I'm a materials engineer ;)

http://www.engineering-dictionary.org/ULTIMATE_STRENGTH
ultimate strength
= the maximum stress (tensile, compressive or shear) a material can sustain without fracture. It is determined by dividing maximum load by the original cross-sectional area of the specimen.

= the maximum resistance to loads that a structure or member is capable of developing before failure occurs, or, with reference to cross sections of members, the largest axial force, shear or moment a structural concrete cross section will support.

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Note added at 4 hrs (2017-09-15 13:42:17 GMT)
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Obs.: "resistência última" is a literal translation of "ultimate strength" (not the other way round).

Strength can be tensile strength (= traction strength), compression strength, or shear strength.
The term itself (resistência última) doesn't specify which one it is, so using "traction" in the translation is not ideal, IMO.

Considering the context, I think it's more likely that the parts are subjected to compression and shear forces than tensile/traction forces. However, you have more context, so you'll probably know this better than me.

Cheers!