Question

A specimen of ductile cast iron having a rectangular cross section of dimensions 4.8 mm x 15.9 mm is deformed in tension. Using the load-elongation data tabulated below, complete problems (a) through (e) a) Plot data as engineering stress versus engineering strain (Use the Excel if possible, and show the graph on a separate sheet, or copy on the bottom.) Load Length N mm 0 75 75.025 4,740 b) Determine the 0.2% offset yield strength; (Plot the data in a suitable graphical form, if needed for questions b) and c) - to have an enlarged strain axis, so that the first part of the deformation process can be enlarged and accurate values can be obtained.) 9,140 75.05 12,920 75.075 75.113 16,540 18,300 75.15 20,170 75.225 22,900 75.375 75.525 25,070 c) What is the modulus of elasticity? 26,800 75.75 76.5 28,640 78 30,240 31,100 79.5 31,280 81 30,820 82.5 29,180 84 27,190 85.5 87 24,140 d) What is the ductility in percentage elongation? 18,970 88.725 Fracture In which part of the stress-strain curve does the necking starts (label the stress) e)

Answer 1

Answer: Cross-sectional area of the specimen= 4.8*15.9= 76.32 mm².

(a)

(b) 0.2% strain offset yield stress = 260 MPa aprrox

Strain Stress 0 0 0.000333333 62.10692 0.000666667 119.7589 450 0.001 169.2872 0.001506667 216.7191 400 0.002 239.7799 350 0.003 264.282 0.005 300.0524 300 0.007 328.4853 250 0.01 351.153 0.02 375.2621 Series1 200 0.04 396.2264 150 0.06 407.4948 0.08 409.8532 100 0.1 403.826 50 0.12 382.3375 0.14 356.2631 0.16 316.2998 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.183 248.5587

(c) modulus of elasticity= slope of curve within proportional limit= (62.10692-0)/(0.00033333-0)= 62.106 MPa

Strain Stress 0 0 0.000333333 62.10692 0.000666667 119.7589 450 0.001 169.2872 0.2 % strain offset 0.001506667 216.7191 400 0.002 239.7799 350 0.003 264.282 0.005 300.0524 300 0.007 328.4853 250 0.01 351.153 0.02 375.2621 Series1 200 0.04 396.2264 150 0.06 407.4948 0.08 409.8532 100 0.1 403.826 50 0.12 382.3375 0.14 356.2631 0.16 316.2998 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.183 248.5587

(d) % elongation= 0.183*100= 18.3%

(e) Necking start around 410 MPa i.e. after ultimate point.