Short fibers reinforced injection molded parts are commonly used in the applications under sustained loads. This requires creep resistance and creep behavior predictions under both short- and long-term service conditions.

This article studies the creep behavior of injection molded polypropylene with short glass fibers at different temperatures and in the presence of a notch. The produced samples were analyzed by means of FT-IR (Fourier-transform infrared spectroscopy) and TGA (thermogravimetric analysis) to obtain and indication on microstructure and fiber content, respectively. Visible light microscopy was used to analyze the fiber orientation. Mechanical properties were measured using tensile testing. Tensile creep testing in an internally fabricated lever-type creep machine at a controlled constant temperature was conducted on plain specimens and specimens with machined notch. Fracture surfaces were analyzed by means of SEM (Scanning Electron Microscopy).

Both creep strength and time to failure decrease with increasing temperature following the power law models. Norton’s power law and Monkman-Grant’s relationship can estimate the time to rupture not only of plain specimens, but also notched, if the stress is amplified by the stress concentration factor. These results can potentially estimate lifetime of injection molded parts with stress concentrations at elevated temperatures.

短纤维增强注塑件通常用于承受持续载荷的应用。这需要在短期和长期服务条件下进行抗蠕变性和蠕变行为预测。

本文研究了具有短玻璃纤维的注塑聚丙烯在不同温度和存在缺口的情况下的蠕变行为。通过FT-IR（傅里叶变换红外光谱）和TGA（热重分析）对生产的样品进行分析，分别获得微观结构和纤维含量的指示。可见光显微镜用于分析纤维取向。使用拉伸试验测量机械性能。在内部制造的杠杆式蠕变机中在受控恒温下对普通试样和带有机加工缺口的试样进行拉伸蠕变试验。通过SEM（扫描电子显微镜）分析断裂表面。

根据幂律模型，蠕变强度和失效时间都随着温度的升高而降低。诺顿幂律和 Monkman-Grant 关系式不仅可以估计普通试样的断裂时间，还可以估计缺口的断裂时间，如果应力被应力集中因子放大。这些结果可以潜在地估计在高温下应力集中的注塑成型零件的寿命。