关键词: 无纺布, 泊松比, 粘弹性, 蠕变, 松弛

Abstract:

The nonwoven is widely used in many industries and occupies a large proportion in the textile industry for its excellent performance, low cost and diversified types,. With the utilization of nonwovens in various industries, the output and usage have increased year by year. Therefore, in order to promote the use of nonwovens, it is necessary to study the mechanical properties of nonwovens. It can be found from the tensile test curve that all kinds of nonwovens have typical viscoelastic properties. Poisson's ratio, as one of the important indexes to measure the mechanical properties of materials, has been concerned and studied by many scholars, and some of them have studied the viscoelastic Poisson's ratio of materials. However, most studies focus on the viscoelastic Poisson's ratio of solid propellants, epoxy resins, and other materials. The research on textile materials has not been reported, but it has great research value.

The conventional polypropylene (PP) meltblown nonwoven was selected as the object, the viscoelastic mechanical behavior of the nonwoven was tested, and its viscoelastic Poisson's ratio was accurately calculated. Based on the theory of viscoelastic mechanics, combined with Laplace transform and creep stress conditions, the exact expression of viscoelastic Poisson's ratio was calculated by transverse strain (under creep conditions) and relaxation modulus. The internal fibers of nonwovens are disordered and thin, so they can be regarded as isotropic materials (ignoring the stress and strain in the thickness direction), and only the twodimensional planar Poisson's ratio is studied. The creep and relaxation experiments of nonwovens were carried out according to the standard GBT 23218.3—2010, and the curves of transverse strain and relaxation modulus were obtained and fitted into the 6thorder Prony series. The Prony series of transverse strain and relaxation modulus were substituted into the expression of viscoelastic Poisson's ratio, and the timevarying curve of viscoelastic Poisson's ratio of nonwovens under creep condition was calculated by using 1stOpt software. In this study, the calculation method of viscoelastic Poisson's ratio was introduced into textile materials, and the viscoelastic Poisson's ratio of the selected nonwoven was analyzed and measured. It is found that as the loading time increases, the viscoelastic Poisson's ratio of the material gradually increases and tends to be constant. The viscoelastic Poisson's ratio approach value of the nonwoven selected in this paper is close to 0.25, which is in line with the Poisson's ratio range of conventional materials and is close to the value of conventional elastic Poisson's ratio in related research.

The method can effectively determine the viscoelastic Poisson's ratio of nonwovens, with simple operation and reliable results, which can provide reference for the determination of Poisson's ratio of other textile materials.. The accurate determination of viscoelastic Poisson's ratio also provides a reference value for the calculation of mechanical indexes involved in the subsequent production and processing of textile materials.

Key words: nonwoven, Poisson's ratio, viscoelasticity, creep, relaxation, time varying curve