The work deals with the fatigue lifetime estimation of Short Fiber Reinforced Thermoplastics (SFRP), with a focus on conjugated effects of thermal aging. Two materials containing 35% (V35) and 50% (V50) weight ratio of short glass fibers were aged for 500 h at 200°C in air and compared to the same materials in a Dry-As-Molded (DAM) state. Monotonic and fatigue tests were performed in samples machined out of injected plates and cut along three different orientations to the injection one (0°, 45°, 90°) in order to capture the anisotropy of the skin-core microstructure, classical in injected SFRP.

Monotonic tensile tests evidenced the stiffening and embrittlement of the Polyamide matrix reported in the literature, nevertheless with an acuity depending on the matrix ratio and fiber orientation. Stress-controlled fatigue tests were performed at constant amplitude, frequency (10 Hz), temperature (200°C) and stress ratio R = 0.1. The fatigue curves of V35 are more affected by aging than those of the V50 material. The combined results from the mean strain evolutions and SEM observations confirmed that the initiation approach for fatigue lifetime estimation was still valid in aged composites. Several fatigue criteria, among the most recently reported in the literature, were evaluated from this database. The effect of aging on the cyclic evolution of the different Fatigue Indicator Parameters (FIP) involved in the criteria was analyzed preliminarily. For the present fatigue conditions, the best criteria for unaged materials (i.e cyclic creep energy-based ones) were shown to still be the best for aged materials. Finally, the ability to predict fatigue lifetime for aged composites from the identification of the fatigue criterion in the unaged state was evaluated.

这项工作涉及短纤维增强热塑性塑料 (SFRP) 的疲劳寿命估计，重点是热老化的共轭效应。两种含有 35% (V35) 和 50% (V50) 重量比的短玻璃纤维的材料在 200°C 的空气中老化 500 小时，并在干燥模塑 (DAM) 状态下与相同材料进行比较。单调和疲劳测试在由注塑板加工而成的样品中进行，并沿三个不同的方向切割到注塑板（0°、45°、90°），以捕捉皮芯微观结构的各向异性，这是注塑 SFRP 中的经典.

单调拉伸试验证明了文献中报道的聚酰胺基体的硬化和脆化，但其敏锐度取决于基体比例和纤维取向。应力控制疲劳测试在恒定幅度、频率 (10 Hz)、温度 (200°C) 和应力比 R = 0.1 下进行。V35 的疲劳曲线比 V50 材料受老化的影响更大。平均应变演化和 SEM 观察的综合结果证实，疲劳寿命估计的初始方法在老化的复合材料中仍然有效。从该数据库中评估了文献中最近报道的几个疲劳标准。初步分析了老化对标准中涉及的不同疲劳指标参数（FIP）循环演化的影响。对于目前的疲劳条件，未老化材料的最佳标准（即基于循环蠕变能量的标准）被证明仍然是老化材料的最佳标准。最后，评估了通过确定未老化状态下的疲劳标准来预测老化复合材料疲劳寿命的能力。