Impact-notch factor

A notched specimen is a test specimen that has been deliberately cut or notched, usually in a V-shape, to induce and locate the point of failure. The notch factor is the ratio of a property, such as impact strength, determined on a plain specimen to the property determined on the notched specimen. 

Energy to break per unit width of sample. (In notched specimens this is taken as the energy to break unit width of notch. In this case the results are quoted in such units as ft lb per inch of notch or joules per millimetre. The values obtained depend on the notch width. For example, it has been found that on reducing the notch width from V" to X the impact strength of a polycarbonate increased by a factor of 5.4 and that of unplasticised PVC by 3.1.)... 

For the purposes of performing an impact test on a material it is proposed to use an elastic stress concentration factor of 3.5. If the notch tip radius is to be 0.25 mm estimate a suitable notch depth. 

Finally, of great importance are finite width effects. The strength of a composite laminate in the presence of a hole, a crack, or impact damage is drastically reduced as the size of the notch covers a significant percentage of one of the dimensions of the structure. Finite width correction factors have been obtained by Tan for holes [19]. 

The report of the inquiry [111] criticised the design and fabrication of the alterations made to the original pontoon. The actual cause of the accident was the failure of some tie bars in the detail around the jacking points. The failure was due to brittle fracture which initiated from severe notches such as a small radius curve at the fillet between the spade end and the shank of the tie bar. Weld defects and fatigue cracks were also present in tie bars subsequently recovered from the sea bed. The tie bars had been flame cut to shape and had weld repairs visible to the eye. There had been no post welding heat treatment of the steel. The steel complied with the original specification but tests showed low Charpy V notch impact values. Photo elastic tests indicated a stress concentration factor of 7 at the fillet between the spade end and the shank. The fracture was initiated in the opinion of the inquiry tribunal by the low ambient temperature of around 3°C. 

Thermal conductivity mW/MK Tensile strength MPa % Elongation Notched Izod impact J/m Coefficient of friction, 3.4 MPa load Wear factor 1/pPa Shore durometer hardness Specific gravity... 

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