Analysis of Adhesive Fracture Testing Methods for Aerospace Use

7 Analysis of Adhesive Fracture Testing Methods for

Downloaded by NANYANG TECHNOLOGICAL UNIV on October 17, 2017 | http://pubs.acs.org Publication Date: August 28, 1980 | doi: 10.1021/bk-1980-0132.ch007

Aerospace Use K. KAWATA, H . FUKUDA, N . TAKEDA, and A. HONDO Institute of Space and Aeronautical Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153, Japan

The determination o f adhesive bond s t r e n g t h and testing meth ods a s s o c i a t e d w i t h the bond s t r e n g t h are the important subjects in composite m a t e r i a l s and s t r u c t u r e s , e s p e c i a l l y their a p p l i c a tion in aerospace use. I n aerospace m a t e r i a l s , p e e l i n g t e s t s are important as well as u s u a l bond shearing t e s t . The apparent strength obtained from the bond shearing t e s t is τcr = P/S where Ρ is the breaking l o a d (kg) and S is the bonded area (mm ) w h i l e the p e e l i n g s t r e n g t h obtained from the p e e l i n g t e s t is P/b where Ρ is the breaking load (g) and b is the w i d t h (mm). These two so called " s t r e n g t h s " are d i f f e r e n t in dimensions and have not been r e l a t e d to each o t h e r . As a result, f o r practical problems these two t e s t s had to be conducted individually to q u a l i f y these two strengths. In the present paper, these two " s t r e n g t h s " are r e l a t e d by the analyses from the u n i f i e d s t a n d p o i n t . That is, the critical s t r e n g t h based upon the energy balance concept (1) is used to establish a relation between these two strengths of adhesive bonded joint and to demonstrate the i n t e r c h a n g e a b i l i t y of these data (2, 3 ) . There are many types o f adhesive joints o r bond s t r e n g t h testing methods as shown in Fig. 1. T - t e s t is t r e a t e d similarly w i t h θ degree p e e l i n g t e s t (2). S i n g l e - l a p ( 3 ) , tapered-lap and scarf-joint (4) are t r e a t e d similarly. A n a l y s i s of this type may be extended to p u l l - o u t t e s t ( 4 ) . 2

When we s u r v e y h i s t o r i c a l l y b r i e f l y , we c i t e t h e p i o n e e r i n g w o r k s o n e n e r g y i n a d h e s i v e p e e l i n g b y T. H a t a (5). A d h e s i v e f r a c t u r e e n e r g y was u s e d b y H. Dannenberg ( 6 ) , Β. M. M a l y s h e v a n d R. L . S a l g a n i k ( 7 ) , and J . D. B u r t o n , W. B. J o n e s a n d M. L . W i l l i a m s (8) t o s t u d y b l i s t e r t e s t . I n t h e f o l l o w i n g s , a n a l y t i c a l r e s u l t s and c o m p a r i s o n s w i t h e x p e r i m e n t a l r e s u l t s a r e m e n t i o n e d f o r t h e t e s t s shown i n F i g . 1. N e x t , a new method t o d e t e r m i n e dynamic f r a c t u r e t o u g h n e s s , t h a t i s , a d h e s i v e f r a c t u r e d s u r f a c e e n e r g y (11) i s p r o p o s e d .

0-8412-0567-l/80/47-132-059$05.00/0

© 1980 American Chemical Society

May; Resins for Aerospace ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

60

RESINS F O R A E R O S P A C E

(2)

—


4

h

——-— (3 a)

U E

(3 b)

M

90'

90'

l_J

(4) Figure 1.

Adhesive bond strength testing methods.

(1) Θ degree peeling test: P, loû ^ « t - t ) 2

2

(8)

N i s p r o p o r t i o n a l t o £, d i f f e r i n g f r o m s i n g l e - l a p j o i n t ( F i g . 7 ) . The e x p e r i m e n t a l d a t a b y de B r u y n e (9) s u p p o r t t h i s s o l u t i o n (Fig. 8). c r


RESINS FOR AEROSPACE


64

Figure 6.

Stresses in a tapered-hp joint (unit width perpendicular to the paper)


KAWATA E T AL.

Adhesive

Fracture

Testing


7.

Figure 8.

Experimental shearing fracture load of adhesive joints by de Bruyne


66

RESINS FOR AEROSPACE

Pull-out

Test

This axisymmetric o


where,

c r

case i s a l s o s o l v e d s i m i l a r l y

= P /7Tr c r

2

( F i g .9 ) :

= / 4 y E / r f (A£)

(9)

2

A = /2G/(E br)»Λ + ρ . f(A£) = ( / l + ρ shA£) /(p + chA£)

(10)

Ρ = E r / { 2 E i a ( l + (a/2r))} > 0

(11)

2

2

So, t h e r e l a t i o n o f O / / 4 y E / r F i g . 4. c r

The

2

vs.

/ 2 G / ( E b r ) £ i s t h e same w i t h 2

Effect of E l a s t i c - p l a s t i c Strip i n Peeling

Strength

When e l a s t i c - p l a s t i c s t r i p i s u s e d i n p e e l i n g t e s t , t h e following c o r r e c t i o n f a c t o r i s introduced (10): The P

cr/

b

same w i t h ( 3 ) * (12)

2

{ 2 Y / ( 1 - C O S 6 ) } ( 1 + | ^ ) ** * ** where,

( 9 = 0 degree) (except i n t h e neighbourhood o f 0 degree) Y : yield stress of strip, ρ : radius of curvature of s t r i p at peeling point.

A New M e t h o d t o D e t e r m i n e Dynamic A d h e s i v e F r a c t u r e d Energy

Surface

As s e e n i n t h e above m e n t i o n e d , t h e v a l u e o f γ i s i m p o r t a n t . U s i n g t h e specimens such as F i g . 1 (2) o r F i g . 10, dynamic a d hesive f r a c t u r e d surface energy f o r s h e a r o r y* f o rtear i s m e a s u r e d b y t h e method o f c o m p a r i n g t h e e n e r g i e s o f t h e i m p a c t i n g mass b e f o r e a n d a f t e r t h e i m p a c t l o a d i n g . By t h e e n e r g y method newly p r o p o s e d , dynamic a d h e s i v e f r a c t u r e d s u r f a c e energy i s de termined from t h e equation ( 1 3 ) ( 1 1 ) , t

Eo/S where,

= 2y

(13)

d

EQ : a b s o r b e d e n e r g y , S : narrowest cross s e c t i o n a l

area.



7.

KAWATA ET AL.

Adhesive

dx

Fracture

67

Testing

/A

"/

f

m

1l i1

—*•

Analysis of Adhesive Fracture Testing Methods for Aerospace Use

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