Evaluating hardness and the S-test

Abstract

The corrugated industry typically quantifies crush resistance using the Concora corrugated medium test (CMT) on fluted medium or flat crush on combined board. These tests compress the materials until the point of complete failure of the flutes. Combined board elastically resists crushing forces until a certain point, the hardness of the structure, while additional load causes permanent damage and deformation. This study investigates how hardness can be measured directly from a load curve collected during CMT (or flat crush) testing and how it varies throughout the North American paper supply. It also explores how hardness correlates with the values obtained from the newly developed S-test. This new test method deserves further study as a potentially more appropriate specification for crush resistance of corrugated medium.