Notch nonlinearities in pseudo-ductile composite laminates: A novel LE/HE sublaminate design

Abstract

Attempts to achieve pseudo-ductility in quasi-isotropic (QI) thin-ply laminates have traditionally relied on stacking [LE/HE/LE] sublaminates, with LE representing low-elongation and HE high-elongation. However, the increase in effective ply thickness led to reduced unnotched strength. Alternatively, in this study, we define a new sublaminate configuration ([LE/HE]) to minimise the increase in ply-block thickness and compare experimentally such hybrid QI thin-ply laminate with a conventional thin-ply QI ( ) laminate. The hybrid specimens demonstrated consistent but modest pseudo-ductile properties (ultimate-to-pseudo-yield strength ratio, =1.1; pseudo-ductile strain, ɛ =0.3%). Using Digital Image Correlation (DIC) and advanced dark-field X-ray imaging, we detected earlier and more pronounced deviations from linear strain fields in hybrids compared to the reference laminates. The hybrid laminates showed an 11.7% reduction in unnotched strength but a 4% increase in notched strength in Open-Hole Tension (OHT) specimens. Thus, the proposed hybridisation introduces new damage mechanisms facilitating stress redistribution, thereby recovering more nominal strength with a reduced impact on the unnotched strength. Our findings suggest viable approaches to integrate pseudo-ductility into thin-ply laminates whilst preserving the inherent advantages of ply thinness

The authors acknowledge the funding and support of Ministerio de Ciencia, Innovación y Universidades, Spain for the project En pos de materiales compuestos de fibra larga híbridos, bio-basados y sostenibles para aplicaciones estructurales, Spain (SUBHYCO) (PID2021-126989OB-I00). Anbazhagan Subramani acknowledges the financial support of the Universitat de Girona, Spain for INV309_2019 and MOB2021. He would also like to thank the Universitat de Girona and Santander Universidades, Switzerland for the financial resources provided through Personal Investigador en formació (IF_UDG), 2020. Open Access funding was provided through the CRUE-CSIC, Switzerland agreement with Elsevier