Full resolution (JPEG) - On this page / på denna sida - Strength of Materials - Torsional strength
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
268 STRENGTH OF MATERIALS.
Therefore, if the constant corresponding to a load, which,
applied to an arm one foot long will twist off or destroy a bar
one inch in diameter, is found, the breaking load for any round
shaft of the same material when under torsional stress may be
easily calculated. The torsional strength (but not the torsional
deflection in degrees) is independent of the length of the shaft.
The strength depends only upon the kind and the amount of
material, and the form of cross-section. A square shaft having
its sides equal to the diameter of a round shaft will have ap-
proximately 20% more strength than the round one, but it will
take nearly 28% more material. A square shaft of the same
area as a round shaft has approximately 15% less torsional
strength than the round one.
Thus :
Formulas for torsional strength relating to solid round
shafts will be
P — n* D*
p
»=i
P 7/1
< = ^r
P = Breaking load in pounds.
D = Diameter of shaft in inches.
m = Length in feet of the arm on which load P is acting.
c = Constant, and it is the load in pounds which, when
applied to an arm one foot long, will twist off or destroy a round
bar one inch in diameter. This constant is obtained from ex-
periments, and is given in Table No. 32.
Rule.—Multiply the cube of the diameter in inches by the
constant c, in pounds, divide this product by the length of the
lever w, in feet, and the quotient is the breaking load in pounds.
TABLE No. 32.—Constant c.
The ultimate torsional strength in pounds of a round beam
one inch in diameter, when load is acting at the end of a lever
one foot long.
Material. Very Good. Medium Good. Poor.
Cast Steel
Machinery Steel* . , .
Wrought Iron ....
Cast-iron
2,000
1,200
800
525
1,000
1,100
580
450
600
700
500
350
* Machinery steel or wrought iron may not actually break at this load, but it
will deflect and yield so it will become useless.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
