Statistical lifetime of composites subjected to random and ordered block
loadings
Abstract
This study presents a procedure based on constant amplitude (CA) fatigue
data to predict the statistical fatigue lifetime of glass/orthopolyester
composites subjected to repeated ordered and random two, three, and six
sequences of block loadings. A numerical routine was developed to detect
cycle-by-cycle the statistical strength degradation progression until
failure, assuming that the strength at the end of a block cycle equals
the strength at the start of the successive one and that the individual
samples’ static strength, residual strength, and fatigue life share the
same rank in their respective cumulative distribution function.
Predictions conform to the statistically undetectable loading sequence
effects and lightly overestimate the lifetimes of random and ordered
high-to-low (1/100 cycles) repeated two-block loadings. The vanishing
effect of the loading sequence when the block extents remain fixed, the
block extent effects for a given three-block sequence, and the lifetimes
of three-block loadings were fully predicted. The six-block sequence’s
experimental lifetimes with different block loading orders and block
extent fell within the predicted lifetimes’ cumulative distribution
function. A reliable damage rule based on residual strength was proposed
and compared to the Miner’s rule.