Sandwich Structures Failure Modes and Their Prevention

Discipline: Structures
Webcast Air Date: September 28, 2016

Typical damage modes in light honeycomb sandwich structures include face sheet/core disbonding and core fracture, both of which can pose a threat to the structural integrity of a component. These damage modes are of particular interest to aviation certification authorities since several in-service occurrences, such as rudder structural failure and other control surface malfunctions, have been attributed to face sheet/core disbonding. Extensive studies have shown that face sheet/core disbonding and core fracture can lead to damage propagation caused by internal pressure changes in the core.

In order to identify, describe and address the phenomenon associated with facesheet/core disbonding, a reliable means of characterizing facesheet/core disbonding must be developed. In addition to the characterization tests, analysis tools are required, to help assess the likelihood of a structure exhibiting critical disbonding. These analysis tools need to be verified and validated.

In this webcast, sandwich structures are introduced and their failure modes are discussed. Actual in-service occurrences are presented and a road map to standardization for facesheet/core disbonding in sandwich composite components is described. An overview is given on the development of test methods that yield a critical strain energy release rate associated with disbonding, with a focus on mode-I dominated loading conditions. Further, an analysis approach is discussed to compute energy release rates along an arbitrarily shaped disbond front. Finally, a brief summary of observations is presented and recommendations for improvements are provided.