Abstract

For the past several years, composite marine structures have been designed but without having a complete characterization the composite materials. The main reason is due to the large quantity of variables that affect the behavior of said materials. One of the tasks that has not been properly characterized is the behavior of composite structures under fatigue loads that appear in marine structures that are subjected to cyclic loads. Therefore, numerical tools that characterize fatigue performance are required in order to design more reliable structures. The formulation proposed in this work is based on the Serial/Parallel Rule of Mixtures [1] and a fatigue damage model [2]. The Serial/Parallel Rule of Mixtures can be understood as a constitutive law manager that provides the response of the composite from the constitutive performance of its constituents. Therefore, the constitutive laws chosen to represent the behavior of each constituent material have to fit with their real performance. Also, the fatigue damage model is based on the use of a reduction function which takes into account the cyclic degradation of the materials, both strength and stiffness degradation, in function of the number of cycles, maximum stress and stress amplitude. Current work presents a numerical tool developed to characterize fatigue in composites. The fatigue behavior of constituent materials is defined using mechanic parameters taken from literature. Afterwards, a reproduction of the tests will be done in order to validate the fatigue formulation proposed. [1] Car, E., Oller, S., Oñate, E. "Estudio del comportamiento no lineal en materiales compuestos", Techincal Report 264,CIMNE, 1997. [2] Oller, Salomon, O., Oñate, E. “A continuum mechanics model for mechanical fatigue analysis", Composite Materials Science, Vol 32, Issue 2, pp 175-195, 2005.

Abstract

The use of composite materials in the naval industry is a fact. Prove of it is composite materials are widely used in the marine industry (e.g. competition vessels and leisure boats), offshore industry and renewable energy industry. If engineers want to design reliable structures made of composites, the numerical tools have to be capable of accurately representing the behaviour of these materials, such as their high anisotropy and non-linear performance. Hence, a good model capable of taking into account the different failure modes of the laminates is required in order to reduce the uncertainty associated with the simulation of composite structures. There are many models capable of simulating the elastic and specific non-linear behaviour of laminates, while also accounting for their anisotropic behaviour. However, few of them are capable to take into account most of the composites failure modes in a general way. This work proposes using one of them, the Serial/Parallel Mixing Theory (SP RoM) [1]. The main advantage of the SP RoM versus other formulations is that the composite performance is obtained from the mechanical properties of its constituent materials. Therefore, once these are calibrated, different composite configurations can be analysed without further calibrations. The Serial/Parallel Mixing Theory (S/P RoM) acts as a constitutive law manager of the constituent materials, being capable of reproducing the composite performance in its linear and non-linear regime. In order to obtain the material parameters required by the formulation, this work proposes a set of different tests to obtain different loading conditions and failure modes. Then, a guideline to get the material parameters from the tests is given. Finally, the numerical results are compared with results obtained from an experimental campaign. These results show that, once all the material parameters are obtained for fibre and matrix, the formulation introduced is capable of representing all the failure modes of the composite for different loading conditions, as well as their failure strength. This work is in the scope of FibreShip Project H2020 [2]. REFERENCES [1] F. Rastellni, S. Oller, O. Salomon, E. Oñate Composite materials non-linear modelling for long fibre reinforced laminates: continuum basis, computational aspects and validations, Computers & Structures, 86 (9) (2008), pp. 879–896 [2] European Union’s Horizon 2020 research and innovation programme under grant agreement nº 723360 “Engineering, production and life-cycle management for the complete construction of large-length FIBRE-based SHIPs”. http://www.fibreship.eu/about

Abstract

The use of composite materials to build marine structures is a fact. Prove of it is the construction of offshore turbines, military vessels, composite risers, etc. However, the characterization of such structures under fatigue loads is not well understood, what implies a larger scantling and safety ratios of the structures. Hence, it is necessary to develop numerical tools in order to predict this failure mode. The purpose of this work is to propose a numerical model for the analysis of the fatigue behaviour of marine structures made of composite laminates, which can be used to understand their behaviour in order to optimize them. The formulation proposed to simulate the fatigue phenomena is based on the Serial/Parallel Rule of Mixtures (S/P RoM) and a fatigue damage model previously developed for metals. The SPRoM can be understood as a constitutive law manager that provides the elastic and non-linear response of the composite from the constitutive performance of its constituent materials. The fatigue damage model is based on the definition of a reduction function which takes into account the cyclic degradation of the materials, acting on strength and stiffness; this function accounts for the number of cycles, maximum stress and stress amplitude. These two formulations are coupled applying the fatigue damage model to both composite components, fibre and matrix. Current work uses the numerical procedure developed to characterize fatigue in composites. The model is calibrated based on the assumption that the failure mechanism of longitudinal loaded UD laminates is fibre-driven, while the failure mechanism of transverse loaded UD laminates is matrix-driven. The composite resulting from this calibration is used, afterwards, to predict the fatigue performance laminated composites with different stacking sequences. The structure chosen for this analysis is a substructure of a fibreglass vessel. This work is in the scope of FibreShip Project H2020.