Fatigue Response of a Host Structure with Interlaced Embedded Devices

A structural tailoring technique known as interlacing was applied to (0°)24T graphite/epoxy specimens. Glass slides, representing inert actuators or sensors, were embedded using three different interlacing configurations that are defined by the location of the continuous and discontinuous plies through the laminate thickness. Twenty spec- imens were loaded in tension-tensi on fatigue and inspected at regular intervals to monitor damage initiation and progression. The results of this research demonstrated that the onset of damage can be delayed and the progression of delamination can be impeded by distributing the material discontinuity of the inclusion through the thickness via interlacing. laminate with an embedded sensor or actua- tor is sensitive to the method of lay-up used to embed the device. Traditional techniques of manufacturing a part with an embedded device have yielded relatively low mechanical prop- erties compared to a similar part with no inclu- sion (1). However, a method of lay-up called interlacing has been developed and proven to substantially increase the strength of a com- posite smart structure under quasistatic load- ing conditions (2). In static tests, interlaced configurations exhibited a two-fold increase in host-structure integrity and, in some cases, pre- vented the occurrence of damage at and near the inclusion. Because multi-functional struc- tures are often under cyclic loading, both ex- ternally applied by surrounding structures and internally applied by embedded actuators, the fatigue response of interlaced configurations is important. To avoid changes in thickness correspond- ing to the device embedded in a composite laminate, material must be removed where the device is placed during the manufacture of the part. Traditionally, neighboring laminae that lay in the plane of the inclusion are cut to fit directly against the perimeter of the de- vice. Then, continuous plies are stacked above and below the plane of the device as shown in Figure 1. The presence of discontinuous plies in the laminate introduces a sharp mate- rial discontinuity that gives rise to interlaminar