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

The strength of a corrugated container is usually determined and reported as crush strength under progressively increasing top-to-bottom compressive load. 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. ASTM Method D4577-66 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 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