Mechanical Engineering Design Notes

Design Contents

Preliminary Matters
Design Methodology
..brain storming
..evaluation matrix
Statistical Considerations
..variability in materials
..variability in dimensions
..variability in loading
.. preferred sizes
Design Factor
Introduction to Failure
Failure Theories
Stress Concentration
..and notch sensitivity
Failure Under Combined Loading
..combined bending and torsion
Failure Under Cyclic Loading
..fracture mechanics
Instability - Buckling
Concentrically Loaded Strut
..slender columns
..Euler formula
..effective length
..short and intermediate columns
Eccentrically Loaded Strut
.. theory
Shock Loading

Range of Materials
..performance indices
..ferrous metals
..alloying additions
..alloy and stainless steels
..tool steels
..aluminium alloys
..titanium alloys
..magnesium alloys

..bolts and bolted joints
..pre-load in bolts
..pre-load in bolts - example
..bolt ultimate strength calculator
..welds and welded joints

..forces acting
..curvature effect
..equations used for design
..materials and manufacture
..effective mass
..Java spring calculation applet with plot


..gear nomenclature
..gear box features
..friction belt drive
..hydraulics and pneumatics

Mechanisms and
4 stroke ICE thermodynamics

..engine mechanism and thermodynamics - applet
..engine mechanism - slider crank - velocity, acceleration diags. and torque, hand calculations

Bearings and Lubrication
..plain bearings
..viscous flow
..Petroff's law
..hydrodynamic bearing design
..computation of a journal bearing with hydrodynamic lubrication
..effects of variation of oil viscosity with temperature
..diagrams from computation results



Bolt Ultimate Strength Calculator

This section calculates the ultimate (beaking) load of ISO metric bolts with fine and coarse pitches using the same method as most published data. This uses the equations from ANSI B1 1-1974 and B18.3.1-1978 which calculates the area carrying the tensile load from the mean of the pitch diameter and the minor diameter.

The minor diameter is given by: dr = d - 1.226869p and the pitch diameter by dm = d - 0.649519p. A slightly different value will be obtained if the 'core' diameter values are used to calculate the tensile stress area.

Unless it is specified that the thread is 'fine pitch' it should be assumed that it is 'coarse pitch'.

The table below shows the pitches corresponding to fine and coarse threads for a range of bolt sizes.

Nominal diameter, mm Fine pitch, mm Coarse pitch, mm
3 n/a 0.5
3.5 n/a 0.6
4 n/a 0.7
5 n/a 0.8
6 n/a 1
7 n/a 1
8 1 1.25
10 1 1.5
12 1.5 1.75
14 1.5 2
16 1.5 2
18 1.5 2.5
20 1.5 2.5
22 1.5 2.5
24 2 3
27 2 3
30 2 3.5
33 2 3.5
36 3 4
39 3 4

Valid bolt grades to be entered in the box below are:

12.9 (alloy steel, quenched and tempered with a minimum UTS of 1220 MPa) or,

8.8 (carbon steel quenched and tempered or carbon steel with additions of boron or chromium or manganese, quenched and tempered) with a minimum UTS of 800 MPa (up to 16 mm diameter - the figures used in the calculations, although above 16 mm diameter 830 MPa UTS can be assumed).

Bolt diameter:
Thread pitch:
Bolt grade:

Answer (Bolt ultimate strength in N):

Return to Page on Bolted Joints.

David J Grieve. Revised: 27th January 2010. Original: 26th August 1999.

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