MGJ/10 OCT 96

PURPOSE

The purpose of this exercise is to obtain a number of experimental results important for the characterization of materials. The hardness test is a mechanical test for material properties which are used in engineering design, analysis of structures, and materials development.

EQUIPMENT

Fractured "halves" of reduced gage section tensile specimen of 6061 T6 aluminum

Fractured "halves" of reduced gage section tensile specimen of 1018 (hot rolled) or A36 steel

Flat coupons of 6061 T6 aluminum

Flat coupons of 1018 (hot rolled) or A36 steel

Rockwell hardness tester with 1/16" ball indenter tip and 100 kg of mass weights.

Tensile test machines with compression platen, 10-mm diameter Brinnell indenter ball fixture and controller

Micro-Mike

PROCEDURE

Brinnell Hardness Test

per E10-84 "Standard Test Method for Brinnell Hardness of Metallic Materials"

Place the flat coupon of one of the materials on the compression platen of the test machine, ensuring that the specimen is centered and resting flat on the platen.

In displacement control adjust the actuator position of the test machine such that the Brinnell indenter ball just contacts the surface of the flat coupon (<-50 N load).

In load control, ramp the load to -500 kg (-4908 N).

Maintain the maximum load for not more than 15 s.

Ramp the load to 0 N.

In displacement control adjust the actuator position of the test machine such that the Brinnell indenter ball is no longer in contact with the surface of the flat coupon.

Remove the flat coupon from the compression specimen

Use the Micro Mike to measure the diameter of the indentation of the surface

Repeat these steps for the other material.

Rockwell Hardness Test

per ASTM E18-92 "Standard Test Method for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials"

Place the gripped end of one half of a fractured tensile specimen of one of the material in the load fixture of the Rockwell hardness tester.

With the load handle pulled forward, raise the specimen and load fixture until the indenter contacts the specimen

Continue raising the specimen until the small dial hand is pointing at the small black dot (this applies a 10 kg preload).

Rotate the Rockwell dial until the large dial hand is pointing at 0.

Depress the loading bar.

Wait until the large dial hand stops moving and hold the load for not more than 25 s.

Pull the load handle forward again

Read the number on the B-scale indicated by the large dial hand

Repeat the Rockwell hardness test for flat coupon.

Repeat these steps for the other material.

ANALYSIS

The analysis is conducted from recorded data.

The Brinnell hardness number is obtained by dividing the applied force (in kilograms) by the curved surface of the indentation which is a segment of sphere such that:

(1)

where P is the applied load in kg, D is the diameter of the ball (10 mm) and is the diameter of the indention.

The Rockwell hardness number (RB) is read directly from the dial of the indenter, but the number must be reported along with the Rockwell scale (otherwise the number is meaningless).

The deformations caused by a hardness indenter are of similar magnitude to those occurring at the ultimate tensile strength of a tension test. However, an important difference is that the material cannot freely flow outward, so that a complex triaxial stress state exists under the indenter. Nevertheless, empirical correlations can be established between hardness and tensile properties, primarily the engineering ultimate tensile strength, Suts.

Use ASTM E 140-88 "Standard Hardness Conversion Tables for Metals (Relationship Between Brinnell Hardness, Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, and Knoop Hardness)" to convert the BHN and RB to ultimate tensile strengths for the two materials.

* REFERENCES

Annual Book or ASTM Standards, American Society for Testing and Materials, Vol. 3.01

E10-84 Standard Test Method for Brinnell Hardness of Metallic Materials

E18-92 Standard Test Method for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials

E 140-88 Standard Hardness Conversion Tables for Metals (Relationship Between Brinnell Hardness, Vickers Hardness, Rockwell Hardness, Rockwell Superficial Hardness, and Knoop Hardness)

LAB REPORT

1. Include the following table in the "Results" section of the lab report.

	1018 (HR) or A36 steel	6061-T6 aluminum
BHN (kg/mm2)......[measured]
BHN (kg/mm2). [literature]
% difference........................................
Suts (MPa) [calculated from BHN]...
Suts (MPa) [literature].........................
% difference........................................
RB ....[measured, flat coupon]..........
RB ....[literature]...................................
% difference........................................
Suts (MPa) [calculated from RB].......
Suts (MPa) [literature].........................
% difference........................................
RB ....[measured, tensile specimen]
RB ....[literature]...................................
% difference........................................
Suts (MPa) [calculated from RB].......
Suts (MPa) [literature].........................
% difference........................................

2. Include the following in the "Results" section of the lab report.

a. Compare results of the hardness tests for each metal to 'book' values from a

source such as the ASM Metals Handbook. Comment on any differences.

b. Compare the size of the artifact (i.e., indentation) from each type of test. Discuss the possible effect of such artifacts on material response if hardness tests are used for quality control of components.

c. Comment on the empirical relations which allow estimates of ultimate tensile strength of each material. Discuss the merits of using either hardness or tensile tests for determining/estimating mechanical properties of materials for engineering design.

3. Include the following information in the "Appendix" of the lab report. THIS MAY NOT BE ALL THAT IS NECESSARY (i.e., don't limit yourself to this list.)

a. Original data sheets and/or printouts

b. All supporting calculations. Include sample calculations if using a spread sheet program. DO NOT INCLUDE ALL TABULATED RAW OR CALCULATED DATA.

MGJ16 OCT 96

NAME______________________________________DATE______________

LAB PARTNER NAMES____________________________________________

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EQUIPMENT IDENTIFICATION______________________________________

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