Load-dependent power-law exponent in creep rupture of heterogeneous materials

Creep tests on heterogeneous materials under subcritical loading typically show a power-law decay in strain rate before failure, with the exponent often considered material dependent but independent of applied stress. By imposing successive small stress relaxations through a displacement feedback loop, we probe creep dynamics and show experimentally that this exponent varies with both applied load and loading direction. Simulations of a disordered fiber bundle model reproduce this load dependence, demonstrating that such models capture essential features of delayed rupture dynamics.