SOUTH AFRICAN NATIONAL STANDARD. Modulus of elasticity and modulus of rupture in static bending of fibreboards Amdt 1

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1 ISBN Any reference to SABS SM 1015 is deemed to be a reference to this standard (Government Notice No. 17 of 8 November 00) SOUTH AFRICAN NATIONAL STANDARD Modulus of elasticity and modulus of rupture in static bending of fibreboards Amdt 1 Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001 Tel: Fax: SABS

2 Table of changes Change No. Date Scope Amdt Amended to change the designation of SABS standards to SANS standards, to change the title and to update referenced standards. Foreword This South African standard was approved by National Committee SABS/TC 1008/SC 0, Wood and associated products Reconstituted timber, in accordance with procedures of the SABS Standards Division, in compliance with annex of the WTO/TBT agreement. This edition cancels and replaces the first edition (SABS SM 1015:1980). A vertical line in the margin shows where the text has been technically modified by amendment No. 1. Reaffirmed and reprinted in October 01. This document will be reviewed every five years and be reaffirmed, amended, revised or withdrawn.

3 Modulus of elasticity and modulus of rupture in static bending of fibreboards Amdt 1 1 Scope 1.1 This method covers the determination of the apparent and of the true modulus of elasticity and of the modulus of rupture in static bending of fibreboard. Amdt 1 NOTE In this method reference is made to the latest issues of SANS 617 and SANS Amdt 1 Principle of the method.1 A test piece is placed on two supports, a load is applied in its centre until failure occurs, and the deformations at loading, the maximum load applied before failure, the distance between the supports, and the width and thickness of the test piece are measured and recorded. The modulus of elasticity is calculated from the slope of the load-deflection curve in the elastic linear region and the span, width, and thickness of the test piece, and the modulus of rupture is determined from the bending moment at the maximum load and the full cross-section of the test piece. Apparatus.1 Measuring instruments as specified in SANS Amdt 1. Testing apparatus that consists essentially of the following (see figure 1): a) Two parallel cylindrical supports which adjust themselves in the horizontal plane under load (i.e. are self-aligning), having a length greater than the width of the test pieces and a diameter (D) of 15 mm ± 0,5 mm, if the thickness of the test piece is < 7 mm, 0 mm ± 0,5 mm, if the thickness of the test piece is > 7 mm. The distance between the supports is adjustable. NOTE In cases where excessive local deformations may occur under the loading points, bearing plates of steel, of thickness not exceeding,5 mm, must be used. b) A testing machine, of accuracy at least 1 % over the loading range used, and fitted with a cylindrical loading head, positioned parallel to the supports and equidistant from them, movable in the vertical direction, and having the same length and diameter as those of the supports. 1

4 c) Suitable means for measuring the deflection of the neutral axis of the test piece in the middle of the span (i.e. vertically below the loading head).. A conditioning chamber capable of maintaining an atmosphere that has a relative humidity of 65 ± 5 % and a temperature of 0 ± C. 4 Preparation of test specimens 4.1 Use test specimens of the appropriate size and quantity given in (and cut and marked in accordance with) SANS 617. Amdt 1 NOTE For boards thinner than 9 mm, 00 mm 150 mm test specimens should be used. Amdt 1 4. Condition the test pieces to constant mass in an atmosphere of relative humidity 65 ± 5 % and temperature 0 ± C. Consider constant mass to be reached when at two successive weighing operations, carried out at an interval of 6 h, the mass does not differ by more than 0,1 % of the final mass of the test piece. 5 Procedure 5.1 Measure, in accordance with SANS 6174, the width and thickness of each test piece as follows: Amdt 1 a) Measure the thickness at the two points shown as circles in figure. b) Measure the width on the transverse axis as shown by the arrows in figure. 5. So adjust, to the nearest millimetre, the distance between the centres of the supports that it is equal to 15 the nominal thickness of the test piece in the case of boards in the range 9 mm to 5 mm of thickness, and 10 the nominal thickness in the case of thicker boards. For boards thinner than 9 mm, use a test span of 150 m. NOTE 1 The span should be estimated from the average actual thickness of the fibreboard and need not be altered for slight variations in the thickness of individual specimens. Amdt 1 NOTE If the deflection of the test piece becomes too large so that rupture (failure) does not occur, the distance between the supports must be reduced for the testing of the bending strength. Amdt 1 5. Immediately after conditioning and measuring, so place the test pieces (in turn) on the supports (with the face-side of the board alternately on the compression and on the tension side) that the transverse axis of the test piece and the axis of the loading head are in the same vertical plane (see figure 1). 5.4 Apply the load (through the loading head) continuously at a constant rate of loading as follows: a) When determining the modulus of elasticity only, the load-deflection curve should be determined up to one-third of the maximum load, therefore choose increments of load of equal magnitude such that not less than 8 (and preferably 15 or more) readings of load and deflection are taken. Automatic load and deflection recording apparatus may be used, provided that the curves obtained are of sufficient magnitude to allow accurate measurement of load and deflection. Measure, to the nearest 0,01 mm, the deflection, s, in the middle of the test piece (below the loading head) using a suitable measuring instrument that is, preferably, fixed to the test piece in such a way that local compressions of the test piece, caused by the supports or the loading head (or both), do not influence the measurement of the deflection.

5 b) When determining the modulus of rupture (bending strength) only, use a rate of loading such that the maximum load is reached within s. c) In a test for both the modulus of elasticity and the modulus of rupture (bending strength) after approximately one-third of the ultimate failing load has been applied, change the constant rate of loading to a value such that failure occurs within the next s. 6 Calculations 6.1 Modulus of elasticity Calculate (and record to the nearest 50 MPa) the modulus of elasticity of each test piece from the following formula (see also figure ): E b where L (F F1 ) 4 b t (s s ) 1 E b = the modulus of elasticity of the test piece, MPa L = the distance between the centres of the supports, to the nearest 0,5 mm, mm b = the width of the test piece, to the nearest 0,1 mm, mm t = the thickness of the test piece, to the nearest 0,05 mm, mm F - F 1 = the increment of load, on the straight line portion of the load-deflection curve, determined to an accuracy of at least 1 %, N s - s 1 = the increment of deflection, at mid-length of the test piece, corresponding to F - F 1 and determined, to the nearest 0,01 mm, from the load-deflection curve, mm 6.1. Take as the modulus of elasticity of a sample board the arithmetical mean (rounded off to the nearest 50 MPa) of the values for all test pieces cut from the board. NOTE Deleted by amendment No Modulus of rupture (bending strength) 6..1 Calculate (and record to the nearest 0,5 MPa) the modulus of rupture from the following formula: σ bb where F L b t σ bb = the bending strength of the test piece, MPa F = the maximum load, to the nearest 1 % of the load, N L = the distance between the centres of the supports, to the nearest 0,5 mm, mm

SOUTH AFRICAN NATIONAL STANDARD

ISBN 978-0-626-33085-9 SOUTH AFRICAN NATIONAL STANDARD Water Free and saline ammonia content Published by SABS Standards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001 Tel: +27 12