Craze zone size

In all papers mentioned above the characterization of the craze growth has been performed by measuring the craze length. By application of the optical interference method the essential information on the growth of craze width is awiilable. Figure 22 shows the interference fringe patterns and measured craze zone sizes at a stationary crack tip in PMMA loaded in a creep test at a constant K,-value at loading times of 150 s and 2 1(F s... 

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... 

PI blended with PMS and then foamed by the thermal decomposition of PMS Nano-foams showed increased craze zone size and higher crack stability than the not-foamed PI films PlummCT et al. 1995 Charlier et al. 1995... 

A third method which recently provided considerable insight into the role of crazes in deformation and fracture of amorphous polymers is the optical interference measurement of crazes (preceding a crack). Since the pioneer work of Kambour, this method has been widely used to determine characteristic craze dimensions and critical displacements. W. Doll gives an overview on recent results and on their interpretation in terms of fracture mechanics parameters (stress intensity factor, plastic zone sizes, fracture surface morphology, fracture energy). 

Fringe number of loaded craze Fringe number of unloaded craze Retarded fatigue crack growth Coordinate Plastic zone size... 

In the previous sections properties of crack tip crazes in thermoplastics within two different regimes of damage behavior have been described, that of stationary and slowly propagating cracks. During steady state slow crack propagation, as described above, at a particular crack speed the crack tip is preceded by a craze zone of constant size, indicating an equilibrium between fibril formation and fibril failure as demonstrated exemplarily in Fig. 3.27 a by two interference micrographs of the... 

The distribution of fibril strain according to Eq. (15) along the craze contour is shown in Fig. 4.22 for the two basically different craze sizes, just after and just before crack jump In the small initial craze the determined values of strain are nearly constant over the major part of the craze zone. In the large craze zone... 

This permits determination of the size A of the craze-tip process-zone size from the above developments as... 

W. Doll, L. Kinczol, and M. G. Schinker, Size and Mechanical Properties of Craze Zones at Propagating Crack Tips in Poly(Methyl Methacrylate) during Fatigue Loading , Polymer 24, 1213-1219 (1983). 

This study (34) implies that a right dispersion of rubber particles may permit optimum stress field overlap that affords lower craze-initiation stresses and therefore can rapidly dissipate the strain energy in the HIPS. A more homogeneous spatial distribution of rubber particles allow for a uniform development of crazes. Prevention of the strain localization phenomenon to avoid the detrimental situation, where crazes prefer to develop in certain areas and quickly lead to a catastrophic crack, could result in a larger total volume of crazed material. Further, Donald and Kramer (22) discovered no crazes nucleating from an isolated rubber particle with diameter smaller than 1 urn because of an insufficient size of stress-enhanced zone. Since Sample-A has a small average particle size it should contain a large number of small rubber particles. Two small rubber... 

The temperature distribution during crack propagation is shown in Fig. 15. As the crack advances, the heat continues to diffuse along the normal to the craze surfaces but the size of the hot zone remains comparable to that of the craze thickness. The maximum temperature increase is located at the crack/craze interface, where the craze thickening and related heat flux into the bulk are maxima. At this location, the temperature reaches the glass transition temperature Tg but plasticity is not enhanced in the bulk, which remains primarily elastic during crack propagation. 

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