Fracture load

Several experiments will now be described from which the foregoing basic stiffness and strength information can be obtained. For many, but not all, composite materials, the stress-strain behavior is linear from zero load to the ultimate or fracture load. Such linear behavior is typical for glass-epoxy composite materials and is quite reasonable for boron-epoxy and graphite-epoxy composite materials except for the shear behavior that is very nonlinear to fracture. 

Deformation rate (in./min) Fracture load (lb) Average initial diameter (in.)... 

Papini M, Femlund G Spelt JK, Effect of crack growth mechanism on the prediction of fracture load of adhesive joints. Comp. Sci. Tech., 52, 1994, 561. 

Theoretical model of mode I delamination of z-pinned DCB has been developed to study the bridging mechanism of z-pin reinforcement. The numerical results show that the fracture load for delamination in the z-pinned DCB is greatly dependant on the fnctional pull-out force Pf. However, since the deformation of the z-pin is relatively small compared to sliding distance, the effects of debonding force and debonding length on the fracture resistance of the DCB are... 

The strength of tablets has traditionally been determined in terms of the force required to fracture a specimen across its diameter, the diametral compression test. The fracture load obtained is usually reported as a hardness value, an unfortunate use of a term that has a specific meaning in materials science, associated with indentation. The use of the fracture load does not allow for compacts of different shapes, diameters or thicknesses to be directly compared. For flat-faced circular tablets, a complete analytical solution exists for the stress state induced during the test (Barcellos and Carneiro 1953), allowing the tensile strength to be determined from the fracture load ... 

In this case, the load-displacement record may be somewhat nonlinear near the maximum load point, i.e., near the fracture load (see Fig. 4.5c). Most valid tests of practical test specimens exhibit this behavior. The nonlinearity represents plastic deformation around the crack border, and slight (irregular) crack extension during the last stage of the test. If the extent of the nonlinearity is not excessive, then it can be ignored and Kic can be calculated from the maximum (or fracture) load and the initial crack diameter lug. 

The specimens were positioned carefully between the pistons of a universal testing machine using a positioning aid to guarantee that the load is applied perpendicular to the notch plane. Then a preload was applied (about 10 % of the estimated fracture load). Then the aid was removed and the load was increased until fracture. The loading rate was selected in such a way that a test can be done within 10 to 20 seconds. The fracture load was used to determine strength (eq. I). 

The linear-slope CDCB specimens shown in Figs. 13 and 14 were used for mode-I fracture tests on FRP-wood bonded interfaces under both dry and wet conditions. A typical specimen under mode-I fracture load is shown in Fig. 15 for phenolic FRP wood interface under dry conditions, and the corresponding critical tip load versus crack opening displacement is plotted in Fig. 16. As an illustration, the fracture surfaces of epoxy FRP-wood with HMR and RF primers on wood substrates are shown in Figs. 17 and 18,... 

Yang S.T., Hu X Z, Wu Z.M. 2011 Influence of local fracture energy distribution on maximum fracture load of three-point-bending notched concrete beams. Engineering Fracture Mechanics, (78) 3289-3299. 

Kic = coefficient of stress intensity under conditions of plane deformation max = coefficient of stress intensity under maximum fracture load Kq = coefficient of stress intensity under the load corresponding to 5% secant line Rff = notch radius... 

Thus, one can identify at least three factors that increase the longterm strength of Sprut-5M adhesive at the stage of formation of the polyurethane network but which have no further effect after the adhesive cures completely. Actually, in this state of the adhesive there is no indication of the structure that is observed with the orientation of the molecular chains there is an abrupt reduction of the opportunity for macroradicals to recombine and for the submicrocracks to be filled. At this stage of curing, despite some decrease of the long-term strength under a load of 50% of the fracture load, the Sprut-5M adhesive has much better resistance to the effect of constant loads than does the polyester adhesive (see Fig. 3.2, curve 1 (after 102 days) and curve 4). 

Keyak, J. H., Rossi, S. A., Jones, K. A., and Skinner, H. B. (1998), Prediction of femoral fracture load using automated finite element modeling, J. Biomech. 31 125-133. 

---