FORT WORTH — The Mimir Chamber Music Festival featured young artists for the second time Saturday at TCU’s PepsiCo Hall.Two young, new and abundantly talented string quartets are in residence under the tutorage of distinguished faculty. First up was The Axiom Quartet, made up of alumni of the Shepherd School of Music at Houston’s Rice University and now affiliated with the Music Preparatory School at the University of St. Thomas.Violinists Juliette Javaheri and Dominika Dancewicz, violist Dawson White and cellist Hellen Weberpal had quite a task in front of them with Felix Mendelssohn’s dark and brooding String Quartet in f minor, Op. 80. The work was written as a response to the death of his beloved sister, Fanny, and is an outpouring of grief in a torrent of notes.Since the forward motion never stops, this is a study in levels of intensity and the Axiom didn’t have a clear picture of the overall architecture. Thus, the musicians went from big moment to big moment without ever going anywhere else.Intonation also suffered, as it usually does when a piece is being overplayed. Still, there was a lot of excellent music-making, and once they get past the notes and absorb the piece into their psyche, they will surely give Mendelssohn’s tragic quartet a more memorable reading.Ludwig van Beethoven’s String Quartet in C Major, Op. 59, No. 3, called the “Rasumovsky” after the Russian count who commissioned it, is a fearsome challenge for any string quartet new or old. The Vivant String Quartet is new. It was formed by acquaintances from the University of North Texas and from the Mimir festival last summer, solely to participate in this festival. It didn’t sound like a new group as it gave a surprisingly excellent performance.Violinists Kevin Smith and Leah Greenfield, violist Robert Switala and cellist Elaine Whitmire are evenly matched technically and musically. Switale is especially adept at blending with either the lower or upper sonorities as his part requires. They took chances throughout, usually with much success. They took the final fugue dangerously fast, but it only occasionally turned into a scramble. The overriding effect was sheer brilliance, enhanced by how much they enjoyed playing it for us.