Mode Fatigue Crack Growth Research Articles

Memory effects in variable amplitude and multiaxial fatigue crack growth: an incremental approach

This paper presents an incremental approach for modelling fatigue crack growth with memory effects due to the non-linear behavior of the material. This approach is developed at LMT since 2003, in collaboration with several industrial partners, mainly with Snecma, SAFRAN Group, EDF and AREVA and SNCF. The first part of this paper presents the context and the objectives, and the key assumptions on which the model is based. The second part presents some examples of applications of the model, fatigue crack growth in mode I conditions, under variable amplitude loading; non-isothermal situations; crack growth in coupled environmental and fatigue loading conditions; extension of the model to non-proportional mixed mode loading conditions, and to short cracks. The last part presents some ongoing work, possible developments and scientific challenges that remain to be overcome.

High cycle fatigue crack growth in Mode I of adhesive layers: modelling, simulation and experiments

The capability to predict high cycle fatigue properties of adhesive joints is important for cost-efficient and rapid product development in the modern automotive industry. Here, the adaptability of adhesives facilitates green technology through the widening of options of choosing and joining optimal materials. In the present paper a continuum damage mechanics model is developed based on the adhesive layer theory. In this theory, through-thickness averaged variables for the adhesive layer are used to characterise the deformation, damage and local loading on the adhesive layer. In FE-simulations, cohesive elements can thereby be used to model the adhesive layer. This simplifies simulations of large scale complex built-up structures. The model is adapted to experimental results for two very different adhesive systems; one relatively stiff rubber based adhesive and one soft polyurethane based adhesive. The model is able to reproduce the experimental results with good accuracy except for the early stage of crack propagation when the loads are relatively large. The model also predicts a threshold value for fatigue crack growth below which no crack growth occurs. The properties of the model are also compared with the properties of Paris’ law. The relations between the parameters of the continuum damage mechanics law and the parameters of Paris’ law are used to adapt the new law. It also shows that the properties of a joined structure influence the Paris’ law properties of the adhesive layer. Thus, the Paris’ law properties of an adhesive layer are not expected to be transferable to joints with adherends having different mechanical properties.

Investigation of mode III fatigue crack growth in rubber based on the pioneering work of Alan N. Gent and coworkers

From 1998 to 2003, Alan N. Gent and some co-workers published a series of papers devoted to the first measurements of fatigue crack growth properties in rubber in mode III loading conditions (Rubber Chemistry and Technology, vol. 71, pp. 76–83; vol. 71, pp. 84–94; vol. 76, pp. 1276–1289). The present paper proposes to revisit this seminal work benefiting from the capabilities of new multiaxial fatigue machines. Then, a new mode III fatigue test for elastomers is developed. A thin bonded disk of rubber with a circumferential cut is subjected to cyclic torsion to investigate the fatigue crack growth in mode III. The corresponding measurement methods for the crack growth rate and the fracture energy are proposed. As a constant small axial extension can be applied and controlled to prevent the cracking surfaces from abrasion and to ensure almost mode III loading conditions, the quality and the relevance of the experimental data are highly enhanced. As a results, the method is applied to an unfilled natural rubber and the crack growth rate is related to the fracture energy for several loading cases. The effects of axial extension, alternate cycles and positive minimum angle cycles are examined. In particular, it is shown that for fully unloaded cycles the crack growth rate laws in modes I and III coincide in the regime of high fracture energies.

Cyclic Plasticity of a Cracked Structure Subjected to Mixed Mode Loading

Cyclic plasticity in the crack tip region is at the origin of various history effects in fatigue. For instance, fatigue crack growth in mode I is delayed after the application of an overload because of the existence of compressive residual stresses in the overload’s plastic zone. Moreover, if the overload’s ratio is large enough, the crack may grow under mixed mode condition until it has gone round the overload’s plastic zone. Thus, crack tip plasticity modifies both the kinetics and the crack’s plane. Therefore modeling the growth of a fatigue crack under complex loading conditions requires considering the effects of crack tip plasticity. Finite element analyses are useful for analyzing crack tip plasticity under various loading conditions. However, the simulation of mixed mode fatigue crack growth by elastic-plastic finite element computations leads to huge computation costs, in particular if the crack doesn’t remain planer. Therefore, in this paper, the finite element method is employed only to build a global constitutive model for crack tip plasticity under mixed mode loading conditions. Then this model can be employed, independently of any FE computation, in a mixed mode fatigue crack growth criterion including memory effects inherited from crack tip plasticity. This model is developed within the framework of the thermodynamics of dissipative processes and includes internal variables that allow modeling the effect of internal stresses and to account for memory effects. The model was developed initially for pure mode I conditions. It was identified and validated for a 0.48%C carbon steel. It was shown that the model allows modeling fatigue crack growth under various variable amplitude loading conditions [1]. The present paper aims at showing that a similar approach can be applied for mixed mode loading conditions so as to model, finally, mixed mode fatigue crack growth.

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Fatigue life of fiber reinforced concrete (FRC) is theoretically analyzed with a fracture mechanics based model. The model accounts for the effect of cycle-dependent crack bridging properties in FRCs and predicts the number of cycles to failure defined by final fracture subsequent to stable fatigue crack growth in Mode I. The resulting theoretical S–N diagram was compared with experimental data reported in literature. The general agreement supports the validity of the current model, and reveals that cycle-dependent degradation of crack bridging controls fatigue life of FRCs. S–N diagrams are essential for material evaluation and structural design, and the model establishes the link between material structure and S–N diagram in an explicit manner, while the conventional stress-life approach realizes the link in an empirical manner.

Fatigue life analysis of fiber reinforced concrete with a fracture mechanics based model

Fatigue life of fiber reinforced concrete (FRC) is theoretically analyzed with a fracture mechanics based model. The model accounts for the effect of cycle-dependent crack bridging properties in FRCs and predicts the number of cycles to failure defined by final fracture subsequent to stable fatigue crack growth in Mode I. The resulting theoretical S–N diagram was compared with experimental data reported in literature. The general agreement supports the validity of the current model, and reveals that cycle-dependent degradation of crack bridging controls fatigue life of FRCs. S–N diagrams are essential for material evaluation and structural design, and the model establishes the link between material structure and S–N diagram in an explicit manner, while the conventional stress-life approach realizes the link in an empirical manner.