MIFACRIT

Methodology Toolbox for Accelerated Fatigue Testing of FRP Materials: Micro-structural Failure Criterion for Multi-axial Fatigue of FRP Structures

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 Obiettivo del progetto (Objective)

'MIFACRIT aims at developing a failure criterion for fiber reinforced polymer (FRP) structures. This criterion shall allow reliability and lifetime assessments of structural parts and systems made of several stack configurations. It shall be deduced from mechanical effects within the microstructure of the FRP structures in order to cover various mechanical loading situations. This ambitious goal is approached by a symbiotic combination of experimental test and anal-ysis work with in-depth assessment and evaluation based on numerical simulation applying fracture / damage mechanics concepts. The material tests comprise visco-elastic characteri-zation and stress tests applying constant strain rate and cyclic loads, respectively. The tests are performed at different temperatures and frequencies. Most importantly, they include a variety of loading situations such as tensile and bending loads but also combinations of normal and shear components. The analysis determines the visco-elastic material properties and the micro-structural effects responsible for damage and failure of the FRP structure in a comprehensive way. The in-depth analysis of the damage and failure effects by means of numerical simulation will apply a two stage (global / local) sub-modeling strategy. The es-sential model parameters are calibrated by measured data and the simulation results are verified by the experimental findings. Combining experiment and simulation this way, the common link between the failure effects caused by the various loading situations will be shown and explained by means of an objective mechanical criterion, which will be indentified and validated throughout the MIFRACRIT project. In addition, threshold quantities will be determined for the criterion found to ultimately provide the means for precise lifetime predic-tions based on this physics of the failure approach.'

Introduzione (Teaser)

Fibre-reinforced plastics (FRPs) are the building block of numerous aerospace structural components made with stacked configurations. EU-funded scientists have conducted extensive testing and numerical modelling to identify critical failure criteria.

Descrizione progetto (Article)

Composites made of a polymeric matrix reinforced with fibres have played an important role in reducing the environmental impact of numerous sectors. They reduce the weight of many structural parts and systems while imparting excellent mechanical properties.

The increasing prevalence of FRPs in safety-critical components highlights the need for advanced and highly accurate testing and failure criteria. The EU-funded project MIFACRIT laid the foundations for a methodology toolbox of accelerated multi-axial fatigue testing with highly accurate failure criteria. The focus was on one-ply and multi-ply sandwich or stacked composites for the aerospace industry.

Multi-axial fatigue loading is, as its name implies, loading along more than one of the three axes of the Cartesian coordinate system. Until recently, most discussions of cyclic loading assumed uni-axial loading. However, in real life, many systems such as rotating shafts and numerous automotive and aircraft components experience a multi-axial state of cyclic stress.

MIFACRIT addressed this situation for the case of FRPs. Its great strength lies in the interplay between extensive experimentation and advanced numerical simulation exploiting methods from fracture and damage mechanics.

Material tests integrated viscoelastic characterisation during constant strain and stress tests during cyclic loading. Both temperature and frequency parameters were varied. The two-stage mathematical modelling accounts for both local and global descriptions. Simulation results were compared to experimental ones in a reiterative way to fine-tune the models. Threshold values for the various criteria were determined.

MIFACRIT developed the procedure to capture elastic properties and failure and damage properties of FRPs by evaluating mechanical effects within the microstructure over various loading conditions. Further optimisation will enhance the reliability of the assessed properties, ensuring accurate prediction of the lifetimes of FRPs under multi-axial load conditions. This in turn will enable more rapid production of high-quality, safety-critical structural components.