Study on Cryomechanics of Woven Glass-Epoxy Laminates

编织玻璃环氧树脂层压板用于磁性聚变反应堆的超导磁体和作为低温液体的密封屏障。这些材料提供热和电绝缘，可以承受大的机械和热负荷。了解机械性能的变化将为超导磁体设计者提供有用的信息。由于材料在裂纹形成或断裂过程中耗散的能量会影响高性能超导磁体的稳定性，因此这种耗散能量的量化对于超导磁体技术以及对材料在低温下的力学行为的理解非常重要。本课题研究了机织玻璃环氧树脂层合板的低温力学特性。研究了具有温度相关性能的G-10CR玻璃环氧树脂层合板的热机械应力问题。这种层状复合材料是由一层有裂纹的层和两层不同物理性质的层结合而成，并在表面突然冷却。得到了瞬态应力强度因子的数值结果，并用图形表示。研究了具有断裂层的G-10CR玻璃环氧树脂层合板在低温拉伸下的奇异应力。得到了不同温度下的应力强度因子和应力奇异阶数的数值结果。研究了具有温度相关性能的G-10CR编织玻璃环氧树脂层合板在均匀轴向拉伸下的边缘和层间应力状态。采用有限元方法研究了编织几何形状和低温温度对双层编织层压板边缘应力和层间应力的影响。有限元结果表明，编织几何结构减小了边缘应力。讨论了具有温度相关性能的G-10CR机织玻璃环氧层合板的热力学响应。采用有限元方法研究了残余热应力和翘曲角对含填充裂纹的双层编织层合板低温力学行为的影响。通过数值计算，用图形显示了不同翘曲角度下的低温力学性能和应力分布。我们还考虑了具有温度相关性质的G-10CR裂纹的瞬态热-机械应力问题。讨论了G-10机织玻璃环氧复合材料的低温断裂行为。采用室温压实拉伸试样进行了平面应变断裂韧性（K_<IC>）试验。采用77K和4K对机织玻璃-环氧复合材料的断裂韧性和温升进行评价。用图形表示了裂纹长度和加载速率对低温断裂行为的影响。裂纹尖端附近的温升与裂纹扩展量和加载速率有关。SEM显微图显示裂纹尖端附近损伤区结构复杂（纤维断裂分层、纤维拔出、环氧树脂断裂）。我们还研究了G-10的非线性断裂行为。在77K下进行了弹塑性断裂韧性（J_<IC>）试验。讨论了单个损伤事件对j积分电阻曲线和J_Q值确定的影响。讨论了G-10CR的低温层间剪切行为。采用断头台剪切试样在室温77K条件下进行层间剪切试验，评价G-10CR玻璃环氧树脂层间剪切强度（ILSS）。三维有限元分析也被用来解释实验测量结果。温度、缺口分离和试样厚度对层间剪切强度的影响用图形表示。少

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