Overview
The FATIMA project proposed by the consortium worked on testing and fatigue prediction of carbon fibre reinforced plastics (CFRP) as required in call JTI-CS-2010-3-ECO-01-007. The challenging objective was to go beyond the state of the art in terms of approaches to account for humidity, multi-ply and multi-axiality effects in organic laminate structures. Intensive work in the field resulted in a number of concepts for accelerated lifetime predictions for carbon fibre reinforced polymers.
Within FATIMA, these concepts were adapted to the material provided by the partners of the Clean Sky consortium. The proposed methodology and integration into the fatigue testing procedure approached expansions addressing humidity effects, different stack-up structures and combined loading of these composite structures. Appropriate models of a multitude of specific laminate structures were provided as a tool box for composing desired laminates consisting of plies with known behaviour. Failure criteria developed for predicting the damage in composite materials due to multi-axial loads were evaluated, selected and advanced to meet the objectives of the call.
Funding
Results
Executive Summary:
The FATIMA project consortium worked on testing and fatigue prediction of fibre reinforced plastics (FRP). The challenging objective was to go beyond the state of the art in terms of approaches to account for humidity, multi-ply, and multi-axiality effects in organic laminate structures.
Objective of FATIMA project was the adaptation and expansion of a methodology of accelerated fatigue testing and predicting of the lifetime of organic fibre reinforced structures, which has been introduced and comprehensively been described by Miyano.
Successful feasibility study of the existing methodology was carried out with the material IS 400, a typical epoxy based material with woven fibre reinforcement. The advance of the methodology was achieved by applying dedicated tests, by using Digital Image Correlation (DIC) methods, and advanced simulation techniques in order to expand the existing methodology towards humidity influence, multi-ply and multi-axiality effects.
The material was supplied by the Clean Sky ED-ITD partners and the tests were carried out in WP1 with equipment capable of varying temperature, frequency, and load amplitude. Thereby the effect of temperature dependent static, transient, dynamic and fatigue contributions was analysed. The methodology is performed based on three kinds of tests: viscoelastic dynamic mechanical analysis (DMA), constant strain rate (CSR), and cyclic fatigue tests at various temperatures, frequencies, and loading ratios. Modes of structural fatigue were analysed and compared to the acceleration factors based on the viscoelastic time-temperature shift function. Thereby the new method was clearly revealing its great potential for predicting the critical number of cycles to failure and its dependency on temperature as well as the long term fatigue strength of fibre reinforces polymers including PCB materials.
The methodology enhancement with respect to multi-ply effects was developed and validated in WP2. After material characterization for the individual plies the visco-elastic properties of the epoxy matrix material were extracted and implemented in the FE simulation macros. Additionally, microscopic investigations delivered the necessary geometric parameters for simulation. After build-up of detailed 3-D finite element models tensile, bending and shear simulations were carried out. Calibration of 3-D numerical models were successfully accomplished and resulted in a good agreement of the effective Young’s modulus with measured data. Additionally a good agreement of storage and the loss modulus was reached between simulation and experimental results obtained by dynamic mechanical analysis (DMA). In accordance with the multi-ply expansion approach a material characterization was simulated using a layered model. In the final step a full FRP stack was modelled according to the respective ply scheme.
After material characterization in WP1 and development of a toolbox for modelling FRP laminates in WP2 the methodology was expanded in WP3 to complex loading situations with combined tension and bending load. Therefore a specially designed specimen holder was used introducing a bending moment in addition to in-axis tension. Based on the experimental tests numerical simulations were performed to understand the multi-axial fatigue loads and the complexity of this combined load configuration. Finally, a number of failure criteria have been developed and tested for analysing, describing, and predicting damage in composite materials due to multi-axial loads.