Hardness Ability to resist deformation, penetration, wear, abrasion, and cutting. Surface, or uniform throughout the metal. Brinell and Rockwell Hardness.

Brinell Hardness Test piece is placed on the screw jack & raised until it touches a 10 mm diameter tungsten carbide ball. The ball is pressed into the test piece by a 3000 kg load (for steel). The diameter of the indentation is measured, the surface area of the mark determined, and the hardness calculated.

Brinnel

Brinell Hardness Brinell hardness test Brinell hardness test

Brinell Hardness The round penetrator deforms the samples and they are generally scrapped afterwards. Limited to softer metals. Very accurate measure. Not good for very hard materials.

Rockwell Hardness A 10 kp load holds a 1.6 mm ball on the test piece. A 60, 100 or 150kp load is then applied to make the impression. The instrument dial measures the depth of the mark and converts it to a hardness reading which is read off the dial. For hard materials, a diamond cone is used and the total load is 150 kp. Test made with the ball are called Rockwell B readings, and those with the cone are called Rockwell C readings

Rockwell

Rockwell Hardness Testing Most commonly used test. Eliminates effects of small surface imperfections by applying preliminary load. Results are very accurate.

Micro-hardness Testing Good for small, thin brittle parts – especially if the part must be used after testing. Use smaller loads (5 – 100kg) & sharp pointed penetrators. Can also test glass & ceramics. Can test areas smaller than the size of a crystal or grain. Found in research labs usually.

Scleroscope Involves raising a precision weight with specific end shape to a specified height inside a tube. Tube is placed over surface to be checked Weight is dropped, allowing the point to hit the surface of the material.  Weight bounces back up the tube Height it bounces to is translated into a hardness value.

Scleroscope

Scleroscope Good correlation to Brinell & Rockwell Hardness scales. Imperfections in surface affect results. Impression left is almost negligible. Machine is small and portable.

Sonodour Measures hardness dependant on the resonant frequency of a piece of metal. Small & portable. Very quick response. Does not damage specimen. Very accurate.

Impact strength Impact strength is the ability of a material to resist sudden impact without fracturing. Also referred to as "Toughness” Impact strength varies with temperature. Temperature goes down - so does impact strength. Izod and the Charpy tests.

Measuring Hardness Penetration Hardness Very accurate Use a precision machine Penetrator presses against metal, measure impression, convert to hardness reading expensive Scratch Hardness Fast & crude Scratch metal sample with edge of tool or object Metal is defined as either ‘hard’ or ‘soft’

File Hardness Scrape metal with edge of file. If it does not scratch it is ‘file hard’ If it does scratch it is not file hard. Fast, simple, convenient Inaccurate Dependant on sensitivity of tester and sharpness of file.

Charpy impact test movie Impact strength Izod Impact Test Charpy Impact Test Charpy impact test Charpy impact test movie

Impact testing

Tensile strength

stress strain