IE42575B1

IE42575B1 - Apparatus for testing or measuring deformation and fracture of test-pieces under multiaxial tension or compression

Info

Publication number: IE42575B1
Application number: IE86076A
Authority: IE
Inventors: C Albertini; M Forlani; U Buzzi; M Montagnani
Original assignee: Euratom
Priority date: 1975-04-24
Filing date: 1976-04-23
Publication date: 1980-09-10
Also published as: LU72357A1; DK185076A; FR2308927A1; BE840277A; DE2617656A1; IT1058135B; FR2308927B1; NL7604358A; IE42575L; GB1512614A

Abstract

1512614 Tri-axial testing EUROPEAN ATOMIC ENERGY COMMUNITY 20 April 1976 [24 April 1975] 15964/76 Heading G1S A test piece 5 is held by bars 3 to three adjacent faces of a cubic member 1, the three opposite faces being provided with three cylindrical blocks 15 each containing a chamber 10 filled with pressurized fluid and a chamber 12 filled with liquid 13 which acts on a piston 11 fixed on a rod 9 attached to the test piece. The rod 11' connects to means 14 for measuring the deformation and the chambers 10, 12 are fed with gas and fluid through ducts 23, 25. Discharge ducts 16 from chambers 12 are connected to a head 17 by a single duct 24, 22 and the liquid pressure is released by fracturing a diaphragm 19 so that if the pressures on each side of the pistons 11 are initially balanced, a tension is applied to the test piece 5. The rate of loading can be varied by selection of an orifice 21. The blocks 15 are reversible so that compression can be applied to one or more axes.

Description

This invention relates to apparatus for testing or measuring deformation and fracture of test-pieces under multiaxial tension or compression.

These tests are often necessary for simulating and 5 studying materials used under breakdown conditions and subjected to stresses and rapid deformation along a number of axes.

In their working environments the materials are stressed along a number of axes, sometimes under dynamic IO conditions.

Devices are known for studying fractures in testpieces produced by tension or compression, but they are generally limited to measurements in one direction.

There are theories based on single-axis tests, which extend the results to two or three-axis tests, but the calculations are only theoretical and approximate and frequently do not correspond with reality and require experimental checking, particularly in the case of tests under rapid dynamic conditions in the plastic domain.

The present invention relates to apparatus for producing simultaneously and measuring deformation and fracture along one, two or three axes at right angles.

The deformation can be obtained by tension and by compression to cover all practical possibilities. - 3 According to the present invention there is provided apparatus for testing or measuring deformation and fracture of test-pieces under multiaxial tension or compression which apparatus comprises a cubic member having an inner cavity for containing a test-piece coaxially disposed with respect to the axes of the cubic member, three adjacent faces of the cubic member being each provided with a means for holding the test-piece and the three opposite faces of the cubic member being each provided with a removable cylindrical block attached thereto, each cylindrical block containing a chamber which can be filled with a fluid under pressure and a cylindrical chamber which can be filled with liquid under pressure, each cylindrical chamber containing a piston secured at one end to a rod, the latter being attached to an extremity of the test-piece when the apparatus is in use, the piston also being secured, at the end remote from said rod, to a bar provided with means for measuring deformation, each block comprising individual ducts for supplying its chambers with fluid and liquid respectively, and discharge ducts from the cylindrical chambers connected by a single duct to common means for reducing the pressure of the liquid in the cylindrical chambers.

Preferably each of the cylindrical blocks can be attached in two positions wherein the relative positions of the two chambers about the piston are reversed, so that the force acting on the test-piece may be changed from tension to compression and vice versa. The deformation and fracture of the test-piece under compression may be obtained by reversing the fluid-liquid circuits and chambers. 43575 - 4 The pressure of the fluid in the fluid chamber and the pressure of the liquid in the cylindrical chamber may be varied. When the apparatus is in use and prior to stress being applied to the test-piece, each piston may be held in equilibrium by the pressures of the fluid and liquid acting on opposite surfaces of the piston.

Each piston may be movable in response to a reduced pressure on one of its surfaces. The common means for reducing the pressure of the liquid may comprise a fragile diaphragm which, upon breaking, produces a reduced pressure on one surface of the piston. Said means may further comprise a striker for breaking the diaphragm.

Each tension bar secured to the pistons may be provided with an extensometer for Use as a deformation transducer element. The invention will now be described, by way of example only, with reference to the accompanying drawings in which:Figure 1 shows the apparatus for testing fractures 20 due to tension only, and Figure 2 shows the adaptation of the apparatus for tests of fracture through compression.

In the two drawings like components bear like reference numerals.

The main body of the apparatus is a cubic member (1). 25 The stationary ends (2) of three securing bars (3) (for simplicity only two of the three bars are shown in the drawings) comprising deformation-measuring elements or strain gauges (not shown) are secured in three adjacent surfaces of the cube.

The other ends (7) of the bars (3) are secured to three ends (4) of a test-piece (5). For simplicity, the - 5 drawings show a cruciform test-piece which is adapted to be tested in two axes at right angles. However the testpiece has two further arms which extend in opposite directions at right angles to the plane of the drawings to one of which the third bar (3) is secured, thus enabling the test-piece to be tested in three axes at right angles to one another .

The other ends (6) of test-piece (5) are secured to the ends (8) of the tension bars (9), each of which extends through a chamber (10) of gas under pressure.

Each of the bars (9) is secured to a piston (11) which can move in a cylindrical chamber (12) which is filled with water or any other liquid (13). The piston (11) is secured to a shaft (11') which is provided with a motion transducer (14) at its end remote from bar (9).

The gas chamber (10), cylinder (12) and elements (11, 11* and 14) are disposed in a cylindrical block (15). A block (15) is provided for each of the three axes of the test-piece.

Each of the three blocks (15) has an inner duct (16) connecting chamber (12), which is filled with compressed water or other liquid up to a common head (17). The head (17) contains a striker (18) for producing a fracture of a fragile diaphragm (19). A disc (20) made for example of metal and formed with a calibrated orifice (21) is disposed at the end of duct (16) and near diaphragm (19). The three ducts (16) (only two are shown here) meet at 24 and are connected via duct (22) to the diaphragm (19).

Under equilibrium conditions, i.e. before the fracture test is initiated, the gas pressure in the chamber (10) via the supply duct (23) is equal to the - 6 pressure of the liquid (13) in cylinder (12). Ducts (23) are supplied by three different sources of gas, so that different rates of deformation and fracture can be obtained along different axes if required. The cylindrical chambers (12) are supplied via ducts (25).

When diaphragm (19) is broken by striker (18) there is a reduction in pressure in cylinders (12) and ducts (16), checked and adjusted by orifice (21), and the three pistons (11) consequently move away from the test-piece (Figure 1) thus subjecting the test-piece to tension along three axes simultaneously, the tensile force depending on the pressure in chamber (10).

Figure 2 shows the same apparatus in the position for operating by compression, i.e. in Figure 2 the test-piece is subjected to axial compression stresses, the apparatus being slightly modified.

By turning block 15 through 180° about an axis normal to its cylindrical axis, the positions of the gas chamber (10) and the liquid chamber (12) relative to the piston (11) , as shown in Figure 1, are reversed, as shown in Figure 2, so that the direction of the forces applied to the test-piece are reversed and the test-piece is subjected to compression instead of tension.

The apparatus can be used when the three blocks (15) are mounted for tests under either tension, as shown in Figure 1, or compression as shown in Figure 2. In addition, if blocks (15) are reversed alternatively, the test-piece can be simultaneously subjected to tension and compression stresses along different axes, thus working out all the six possible combinations of mixed tension and compression stresses along the three different axes. 2 5 7 5 The apparatus described above besides being suitable for simultaneous compression and tension tests on a single test-piece along different axes, can also be used to carry out the tests at a constant deformation speed or with a constant load if required, by charging liquid (13) in chamber (12) and duct (16).

If water or another liquid is substituted for the gas in chamber (10), and if the braking element of disc (20) is omitted, the pressure of the liquid in chambers lo (12) and ducts (16) rapidly decreases when the diaphragm is broken, resulting in a load on the test-piece corresponding to the pressure exerted by fluid (10) on piston (11).

The range of strain rates obtainable by the apparatus of this invention is very noteworthy, between 1 and 100 sec-1. If required, the acting force can be made different along different axes by varying the pressure of fluid, in the different chambers (10) and the deformation rate can be changed by varying the size of the orifice (21).

Since, in practice, materials are stressed along a number of axes, the diaphragm-breaking system and the convergence of ducts (16) at (24) enable the stresses to be exactly synchronised along different axes.

Claims

1. CLAIMS :1. Apparatus for testing or measuring deformation and fracture of test-pieces under multiaxial tension or compression which apparatus comprises a cubic member having an inner cavity for containing a test-piece coaxially disposed with respect to the axes of the cubic member, three adjacent faces of the cubic member being each provided with a means for holding the test-piece and the three opposite faces of the cubic member being each provided with a removable cylindrical block attached thereto, each cylindrical block containing a chamber which can be filled with a fluid under pressure and a cylindrical chamber which can be filled with liquid under pressure, each cylindrical chamber containing a piston secured at one end to a rod, the latter being attached to an extremity of the test-piece when the apparatus is in use, the piston also being secured, at the end remote from said rod, to a bar provided with means for measuring deformation, each block comprising individual ducts for supplying its chambers with fluid and liquid respectively, and discharge ducts from the cylindrical chambers connected by a single duct to common means for reducing the pressure of the liquid in the cylindrical chambers.

2. Apparatus as claimed in claim 1 wherein each of the cylindrical blocks can be attached in two positions wherein the relative positions of the two chambers about the piston are reversed.

3. Apparatus as claimed in claim 1 or claim 2 comprising means for varying the pressure of the liquid in the cylindrical chamber.

4. Apparatus as claimed in any one of claims 1 to 3 comprising means for varying the pressure of the fluid in the fluid chamber. 4 2 5 7 5 - 9 5. Apparatus as claimed in any one of Claims 1 to 4 wherein, when the apparatus is in use and prior to stress being applied to the test-piece, each piston is held in equilibrium by the pressures of the fluid and liquid acting

5. On opposite surfaces of the piston.

6. Apparatus as claimed in any one of Claims 1 to 5 wherein each bar has an extensometer for use as a deformation transducer element.

7. Apparatus as claimed in any one of the preceding 10 Claims wherein each piston is movable in response to a reduced pressure on one surface thereof.

8. Apparatus as claimed in any one of Claims 1 to 7 wherein the common means for reducing the pressure of the liquid comprises a fragile diaphragm which upon breaking 15 produces a reduced pressure on one surface of tho piston.

9. Apparatus as claimed in Claim 8 wherein the common means for reducing the pressure of the fluid further comprises a striker for breaking the diaphragm.

10. Apparatus for testing deformation and fracture 20 of test-pieces under tension or compression substantially as hereinbefore described with reference to and as shown in the accompanying drawings.