The characterisation of the very high cycle fatigue (VHCF) regime has become pertinent due to the interest of extending the service life of engineering structures. However, the fatigue testing of materials at the longer lives of VHCF regime (usually greater than 10 million of cycles) is by far most efficient with an ultrasonic fatigue testing system, which introduces new challenges such as the specimen’s design. As a consequence, the fatigue behaviour in the VHCF regime under the presence of stress states different from the uniaxial one is not well known. Thus, in this work, the fatigue behaviour of S690QL structural steel is analysed for the case of a biaxial stress state. A cruciform specimen was developed by finite element model analysis and, consequently, it was experimentally validated. Moreover, several specimens were tested and a mean stress-life curve estimated, considering the von Mises stresses. Additionally, the mechanism of fatigue crack initiation was assessed and the fracture surfaces were analysed.

中文翻译：

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用于海上应用的结构钢在双轴应力状态下的极高周疲劳性能

由于延长工程结构的使用寿命，甚高周疲劳 （VHCF） 状态的表征变得非常重要。然而，到目前为止，使用超声疲劳测试系统对 VHCF 状态的较长寿命（通常大于 1000 万次循环）的材料进行疲劳测试的效率最高，这带来了新的挑战，例如试样的设计。因此，VHCF 状态在存在不同于单轴应力状态的疲劳行为并不为人所知。因此，在这项工作中，分析了 S690QL 结构钢在双轴应力状态下的疲劳行为。通过有限元模型分析开发了十字形试样，并因此对其进行了实验验证。此外，还测试了几个试样，并考虑了 von Mises 应力，估计了平均应力-寿命曲线。此外，还评估了疲劳裂纹萌生的机制并分析了断裂表面。