Apparatus for Evaluating Stability of Corrugated Board Under Load in Cyclic Humidity Environment

Abstract

The strength of a corrugated container is usually determined and reported as crush strength under progressively increasing top-to-bottom compressive load. 1 The test is performed in seconds in a controlled constant temperature and relative humidity environment. However, a dynamic strength test under controlled conditions cannot account for the reduction in load-carrying ability inherent in the extended duration and changing humidity environment of actual warehousing and storage. In actual use, the container may be required to carry load for a period of many months, experiencing dozens of cyclic changes in relative humidity and, less significantly, temperature. Apparently, other means are needed to effectively measure and predict the long-term, load-carrying ability of corrugated board and containers in the actual service environment. 2-4 ASTM Method D4577-66 5 has been approved for the testing of containers, but suitable standards have not been set for testing paperboard and corrugated board.In 1987, Considine and Gunderson 6 described a method for mechanical testing of paperboard during compressive creep in a cyclic humidity environment. The USDA Forest Service, Forest Products Laboratory (FPL), recently developed a device for evaluating corrugated board (the composite of linerboard faces and fluted corrugating medium) under conditions of constant load in a cyclic humidity environment. In this new device, corrugated board specimens can be loaded in either edgewise compression or flat-wise bending. Corrugated board performance in these two modes is generally accepted as the dominant factor in determining container strength in dynamic tests.' Because our constant load tests are necessarily of extended duration, testing multiple specimens at the same time is most efficient. The FPL apparatus is D.E. Gunderson is Research General Engineer. and T.L. Laufenberg is Supervisory Research General Engineer, USDA Forest Service, Forest Products Laboratory, Madison, WI.configured to load 28 specimens in edgewise compression and 30 specimens in four-point bending, but it can be reconfigured to test as many as 70 specimens in compression or 50 in bending. LOADING APPARATUS AND SPECIMEN DESCRIPTION CompressionThe compression load frame is designed to provide constant edgewise load to the specimen. While under load, the specimen swells and shrinks as the relative humidity (RH) increases and decreases. Also, specimen height decreases progressively (compressive creep) over the extended load period.Design of the compression load frame is shown schematically in Fig. 1. Access for installing or removing specimens is convenient because the load head is cantilevered from the guide rod. Load applied to the specimen may be increased or decreased by adjusting the position of the weight to the left or right on the lever arm. Load is applied to, or removed from, all specimens at the same time by lowering, or raising, the weight elevator.The platform (Fig. 1), which carries multiple load devices. is 305 by 710 mm and includes 14 separate lo...

Static and Dynamic Strength of Paperboard Containers Subjected to Variations in Climatic Conditions

“…They also presented results for the time to failure under a constant static load for various levels of moisture content. A relationship between moisture content and compressive strength for specific corrugated samples was also presented by Hung et al Gunderson and Laufenberg also evaluated the load carrying capability of corrugated board but under cyclic humidity environments (50–90% RH) using long‐term load, edgewise compression and multi‐point bending tests. The work clearly identified the susceptibility of uncoated paperboard samples at elevated levels of RH with multiple failures at the 90% RH cycles.…”