Load-extension Diagrams Research Articles

A New Apparatus for Studying the Elastic Properties of Filamentous Materials

A new apparatus is described with which it is possible to make load-extension diagrams for various filamentous materials. The principle of chainomatic weight application is used for the gradual application of reasonably heavy loads. An analogous construction can be used in a great many more instances where mercury or shot loading is used at the present. Load-extension diagrams have been taken with this instrument and the relations investigated with reference to the formation of hysteresis loops at various points of stress application and load removal. These hysteresis loops and stress-strain diagrams are characteristic for specific materials and are of assistance in their identification by physical methods. In addition to being of value from a physical and analytical viewpoint the investigation of the loading and deloading characteristics offers means of investigating the change of the physical characteristics of filamentous materials under conditions of controlled strain.

33—A NEW AUTOGRAPHIC LOAD-EXTENSION RECORDER

ABSTRACT A method is described of obtaining load-extension diagrams of textile yarns and fibres with constant rate of loading throughout each test, and giving diagrams in rectangular co-ordinates. The novel point in the method consists in the application of the load through a spiral spring by the rotation of a torsion-head at constant speed. Two instruments are described—one for threads of strength between 50 and 500 grams, and the other for filaments and hairs of strength below 20 grams.

Testing instruments for yarns and fibres

A ballistic instrument for measuring the work done in breaking a thread or bundie of filaments is described. The thread is mounted between two clamps, one of which is incorporated into a pendulum at its centre of percussion, the other rests on a ledge on the pendulum, the instrument being contrived so that this clamp is caught on fixed projections when the pendulum is at the lowest part of its swing. The energy absorbed in breaking a thread is measured in terms of the consequent decrease of the arc of swing of the pendulum after falling from a definite height. The extensometer described gives load-extension diagrams of single ultimate filaments of silk. Tensions on the filament under test produce torsions on a steel blade; these are recorded by the consequent deflections in a vertical plane of a beam of light which falls on a photographic film. The elongations of the filament corresponding to these tensions are proportional to the (corrected) horizontal movements of this film, which records load-extension diagrams with rectangular co-ordinates.

Recent developments in tensile testing

The study of the behaviour of metals on removal and re-application of load has been facilitated by the Dalby Autographic Load-Extension Recorders. Prof. Dalby has described these instruments and the specially designed, hydraulic press in which the tensile tests are carried out, and has shown that metal possesses elastic properties right up to fracture. Up to a certain limiting stress the extension is proportional to the applied load; when this stress is exceeded the metal loses its proportional elasticity but retains the property of non proportional elasticity. When the material has passed into the condition of non-proportional elasticity, the removal and re application of the load causes a loop to be traced in the recorded load-extension diagram. Looping is a general property of metals, and the loops obtained from different metals have distinguishing characteristics. Prof. Dalby has also shown that the loop area increases with permanent set, tending towards a maximum value, and that loop area plotted against permanent set gives a smooth curve. This will be referred to as the “normal curve” for a metal.

Societies and Academies

Societies and Academies

THE ELASTICITY AND TENSILE STRENGTH OF STARCH

Abstract The importance of starch in the sizing of cotton warps depends very largely on the tenacity with which it binds the hairs in the yarn together. Since it is very difficult to find a material to which starch paste does not adhere very firmly on drying, it is presumed that its value in sizing is mainly determined by the mechanical strength of the dried deposit of starch itself. Various pure starch pastes and mixtures containing the common sizing ingredients have therefore been evaporated to thin films on sheets of polished brass or ferrotype, and the tensile properties of these films have been studied by means of an apparatus which automatically drew their load—extension diagrams. The films were tested at 20°C, and at 34% and 66% relative humidities. The results show that a starch film behaves very much like a ductile metal, such as copper, on loading and unloading, and that there is scarcely any difference between the elastic properties of maize, farina and sago. In dry air, the films are harder an...

IV. Researches on the elastic properties and the plastic extension of metals

On March 7, 1912, I described an instrument which gives photographically a load-extension diagram of a metal test piece during the process of stretching it to fracture. On February 13, 1913, I described further experiments with the instrument. A diagram was shown which was taken from a test piece broken in ten seconds. It is safe to say that up to that time no apparatus existed which would give a complete record of the load-extension relation during such a quick break.

Societies and Academies

Societies and Academies

Load-extension diagrams taken with the optical load-extension indicator

This paper may be regarded as a continuation of that communicated in January, 1912, wherein I described a new optical apparatus by means of which it is possible to obtain load-extension diagrams free from the inertia effects of the parts of the testing machine in which the materials are strained and broken. The apparatus is automatic in its action and gives a true record of the physical properties of the materials. The curve corresponding to the straining and breaking of a specimen is drawn by means of a spot of light moving over a photographic plate placed in the camera which forms part of the instrument. There is no practical limit to the speed at which a diagram can be taken other than that imposed by the "rapidity" of the plate.

An optical load-extension indicator, together with some diagrams obtained therewith

The object of this paper is to describe an instrument by means of which load-extension diagrams of different materials may be obtained with precision, and to show some of the diagrams obtained therewith. The majority of machines for testing the strength of materials are fitted with apparatus for the purpose of obtaining automatically load-extension diagrams of the specimens tested. In a common form of the instrument the diagram is drawn by a pencil or tracing point on a sheet of paper wrapped round a drum. The pencil is constrained so that it is only free to move in a direction parallel to the axis of the drum. The instrument can be attached to the frame of the machine, or to a support external to the frame. The pencil receives a motion proportional to the extension of the specimen through the agency of a fine wire carried over guide pullers to clips fixed at a definite distance apart on the specimen, whilst simultaneously the drum receives an angular displacement proportional to the load applied to the specimen by means of a wire led over guide pullers and fastened to the jockey weight.