WöHLER, AUGUST

(b. Soltau, Germany, 22 June 1819; d. Honnover, Germany, 21 March 1914)

material testing.

Wöhler came from a Protestant family from the small town of Soltau in the Luneburg Heath. His father, Georg Heinrich Wöhler, was a teacher at and rector of the local school, where Wöhler studied for a time. To encourage his mathematical gifts, the boy was sent to the technical college (which later became the Technische Hochschule) in Hannover, headed at the time by the technologist Karl Karmarsch. Having very successfully completed his studies with the aid of a scholarship, Wöhler began a short period of practical training. In 1840 he joined the Borsig engineering works in Berlin, where he gained practical experience in the construction of railway lines. After returning briefly to Hannover in 1843, he went to Belgium to learn how to operate a locomotive and then became an engineer on the first Hannoverian railroad (Hannover to Lehrte). In 1844 Wöhler was promoted to administrative engineer, and in 1847 he became chief superintendent of rolling stock on the Lower Silesia-Brandenburg Railroad (Berlin to Frankfurt-an-der-Oder to Breslau), which was taken over by the state in 1854. His brilliant work in this post was of lasting influence. In 1874 he was named imperial railway director and was placed on the newly created management board of the Imperial Railways in Strasbourg, on which he remained until 1889. His many awards included an honorary doctorate in engineering.

Wöhler’s important scientific achievements originated in the problems he encountered while working for the railroads. They consisted in the study and description of the dynamic strength of engineering materials and, more generally, in the creation of modern technique for testing materials.

In 1852 the Prussian minister of commerce, industry, and public works appointed Wöhler to a commission established to investigate the causes of axle breakage and train derailments. Wöhler’s first publications dealt with the theory of elasticity. In 1855 he derived the formulas for calculating the sag of lattice girders, commonly called the equation of three moments (Zeitschrift für Bauwesen, 5 , 122–166); these formulas were published two years before the work of Clapeyron, for whom they are often named. At the same time Wöhler recommended that bridge girders be supported at one end on roller bearings to absorb thermal expansion–a precaution that became universal practice.

Wöhler gained broad recognition through his fatigue bending tests, for which he constructed the experimental apparatus. In them the tested material, usually iron or steel, was subjected to a sequence of stresses that bent or turned it back and forth millions of times. Wöhler distinguished between static, increasing, and alternating loads; and he arrived at universally valid results, known as Wöhler’s laws. They can be understood from a consideration of the fatigue strength diagram, a curve that shows the dependence of the time strength of a given construction material on the number of load-application cycle borne. The first of Wöhler’s four laws states (in his formulation of 1870): “The failure of the material can . . . occur through constantly repeated vibrations, no single one of which reaches the absolute repture limit. The differences of the tensions, which frame the vibrations, are decisive for failure of cohesion” (Zeitschrift für Bauwesen, 20 , 83).

Wöhler’s results, illustrated by pieces broken in fatigue tests, were presented at the Paris Exposition in 1867, at which his work first came to the attention of the English (see Engineering, 2 [1867], 160). Also in 1867 Wöhler urged the “introduction of a government-approved classification for iron and steel” and the establishment of a government bureau for testing materials. These proposals were not implemented until sometime later, and then only gradually; but they greatly promoted the development of uniform quality in the manufacture of construction materials, as well as progress toward an “honest trade” in them.

BIBLIOGRAPHY

I. Original Works. A list of Wöhler’s writings is in R. Blaum, “August Wöhler” (see below). Between 1851 and 1898 Wöhler published 42 articles in German technical periodicals. The most important include “Theorie rechteckiger eiserner Brückenbalen mit Gitterwänden und mit Blechwänden,” in Zeitschrift für Bauwesen, 5 (1855), 122–166; “Resultate der in der Central-Werkstatt der Niederschlesisch-Märkischen Eisenbahn zu Frankfurt a. d. O. angestellten Versuche über die relative Festigkeit von Eisen, Stahl und Kupfer.” ibid., 16 (1866), 67–84; and “Über die Festigkeitsversuche mit Eisen und Stahl,” ibid., 20 (1870), 73–106.

II. Secondary Literature. See R. Blaum, “August Wöhler,” in Beiträge zur Geschichte der Technik und Industrie, 8 (1918) 35–55, with bibliography and portrait; and “August Wöhler,” in Deutsches biographisches jahrbuch, Überleitungsband I (Stuttgart, 1925), 103–107; F. G. Braune, “Zum 150. Geburtstag von August Wöhler, in Technik, 24 (1969), 400–402; A. J. Kennedy, “Fatigue Since Wöhler: A Century of Research,” in Engineering (London), 186 (1958), 781–782; L. Troske, “August Wöhler,” in Zentralblatt der Bauverwaltung,34 (1914), 242–244, with portrait and bibliography; and W. Ruske, “August Wöhler (1819–1914) zur 150. wiederkehr seines Geburtstages,” in Materialprüfung, 11 (1969), 181–188.

Ludolf Von Mackensen