Craze size, influence

Influence of Stress Intensity Factor on Craze Size.159... 

Both principal fracture mechanisms, shear yielding and crazing, are influenced by the particle size. In PPBC matrix, where spherical elastomeric particles are chemically bonded, the energy absorption takes place mainly by deformation of the matrix. In such systems, a large amount of shear yielding is to be expected. The shear yielding becomes more prominent upon increasing the concentration of EPDM as well as reduction of their particle size. The micro-shear bands in the fracture surface (Pig. 10.23e) clearly support these expectations. 

The effect of R-ratio (0.1 R 0.7) on the craze zone size of PMMA has also been investigated in the range of 0.4 g 1.0 MPa /m at 1 Hz no consistent or significant influence could be established this context it should be... 

The rubbery particles promote the absorption of strain energy by complex interactions, which are thought to involve both craze formation and shear deformations. The overall mechanism is influenced by the size of the microscopic rubbery particles. 

The dominant mechanism of deformation depends mainly on the type and properties of the matrix polymer, but can vary also with the test temperature, the strain rate, and the morphology, shape, and size of the modifier particles (Bucknall 1977, 1997, 2000 Michler 2005 Michler and Balta-Calleja 2012 Michler and Starke 1996). Properties of the matrix determine not only the type of the local yield zones but also the critical parameters for toughening. In amorphous polymers with the dominant formation of crazes, the particle diameter, D, is of primary importance, while in some other amorphous and in semicrystalline polymers with the dominant formation of dilatational shear bands or intense shear yielding, the interparticle distance ID, i.e., the thickness of the matrix ligaments between particles, seems to be also an important parameter influencing the efficiency of toughening. This parameter can be adjusted by various combinations of modifier particle volume fraction and particle size. 

In addition to influences of mechanical load on degradation in polymer chains, unexpected degradation can occur due to the initiation of specific micromechanical processes and mechanisms. Such mechanisms (shear flow, craze formation, cavitation, etc.) are initiated in particular in inhomogeneous polymers (blends, filled and reinforced plastics, etc.) by inhomogeneous stress distributions caused by external mechanical loads. Typical examples for such physical aging processes are ABS materials with an unfavorable size distribution of rubber particles [72],... 

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