Total specific work of fracture

The term fracture toughness or toughness with a symbol, R or Gc, used throughout this chapter refers to the work dissipated in creating new fracture surfaces of a unit nominal cross-sectional area, or the critical potential energy release rate, of a composite specimen with a unit kJ/m. Fracture toughness is also often measured in terms of the critical stress intensity factor, with a unit MPay/m, based on linear elastic fracture mechanics (LEFM) principle. The various micro-failure mechanisms that make up the total specific work of fracture or fracture toughness are discussed in this section. 

The failure processes in thermoplastics composites with aligned glass fibers of sub-critical transfer length have been characterized (Lauke and Schultrich, 1983, 1986a, b Lauke et al., 1985 Lauke and Pompe, 1988) in terms of matrix fracture mode which is determined mainly by the ductility of the matrix material, loading rate and temperature. The total specific work of fracture, / t, is expressed as the sum... 

Fig. 4. Effect of temperature a) and displacement rate b) on the total specific work of fracture (wf) versus ligament length curves.

By partitionig the total specific work of fracture energy into a yielding related (Wy) and a necking/tearing (Wj, ) related component, the specific terms Wg y and Wg can be obtained, that... 

The total specific work of fracture, M/Ft, can be treated as the sum of three effects, the energies involved in ... 

Figure 4. Plot of total specific work of fracture (w f) vs. ligament length (L) for DDENT specimens of HDPE determined at...

Figure 11.35 Specific total work of fracture vs. ligament length plots for the tensile SEN specimens of a-PP and (3-PP. Note. The data related to fast fracture of ct-PP at L >15 mm (filled circles) are excluded. (From Reference 24 with permission from John Wiley Sons.)...

Figure 12.23 Schematic diagram showing specific total work of fracture against ligament length...

Figure 13.39 Specific total work of fracture Wf versus ligament length I for deeply doubleedge-notched tension (DENT) ( ) and single-edge-notched bend (SENB) ( ) 3 mm thick polypropylene random copolymer samples. (Reproduced from Easce, L, Bernal, C, Erontini, P. et al. (2001) On the Impact essential work of fracture of ductile polymers. Polym. Eng. Sci., 41, 1. Copyright (2001) John Wiley Sons, Ltd.)...

Karger-Kocsis and Varga determined the plane stress We and (3wp values of (3-PP using SEN and DENT specimens with dimensions of 100 mm x 35 mm x 1mm under tensile mode (24,25). Figure 11.34a and b shows typical load-displacement curves for the a-PP and (3-PP SEN specimens with different ligament lengths. Selfsimilarity in the shape of the load-displacement curves for the a-PP is not maintained when L > 15 mm. At this stage, the samples fail with fast fracture due to an incomplete development of the plastic zone. The EWE approach becomes invalid for the a-PP. By contrast, the (3-PP specimens show more ductile behavior as evidenced by nonlinearity in the force-displacement curves. The specific total fracture work... 

In the complementary approach, that based on measurement of the total Izod fracture work W, the critical specific fracture work Gc is determined as... 

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