7 Experimental Testing

7.1 Testing Problem
7.2 Standard and Methods Available
7.3 Physical Properties
7.4 Mechanical Properties

Composite materials, in the sense of being high performance materials for structural
applications, have been used increasingly since the early 1960's. Initially, conventional test
methods, originally developed for determining the physical and mechanical properties of
metals and other homogeneous and isotropic construction materials, were used. It was soon
recognized, however, that these new materials, being non-homogeneous and anisotropic,
required special consideration in terms of physical and mechanical properties determinations.

7.1 Test Problem 

Anisotropic

Thermohumid Conditions

7.2 Standard and Methods Available

Slip over

7.3 Physical Properties

Slip over

7.4 Mechanical Properties

Strain Gages

The electrical resistance strain gage uses the phenomenon that the resistance of certain
materials is related to the strain to which they are subjected.

(a) Wire -- made from certain metal alloys usually mounted in a paper carrier.

(b) Metal foil -- photoetched grids, usually mounted on a plastic backing for support. A very
      wide variety of grid configurations and sizes is possible. These are the most commonly
      used type of gage today.

(c) Semiconductor gages -- piezoresistive materials have extremely high sensitivities (up to
     100 times greater than the metal alloys.) However, unlike the metal foil and wire grid gages
     the relationship between resistance change and strain is nonlinear.