GB2068557A

GB2068557A - Deflection testing

Info

Publication number: GB2068557A
Application number: GB8002645A
Authority: GB
Original assignee: SONTRIN ENG SALES Ltd
Current assignee: SONTRIN ENG SALES Ltd
Priority date: 1980-01-25
Filing date: 1980-01-25
Publication date: 1981-08-12

Abstract

A method of deflection testing a member, comprises applying a load, gradually increasing towards a predetermined maximum, at a point intermediate of two support positions of a member to be tested and electrically/electronically measuring the load and deflection of the member at or adjacent the point at which the load is applied. The apparatus comprises means for carrying out each of these steps. <IMAGE>

Description

SPECIFICATION Improvements in or relating to deflection testing This invention relates to a method of and apparatus for deflection testing and is particularly, but not exclusively, concerned with stress grading of timber.

In recent times, there has been a marked increase in demand for stress graded timber for use in structural locations, for example, roof and floor joists and trussed rafters in the Timber and Building Industry. This is causing a number of problems, mainly due to the fact that, as engineering members, the timber in structural locations requires to be very carefully stress graded. This means that large quantities of selected material, normally in a range of sizes from 38 x 75 mm to 38 x 225 mm and from 75 x 75 mm to 75 x 225 mm are required. One of the present methods of stress grading is a visual method. However, visual grading is uneconomic both as regards man-hours and materials, since, for example, the visual grading rules were not designed for these relatively small and thin sections of timber, but were formulated for grading any size of timber member.Also used to a limited extent is a purely mechanical method of measuring.

It is an object of the present invention to provide a method of and apparatus for inexpensively testing materiais such as timber.

According to one aspect of the present invention there is provided a method of deflection testing a member, which comprises applying a load, gradually increasing towards a predetermined maximum, at a point intermediate of two support positions of a member to be tested and electrically/electronically measuring the load and deflection of the member at or adjacent the point at which the load is applied. If the measured deflection exceeds a predetermined value, the force is to be released to avoid excess strain on the member. If the measured deflection is less than a predetermined value at the maximum force, the member has a stress grading at least as high as the stress grading corresponding to the maximum loading with the fuli predetermined deflection figure at the particular spacing of the supports, for a given size of member.

According to a preferred embodiment of the present invention, the measuring in the method defined in the preceding paragraph is effected by a slider of a rectilinear potentiometer being moved with the load applying means. The load is preferably applied pneumatically.

According to a further aspect of the present invention there is provided a device for deflection testing a member, which comprises means for supporting a member to be tested at two support positions, means for applying a load, gradually increasing towards a predetermined maximum, on the member to be tested intermediate of the two support positions, and means for electrically/electronically measuring the deflection of the member at or adjacent the point at which the load is applied. Preferably, the measuring means comprises a slide of a rectilinear potentiometer movable with the load applying means so as to provide an indication of the deflection on deflection indicating means.

Normally, the load is applied by a pneumatic cylinder, actuated by a microswitch on each support member, automatically operated when the member to be tested is placed thereon. It follows, therefore, that until the member to be tested is in the correct position, the loading cylinder will not operate. The ram of the pneumatic cylinder is, for example, provided with a protruding microswitch or electronic sensor to sense the exact position that the face of the ram meets the member being tested. In this manner, the ram can "sense" the position of the member to be tested even if the member is cambered in either direction and accordingly camber of the member does not effect the deflection measurement. The further movement forward of the ram is then measured using a slide on a rectilinear potentiometer.If the predetermined deflection is reached or exceeded, an alarm can be operated and the air shut off and vented from the loading cylinder. If, for example, timber was being tested, this would prevent destruction of the timber, although the same would be rejected as having failed to withstand the predetermined load without deflection of the precalcuiated amount, which depends on the distance between the supports and thickness and size of the timber and the stress grading to be tested for. If the maximum load is exerted on the timber and the deflection does not reach the predetermined value, the timber has passed the test and accordingly may be marked as such. Suitable marking means are preferably actuated on the completion of a fixed load exertion time to mark the timber while the load is decreasing but while the timber is still under load.If the timber fails the test, a cut out is provided to stop the marker being actuated.

Suitable marking means are, for example, variable-head branding irons and ink-markers. On release of the load, the timber or other member being tested is removed from the supports, whereupon another test can be commenced. The load applied is conveniently measured by a load cell.

Whilst the invention is particularly concerned with non-destructive testing of timber, the same could also be used for non-destructive testing of, for example, high density plastics material members and also, for example, for the destructive testing of members to find the actual breaking load of said members.

The accompanying drawing shows a perspective view of an embodiment of a device for deflection testing a member in accordance with the present invention.

1. A method of deflection testing a member, which comprises applying a load, gradually

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in or relating to deflection testing This invention relates to a method of and apparatus for deflection testing and is particularly, but not exclusively, concerned with stress grading of timber. In recent times, there has been a marked increase in demand for stress graded timber for use in structural locations, for example, roof and floor joists and trussed rafters in the Timber and Building Industry. This is causing a number of problems, mainly due to the fact that, as engineering members, the timber in structural locations requires to be very carefully stress graded. This means that large quantities of selected material, normally in a range of sizes from 38 x 75 mm to 38 x 225 mm and from 75 x 75 mm to 75 x 225 mm are required. One of the present methods of stress grading is a visual method. However, visual grading is uneconomic both as regards man-hours and materials, since, for example, the visual grading rules were not designed for these relatively small and thin sections of timber, but were formulated for grading any size of timber member.Also used to a limited extent is a purely mechanical method of measuring. It is an object of the present invention to provide a method of and apparatus for inexpensively testing materiais such as timber. According to one aspect of the present invention there is provided a method of deflection testing a member, which comprises applying a load, gradually increasing towards a predetermined maximum, at a point intermediate of two support positions of a member to be tested and electrically/electronically measuring the load and deflection of the member at or adjacent the point at which the load is applied. If the measured deflection exceeds a predetermined value, the force is to be released to avoid excess strain on the member. If the measured deflection is less than a predetermined value at the maximum force, the member has a stress grading at least as high as the stress grading corresponding to the maximum loading with the fuli predetermined deflection figure at the particular spacing of the supports, for a given size of member. According to a preferred embodiment of the present invention, the measuring in the method defined in the preceding paragraph is effected by a slider of a rectilinear potentiometer being moved with the load applying means. The load is preferably applied pneumatically. According to a further aspect of the present invention there is provided a device for deflection testing a member, which comprises means for supporting a member to be tested at two support positions, means for applying a load, gradually increasing towards a predetermined maximum, on the member to be tested intermediate of the two support positions, and means for electrically/electronically measuring the deflection of the member at or adjacent the point at which the load is applied. Preferably, the measuring means comprises a slide of a rectilinear potentiometer movable with the load applying means so as to provide an indication of the deflection on deflection indicating means. Normally, the load is applied by a pneumatic cylinder, actuated by a microswitch on each support member, automatically operated when the member to be tested is placed thereon. It follows, therefore, that until the member to be tested is in the correct position, the loading cylinder will not operate. The ram of the pneumatic cylinder is, for example, provided with a protruding microswitch or electronic sensor to sense the exact position that the face of the ram meets the member being tested. In this manner, the ram can "sense" the position of the member to be tested even if the member is cambered in either direction and accordingly camber of the member does not effect the deflection measurement. The further movement forward of the ram is then measured using a slide on a rectilinear potentiometer.If the predetermined deflection is reached or exceeded, an alarm can be operated and the air shut off and vented from the loading cylinder. If, for example, timber was being tested, this would prevent destruction of the timber, although the same would be rejected as having failed to withstand the predetermined load without deflection of the precalcuiated amount, which depends on the distance between the supports and thickness and size of the timber and the stress grading to be tested for. If the maximum load is exerted on the timber and the deflection does not reach the predetermined value, the timber has passed the test and accordingly may be marked as such. Suitable marking means are preferably actuated on the completion of a fixed load exertion time to mark the timber while the load is decreasing but while the timber is still under load.If the timber fails the test, a cut out is provided to stop the marker being actuated. Suitable marking means are, for example, variable-head branding irons and ink-markers. On release of the load, the timber or other member being tested is removed from the supports, whereupon another test can be commenced. The load applied is conveniently measured by a load cell. Whilst the invention is particularly concerned with non-destructive testing of timber, the same could also be used for non-destructive testing of, for example, high density plastics material members and also, for example, for the destructive testing of members to find the actual breaking load of said members. The accompanying drawing shows a perspective view of an embodiment of a device for deflection testing a member in accordance with the present invention. CLAIMS

1. A method of deflection testing a member, which comprises applying a load, gradually increasing towards a predetermined maximum, at a point intermediate of two support positions of a member to be tested and electrically/electronically measuring the load and deflection of the member at or adjacent the point at which the load is applied.

2. A method according to Claim 1, wherein the measuring is responsive to application of the load on the member.

3. A method according to Claim 1 or 2, wherein the measuring is effected through the intermediary of a slide of a rectilinear potentiometer moving with the means applying the load so asto provide an indication of the deflection.

4. A method according to any one of the preceding claims, wherein the load is applied pneumatically and monitored electronically.

5. A method according to any one of the preceding claims, wherein, if the deflection reaches a predetermined maximum, the load is automatically released.

6. A method according to any one of the preceding claims, wherein the member is marked to show that the same attained a particular stress grading.

7. A method according to Claim 6, wherein the markings are effected with an electrically operable branding iron.

8. A device for deflection testing a member, which comprises means for supporting a member to be tested at two support positions, means for applying a load, gradually increasing towards a predetermined maximum, on the member to be tested intermediate of the two support positions, and means for electrically/electronically measuring the deflection of the member at or adjacent the point at which the load is applied.

9. A device according to Claim 8, wherein the measuring means is responsive to pplication of the load applying means on the member.

10. A device according to Claim 8 or 9, wherein the measuring means comprises a slide of a rectilinear potentiometer movable with the load applying means so as to provide an indication of the deflection on deflection indicating means.

11. A device according to any of Claims 8 to 10, wherein the load applying means is pneumatically operable.

12. A device according to any one of Claims 8 to 11, wherein means are provided whereby, if the deflection reaches a predetermined maximum, the load applying means is automatically rendered inoperative.

13. A device according to any one of Claims 8 to 12, wherein marking means are provided which are capable of marking a member to show that the same attained a particular stress grading.

14. A device according to Claim 13, wherein the marking means comprises an electrically operable branding iron.

1 5. A member whenever tested by the method of any one of Claims 1 to 7 and/or with the apparatus of any one of Claims 8 to 14.

16. Any novel feature or combination of features described herein.