Fracture Energy ranking

V. RELATIVE RANKING OF FRACTURE ENERGIES OF GLASSY POLYMERS... 

Since fracture energy is affected by the molecular weight, crack speed, molecular orientation, etc., ideally we should rank fracture energies of glassy polymers under the same conditions. Since this is not possible when literature values are compared, we attempt to use the range of fracture energies instead of a single value for each polymer. 

In Figure 8, we can readily rank the following polymers with a decreasing fracture energy ... 

Figure 8. Relative ranking of fracture energies of glassy polymers versus metals and nonmetals.

All of these tests give a number , perhaps in the form of a force per unit area or an energy per unit area, which may be loosely termed the adhesion . It is important to realize that this nnmber reflects the properties of the joint-substrate, adhesive, interface and the interactions between them. Thus, changes in the dimensions of a joint commonly change the value of adhesion measured different tests will not necessarily rank a series of adhesives or surface treatments in the same order. It is only Fracture mechanics tests that make any claim to measure a fundamental property, and, even here, great care is needed in interpreting the results (see Adhesion - fundamentai and practicai). 

It should be pointed out that while the indirect methods provide a qualitative method of ranking the adhesion between fiber and matrix and the composite lamina test methods actually measure fiber-matrix interface sensitive composite properties, the direct methods not only provide a measure of fiber-matrix adhesion but can also provide information about fiber-matrix failure mode and a method to measure the energy involved in fracture of the fiber-matrix interface. This last parameter is important in relating fiber-matrix adhesion to composite toughness. 

---