Many machine parts are exposed to the cyclic loading. It occurs
cyclic stress which can result in microcracks damage of a material.
If the stress is lower than the yield strength, damage cumulates
until the crack initiates and
resulting fast fracture. This process of cumulation during cyclic
loading is
called fatigue.

Fatigue and Failure of Machine
Parts

1. In 1829, he observed, studied and reported the failure of

iron

mine-hoist chains arising from repeated small loadings,

the first recorded account of metal fatigue. He built a machine
which repeatedly loaded a chain. His finding was that fatigue
was not associated with an accidental overload, but was
dependent on load and the number of repetitions of load
cycles.

He invented a twisted steel

cable

, later known as an "Albert

Rope", which was first used in the Clausthal Caroline mine in

1834 and was the forerunner of the modern

wire rope

.

Wilhelm August Julius

Albert (1787 – 1846)

Jean Victor Poncelet

(1788-1867)

 

   

        

       

2.

French

engineer

and

mathematician

who served most notably as the

commandant general of the

École Polytechnique

. As a military engineer,

he served in

Napoleon

's campaign against the

Russian Empire

in 1812, in

which he was captured and held prisoner until 1814. Later, he served as a

professor

of

mechanics

at the École d’Application in his home town of

Metz

, during which time he published Introduction à la mécanique

industrielle, a work he is famous for, and improved the design of

turbines

and

water wheels

. After this

,

he served as professor at the

Faculté des

Sciences

at the

University of Paris

, and finally as the commandant general

of his alma mater, the École Polytechnique.

[1]

(1822) Traité des propriétés projectives des figures
(1826) Cours de mécanique appliqué aux machines
(1829) Introduction à la mécanique industrielle
(1862/64) Applications d'analyse et de géométrie

In 1829 he used the term fatigue for the first time.

Rankine was one of the first engineers to recognise that

fatigue

failures of railway axles was caused by the initiation and growth of
brittle cracks. In the early 1840s he examined many broken axles,
especially after the

Versailles train crash

of 1842 when a locomotive

axle suddenly fractured and led to the death of over 50 passengers.
He showed that the axles had failed by progressive growth of a brittle
crack from a shoulder or other

stress concentration

source on the

shaft, such as a

keyway

. He was supported by similar direct analysis of

failed axles by

Joseph Glynn

, where the axles failed by slow growth of

a brittle crack in a process now known as

metal fatigue

. It was likely

that the front axle of one of the locomotives involved in the

Versailles

train crash

failed in a similar way. Rankine presented his conclusions in

a paper delivered to the Institution of Civil Engineers. His work was
ignored however, by many engineers who persisted in believing that
stress could cause "re-crystallisation" of the metal, a myth which has
persisted even to recent times. The theory of recrystallisation was
quite wrong, and inhibited worthwhile research until the work of

William Fairbairn

a few years later, which showed the weakening effect

of repeated flexure on large beams. Nevertheless, fatigue remained a
serious and poorly understood phenomenon, and was the root cause
of many accidents on the railways and elsewhere. It is still a serious
problem, but at least is much better understood today, and so can be
prevented by careful design.

William John

Macquorne

Rankine

(1820 – (1872)

August Wöhler (22 June 1819 - 21 March 1914) was a

German

engineer

, best remembered for his systematic investigations of

metal fatigue

.

Born in the town of

Soltau

, the son of local

teacher

Georg Heinrich

Wöhler showed early mathematical ability and won a

scholarship

to

study at the Technische Hochschule in

Hannover

, under the direction

of

Karl Karmarsch

.

In 1840, he was recruited to the

Borsig

works in

Berlin

where he

worked on the manufacture of

rail tracks

. In 1843, after a brief stay

in Hannover, he started to receive instruction in

locomotive

driving in

Belgium

, returning as an engineer on the Hannover to

Lehrte

line. By

1847, Wöhler was chief superintendent of

rolling stock

on the Lower

Silesia-Brandenberg Railroad. His growing reputation led to his

appointment in 1852 by the

Prussian

minister of commerce to

investigate the causes of

fracture

in railroad

axles

, work that was to

occupy Wöhler over the next two decades.

The railroad was

nationalised

in 1854

and the recognition of his keen
administration and technical
leadership resulted in his appointment
as director of the newly formed

Imperial Railways

, based at the

board's headquarters in

Strasbourg

, a

post he held until his retirement in
1889.
Wöhler started his axle investigations
by research into the theory of

elasticity

and was led, in 1855, to a

method for predicting the deflection
of

lattice beams

that anticipated the

work of Émile Clapeyron1. He also
introduced the practice of supporting
one end of a bridge on roller bearings
to allow for thermal expansion.