Stress Analysis Of Composite Laminates At Cryogenic Conditions

Advanced composite materials have been widely used in military and civil engineering structures for its high modulus, good corrosion resistance, flexibility and low cost design. However, the composite materials also have many shortcomings, such as non-uniformity, anisotropy, laminar resistance and sensitivity to the environment, so the deformation and failure mechanisms are extremely complicated. Therefore, the study of advanced composite materials/structures in the field of academia and engineering has become a contemporarily popular topic. The study focuses on composite materials tank used for cryogenic propellant. To start with, mechanical and thermal constitutive relations of E-Glass/Epoxy and Graphite/Epoxy, are designed respectively for composite materials tank on the basis of composite micro-mechanical model.Afterwards, the study takes typical holeless/hole laminated structure as the object and applies the finite element method to analyze the in and out of plane stress distribution features in low temperature. The thesis will be invaluable as a reference to the evaluation of the target system and its safety. This study is part of special funding of State Key Laboratory Of Structural Analysis for Industrial Equipment (SS13205,2013-2014).There are a few major components as follows.1. The mechanical and thermal constitutive relations of fiber reinforced resin matrix composite materials for cryogenic environment.According to the results of the experiment on the properties of resin at low temperature, the formula of resin properties as a function of low temperature can be obtained through numerical fitting expression.In addition,composite micro-mechanical model and Haplin-Tsai formula can lead to mechanical and thermal constitutive relations of E-Glass/Epoxy and Graphite/Epoxy single plate at low temperature.2. Interlaminar stress analysis of composite laminate around the holeFirstly, typical example verifies the reliability of the finite element model of stress analysis between layers. Then, based on the free boundary stress analysis of [00/450/-450/900]s laminates at low temperature, the effects of temperature and fiber percentage and Haplin-Tsai model specifications on free boundary in-layer strains are examined. In conclusion, the interlaminar stresses around free boundary increases.3. Interlaminar stresses of laminate closed to the hole for cryogenic environmentTo start with, the data of typical laminate with curve free boundary verifies the reliability of finite element model. In accordance, the finite element analysis of [00/900]s laminate with a cutout for cryogenic environment leads to the hole-edge stress distribution pattern of E-Glass/Epoxy and Graphite/Epoxy. Meanwhile, the effects of temperature and fiber percentage on the hole-edge interlaminar stresses are also examined.