Slavković Vukašin, Hanželič Blaž, Plesec Vasja, Milenković Strahinja, Harih Gregor
Faculty of Engineering, University of Kragujevac, Sestre Janjic 6, 34000 Kragujevac, Serbia.
Laboratory for Integrated Product Development and CAD, Faculty of Mechanical Engineering, University of Maribor, Smetanova ulica 17, SI-2000 Maribor, Slovenia.
Polymers (Basel). 2024 May 29;16(11):1526. doi: 10.3390/polym16111526.
This study investigated the thermomechanical behavior of 4D-printed polylactic acid (PLA), focusing on its response to varying temperatures and strain rates in a wide range below the glass transition temperature (T). The material was characterized using tension, compression, and dynamic mechanical thermal analysis (DMTA), confirming PLA's strong dependency on strain rate and temperature. The glass transition temperature of 4D-printed PLA was determined to be 65 °C using a thermal analysis (DMTA). The elastic modulus changed from 1045.7 MPa in the glassy phase to 1.2 MPa in the rubber phase, showing the great shape memory potential of 4D-printed PLA. The filament tension tests revealed that the material's yield stress strongly depended on the strain rate at room temperature, with values ranging from 56 MPa to 43 MPA as the strain rate decreased. Using a commercial FDM Ultimaker printer, cylindrical compression samples were 3D-printed and then characterized under thermo-mechanical conditions. Thermo-mechanical compression tests were conducted at strain rates ranging from 0.0001 s to 0.1 s and at temperatures below the glass transition temperature (T) at 25, 37, and 50 °C. The conducted experimental tests showed that the material had distinct yield stress, strain softening, and strain hardening at very large deformations. Clear strain rate dependence was observed, particularly at quasi-static rates, with the temperature and strain rate significantly influencing PLA's mechanical properties, including yield stress. Yield stress values varied from 110 MPa at room temperature with a strain rate of 0.1 s to 42 MPa at 50 °C with a strain rate of 0.0001 s. This study also included thermo-mechanical adiabatic tests, which revealed that higher strain rates of 0.01 s and 0.1 s led to self-heating due to non-dissipated generated heat. This internal heating caused additional softening at higher strain rates and lower stress values. Thermal imaging revealed temperature increases of 15 °C and 18 °C for strain rates of 0.01 s and 0.1 s, respectively.
本研究调查了4D打印聚乳酸（PLA）的热机械行为，重点关注其在低于玻璃化转变温度（T）的宽范围内对不同温度和应变速率的响应。使用拉伸、压缩和动态机械热分析（DMTA）对该材料进行了表征，证实了PLA对应变速率和温度的强烈依赖性。通过热分析（DMTA）确定4D打印PLA的玻璃化转变温度为65°C。弹性模量从玻璃态的1045.7MPa变化到橡胶态的1.2MPa，显示出4D打印PLA具有巨大的形状记忆潜力。长丝拉伸试验表明，材料的屈服应力在室温下强烈依赖于应变速率，随着应变速率降低，其值在56MPa至43MPa范围内变化。使用商用FDM Ultimaker打印机3D打印圆柱形压缩样品，然后在热机械条件下对其进行表征。热机械压缩试验在应变速率为0.0001s至0.1s以及温度低于玻璃化转变温度（T）的25°C、37°C和50°C下进行。所进行的实验测试表明，该材料在非常大的变形下具有明显的屈服应力、应变软化和应变硬化。观察到明显的应变速率依赖性，特别是在准静态速率下，温度和应变速率显著影响PLA的机械性能，包括屈服应力。屈服应力值从室温下应变速率为0.1s时的110MPa变化到50°C下应变速率为0.0001s时的42MPa。本研究还包括热机械绝热试验，结果表明，较高的应变速率0.01s和0.1s会由于产生的热量未消散而导致自热。这种内部加热在较高应变速率下导致额外的软化和较低的应力值。热成像显示，应变速率为0.01s和0.1s时温度分别升高15°C和18°C。
