Technique for measuring the complex shear modulus utilizing laser interferometry

Claim 1

A method for measuring the dynamic complex shear modulus of a viscoelastic material comprising the steps of: fixedly mounting a rod of circular cross section of the material with a length L at one of its ends; maintaining the rod at a predetermined temperature; introducing a sinusoidal torsional wave of a selected number of frequencies within a predetermined range of frequencies into the rod; measuring the deflection, theta L, of the rod at its free end, at a point midway its length theta L/2, and at a point one quarter of the length of the rod from its fixed end, theta L/4, for each of the selected frequencies; A. for frequencies below the last maximum in R4 determine the complex shear modulus G* for the given frequency f according to the following relationship

Claim 2

A method for measuring the dynamic complex shear modulus of a viscoelastic material comprising the steps of: fixedly mounting a rod of circular cross section of the material with a length L at one of its ends; maintaining the rod at a predetermined temperature; introducing a sinusoidal torsional wave of a selected number of frequencies within a predetermined range of frequencies into the rod; measuring the deflection, theta L, of the rod at its free end, at a point midway its length theta L/2, and at a point one quarter of the length of the rod from its fixed end, theta L/4, for each of the selected frequencies; A. for frequencies below the last maximum in R4 determine the complex shear modulus G* for the given frequency f according to the following relationship

Claim 3

An apparatus for measuring the torsional displacement of a sample rod of viscoelastic under sinusoidal torsional waves at lineal points critical for the determination of the dynamic complex shear modulus of the material, comprising: an environmental housing for enclosing the sample rod and controlling the temperature thereof; means for securing one end of said rod in said environmental housing; means attached to the unconstrained end of the sample rod for introducing sinusoidal torsional waves therein; means for producing a beam of collimated light and introducing the same into said environmental housing to impinge upon said sample rod; means interposed along said beam of light, for splitting said beam of collimated light into two beams; means for reflecting one of said split beams, mounted perpendicularly and in a plane parallel to the axis of the rod for successively measuring the rotational displacement of said sample rod along the length thereof, one at the unconstrained end, another at a point midway along its length, and still another at a point one-quarter of the length from the secured end; means for combining said split beams reflected from said reflecting means with the other of said split beams; and means for counting the interference fringes produced by the combining means, thus determining the torsional displacement of each of said reflecting means at the selected frequency.

Claim 4

An apparatus for measuring the torsional displacement of a sample rod of viscoelastic under sinusoidal torsional waves at lineal points critical for the determination of the dynamic complex shear modulus of the material, comprising: an environmental housing for enclosing the sample rod and controlling the temperature thereof; means for securing one end of said rod in said environmental housing; means attached to the unconstrained end of the sample rod for introducing sinusoidal torsional waves therein; means for producing a beam of collimated light and introducing the same into said environmental housing to impinge upon said sample rod; means interposed along said beam of light, for splitting said beam of collimated light into two beams; means for reflecting one of said split beams, mounted perpendicularly and in a plane parallel to the axis of the rod for successively measuring the rotational displacement of said sample rod along the length thereof, one at the unconstrained end, another at a point midway along its length, and still another at a point one-quarter of the length from the secured end; means for combining said split beams reflected from said reflecting means with the other of said split beams; and means for counting the interference fringes produced by the combining means, thus determining the torsional displacement of each of said reflecting means at the selected frequency.