In　this　study,　we　investigate　the　targeted　energy　transfer　(TET)　from　a　simply　supported　beam　that　is　subjected　to　thermal　variations　and　external　excitations　to　a　local　nonlinear　energy　sink　(NES).　We　derive　the　governing　equation　of　motion　for　the　beam　with　an　NES　device　and　study　the　influences　of　NES　parameters　on　the　vibration-suppressing　effect.　We　obtain　the　optimized　parameters　of　the　NES　under　constant-amplitude　harmonic　excitation　at　room　temperature.　The　optimized　NES　gradually　loses　its　vibration　absorption　efficiency　as　the　excitation　amplitude　and　temperature　increase.　We　change　the　nonlinear　stiffness　of　the　NES　to　mitigate　the　influence　of　temperature　variation　and　show　that　NES　efficiency　can　be　enhanced　by　reducing　the　nonlinear　stiffness.　We　propose　a　variable-stiffness　NES,　and　the　results　demonstrate　this　NES　is　best　for　maintaining　efficiency　over　the　whole　temperature　range.　We　also　analyze　the　transient　responses　of　the　system　under　impulse　loads.　Results　indicate　that,　like　the　performance　of　the　system　subjected　to　harmonic　excitation,　an　NES　with　relatively　low　stiffness　can　better　suppress　vibration　with　increasing　impulse　amplitude　and　temperature.