It is well known that materials subjected to cyclic loads increase their temperatures, either by elastic or much more intensely by plastic straining mechanisms. Because fatigue damage is a dissipative process associated with cyclic plastic strains, such temperature increments are much larger for loads above the fatigue limit than below it. Since standard techniques to measure fatigue limits are too laborious, even the accelerated ones like Dixon’s up-and-down method, due to the very longtime required to run the tests, La Rosa and Risitano proposed a quick thermographic approach to measure fatigue limits based on temperature increments observed during fatigue tests. This method works very well for steels, but not so well for Al alloys, albeit they would be even more useful for them, whose fatigue limits are associated with a much larger number of cycles than the steels. This work investigates the limitations of the thermographic method when it is used to evaluate an Al 6351-T6 alloy fatigue limit, and of the alternative method of extrapolating its measured εN curve to very long lives. In addition, alternative ways to obtain a better fatigue limit estimate based on thermal data are discussed.

众所周知，承受周期性载荷的材料通过弹性或通过塑性应变机制更加强烈地提高其温度。因为疲劳损伤是与周期性塑性应变相关的耗散过程，所以对于高于疲劳极限的载荷，其温度增量要低于低于疲劳极限的载荷的温度增量大得多。由于标准的测量疲劳极限的方法太费力，甚至由于Dixon的上下方法之类的加速方法，由于运行测试所需的时间很长，La Rosa和Risitano提出了一种快速热成像方法来基于疲劳极限进行测量。在疲劳测试期间观察到温度升高。这种方法对钢材非常有效，但对铝合金却不太好，尽管它们对铝合金甚至更有用，其疲劳极限比钢具有更多的循环次数。这项工作研究了热成像法在评估Al 6351-T6合金疲劳极限时的局限性，以及将测得的εN曲线外推至非常长寿命的另一种方法。另外，讨论了基于热数据获得更好的疲劳极限估计值的替代方法。