Anastasios Vasilopoulos

Introduction to the fatigue life prediction of composite materials and structures: past, present and future prospects

This chapter aims to provide an overview of the fatigue life prediction methods for composite materials and structures, recalling methods used in the past, discovering the present status and attempting to foresee future trends.

Fatigue life prediction of composite materials under realistic loading conditions (variable amplitude loading)

Two of the most widely used methods for the fatigue life prediction of composite materials under variable amplitude (VA) loading patterns are presented in this chapter. The first method is based on the theoretical formulation and use of a damage summation rule to predict life under VA loading without recourse to experimental observation of the damage accumulation process. An alternative to this classic fatigue life prediction methodology are the residual strength fatigue theories, where residual strength is used as the damage metric. Comparison of the remaining strength of the material to the static strength allows the estimation of the fatigue cycles until failure. The basic fatigue modeling introduced in previous chapters of this book for interpretation of the fatigue data ( Chapter 2), residual strength theories ( Chapter 3), and constant life diagrams ( Chapter 6) is combined here to establish fatigue life prediction methodologies.

Construction Engineering: Fatigue life prediction of adhesively bonded textile composites

A number of construction engineering applications for textiles made of composite materials are presented in this chapter. All these structures were fabricated by connecting several subcomponents, usually by using adhesives. Although composite materials are designated to be fatigue-insensitive, especially when compared to metallic ones, they also suffer from fatigue loads. The aim of this chapter is to present the different types of adhesively bonded connections between textile fiber-reinforced polymer composite materials in construction engineering and the description of the available methods for the life modeling and prediction of their fatigue life.

Mode I fatigue and fracture behavior of adhesively-bonded pultruded glass fiber-reinforced polymer (GFRP) composite joints

The fatigue/fracture behavior of adhesively-bonded pultruded glass fiber-reinforced polymer (GFRP) joints is significantly affected by the loading ratio. This effect is analyzed in this chapter through a complete fatigue/fracture database, derived during recent years, and correlated with the exhibited failure processes of the examined joints. A phenomenologically based criterion is then used for the simulation of the exhibited behavior and the prediction of the fatigue/fracture behavior of the examined joints under different loading conditions. It is shown in this chapter that, upon accurate estimation of the model parameters, it is possible to reliably predict fatigue crack growth curves for several unknown loading conditions, thereby assisting the development of methodologies for the fatigue life prediction of joints under realistic loading conditions.

Fatigue and fracture behavior of adhesively-bonded composite structural joints

Constant amplitude fatigue loading spectra stand for only a small percentage of the real loading of a structure, although they can be used to investigate the fatigue and fracture behavior of structural elements. The fatigue and fracture behavior of adhesively-bonded structural joints under different constant amplitude loading patterns has been experimentally investigated and the results are presented in this chapter. Double-lap joints composed of pultruded glass-fiber-reinforced polymer-matrix laminates bonded by an epoxy adhesive were examined. The dominant failure modes are described and the stiffness degradation trends under tensile or compressive fatigue loads are presented. The results show a significant effect of the loading pattern on the lifetime and fracture behavior of the joints examined.

Mixed-mode fatigue and fracture behavior of adhesively-bonded composite joints

The mixed-mode fatigue and fracture behaviors of adhesively-bonded pultruded glass fiber-reinforced polymer joints are presented in this chapter. These behaviors are based on experimental investigations using asymmetric mixed-mode bending specimens. In such specimens, the crack propagated along paths outside the symmetry plane, and therefore mode partitioning could not be performed in the standardized way as for symmetric specimens. Existing techniques for the characterization of the mixed-mode fracture behavior of adhesively-bonded joints, the partitioning of the fracture mode components, and the modeling of the fiber bridging that affects the total fracture energy are presented in this chapter.

Simulating the effect of fiber bridging and asymmetry on the fracture behavior of adhesively-bonded composite joints

The fracture behavior of adhesively-bonded pultruded double cantilever beam specimens is studied in this chapter. The crack propagates along paths away from the symmetry plane and is accompanied by fiber bridging. Finite element models are developed to quantify the effects of asymmetry and fiber bridging on the fracture energy. The virtual crack closure technique can be used for calculation of the fracture components at the crack tip and an exponential traction–separation cohesive law can be applied to simulate the fiber-bridging zone. The cohesive zone model developed in this chapter can be used for simulating progressive crack propagation in other joint configurations composed of the same adherends and adhesive.

Block and variable amplitude fatigue and fracture behavior of adhesively-bonded composite structural joints

The fatigue behavior of adhesively-bonded glass fiber-reinforced polymer (GFRP) joints is affected by the loading sequence. Analysis of several experimental data for composite materials and adhesively-bonded composite joints showed that the loading sequence effect is a function of the loading type, the applied loading levels and the material under investigation. Exhibited failure modes, related to the loading pattern, significantly affect the development of damage in adhesively-bonded composite joints. The aim of this chapter is to investigate the load sequence effect of both block and variable amplitude loading conditions on the fatigue behavior of adhesively-bonded pultruded GFRP joints.

Predicting the fatigue life of adhesively-bonded structural composite joints

The choice of a particular (an appropriate) fatigue theory for composite materials and structures is based on the material’s behavior under the given loading pattern and the experience of the user. One of the most explicit and straightforward ways to represent experimental fatigue data is the S–N diagram that is preferred to other ways since it requires the minimum of experimental data. The effect of the loading is assessed by using constant life diagrams. This chapter aims to provide an overview of the commonly used S–N curves and the available constant life diagram formulations for the simulation of the fatigue behavior of composite materials and adhesively-bonded structural composite joints.

Novel computational methods for fatig life modeling of composite materials

Novel computational methods such as artificial neural networks, adaptive neuro-fuzzy inference systems and genetic programming are used in this chapter for the modeling of the nonlinear behavior of composite laminates subjected to constant amplitude loading. The examined computational methods are stochastic nonlinear regression tools, and can therefore be used to model the fatigue behavior of any material, provided that sufficient data are available for training. They are material-independent methods that simply follow the trend of the available data, in each case giving the best estimate of their behavior. Application on a wide range of experimental data gathered after fatigue testing glass/epoxy and glass/polyester laminates proved that their modeling ability compares favorably with, and is to some extent superior to, other modeling techniques.