Bolt preload is a critical parameter in bolted connections with a strong influence on their general structural behavior. Traditional bolt preload estimation methods are sensitive to the surface conditions of the fastening elements while more accurate measuring methods might require significant modifications of the connection, such as embedded sensors. In this study, a novel contactless bolt preload monitoring method based on Digital Image Correlation measurements of the bolt elongation was developed. A fixed bolted setup was designed to validate the optical measurements with laser triangulation and three-dimensional point tracking, while the bolt preload was monitored with an embedded load cell. Two M16 bolt classes, 8.8 and 10.9, and multiple bolt lengths were evaluated. The bolt preload and displacement results correlated well with the available bolt theoretical models and an accurate preload estimation was possible. An analysis on the method resolution demonstrates that better resolutions are achieved with slender and long bolts. The method resolution is estimated to be under 2.25% and 1.8% of the recommended bolt preload value for each bolt class, respectively.

螺栓预紧力是螺栓连接中的一个关键参数，对它们的一般结构行为有很大影响。传统的螺栓预紧力估计方法对紧固元件的表面状况很敏感，而更准确的测量方法可能需要对连接进行重大修改，例如嵌入式传感器。在这项研究中，开发了一种基于螺栓伸长的数字图像相关测量的新型非接触式螺栓预紧监测方法。固定螺栓设置旨在通过激光三角测量和三维点跟踪来验证光学测量，同时使用嵌入式称重传感器监测螺栓预紧力。评估了两种 M16 螺栓等级，8.8 和 10.9，以及多种螺栓长度。螺栓预紧力和位移结果与可用的螺栓理论模型很好地相关，并且准确的预紧力估计是可能的。对方法分辨率的分析表明，使用细长螺栓可以获得更好的分辨率。估计方法分辨率分别低于每个螺栓等级推荐螺栓预紧力值的 2.25% 和 1.8%。