An experimental investigation of the mini-sandwich laminate as used to obtain unidirectional composite compression strengths

A mini-sandwich laminate configuration was used to test unidirectional AS4/3501-6 carbon/epoxy and S-2/5216 glass/epoxy composite material systems in established shear- and end-loaded compression test fixtures. Four different analysis techniques were used to predict the unidirectional lamina strength and stiffness from the measured tabbed and untabbed mini-sandwich specimen strength. The unidirectional composite compressive strengths obtained from both co-cured and adhesively bonded mini-sandwich specimens tested in the IITRI fixture using a nonlinear laminate theory analysis technique produced the highest strength values. Although the unidirectional composite compressive strengths measured using these specimens were higher than strengths typically obtained using conventional unidirectional specimen configurations, the adhesive bond between the face sheets and the 3501-6 epoxy resin core of the co-cured mini-sandwich specimens and the Poisson's effect in the core material were identified as possible limitations to this test method.