Measuring and testing – Specimen stress or strain – or testing by stress or strain... – By loading of specimen
Patent
1997-11-12
2000-03-28
Noori, Max
Measuring and testing
Specimen stress or strain, or testing by stress or strain...
By loading of specimen
73851, G01N 320
Patent
active
060416610
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of testing paper board and cardboard products to measure and determine the integrity and quality of the paper board or cardboard product. In particular, the method of testing is directed to measuring and determining the compressive failure characteristics of corrugated board for use in box manufacture.
When corrugated board is used in box construction, the failure of the board will generally occur where the liner of the board structure is required to sustain the largest strains. A large displacement bending mode is observed, where the liner on the concave side is required to sustain the strains as previously mentioned. Generally, these compressive strains are accommodated by localised buckling of the liner between the flute tips of the corrugated board. The stress at which this happens depends upon the material used in constructing the board and the integrity with which the board has been formed and in particular, how the components have been glued together.
When strains become sufficiently large the liner becomes unstable, so that the energy stored in the board is dissipated in a very localised region involving the collapse of the liner material itself.
A number of attempts have been made to ascertain the integrity and quality of any particular board product to be used in box manufacture. One particular method is what is called the "Edge Crush Test" (ECT). There have been a number of methods developed to measure the edgewise compressive strength, but essentially what is common to all methods is that, a sample of board product is crushed. The difficulties with most of the ECT methods is that the edges always tend to fail first and whether the sample fails at the edges seems to be dependent upon whether or not the sample has been correctly cut. There are two major reasons why edge failure testing is not desirable. The first is that most corrugated board product when used in box manufacture does not fail at the edges. Secondly, there is a need to have a test which has easily reproducible results and is not dependent upon how accurately the sample is cut.
Some attempts have been made to address these problems of edgewise failure and ease of obtaining reproducible results using the conventional ECT, however, all of the methods to date have required either extremely complex machinery to prepare the uniquely shaped samples and equally complex machinery to perform the crushing action. In most instances the results have not been reliable or reproducible.
The other problem associated with existing edgewise crush strength tests is that both liner boards are compressed at the same level. In order to determine the compressive strength of the board product, prior art edge crush tests provide an averaged value from the inside and outside liner for the compressive strength of the sample. The average values obtained from prior art methods do not mirror accurately what happens during box failure where it is usually the inside liner, which is under the most strain, that fails.
Another method previously used to determine the integrity characteristics of a sample of board product is the pinch test. In this test the sample is gripped at either end and the ends are merely pushed together. As with the edge crush tests the problems associated with this method is that quite often there is failure at the edges as opposed to the centre of the sample. Furthermore, there are additional stresses introduced at the edges of the sample as a result of the clamping means, resulting in particularly unreliable indications of failure characteristics.
Thus there was, prior to the present invention, a need for a means of determining accurately and quantitatively the quality and strength characteristics of corrugated board for use in box manufacture, in order to predict its behaviour in use.
The present invention provides a method of characterising the compressive failure characteristics of board product including the steps of: face until the sample fails; and
It is preferred that the sample is aligned within two
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Amcor Limited
Noori Max
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