Open Hole Compression Strength and Failure Characterization in Tape Laminates

Bau, H., Hoyt, D.M., Rousseau, C.Q.

Composite Structures: Theory and Practice, ASTM STP 1383, 2000.

Open hole compression (OHC) design criteria often size the thicknesses of composite aircraft skin structures. Therefore, there can be a significant payoff in improving OHC allowables through better characterization of OHC strength and behavior. This study, using progressive damage analysis and empirical methods, provides new insight into OHC strength and failure behavior.

OHC failure behavior was modeled using PDHOLEC, a progressive damage, 2-D finite element code. Ultimate strength predictions were combined into carpet plots over a wide range of layups in three graphite composite material systems. A detailed evaluation of PDHOLEC progressive failure output resulted in the identification of several distinct predicted failure mechanisms. Predicted failure mechanisms and ultimate strengths are compared to OHC test data.

Two distinct failure mechanisms for OHC configurations were identified based on the PDHOLEC failure study and strength trend studies of test data: a 0° ply kinking/buckling failure mechanism and a matrix cracking mechanism. The PDHOLEC predictions and test data were grouped by the identified failure mechanisms. Then curve fit equations were generated to characterize the ultimate strength behavior for each failure mechanism.

KEYWORDS: composites, stress concentrations, compression, progressive damage, finite element analysis, notches, open hole, strength, failure mechanisms