Expt 5(a) - Rotating Bending Fatigue Testing.pdf(2)

ME 218: SOLID MECHANICS LABORATORY

ROTATI N G BE N D I N G FAT IG U E T EST I N G EXPERIMENT NO.5(A)

BATCH: A8 07010042-07010046

R O T AT I N G B E N D I N G FAT I G U E TESTING EXPERIME NT NO.5 (A )

AIM

1. Study the effect of cantilever loading on standard rotating bending fatigue specimen. 2. To study the characteristics of S-N curve for ferrous materials. A PPA R A TU S 1. 2. 3.

Specimen vernier caliper. fatigue testing machine

PRO C ED UR E

The following procedure has been followed: 1. Measure the specimen dimensions most importantly the least diameter (d). 2. Initially adjust the load to zero position. 3. Load the specimen into the collet of machine spindle and check for runout at different locations. Adjust the specimen until required alignment and trueness is achieved. 4. Adjust the poise weight to known value of bending moment and lock it. 5. With the spindle revolving, adjust the cutoff switch as instructed. 6. Note down the value of bending moment applied and also the no. of stress cycle reached by specimen to failure and plot S-N curve.

O B SERVA TI O N S

The specimen we have taken is ENI (steel with 0.55% carbon) Diameter of specimen=6.38mm.

2

Applied load=110 kgf .cm. No. of cycles=17400 At N=103 , the value of S=0.9 Su. And at N=106, the value of S=0.9 Su.

C A L C U LA TI O N S

M = πSd3/32 M = 0.0982 Sd3 . Where, M = setting for poise weight in kg cm. S = desired bending stress level in specimen at minimum cross-section in MPa. d = diameter of specimen at minimum cross-section in cm. M=110 kg.f.cm d=6.38mm →S=423.14MPa Ultimate tensile strength of the specimen=720MPa log S=2.63 log N=4.24

3

G R A PH

log S vs log N 2.85

3, 2.81

2.8 2.75 2.7 2.65 2.6

6, 2.56

10, 2.56

15, 2.56

2.55 2.5 0

2

4

6

8

E R ROR C A LC U L A TIO N

Slope=2.81-2.56/(3-6)=-0.0833 Equation of line→y=-0.0833x+3.06 Theoretical value at (x=4.24) =2.70 Stress amplitude at x(=4.24) theoretical=501.18MPa Relative error=(501.18-423.14)/501.18=0.156

4

10

12

14

16

C O N C LU SI O N

Experimentally determined point is close to the theoretical value. No.of cycles are less than actual no.of cycles because stress is high enough for plastic deformation to occur, the account in terms of stress is less useful and the strain in the material offers a simpler description .

D E TA I L S O F TH E STU DE N TS

ROLL NUMBER

NAME

07010042

Repaka Jyoti Swaroop

07010043

Sharath Chandra Pawar

07010044

Puvvada N V Prudhvi Teja

07010045

J G M V Pramod

07010046

Vishnu Narayanan Suresh

5