PSI - Issue 28

6

Anurag Singh et al. / Procedia Structural Integrity 28 (2020) 2206–2217 Anurag Singh/ Structural Integrity Procedia 00 (2019) 000 – 000

2211

using the modified beam theory (MBT). The delamination crack front grows from the insert, a resistance-type fracture behaviour develops and then stabilises with further delamination growth. A resistance curve (R curve) in the figure depicts the mode I critical energy release rate, G IC, as a function of delamination length to characterise the initiation and propagation of delamination in a unidirectional specimen. Initiation value of G IC was determined using the load and deflection measured at the point of deviation from linearity in the load-displacement curve. The initial delamination length, a 0 , is the distance from the load line to the end of the insert. Mode I critical energy release rate, G IC . The beam theory expression for the strain energy release rate of a perfectly built-in double cantilever beam is:

3  

G P I 2

(6)

ba

Where, 

P = load, N

δ = load point displacement, b = width of the specimen, mm a = delamination length, mm

   

h= thickness of specimen, mm To avoid overestimation of G I considering the imperfectly built-in simply supported beam in DCB as slightly longer delamination, a + |Δ|, where Δ is determined experimentally by generating a least -squares plot of the cube root of compliance, C 1/3 , as a function of delamination length. The compliance, C is the ratio of the load point displacement   to the applied load P . Equation 7 calculates the Mode I interlaminar fracture toughness, and equation 8 computes the modulus, E if .

3



2 ( b a G P I 

(7)

)

 

3 ) l P

64(

a

3    bh

E if



(8)

Figure 3 a) Specimen with end blocks mounted b) DCB test configuration c) Open-jaw configuration at the end of the test.