Simulation On Fiber Arrangement In The Sliver And Its Effect On Yarn Qualities

The influence of fiber properties on yarn qualities has always been one of classical tissues in the textile research field.Fiber arrangement in the sliver not only has great impact on spinning process,but also decides yarn qualities,such as yarn unevenness and strength,which will further influence the subsequent weaving process and the final textile quality.Fiber random arrangement in the sliver largely depends on fiber geometrical characteristics,such as fiber length and fineness.Therefore,simulation on fiber random arrangement in the sliver could be helpful in understanding the influence of fiber geometrical characteristics on yarn properties theoretically.This would provide directive significance to optimize the assorting of raw materials,improve yarn spinning process and produce high quality yarns analytically.The study started from simulation on fiber random arrangement in the sliver,from which the joint effect of fiber length and fineness on yarn limit irregularity(or called theoretical unevenness)was discussed.Subsequently,calculation of yarn strength was developed based on the simulation,and the influential factors of yarn strength were then analyzed.Fibers on yarn breaking section may break or slip during yarn stretching process,which depends on critical slipping length.The solution of critical slipping length not only involves fiber properties,but also depends on yarn twisting.Yarn twisting also determines the actual contributions that breaking and slipping fibers made to yarn strength.This work includes theoretical model development by simulation,and calculation verification by experimental results and reference data.Because of the randomness of fiber position,length and fineness,Monte Carlo method was adopted to generate these variables,which was in accord with tested results.Geometrical-probabilistic method was also adopted for analysis of yarn properties and derivation of critical slipping length.The simulation did not take the effect of fiber shapes(or fiber hooks)and mechanical factors during spinning process into consideration for simplified calculation.The dissertation covers fiver chapters according to their respective specific researches,which are presented as below:Chapter One introduces the study background,especially the domestic and international study on fiber random distribution in the yarn or sliver,as well as theoretical models on yarn irregularity and strength.The existing problems of these researches are also introduced.Chapter Two proposes the simulation method on fiber random arrangement in the sliver based on the assumption that all fiber left heads conform to uniform distribution along sliver axis.Limit irregularity of sliver could be expressed as the variance of the total weight of fibers within each yarn subsection.Take calculation of yarn 8mm-term limit irregularity for example.If fiber length distribution is considered only,it could be seen from the calculation results that yarn limit irregularity grows with the increase of fiber length and then tends to stable,which is in great agreement with Suh's theory and tested results.For yarns composed of fibers with unequal lengths,their irregularities are only influenced by their average fiber length,and are irrelevant to the type of fiber length distribution.If fiber fineness distribution is taken into consideration,it could be seen that the yarn limit irregularity calculated considering fiber fineness distribution is larger than that without considering the effect of fiber fineness.When fiber fineness CV gets larger,the difference between the two results also becomes larger,and the result considering fiber fineness distribution is much closer to tested results,which indicates that the influence of fiber fineness on yarn limit irregularity is significant.In addition,when considering the joint effect of fiber length and fineness,the sequence of each factor for yarn limit irregularity is mean fiber fineness > fiber fineness CV > mean fiber length > fiber length CV.Simulation on fiber random arrangement in the sliver could directly reflect sliver uniformity,and therefore it could provide feasible method for prediction of yarn actual irregularity and yarn strength.Chapter Three proposed a yarn strength calculation method based on fiber random arrangement in the yarn.During yarn stretching process,whether fiber breaks or slips depends upon critical slipping length.The contributions that breaking fibers make to yarn strength are their breaking strengths,while the contributions that slipping fibers make to yarn strength are their average frictional slipping force.Therefore,the strength of each yarn cross section could be calculated and recorded,and the minimum value would be yarn strength.It could be seen from the calculation results that when fiber length gets longer,or critical slipping length gets shorter,the number of breaking fibers will get larger,and the number of slipping fibers will get smaller,which leads to the increase of yarn strength.The trend is in accordance with tested results.However,for yarns composed of fibers with unequal lengths,yarn strength is also relevant to the type of fiber length distribution.Besides,when the length of simulated yarn section is longer,the calculated strength of yarn strength is getting lower,which is in good agreement with the theoretical and experimental results of previous researches.Due to consideration of variance of fiber number in the yarn cross section,it is more reasonable to calculate yarn strength by simulating fiber random arrangement in the yarn,which could directly reflect the effect of fiber length on yarn strength,as well as the weakest point of yarn section.Therefore,the method could be applied to yarn strength prediction.Chapter Four discusses the approximate calculation of critical slipping length based on the idealized assumption of staple yarn structure.Simulation on yarn strength mentioned in Chapter Three is also revised.The approximate expression of critical slipping length not only considers fiber mechanical properties,but also takes yarn twisting into consideration.Calculation indicates that critical slipping length decreases with the increase of yarn twist multiplier.Due to fiber strength loss caused by yarn twisting,the contribution that breaking and slipping fibers made to yarn strength should be revised,which will be induced into the simulation method mentioned in Chapter Three to calculate yarn strength.From the calculation results,yarn strength rises to its highest values and then drops with the increase of yarn twist multiplier,which is in agreement with tested results.The drop of critical slipping length leads to more fibers break and less fibers slip,which leads to the rising of yarn strength at lower twist multiplier.While at higher twist multiplier,the great loss of fiber strength leads to the significant reduction of the effective fiber strength,and at the same time the component of fiber effect strength along yarn axis also declines drastically,which plays the dominant role in the decline of yarn strength.For yarns composed of fibers with the identical length,the sequence of each factor for yarn strength is fiber fineness > fiber strength > fiber length.Solution of critical slipping length and revision of yarn strength calculation could reveal the yarn breaking mechanism with the change of yarn twist multiplier more directly,and therefore the method is reasonable and reliable.Chapter Five makes conclusion on the main contribution of the study and its existing problems.The outlook of this study is also proposed.In conclusion,this study promotes simulation method on fiber random arrangement in the sliver or yarn,based on which yarn limit irregularity and strength could be calculated.This simulation method could directly reflect the influence of fiber geometrical properties on yarn quality,and it provides theoretical and quantitative reference for fiber raw materials assorting,spinning process optimizing,and yarn quality prediction.