Flat Crush Test (FCT), also known as flat compression resistance, is a testing method used to measure the strength of a material, typically corrugated cardboard, when subjected to compression forces. The objective is to determine its ability to withstand mechanical stress during transportation, storage, or use. This testing method is defined in the international standard ISO 3035.
The FCT involves applying increasing pressure to a surface of corrugated cardboard until it either fails or deforms significantly. The results provide an indication of the material's robustness and its capacity to bear loads and stresses during intended use.
The FCT test is typically conducted using a compression testing machine specifically designed for this purpose. The corrugated cardboard sample is placed between two parallel plates of the machine, and a compressive force is gradually applied. The maximum force that the sample can withstand before deformation is recorded and expressed in kilonewtons per square meter (kN/m²) or more commonly in newtons per square millimeter (N/mm²).
According to ISO 3035, the corrugated cardboard sample to be tested should be a square with sides measuring 50mm. The cardboard should be conditioned at a temperature of 23±1°C and a relative humidity of 50±2% for at least 24 hours prior to the test.
The higher the FCT value, the better the cardboard is able to resist compression. A low flat crush resistance may indicate a lower-quality material or an inappropriate corrugated cardboard design. Conversely, a high FCT value may indicate superior material quality or an effective corrugated cardboard design.