A comparison between creep of laminated aluminum and the transverse creep behavior of a unidirectional boron-aluminum composite

Abstract

The transverse creep behavior of a unidirectional 30 vol pct boron/1145-0 aluminum composite material was investigated over the temperature range 573 to 773 K. The creep curve of the composite exhibited primary, steady state, and tertiary stages of creep, as did the unreinforced laminated matrix; however, the primary stage of creep was consid-erably less pronounced in the composite than in the matrix. The minimum (or steady state) creep rate of the composite was less than that of the laminated matrix alone below a transition stress Σ = 1.74 × 10−4E whereE is Young's Modulus of aluminum. Above this transition stress, the minimum creep rate of the composite exceeds that of the unreinforced matrix; further, the strain to failure of the composite generally decreased when the applied stress was above the transition stress. The temperature dependence of the minimum creep rate was the same for both the composite and the laminated matrix. Failure in the composite was initiated by debonding of the filament-matrix interface and it is suggested that debonding of the interface contributes in an additive way to the creep of the composite and to a greater extent at high stresses, leading to the transition stress observed.