Mechanical characterization at room and cryogenic temperature of thin-ply CFRP laminates manufactured by filament winding

Abstract

A safe design of composite tanks for liquid hydrogen is one of the strongest challenges in the coming years. This paper describes an approach to characterize the influence of cryogenic temperature on the mechanical properties of a thin-ply carbon/epoxy material manufactured by wet filament winding. The aim is to obtain the properties required for lightweight design of a suitable thin-ply layup for future use as a cylindrical tube in a linerless tank for storage of liquid hydrogen at cryogenic temperature and interior pressure. A methodology is presented for determining the ply properties required as input parameters in analytical models describing the constitutive relationships, strength-based failure criteria, and fracture mechanics for in-situ strength predictions within thin-ply theory. Therefore, tensile and shear behavior, as well as interlaminar toughness of flat wet filament wound laminates have been determined experimentally at room and cryogenic temperature. Additionally, the variation of coefficients of thermal expansion and dynamic mechanical analyses over temperature have been investigated. Since the ply properties are a function of the fiber volume fraction and quality obtained during wet filament winding, an integration of micromechanics is provided on how to adjust properties based on different fiber volume fractions obtained from nominally unidirectional coupon specimens for use in design of real angle-ply cylinders. A methodology is proposed to reach the relevant mechanical properties for design making use of a limited set of experimental properties, based on challenges to test at −253°C (20 K). An outlook on potential improvements regarding mechanical testing at cryogenic temperature is provided.