Strain induced strengthening of soft thermoplastic polyurethanes under cyclic deformation
Strain induced strengthening of soft thermoplastic polyurethanes under cyclic deformation
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DOI：
10.1002/pol.20210060
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发表时间：
2021-04
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通讯作者：
G. Scetta;Jianzhu Ju;N. Selles;P. Heuillet;M. Ciccotti;C. Creton
中科院分区：
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作者：
G. Scetta;Jianzhu Ju;N. Selles;P. Heuillet;M. Ciccotti;C. Creton
我们研究了三种不同商业热塑性聚氨酯弹性体(TPU)的单轴拉伸循环力学行为，通常被认为是普通填充弹性体的可持续替代。X射线分析表明，所有的TPU都具有相似的硬段含量和线弹性系数，但大应变特性却明显不同。尽管有这些差异，我们发现在阶跃循环加载条件下的硬化效应与化学交联填充橡胶中观察到的常见软化(也称为Mullins效应)有很大不同。我们认为这种自我增强与硬结构域的碎裂有关，硬结构域自然存在于TPU中，存在于更小但更多的亚基中，可能作为新的物理交联点。所提出的硬化机制与在拉伸天然橡胶中观察到的应变诱导结晶没有什么不同，但它呈现出持久性。特别是，它可能会在存在不均匀应变场的地方产生局部强化，就像在循环疲劳中裂纹扩展的情况一样，为众所周知的热塑性聚氨酯的韧性和耐磨性提供了潜在的解释。
We investigate the cyclic mechanical behavior in uniaxial tension of three different commercial thermoplastic polyurethane elastomers (TPU) often considered as a sustainable replacement for common filled elastomers. All TPU have similar hard segment contents and linear moduli but sensibly different large strain properties as shown by X-Ray analysis. Despite these differences, we found a stiffening effect after conditioning in step cyclic loading which greatly differs from the common softening (also referred as Mullins effect) observed in chemically crosslinked filled rubbers. We propose that this self-reinforcement is related to the fragmentation of hard domains, naturally present in TPU, in smaller but more numerous subunits that may act as new physical crosslinking points. The proposed stiffening mechanism is not dissimilar to the strain-induced crystallization observed in stretched natural rubber, but it presents a persistent nature. In particular, it may cause a local reinforcement where an inhomogeneous strain field is present, as is the case of a crack propagating in cyclic fatigue, providing a potential explanation for the well-known toughness and wear resistance of TPU.