Corrugated Board - Ring Crush Test : Ring Crush is a traditional test of linerboard and corrugating medium strength. Ring crush measures compression resistance, and this compression strength is considered to relate to the eventual compression strength of combined board made from the component. Linerboard called high strength or high performance linerboard is board that is able to achieve a specified minimum ring crush at basis weights that are lower than traditional basis weights. Corrugated Board - Concora Crush Test : The Concora Crush Tester performs a series of tests to determine the rigidity and crush resistance of corrugated material. It is used in conjunction with the Concora Liner Tester. The first test measures the flat crushing resistance of a laboratory-fluted corrugated material. The second test determines the edgewise strength, parallel to the flutes, of a short column of single-, double-, or triple-wall corrugated board. The third test evaluates the ability of corrugated material to contribute to the compression strength of a corrugated box by measuring the edgewise compression strength of a laboratory-fluted strip of corrugated material in a direction parallel to the fluted tips. Corrugated Board - Flat Crush Strength : The flat crush test is a measure of the resistance of the flutes in corrugated board to a crushing force applied to the surface of the board under prescribed conditions. Flat crush is a measure of the flute rigidity of corrugated board. A high flat crush value indicates a combination of good flute formation and at least adequate strength medium. Low flat crush may indicate a number of conditions including low strength medium, leaning flutes and crushed flutes.

From: http://www.thaicorrugated.com/knowledge.php?cid=30