  Prediction of breakdown in disordered solids under external loading in a
question of paramount importance. Here we use a fiber bundle model for
disordered solids and record the time series of the avalanche sizes and energy
bursts. The time series contains statistical regularities that not only signify
universality in the critical behavior of the process of fracture, but also
reflect signals of proximity to a catastrophic failure. A systematic analysis
of these series using supervised machine learning can predict the time to
failure. Different features of the time series become important in different
variants of training samples. We explain the reasons for such switch over of
importance among different features. We show that inequality measures for
avalanche time series play a crucial role in imminent failure predictions,
especially for imperfect training sets i.e., when simulation parameters of
training samples differ considerably from those of the testing samples. We also
show the variation of predictability of the system as the interaction range and
strengths of disorders are varied in the samples, varying the failure mode from
brittle to quasi-brittle (with interaction range) and from nucleation to
percolation (with disorder strength). The effectiveness of the supervised
learning is best when the samples just enter the quasi-brittle mode of failure
showing scale-free avalanche size distributions.
