In this work, polyacrylamide (PAAm) hydrogels with different water contents (WCs) were prepared, and stress-controlled cyclic experiments were carried out. The effect of water content on the mechanical behavior of PAAm hydrogels was observed through stress–strain curves, apparent modulus, and dissipation energy across various loading cycles. It is concluded that with the increase in the WC, the peak and valley strains and the dissipation energy increase while the apparent modulus decreases. The WC significantly influences the evolution of dissipation energy with the increase of the loading cycles. For PAAm hydrogels with a relatively high WC (from 96% to 67%), the dissipation energy decreases appreciably between the first and the second loading cycles and then remains stable with increasing the loading cycles further. However, for PAAm hydrogels with a relatively low WC (50% and 34%), the dissipation energy decreases significantly between the first two cycles and then increases with increasing the loading cycles. Experimental results obtained under constant relative humidity and constant WC were compared, validating that the water loss leads to a decrease in the strain and an increase in the apparent modulus during the loading cycles.

中文翻译：

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含水量对应力控制循环载荷下聚丙烯酰胺水凝胶机械响应的影响


本工作制备了不同含水量 （WCs） 的聚丙烯酰胺 （PAAm） 水凝胶，并进行了应力控制循环实验。通过各种加载循环中的应力-应变曲线、表观模量和耗散能量来观察含水量对 PAAm 水凝胶机械行为的影响。结果表明，随着 WC 的增加，峰谷应变和耗散能量增加，而表观模量减小。WC 会随着加载循环次数的增加而显著影响耗散能量的演变。对于具有相对较高 WC （从 96% 到 67%）的 PAAm 水凝胶，耗散能量在第一次和第二次加载循环之间明显降低，然后随着加载循环的进一步增加而保持稳定。然而，对于具有相对较低 WC （50% 和 34%） 的 PAAm 水凝胶，耗散能量在前两个循环之间显着降低，然后随着加载循环的增加而增加。比较了在恒定相对湿度和恒定 WC 下获得的实验结果，验证了水分损失导致加载循环期间应变的降低和表观模量的增加。