A Study on Dynamic Strength of Welded Specimens of plastics

Abstract

Dynamic strength of plastics has been studied by engineers for many years, but no satisfactory solutions arc available as yet.
What strength the weldments possess in comparison with the base materials is considered in this report.
The disturbance characteristics and the states of destruction are studied by varying the temperature.
The number of repeated cycles to failure of P.V.C. base plates reduces with the rise of temperature, and this reduction is remarkable above 50°C. The endurance limit at 20°C is 2.5 Kg/mm². This is about 37% of its tensile stress.
The maximum joint efficiency of P.V.C. plates processed with hot jet welding is over 74% at 30°C.
The endurance limit is 2.37 Kg/mm², and the endurance limit ratio of the weld to the base materials is nearly equal.
The endurance limits of P.V.C. pipe base material and welds by hot plate welding are 1 Kg/mm² and 0.5 Kg/mm² respectively. The S-N curve of the heated plate welded P.V.C. plate at 30°C augrees approximately with the base materials at 30°-40°C.
The endurance limit of low pressure polyethylene treated with frictional welding is 0.44 Kg/mm² at 20°C, and that of its base materials is 0.58 Kg/mm² when the number of repeated bending cycles is 5×10⁶.