Dakota Ultrasonics MINI--MAX - Manual (Page 109)

MINI-MAX Ultrasonic Bolt Tension Monitor
103
load measurement will also be off by 5% proportionally. For a cylindrical bolt with
the same geometry, the area may be approximated as follows:
2
2
⎟
⎠
⎞
⎜
⎝
⎛
=
D
A
π
Area
D = minor diameter of the bolt, allowing for
threads.
For bolts with complex geometry, the areas should be estimated by averaging
each individual area and length. In the case of a hollow fastener, the area of the
hole must be subtracted from the overall area. The area of a fastener with
complex geometry can be estimated as follows:
∑
∑
=
L
AL
A
AVG
Average Area
A = Area of a region
L = Length of a region
The value for the Modulus of Elasticity, or Young’s Modulus, should be provided
directly from the manufacturer of the bolts.
E = Modulus of Elasticity of the Bolt Material From Manufacturer
The effective length is the average length of the fastener under stress when a load is
applied. For an applied constant load, the elongation of a fastener is directly
proportional to the effective length. Therefore, errors in the effective length will result in
load errors by a proportional amount. The effective length of a fastener is a combination
of the actual clamp length of the joint being fastened, plus that area of stress found in
the head, nut(s), and or blind hole of the fastener.