Chagiga 7b - Korban Simcha: Is the Mitzvah Just Eating?

R' Yossi already posted twice on this issue - see the first post on chagiga and see the hebrew post on 6b.

Tosafos 7b d.h. olos, explains in the name of Rabbeinu Elchanan and the R"i that although one can fulfill the obligation of simcha by eating the meat of nedarim and nedavos, that is only if the korban was brought with the intention of serving as a simcha offering. But, if it was brought to be only to fulfill a neder, it would not qualify for simcha. Clearly, Tosafos assumes that the mitzvah of Simcah is not just in the eating of the meat but also in the sacrificing of the animal to be a Shalmei Simcha.