Issue 71

E. Kormanikova et alii, Fracture and Structural Integrity, 71 (2025) 182-192; DOI: 10.3221/IGF-ESIS.71.13

( ) = x ζ 0

(2)

signifies that the adhesive is completely damaged at a specific point. i.e. complete delamination. ( ) = x ζ 1

(3)

indicates an undamaged interface. The total ERR in DCB sample can be formulated as

dU b da 1

=−

G

(4)

where dU is stress increment, da is length increment (or crack increment) and b is width of sample. With respect to the examination of the DCB sample using Mode I, the value of the ERR can be expressed using the Euler-Bernoulli theory as

2 2

F a

(5)

= I

G

bEI

where EI is bending stiffness. According to ASTM standards [21], there are several ways to determine the value of ERR, one of the methods is the so called Modified Beam Theory (MBT). The I G value according to this theory is determined as

δ

F

3

= I

G

(6)

ba

2

Due to the fact that the experiment is partially imperfect due to theoretical studies, a correction is introduced, which assumes that the delamination value is increased by the value | Δ |. Thus, the total crack length is (a + | Δ |) and so the adjusted I G calculation looks as follows

δ

F

( b a 3

=

(7)

G

)

I

+ ∆

2

where Δ is calculated in accordance with the ASTM standards.

M ATERIAL CHARACTERISTICS OF COMBINED LAMINATE COMPOSED OF SUBLAMINATES f the laminate consists of S sublaminates, each containing n q plies, where q = 1,…, S , then components of in-plane stiffness matrix A can be expressed as the sum of S terms [22]

I

( ) ij A

( ) A E h 1 = ∑ n ij ij kn =

∑

∑

∑

n

n

S q

+

+ + ...

=

( ) E h ij kn

( ij kn E h )

(8)

S

2

kn

kn

kn

=

=

=

k

k

k

1

1

1

1

q

S

1

2

S

1

2

1

E is component of transformed reduced stiffness matrix of the k th layer of the q th

q kn h

where

is thickness and

( )

q ij kn

sublaminate, and ( ) ij q A is the component of the in-plane stiffness matrix of the q For the two sublaminates M and N the combined in-plane stiffness matrix A is ( ) ( ) ( ) = + ij ij ij MN M N A A A .

th sublaminate.

(9)

184