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Nickel titanium, also known as nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages.Different alloys are named according to the weight percentage of nickel; e.g., nitinol 55 and nitinol 60.
NiTiNOL 60, or 60 NiTiNOL, is a Nickel Titanium alloy (nominally Ni-40wt% Ti) discovered in the late 1950s by the U. S. Naval Ordnance Laboratory (hence the "NOL" portion of the name NiTiNOL). [1] Depending upon the heat treat history, 60 NiTiNOL has the ability to exhibit either superelastic properties in the hardened state or shape memory ...
The yield strength of shape-memory alloys is lower than that of conventional steel, but some compositions have a higher yield strength than plastic or aluminum. The yield stress for Ni Ti can reach 500 MPa. The high cost of the metal itself and the processing requirements make it difficult and expensive to implement SMAs into a design.
The ultimate tensile strength of a material is an intensive property; therefore its value does not depend on the size of the test specimen.However, depending on the material, it may be dependent on other factors, such as the preparation of the specimen, the presence or otherwise of surface defects, and the temperature of the test environment and material.
In one study, strain hardening exponent values extracted from tensile data from 58 steel pipes from natural gas pipelines were found to range from 0.08 to 0.25, [1] with the lower end of the range dominated by high-strength low alloy steels and the upper end of the range mostly normalized steels.
If HV is first expressed in N/mm 2 (MPa), or otherwise by converting from kgf/mm 2, then the tensile strength (in MPa) of the material can be approximated as σ u ≈ HV/ c, where c is a constant determined by yield strength, Poisson's ratio, work-hardening exponent and geometrical factors – usually ranging between 2 and 4. [9]
The ultimate strength is the maximum stress that a material can withstand before it breaks or weakens. [12] For example, the ultimate tensile strength (UTS) of AISI 1018 Steel is 440 MPa. In Imperial units, the unit of stress is given as lbf/in 2 or pounds-force per square inch. This unit is often abbreviated as psi.
It also corresponds to the “strength” (ultimate tensile stress), at least for metals that do neck (which covers the majority of “engineering” metals). On the other hand, the peak in a nominal stress-strain curve is commonly a fairly flat plateau, rather than a sharp maximum, so accurate assessment of the strain at the onset of necking ...