Evaluation of different methods of relaxation modulus extraction for linear viscoelastic materials from ramp-constant strain experiments

Abstract

Experimental determination of relaxation modulus of linear viscoelastic materials, in principle, requires the application of an ideal step strain to the specimen. This could not be achieved in practice, however, and is replaced by a ramp-constant strain history. The material response to the ramp-constant strain deviates from its ideal step response and should be corrected. Different correction methods have been proposed for the full-range modulus extraction from ramp-constant strain experiments, and among them the three methods of Zapas–Phillips, Lee–Knauss, and Sorvari–Malinen are distinguishable. Few comparative studies have been performed on these methods, all of which have been based on the simulated response of a hypothetic material rather than on the real experimental data. Furthermore, the simulations have been performed assuming specific material models not essentially appropriate for the material parameter extraction purposes, leading to undesirable errors in the simulation results. In this paper, the above-mentioned methods are compared based on both simulation and experimental approaches. The simulation results show that all methods effectively improve the range of modulus extraction compared to the well-known “ten-times rule”, and the Lee–Knauss method provides the best predictions, in contrast to some of the previously published results. Considering the experimental results, however, it is observed that all the modulus extraction methods lose their performance if a sufficiently small sampling rate is not provided by the experimental data acquisition system. It has been discussed that the conclusion of some authors regarding the invalidity of ten-times-rule stems from a misinterpretation of their simulation results and is faultful.

Development and research of tillage operating device with polymeric materials

“…Several comparative studies of the methods were carried out, all of which were based on simulated reaction of a hypothetical material, but not on real experimental data [8].…”

“…Basing on the research on the modeling results using [2][3][4][5][6][7][8][9][10][11], the design of new tillage operating device with polymeric materials was developed.…”

Study on the Testing Method of Relaxation Modulus under Spherical Indenter Loading

“…A large number of scholars have studied and analyzed this, hoping to reduce the influence of the strain application process on the relaxation modulus test process through a reasonable method. Some scholars used the step strain history method of the indentation instrument to measure the relaxation modulus by correcting the data in the relaxation stage [6][7][8][9][10]. e correction method of Zapas and Phillips [6] is the simplest, which is calculated by moving the relaxation area forward for a certain time range.…”

“…Of course, some scholars calculate the relaxation modulus by adding correction factors [8][9][10]. Among them, the best method is to calculate the relaxation modulus by using the measured data with the minimum error between the relaxation data after 5t 0 -10t 0 and the ideal step loading in a recursive manner [6,7].…”

Identifying the parameters of viscoelastic model for a gel-type material as representative of cardiac muscle in dynamic tests

“…In principle, the tests by using the stress relaxation test method require the application of an instantaneous strain to the specimen. This is impossible in practice, 42 hence, the process of parameter identification is performed by regarding and disregarding the initial ramp influences in the stress relaxation tests. The analytical curves that plotted in the time domain by utilizing the identified parameters by regarding the effects of the initial ramp show a great adaptation with experimental results.…”