Compressibility of natural rubber at pressures below 500 kg/cm2

Abstract

The specifi c volumes of unvulca nizcd natural rubbcr and of a peroxide-cured vulcan izate of natural rubber were meas ured at press ures of 1-500 kg/cm2 at temperatur cs from 0 to 25°C. Observations on mercury-filled d ilatometers were made through a window in t he press urc system. No t ime effects or hysteres is phenomcna were observed. The spec ific volumc 17 in cm 3 /g over t he range studi ed can be r epresen ted by 17= V o,2511 + A(t -25 ) 111 + [a 25 + k,(t -25 )whcre P is t he press ure in k g/cm2, and t tIl e tcmperatu re in °C. The constants for thc un v ulcanized and for t he peroxide-cured samples are: 170,25 = 1.0951 and 1.1032 cm 3 /g; 10'A = 6.54 and 6.36 pCI' degree ; 106a25= -50.5 and -50.4 (kg/ cm2)-'; 106k ,= -0. 227 a nd -0.203 per dcgrec ; 1091325 = 10 and 11.5 (kg/cm2)-2; and 109k 2= 0.O L 18 and 0.073 p CI' degree, r es pcctively. The oompr essibili ty of unvulcanizcd natural rubbcr at 25° a nd 1 k g/cm2 is t hus 50.5 X 10-6 (kg/Clu2) -1 fa llin g to 40.6 X 10-6 (kg/ cm2) -1 at a press lll'e of 500 kg/cm 2. It I S concluded that a low deg rce of vulcanization produces no ignifi ca n t chan ges in the constants lis ted. The valu cs a re no t far d iffcren t from those obtained by extrapolating to zero s ulfur co ntcnt the observa tio ns of Scott on t ile rubbersulfur system. Calcula tions of valu es of compressibility (a nd i ts r eciprocal thc bulk modulus), " in te rn al press ure", bulk wave vclocity, difference be twee n sp ecifi c heats and severa l other physical propert ies are in r easonable agree mcnt with those obtained by d i;'ect obser vat ion by oth er worke rs. For t he prcd ietion of valu es at press ures above 50'0 ko-/eln2 the use of the Tait eq uation is recomme nd ed.

On the volumetric part of strain-energy functions used in the constitutive modeling of slightly compressible solid rubbers

“…Nevertheless elegant hydrostatic compression experiments have been performed by, amongst others, Penn (1970), Christensen and Hoeve (1970), Copeland (1948) and Wood and Martin (1964). The experimental procedure is essentially the same in all cases and a description is given, for example, in Wood and Martin (1964). The experimental data of Wood and Martin (1964) are very clearly presented.…”

“…The dilatation or hydrostatic compression test involves the hydrostatic compression of a rubber sample and therefore is a difficult experiment to perform. Nevertheless elegant hydrostatic compression experiments have been performed by, amongst others, Penn (1970), Christensen and Hoeve (1970), Copeland (1948) and Wood and Martin (1964). The experimental procedure is essentially the same in all cases and a description is given, for example, in Wood and Martin (1964).…”

The Compression of Bonded Rubber Disks

“…The maximum hydrostatic pressure of the test is 200 MPa. The bulk modulus for peroxide cured natural rubber was previously measured by Wood and Martin 26 and Moonan and Tschoegl. 27 At ambient pressure, they obtained B = 1946 MPa and 1690 MPa respectively, which bracket the present measurement.…”

Thermomechanical constraints and constitutive formulations in thermoelasticity

“…When T = 0 and λ = 1, ∂J/∂θ| T=0 can be obtained from (4.18) and substituting the result into (4.10) gives C p -temperature curve shown in Figure 4.2. The results are compared with the unconstrained case and the experimental data of Wood and Martin [14]. Since the stress responses in isothermal deformation are the same for both constrained and unconstrained cases (see (4.4) and (4.10)), assume an isentropic deformation and compare the stress and temperature responses for the two cases.…”

“…We use thermoelastic material parameters of a peroxide-cured vulcanizate of natural rubber (see Chadwick [3] and Wood and Martin [14]) and they are the density ρ 0 = 906.5kg/m 3 , the shear modulus µ = 4.2 × 10 2 kPa, the isothermal bulk modulus κ = 1.95 × 10 6 kPa, the volume coefficient of thermal expansion α = 6.36 × 10 −4 K −1 , and the material parameters m = 9 and n = 5/2. The initial temperature θ 0 is 25…”