Study On Out-of-Plane Deformation And Dynamic Permeability Of Tight Fabrics Under Air Impact

Tight fabric,with high strength,small deformation and weak air permeability,is a common fabric for most airbag protective devices?such as automotive airbags,wearable airbags,soft landing cushion airbags,etc.?.When the tight fabric is protected,the impact time is extended,the impact force is reduced,and a good protection effect can be achieved.During this process,the interwoven structure in the fabric will undergo out-of-plane deformation due to the high pressure,and the fabric porosity and gas permeability will also change,which will affect the time and effect of the buffering.It will be of great significance to study the changes of out-of-plane deformation and dynamic permeability of the fabric under airflow impact.At present,the research on the deformation of the underlying pressure of tight fabrics at home and abroad lacks theoretical depth.Based on the experimental study of compact fabric structure and deformation,the mechanical problems of linear materials such as fiber yarns and their interweaving structures under the impact of airflow are explored from the perspective of mathematical mechanism,and the predictability,simulation and influence on dynamic permeability of out-of-plane deformation provide theoretical guidance for designing new impact-resistant emergency protective fabrics.Therefore,this topic mainly involves three series of research contents:First,the study of tight fabric structure and mechanical parameters under airflow impact,mainly to explore the structural and mechanical properties of different tightness woven fabrics under external quasi-static pressure.The results show that there is a critical point in the tight fabric structure and tightness.When the fabric tightness is higher than the critical point,the high-pressure airflow impact causes the adjacent yarns of the fabric to more closely overlap,resulting in an increase in the out-of-plane deformation of the fabric,and the gas permeability is reduced,the protective buffering time is prolonged;when the fabric structure or tightness is lower than the critical point,the airflow impacts the fabric caused out-of-plane deformation,the pores between the fabric yarns increase,the gas permeability increases,and the protection buffer time is shortened.In addition,studying the variation of Poisson's ratio and modulus during the in-plane elongation of fabric.It is found that the Poisson's ratio of the yarn interweaving structure changes with tensile strain.Among them,when the tensile section width of the fabric is small,the fabric elasticity is large,the tensile is close to the nip point area and along the weft direction,the Poisson's ratio of the fabric is relatively large.According to the stress-strain tensile curve,the subject also measures the modulus of the five fabrics,which provides a reference value for the second part of the study–the establishment of mathematical models and prediction of out-of-plane deformation.Second,the mechanism analysis of the outer deformation of tight fabric under quasi-static air pressure.In this paper,five kinds of fabrics with different tight structures were designed and manufactured.The fabric deformation test was carried out under quasi-static air pressure under the condition of square and circular boundary constraints by self-built fabric out-of-plane deformation instrument,and the deformation profile curve and maximum deformation w₀ of the fabric were obtained.It was found that the out-of-plane deformation of the fabric is positive correlated with the Poisson's ratio and negatively correlated with the modulus.Combining the“energy minimization theory”and the“plate and shell theory”,the system energy balance equation?mechanism model?of two kinds of constrained compact fabrics under the pressure equalization is established,and the maximum deformation amount w₀ and deformation contour curve of the fabric deformation system is established from the perspective of energy minimization.By comparing the measured values of the five tight fabric deformations with the analytical prediction values,the error between the experimental values and the theoretical prediction values is less than 12.6%under circular constraints and less than 20%under square constraints,which are less than the allowable error value in engineering.It proves that the mathematical model has certain accuracy and can predict the out-of-plane deformation of other compact fabrics under quasi-static air pressure.Third,the study of the out-of-plane deformation and air permeability of compact fabric under dynamic airflow impact.This subject uses the experimental method to analyze and compare the dynamic laws and the changes of gas permeability of the above five different compact fabrics under dynamic air pressure.Experiments show that under dynamic air pressure,the fabric deforms rapidly in the early stage,reaches a relatively stable deformation within 2s,and creeps with the extension of the force time.Under the condition of multiple airflow impacts on the same fabric,w₀ will increase.The permeability of the fabric is closely related to the tightness of the fabric.When the fabric with tightness is above the critical point,its initial gas permeability gradually decreases under high pressure impact.In the process of continuous airflow impact,the air permeability of the fabric is continuously increased,eventually reaching a maximum.In addition,dynamic gas permeability is also closely related to the initial gas pressure value experienced by the fabric and the morphology of the yarns in the fabric.