First observations of pseudo-ductility in three-point bending tests on CFRP angle-ply laminates

Significance 

Excellent torsional stiffness generated by angle-ply laminates at ±45° configurations favor their wide applicability in the industry, while in laboratories it is commonly used for the purposes of determining material in-plane shear properties due to the relative simplicity of the tensile test method applied. When it comes to uniaxial testing, the ±45° angle-ply laminates at times develop pseudo-ductile effects. Pseudo-ductility could be sought in composite structures to avoid their brittle behavior and, consequently, to withstand higher levels of external loading due to an extended non-linear response. Presently, there exists a plethora of literature regarding the angle-ply laminates submitted to uniaxial tests. Nevertheless, the pseudo-ductile effects appear also under flexural loading because tension and compression are applied in different regions of the cross-sections simultaneously. In this sense, bending testing presents a higher degree of complexity introduced by the variation of the strain through the cross-section thickness. Therefore, there is need, urge and drive to comprehend pseudo-ductile flexural response of symmetric ±45° angle-ply laminates as flexion is a very frequent loading case in structures under working conditions.

Recently, a team of researchers from the University of Castilla-La Mancha in Spain investigated the three-point bending response of symmetric ±45° angle-ply laminates built with unidirectional and continuous carbon fiber-reinforced epoxy laminae. They purposed to cross-examine the pseudo-ductile effects considering that pseudo-ductility refers to the non-linearity driven by the accumulation of damage and yielding of the matrix that favors the fiber reorientation. Their work is currently published in the research journal, Composites Science and Technology.

For the purposes of their work, the research technique utilized entailed evaluation of the classical laminated plate theory in order to quantify the coupling of forces based on the theoretical knowledge of the neutral axis deviation and the different material behavior under tension and compression. Next, Serna Moreno and colleagues tested the proposed laminates in order to verify the correctness of the analytical predictions acquiring the displacement and strain fields by means of Digital Image Correlation techniques. In addition, optical visualization and Scanning Electron Microscopy were employed in order to assess experimentally the first failure mode induced.

By comparing the effects of the pseudo-ductility in flexural testing and the experimental response of both laminates, the researchers observed that similar in-plane linear response were recorded. Additionally, it was also seen that the main differences in the mechanical response could be attributed to the stacking sequence, as the effective ply-thickness in the first sample was half that of the alternate laminate. Finally, the researchers were able to develop analytical predictions of different parameters of the linear response by considering the different tensile and compressive mechanical performance of the material, as well as the numerical optimal design of the stacking sequences that reduce the bending-twisting coupling and increase the pseudo-ductile effect.

In conclusion, University of Castilla-La Mancha study presented an excellent investigation of the flexural response of [+45 -45]6S and [+452 -452]3S laminates. In so doing, they discovered that similar linear behavior was eminent for the two samples, but different non-linear phases. Altogether, it has been shown in this work that it is possible to remove the inherent limitation and enlarge the design space by using thin ply angle-ply laminates that exhibit a non-linear ‘pseudo-ductile’ stress-strain response.

*This work was financially supported by the Ministerio de Economía y Competitividad of Spain under the grant DPI2016-77715-R.

First observations of pseudo-ductility in three-point bending tests on CFRP angle-ply laminates Advances in Engineering

About the author

MC Serna Moreno Industrial Engineer (2002) and Doctor in Industrial Engineering (2006) from the University of Castilla La-Mancha (UCLM) of Spain. In 2009 she became Associate Professor (tenured) of the Area of Continuum Mechanics and Theory of Structures in the UCLM. She has been postdoc in the institute GSI-Helmholtzzentrum für Schwerionenforschung GmbH of Darmstadt (Germany) and guest researcher in the University of Sheffield (England).

Her principal scientific interests are related with the strength of materials, continuum mechanics and numerical modelling. The investigation in which she has been involved has been variated, participating in several research projects (national and regional), publications in JCR journals (Q1), international conference papers and supervising PhD Thesis. Nowadays her main line of research is focused on the structural response of composite materials from the experimental, analytical and numerical points of view. In this context, she is reviewer of research projects for the Spanish National Agency of Evaluation and Prospective (ANEP), she takes part of the editorial board of the journal “Materiales Compuestos” from the Spanish Association of Composite Materials (AEMAC) and she belongs to the European Society of Composite Materials (ESCM).

About the author

Sergio Horta Muñoz obtained the BSc in Mechanical Engineering in 2015 and the MSc in Industrial Engineer in 2017 at the University of Castilla La-Mancha (UCLM). Currently, he is studying the PhD at the same university under the supervision of Dr. María del Carmen Serna Moreno. He is beneficiary of a predoctoral grant from the Castilla-La Mancha Government.

His thesis is focused on the study of the mechanical behaviour of carbon fibre reinforced polymer matrix composite under multiaxial loading. This characterization is achieved through analytical, numerical and experimental approaches, including non-standardized tests and advanced numerical simulations based on the Finite Element Method. These scientific studies allowed him to obtain two awards for his Degree and Master Theses: a prize from the Association of Graduates and Technical Engineers of Ciudad Real (COGITI) and another from the company AIRBUS.

About the author

Dr. Ana Romero graduated with BSc in Industrial Engineering from University of Castilla-La Mancha (UCLM) in 2010 obtaining the award for the best project end of career granted by the company Airbus S.A.S. She is Doctor CUM LAUDE for the Doctorate program in Sciences and Technologies Applied to Industrial Engineering since 2016 and has a second postgraduate degree (Master’s Degree in Industrial Engineering) obtained at the UCLM in 2012. She begins her research career at the National Center for Metallurgical Research (CENIM-CSIC) in 2011, where she joined to work under a project obtained in the National Research Aid Plan, to continue her professional career as a researcher in UCLM since 2012, where she has worked continuously as an Associate Professor in addition to having been hired under public and private funding research projects. Since 2017, she combines this work with that of professor at the Nebrija University.

She has published 15 scientific articles indexed in JCR, mostly in Q1, the participation in 8 research projects obtained in public and competitive calls, and in more than 20 publications in national and international scientific congresses of recognized prestige.

Her research is focused on the development of new materials (metal and composite materials of metal and polymer matrix reinforced with particles and fibers), in the characterization (physical, mechanical and magnetic) of the same and in the use of processing techniques of manual stacking, powder metallurgy, and advanced as powder injection molding and high energy techniques.

About the author

Dr. C. Rappold Master of Engineering and Research (2006) from ENSPS – Strasbourg (France) and Doctor (2010) in Nuclear physics from the university of Strasbourg. He was postdoctoral fellow at the Helmholtz Institute of Mainz (Germany) and at the University Justus Liebig Giessen (Germany) jointly with the research center GSI Helmholtz Centre for Heavy Ion Research (Germany). He has been research associate at the research center GSI since then. He has been invited as guest researcher several times to the university of Castilla La Mancha (Spain).

His scientific research has been focused on experimental study of hypernuclear matter, along with statistical data analysis, optimal design and other numerical optimization problems. He had one of major role in the HypHI collaboration, which aimed at performing hypernuclear spectroscopy by means of heavy-ion induced reactions. He has as well participated in the A1, η-PRiME and SuperFRS collaborations. He has been author in more than 20 publications, and 30 conference proceedings of international conferences. In 2015, he was conferred the international ‘GENCO Young Scientist Award’ recognizing outstanding achievements of young scientists in the field of exotic nuclei and super heavy elements.

About the author

Juan Luis Martínez Vicente Lecturer professor of the area of Continuum Mechanics and Theory of Structures at the University of Castilla-La Mancha, Spain. He was Visiting Lecturer at the University of Sheffield, United Kingdom. He received his PhD and MSc degree from the Higher Technical School of Industrial Engineering of the University of Castilla-La Mancha. His research interests include multiaxial behaviour of fibre-reinforced composite structures under complex loading cases, Influence of notched composite structures and characterization of nanocomposites mechanical properties.

He has co-authored 10 peer-reviewed journal articles. He is member of COMES research group based at the University of Castilla-La Mancha and research of Computer-Aided Aerospace and Mechanical Engineering research group-CA2M based at the University of Sheffield. He is member of the Spanish Society of Composite Materials (AEMAC) and Spanish Society of Materials (SOCIEMAT).

Email: [email protected]

About the author

Pablo A. Morales Rodríguez received his BS, MSc degree and PhD in Science and Agricultural Engineering from the School of Agricultural Engineering at the University of Castilla-La Mancha. He currently holds a position of part-time lecturer at the same university in the area of agroforestry engineering.

His research focuses on issues related to strength of materials and structures, specifically on the design of lightweight mansard portal frames and their joints. He is currently working on the evaluation and testing of mechanical properties of wood and novel advances composite materials. He has already published some articles in indexed engineering journals and taken part in several international conferences.

About the author

Juan José López Cela Mechanical Engineer (1989) and Phd (1993) from the Politechnical University of Madrid. Full Professor in the area of Continuum Mechanics and Theory of Structures at the University of Castilla-La Mancha, Spain. He has been Visiting Research at the Joint Research Center (JRC) in Ispra (Italy) and Guest Research at Gesellschaft für Schwerionenforschung (GSI) in Darmstadt (Germany).

He leads the group of Computational Mechanics and Engineering Structures – COMES based at the University of Castilla-La Mancha. His main research lines include multiaxial behaviour of fibre-reinforced composite structures, dynamics of structures, instabilities in accelerated solids, finite element analysis of structures, behaviour models (plasticity-viscoplasticity, location). He has co-authored 40 peer-reviewed journal articles published in top international journals, indexed by Journal Citation Reports (JCR). He has been main researcher in several research projects.

Regarding his experience in university management, nowadays, he is vice-chancellor for Teaching staff of the University of Castilla-La Mancha.

Email: [email protected]

Reference

M.C. Serna Moreno, S. Horta Munoz, A. Romero Gutiérrez, C. Rappold, J.L. Martínez Vicente, P.A. Morales-Rodríguez, J.J. Lopez Cela. Pseudo-ductility in flexural testing of symmetric ±45° angle-ply CFRP laminates. Composites Science and Technology, volume 156 (2018) page 8-18

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