Can we predict/estimate the variation in fracture toughness based on mechanical properties (i.e. yield, tensile strength, hardness, % elongation, fatigue strength and impact toughens etc.).
Sanjay:
There are several models to predict fracture toughness, be it KIc or JIc, and its variation - some are purely empirical based on experimental data, but the most informative are the ones that are micro-mechanistic in nature (akin to modeling Orowan bypassing to predict the yield strength). In their simplest form, the latter approaches are based on criteria involving a critical stress across a characteristic distance (or volume) for brittle fracture ahead of a crack tip - this was originally done in the so-called RKR model - which was first developed for brittle cleavage fracture in steels, and corresponding models involving a stress-state modified critical strain across a characteristic distance ahead of a crack tip for ductile fracture (e.g., by microvoid coalescence). These approaches can predict the toughness from such mechanical properties as strength, ductility, strain hardening coefficient and the salient length-scales in the microstructure. Additionally, many of these models have been reformulated in statistical terms, in particular using weakest-link statistics for the critical fracture stress models, which among other aspects can give estimates of the expected variation in toughness values.
If your interested, the attached manuscripts provide an overview of such models and give an example where they can be developed in statistical terms.
ROR
Sanjay: With reference to your question on how the fracture toughness, and its variation, can depend on mechanical properties, here are the papers indicated in my previous response related to the simple modeling of fracture to achieve this objective. ROR
Hi Sanjay Samant
to consult this
C. Bathias, Coll., Matériaux composites, DUNOD, 2ème édition, 2009.
Dear Sanjay,
Depends on many factors.
It(K1c) depends on n and in many cases it is considerably different from zero(usually reaches critical value, which is materials property). It also depends on the depending on the relative size of the plastic zone.
It can also depend on grain boundary, inclusion, transformation toughening, extrinsic mechanics (crack wedging, micro cracking etc.) and intrinsic mechanism (changes in the crack path, crack bifurcation -grain structure, crack deflection-secondary phases etc.)
A components thickness affects the constraint conditions at the tip of a crack with thin components having plane stress conditions and thick components having plane strain conditions. Plane strain conditions give the lowest fracture toughness value and are a material property.
For J1c, effect of strain hardening is not important) it depends on contour path integral around the crack tip where the path begins and ends on either crack surfaces, suppose tip is not sharp , it is blunt than value will be less. material in terms of amount of stress energy required for a crack to grow.
It depends on the initial ligament length given by the difference between width and initial crack length, plastic area under the load-displacement curve .
Basically both depend upon plastic area.
Hope it is helpful for you.
Ashish
Hi Sanjay, because Toughness indicates how much energy a material can absorb till the point of fracture or before rupturing, the area under the stress–strain curve of tensile testing can be used as the value of Toughness. So a rough estimation may be written as:
Toughness = Elongation × (Proof stress + Tensile strength)/2
On the other hand, KIc and JIc are the parameters relating to crack tip field, and in principal aspect they are hard to be related to the tensile strength etc.
Dear Sanjay,
Generally, fracture toughness is a function of ductility and strength. It is obvious that (K1C and JIC) are different for different materials. There are some correlation are available in literature. Probably you can look into the Prof R O Richie papers.
best wishes
Nani Babu
The toughness calculated from the mechanical properties (yield stress, tensile strength, and elongation) was found to correlate with the Charpy impact energy, and it is known that CVN is in good agreement with the fracture toughness. Ref.:
Preprint A simplified toughness estimation method based on standard t...
- Badges
- Science topic
- Similar topics
- Geoscience
- Asia
- India