IE902483A1 - A dynamic torsion test device for a sample - Google Patents

Abstract

The invention relates to a testing device comprising, in axial alignment - a generator (5) capable of creating at least one torsional force, - a bar (7) transmitting this force from the generator to the specimen (1) coupled to the end of the bar, - a locking device (8) capable of rapidly locking and releasing the said bar, this device being applied to the bar (7) at a point located between the specimen (1) and the generator (5). According to the invention, there is provided, between the said bar (7) and the specimen (1), a member (9) for favoured transmission of traverse waves, this member comprising - a cylindrical core (11) made from a metal of moderate elastic modulus, and equipped with flanges (13, 16) at the two ends, - a plurality of fibres (12), which helically surround the core (11), are parallel to each other and which are fixed to the two flanges (13, 16) in a stretched manner and which have an elastic modulus substantially higher than the core (11).

Description

The invention relates to a dynamic torsion test device for a sample, comprising in axial alignment - a generator apt to create at least a torsion force,, - a bar transmitting this force from the generator to the sample which is coupled to the end of the bar, - a blocking device apt to block and to abruptly release said bar, this device being applied to the bar at a point situated between the sample and the generator.

A traction test device is known from the publication Institute of Physics Conference Series N° 21, 1974, pages 22 to 30. It actually shows a traction force generator constituted by a differential screw and coupled to one end of a first bar, the other end of which is connected to a second bar via the sample. A blocking device which permits to block and to abruptly free this bar on command is situated at an intermediate point between the sample and said generator. Strain gauge means are disposed between this blocking device and the sample on the one hand, and between the sample and the free end of the second bar on the other hand.

During functioning, the first bar is loaded in traction by the generator and then the blocking device is abruptly released, which makes a traction wave propagate along the first bar from this device towards the sample. The measurement means such as a strain gauge are placed on the two bars on either side of the sample for measuring the force to which the sample has been submitted up to the breaking point .

Such a device is not suited for the study of the effects which the torsion exerts in a sample. In fact, when a torsion generIE 902483 - 2 ator instead of a traction generator loads the first bar up to the torsion blocking device and when the blocking device is then released, it can be observed that a great part of the torsion energy stored in the first bar changes into traction, this force propagating at a speed which is substantially higher than the transversal wave or the torsion wave. Prior to the arrival of the transversal wave, the sample is thus submitted to a traction stress which precedes the transversal wave and this all the more as the sample is at a distance to the blocking device. In order to reduce this phenomenon, the sample would thus have to be approached to the blocking device, but this approach is limited, since generally a strain measurement device has to be placed between the sample and the blocking device .

The invention thus aims at conceiving a dynamic torsion test device permitting to enlargen the test variations and in particular to submit the sample to a torsion force which precedes any traction force.

This aim is achieved by the device such as defined above, which is wherein between said bar and the sample an element for the privileged transmission of transversal waves is provided, this element comprising: - a cylindrical core made of a metal with a moderated elasticity module and supplied with flanges on both ends, - a plurality of fibers which surround the core helically and parallelly to each other, which are secured to the two flanges in a tight way and which present an elasticity module which is substantially higher than that of the core.

As to a preferred embodiment of the invention, and in particular to its element for the privileged transmission of transversal waves, reference is made to the sub-claims. - 3 The invention will now be described more in detail by means of a preferred embodiment, and the annexed drawings.

Figure 1 shows schematically a test device according to the 5 invent ion .

Figure device 2 shows a partially cut view of an element used in the according to figure 1. 10 Figure f igure 3 shows a 1 . sample to be used in the device according to The device shown in figure 1 serves to submit a sample 1 to static and dynamic traction and torsion tests, the sequence of the different strains being selected by the operator.

The sample serving for the test is constituted, as can be seen more clearly in figure 3, by a cylinder 2 with an outer diameter D which is axially followed by a tube 3 the inner diameter D' of which is larger than D. The tube 3 and the cylinder 2 are made of a single piece, and the transition zone 4 between the cylinder and the tube constitutes the real test zone.

Traction and torsion forces for the dynamic test are en- gendered by a generator 5, which is connected to the samp] e 1. 2 5 by an energy storing bar 7 and an element 9 for the privileg- ed transmission of traction forces. Near its right end in figure 1, the bar 7 traverses a blocking device 8 which is conceived to block the bar and to release it on command from an operator. This device can be of the type described and shown in the document Institute of Physics Conference Series cited above .

The cylinder 2 of the sample is fixed to another bar 7', which finally terminates in another traction and/or torsion force generator 6 serving to impart static forces onto the sample.

All the elements mentioned are aligned according to a common axis 10.

Finally., two biaxial strain gauges 14 and 15 are schematically 5 shown in figure 1, which are applied against the two bars 7 and 7' at a distance from the sample 1.

The different elements of the device are aligned according to a common axis 10 and are fixed to each other by screwing, welding or bolting.

An essential element of the device according to the invention is the element 9 for the privileged transmission of transversal waves, which is shown in detail in figure 2. It is com15 posed of a cylindrical and tubular core 11, made of a metal with a moderate elasticity module and provided with two flanges 13 and 16 at its two ends, and with a plurality of fibers 12 which surround this core helically and parallelly to each other and which are fixed to the two flanges 13 and 16. These fibers are made of a metal with an elasticity module which is substantially higher than that of the core, if, for example, the core is made of aluminum., the fibers are on the basis of molybdenum, osmium or rhenium.

One of the flanges, 13, is an integral part of the core 11. whereas the other flange, 16, constitutes a nut which is screwed on a thread of the core 11. This flange 16 is fixed either by a counter-nut (not shown) or by welding. The thread 17 can also serve for coupling the sample 1 when the latter comprises a corresponding inner thread.

The propagation speed of a mechanical wave is porportional to the root of the elasticity module of the material. Due to the elasticity module of the fibers 12 which is very high with respect to the core 11, a transversal wave originated by a - 5 torsional pre-stressing of the bar 7 is released by the blocking device 8 and it is at once transmitted by the fibers 12 to the flange 16 and thus to the sample 1. Even if the release of the blocking device 8 has, in surplus, caused, a longitudinal wave to travel towards the sample 1, the transversal wave succeeds in overtaking the longitudinal wave in the element 9. By suitably selecting the length of the element 9 and the spiral pitch of the fibers 12, the sample can be submitted to any strain history, and, in particular, the zone 4 of the sample can be submitted, in a dynamic test, either to simultaneous traction and torsion stresses, or to a succession of traction and torsion stresses, or to a succession of torsion and traction stresses. The invention thus offers to the searcher any liberty to establish a stress history.

The invention is not limited to the embodiment described above. Without leaving the scope of the invention, an element 9 with a full or tubular core can be chosen, and several blocking devices such as 8 can be provided along the bar 7, thus permitting to impart pre-stresses differing from one section to the other and to discharge the different, pre-stresses successively onto the sample.

Further, one can choose for the core on the one hand and the fibers on the other hand materials the elasticity modules of which are even more distant from each other than those of steel and aluminum are from molybdenum, osmium and rhenium.

Claims (5)

1. A dynamic torsion test device for a sample, comprising in axial alignment 5 - a generator apt to create at least a torsion force, - a bar transmitting this force from the generator to the sample which is coupled to the end of the bar, - a blocking device apt to block and to abruptly release said bar, this device being applied to the bar at a point situated 10 between the sample and the generator, wherein between said bar and the sample an element for privileged transmission of transversal waves is provided, this element comprising - a cylindrical core made of a metal with a moderate elasticity module, and provided with flanges on both ends, 15 - a plurality of fibers which surround the core helically and parallelly to each other, which are secured to the two flanges in a tight fashion and which present an elasticity module which is substantially higher than that of the core. 20

2. A device according to claim 1, wherein one of the flanges is an integral part of the core, whereas the other flange constitutes a nut which is screwed onto a thread of the core.

3. A device according to one of the preceding claims, wherein 25 the fibers are secured to the cylindrical core over at least part of their length between the flanges, for example by welding or gluing.

4. A device according to one of the preceding claims, wherein 30 the core is made of a metal on the basis of steel or aluminium . 5. A device according to one of the preceding claims, wherein the fibers are made of a metal on the basis of molybdenum, 35 osmium or rhenium. 6. A device according to one of the preceding claims, wherein said core is of tubular shape.

5. 7. A device as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.