The Ernst tester is a small versatile tool that requires access to only one side of the material being tested. There are two models of the tester-one for testing hardened steels and hard alloys and one for testing unhardened steels and most nonferrous metals. It has a diamond point penetrator, and it is read directly from the Rockwell A or B or the Brinell scales, depending on the model used. Figure 1-31 shows the Ernst portable hardness tester and its proper use.

The correct procedures for using the Ernst tester are as follows:

1. Solidly support the metal being tested by placing a bucking bar behind the metal. This will minimize flexing of the metal and yield a more accurate reading of hardness.

2. The handgrip must be pressed down with a steady, even force to ensure accurate readings.

3. Press down until the fluid column has stopped moving. The hardness value is given at the point where the fluid column has stopped moving on the scale.

As with other portable testers of similar type, the material must be smooth and backed up so there will be no tendency to sag under the load applied on the tester. The test block supplied with each tester should be used frequently to check its performance.

Learning Objective: Identify properties of non-metallic and composite materials used in aircraft construction.

Transparent plastics, reinforced plastics, and composite materials are common materials used in aircraft construction. Sandwich construction is used for radomes as well as for structural areas where strength and rigidity are important.