modulus of toughness, higher fracture toughness.
https://www.youtube.com/watch?v=Eh8YWTX-hUc
I like this question a lot! Let's go discuss this.
I hope to help you.
Thank you very much for your answer Gilberto.
About 1: I mean that in cases of impact test and fracture toughness test, linear elastic fracture mechanics and elasic-plastic fracture mechanic are valid respectively. On the other hand, when we examine the stress strain curve we think of a solid-continuous body without flaws and notches. I suppose it is not theory of elasticity as it concers only the elastic section of the curve.
About 2: Indeed, modulus of toughness has units of energy/volume which equals to pressure units. J-integral has the same units too. As far as I know there is a positive relationship between impact and fracture toughness as there are equations that correlate them (maybe exceptions exist). On the other hand, I doubt if modulus of toughness as a positive relationship with the other two. I am not sure.
Hi there! Very interesting question ;)
1. I would associate the concept of Toughness Modulus to the continuum theory, as it doesn´t considerates the presence of a stress concentrator. However, I advice you to be careful when saying that impact toughness is related to LEFM and fracture toughness to EPFM, this is not true! You can approximate Impact toughness to Fracture Toughness in specific cases and it´s not very recommendable.
2. You could assume that if you have higher toughness modulus, you will have higher fracture toughness, but you should be careful, because FT is very dependable of microstructural factors, such as second-phase particle size, which may not reflect in a traditional stress-strain diagram obtained from a tensile test.
Have you found something the literature (Anderson, Gross & Seelig)?
Regards!
Hi Germán,
1. You 're right about toughness modulus. It is associated with continuum theory or continuum mechanics. Considering LEFM and EPFM, as far as I know the Charpy test provides more accurate results in case of low absorbed energies where the plastic behavior of the material is restricted (LEFM). Could you mention a relevant reference in this topic?
2. Concidering your answer on the second topic, I agree with the second part: " FT is very dependable of microstructural factors, such as second-phase particle size, which may not reflect in a traditional stress-strain diagram obtained from a tensile test. "
If you could suggest literature it would be certainly helpful! There are considerably few publications and books, dealing with modulus of toughness. I can hardly find any.
Thank you.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys
- Steel