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Page 1: A device for compressing paperboard edgewise in … · A device for compressing paperboard edgewise in the SEM I B Sachs Forest Products Laboratory†, Forest Service, US Department

J. Phys. E: Sci. Instrum., Vol. 18, 1985. Printed in Great Britain

Design note

A device for compressing paperboard edgewise in the SEM

I B Sachs Forest Products Laboratory†, Forest Service, US Department of Agriculture, PO Box 5130, Madison, WI, USA 53705

Received 9 August 1984

Abstract. Paperboard containers often fail because of insufficient strength under compressive loading. To overcome this problem, we need to understand the mechanisms involved in compressive failure of paperboard. A device for compressing paperboard samples was built at the Forest Products Laboratory for use in the scanning electron microscope (SEM) to observe the mechanism by which such failures occur under edgewise compression.

Corrugated fibreboard containers are subjected to compressive loading when stacked in palletised shipping and warehousing. Under these conditions, the corners and sides of the container bear the load and as such are under compressive loading (Grangard and Kubat 1969, Grangard 1970, McKee et al 1963). The ability of the container to perform under these conditions without failing is greatly influenced by the performance of the paperboard that makes up the container. Therefore, it is necessary to ( 1 ) obtain information on the maximum amount of deformation the paperboard can withstand in edgewise compression prior to failure and (2) determine the mechanism by which paperboard failures occur under short column edgewise compression. With this knowledge, methods can be found to produce paperboard with increased edgewise compressive strength.

Devices have been developed to measure paperboard edgewise compressive strength (Cavlin and Fellers 1975, Gunderson 1981, Jackson et al 1976, Sachs and Kuster 1980, Setterholm and Gertjejansen 1965, Stockmann 1976). However, to study the failure mechanism of paperboard in a dynamic mode, one needs to observe and record the changes that occur in the paperboard as it is being compressed.

The scanning electron microscope (SEM) can be used in such failure analysis because of its depth of focus and range of magnification. In addition, its fast observation time and high

† The Laboratory is maintained in cooperation with the University of Wisconsin, Madison, WI.

resolution should allow quick and easy inspection of failure of the paperboard under edgewise compression. To observe and record changes using an SEM, however, the paperboard sample must be in the electron beam while it is being compressed. Therefore, a small testing device for use in the SEM is needed as a tool for characterising and identifying the failure mechanism. In this report, I describe such a testing device, designed and built at the Forest Products Laboratory, that can hold a paperboard sample in the SEM electron beam while being compressed edgewise.

The device, as shown in figures 1 and 2, with attached load cell (D)†, was built in order to keep compression forces

Figure 1. Schematic of compression device and load cell (MC84 9053). A, lead screw; B, wiring from strain gauge to miniature cable connector; C, strain gauges; D, load cell; E, extension rod from load cell; F, sliding jaw; G, fixed jaw; H, paperboard sample; I, locking screws; J, steel rods on which jaws move.

unidirectional as the paperboard sample (H) is compressed. The device is made of brass and is small enough - 66.6 mm long by 19.0 mm wide by 25.4 mm high-to fit into the specimen chamber (L) of an SEM. The paperboard samples are held in two brass jaws, one sliding (F) and one fixed (G), each measuring 22.2 mm high by 19.0 mm wide by 9.5 mm thick. The sliding jaw (F) moves on two steel rods (J) located at the bottom of the jaws. The jaws are moved by hand turning the microscope rotation knob (M), located outside the specimen chamber (L). As the knob is turned, the lead screw (A) advances, pushing on the load cell (D). A rod (E) extending from the load cell pushes the sliding jaw (F), which in turn is pushed towards the fixed jaw (G), compressing the paperboard sample (H).

The load cell (D) is used to measure the compressive load. The load cell is a ring of aluminium 25.2 mm outside diameter, 19.0 mm inside diameter, and 3.1 mm thick. Four strain gauges (C) are bonded to the aluminium ring forming an electronic bridge. Lead wires (B) from the strain gauges are connected through a port in the column of the microscope to an amplifier signal conditioner, digital voltmeter, and chart recorder that records the load.

† Letters in parentheses refers to markers on figures 1 and 2.

1985 The Institute of Physics 101

Page 2: A device for compressing paperboard edgewise in … · A device for compressing paperboard edgewise in the SEM I B Sachs Forest Products Laboratory†, Forest Service, US Department

Design note

Sachs I B and Kuster T A 1980 Edgewise compression failure mechanism of linerboard observed in a dynamic mode Tappi63 10 69 Setterholm V C and Gertjejansen R O 1965 Method for measuring compressive properties ofpaper Tappi 48 5 308 Stockmann J E 1976 Measurement ofintrinsic compressive strength of paper Tappi 59 7 93

Figure 2. Compression device and load cell mounted in SEM specimen chamber (MC84 9052). A, lead screw; B, wiring from strain gauge to miniature cable connector; C, strain gauges; D, load cell; E, extension rod from load cell; F, slidingjaw: G, fixed jaw; H, paperboard sample; I, locking screws; J, steel rods on which jaws move; K, SEM collector; L, SEM specimen chamber: M, microscope rotation knob.

The paperboard sample (H) is clamped into place at the top of the two jaws (F, G) by means of the locking screws (I). Thus the sample, which measures 4.0 mm by 12.0 mm. is directly in line with the applied load. Jaw separation at the start of compression is 0.5 mm. Very small jaw separations are used to get short specimen span length in order to avoid buckling of the paperboard sample under compression. Compressive strength is a mechanical property of paper, and with this device, in conjunction with the SEM, one can look at the direct compression failure ofpaperboard.

To prevent charging within the microscope from the electron beam. the paperboard samples are coated with a grounding metal (approximately 20 nm of gold). In this way the paperboard sample is directly observed as it is being compressed.

Using the described SEM compression device, we observed and recorded for the first time the dynamic failure of paperboard subjected to short column edgewise compression (Sachs and Kuster1980).

References Cavlin S and Fellers C 1975 A new method for measuring the edgewise compression properties ofpaper Svensk Papperstidn. 9 329 Grangard H 1970 Compression of board cartons Svensk Papperstidn. 17 487 Grangard H and Kubat J 1969 Some aspects of the compressive strength of cartons Svensk Papperstidn. 15 466 Gunderson D E 1981 A method for compressive creep testing of paperboard Tappi 64 11 67 Jackson C A, Koning J W Jr and Gatz W A 1976 Edgewise compressive test of paperboard by a new method Pulp and Paper Can. 77 10 T180 McKee R C, Gander J W and Wachuta J R 1963 Compression strength formula for corrugated boxes Paperboard Packaging 48 149

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