Page 174 - Plastics Engineering

Mechanical Behaviour of Plastics 157

Example 2.23 A series of Charpy impact tests on uPVC specimens with a
range of crack depths gave the following results

Crack length (mm) 1 2 3 4 5
Fracture Energy (mJ) 100 62 46.5 37 31
If the sample section is 10 mm x 10 mm and the support width is 40 mm,
calculate the fracture toughness of the uPVC. The modulus of the uPVC is
2 GN/m2.
Solution Since B = D = 10 mm and using the values of 0 from Table 2.3
we may obtain the following information.
a(mm) a/D 0 BD@ UW)
1 0.1 0.781 78.1 x lop6 100
2 0.2 0.468 46.8 x 62
3 0.3 0.354 35.4 x 46.5
4 0.4 0.287 28.7 x 37
5 0.5 0.233 23.3 x 31

A graph of U against BD0 is given in Fig. 2.84. The slope of this gives
G, = 1.33 M/m2.
Then from equation (2.108) the fracture toughness is given by
K, = = d2 x lo9 x 1.33 x lo3 = 1.63 MN m-3/2

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