Standardization Of The Method Of Measuring Fiber Dynamic Elastic Modulus By Sound Velocity Method

Elastic modulus is the ratio of stress and strain in the elastic deformation stage of a material to characterize its rigidity.It is also one of the basic physical properties of textile fibers.The commonly used stress-strain curve method results in relaxation of the specimen due to slow stretching speed,and monotonic continuous heavy load stress cannot reflect the changes in material structure and the actual stress state during use.Moreover,the specimen must be destroyed and cannot be measured repeatedly.To overcome the inherent defects of the stretching method,the sonic pulse propagation method based on high-frequency alternating light load disturbance of sound waves for measuring the elastic modulus(sonic modulus)of fibers,which is an important aspect of approaching the actual stress and strain state from another perspective,is widely used in teaching,scientific research,and industrial fields,but there is no relevant national standard.This article uses a domestic fiber orientation measuring instrument to measure the acoustic travel time of polyester monofilament(melt spinning),acrylic multifilament(melt spinning),viscose fiber(regeneration),and nylon multifilament(melt spinning)under different pre tension and different transducer spacing.It is found that the scattered point data of acoustic travel time transducer spacing is consistent with the least squares fitting line,indicating that the delay time of the instrument system can be calculated using the multi-point extrapolation method.The sound velocity and dynamic elastic modulus in the fibers are further calculated based on the sound velocity values of randomly oriented fibers.Through empirical analysis of these data,the cooperative enterprise research institute has used similar imported dynamic modulus of elasticity meters for re-determination and confirmation,and has written a national standard(Determination of dynamic modulus of elasticity of chemical fibers using acoustic pulse propagation method)preparation explanation,forming a national standard draft.This method utilizes the low dimensional characteristics of fiber materials,avoids the density measurement process,and accurately expresses the elastic modulus and is related to the orientation structure parameters using only linear density.It does not require analysis of stress-strain curves,and achieves non-destructive and repeatable testing of samples.The operation is simple,fast,and reliable,which is not only suitable for routine monitoring of traditional chemical fiber production processes,but also for the development of high-performance national defense and medical biological fibers,fill in the long vacant national standard and align it with relevant international standards,providing theoretical and experimental basis for improving domestic instruments.The data results of using the same method to measure polyester and nylon elastic fibers,which are commonly used in the chemical fiber industry,show that due to their false twisting deformation,it is difficult to accurately observe the strain caused by small perturbations of pulse sound waves.The use of sound velocity method to measure modulus and orientation is only for reference,and lower modulus spandex is also not applicable.This article also compared the initial modulus and acoustic modulus of the same sample of polyester,acrylic,and nylon fibers using quasi-static tensile method and sound velocity method.It was found that the acoustic modulus value was generally higher than the initial modulus value,and the specific correlation between the two needs further investigation.