Testing viscoelastic solids

An apparatus for testing a viscoelastic material to determine the physical-structural properties of the material comprising:

• a holding means connected to the material for holding the material in a predetermined position during testing;
• a pretension means coupled to the material for applying tension to the material during testing;
• a displacement generator having an eccentric means coupled to the material for applying cyclic displacement to the material;
• a first force transforming means for transforming mechanical stress applied to the material into an electrical stress signal;
• a second force transforming means for transforming mechanical strain applied to the material into an electrical strain signal;
• and
• a third force transforming means arranged at an angle of 90.degree. with reference to said first force transforming device and with reference to said second force transforming device for transforming mechanical strain applied to the material into an electrical differentiated strain signal.

A method for testing a viscoelastic material and measuring selected properties comprising:

• applying strain to the material, with resulting stress also applied to the material;
• transforming said strain applied to the material into an electrical strain signal having a strain wave form and an amplitude;
• transforming said resulting stress applied to the material into an electrical stress signal having a stress wave form and an amplitude;
• controlling said strain applied to the material to produce at least a substantially sinusoidal strain wave form representing strain;
• and
• allowing said stress to vary to produce a stress wave form representing stress.

An apparatus for testing a viscoelastic material to determine the physical-structural properties of the material comprising:

• a holding means connected to the material for holding the material in a predetermined position during testing;
• a pretension means coupled to the material for applying tension to the material during testing;
• a displacement generator having an eccentric means coupled to the material for applying cyclic displacement to the material;
• a first force transforming means for transforming mechanical stress applied to the material into an electrical stress signal;
• a second force transforming means for transforming mechanical strain applied to the material into an electrical strain signal;
• a third force transforming means arranged at an angle of 90.degree. with reference to said first force transforming device and with reference to said second force transforming device for transforming mechanical strain applied to the material into an electrical differentiated strain signal;
• a position transforming means connected to said pretension means for transforming instantaneous elongation in the material into an electrical signal;
• an integrating means for integration of a stress-strain hysteresis loop;
• a display means for displaying an output of the integrating means to measure the area of the hysteresis loop and thereby determine energy loss;
• and
• a temperature chamber for controlling the temperature of the environment in which the material is held during testing;
• wherein:
• said strain signal has at least a substantially sinusoidal wave form;
• and there is a phase lag between said stress signal and said strain signal, which may vary in amount and direction as a function of time;
• said eccentric means comprise:
• a drive means which is a source of rotating power to the eccentric mechanical means;
• a rotatably concentric head driven by said drive means and having a center;
• an eccentric slide mounted on said concentric head for rotation therewith, said eccentric slide having an eccentric shaft, said eccentric slide movable with reference to said concentric head for eccentric displacement of said eccentric shaft from said center of concentric head;
• a centerpiece mounted on said eccentric shaft and coupled to the material for transmitting cyclic displacement of said material, said eccentric shaft rotatable with reference to said centerpiece;
• an eccentric adjustment means for adjustment of said displacement of said eccentric shaft with reference to said center of said concentric head;
• said concentric head having a front planar surface and a slot in said front planar surface;
• said slot having a longitudinal centerline;
• said eccentric slide having a front planar surface and a longitudinal centerline, said eccentric slide disposed in said slot of said concentric head;
• an eccentric alignment mean for aligning said longitudinal centerline of said eccentric slide with reference to said longitudinal centerline of said slot in said concentric head;
• and
• a planar adjustment means for adjusting said front planar surface of said eccentric slide in a parallel position with reference to said front planar surface of said concentric head.

A method for testing a viscoelastic material and measuring selected properties comprising:

• applying strain to the material, with resulting stress also applied to the material;
• transforming said strain applied to the material into an electrical strain signal having a strain wave form and an amplitude;
• transforming said resulting stress applied to the material into an electrical stress signal having a stress wave form and an amplitude;
• controlling said strain applied to the material to produce at least a substantially sinusoidal strain wave form representing strain;
• allowing said stress to vary to produce a stress wave form representing stress;
• displaying the strain wave form and the stress wave form as a function of time on the same scale;
• arranging the amplitudes of the strain wave form and the stress wave form to be equal, thereby allowing observation of a phase lag between the strain wave form and the stress wave form, the phase lag varying in amount and sometimes in direction, depending upon the characteristics of the material;
• displaying the stress wave form along a vertical axis;
• displaying the strain wave form along a horizontal axis, said stress wave form and said strain wave form thereby forming a hysteresis loop;
• transforming said strain applied to the material into a differentiated strain signal by differentiating said strain signal mechanically;
• and
• integrating said differentiated strain signal and said stress signal to determine the area of the hysteresis loop, said area indicating energy loss in the material.