Study on Cryomechanics of Woven Glass-Epoxy Laminates

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Woven glass-epoxy laminates are used in superconducting magnets for magnetic fusion reactors and as barriers for containment of cryogenic liquids. These materials provide thermal and electrical insulation and can be subjected to large mechanical and thermal loads. Understanding variations in mechanical properties will provide useful information to the superconducting magnet designer. Because energy dissipated during crack formation or fracture of materials can affect the stability of the high performance superconducting magnets, quantification of such dissipative energy is important for superconducting magnet technology in partcular and for the understanding of mechanical behavior of materials at low temperatures in general.In this research project, the cryomechanics of woven glass-epoxy laminates is investigated.1. We consider the thermal-mechanical stress problem of cracked G-10CR glass-epoxy laminates with temperature dependent properties. The layred composite is made of one cracked … More layr bonded between two other layrs of different physical properties, and it is suddenly cooled at the surfaces. Numerical results on the transient stress intensity factor are obtained and are shown graphically.2. We examine the singular stresses of G-10CR glass-epoxy laminates with a broken layr under tension at low temperatures. Numerical results on the stress intensity factor and the order of stress singularity at different temperatures are obtained.3. We study the edge and interlaminar stress states of G-10CR woven glass-epoxy laminates with temperature dependent properties under uniform axial extension. A finite element method was used to study the influence of weave geometry and cryogenic temperatures on the edge and interlaminar stresses of two-layr woven laminates. Finite element results demonstrated that the weave geometry reduces edge stresses.4. We discuss the thermomechanical response of cracked G-10CR woven glass-epoxy laminates with temperature dependent properties. A finite element method was used to study the influence of residual thermal stresses and warp angles on the mechanical behavior of a two-layr woven laminate with a fill crack at low temperatures. Numerical calculations were carried out, and the mechanical properties and stress distributions at low temperatures are shown graphically for various warp angles. We also consider the transient thermal-mechanical stress problem of cracked G-10CR with temperature dependent properties.5. We discuss the low temperature fracture behavior of G-10 woven glass-epoxy laminates. Plane-strain fracture toughness (K_<IC>) tests were carried out with compact tension specimens at room temperature. 77K and 4K to evaluate the fracture toughness and temperature rise of woven glass-epoxy laminates. The influence of the crack length and loading rate on the low temperature fracture behavior is shown graphically. The temperature rise near the crack tip correlated with the amount of crack extension and loading rate. SEM micrograph shows the complicated structure of the damage zone near the crack tip (broken and delamination fibers, fiber pull-out, broken epoxy resin). We also study the nonlinear fracture behavior of G-10. Elastic-plastic fracture toughness (J_<IC>) tests were performed at 77K.The effect of individual damage events on the determination of J-integral resistance curves and J_Q values is discussed.6. We discuss the low temperature interlaminar shear behavior of G-10CR.Interlaminar shear tests were carried out with guillotine shear specimens at room temperature and 77K to evaluate the interlaminar shear strength (ILSS) of G-10CR glass-epoxy laminates. A three-dimensional finite element analysis was also used to interpret the experimental measurements. The effect of temperatures, notch separation and specimen thickness on interlaminar shear strength is shown graphically. Less