BS 373-1957 Methods of testing small clear specimens of timber《无节疤小木材样品的试验方法》.pdf

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1、BRITISH STANDARD BS373:1957 Methods of testing small clear specimens of timber UDC 674.01:620.1BS373:1957 This British Standard, having been approved by the TimberIndustry Standards Committee and endorsed by theChairman of the BuildingDivisional Council, waspublished under the authorityof the Genera

2、l Councilon 21 February1957 BSI 07-1999 First published December1929 First revision September1938 Second revision February1957 The following BSI references relate to the work on this standard: Committee reference TIB/2 Draft for comment CW(TIB)3312 ISBN 0 580 00684 0 Co-operating organizations The T

3、imber Industry Standards Committee, under whose supervision this British Standard was prepared consists of representatives from the following Government departments and scientific and industrial organizations: British Door Association British Furniture Trade Confederation British Railways, The Briti

4、sh Transport Commission D.S.I.R. Forest Products Research Laboratory* English Joinery Manufacturers Association (Incorporated) Flush Door Manufacturers Association Institution of Civil Engineers Institution of Municipal Engineers Institution of Structural Engineers Ministry of Housing and Local Gove

5、rnment Ministry of Works National Federation of Building Trades Employers Royal Institute of British Architects Royal Institution of Chartered Surveyors Timber Development Association* Timber Trade Federation of the U.K. The Government department and scientific and industrial organization marked wit

6、h an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the preparation of this British Standard: Ministry of Supply Amendments issued since publication Amd. No. Date CommentsBS373:1957 BSI 07-1999 i Contents Page Co-operating organizat

7、ions Inside front cover Foreword ii 1 Scope 1 2 Moisture content 1 3 Control of moisture content 1 4 Control of temperature 1 5 Specific gravity and weight per cubic foot 1 6 Static bending test 1 7 Impact test 2 8 Compression tests 2 9 Janka indentation test 3 10 Shear parallel to grain test 3 11 C

8、leavage test 3 12 Tensile test 4 13 Permissible variations 4 14 Radial and tangential shrinkage 4 Appendix A Formulae and methods of computing physical properties 5 Appendix B Tests recommended to indicate the suitability of timber forspecificuses 11 Figure 1 3 Figure 1a Beam test. Central loading f

9、or2in. or2cm standard test piece 12 Figure 1b Beam test. Four point loading method 12 Figure 2 Impact test (2in. standard) 13 Figure 3 Impact test (2cm standard) 14 Figure 4 Form of test pieces for compression parallel to grain 14 Figure 5 Suitable arrangement for compression test parallel to grain

10、(2in.standard) 15 Figure 6 Compression parallel to grain (2cm standard) 16 Figure 7 Test piece for compression perpendicular to grain 17 Figure 8 Janka indentation test 17 Figure 9 Test pieces for shear parallel to grain 18 Figure 10 Test for shear parallel to grain (2in. standard) 18 Figure 11 Test

11、 for shear parallel to grain (2cm standard) 19 Figure 12 Test for cleavage (2in. standard) 20 Figure 13 Test for cleavage (2cm standard) 21 Figure 14 Test piece for tension parallel to grain test 22 Figure 15 Grip ends for Figure 14 specimen 23 Figure 16 Test piece for tension perpendicular to grain

12、 24BS373:1957 ii BSI 07-1999 Foreword This standard makes reference to the following British Standard: BS1610, Verification of testing machines. This second revision of the British Standard methods of testing small clear specimens of timber, which was originally issued in1929, has been issued under

13、the authority of the Timber Industry Standards Committee and was rendered necessary by the recent introduction into the United Kingdom of the2cm system of testing. The2cm system of testing is one of the principal schemes accepted internationally for the testing of small clear specimens. It has a tes

14、t-piece of2cm square cross-section, instead of the original2in. standard with its larger test-piece of2in. square cross-section. The introduction of the smaller test piece (which will be referred to in this specification as the2cm standard), has necessitated modification to much of the existing test

15、ing equipment and the techniques now incorporated conform generally to those accepted internationally. The testing of small clear specimens of timber has as its main purpose the provision of data for the comparison of the strength properties of different species. Timbers should be tested both in the

16、 green condition and in the seasoned condition. The test results may be used also to determine the relation between strength and such properties as density, to determine the effect on strength of various treatments, and to assist in the establishment of design functions for structural timbers. Almos

17、t all the mechanical properties of seasoned timber vary with moisture content and it is therefore important that the moisture content of all test pieces be known at the time of test. When comparing results obtained with seasoned material, due allowance must be made for the effects of differences in

18、moisture content. As the mechanical properties vary with the rate of application of load it is desirable that the specific rates should be adhered to wherever possible in order that comparable results may be obtained. If the testing machine be of a type which does not permit the specified rate of lo

19、ading, the actual rate employed should be recorded with the results obtained in order that these results may be corrected as and when the relationship between the observed mechanical property and the rate of application of the load has been definitely established. The rates of strain which are speci

20、fied for the2in. and2cm test pieces have in some cases been founded on the established practice of those who have been accustomed to use these sizes rather than on any scientific basis of similarity. It is recognized that some of the tests specified are of an arbitrary nature and are intended to pro

21、vide comparative data rather than to measure absolute properties of the material. They have been included because they have been generally adopted and have produced useful results not only in the comparison of species of timber but also in the improvement of the design of timber structures and the g

22、eneral economic application of timber in manufacturing processes. The results of tests made with the2cm standard are not, owing to dimensional effect, directly comparable in all properties with those for the2in. standard. A more extensive comparison with the results of tests from laboratories, both

23、at home and abroad, may be obtained if the results of material tested in accordance with the former standard are corrected to the equivalent values for the2in. standard.BS373:1957 BSI 07-1999 iii This specification, however, does not give factors for the conversion of the results of tests made with

24、the2cm standard to the equivalent values for the2in. standard, nor does it cover the procedure adopted for the sampling of material for test, for the conversion of the log or for the preparation of the test pieces. Such information may be obtained from other publications, such as the Forest Products

25、 Research Laboratorys Project1 and Bulletins No.28 and34, as well as from standard D143-52 of the American Society for Testing Materials and The Sampling of Timber for Mechanical Tests, F.G. Pearson, Australian journal of applied Science Vol3, No.1. A British Standard does not purport to include all

26、 the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv,

27、 pages1to24 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.iv blankBS373:1957 BSI 07-1999 1 1 Scope This British Standard gives methods of test for the provision o

28、f data for the comparison of the strength properties of different species of timber. 2 Moisture content Immediately after each mechanical test has been made, a small sample for determination of moisture content shall be cut from each test piece. The sample shall consist of a transverse section from

29、near the point of fracture, but for the2cm standard the compression parallel-to-grain test piece as a whole shall be used as the sample. The sample shall be weighed and then dried in an oven at a temperature of103 2 C (217 4 F) until the weight is constant. The loss in weight expressed as a percenta

30、ge of the final oven-dry weight shall be taken as the moisture content of the test piece. The value so obtained shall be recorded with the results of the particular test to which it refers. NOTE 1Great care should be taken to prevent any change in moisture content between the cutting of the sample a

31、nd the first weighing and between removal from the oven and the subsequent weighing. NOTE 2If it is required to determine the moisture content of a specimen of timber, apart from its mechanical properties, a transverse sample of the specimen should be taken as a cross section of the piece at a dista

32、nce b + h from one end, where b and h are the cross sectional dimensions of the piece. 3 Control of moisture content Before the preparation of test pieces for testing in the seasoned condition, the material shall be brought practically to constant weight by storage under controlled temperature and h

33、umidity conditions(20 3 C) (68 6 F) and65 2 percent relative humidity. Changes in moisture content during the preparation of test pieces should be avoided. The tests shall be made under such conditions that large changes in moisture content will not occur. 4 Control of temperature To avoid significa

34、nt changes in strength properties, all test pieces shall be tested within the temperature range20 3 C (68 6 F). The temperature at the time of test shall be recorded. NOTEIn following the recommendation that the temperature be controlled at20 3 C (68 6 F) it is desirable to maintain the temperature

35、as nearly constant as possible within this range. 5 Specific gravity and weight per cubic foot In the2in. standard, all test pieces shall be weighed and their dimensions determined before test. The specific gravities at test and when oven-dry shall be calculated for each test piece. From these the e

36、quivalent densities in pounds per cubic foot can be obtained. For the2cm standard, the compression parallel-to-grain test piece which has been used for moisture content control shall subsequently be used for the determination of the specific gravities as for the2in. test-piece. NOTE 1Conventions for

37、 grain direction are illustrated in Clause 8. NOTE 2The2cm compression parallel-to-grain test piece has to be end matched with the test pieces used for determining all other strength properties. NOTE 3If it is required to know the specific gravity or the density in pounds per cubic foot of a timber

38、apart from any of its other properties, a sample should be taken as a cross-section of the specimen about # in. thick at a distance b + h from one end, where b and h are the dimensions of the cross-section of the specimen. The density in pounds per cubic foot may alternatively be obtained with suffi

39、cient accuracy by weighing a sample2in. 1in. 1.9in. The weight in grammes of this piece is numerically equal to the weight in pounds per cubic foot, from which the specific gravity can be determined by dividing by62.35. 6 Static bending test The static bending test shall be carried out by either a t

40、he central loading method, or b the four-point loading method. See Figure 1 (Figure 1a and Figure 1b). NOTEFor general standard testing of timber for the comparison of different species, the central loading method is sufficiently accurate. Where a more accurate determination of the modulus of elasti

41、city is required (as, for example, in some stress calculations) the four-point loading method has to be employed. By this method the beam is subjected to a uniform bending moment over a considerable proportion of its length and the Modulus of Elasticity can be calculated without the necessity of all

42、owing for shear deflection which occurs along the whole length of a beam loaded at the centre. The dimensions of the central loading test piece shall be2in. by2in. by30in. for the2in. standard, or2cm by2cm by30cm for the2cm standard, and those of the four-point loading test piece2in. by2in. by40in.

43、In close-grained timber a width of1in. may be used for the four-point loading method where a width of2in. cannot be obtained. For the2in. standard the depth of the beam shall be parallel to the radial face of the test piece. The orientation of the annual rings in the2cm standard test piece shall be

44、parallel to the direction of loading.BS373:1957 2 BSI 07-1999 In the central loading method the distance between the points of support of the test piece shall be28in., or28cm, according to the standard used, and the load shall be applied as shown in Figure 1a. For the2in. standard the loading heads

45、shall move at a constant speed of0.10in/min and for the2cm standard,0.26in/min. The contour of the loading head which is in contact with the beam shall have for the2in. standard the same form as that shown for the falling tup in Figure 2 and for the2cm standard the same form (but30mm radius) as that

46、 shown for the falling tup in Figure 3. For the four-point loading method the distance between the points of support shall be36in. and the distance between the points of application of the load and the supports (dimension a, Figure 1b) shall be6in. The load shall be applied at such a rate that the l

47、oading head moves at a constant speed of0.13in/min. The test pieces shall be supported at the ends in such a way that they will be quite free to follow the bending action and will not be restrained by friction which would resist the bending and tend to introduce longitudinal stresses. The deflection

48、 of the beam at mid length shall be measured with reference to the outer points of loading in the central loading method and to the ends of the gauge length l (Figure 1b) in the four-point loading method. 7 Impact test The dimensions of the2in. standard test piece shall be2in. by2in. by30in. The met

49、hod by which the test shall be made is shown diagrammatically in Figure 2. The entire apparatus shall be securely bolted to a solid foundation. The test piece shall be placed in the machine, at28in. centres, with the heart side uppermost. The load shall be applied at the centre of the test piece by the impact of a weight (tup) of50lb falling freely from successive heights increasing by regular increments. The first drop shall be from a height of2in. and this shall be followed by drops from heights increasing by1in. at a t