Effect of fibre concentration on the mechanical properties of welded reinforced polypropylene

The effects of fibre concentration on the mechanical response of welded glass-fibre-reinforced polypropylene (GF-PP) were studied in-depth. Experimental observations during tensile tests of unwelded and welded GF-PP have shown a weld ratio reduction - ratio between the strength of the welded material and that of the bulk material - as high as 60%. For all conditions studied, no significant change in the polymer matrix was observed. Increasing the fibre content on the welded material was additionally associated with a decrease in the stress at break and the strain at the maximum stress, respectively 68 and 84% for 50 wt% GF-PP. The DIC technique was used to retrieve the local response in the welded zone, showing local strain as high as 19.5 times the macroscopic strain. Using X-ray microtomography, the strain magnification could be explained by the significant increase of the fibre density at the welded zone. It was also shown that at least 2/3 of the fibres were orientated within the weld plane limiting the transverse strain, favouring void nucleation and embrittlement of the material. As a consequence, the rupture can be explained by the amplification of the strain linked with the fibre concentration and orientation of the welded material.

Automated summary

This study investigates the effects of fibre concentration on the mechanical response of welded glass-fibre-reinforced polypropylene (GF-PP). Experimental observations reveal a significant reduction in weld ratio, up to 60%, indicating a decreased strength compared to the bulk material. Increasing fibre content in the welded material results in a decrease in stress at break and strain at the maximum stress. The use of DIC technique and X-ray microtomography further confirms the localized strain amplification in the welded zone due to the significant increase in fibre density.