The elasticity of elastomers is due to entropic effect. Without stress, a polymer chain likes to coil together and form a spheric shape to increase the entropy. When you stretch it, its configuration becomes an elliptical shape. With the further increase of the stress, you can stretch the chain to almost a strand, finally start to stretch the bond and reach a stretch limit. The stretch limit is decribed in some models of rubber elasticity, for example, Gent model. I think this is the molecular picture of rubber elasticity and where the nonlinearity comes from.
Definately you are right.But as we know that elastomers are in the forms of coils and we know that the degree of randomness is entropy.It means that with the increasing stress coil gets alligned and entropy decreases up to a certain extent.But what happens exactly I dont know.If you have a paper then please mail me on this raj.mit.mech [at] gmail.com
You may refer to the following papers which provide more information on the entropic elasticity of elastomer
1.Arruda, E. M. and Boyce, M. C., 1993, A three-dimensional model for the large sretch behavior of rubber elastic materials,, J. Mech. Phys. Solids, 41(2), pp. 389–412.
2. Mary C. Boyce, Direct Comparison of the Gent and the Arruda-Boyce Constitutive Models of Rubber Elasticity Rubber Chem. Technol. 69, 781 (1996); doi:10.5254/1.3538401 (5 pages)
Bo Li
Ph.D.student
School of Mechanical Engineering
28 West Xianing Road
Xian Jiaotong University
Xian, Shaanxi, 710049
Email: blancolee [at] gmail.comboli.xjtu [at] stu.xjtu.edu.cn
Why the stress value is decreasing in the case of loading where as it is incresing with respect to time int the stress-relaxation test(UNiaxial tensile test at molecular level)
elasticity of elastomers
The elasticity of elastomers is due to entropic effect. Without stress, a polymer chain likes to coil together and form a spheric shape to increase the entropy. When you stretch it, its configuration becomes an elliptical shape. With the further increase of the stress, you can stretch the chain to almost a strand, finally start to stretch the bond and reach a stretch limit. The stretch limit is decribed in some models of rubber elasticity, for example, Gent model. I think this is the molecular picture of rubber elasticity and where the nonlinearity comes from.
In reply to elasticity of elastomers by Lihua Jin
Definately you are
Definately you are right.But as we know that elastomers are in the forms of coils and we know that the degree of randomness is entropy.It means that with the increasing stress coil gets alligned and entropy decreases up to a certain extent.But what happens exactly I dont know.If you have a paper then please mail me on this raj.mit.mech [at] gmail.com
Thanking You
RajKumar sahu
Phd Scholar
IIT Patna
In reply to Definately you are by rks2010
class website
You may want to take a look at the following class website.
http://www.doitpoms.ac.uk/tlplib/stiffness-of-rubber/index.php
Papers as reference on the entropic elasticity
You may refer to the following papers which provide more information on the entropic elasticity of elastomer
1.Arruda, E. M. and Boyce, M. C., 1993, A three-dimensional model for the large sretch behavior of rubber elastic materials,, J. Mech. Phys. Solids, 41(2), pp. 389–412.
2. Mary C. Boyce, Direct Comparison of the Gent and the Arruda-Boyce Constitutive Models of Rubber Elasticity Rubber Chem. Technol. 69, 781 (1996); doi:10.5254/1.3538401 (5 pages)
Bo Li
Ph.D.student
School of Mechanical Engineering
28 West Xianing Road
Xian Jiaotong University
Xian, Shaanxi, 710049
Email: blancolee [at] gmail.com boli.xjtu [at] stu.xjtu.edu.cn
relaxation
Why the stress value is decreasing in the case of loading where as it is incresing with respect to time int the stress-relaxation test(UNiaxial tensile test at molecular level)
Thanking You
RajKumar sahu
Phd Scholar
IIT Patna