Hardness Testing

Hardness Testing - EMSE 201 Introduction to Ma teria ls...

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EMSE 201 — Introduction to Materials Science and Engineering Hardness Testing Case Western Reserve University 1 rev. 10/01/07 I. (Indentation) Hardness Testing (Callister, § 6.10) A. Hardness — general remarks 1. Measure of a material’s ability to resist surface indentation or scratching 2. A difficult property to describe in terms of first principles value depends greatly on method of testing 3. Different testing methods different scales and values B. Used in polymer testing: Rebound (dynamic) hardness 1. Shore scleroscope - measures bounce height of a standard hammer C. Sidebar: Scratch hardness — Moh’s scale 1. 1(talc) — 10 (diamond) 2. Ranks materials, but the gradations are uneven ( e.g. , 10 is not twice as hard as 5) 3. Mainly of historical interest, … 4. … but simplicity of test and its familiarity have kept it alive, e.g. when new materials (fullerenes, Ti 3 SiC 2 ) are discovered D. Brinell — developed by Dr. J. A. Brinell of Sweden around 1900 1. Specifications a. 1 cm dia. hardened steel or tungsten carbide ball (ASTM specification) b. 500-3000 kg load (ASTM specification) c. 10-30 s duration d. Defined as load/contact area e. BHN ! P " D 2 D # D 2 # d 2 ( ) = 3000 157 # 15.7 100 # d 2 i. P: load, kg (usu. 3000) ii. D: indenter diameter, mm (usu. 10) iii. d: indentation diameter, mm f. Units: kg/mm 2 , but not a pressure nor a stress (even if it were kgf per mm 2 ) 2. Characteristics a. Calculate extreme cases:
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EMSE 201 — Introduction to Materials Science and Engineering Hardness Testing Case Western Reserve University 2 rev. 10/01/07 i. High hardness: d=0 BHN = ii. Low hardness: d=10 BHN = 19.1 b. Gives a macrohardness — properties of a few mm
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Hardness Testing - EMSE 201 Introduction to Ma teria ls...

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