1、 ISO 2013 Pallets for materials handling Flat pallets Part 4: Procedure for predicting creep responses in stiffness tests for plastic pallets using regression analyses Palettes pour la manutention Palettes plates Partie 4: Mode opratoire pour prdire les rponses au fluage lors des essais de rigidit d
2、es palettes en plastique en utilisant des analyses de rgression TECHNICAL SPECIFICATION ISO/TS 8611-4 First edition 2013-10-15 Reference number ISO/TS 8611-4:2013(E) ISO/TS 8611-4:2013(E)ii ISO 2013 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2013 All rights reserved. Unless otherwise speci
3、fied, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or IS
4、Os member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ISO/TS 8611-4:2013(E) ISO 2013 All rights reserved iii Contents Page Foreword iv 1 Scop
5、e . 1 2 Normative references 1 3 T erms and definitions . 1 4 Symbols and abbreviated terms . 2 5 Procedure for predicting creep responses 2 5.1 Purpose 2 5.2 Test procedure . 3 5.3 Specification of regression models 3 5.4 Predicting the deflections under the test load and during the relaxation time
6、 4 5.5 Statistical testing for the standard performance limit 5 6 Test report . 6 Annex A (informative) An example of predicting creep responses in order to reduce the full test load duration 7 Bibliography .10 ISO/TS 8611-4:2013(E) Foreword ISO (the International Organization for Standardization) i
7、s a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represe
8、nted on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develo
9、p this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/I
10、EC Directives, Part 2 (see www.iso.org/directives). Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during th
11、e development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents). Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. For an explanation on the meaning
12、 of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information The committee responsible for this document is ISO/TC 51, Pa
13、lle t s for unit lo ad me t ho d of mat er ial s handling. ISO 8611 consists of the following parts, under the general title Pallet s for materials handling Flat pallet s: Part 1: Test methods Part 2: Performance requirements and selection of tests Part 3: Maximum working loads Part 4: Procedure for
14、 predicting creep responses in stiffness tests for plastic pallets using regression analyses Technical Specificationiv ISO 2013 All rights reserved TECHNICAL SPECIFICATION ISO/TS 8611-4:2013(E) Pallets for materials handling Flat pallets Part 4: Procedure for predicting creep responses in stiffness
15、tests for plastic pallets using regression analyses 1 Scope This part of ISO 8611 presents a procedure for predicting creep responses in stiffness tests for plastic pallets to shorten the test period. Based on regression analyses, deflections during full load and relaxation periods are predicted. Th
16、is part of ISO 8611 is for use with the static stiffness tests such as tests 1b, 3b, 4b, 5b, and 7b referred to in ISO 8611-1:2011, and is for application at ambient temperature only. Annex A gives an informative example of this process. 2 Normative references The following documents, in whole or in
17、 part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 445, Pallets for materials handling Vocabu
18、lary ISO 8611-1:2011, Pallets for materials handling Flat pallets Part 1: Test methods ISO 8611-2:2011, Pallets for materials handling Flat pallets Part 2: Performance requirements and selection of tests 3 T erms a nd definiti ons For the purposes of this document, the terms and definitions given in
19、 ISO 445 and the following apply. 3.1 regression analysis statistical technique for modelling and analysing the relationship between several variables, where the focus is on the relationship between a dependent variable and one or more independent variables 3.2 least square method statistical method
20、 of estimating the coefficients in the regression model such that the sum of squared residuals are minimized, where the residual is the difference between an observed value and the value provided by the model 3.3 test period period required for the stiffness test of plastic pallets, which is divided
21、 into full test load period and relaxation period 3.4 full test load period full period required for the stiffness test of plastic pallets under load, which lasts for 24 h or 48 h depending upon the type of tests ISO 2013 All rights reserved 1 ISO/TS 8611-4:2013(E) 3.5 relaxation period period requi
22、red for the stiffness test of plastic pallets after releasing load, which lasts for 2 h from the outset of releasing 3.6 reduced test period reduced period required for the stiffness test of plastic pallets under load, which lasts for 4 h 3.7 relaxation period of the full test period required for th
23、e stiffness test of plastic pallets after releasing load, which lasts for 2 h from the end of the full test load period 3.8 relaxation period of the reduced test period required for the reduced stiffness test of plastic pallets after releasing load, which lasts for 2 h from the end of reduced full l
24、oad period 4 Symbols and abbreviated terms b 0 , b 1 regression coefficients b 0 *, b 1 * estimated regression coefficients Y(t)* deflection predicted at time t (mm) Y(t) deflection actually measured at time t (mm) e(t) regression error at time t ln(t) natural logarithm of time t 5 Procedure for pre
25、dicting creep responses 5.1 Purpose Stiffness tests for plastic pallets, including tests 1b, 3b, 4b, 5b, and 7b in ISO 8611-1:2011, require test durations of 24 h to 48 h, depending on the type of test measurement. These test durations are essential because plastic pallets and pallet decks creep whi
26、le placed in storage racks or stack storage. However, it is of great benefit in saving time and cost if creep deflections can be predicted for the entire test period from the test data of the first 4 h. Using the method described in this part of ISO 8611, test duration can be reduced while keeping t
27、he same time of relaxation as in ISO 8611-1:2011, as recommended in Table 1. This part of ISO 8611 shows how to conduct the stiffness tests based on the predicted value of creep responses during the loading and relaxation periods. Table 1 Full load duration and reduced duration recommended for stati
28、c stiffness tests Pallet material and tests Test period (h) Reduced test period (h) Relaxation time (h) Where plastics or plastic parts dictate overall performance tests 1b, 3b, 5b, and 7b 24 4 2 test 4b 48 4 22 ISO 2013 All rights reserved ISO/TS 8611-4:2013(E) 5.2 Test procedure At least three pla
29、stic pallets for each test shall be used as specified in Clause 5 of I SO 8611-2:2011. Deflections at the specified locations on the pallet shall be recorded continuously during the creep test. The frequency of 1 observation per 30 s is recommended for the first hour of testing, and the recommended
30、frequency for the remainder of the creep test is 1 every 10 min interval. The recommended extraction interval for relaxation is 1 observation every 30 s. The following steps shall be used to predict the creep responses. 1) Test the first pallet for both the full load period (24 h; 48 h for test 4b)
31、and the relaxation period (2 h). Deflections at specified intervals shall be measured while pallet creeps. If the deflection measured at the end of the full load or the relaxation period exceeds the standard performance limits specified in Table 1 of ISO 8611-2:2011, stop the test. The pallets in th
32、e lot shall be declared as failed for the stiffness test. Otherwise, proceed with step 2. 2) Test the second pallet for the reduced test duration with 4 h load. Use Formula (1) to estimate the regression coefficients for the loading test period. Then predict the deflections for the remainder beyond
33、the reduced test duration, which span from 4 h to 24 h (or 48 h), based on Formula (1). If the deflection predicted at the end of the full load period exceeds the standard performance limit specified in Table 1 of ISO 8611-2:2011, stop the test. The pallet shall be declared as failed for the stiffne
34、ss test. Otherwise, proceed to step 3 to test for the relaxation period. The performance limit test shall be done based on t-test procedure. 3) Test the second pallet for the 2 h relaxation period of the reduced test and obtain the data. Use Formula (2) to estimate the regression coefficients for th
35、e relaxation period. Then predict the deflections in the relaxation period of the full test, which cover from 24 h to 26 h (or 48 h to 50 h), based on Formula (2). If the deflection predicted at the end of the relaxation period of the full test exceeds the standard performance limit specified in Tab
36、le 1 of ISO 8611-2:2011, stop the test. The pallet shall be declared as failed for the stiffness test. Otherwise, proceed to step 4. The performance limit test shall be done based on t-test procedure. 4) Test the third pallet and repeat steps 2 to step 3. 5.3 Specification of r egr ession models The
37、 regression model in Formula (1) shall be used for fitting sample data from the loading period. Y(t) = b 0+ b 1 ln(t) + e(t) (1) where Y(t) is the pallet deflection occurred at time t (mm); t is the time in minutes; b 0 , b 1 is the set of regression coefficients; e(t) is the error at time t, indepe
38、ndently and identically distributed as normal. ISO 2013 All rights reserved 3 ISO/TS 8611-4:2013(E) Formula (2) shall be used for fitting sample data from the relaxation period for 0 t 2 h. R(t) = b 0+ b 1 ln(t) + e(t) (2) where R(t) is the ratio of deflections at the relaxation period, Z(t) divided
39、 by Z p (t); Z(t) is the deflection in t minutes relaxation from the full test pallet; Z p (t) is the deflection in t minutes relaxation from the reduced test pallet; e(t) is the error at time t, independently and identically distributed as normal. 5.4 Pr edicting the defl ections under the t est lo
40、 ad and during the r elax ation time 5.4.1 Purpose Two performance requirements shall be measured in order to evaluate the bending stiffness of pallets. The first requirement is the bending deflection for the test load period and the second is the bending deflection for the relaxation time. 5.4.2 Pr
41、 edicting the defl ections during the full t est load period 5.4.2.1 Measuring the ac tual deflections The first pallet shall be tested as specified in 5.2 for both the full test load period and the relaxation period, and the deflection shall be measured at the end of the full test load period. 5.4.
42、2.2 Calculating the p r edict ed deflections For the second pallet, the test duration shall be 4 h as specified in Table 1. Regression coefficients are estimated based on the least squares method, and then the deflections at the end of full duration are predicted. The deflections in the full load pe
43、riod for the partially tested pallet shall be predicted using the estimations from Formula (3). Y(t)* = b 0 * + b 1 *ln(t) (3) where Y(t)* is the pallet deflection estimated at time t (mm); t is the time in minutes; b 0 *, b 1 * is the set of estimated regression coefficients. The same procedure sha
44、ll be applied to the third pallet. 5.4.3 Pr edicting the defl ections during the r elax ation period 5.4.3.1 Measuring the ac tual deflections The deflections during the relaxation period, after unloading, shall be measured at both the full test period and the reduced period.4 ISO 2013 All rights re
45、served ISO/TS 8611-4:2013(E) 5.4.3.2 Calculating the p r edict ed deflections The deflections for the relaxation period of reduced test shall be estimated using the deflection ratio of fully tested pallet to partially tested pallet as specified in Formula (2) and (3). The deflections in the relaxati
46、on period of the partially tested pallet shall be predicted using the estimated Formula (4) as follows. Z(t)* = Z p (t)b 0 * + b 1 *ln(t) (4) where Z(t)* is the hypothetical deflection in t minutes relaxation, if the partially-tested pallet is put to full test, of which deflections shall be predicte
47、d using the regression model; b 0 *, b 1 * is the set of estimated regression coefficients based on Formula (2). The same procedure shall be applied to the third pallet. 5.5 Statistical testing for the standard performance limit 5.5.1 Purpose Using t-test procedure, the predicted deflections for the
48、 hypothetical full period of pallets shall be tested if the predicted deflection of the pallet falls within the standard performance limit. 5.5.2 t-test procedure for the loading period The t-test procedure is formulated as follows. Set up the null hypothesis “predicted deflection is above the stand
49、ard limit, C.” That is, the null hypothesis is that the pallet fails the performance test. Then the alternative hypothesis is that predicted deflection is not above standard limit. Under the null hypothesis, T-stat is computed as T-stat = (Y* 24 h or 48 h C)/SE(Y* 24 h or 48 h ). T-stat is approximately distributed as t-distribution with (n 2) degrees of freedom, where Y* 24 h or 48 his the deflection predicted at 24 h or 48 h; C is the standard performance limit for the loading period according to ISO
