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Welding in the World

, Volume 62, Issue 5, pp 997–1012 | Cite as

Factors influencing the fiber orientation in welding of fiber-reinforced thermoplastics

  • Isabel Fiebig
  • Volker Schoeppner
Research Paper
  • 29 Downloads

Abstract

In welding of fiber-reinforced thermoplastics, the welding pressure initiates squeeze flow of melt into the weld bead. This leads to reorientation of fibers into the flow direction. Therefore, the fibers in the weld are mainly oriented perpendicular to the joining direction. Since this is mostly identical to the load direction, the reinforcing effect of fibers is not effective in the weld because fibers only have a reinforcing effect on the polymer when they are aligned along the load direction. Current investigations at the Kunststofftechnik Paderborn (KTP) aim at reaching an effective reinforcing effect of fibers in the weld of fiber-reinforced thermoplastics. The experiments are carried out on polypropylene and polyamide. Three different grades of PP are used: unreinforced, short glass fiber-reinforced, and long glass fiber-reinforced PP with 30% fiber content each. The used grades of PA differ in viscosity and shear thinning behavior. Experiments are being conducted on influences on the weld strength and the fiber orientation in the weld for hot plate welding. Common welding parameters are varied. One aim of the investigations is to find a correlation between the flow velocity during squeeze flow and weld strength or fiber orientation.

Keywords

Polymer joining Fiber-reinforced thermoplastics Composites Hot plate welding Fiber orientation CT analysis 

Abbreviations

a, b, c

position of ROI’s in CT analysis

axx, ayy, azz

component of orientation tensor

b

width

CT

computed tomography

d

thickness

DP

design point

DVS

German Welding Association

\( \frac{dp}{dx} \)

pressure gradient in x-direction

F

joining force

fz

welding factor

GF

glass fiber-reinforced

h

melt layer height

h0

melt layer height at beginning of joining phase

HP

hot plate (welding)

hresidual

melt layer height at end of joining phase

K

flow consistency index

L0

melt layer thickness after heating

n

flow behavior index

P

unit vector

PA

polyamide

pF

welding pressure

PP

polypropylene

px, py, pz

component of the unit vector P

ROI

region of interest

sJ

joining displacement

THP

hot plate temperature

TM

crystalline melt temperature

vJ

joining velocity

vx

flow velocity in x-direction

vy

joining velocity

xa, xb, xc

position for calculation of flow velocity in squeeze flow

\( \dot{\gamma} \)

shear rate

σW

weld strength

Notes

Acknowledgements

The IGF Project 18702N of the research association “Forschungsvereinigung Schweißen und verwandte Verfahren e. V. des DVS. Aachener Straße 172. 40223 Düsseldorf” was, on the basis of a resolution of the German Bundestag, promoted by the German Ministry of Economic Affairs and Energy via AiF within the framework of the program for the promotion of joint industrial research and development (IGF).

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Copyright information

© International Institute of Welding 2018

Authors and Affiliations

  1. 1.Kunststofftechnik PaderbornPaderborn UniversityPaderbornGermany

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