A Technique f o r Displaying t h e Crack P a t t e r n Obtained Using a Br i t t l e Coating

by James Huang, K. K . Hu, S. E . Swartz

Kansas S t a t e Un ive r s i ty

Numerous techniques e x i s t f o r observing and d i s p l a y i n g the crack p a t t e r n s assoc- i a t e d w i t h t h e use of b r i t t l e coa t ings . p a r t i c u l a r l y easy t o u s e and which g ives e x c e l l e n t c o n t r a s t . This technique has undoubtedly been used by o t h e r s b u t appa ren t ly i s n o t s o widely known.

This n o t e d e s c r i b e s a technique which is

The problem w a s t o determine c r i t i c a l l o c a t i o n s i n t h e web of a wide f lange beam adjacent t o a cu tou t a t which more p r e c i s e s t r a i n measuring devices could be a t tached . I n a d d i t i o n , a whole f i e l d p a t t e r n f o r an unre inforced ho le w a s t o be cont ras ted with a similar p a t t e r n wi th t h e ho le r e in fo rced .

Surface p repa ra t ions included removal of rough materials, c leaning and degreasing. Following t h i s aluminum r e f l e c t i v e undercoat ing w a s appl ied and cured. coat ing w a s then app l i ed and cured .

The b r i t t l e

Af t e r l oad w a s app l i ed and the crack p a t t e r n developed t h e r e w a s a problem i n d isp lay ing t h e c racks f o r t h e purpose of documentation by photography. procedure w a s used t o enhance t h e c rack d i sp lay .

The following

1. A f t e r t h e c racks developed, p r o t e c t i v e cream (West, P r o t e c t i v e C r e a m 411) w a s s l i g h t l y f i l l e d i n t o t h e c racks and t h e excess cream w a s removed wi th a paper t i s s u e .

2 . A r e d , dye e t chan t (Magnaflux, Dye-etchant ST 1300A) w a s brushed uniformly on t h e whole s u r f a c e of t h e coa t ing and aga in t h e excess w a s removed with a pape r t i s s u e .

3. The loads were removed t o make t h e c racks smaller, thus squeezing out t h e cream and then e l e c t r i f i e d p a r t i c l e s (Magnaflux, S t a t i f l u x SXP-1) w e r e sprayed as soon as p o s s i b l e , i . e . , be fo re t h e dye e t chan t completely d r i ed .

4. The p i c t u r e shown w a s taken w i t h KODAK Pan-X (Fx 135-20) b lack and white f i lm .

SOCIETY FOR EXPERIMENTAL STRESS ANALYSIS