Abstract:

This paper presents a special layup concept-----softeningstrip design. The combination of different layups and/or different materials can be used to provide a low-stress and high-toughness region to prevent from crack propagation. Using the concept of softening strip, the potential to improve the damage tolerance of graphite/epoxy laminated composite plates under the action of uniaxial tension is investigated by means of analyses and tests.The specimens were made from [0/ + 45/0]s T300/648 laminates with two pieces of softening-strips （graphite-glass hybrid composite）. The effect of crack arrestment and the failure mechanism of the softening strips are studied in the tests through different measure procedures.The ultimate failure load and the load at the onset of rapid crack propagation are tested. In addition, the influence of the crack size and the parameters of the softening strips on the damage tolerance capability are also analysed.The softening strip concept can be used to meet the damage tolerance requirement with less weight penalty.

Key words: softening strip, crack propagation, damage tolerance, crack arrestment mechanism, ultimate failure load