ABSTRACT

With the increased use of toughened epoxy adhesives in current transportation lightweighting efforts, it is critical that damage mechanisms, such as strain whitening, are understood and quantified. Damage quantification is needed for the constitutive models used in structural design; however, thin bond lines in adhesive joints limit direct observation. In this study, microscope observations of bulk toughened epoxy adhesive specimens subjected to tensile loading were linked to damage. Cracks on the surface opened during loading, leading to strain whitening at the crack tips and the initiation and propagation of shear bands. The stresses approximated at the crack tips suggested that particle cavitation could be occurring in these regions. Changes in specimen stiffness were linked to crack growth and the formation of shear bands. Material damage calculated using traditional load-unload stiffness (D ~ 35%) was higher than other methods such as change in material strength (D ~ 18%) and damage from changes in stiffness during load-reload (D ~ 19%). The differences were attributed to short-term viscoelastic effects. A new approach calculated damage from the strain whitening on the free surface (D ~ 21%). Values were in agreement with damage figures from other methods. The technique can quantify damage over the loading history and identify areas of damage localization.

摘要

随着在当前运输轻量化工作中增加使用增韧环氧树脂粘合剂，了解和量化损伤机制（例如应变白化）至关重要。结构设计中使用的本构模型需要进行损伤量化；然而，粘合接头中的薄粘合线限制了直接观察。在这项研究中，对经受拉伸载荷的大块增韧环氧树脂粘合剂试样的显微镜观察与损伤有关。加载过程中表面裂纹打开，导致裂纹尖端的应变变白以及剪切带的产生和扩展。裂纹尖端处近似的应力表明，这些区域可能发生颗粒空化。试样刚度的变化与裂纹扩展和剪切带的形成有关。使用传统的加载-卸载刚度计算的材料损坏 (D ~ 35%) 高于其他方法，例如材料强度变化 (D ~ 18%) 和加载-重载期间刚度变化造成的损坏 (D ~ 19%)。这些差异归因于短期粘弹性效应。一种新方法计算了自由表面上的应变白化造成的损伤（D ~ 21%）。数值与其他方法的损坏数据一致。该技术可以量化加载历史中的损坏并识别损坏定位区域。一种新方法计算了自由表面上的应变白化造成的损伤（D ~ 21%）。数值与其他方法的损坏数据一致。该技术可以量化加载历史中的损坏并识别损坏定位区域。一种新方法计算了自由表面上的应变白化造成的损伤（D ~ 21%）。数值与其他方法的损坏数据一致。该技术可以量化加载历史中的损坏并识别损坏定位区域。