Histories

Title Information
Applicant COURTAULDS LTD (GB)

Inventor GADD MICHAEL STEPHEN

Publication Date 1970-06-03

Int. Classification G01N3/04; G01N3/00;

European Classification G01N3/04

Application number GB19660044471 19661005

Priority number(s) GB19660044471 19661005

Also published as CH486019 (A)

GB F 4447166 A

PRS Code PS; PLNP

PRS Date 1970/10/14; 1974/05/01

Code Expl. + PATENT SEALED
- PATENT LAPSED THROUGH NONPAYMENT OF RENEWAL FEES






Title Information

INPADOC patent family
1 Tensile Testing Apparatus
Inventor: MICHAEL STEPHEN GADD (GB) Applicant: COURTAULDS LTD (GB) (BR)
EC: G01N3/04 IPC: G01N3/04;G01N3/00; (IPC1-7): G01N3/04
Publication info: CH486019 A - 1970-02-15
2 Tensile Testing Apparatus
Inventor: GADD MICHAEL STEPHEN Applicant: COURTAULDS LTD (GB) (BR)
EC: G01N3/04 IPC: G01N3/04;G01N3/00
Publication info: GB1193620 A - 1970-06-03



INPADOC patent family

List of citing documents



List of citing documents

Claims
**WARNING** start of CLMS field may overlap end of DESC **.

have a shape defined by the equation (1) but over that part the pressure between filament and the surface is constant.

This can be shown mathematically by consideration of the equation relating the tension in a filament wrapped about an angle9 of a bollard, with the tension(To) where8=00.

T=To e-l"e

The pressure (P) exerted by the filament on the surface of the bollard, at a point where the radius of curvature is r, is propor

T tional to-; this equation being obtained

r by resolving the tension in the filament into tangential and normal forces. In this embodiment of the invention, r=rO e- therefore

TOe-l'

Pe

r0e-0 from which equationeZ can be cancelled showing that the pressure exerted by the filament on the bollard is uniform at any point on their line of contact for a bollard of the shape defined.

A bollard having the ideal shape is difficult to machine accurately and an alternative curved surface which is quite satisfactory for most applications and can readily be machined is the polar curve defined by the equation:

r=r (l-AO) (2)

In this case the origin, from which the distancesr and r are measured to points on the curve, lies on the curve itself. This is accomplished by choosing the value of the constant

A tobe - which makes r=O when0=1800 r (i.e. r radians).

In this case the pressure between filaments and the bollard's surface actually increases slightly over the part of the surface conforming to the equation (2), but the tension in the filaments does not rise to the point where their premature fracture occurs.

Embodiments of the invention are shown, by way of example, in the drawing accompanying the provisional specification, both of the Figures of which are diagrammatic elevations.

In the Figures the end of a test length of a filament 1 is wrapped about part of the surface of a bollard 2 which is rigidly attached to a part of a tensile testing apparatus (not shown). The end of the filament is gripped between the bollard and a clamping member 3 which is urged towards the bollard by a screw 4 passing through a complementarily threaded part (not shown) also attached to the apparatus.

The difference between the Figures lies in the shapes of the bollards. That in Figure 1 has a curved surface corresponding to equation (1) whilst, that in Figure 2 corresponds to equation (2). In both of the Figures the dimensions r,r0 and 8 are shown.

For testing most yarns we have found that bollards shaped according to either Figure 1 or Figure 2 can be used satisfactorily with the value ofr0 as low asa '. The length of the yarns in contact with the bollards is thus shorter than on conventional equipment, leading to greater accuracy of results.

In a bollard where the shape of the curved part of its surface does not conform exactly to one of the polar curves defined by the equations (1) and (2), but the radius of curvature of the bollard's surface decreases in accordance with this invention, it will be appreciated that considerable advantages are still gained in the use of such a bollard because the pressure exerted by the filament on the bollard may be maintained at a higher level than hitherto over their area of contact. It is therefore possible to use a bollard which is smaller than necessary hitherto whilst considerably decreasing the risk of breakage of filaments at the clamps. With the use of a smaller bollard the accuracy of testing is increased because the test length of the filaments is more accurately known.

WHAT WE CLAIMIS:

1. A filament clamp for a tensile testing apparatus comprising a bollard around at least part of which a filament can be passed and a clamping member which can be moved towards the bollard for gripping a filament therebetween, at least a part of the surface of the bollard, between the point at which it is to be met by a filament passed over it, when in use in a tensile testing apparatus, and the point on the surface at which the clamping member can contact the filament for clamping it to the bollard, being a smooth curve having a radius of curvature decreasing in the direction towards the clamping member.

2. A filament clamp as claimed in claim 1, in which the radius of curvature of the bollard surface decreases smoothly from the point at which it is met by a filament passed over it when in use to the point at which it is met by the clamping member.

3. A filament clamp as claimed in claims 1 or 2, in which the part of the surface against which a filament is clamped by the clamping member is flat, this flat damping part being adjacent to the part of the surface having the smallest radius of curvature.

4. A filament clamp as claimed in claim

1, in which the part of the surface between the point at which it is to be met by a filament passed over it, when in use in a tensile testing apparatus, and the point on the surface at which the clamping member can contact the filament for clamping it to the bollard approximates to the polar curve defined by the equation:

r=rO e-8 where r, r,, P and 6 have the meanings ascribed in the specification.

5. A filament clamp as claimed in claim 1, in which the part of the surface between the point at which it is to be met by a filament passed over it, when in use in a tensile testing apparatus, and the point on the surface at which the clamping member can contact the filament for clamping it to the bollard approximates to the polar curve defined by the equation ~~~~~~~~~~~~~~~~~ r=rO (1-AO) where r,r0 and9 have the meaning ascribed in the specification and Aequals -.

Ir

6. A filament clamp for a tensile testing apparatus substantially as hereinbefore des-: cribed with reference to, and as illustratedin, the drawing accompanying the provisional specification.

7. Tensile testing apparatus comprising a pair offilament clamps as claimed in any of the preceding claims.





Claims

Description
COMPLETE SPECIFICATION

Tensile Testing Apparatus

We, COURTAULDS LIMITED, a BritishCom- pany, of 18, Hanover Square, London, W.1,

England, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the followingStatement:

This application relates to apparatus for determining the tensile properties of elongated articles, for example filaments, yarns, wires and the like, collectively referred to hereinafter as filaments.

To determine the tensile properties of a filament, each end of the gauge length of the filament is clamped in some way and the clamps are then moved apart until the filament breaks, when the length and load at breakage are measured. With a filament of high tensile strength the clamping force has to be very considerable to prevent the filament slipping in the clamps. However, the use of large clamping forces introduces the risk of damaging the filament by the clamps.

It has been proposed to use as a clamp a cylindrical bollard around which the filament may be wrapped in at least part of a turn so that the tension in the filament is reduced by friction in passing around the bollard to a point where it can safely be clamped between the bollard and a block which can be screwed up to the bollard.

However, the cylindrical bollards used hitherto suffer from the disadvantage that the radius of the bollard has to be relatively large to prevent a large tension differential across the width of the filament, which could lead to premature fracture, particularly around the point where the filament leaves the bollard and the tension is at its greatest. The use of a relatively large diameter bollard decreases the accuracy of the test result because of the slip of the filament over the bollard's surface and hence the indeterminate test length of the filament.

According to the present invention a filament clamp for a tensile testing apparatus comprises a bollard around at least part of which a filament can be passed and a clamping member which can be moved towards the bollard for gripping a filament therebetween, at least a part of the surface of the bollard, between the point at which it is to be met by a filament passed over it, when in use in a tensile testing apparatus, and the point on the surface at which the clamping member can contact the filament for clamping it to the bollard, being a smooth curve having a radius of curvature decreasing in the direction towards the clamping member.

Preferably the radius of curvature of the bollard surface decreases smoothly from the point at which it is met by a filament passed over it when in use to the point at which it is met by the clamping member. Preferably, the part of the surface against which a filament is clamped by the clamping member is flat, this flat clamping part being adjacent to the part of the surface having the smallest radius of curvature.

The ideal shape of the curved part of the surface of the bollard is the polar curve defined by the equation

r=rO e-l (1)

This equation defines a plane spiral,r0 being the radial distance of a first point on the spiral from the origin, r being a shorter radial distance from the origin to a second point on thespiral, ,a being the coefficient of friction between the filament and the surface, and 0 being the angle subtended at the origin by a line connecting the first and second points. Only a part of a bollard's surface can have a shape defined by the equation (1) but over that part the pressure between filament and the surface is constant.

This can be shown mathematically by consideration of the equation relating the tension in a filament wrapped about an angle9 of a bollard, with the tension(To) where8=00.

T=To e-l"e

The pressure (P) exerted by the filament on the surface of the bollard, at a point where the radius of curvature is r, is propor

T tional to-; this equation being obtained

r by resolving the tension in the filament into tangential and normal forces. In this embodiment of the invention, r=rO e- therefore

TOe-l'

Pe

r0e-0 from which equationeZ can be cancelled showing that the pressure exerted by the filament on the bollard is uniform at any point on their line of contact for a bollard of the shape defined.

A bollard having the ideal shape is difficult to machine accurately and an alternative curved surface which is quite satisfactory for most applications and can readily be machined is the polar curve defined by the equation:

r=r (l-AO) (2)

In this case the origin, from which the distancesr and r are measured to points on the curve, lies on the curve itself. This is accomplished by choosing the value of the constant

A tobe - which makes r=O when0=1800 r (i.e. r radians).

In this case the pressure between filaments and the bollard's surface actually increases slightly over the part of the surface conforming to the equation (2), but the tension in the filaments does not rise to the point where their premature fracture occurs.

Embodiments of the invention are shown, by way of example, in the drawing accompanying the provisional specification, both of the Figures of which are diagrammatic elevations.

In the Figures the end of a test length of a filament 1 is wrapped about part of the surface of a bollard 2 which is rigidly attached to a part of a tensile testing apparatus (not shown). The end of the filament is gripped between the bollard and a clamping member 3 which is urged towards the bollard by a screw 4 passing through a complementarily threaded part (not shown) also attached to the apparatus.

The difference between the Figures lies in the shapes of the bollards. That in Figure 1 has a curved surface corresponding to equation (1) whilst, that in Figure 2 corresponds to equation (2). In both of the Figures the dimensions r,r0 and 8 are shown.

For testing most yarns we have found that bollards shaped according to either Figure 1 or Figure 2 can be used satisfactorily with the value ofr0 as low asa '. The length of the yarns in contact with the bollards is thus shorter than on conventional equipment, leading to greater accuracy of results.

In a bollard where the shape of the curved part of its surface does not conform exactly to one of the polar curves defined by the equations (1) and (2), but the radius of curvature of the bollard's surface decreases in accordance with this invention, it will be appreciated that considerable advantages are still gained in the use of such a bollard because the pressure exerted by the filament on the bollard may be maintained at a higher level than hitherto over their area of contact. It is therefore possible to use a bollard which is smaller than necessary hitherto whilst considerably decreasing the risk of breakage of filaments at the clamps. With the use of a smaller bollard the accuracy of testing is increased because the test length of the filaments is more accurately known.

WHAT WE CLAIMIS:

1. A filament clamp for a tensile testing apparatus comprising a bollard around at least part of which a filament can be passed and a clamping member which can be moved towards the bollard for gripping a filament therebetween, at least a part of the surface of the bollard, between the point at which it is to be met by a filament passed over it, when in use in a tensile testing apparatus, and the point on the surface at which the clamping member can contact the filament for clamping it to the bollard, being a smooth curve having a radius of curvature decreasing in the direction towards the clamping member.

2. A filament clamp as claimed in claim 1, in which the radius of curvature of the bollard surface decreases smoothly from the point at which it is met by a filament passed over it when in use to the point at which it is met by the clamping member.

3. A filament clamp as claimed in claims 1 or 2, in which the part of the surface against which a filament is clamped by the clamping member is flat, this flat damping part being adjacent to the part of the surface having the smallest radius of curvature.

**WARNING** end of DESC field may overlap start of CLMS **.