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Ultrasonic welding using tie‐layer materials. part II: Factors affecting the lap‐shear strength of ultrasonic welds
Author(s) -
Ramarathnam G.,
North T. H.,
Woodhams R. T.
Publication year - 1992
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760320907
Subject(s) - materials science , melt flow index , composite material , polypropylene , ultrasonic sensor , welding , cavitation , shear (geology) , lap joint , layer (electronics) , shear strength (soil) , adhesive , polymer , physics , environmental science , acoustics , mechanics , soil science , copolymer , soil water
The influence of tie‐layer Melt Flow Index on the lap‐shear strength of ultrasonic welds in oriented polypropylene (OPP) has been evaluated. The tie‐layer Melt Flow Index was varied from 0.03 dg/min to 2600 dg/min; the highest lap‐shear strength properties were obtained using tie‐layers that had melt flow index values between 30 and 100 dg/min. When using low Melt Flow Index tie‐layers, hot spot formation and concomitant changes in fusion zone and heat‐affected‐zone dimensions produced stress concentrations that promoted failure in oriented polypropylene material away from the bondline region. When very high Melt Flow Index (2600 dg/min) tie‐layers were used, the mode of failure during lap‐shear testing was a mix of cohesive, in oriented polypropylene, and adhesive failure. The molecular weight of material at the bondline was not markedly affected by the thermal cycle produced during ultrasonic welding. Only the flash ejected when using low Melt Flow Index tie‐layers exhibited any evidence of degradation; it is suggested that the ejected flash may have been degraded because of a combination of thermal, cavitation, and thermo‐oxidative processes.