Apparatus and method for testing edge strength of sheet of material having detection mechanism for optically measuring strain in sheet

A method of testing edge strength of a sheet of material along an edge of the sheet, the method comprising:

• applying a surface pattern of visual markers on a surface of the sheet in a region of interest along the edge of the sheet;
• obtaining a first optical image of the surface of the sheet in the region of interest without any 3-point bending load applied to the region of interest;
• applying a 3-point bending load to the region of interest along the edge of the sheet;
• obtaining a second optical image of the surface of the sheet in the region of interest while the 3-point bending load is being applied to the region of interest;
• and
• determining stress on the surface of the region of interest along the edge of the sheet resulting from the application of the 3-point bending load based on the first optical image and the second optical image, wherein the surface pattern facilitates optically measuring the strain in the sheet of material.

A method of testing edge strength of a sheet of material along an edge of the sheet using a test apparatus that comprises a test region, the method comprising:

• applying a surface pattern of visual markers on a surface of the sheet in a region of interest along the edge of the sheet;
• continuously advancing the sheet of material through the test apparatus wherein the edge of the sheet is advanced through the test region while applying a 3-point bending load to the portion of the sheet passing through the test region;
• obtaining a first optical image of the surface of the sheet in the region of interest while the edge of the sheet is continuously advancing through the test region but before the region of interest reaches the test region;
• obtaining a second optical image of the surface of the sheet's region of interest when the region of interest advances into the test region while the 3-point bending load is being applied;
• and
• determining stress on the surface of the region of interest along the edge of the sheet resulting from the application of the 3-point bending load based on the first optical image and the second optical image, wherein a pattern provided on a surface of the sheet in the test region facilitates optically measuring the strain in the sheet of material.