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An engineering method is suggested for prediction of impact response and damage of flat sandwich panels. The approach accounts for local core crushing, delamination and large face sheet deflections and does not rely on empirical indentation laws. Different models are suggested depending upon the impactor mass being either larger or significantly smaller than the mass of the impacted panel. The solution for large mass impact is based on closed form expressions. The solution for small mass impact is obtained from a dimensionless two-parameter integral equation. The validity of the approach is demonstrated on a number of static indentation experiments and impacts on sandwich panels.

The problem of impact damage in laminated composite structures, and the consequent reduction in residual strength, has been a topic of continual research for over two decades. The number of journal papers on the subject now runs into four figures and most have been conscientiously reviewed by Abrate(1991, 1994, 1998). This review is not intended to be in the academic tradition, with emphasis on acknowledging the authorship of all the various research initiatives. Instead we present our opinions so that the reader can appreciate our current understanding of the problem, our capability of predicting by analysis, and the scope of the design tools for avoiding structural damage, or at least designing damage tolerant aerospace structures.