Notch stiffness

The results of comparison for HDPE samples with sharp notch and without it show, that notch (stiff macroscopic defect) introduction results to V reduction, that is, local order level enhancement, which is expressed in mechanical vitrification of devitrificated amorphous phase part [59]. This effect defines molecular mobility considerable reduction, expressed by decrease, and reduction. The last factor results to d decrease up to the values typical for quasibrittle fracture, that is, d < 2.5 [6]. 

These values are determined by experiment. It is, however, by no means a trivial task to measure the lamina compressive and shear strengths (52,53). Also the failure of the first ply of a laminate does not necessarily coincide with the maximum load that the laminate can sustain. In many practical composite laminates first-ply failure may be accompanied by a very small reduction in the laminate stiffness. Local ply-level failures can reduce the stress-raising effects of notches and enhance fatigue performance (54). 

For a part to exhibit stmctural stiffness, flexural moduH should be above 2000 N/mm (290,000 psi). Notched l2od impact values should be deterrnined at different thicknesses. Some plastics exhibit different notch sensitivities. For example, PC, 3.2 mm thick, has a notched l2od impact of 800 J/m (15 fdbf/in.) which drops to 100 J/m (1.9 fflbf/in.) at 6.4-mm thickness. On the other hand, one bisphenol A phthalate-based polyarylate resin maintains a 250-J /m (4.7-fdbf/in.) notched l2od impact at both thicknesses. Toughness depends on the stmcture of the part under consideration as well as the plastic employed to make the part. Mechanical properties, like electrical properties, ate also subject to thermal and water-content changes. 

Polyarylate It is a form of aromatic polyester (amorphous) exhibiting an excellent balance of properties such as stiffness, UV resistance, combustion resistance, high heat-distortion temperature, low notch sensitivity, and good electrical insulating values. It is used for solar glazing, safety equipment, electrical hardware, transportation components and in the construction industry. 

Polysulfone It is a high performance amorphous plastic that is tough, highly heat resistant, strong and stiff. Products are transparent and slightly clouded amber in color. Material exhibits notch sensitivity and is attacked by ketones, esters, and aromatic hydrocarbons. Other similar types in this group include polyethersulfone, polyphenyl-sulfone, and polyarylsulfone. Use includes medical equipment, solar-heating applications and other performance applications where flame retardance, autoclavability and transparency are needed. 

Impact Modifiers. Notched impact strength and ductility can be improved with the incorporation of impact modifiers, which also can lower the britde— ductile transition temperature and give much improved low temperature toughness. Impact modifiers are rubbers (often olefin copolymers) that are either modified or contain functional groups to make them more compatible with the nylon matrix. Dispersion of the mbber into small (micrometer size) particles is important in order to obtain effective toughening (29). Impact modifiers can be combined with other additives, such as glass fiber and minerals, in order to obtain a particular balance of stiffness and toughness. 

PVC has a unique ability to be compounded with a wide variety of additives, making it possible to produce materials that range from flexible elastomers to rigid compounds, that are virtually unbreakable with a notched Izod impact greater than 0.5 J/mm at —40 C, that are weatherable with good property retention for over 30 years, as well as compounds that have stiff melts and litde elastic recovery for outstanding dimensional control in profile extrusion, and also low viscosity melts for thin-walled injection molding. 

Fig 3. Layout of the test for the contact stiffness test with an un-notched PE specimen. 

In order to calculate the fracture properties from the SENS test it Is necessary either to know or derive the stiffness of the specimen and the contact stiffness between the striker and the specimen. For this work the contact stiffness was measured directly by striking a fully supported and un-notched specimen fig 3. Striker force and displacement were measured and used to determine the contact stiffness. Test were conducted at an Impact velocity of 0.5ms, and the contact stiffness was 3.7MPa for the PE, lOMPa for the PMMA and 7.69MPa for the PVC. 

Cut a notched metal contact disk to provide clearance for length of stiff insulated wire and Vi to 14 in. from walla of can. 

The blends could also contain inorganic fillers, other resins, elastomers, and additives. The materials had good impact and notched impact strength, combined with stiffness and toughness. They have been used for the same applications as new materials, instead of having to be downcycled [Timmermann et al., 1994]. 

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