This paper addresses the effects of different stacking sequences and seawater on the buckling behavior of hybrid composite plates. For the buckling tests, 12-layered hybrid composite plates were produced using different combinations of carbon, E-glass and aramid fibers, with an epoxy resin system as the matrix (Araldite LY1564/Aradur 3486). The hybrid composite plates were designed at the symmetric orientation angles of [(0/90)3]s, [(30/−60)3]s, [(45/−45)3]s and an anti-symmetric orientation angle of [(0/90)3]2. The hybrid composite samples were divided into groups and were subjected to buckling tests after being kept in different settings for varying periods of time (room temperature for 90 days, Black Sea water for 90 days, Mediterranean Sea water for 90 days, Mediterranean Sea water for 150 days). In light of the data obtained from the tests, the buckling behaviors of the layered hybrid composite plates were examined. The highest critical buckling load occurred in the carbon/aramid/glass (CAG) hybrid samples with the stacking sequence of [(0/90)3]s, whereas the lowest critical buckling load occurred in the carbon/aramid/glass (CAG45) hybrid samples with the stacking sequence of [(45/−45)3]s. It was observed that the critical buckling loads of the samples immersed in seawater decreased when compared to the critical buckling loads of the samples kept at room temperature. It was also found that the critical buckling loads of the hybrid samples immersed in the Mediterranean Sea water, which has high salinity, were lower than the critical buckling loads of the hybrid samples immersed in the Black Sea water, which has lower salinity.

In this study, the effect of cold environment on the buckling behavior of hybrid composites kept at −18°C for certain periods was investigated. For the buckling tests, hybrid composite plates with different fiber combinations were produced using three different fibers—carbon twill, E-glass twill, and aramid twill—and an epoxy resin (Araldite/Aradur) as the matrix material. Specimens for the buckling experiments were cut from the 12-layer hybrid composite plates and the hybrid composite specimens were then divided into three different groups. The specimens in Groups I and II were kept in a refrigerator for 90 days and 150 days, respectively, while Group III specimens were kept under room conditions as the control group. The hybrid composite specimens were subjected to buckling tests as soon as their waiting times were over. The buckling behaviors of hybrid composites with different stacking sequences were examined on the basis of the data obtained from the buckling experiments. The load–displacement curves obtained from the experiments were used to calculate the critical buckling loads ( P crs) for each hybrid configuration. The P cr was found to be highest for the hybrid configuration CAG (carbon/aramid/glass) with the stacking sequence [(0/−90)3]s and lowest for the hybrid configuration CAG45 with the stacking sequence [(45/−45)3]s. The hybrid composite specimens kept in a cold environment were found to have higher P crs than those kept under room conditions. The difference was greater in the case of the hybrid specimens kept in the cold environment for 150 days.

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