We present an experimental realization with electrical composites of t
he thermal fuse model [D. Sornette and C. Vanneste, Phys. Rev. Lett. 6
8, 612 (1992)], proposed as a paradigm of dynamical rupture in heterog
eneous media. An isolating polymer matrix is filled with conducting pa
rticles, and the particle-particle contacts evolve due to thermal expa
nsion of the matrix as a function of the applied current I. Above a cr
itical current, the electric resistance R increases as a power law of
time to rupture R similar to (t(r) - t)(-alpha), with alpha similar or
equal to 0.65, and the breakdown time t(r) scales as t(r) similar to
I-2 in agreement with the model.