Application of Pulse Strain as a Method of Viscoelastic Measurement

Pulse Strain Method for viscoelastic measurements is presented, which is based on the Raised Cosine Pulse Method (RCP Method). According to the RCP Method, frequency dependence of complex shear modulus is given by the Fourier transform of shear stress as the response to a pulse strain of cosine type. However, frequency range of observation is limited to only 1 or 2 decades in lower region of fundamental frequency of applied pulse strain. To expand the frequency range, we have modified the RCP Method using Rectangular Pulse Strain, which includes high-frequency components (RAP Method). Comparison among the RCP Method, RAP Method and conventional dynamic methods was made on a 20% polystyrene solution in diethylphthalate. In the case of the RAP Method, frequency range was expanded to higher frequencies of fundamental frequency of applied pulse strain compared with the RCP Method. Computer simulation of Pulse Strain Method was made to know the requirements for further expansion of frequency range. The shear stress as the response to pulse strain was calculated for a Maxwell model using the Boltzmann superposition principle, and then complex shear modulus was calculated from Fourier transform of pulse strain and shear stress. The obtained shear modulus from simulation was compared with the theoretical value. It has been shown that resolution and response time of a torque transducer are important to make the best use of Pulse Strain Method. The requirements for a torque transducer are as follows, resolution is 1/10000, and response time is 0.1 ms.