What is the repetition of same stressed vowel sounds?

The repetition of the same stressed vowel sounds is called assonance.

Example:

"The sea shells seem to sing a song of the sea."

Here, the repeated short "e" sound in "sea," "shells," "seem," "sing," and "sea" creates assonance.

Assonance is a literary device often used in poetry and prose to create a musical effect, add emphasis, or connect related words or ideas.