  Accelerated degradation tests are used to provide accurate estimation of
lifetime properties of highly reliable products within a relatively short
testing time. There data from particular tests at high levels of stress
(e.\,g.\ temperature, voltage, or vibration) are extrapolated, through a
physically meaningful model, to obtain estimates of lifetime quantiles under
normal use conditions. In this work, we consider repeated measures accelerated
degradation tests with multiple stress variables, where the degradation paths
are assumed to follow a linear mixed effects model which is quite common in
settings when repeated measures are made. We derive optimal experimental
designs for minimizing the asymptotic variance for estimating the median
failure time under normal use conditions when the time points for measurements
are either fixed in advance or are also to be optimized.
