Work

On the assessment of strength and durability of weld lines in injection-moulded unreinforced and short glass fiber reinforced polypropylene

Year: 2025

Type: article

Abstract: Identifying and predicting the performance of process-induced defects, such as weld lines in injection-moulded thermoplastic components, is critical for failure assessment. While previous studies have addressed various weld line phenomena, accurately predicting their instantaneous and long-term strength remains a challenge. This study investigates the thermo-mechanical performance of unreinforced, and 30% glass fiber-reinforced isotactic polypropylene (iPP) processed by injection moulding into specimens containing a central weld line due to a stagnating flow. Short-term experiments on smooth tensile bars at various strain rates (from 10-6 to 10-2 s-1) and temperatures (-20°C, 23°C and 80°C) identify plasticity driven failure kinetics with a transition towards brittle crack-growth driven failure at high temperatures and low strain rates. Long-term plasticity driven performance is assessed through creep-to-rupture and cyclic fatigue tests on tensile bars and identify the same transition from ductile-to-brittle failure, as well as a clear discrepancy in perceived plasticity-governed strength when comparing short- and long-term experiments. A key novelty of the work is the use of stress rate-controlled tensile experiments, rationalising this observed discrepancy in strength that is explained by strain localization. All observations are accurately captured using Ree-Eyring flow theory. The crack-growth governed failure of the weld line is explored by including fatigue crack growth experiments on CT specimens on both unreinforced and reinforced materials and general findings are presented.

Source: Polymer Testing

DOI: 10.1016/j.polymertesting.2025.109035

Authors: Aitor Arriaga, Sten J.J. van den Broek, Leon E. Govaert, Tom A.P. Engels

Institutions: Leartiker, Eindhoven University of Technology

Language: English

Topic: Injection Molding Process and Properties

Subfield: Mechanical Engineering

Field: Engineering

Domain: Physical Sciences

SDG: Industry, innovation and infrastructure

Open Access status: gold

Estimated APC paid: $3,370