A

MACHINE

LIFE

OF

FOR WELDED

INVESTIGATING

THE

FATIGUE

STRUCTURES

L. N. Semenov, V. and V. A. Reznichenko

P.

UDC 539.4

Prokhnich,

At p r e s e n t fatigue t e s t s of f u l l - s i z e s t r u c t u r e s cause significant difficulties since the industry does not produce the a p p r o p r i a t e powerful equipment. In this w o r k we investigated the fatigue life of thin sheet welded s t r u c t u r e s of AMg5 alloy in a l t e r n a t i n g sign v a r i a b l e loading with specified levels of s t r e s s e s . The s t r u c t u r e was a 2 x 2300 x 1200 m m sheet welded in the middle with five stiffening r i b s (4 x 35 x 60 m m angles). To m a k e the t e s t s , a special unit was designed and built and an automated s y s t e m of controlling loading a c c o r d i n g to a specified p r o g r a m of s t r e s s e s and a hydraulic s y s t e m * was developed (Fig. 1). F r o m bank 3 the working fluid (MGE oil) is d e l i v e r e d to axial plunger pump 2 and then through filter 5and the t w o - s t a g e gate valve d i s t r i b u t o r with e l e c t r o m a g n e t i c control 6; it is then fed to working cavity of the single action actuating m e c h a n i s m 7. In the r e t u r n t r a v e l of the actuating m e c h a n i s m the oil is fed back to the d i s t r i butor and then through the r e t u r n line to the tank. The hydraulic stand is powered f r o m a type NR-2.5 v a r i a b l e rate axial plunger pump. It c r e a t e s a m a x i m u m p r e s s u r e of :100 k g ~ c m 2 and its m a x i m u m output is 50 l i t e r s / m i n . The pump is o p e r a t e d by the 4.8-kW 3 5 0 0 - r p m e l e c t r i c m o t o r 1. The oil is cleaned by a type FG-2 f i l t e r with 0. 0 1 - m m - d i a m . cleaning e l e m e n t holes. The cleaning e l e m e n t of the filter is r e p l a c e a b l e and it p r o t e c t s the d i s t r i b u t o r and the actuating m e c h anism from wear. The flow of liquid is distributed by the type GA-46/3 gate valve d i s t r i b u t o r with an e l e c t r o m a g n e t i c cont r o l l e r . The d i s t r i b u t o r is a gate v a l v e - gate valve s y s t e m . The f i r s t gate valve converts d i s p l a c e m e n t into a h y d r a t d i c signal, p r e s s u r e and consumption, and the h y d r a u l i c signal is converted into d i s p l a c e m e n t of the *Ya. G. Kuzin and A. G. D r o b y s h e v p a r t i c i p a t e d in the d e v e l o p m e n t of the hydraulic s y s t e m .

!6 To control [ ~ 7 ~ _ ,

[

Fig. 1. Hydraulic plan of the unit (solid line is the f o r c e line and broken, the r e t u r n line). Branch L a b o r a t o r y , Strength of Fishing Ships of the Ministry of the Fishing Industry of the USSR, Kaliningrad. T r a n s l a t e d f r o m P r o b l e m y P r o c h n o s t i , No. 5, pp. 114-116, May, 1978. Original a r t i c l e submitted D e c e m b e r 22, 1976. 0039-2316/78/1005-0609S07.50

9 1979 Plenum Publishing C o r p o r a t i o n

609

o,

kgf/crn 2 ?

-] d

;

iL Fig. 2.

I

I

J

Block plan of the load control unit.

Fig. 3.

Static (1) and dynamic (2) c a l i b r a tion of the s y s t e m .

second gate valve, which provides a consumption of liquid of about 60 liters/min. In this way there is double c o n v e r s i o n of the m e c h a n i c a l e n e r g y into h y d r a u l i c and the r e v e r s e . To control the gate valve solenoids with a 24-V dc power supply a r e used. The actuating m e c h a n i s m of the unit is s t r a i g h t - t h r o u g h single-acting. The inner d i a m e t e r of the cylinder is 200 m m and it designed for a load of 50 tons. To p r o t e c t the hydraulic s y s t e m f r o m o v e r l o a d s , there is a type GA-22 ball type safety valve 4, which controls the p r e s s u r e within the limits of 18-100 kgf/cm 2. The safety valve is actuated at the m o m e n t of switching of the distributor and b y p a s s e s a portion of the liquid f r o m the force line to the r e t u r n line. The s y s t e m is connected by steel tubing (material 10 steel, inner diam. 12 m m , outer 14 mm) with c o n e cone fittings. The piping is connected to the e l e m e n t s of the s y s t e m with couplings, nipples, and coupling nuts. F o r reliable operation the s y s t e m is filled with MGE or AMG-10 hydraulic fluid but it may also operate with AU spindle oil o r t r a n s f o r m e r oil. The d i s t r i b u t o r is controlled automatically with the help of a load control block operating with feedback f r o m the m e c h a n i c a l s t r e s s . The block plan of the load control unit is shown in Fig. 2. The signal f r o m the s e n s o r is fed through the amplifier Amp to the level control block LCB, which s p e c i fies the values of the upper and lower levels of cyclic s t r e s s e s . The initial setting of the specified level of s t r e s s e s is done manually with c o a r s e and fine adjustment p o t e n t i o m e t e r s placed on the front panel of the ins t r u m e n t for each level s e p a r a t e l y . Upon the signal reaching the set level, an impulse of c u r r e n t acting on the switching elements SE, which control operation of the force loading unit, is fed to the c o r r e s p o n d i n g internal s t o r a g e block IS. The internal storage blocks, using t r i g g e r circuits with s e p a r a t e potential-impulse inputs, maintain the c o r r e s p o n d i n g switching element in a definite position during the time of the whole half cycle of load actions. With a change in the direction of application of the load to the test object the r e v e r s e sign s t r e s s causes tripping of the c i r c u i t of the other specified level and switching of the element controlling loading. In the case of conWol of the hydraulic s y s t e m in loading by s t r e s s e s of a single sign a d i s p l a c e m e n t c o r responding to approximately half the specified range of load is delivered f r o m the p r o g r a m m e d control unit to the level control block. The c i r c u i t of the level control block is constructed on the principle of t r a n s i s t o r c o m p a r a t o r s in which the input signal f r o m the input unit IU is c o m p a r e d with a stable r e f e r e n c e voltage. The logic block LB p r e vents simultaneous tripping of both switching elements and f o r m s a command for the p r o g r a m m e d control unit PCU after the completion of each load cycle. The p r o g r a m m e d control unit has a p r o t e c t i o n and control block PCB which turns off the power to the f o r c e loading s y s t e m if the value of the effective s t r e s s or deformation exceeds a specified critical value. The block contains e l e m e n t s making it possible to m e a s u r e the stability of the power supply, the value of the signal supplied from the feedback s e n s o r , the direction of the f o r c e acting on the s t r u c t u r e being tested, and counting of the cycles. The p r o g r a m m e d control unit may operate with any type of s e n s o r having an e l e c t r i c a l output (displacem e n t induction s e n s o r s , e l e c t r o m a n o m e t e r s , t r a v e l and p r e s s u r e s e n s o r s , differential s e n s o r s , r e s i s t a n c e

610

s t r a i n g a u g e s , t h e r m o c o u p l e s , e t c . ) . They a r e connected through s p e c i a l inputs (broken l i n e s in F i g . 2). The unit is made in the f o r m of a d e s k - t o p i n s t r u m e n t , has convenient a d j u s t m e n t , and is d e s i g n e d f o r long c o n tinuous o p e r a t i o n . The s p e c i f i e d l e v e l of a l t e r n a t i n g s t r e s s e s w a s e s t a b l i s h e d in the following m a n n e r . T h r e e p a i r s of r e s i s t a n c e s t r a i n gauges with a b a s e of 20 m m c e m e n t e d to the Stiffening r i b s w e r e connected to a K-12-22 o s c i l l o g r a p h . A t l o a d s c o r r e s p o n d i n g to n o m i n a l s t r e s s e s of 150, 450, 550, and 750 kgf/cm 2 the s i g n a l s f r o m the s e n s o r s w e r e r e c o r d e d on p h o t o g r a p h i c p a p e r . In s t a t i c loading this is a s t r a i g h t line. In a c c o r d a n c e with the r e c o r d obtained in c y c l i c loading the l o w e r and u p p e r l e v e l s of s i g n a l s c o r r e s p o n d i n g to the s p e c i f i e d a l t e r n a t i n g s t r e s s e s a r e d e t e r m i n e d on the c o n t r o l l i n g i n s t r u m e n t . F u r t h e r control of the load is done a u t o m a t i c a l l y . S t a b i l i t y in the o p e r a t i o n of the unit is m e a s u r e d with a K - 1 2 - 2 2 o s c i l l o g r a p h . Each 2000 load c y c l e s a r e c o r d was made on p h o t o g r a p h i c p a p e r and it was c o m p a r e d with the d a t a of s t a t i c c a l i b r a t i o n . F i g u r e 3 shows the plan of c a l i b r a t i o n of the s y s t e m and the c h a r a c t e r of the load c y c l e . In c o n t r o l l i n g through the GA 46/3 t w o - s t a g e gate valve d i s t r i b u t o r , the load cycle is s a w - t o o t h shaped and the loading f r e quency in the t e s t s w a s 0.8-1.0 c y c l e s / s e c . Such a low l o a d i n g f r e q u e n c y was chosen as a r e s u l t of the fact that at 6-7 c y c l e s / s e c the t e s t stand b e c o m e s r e s o n a n t . A total of seven s t r u c t u r e s w e r e t e s t e d . The t e s t s c o n f i r m e d the e f f e c t i v e n e s s of the stand and the a d e quate a c c u r a c y of the loading and a u t o m a t i c c o n t r o l s y s t e m s . Steel w e l d e d s t r u c t u r e s w e r e a l s o fatigue t e s t e d on this stand in the range of s t r e s s e s of 400-2200 kgf/ cm 2. The unit d e s c r i b e d m a k e s it p o s s i b l e to f a t i g u e - t e s t l a r g e s t r u c t u r e s in constant sign loading with a load up to 00 tons.

USING

STRAIN M. A.

L. L.

GAUGES

Daichik, Polyakov,

IN A R E A C T O R

EXPERIMENT

Y u . G. L a k i n , a n d B. V . F e t i s o v

UDC 531.781.2:621.039

R e s u l t s a r e p r e s e n t e d in this w o r k f r o m a study of the i r r a d i a t i o n effect on the p r o p e r t i e s of t h e r m a l l y s t a b l e n i c k e l - m o l y b d e n u m N M P - 4 3 0 t e n s o r e s i s t o r s . T h i s type of t h e r m a l l y s t a b l e t e n s o r e s i s t o r (unique m a n u f a c t u r e d in s e r i e s ) w a s chosen for the study since t e m p e r a t u r e s 200-400~ a r e usual in i n t r a r e a c t o r e x periments. The following p r o p e r t i e s of the t e n s o r e s i s t o r s w e r e studied: s t a r t i n g e l e c t r i c a l r e s i s t a n c e , t e m p e r a t u r e c h a r a c t e r i s t i c , and the i n s u l a t i o n r e s i s t a n c e . It is known that the l a r g e s t e r r o r in using t e n s o r e s i s t o r s of the i n d i c a t e d type under r e a c t o r i r r a d i a t i o n conditions is due to the change in the s t a r t i n g e l e c t r i c a l r e s i s t a n c e of the t e n s o r e s i s t o r s which is r e l a t e d to the s t r u c t u r a l r e a r r a n g e m e n t of the alloy of the s t r a i n - s e n s i t i v e e l e m e n t under the action of the neutron flux [1, 2]. A study of the r e s i s t a n c e change in t e n s o r e s i s t o r s in d i f f e r e n t types of r e a c t o r s (IRT, I V V - 2 , TVR, and BR-5) showed that the c u r v e s for the change in r e s i s t a n c e as a function of the i n t e g r a l flux of the r a p i d n e u t r o n s (with e n e r g i e s En > 0.1 MeV) do not a g r e e , although the change in r e s i s t a n c e has a s i m i l a r m o n o t o n i c a l l y i n c r e a s i n g n a t u r e (Fig. 1). Since the r a d i a t i o n conditions ( e n e r g e t i c s p e c t r u m of the neutron flux, its d e n s i t y , and the r a d i a t i o n t e m p e r a t u r e ) have a combined effect on the change in e l e c t r i c a l r e s i s t a n c e of the t e n s o r e s i s t o r s , it is d i f f i c u l t to c o m p a r e r e s u l t s f r o m individual s t u d i e s and, c o n s e q u e n t l y , to use them when m e a s u r i n g s t r a i n s on f u l l - s c a l e o b j e c t s . In this connection an a t t e m p t was u n d e r t a k e n to p r e s e n t the e x p e r i m e n t a l r e s u l t s in the f o r m of a d e pendence on some g e n e r a l i z e d p a r a m e t e r which would m o s t c o m p l e t e l y c h a r a c t e r i z e the r a d i a t i o n conditions,

Moscow. T r a n s l a t e d f r o m P r o b l e m y P r o c h n o s t i , No. 5, pp. 117-119, May, 1978. O r i g i n a l a r t i cle s u b m i t t e d O c t o b e r 14, 1976.

0039-2316/78/1005-0611 807.50

9 1979 Plenum P u b l i s h i n g C o r p o r a t i o n

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