Strain rate effects on steel strength

[SteveO]

I was wondering exactly how yield and tensile strength increases with increasing levels of strain rate for a typical steel grade? I understand dislocations are generated during straining (work hardening), but what happens at higher strain rates which increases the strength?

 

[Astronuc]

I was wondering exactly how yield and tensile strength increases with increasing levels of strain rate for a typical steel grade? I understand dislocations are generated during straining (work hardening), but what happens at higher strain rates which increases the strength?

The effect of increasing yield and tensile strength with increasing strain/strain rate is observed in many, if not most, metals, and even polymers.

In metals, this would have to do with the rate of dislocation/defect generation and dislocation pile-up. The dislocations diffuse through the crystal structure (from inside grains to grain boundaries). If the rate of dilocation generation exceeds the rate at which the diffuse to gb, then the dislocation density has to increase, which causes an increase in strength.

In addition, dislocations may cancel, but if the do not diffuse fast enough, they will not cancel.

Try this paper Adams, Kenneth Hoyt (1965-05-21) http://etd.caltech.edu/etd/available/etd-09102002-095733/

 

[ravenprp]

The strength of steel is influenced by a variety of factors, including composition, microstructure, and processing methods. However, strain rate is also an important factor that can significantly impact the strength of steel.

At low strain rates, steel exhibits a phenomenon known as work hardening, where dislocations are generated and accumulate within the material. This results in an increase in strength as the dislocations impede the movement of other dislocations, making it more difficult for the material to deform.

At higher strain rates, the rate of dislocation generation and accumulation also increases, leading to a further increase in strength. This is because the dislocations have less time to rearrange and become more organized, resulting in a higher density of dislocations and a stronger material.

Additionally, at higher strain rates, the time available for dislocation annihilation is reduced, meaning that the dislocations remain in the material for longer periods. This results in a more pronounced work hardening effect and a higher overall strength.

It is important to note that the increase in strength with increasing strain rate is not linear and can vary depending on the specific steel grade and its microstructure. However, in general, higher strain rates lead to a higher strength in steel due to the increased rate of dislocation generation and accumulation, as well as a more pronounced work hardening effect.