Study On The Characterization Of Pressure Distribution Of Warp-knitted Spacer Fabric

Spacer fabric, consisting of a bottom layer, an upper layer and a middle layer, has becomingpopular in apparel, medicals and automobiles for light weight, good permeability and outstandingpressure distribution performance.Because of the spacer yarn elastic system and good extension flexibility of the warp-knittedsurface structure, the warp-knitted spacer fabric can significantly reduce the max pressure anddistributing the pressure under uneven compression. Through the pressure parameters and contactanalysis in spherical compression, combining the subjective evaluation and characteristicparameters results in seating pressure distribution experiment, this paper focus on the compressionbehavior of warp-knitted spacer fabric, especially when it apply as cushions. According to theanalysis results of relevant experiment, the following conclusion are drawn:(1) In the spacer fabric spherical compression process of75%thickness reduction, after datanormalization and linear-regression analysis, it was found that the influence factors, including thestitch density, thickness, spacer yarn diameter, spacer yarn arrangement density, spacer yarninclination angle, and the maximum pressure, compression work and degree of linearity in flatcompression, have high relevance with the characterization of spherical compression where thecomplex correlation coefficient is above0.99.There is no direct linear relationship betweencharacteristic values in flat compression and spherical compression, but combined with the structureparameters, the characteristic values in flat compression can influence the result of sphericalcompression. The feature of spacer yarn which put lots influence on the flat compressionperformance has been weakening in spherical compression and the total structure parametersespecially the stitch density of upper surface influence the spherical compression a lot.(2) Through testing and analysis the ratio of compression depth (C) and contact depth (H) inthe spherical compression experiment vary in the diameter of indenter, and the thickness of spacerfabrics, it is found that the ratio is not related to the diameter of indenter but the compression performance of the spacer fabric itself. And it infers the connection between this geometricparameter and pressure distribution properties. At the same time, related to the geometricrelationship, the ratio of max contact depth (Hmax) and radius of indenter (R), as well as pressureand contact area (S) during compression were got in the experiment. According to subjectiveevaluation experiment result, H/C and Hmax/R are positive factors while F/S is negative influencefactors to the human comfort.(3) The pressure gradient integral (GI) can infer the severe degree of pressure centration whichis closely related to the pressure comfort of human feelings. Peak pressure, average pressure, contactarea, mean gradient integral are closely linked with human feelings. The pressure gradient integralis in inverse proportion to human comfort. With the pressure gradient integral based, combined withthe pressure peak value and average value can express the pressure distribution performance ofwarp-knitted spacer fabric and predict the pressure comfort of applying as cushion.(4) The improvement rate and pressure distribute percentage can be used to characterize thepressure distribution performance of spacer fabric in the situation of actual use. It was found in theexperiment that, the pressure distribution performance was better express in the trial of volunteerswith light weight, where the improvement rate is over50%which is about1.6times as heavy weight;different fabric has different pressure distribute percentage，and the percentage of A2fabric is16%higher than A1fabric inferring a better pressure distribution. The unit weight of residual rate can befurther eliminated weight effect on slow pressure effect, ease the pressure effect of the targetpopulation to get maximum use of different fabrics. The unit weight of residual rate can be furthereliminated weight effect on pressure distribution, which lead a better access to set the targetconsumer during application.(5) Human test which aimed at subjective evaluation for fabrics combination was conductedon nine testers. According to four independent variables obtained from test, pressure peak (TP),average pressure (AP), contact area(S) and gradient integral (GI) were involved in effect factoranalysis. The result shows, all multiple correlation coefficients are above0.8with the highestreaching0.99891. After removing lower correlation variables, the multiple correlation coefficientdecreases, which shows that human subjective feeling has intense relationships with pressurepeak(TP),average pressure(AP), contact area(S) and gradient integral(GI).(6) Stacking makes effect on fabric pressure distribution. Thin spacer fabrics stack-upcontributes little even counter to improving pressure distribution, while the weaving production andsetting process of spacer fabric with thickness above20mm is complex but low economic benefit.Medium thickness (10mm-15mm) of spacer fabrics stacking can produce the best pressuredistribution effect at the same time, where the production is convenient, economical and practical.(7) The pressure distribution of the image got in the spherical compression test was similar to the pressure distribution at the buttocks of sitting posture: the pressure distribution under lowercompression rate was more similar to the situation of volunteer with light weight while the highercompression rate was more similar to the situation of volunteer with heavy weight. The result ofspherical compression may help to indicate the pressure distribution in practical application ofdifferent weight people.