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Material Science For Engineering I

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Published in: Mechanical
1,960 Views

It contains the content of material testing under various loads

Sidhant S / Bathinda

7 years of teaching experience

Qualification: mechanical engineering

Teaches: Geography, History, Mathematics, Science, Mechanical

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  1. Testing of Materials Assess properties — Stress data for design/ specification — Surface / sub surface defects Chemical composition — Suitability for an application Types of Test Destructive/ non-destructive Tensile, hardness, impact, fatigue, creep X-Ray, ultrasonic, electron probe analyzer, SEM, T EM, SPM Tensile test Ascertain mechanical properties like elastic limit, yield point, Young's modulus, ultimate strength, elongation, area reduction — Specimen subjected to gradual, static increasing load until it breaks; graph of stress/ strain is plotted — Specimen std shape, size, gauge & gripping length D -12mm, gauge -5d/10d, PL 5.5d, fillet- 3mm
  2. N/A
  3. Ductile material Stress Strain Curves Brittle material A proportionality, B elastic limits, C yield stress point, D Ultimate tensile E Fracture point/ stress strength, D-E local necking, $trafrJ Brittle faitute Elastic limit plastic behavior Strain (Percent)
  4. Tensile test Proof stress ...contd Non-ferrous don't show defined yield point Proof stress is stress required to produce permanent elongation equal to specified %age of elongation; specimen 50mm, 0.1% proof stress is that stress which produces 0.05mm elongation elastic range linear range 1 plastic tion 1 dastic limit law) proportionality limit permanent strain failure Strain (t)
  5. Hardness Hardness Resistance to permanent indentation — Energy absorbed under impact Resistance to scratching/ abrasion Hardness order; talc, gypsum, calcite, fluorite, ... , quartz, topaz, corundum, diamond — Important for die, punch, gauges, cutting tools, bearing surfaces — Easy, rapid & reliable — Inexpensive, simple Non destructive — Estimate other mechanical (tensile Strength) properties Commonly used ; - industry & research — Evaluate effect of hot/cold working and heat treatment Types of Test Brinell hardness, Rockwell, Vicker's, rebound hardness test
  6. Hardness Testing Brinell Hardness Determine hardness of metallic material, Uniformity of samples, Check Quality of products Not for very hard or thin material — Hardened steel ball dia D 10mm +- 0.0045, 3000kg, 1500kg(soft) — Load application gradual for 15/30 sec for hard/softer metals Measure d dia of indentation with microscope to nearest 0.2 mm BHN=P/A; A contact area of spherical segment = TtxDxt; Not for indentation near edge; dist from edge > 2.5 d — Surface flat, clean, well polished — Specimen thickness > 10d Measure dia d in two normal directions and take mean dia Turn the ball to reduce distorsion errors — Some BHN lead 4-8; Zn 25-40; a 115-200; Ni 130-160; HSS 450-700
  7. Hardness Testing Rockwell Hardness ...contd Simple, no measurement of diameter on microscope, no surface polishing — Faster and hence used for industrial work , Dial gives direct reading Different scales A to H; B & C commonly used Ball dia 1.58 mm for softer materials RHB and diamond cone indenter for hard material cone angle 120, spherical tip 0.2 mm radius Minor load 10kg, major load 100kg for B scale and 150 kg for C scale — 40 RHB Rockwell hardness of 40 on C scale; RHC 80 — Load application gradual for 10-20/30-35 sec for hard/softer metals Measure d dia of indentation with microscope to nearest 0.002 mm — RB = (130-depth of indentation)/O.002 — RC = (100-depth of indentation)/O.02 Not for indentation near edge; dist from edge > 2.5 d ; distance b/w adjacent indentation 3-5 times dia of indentation — Surface dry, clean, free from oxides — Specimen thickness > 10d
  8. Hardness Testing Vicker's Hardness ...contd — Similar to Brinell hardness test eliminates most error and variations Uses diamond square based pyramid with 136 angle — Load varies from 5 to 120 kg in increment of 5 kg - VI-IN = 1.854P/ L*L; — Typical VHN ; Steel 210; L length of diagonal diamond 8400; Aluminium 22; Tungsten carbide 2100; Lead 12 kg/ sq mm — For thinner material 0.15 mm — Small impression suitable for hardened material Rebound (Shore's Scleroscope) test Hardness in terms of elasticity metal at high temp No visible impression; Testing rolls, dies and gears Diamond pointer hammer weigh 2.5 gm , falls from 250 mm down thro' a glass tube graduated in 140 equal parts; Height of first rebound is index of hardness

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