Impact Testing of Polyvinyl Chloride Sheet

Abstract

High speed impact testing is important and necessary, because materials tested at static speed show quite different behaviour in case of high speeds. The impact machine used in this study is a rotary disk type impact tensile testing machine. The diameter of the disk is 1800mm and the thickness is 100mm. The disk is a Ni-Mo-V steel forging, which weighs 2300kg and rotates up to 1450rpm. The speed of the disk reaches 140m/sec when it rotates at 1450rpm, and the sample of the fiber or high polymer is pulled by the jaw at the same speed. The tensile load is measured and detected by strain gauge fixed on the sample holder and the output of the strain gauge is led to the vertical axis of the synchroscope. The horizontal axis of this synchroscope is time axis and is drawn by a single sweeper driven by an outside circuit containing 45 volt.Various plasticizers such as n-dioctyl phthalate, dioctyl adipate, tricresyl phosphate were added to study their effect on the impact behaviour of polyvinyl chloride sheet. The rolling of the mixture was done in 100-180°C for 10 minutes and the pressing was done for 5 minutes in 105-165°C under a load of 150kg/cm2. The sheet was punched in to the shape of dumbell and used as sample. The effect of degree of polymerization and added amount of vinyl acetate was also studied. The breaking stress of polyvinyl chloride decreases with the increase of the amount of plasticizer and the effect of strain rate is not clear in this case. The breaking stress increases a little while the degree of polymerization rises and decreases when the added amount of vinyl acetate increases. These tests were done at various impact speed from static speed to 2200000%/min. The sample containing different amount of vinyl acetate (8%, 15%) goes through at 1000000%/min, but the sample containing less amount of vinyl acetate shows this maximum at a little higher speed. Young's modulus was determined from the slope of the stress-strain curve. The value of the modulus goes through a maximum at a certain speed and then possesses an equilibrium value. The breaking energy of P.V.C. containing large amount of plasticizer is much greater at static speed, but the sample containing no amount of plasticizer shows a greater value at high impact speed. At impact speeds all the crossections of the broken samples are perpendicular in respect to the main axis of the sample. The extension of the sample was measured by giving standard marks at an interval of 1.28mm and the distance between these marks were read after impact tests. The result shows that the sample containing less and no amount of plasticizer do not extend at different speeds but the sample containing more amount of plasticizer extend more at static speed and less at high speed. This shows easiness of plastic flow at high speed. At a certain speed the value of extension drops sharply and this speed shifts toward higher value when the amount of plasticizer increases. The decrease of cross-sectional area is less in case of high speed. The critical velocity measured from the stress-strain curve drawn at impact speed shows that it increases with the addition of plasticizer and its value was compared with that of textile fiber. The propagation of plastic wave was also determined.