Analysis of Strength of Connecting Rods - Lab Report Example

Hardness is a measure of the resistance of a metal to permanent (plastic) deformation. The hardness of the metal is measured by forcing an indenter into its surface. The indenter material which is usually a ball, pyramid, or cone, is made of a material much harder than the material being tested. For example, hardened steel, tungsten carbide, or diamond are commonly used materials for indenters. For most standard hardness tests a known load is applied slowly by pressing the indenter at 90 degrees into the metal surface being tested.

After the indentation has been made, the indenter is withdrawn from the surface as shown in the figure. An empirical hardness number is then calculated or read off a dial (or digital display), which is based on the cross-sectional area of depth of the impression.The hardness of a metal depends on the ease with which it plastically deforms. Thus a relationship between hardness and strength for a particular metal can be determined empirically. The hardness test is much simpler than the tensile test and can be non-destructive (i.e., the small indentation of the indenter may not be detrimental to the use of an object).

For these reasons, the hardness test is used extensively in industry for quality control.The Rockwell Hardness test consists of many different scales for a range of different hardnesses. The B and C scales are the types used in this experiment. The B scale uses the spherical steel penetrator and the C scale uses the diamond cone-shaped penetrator. Procedure for Experiment1. Make certain the crank. It is kept in a forward position, nearest to you.2. Place the sample on the anvil, in position for the test.3. Select 100 and 150 kg combination of weights (being at the rear of the machine). 4. Slowly turn the wheel spokes clockwise.

This raises the anvil and sample toward the penetrator tip. After contact is gently made, continue raising the sample until a small pointer is about in line with the small black dot and the large pointer is within the colored sector. The minor load has now been applied to the sample.5. After step 4, the large pointer on the dial is nearly vertical. Now, turn the knurled collar until the SET line on the dial scale is in line with and under the large pointer.6. Depress the trip lever. This triggers the mechanism that applies the major load.

The crank will automatically move away from you.7. After the crank has come to rest, gently pull the crank back toward you as far as it will go.