Issue 31

J. Lopes et alii, Frattura ed Integrità Strutturale, 31 (2015) 67-79; DOI: 10.3221/IGF-ESIS.31.06 77 C ONCLUSIONS AND FUTURE WORK ybrid CFRP/Steel composites have a maximum ILSS very close to the ILSS of a reference beam. Hybrid CFRP/Steel composites are a competitive and cost effective alternative to CFRP/Ti alloy. It has a similar maximum ILSS while the cost of the austenitic steel is significantly lower than the cost of Ti alloys. Vacuum blasting is the surface treatment that withstands higher ILSS from all the tested surface treatments. It is also simpler than pickling or grit blasting. The vacuum blasting treatment with one day storage has a maximum apparent ILSS close to the reference beam (less 0.16 MPa). This shows that the one day storage between treatment and lay-up does not affect the shear stress capability. This is a very important advantage in terms of manufacturing process. The FEM model is able to predict the maximum ILSS of the hybrid CFRP/Steel beam which is the main engineering parameter. The discrepancy between the measured displacement and the numerical displacement is not fully understood. Although the available data suggests that it is due to the compliance of the testing machine, only a dedicated test program to determine the eventual compliance using DIC technology [29] would definitely demonstrate the effect of the compliance The size of the specimens prescribed by EN14130 is very small. This small size enhances the effect of the compliance of the testing machines. It is suggested therefore that in a future research of inter-laminar shear stress by three-point bending the size of the specimens should be bigger than the size prescribed by EN14130 in order to reduce the effect of the factors that induce uncertainty in this test. The short beam tests have some shortcomings, particularly when comparing with numerical simulations. It involves contact formulation and the shear stress is an induced stress caused by transverse shear of the loading member. These disadvantages leads to a next step of the study of shear stress of hybrid CFRP/Steel composites that is the single lap shear tests (SLS). A CKNOWLEDGEMENTS he first author’s research is supported by the research grant BD/51597/2010 provided by the Portuguese Foundation for Science and Technology. The support of the Institute of Composite Structures and Adaptive Systems of the German Aerospace Centre in the manufacturing and testing of the specimens is acknowledged. A CRONYMS AND DEFINITIONS CFRP – Carbon Fibre Reinforced Polymer CTE – Coefficient of Thermal Expansion CZM – Cohesive Zone Method DCB – Double Cantilever Beam DIC – Digital Image Correlation ECT – Edge Crack Torsion ENF – End Notch Flexure FEM – Finite Element Method ILSS – Inter-laminar Shear Stress LVDT – Linear Variable Differential Transformer MMB – Mixed Mode Bending QUADS – Quadratic Nominal Stress Criterion SLS – Single Lap Shear VCCT – Virtual Crack Closure Technique R EFERENCES [1] ESD Symposium Committe, ESD Terms and Definitions (Version 12), Massachussets Institute of Technology Engineering Systems Division, (2001). H T