ISO/TS 8611-4:2013

TECHNICAL ISO/TS
SPECIFICATION 8611-4
First edition
2013-10-15
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 opératoire pour prédire les réponses au fluage
lors des essais de rigidité des palettes en plastique en utilisant des
analyses de régression
Reference number
©
ISO 2013
© ISO 2013
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ii © ISO 2013 – All rights reserved

Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms 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 . 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
Foreword
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to Trade (TBT) see the following URL: Foreword - Supplementary information
The committee responsible for this document is ISO/TC 51, Pallets for unit load method of materials handling.
ISO 8611 consists of the following parts, under the general title Pallets for materials handling — Flat pallets:
— Part 1: Test methods
— Part 2: Performance requirements and selection of tests
— Part 3: Maximum working loads
— Part 4: Procedure for predicting creep responses in stiffness tests for plastic pallets using regression
analyses [Technical Specification]
iv © 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 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. This 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 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 — Vocabulary
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 Terms and definitions
For the purposes of this document, the terms and definitions given in 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 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 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
3.5
relaxation period
period required 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 the 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 load period
4 Symbols and abbreviated terms
b, b regression coefficients
0 1
b*, b * estimated regression coefficients
0 1
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 predicting 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 while 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 the 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 static stiffness tests
Pallet material and tests Test period Reduced test Relaxation
(h) period time
(h) (h)
Where plastics or plastic parts dictate tests 1b, 3b, 5b, and 24 4 2
overall performance 7b
test 4b 48 4 2
2 © ISO 2013 – All rights reserved

5.2 Test procedure
At least three plastic pallets for each test shall be used as specified in Clause 5 of ISO 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 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) 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 the 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 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
stiffness 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 the 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 Table 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 regression models
The regression model in Formula (1) shall be used for fitting sample data from the loading period.
Y(t)  = b + b [ln(t)] + e(t)
0 1
(1)
where
Y(t) is the pallet deflection occurred at time t (mm);
t is the time in minutes;
b, b is the set of regression coefficients;
0 1
e(t) is the error at time t, independently and identically distributed as normal.
Formula (2) shall be used for fitting sample data from the relaxation period for 0 ≤ t ≤ 2 h.
R(t) = b + b [ln(t)] + e(t)
0 1
(2)
where
R(t) is the ratio of deflections at the relaxation period, Z(t) divided by Z (t);
p
Z(t) is the deflection in t minutes relaxation from the full test pallet;
Z (t) is the deflection in t minutes relaxation from the reduced test pallet;
p
e(t) is the error at time t, independently and identically distributed as normal.
5.4 Predicting the deflections under the test load and during the relaxation 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 Predicting the deflections during the full
...