拉伸试验机r值异常的具体表现及原因分析

Concrete manifestation and cause analysis of the abnormal r-value of the tensile testing machine

采用3种不同工作方式引伸计对实验室拉伸试验机测量r值进行测量,通过对比异常曲线和异常值的具体表现,认定r值异常曲线除了与试验宽度方向的形状公差以及表面粗糙度以及试样装夹时的对中度有关外,主要原因是宽度引伸计跟踪异常。宽度方向曲线是否出现突变和跃升与宽度引伸计的机械结构密切相关;当宽度引伸计机械结构异常时,测量的拉伸曲线将出现突变和跃升,严重影响r值测量的准确性。对比机械引伸计与光学引伸计,光学引伸计不与试样接触,可以保证宽度方向的变形跟踪正常,从而保证r值测量的准确性和重复性。

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.