1) Anything that evolves NECESSARILY evolves over time, so the French is largely redundant.

2) Unless we assume an error in the French, "significatiVE" NECESSARILY refers to "évolution".

3) Break it down this way :
on s'intéresse à son (évolution dans le temps) significative de (l'évolution d'une dégradation).

4) A machine is "evolving" (over time) at ALL times. Only part of that gradual "evolution" will necessarily be related to the "evolution of damage", e.g. temperature or oil pressure will rise or fall, parts will gradually wear more and more, but only when certain conditions are united can it be said their "evolution" contributes to - or corresponds to - the "evolution of the failure".

5) "Significative" here, while qualifying "évolution", does not mean "significant = important" but has that other meaning of "signifier = what it signifies".
Thus, while oil pressure and temp., say, might "evolve" while an engine is running under varying conditions, they will not be of relevance/significance to any failure. When, for whatever reason, they get to the point where the engine starts performing poorly, potentially inducing failure, that is the "evolution (over time)" they are concerned with, e.g. the speed at which oil temperature rises and oil temperature drops, rather than merely the max temp and min pressure.

"What is important is not so much the absolute value of a given parameter, but rather (that part of) the (gradual - if you feel "dans le temps" is necessary) evolution/development of that parameter which (evolution) is directly related to the evolution/development of the damage."