Guidelines and Limitations of the Compact Compression Specimen

Damage initiation and propagation material models for carbon fiber composites can be categorized according to the loading applied to constituent components. An example of such categorization is fiber tension, fiber compression, matrix tension, and matrix compression material models. Of these, matrix compression has been by far the least studied based on amount of published literature. Recent work at Oregon State University (OSU) has begun to address this lack of study. OSU researchers have published several papers culminating in the specification of an effective test specimen for isolating matrix compression damage initiation and propagation in carbon fiber laminates. While providing compelling results indicating the effectiveness and usefulness of this test specimen, little or no information has been provided regarding its manufacture, usable notch lengths, and optimum loading rate during testing. Experience at OSU has shown that this information is critical and not trivial to obtain. The purpose of this paper is to provide specific guidelines and “lessons learned” needed for other researchers to efficiently and effectively use this specimen in a comprehensive study. Test specimens are manufactured in the OSU Composites Materials Manufacturing Laboratory using typical commercial pre-peg carbon fiber following the specified layup and curing procedures. Once the material was cured the carbon fiber plate was then water-jet cut into the desired geometry and notch length. Usable notch length and optimum loading rate was determined by testing a series of specimens. All testing was conducted at an OSU lab using a universal testing machine with Digital Image Correlation (DIC) data collected. Specimens were preloaded and matrix compression initiation and propagation data collected until tensile failure occurred on the back edge of the specimen. Testing showed that shorter notch lengths result in inconsistent data and longer in effective initiation but limited propagation due to reduced ligament length. Testing suggested that a speed less than 5 mm/min gave the best results as faster displacement rates caused less crack propagation to occur, while increasing the likelihood of the specimen to fail in tension along its back edge. Through the use of these guidelines, researchers are able to manufacture and use an effective test specimen for the investigation of matrix compression damage initiation and propagation.