Characterisation and prediction of failure in injection-moulded short-fibre composites from coupons to components
File(s)
Author(s)
Fujita, Yuki
Type
Thesis
Abstract
Injection-moulded (IM) short-glass fibre reinforced thermoplastics (SFRPs) have drawn large interest from automotive industry for cost and weight reduction. The injection-moulding process creates a core-shell micro-structure with complex fibre orientation, leading to anisotropic and heterogeneous properties and failure modes, which complicates the design of IM-SFRP components. When designing such components, it is necessary to predict when and where failure will occur. However, existing failure criteria for SFRPs underestimate the failure load, because they consider failure initiation only and neglect the material’s toughness. The objective of this work was to develop a Finite-Element (FE) based methodology to accurately predict the performance of polyamide 6.6 based IM-SFRPs, by accounting for the material’s progressive failure.
The initiation and propagation fracture toughnesses (Full R-curves) were characterised from Compact Tension tests with the combined effect of fibre orientation, moisture and temperature. FE simulations have demonstrated the need to consider both initiation and propagation toughnesses to predict the response of notched coupons.
State-of-the-art structural FE simulations, coupled with fibre orientation fields, were conducted using IM-SFRP automotive (sub)components. The conventional methodology using failure initiation criterion underestimated the maximum load by 20%. By introducing the experimentally-measured toughnesses, this methodology showed excellent agreement (within 3% error) with the tests under all conditions, highlighting the importance of accounting for the material’s toughness to predict the ultimate failure of IM-SFRPs.
Damage initiation and propagation in the (sub)components were predicted by the proposed FE simulations. Using fractographic analyses, the sequence of failure events in the (sub)components were inferred experimentally. These results presented good agreement, demonstrating that fractography has been successfully used to support the proposed models.
This research demonstrates that accounting for the material’s toughness is required to accurately predict the ultimate failure of IM-SFRP components. The output of this research will contribute to design safer and more efficient damage-tolerant IM-SFRP components.
The initiation and propagation fracture toughnesses (Full R-curves) were characterised from Compact Tension tests with the combined effect of fibre orientation, moisture and temperature. FE simulations have demonstrated the need to consider both initiation and propagation toughnesses to predict the response of notched coupons.
State-of-the-art structural FE simulations, coupled with fibre orientation fields, were conducted using IM-SFRP automotive (sub)components. The conventional methodology using failure initiation criterion underestimated the maximum load by 20%. By introducing the experimentally-measured toughnesses, this methodology showed excellent agreement (within 3% error) with the tests under all conditions, highlighting the importance of accounting for the material’s toughness to predict the ultimate failure of IM-SFRPs.
Damage initiation and propagation in the (sub)components were predicted by the proposed FE simulations. Using fractographic analyses, the sequence of failure events in the (sub)components were inferred experimentally. These results presented good agreement, demonstrating that fractography has been successfully used to support the proposed models.
This research demonstrates that accounting for the material’s toughness is required to accurately predict the ultimate failure of IM-SFRP components. The output of this research will contribute to design safer and more efficient damage-tolerant IM-SFRP components.
Version
Open Access
Date Issued
2024-04
Date Awarded
2024-11
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Pimenta, Soraia
Greenhalgh, Emile
Sponsor
Asahi Kasei Corporation
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)