Tension-compression cyclic behaviour of ultra-thin 90º ply blocks in CFRP laminates
Topic(s) : Special Sessions
Co-authors :
Serafín SÁNCHEZ-CARMONA (SPAIN), María Luisa VELASCO (SPAIN), Carlos SANDINO (SPAIN), Elena CORREA (SPAIN)Abstract :
Most composite structural components are subjected to fatigue during their life cycles. For instance, aircraft wing skins are constantly subjected to either tension or compression. Hence, it is a challenging task to broaden the scientific community's horizons about tension-compression (T-C) cyclic loading, which is an open research topic in the composite field. There are different works related to this matter, such as [1] and [2]. The comprehension of the appearance and growth of the different types of damages associated with the failure of composite materials at the microscopic level under fatigue has motivated this study when ultra-thin plies are involved.
As the damage appearance is due to the tensile part of the load cycles, the specimen design is the same as the one used in tension-tension fatigue in a previous author’s work [3]. In order to prevent buckling in the compressive part of the load cycles, a tailor-made anti-buckling device is used, similar to that employed in previous works [1].
Carbon/epoxy cross-ply laminates made of conventional (150 g/m2) and ultra-thin (30 g/m2) plies are selected to define the experimental programmes. These laminates are cyclically tested at different stress ratios at 3Hz. The damage inspection is performed using a digital microscope along the specimen’s free edges, considering the biaxial stress state that occurs caused by the edge effect phenomenon [4].
A comparison of the appearance and growth of damages that are observed in both conventional and ultra-thin 90º ply blocks is carried out. As expected, there is an advance in the appearance of the first transverse damage in the 90º ply block of a cross-ply laminate under T-C cyclic loading compared to the T-T case. This advance seems to be more pronounced when ultra-thin plies are used in the 90º ply block of a cross-ply laminate. The damage progression of ultra-thin plies under T-C cyclic loading leads to different behaviour concerning the conventional ones.
As the damage appearance is due to the tensile part of the load cycles, the specimen design is the same as the one used in tension-tension fatigue in a previous author’s work [3]. In order to prevent buckling in the compressive part of the load cycles, a tailor-made anti-buckling device is used, similar to that employed in previous works [1].
Carbon/epoxy cross-ply laminates made of conventional (150 g/m2) and ultra-thin (30 g/m2) plies are selected to define the experimental programmes. These laminates are cyclically tested at different stress ratios at 3Hz. The damage inspection is performed using a digital microscope along the specimen’s free edges, considering the biaxial stress state that occurs caused by the edge effect phenomenon [4].
A comparison of the appearance and growth of damages that are observed in both conventional and ultra-thin 90º ply blocks is carried out. As expected, there is an advance in the appearance of the first transverse damage in the 90º ply block of a cross-ply laminate under T-C cyclic loading compared to the T-T case. This advance seems to be more pronounced when ultra-thin plies are used in the 90º ply block of a cross-ply laminate. The damage progression of ultra-thin plies under T-C cyclic loading leads to different behaviour concerning the conventional ones.