US3407651A - Tensile testing machine - Google Patents

Description

Oct. 29, 1968 Y. SOPHY TENSILE TESTING MACHINE Filed Aug. 30, 1966 United States Patent Office 3,407,651 Patented Oct. 29, 1968 3,407,651 TENSILE TESTING MACHINE Yvon Sophy, Saint-Maurice, France, assignor to Commissariat a IEnergie Atomique, Paris, France Filed Aug. 30, 1966, Ser. No. 576,142 Claims priority, applicatign France, Sept. 2, 1965,

30, 2 Claims. (Cl. 73-97) ABSTRACT OF THE DISCLOSURE The present invention is concerned with a tensile testing machine which makes it possible to apply a constant tractive force on a test-piece at a relatively very high rate of the order of 40 to 50 m./s. in particular.

It is known that conventional tensile testing machines which apply either hydraulic or electro-mechanical principles permit a working speed which is usually very low, namely either below or equal to 1 cm./s., higher speeds being permited only as a result of certain extrapolations but in any case not exceeding 1 m./s. In order to attain speeds of an even higher order, it is necessary to have recourse to other machines which operate on the principle of expansion of compressed gases, these gases being preferably produced by the combustion of an explosive powder. However, in the case just referred-to, a number of drawbacks must be taken into consideration. In the first place, the powder ignition time is substantial compared with the duration of the test, which makes it diflicult to ensure good synchronization of measurements. In the second place, the profile of the pressure curve as a function of time is a bell-shaped curve, the shape of which is very variable from one test to another in respect of a same weight of powder. Finally, when the pressure chamber inside which the combustion of powder takes place is connected to the atmosphere, both flamesand smoke are liable to hinder certain optical observations.

The aim of this invention is to overcome the disadvantages referred-to above and is accordingly concerned with a tensile testing machine which utilizes the expansion of a previously compressed gas, the initial instant of commencement of said expansion being controlled with high precision by the sudden rupture of a component by means of an explosive charge after the test-piece has been loaded.

Said tensile testing machine is characterized in that it comprises a stationary cylinder which is fitted internally with a movable piston, a piston-rod coupled to the extremity of a test-piece, a rigid head positionally adjustable relatively to said stationary cylinder and coupled to the other extremity of said test-piece, means whereby a compressed gas at variable pressure is admitted into said stationary cylinder on one face of said piston, frangible member which provides a temporary coupling between said movable piston and said stationary cylinder and which is adapted to fail by fast fracture initiated by explosive means.

Preferably, the frangible member which is adapted to fail by fast fracture is constituted by at least one coupling tube having a zone of lesser resistance which can be caused to fracture at a precise predetermined instant by firing an explosive charge. Advantageously, each coupling tube is enclosed within a demountable support bracket constructed in two sections respectively coupled to the movable piston and the stationary cylinder, vents being provided through said support bracket so as to permit the discharge of burnt gases after explosion of the charge.

In a preferred embodiment, the stationary cylinder comprises a hydraulic brake which absorbs the residual energy of the compressed gas at the end of travel of the movable piston, said brake being constituted by a second piston having a conical profile and adapted to deliver progressively a viscous fluid and especially oil into a low-pressure storage tank which is connected to said stationary cylinder. In addition, and in accordance with a further characteristic feature, the rigid head is provided for the positional adjustment thereof with a hand-wheel designed to cooperate with a screw which is rigidly fixed to said cylinder, said head being fitted with a detachable rod, the extremity of said rod being adapted 0t receive the test-piece. As a further adantageous feature, said rod can serve as a dynamometer by measuring its deformation. Finally, the means employed for admitting a compressed-gas pressure into the cylinder are preferably constituted by a compressor which may be associated with a motor pump and oil supply tank so as to increase the gas pressure within a chamber which communicates with said stationary cylinder.

All of the features outlined in the foregoing are preferably employed at the same time but could if necessary be employed independently and will in any case be more clearly brought out by the following description of one example of construction which is given solely by way of indication and not in any limiting sense, reference being had to the accompanying drawings, in which:

FIG. 1 is a diagrammatic sectional view of a tensile testing machine which is constructed in accordance with the invention;

FIG. 2 is a sectional view on a larger scale showing a detail of FIG. 1.

The machine which is shown in FIG. 1 essentially comprises a cylinder block 1 inside which is provided a chamber 2, a piston 4 mounted within said chamber, a pistonrod 5 provided with an extension in the form of a crosshead 6 on which is fixed one of the extremities of a metal test-piece 7 with a view to subjecting this latter to a high-speed tensile test. The other extremity of said testpiece 7 is secured by any suitable means to a detachable rod 8 which is in turn secured to a rigid head 9 placed above the cylinder block 1. The position of said head relatively to the cylinder block can be adjusted by means of a hand-wheel 10 forming a nut which is adapted to cooperate with a screw 11, the lower end 12 of which is rigidly secured to the cylinder block 1. by means of a fixing member 13.

In accordance with the invention, the crosshead 6 is coupled with the stationary cylinder 1 by means of a support bracket 14 which is secured to said cylinder by means of the screw 11, the coupling between said crosshead and said bracket being provided by two detonation tubes 15, one particular design of which is illustrated on a larger scale in FIG. 2. Each coupling or detonation tube comprises a body 16 of cylindrical shape having a necked central portion 17. As a preferable feature, the body 16 is formed of high-tensile steel in such a manner that the lower resistance of the portion 17 makes it possible to produce a clean fracture of the coupling tube at this point. The coupling tube is accordingly provided with a blindend bore 18 within which is introduced an explosive charge 19, then a detonator 20 which is connected by lead-wires such as the wire 21 to an electrical apparatus (not shown in the drawings) for the purpose of firing the detonator and instantaneously fracturing the coupling tube in its necked portion 17. The support bracket 14 is provided with vents for the discharge of burnt gases. The coupling tube 15 is secured at one end to the support 3 bracket 14 by means of a nut 22 and at the other end to the crosshead 6 by virtue of the threaded portion 23 of said tube.

The space 24 which is formed within the chamber 2 of the cylinder block 1 above the piston 4 communicates by way of a duct 25 with a vessel or bottle 26 and by way of a small duct 27 with a line 28 which is connected with interposition of a non-return valve 29 to a conventional compressor (not shown in the drawings). A neeedle valve 30 provides a connection between the bottle 26 and the duct 25 whilst a second small duct 31 or by-pass duct is fitted with a valve 32. The intended functiOn of said sec ond small duct is to permit the opening of the needle valve 30 without undue effort and generally to duplicate the connection just mentioned. A third valve 33 serves to connect the space 24 to the atmosphere whilst a gate-valve 52 serves to connect the vessel 26 to the atmosphere via the line 53.

The piston 4 also defines within the chamber 2 a space 34 within which is mounted a second piston 35, the end 36 of which has a slightly conical profile which enables said piston to perform the function of a hydraulic brake. With this object in view, the lower end of the chamber 2 is connected to a casing 37 which forms an extension of the cylinder block 1 and terminate in a tubular chamber 38 containing a given quantity 39 of a viscous damping fluid and especially oil. Provision is made above the oil level within the tubular chamber 38 for a gas cushion 40 which preferably consists of slightly compressed air, said gas being admitted through a line 41 fitted with gatevalves 42 and 43 and a relief-valve 44, the gas pressure being adjusted to a fairly low value which is controlled by means of a manometer 45. Finally, provision is made for a connecting-pipe 46 between the tubular chamber 38 and the space 34 of the cylinder 2 for the purpose of establishing pressure equilibrium and returning the damping piston 35 and the piston 4 to their initial positions as will become apparent hereinafter.

The equipment of the machine is completed by a motor pump set 48 of conventional design for delivering oil from a supply tank 49 through a pipe 50 to the lower end of the bottle 26, the level within this latter being measured and controlled by means of an apparatus 51.

The operation of the tensile testing machine as hereinabove described is as follows: the detonation tubes 15 having been placed in position in such a manner as to couple the crosshead 6 to the support bracket 14, the test-piece 7 is secured at one end to the crosshead 6 and at the other end to the rod 8, the position of which is adjusted together with the position of the head 9 by means of the hand-wheel 10. Once this operation has been completed, a compressed-gas or compressed-air pressure is admitted into the tubular chamber 38 via the pipe 41, said pressure being equal to approximately 1 bar. The gate-valve 43 is then closed, the pistons 4 and 35 being in the positions shown in FIG. 1. The pressure within the bottle 26 is regulated to a predetermined value which is equal to 200 bars at a maximum value. Once this pressure has been reached, the by-pass valve 32 and then the main valve 30 are opened, the pressure is exerted on that face of the piston 4 which is in contact with the space 24. At this moment, the firing of the detonation tubes 15 is triggered and the instantaneous rupture of said tubes is accordingly initiated. The pressurized gas contained in the cylinder block 1 expands and the piston 4 exerts a tensile stress on the test-piece with sufficient acceleration to 0b- Cit tain the desired speed (by way of example, in the case of a working stroke of the piston of approximately 50 millimeters, the speed obtained is of the order of 48 m./s.) At the end of travel, the piston 4 comes into contact with the second piston 35 which, by means of its conical portion 36, progressively drives the oil 39 back into the tubular chamber 38 through an orifice which becomes increasingly narrow until the speed is reduced to Zero.

In order to carry out a test under an even higher pressure, the mode of operation is initially similar to the process which has been described above, the pressure of the gas within the bottle 26 being set at the maximum value delivered by the compressor. The motor pump set 48 is then started up so as to deliver the oil contained in the supply tank 49 through the pipe 50 into the bottle 26 and thus to establish the new pressure which is desired. The machine then operates as in the condition previously described, the oil being returned to the supply tank 49 by means of a valve 47.

As is readily apparent, the invention is not limited to the mode of construction which has been described in the foregoing in reference to the accompanying drawings and which has been given solely by way of example.

What I claim is:

1. A high speed tensile testing machine for a test piece comprising a stationary cylinder block, a movable piston in said block, a piston rod coupled to said piston and to an extremity of the test piece, a rigid head carried by and positionally adjustable relative to said cylinder block and coupled to the other extremity of the test piece, means for admitting a compressed gas at variable pressure into said cylinder block on the face of said piston adjacent the test piece, a frangible member providing a temporary coupling between said piston and said cylinder block preventing movement of said piston by the compressed gas, said frangible member failing by fast fracture and comprising at least one coupling tube, said tube including a zone of lesser resistance, an explosive charge in said tube whereby said tube may be fractured at a predetermined instant by firing said explosive charge, a demountable support bracket on said cylinder block enclosing said tube, said tube being constructed in two sections respectively coupled to said piston and to said cylinder block and vents through said support bracket for discharge of burnt gases after explosion of the charge.

2. A tensile testing machine as described in claim 1, said cylinder block including a hydraulic brake absorbing the residual energy of the decompressed gas at the end of travel of said piston, said brake comprising a second piston with a conical profile and delivering progressively a viscous fluid into a low pressure storage tank connected to said cylinder block.

References Cited UNITED STATES PATENTS 3,057,190 lO/1962 Minke 73-89 3,102,421 9/1963 Cosner 73-97 3,142,980 8/1964 Andersen 73-97 3,218,847 11/1965 Starer et al. 7395 RICHARD C. QUEISSER, Primafy Examiner.

I. H. WILLIAMSON, Assistant Examiner.

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