Abstract： Different working modes were used to measure the r-value measured by the laboratory tensile testing machine. By comparing the specific performance of the abnormal curve and the abnormal value， it was concluded that the abnormal curve of r-value was related to the shape tolerance of the width direction of the test， the surface roughness and the moderation of the sample when clamped. The main reason was the abnormal tracking of the width extensometer. Whether there is a sudden change or jump in the width direction curve is closely related to the mechanical structure of the width extensometer. When the mechanical structure of the width extensometer is abnormal， the measured tensile curve will appear sudden change and jump， which seriously affects the accuracy of r-value measurement. Compared with mechanical extensometers and optical extensometers， optical extensometers are not in contact with the sample， which can ensure the normal tracking of deformation in width direction， thus ensuring the accuracy and repeatability of r-value measurement.
孙志鹏， 徐 雁， 宋祖峰. 拉伸试验机r值异常的具体表现及原因分析[J]. 物理测试, 2020, 38(1): 24-.
SUN Zhi-peng， XU Yan， SONG Zu-feng. Concrete manifestation and cause analysis of the abnormal r-value of the tensile testing machine. PHYSICS EXAMINATION AND TESTING, 2020, 38(1): 24-.
2020, Vol. 38 
