Impact fracture ductile

Failure Morphologies. Ductile failure of notched polycarbonate specimens has long been recognized to occur with shear yielding from the notch tip (6). This occurs for the block polymers for all rates of test. Hull and Owen (5) recently reported from micrographic studies of impact fracture surfaces that the brittle failure of polycarbonate involves the formation and breakdown of a craze at the notch tip. The ductile-... 

When the material exhibits a ductile behavior in impact fracture, unstable fracture does not occur. The crack propagation is generally completely stable. 

Since Wf = U and A = It, Equation (14) is similar to Equation (12). It has therefore been argued [23] that the impact fracture energy at crack initiation in polymers with ductile behavior G is rather the essential fracture work we. Furthermore, the second parameter representing the variation of the impact fracture energy during stable crack growth, T, has been attributed to the work dissipated in the outer plastic zone and is not related to the fracture process [23]. 

Key words fracture toughness, J-integral, master curve, irradiation, crack-arrest, embrittlement, Charpy impact, nil-ductility transition (NDT) temperature, pressurized water reactor (PWR). 

Figure 23.12. SEM micrographs of the impact fracture surface of self-reinforced HDPE/LDPE (80/20 wt%) prepared by OPIM. (a) The whole fracture surface showed multilayer structure of sample (b) the fracture surface of shear layer exhibited a brittle fracture (c) the fracture surface of central layer showed ductile breaks and contributes to the increase of toughness...

A TEM study of poly(vinyl chloride)/chlori-nated polyethylene (PVC/CPE) assessed the dispersed phase morphology for correlation with impact properties [342]. Microtomed sections of the blend were stained by a two stage osmium tetroxide method to reveal the CPE phase [343] as the concentration increased, the discrete two phase morphology changed to a continuous network resulting in a transition from brittle to ductile impact fracture (shown... 

Examination of oven-aged samples has demonstrated that substantial degradation is limited to the outer surface (34), ie, the oxidation process is diffusion limited. Consistent with this conclusion is the observation that oxidation rates are dependent on sample thickness (32). Impact property measurements by high speed puncture tests have shown that the critical thickness of the degraded layer at which surface fracture changes from ductile to brittle is about 0.2 mm. Removal of the degraded layer restores ductiHty (34). Effects of embrittled surface thickness on impact have been studied using ABS coated with styrene—acrylonitrile copolymer (35). 

Material behavior have many classifications. Examples are (1) creep, and relaxation behavior with a primary load environment of high or moderate temperatures (2) fatigue, viscoelastic, and elastic range vibration or impact (3) fluidlike flow, as a solid to a gas, which is a very high velocity or hypervelocity impact and (4) crack propagation and environmental embrittlement, as well as ductile and brittle fractures. 

Impact modifiers for PET are generally elastomeric compounds that increase impact strength and elongation while usually decreasing modulus. An effective way to enhance the impact strength and to induce a brittle/ductile transition of the fracture mode, is by the dispersion of a rubber phase within the PET matrix. The... 

Figure 13. Impact energy at 100% ductile fracture temperature, which is shelf energy, as a function of REM-to-sulfur ratio retained in the 80,000 psi steel. Note the progressive effect of increasing REM additions on the transverse impacts while the longitudinal values remain virtually unchanged. The X points represent untreated steel.

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