Improving the fracture toughness and the cyclic-fatigue resistance of epoxy-polymer blends
Improving the fracture toughness and the cyclic-fatigue resistance of epoxy-polymer blends
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DOI：
10.1016/j.polymer.2014.10.018
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发表时间：
2014-11-18
期刊：
影响因子：
4.6
通讯作者：
Taylor, A. C.
中科院分区：
文献类型：
--
作者：
Kinloch, A. J.;Lee, S. H.;Taylor, A. C.
相对坚韧的环氧共混聚合物现在在商业上可用作粘合剂和纤维复合材料的基体。然而，在某些应用中，另一个同样重要甚至更重要的失效特性是环氧聚合物对循环疲劳载荷的抵抗力。然而，环氧聚合物的循环疲劳行为尚未得到详细的研究，特别是环氧聚合物的材料已通过形成聚合物共混物进行改性，以增加其在准静态测试率或冲击测试率下的韧性。因此，目前工作的一个主要目的是对一系列橡胶和热塑性材料进行新的研究，以改性环氧聚合物，以研究在给定的配方中是否可以同时实现相对较高的韧性和显著改善的循环疲劳行为。未改性的环氧聚合物的断裂能G（Ic）为495 J/m(2)，疲劳循环中最大应变能释放率的阈值G（th）为155 J/m(2)，低于此值则没有明显的裂纹扩展。已经确定了几种环氧聚合物共混物，它们确实显示出这些值的显著增加，这些性能的最佳组合可能是用聚（丙二醇）基聚氨酯（PU）改性剂改性的环氧聚合物：无论是单独使用还是作为“杂化”聚合物共混物与基于丁苯橡胶核心的核壳橡胶（CSii）颗粒结合使用。对于这些pu基环氧聚合物，G（Ic）和G（th）的值分别增加到约2475 J/m(2)和445 J/m(2)。由聚合物共混改性剂的加入引起的增韧机制表明，在环氧共混聚合物中存在多相是获得相对较高的G（Ic）和G（th）值的关键要求。这是由于第二相颗粒引发了环氧基相的塑性变形，这是能量耗散和增韧的主要来源。反过来，环氧基相塑性变形所耗散的能量明显受到环氧共混聚合物这一相所表现出的延性程度的极大影响。因此，观察到的增韧程度的另一个重要特征是改性剂对环氧基相屈服应力和塑性破坏应变的影响。(C) 2014年作者。Elsevier Ltd.出版。
Relatively tough epoxy-blend polymers are now commercially available for use as adhesives and as the matrices for fibre composites. Nevertheless, another failure property which may be of equal, or even of greater, importance in some applications is the resistance of the epoxy polymer to cyclic-fatigue loading. However, the cyclic-fatigue behaviour of epoxy polymers has not been studied in great detail, especially for epoxy polymers where the material has been modified by forming a polymer blend in order to increase its toughness under quasi-static test rates or impact test rates. Therefore, a major aim of the present work has been to undertake a novel investigation of a range of rubber and thermoplastic materials to modify an epoxy polymer to study whether both a relatively high toughness and a significantly improved cyclic-fatigue behaviour can be simultaneously achieved in a given formulation. The unmodified epoxy-polymer possessed a value of the fracture energy, G(Ic), of 495 J/m(2) and a value for the threshold value of the maximum strain-energy release rate in a fatigue cycle, G(th), (below which no significant crack growth occurs) of 155 J/m(2). Several epoxy-polymer blends have been identified which do show major increases in these values and probably the best combination of such properties were for the epoxy-polymers modified with a poly(polypropylene-glycol)-based polyurethane (PU) modifier: either when used by itself or as a 'hybrid' polymer-blend in combination with core shell rubber (CSii) particles, based upon a styrene-butadiene rubber core. For these PU-based epoxy polymers the values of G(Ic) and G(th) were found to increase to values of about 2475 J/m(2) and 445 J/m(2), respectively. The mechanisms of toughening that were induced by the addition of the polymer-blend modifier revealed that the presence of a multiphase in the epoxy-blend polymer was a critical requirement in achieving relatively high values of G(Ic) and G(th). This was due to the second-phase particles initiating plastic deformation of the epoxy-matrix phase, which was the major source of energy dissipation and toughening. In turn, the extent of energy dissipated by the plastic deformation of the epoxy-matrix phase is clearly greatly influenced by the degree of ductility exhibited by this phase of the epoxy-blend polymer. Thus, another important feature of the degree of toughening observed is the effect that the modifier has upon the yield stress and plastic failure strain of the epoxy-matrix phase. (C) 2014 The Authors. Published by Elsevier Ltd.