GB2223854A

GB2223854A - System for interfacing test fixtures to dynamic test equipment

Info

Publication number: GB2223854A
Application number: GB8824089A
Authority: GB
Inventors: Peter Stewart Robison; Graham Douglass
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-10-14
Filing date: 1988-10-14
Publication date: 1990-04-18
Also published as: GB8824089D0

Abstract

An adaptor 6 integral with or fixed to dynamic test equipment 2 has a single large locating projection or aperture on which a test rig or fixture 3 with a single complementary mounting aperture or projection is secured. The dynamic test equipment may be an electrodynamic, hydraulic or other generator of shock, vibration or transient loading or an intermediate support such as a slip table or swing. As shown, the adaptor 6 is secured to test equipment 2 by an array of countersunk bolts and is provided with a single threaded projection 4 on which is screwed test rig or fixture 3. A conical interface 9 between adaptor 6 and fixture 3 reduces relative radial movement. The fixture 3 has a specimen mounted on it by a pattern of fasteners. The adaptor may have a threaded socket in which a threaded projection of fixture 3 is secured. Locking screws or clamps may be provided to prevent loosening of the joint between fixture 3 and adaptor 6. Instead of screws threads, a bayonet type connection may be used. Alternatively, a mechanical or fluid actuated clamp mounted on the adaptor 6 engages in a tapered recess in the base of fixture 3 to secure it in position. <IMAGE>

Description

SYSTEM FOR INTERFACING TEST FIXTURES TO DYNAJIIC TEST EQUIPMENT This invention relates to a system for interfacing a test fixture or rig to the table of an item of dynamic test equipment, or incorporation of the interfacing system features into the dynamic test equipment itself.

Dynamic equipment being any means of generating vibration, shock or transient loading.

r In order to perform dynamic tests upon specimens to prove either their structural integrity or performance under environmental conditions, it is necessary to mount the specimen in its correct attitude and configuration on the test equipment, such as an electrodynamic, hydraulic or other vibration generator, or any intermediate support such as a slip table or swing.

A fixture, rig, or head expander is bolted directly to the test equipment to provide either support for the specimen or enhancement of the test equipments own mounting area. This latter case arising when a larger or more specialist mounting area is necessary to accommodate the specimen and its supporting structure.

The presence of a test fixture reduces the available specimen payload or limits the performance of the test equipment, therefore making an optimised fixture design desirable. However the design and manufacture of the test fixture is greatly influenced by the necessity to incorporate the bolt pattern compatible with the mounting area of the dynamic test equipment.

According to the present invention there is a test fixture which embodies a single, large screw thread, or other locating feature such as interlocking lugs or clamps that enables the fixture to be mounted onto an adaptor plate, which is in turn fastened to the table of the dynamic test equipment. The adaptor plate and its fixture interface may be an actual extension of the dynamic test equipments reciprocating elements, in order to reduce mass and increase the available thrust.

This system allows a single fixture to be used on several different items of dynamic test equipment, either via adaptor plates for each machine or via a single adaptor plate accommodating the various mounting patterns.

Conversely several different fixtures incorporating the screw thread, or other locating feature such as interlocking lugs or clamps may be used at different times on the same piece of dynamic test equipment.

The contact area of the single large screw thread exceeds that afforded by a conventional pattern of fasteners, thus providing better transmission of the input forces to the specimen.

Eliminating the need to provide access for fasteners to attach the fixture to the test equipment table, allows a reduction in height and complexity of the fixture design. This not only improves transmissibility and reduces fixture weight, but also reduces movement at the specimen location in directions other than that specified for the test.

The specific embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 shows a schematic representation of a typical test arrangement; Figure 2 shows 2 cross-sectional view of a typical test arrangement employing an externally screw-threaded adaptor; Figure 3 shows a perspective view of an adaptor featuring an external sorew-thread; Figure 4 shows a cross-sectional view of typical test arrangement employing an internally screw-threaded adaptor; Figure 5 shows a perspective view of an adaptor featuring an internal screw-thread; Figures 6, 7 and 8 illustrate three methods of preventing unwinding of the fixture from the adaptor plate under the influence of the test loading; Figure 9 shows an internal clamping device that replaces the screw-thread;; Figure 10 shows a quick release lug that replaces the screw-thread.

Referring to the drawings the adaptor 1 is attached to a proprietory dynamic test equipment 2 via a compatible pattern of fasteners, or the adaptor 1 is an integral part of the dynamic test equipment 2. The fixture 3 is located on the adaptor via the large screw-threaded interface 4. Finally the specimen 5 (or specimen and additional fixturing) is mounted onto the fixture via a pattern of fasteners.

Figures 2 and 3 show an externally screw-threaded adaptor 6 with a pattern of counter bored clearance holes 7. This allows the fasteners corresponding to the dynamic test equipment mounting area to be recessed clear of the fixture.

A further embodiment of the adaptor employing an internal screwthread 8 is shown in Figures 4 and 5.

In order to prevent radial movement between the fixture and the adaptor, the main contact faces 9 could be tapered.

In order to prevent unscrewing of the fixture from the adaptor due to vibration when under test, a simple locking device 10 is incorporated.

The features described in the previous two paragraphs are necessary to achieve the most efficient transmission of the driving force from the dynamic test equipment through to the specimen.

As an alternative to the screw-threaded interface either an internal (or external) clamping device or lug system (figures 9 and 10 respectively) would allow a quick release capability. The clamping device being actuated by means of mechanical, gas or fluid systems.

Claims

1. A test fixture, rig or head expander which embodies a single, large screw-thread that enables the test fixture, rig or head expander to be mounted onto an adaptor plate, which is in turn fastened to the table of the dynamic test equipment used to apply the input forces.

2. A system as described in Claim 1 in which the adaptor features the screw-thread machined externally.

3. A system as described in Claim 1 in which the adaptor features the screw-thread machined internally.

4. A system as described in Claim 1 in which the screw-threaded adaptor is replaced by a clamping device (either internal or external), actuated by mechanical, gas or fluid means.

5. A system as described in Claim 1 in which the screw-threaded adaptor is replaced by a lug device.

6. An adaptor as described in Claims 1, 2 and 3 being machined to include fastener patterns suitable for more than one piece of dynamic test equipment.

7. The inclusion of tapered contact faces between the test fixture, rig or head expander and the adaptor as described in Claims 1, 2 and 3, in order to remove radial novenent between these to components.

8. A locking device in addition to Claims 1, 2, 3, 4 and 5 which prevents the test fixture, rig or head expander unwinding from the adaptor under the influence of vibration.

9. The adaptor plate as described in Claims 1, 2 and 3 is deleted, and the single, large screw-threaded interface is manufactured integral with the moving element of the dynamic test equipm & t.

10. The adaptor plate as described in Claims 4 and 5 is deleted, and the clamping device or lugs are manufactured integral with the moving element of the dynamic test equipment.