The present study analyzed the fatigue performance of prefabricated fiber reinforced composite posts (FRC post) with different diameters by means of two different fatigue testing methods. A total of 69 FRC double-tapered posts, presenting 20 mm in length associated with different coronal diameters (1.4, 1.6, 2.0 mm) were embedded with acrylic resin in PVC cylinders, maintaining 6 mm free from the coronal part of the post. The posts of each diameter were submitted to step stress testing (inclination: 45°; initial load: 20 N; step-size: 10 N; cycles per step: 18,000; frequency: 5 Hz) (n = 5) or staircase testing (inclination: 45°; initial load: 60% of the monotonic load-to-fracture reported on existing literature; increment: 10% of the monotonic load-to-fracture reported on existing literature; cycles: 18,000; frequency: 5 Hz) (n = 18). The statistical differences were determined for Kaplan-Meier and Mantel-Cox (Log-Rank) tests for step stress testing and based on confidence interval overlapping for staircase testing. All the failures were analyzed in a stereomicroscope (10 × magnification) after the tests, and representative samples were analyzed by scanning electron microscope (500 × and 1000 × magnification). The FRC post with the wider diameter had greater fatigue failure load in step stress testing (DT1.4–56 N < DT1.6–60 N < DT2–100 N) however, a significant difference for the staircase testing was only found for DT1.4 and DT2 (DT1.4–57.4 N ≤ DT1.6–62.2 N ≤ DT2–74.5 N). Additionally, the step stress test revealed that the wider the FRC post diameter, the greater the number of cycles required for failure (DT1.4–73,319 < DT1.6–99,305 < DT2–154,743). A central longitudinal crack perpendicular to the applied load direction was the failure pattern observed for all conditions tested. Thus, the fatigue performance of FRC posts is influenced by its coronal diameter (wider diameter means higher failure loads and number of cycles for failure), but the fatigue test used (staircase or step stress) had no influence on the outcome, expressing similar results.

本研究通过两种不同的疲劳测试方法，对不同直径的预制纤维增强复合材料桩（FRC桩）的疲劳性能进行了分析。总共69个FRC双锥柱，其长度为20 mm，与不同的冠状直径（1.4、1.6、2.0 mm）相关，被丙烯酸树脂嵌入PVC圆柱体中，与柱的冠状部分保持6mm的距离。每个直径的立柱都经过阶梯应力测试（倾斜度：45°；初始载荷：20 N；步长：10 N；每步循环数：18,000；频率：5 Hz）（n = 5）或阶梯测试（倾斜度：45°;初始载荷：现有文献报道的单调断裂载荷的60％;增量：现有文献报道的单调断裂载荷的10％;循环：18,000;频率：5 Hz）（ n = 18）。统计差异是针对逐步应力测试的Kaplan-Meier和Mantel-Cox（Log-Rank）测试以及基于阶梯测试的置信区间重叠确定的。试验后，所有故障均通过体视显微镜（放大10倍）进行分析，代表性样品通过扫描电子显微镜（放大500倍和放大1000倍）进行分析。直径较大的FRC柱在阶跃应力测试中具有更大的疲劳破坏负荷（DT1.4–56 N <DT1.6–60 N <DT2–100 N），但是，仅在DT1中发现阶梯测试的显着差异.4和DT2（DT1.4–57.4 N≤DT1.6–62.2 N≤DT2–74.5 N）。此外，阶跃应力测试表明，FRC柱直径越宽，失效所需的循环次数就越多（DT1.4-73,319 <DT1.6-99,305 <DT2-154,743）。垂直于外加载荷方向的中央纵向裂纹是在所有测试条件下观察到的破坏模式。因此，FRC柱的疲劳性能受到其冠状直径的影响（直径越大，意味着更高的失效载荷和失效循环次数），但是所使用的疲劳测试（楼梯或台阶应力）对结果没有影响，结果相似。