PSI - Issue 2_B

A.J. Kinloch et al. / Procedia Structural Integrity 2 (2016) 221–226 Kinloch et al./Structural Integrity Procedia 00 (2016) 000–000

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model and predict the rate of fatigue crack-growth in the adhesive layer. In the present paper, two examples have been selected which consist of different designs of adhesively-bonded joints where naturally-occurring disbonds have been allowed to initiate and grow under cyclic-fatigue loading in: (i) a symmetrical double over-lap adhesively-bonded specimen (Cheuk et al. 2005) and (ii) an asymmetrical adhesively-bonded doubler joint. Both designs are typical of adhesively-bonded repairs (Pascoe et al. 2013a). It has been found that, in both cases, the use of the Hartman-Schijve equation, coupled with the finite-element analysis, gives rise to computed crack length, a , versus number, N , of fatigue-cycle histories that are in very good agreement with the experimental measurements, as shown for example in Fig. 2.

1,0E-04

y = 8.40E-09 x 2.00

1,0E-05

1,0E-06

100C, R = -1 20C, R = -1 -50C, R = -1 100C, R=0

Mode II tests

1,0E-07 da/dN (m/cycle)

Mode I 40% RH, R = -1 Mode I 90% RH, R = -1

1,0E-08

(  √ G -  √ G thr )/ √ (1- √ (G max /A)) (√(J/m 2 )

1,0E-09

0,1

1

10

100 1000 10000

Fig. 1. The Hartman-Schijve representation of the Mode I and Mode II fatigue behaviour for the epoxy-film adhesive ‘FM300K’.

Table 1. Values of the parameters employed in the Hartman and Schijve Eqn. (1) for Mode I crack growth in the ‘FM300K’ adhesive.

∆�� ���� (√(J/m 2 )) 9.8

Test

D (m/cycle)

A (J/m 2 )

n

40% RH

8.40 x 10 -9 8.40 x 10 -9

2.00 2.00

630 630

80-90% RH

10.5