AXIAL FORCE MEASUREMENT METHOD

To provide an axial force measurement method for measuring the axial force of a fastening element highly accurately by taking a bending moment applied when fastening the fastening element into account.SOLUTION: An axial force measurement method for measuring the axial force of a fastening element by comparing the change of a pattern on the front surface of the fastening element before and after fastening comprises the steps of: imaging the pattern before and after the fastening of the fastening element; calculating a change amount of the pattern from the image of the pattern before and after the fastening to acquire the distortion distribution of the fastening element on the basis of the change amount of the pattern; and collating the distortion distribution based on a ratio of the axial force of the fastening element to a bending moment of the fastening element with the distortion distribution acquired from the image of the pattern to measure the axial force of the fastening element.SELECTED DRAWING: Figure 2 【課題】本発明は、締結要素を締め付ける際に加わる曲げモーメントを加味し、高精度に締結要素の軸力を測定する軸力測定方法を提供する。【解決手段】本発明の軸力測定方法は、締結要素の表面における模様の変化を締結前後で比較して、締結要素の軸力を測定する軸力測定方法において、締結要素の締結前後の模様を撮像する工程と、締結前後の模様の画像から模様の変化量を算出し、模様の変化量に基づいて、締結要素のひずみ分布を取得する工程と、締結要素の軸力と締結要素の曲げモーメントとの比率に基づくひずみ分布と、模様の画像から取得されたひずみ分布と、を照合し、締結要素の軸力を測定する工程と、を有することを特徴とする。【選択図】 図２