Microstructure evolution during tensile loading histories of a polyurea
Microstructure evolution during tensile loading histories of a polyurea
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DOI：
10.1002/polb.22352
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发表时间：
2011-12
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影响因子：
--
通讯作者：
R. G. Rinaldi;M. Boyce;S. Weigand;D. Londono;M. Guise
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文献类型：
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作者：
R. G. Rinaldi;M. Boyce;S. Weigand;D. Londono;M. Guise
利用原位小角和广角X射线散射（SAXS/WAXS）研究了一种类碳化硅聚脲在不同拉伸载荷历史过程中硬/软畴微结构的演变。非线性应力-应变行为最初是刚性的，侧翻屈服于更柔顺的响应;卸载是高度非线性的，显示出大量的滞后，同时也表现出显着的恢复。弯曲显示出明显更柔顺的“软化”行为和显著降低的滞后。WAXS峰监测硬域内规则特征的特征尺寸;峰位置保持不变，拉伸变形表明域内内部结构没有分离，但峰强度变得各向异性，变形以可逆的方式演变，与拉伸引起的取向一致。SAXS配置文件提供主要硬域之间的信息。SAXS峰被发现转移与拉伸载荷在一个相对仿射的方式拉伸真应变约0.4，其中，使用布拉格减少，以帮助解释，揭示了轴向增加和横向减少域间间距;这种演变是可逆的应变小于约0.4。增加轴向应变超过{约}0.4的真实应变伴随着轴向布拉格间距的急剧、渐进和不可逆的减小，这表明硬域聚集体网络结构中的断裂。在拉伸过程中，可以看到四点模式。在第一个负载循环期间的网络结构的故障给出了一个新的结构，为后续的负载循环，这被认为是在一个可逆的方式演变为应变小于或等于先前的最大应变。然而，对于应变超过先前的最大应变偏移，额外的breakdown是found. These SAXS结果表明，在硬域聚集网络结构的故障是一个管理机制的大耗散（滞后）循环的第一个负载周期，也负责软化再加载响应。在随后的负载循环期间没有结构破坏对应于显著降低的滞后回线以及稳定的软化行为。原始和先前变形的样品的DMA数据显示，在预变形的样品中，更顺应的储能模量，支持软化的循环应力-应变数据和在SAXS中观察到的结构分解;损耗模量与变形不变，这与DMA中测量的损耗特征相关，具有时间依赖性粘度，而不是由于结构分解而导致的损耗。«少
The evolution in the hard/soft domain microstructure of an elastomeric-like polyurea during different tensile loading histories was studied using in situ small- and wide-angle X-ray scattering (SAXS/WAXS). The nonlinear stress-strain behavior is initially stiff with a rollover yield to a more compliant response; unloading is highly nonlinear showing substantial hysteresis while also exhibiting significant recovery. Reloading reveals a substantially more compliant 'softened' behavior and dramatically reduced hysteresis. WAXS peaks monitor characteristic dimensions of regular features within the hard domains; the peak location remains unchanged with tensile deformation indicating no separation of the internal structure within a domain, but the peak intensity becomes anisotropic with deformation evolving in a reversible manner consistent with orientation due to stretch. The SAXS profiles provide information between major hard domains. SAXS peaks are found to shift with tensile loading in a relatively affine manner up to a tensile true strain of {approx}0.4, which, using a Bragg reduction to aid interpretation, reveals an axial increase and a transverse decrease in interdomain spacings; this evolution is reversible for strains less than {approx}0.4. Increasing axial strain beyond a true strain of {approx}0.4 is accompanied by a dramatic, progressive, and irreversible reduction in axial Bragg spacing, indicating a breakdownmore » in the hard domain aggregate network structure. A four-point pattern is seen to develop during stretching. The breakdown in networked structure during a first load cycle gives a new structure for subsequent load cycles, which is seen to evolve in a reversible manner for strains less than or equal to the prior maximum strain. However, for strains exceeding the prior maximum strain excursion, additional breakdown is found. These SAXS results show that a breakdown in the hard domain aggregate network structure is a governing mechanism for the large dissipation (hysteresis) loops of the first load cycle and are also responsible for the softened reloading response. The absence of structure breakdown during subsequent load cycles corresponds to the substantially reduced hysteresis loops as well as the stable softened behavior. DMA data on pristine and previously deformed samples show a more compliant storage modulus in the predeformed sample, supporting the softened cyclic stress-strain data and the structural breakdown observed in the SAXS; the loss modulus was unchanged with deformation, which correlates with the lossy features measured in DMA with time-dependent viscosity rather than losses due to structural breakdown.« less