Measure of Shear and Compression Components of Puncture Tests

SUMMARY A study was designed to separate and measure the compression components (proportional to area) and the shear components (proportional to perimeter) of a simple puncture test. Two sets of punches were used (one with a constant area and a variable perimeter, and the other with a constant perimeter and a variable area) to measure the compression and shear components in puncture tests on foam plastic board and representative foods. The puncture force for both can be expressed by the equation F = K,P + K,A + C , where K., K , and C are constants, P is the perimeter of the punch, and A is the area of the punch. K , represents the shear coefficient and Kc the compression coefficient of the food being tested. For a given punch, F depends upon K , and K , which are properties of the material being tested. For a given material, F depends on the perimeter and area of the punch. These results can be used as a basis for design of punch shape and size in a practical puncture test. The shear component of a puncture test can be increased or decreased relative to the compression component by manipulating the perimeter/ area ratio of the punch.