Exploiting thin-ply materials to establish controlled failure in carbon fibre composites Tamas Rev Dr Gergely Czél, The 8th Annual Conference of the CDT Professor Michael R. Wisnom in Advanced Composites for Innovation and Science (ACCIS CDT) Bristol, 16th of April, 2019 Bristol, UK
2 Contents Introduction and background PhD outline Longitudinal tension – transverse compression Conclusions and Future work Exploiting thin-ply materials to establish controlled failure in carbon fibre composites
3 Introduction • Significant role of composite materials • Key challenge for many industries – Determining UD ply strength the most accurate way possible – Taking material variability into account as recommended by aeronautical standards [1] – Establish behaviour in realistic operation conditions (multi-axial loadings) • Ultimate goal – Reduce costs and product lead-time – Ensure safe operation in service Exploiting thin-ply materials to establish controlled failure in carbon fibre composites
4 Background [2] Hinton et al, ICCM13’ Proceedings (2000) • Failure prediction of composite materials – No universally accepted criterion (WWFE) – Low confidence in failure prediction – Difficulty of obtaining reliable data • Lead to premature failure, • Knock-down in strength • Lower measured strain to failure • Main objective of PhD – To exploit thin-ply composites to establish controlled failure in order to • Investigate the effect of different stress components on the fibre direction failure strain • Provide visual indication of damage Exploiting thin-ply materials to establish controlled failure in carbon fibre composites
5 PhD outline / summary • Design specimens to obtain controlled behaviour – Using thin-ply materials to isolate failure mechanisms • Suppressed damage mechanism such as delamination and matrix cracking – 1. Purpose designing to achieve a desired failure mode → UD hybrid composite overload sensors [3] – 2. Controlling failure mechanism • Generate multi-axial stress state in UD layers → by using novel test methods – (a) Longitudinal tension – shear Jalalvand et al. [4] Completed – (b) Longitudinal tension – transverse compression – (c) Longitudinal tension – transverse tension In progress – (d) Longitudinal compression – transverse tension (a) (b) (c) (d) Exploiting thin-ply materials to establish controlled failure in carbon fibre composites
6 Longitudinal tension- transverse compression Long. Trans. Stress at Transverse Strain at Lay-up Strain at failure compressive failure failure [%] [MPa] stress [MPa] [%] 0 1.62 -0.04 1696.3 0.00 [SG 2 /±15 6 /0 2 ] s 1.60 -1.05 1069.3 -36.50 [±20 6 /0 2 ] s 1.62 -2.84 1052.6 -141.48 [±28 6 /0 2 ] s 1.62 -2.91 622.4 -142.40 • Novel tensile test configuration • High in-plane transverse compressive stresses • Negligible effect of high transverse stresses ! Exploiting thin-ply materials to establish controlled failure in carbon fibre composites
Conclusions 7 • A novel test configuration was introduced incorporating a thin-ply composite laminate under a bi-axial stress state • Very high, indirectly applied in-plane transverse strain – Low variability – Equivalent to 145 MPa transverse compressive stress (assuming a linear response) • Fibre failure mode was observed for all configurations Overall transverse strains are higher than in typical multi-directional laminates → • exceeding 90° fibre direction compressive strain to failure → Tensile failure is negligibly affected by transverse compressive stresses • • Future work: completing the tension – tension and compression – tension quadrants Exploiting thin-ply materials to establish controlled failure in carbon fibre composites
Thank you for listening! Any questions? tamas.rev@bristol.ac.uk References [1] F. Laurin, P. Paulmier, and F.- X. Irisarri, “Determination of the longitudinal compressive strength of a CFRP ply through a tensile test on a laminate,” Compos. Part A Appl. Sci. Manuf., vol. 113, pp. 209 – 219, Oct. 2018. [2] M. J. Hinton, A. S. Kaddour, and P. D. Soden , “Predicting Failure in Fibre Composites : Lessons Learned From the World- Wide Failure Exercise,” in ICCM 13 - 13th International Conference on Composite Materials, 2000, no. November, pp. 1 – 13. [3] G. Czél, M. Jalalvand, and M. R. Wisnom, “Hybrid specimens eliminating stress concentrations in tensile and compressive testing of unidirectional composites,” Compos. Part A Appl. Sci. Manuf., vol. 91, pp. 436 – 447, 2016 [4] M . Jalalvand, M. Fotouhi, M. C. Leong, and M. R. Wisnom, “A NOVEL TECHNIQUE TO ACCURATELY MEASURE THE FIBRE FAILURE STRAIN IN COMPOSITE LAMINATES UNDER A COMBINED IN-PLANE TENSION AND SHEAR STRESS STATE,” no. August, 2017.
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