Cracking in asphalt materials

This chapter provides a comprehensive review of both laboratory characterization and modelling of bulk material fracture in asphalt mixtures. For the purpose of organization, this chapter is divided into a section on laboratory tests and a section on models. The laboratory characterization section is further subdivided on the basis of predominant loading conditions (monotonic vs. cyclic). The section on constitutive models is subdivided into two sections, the first one containing fracture mechanics based models for crack initiation and propagation that do not include material degradation due to cyclic loading conditions. The second section discusses phenomenological models that have been developed for crack growth through the use of dissipated energy and damage accumulation concepts. These latter models have the capability to simulate degradation of material capacity upon exceeding a threshold number of loading cycles.Peer ReviewedPostprint (author's final draft

Damage analysis and fracture toughness evaluation in a thin woven composite laminate under static tension using infrared thermography

This work deals with the issue of damage growth in thin woven composite laminates subjected to tensile loading. The conducted tensile tests were monitored on-line with an infrared camera, and tested specimens were analysed using Scanning Electron Microscopy (SEM). Combined with SEM micrographs, observation of heat source fields enabled us to assess the damage sequence. Transverse weft cracking was confirmed to be the main damage mode and fiber breakage was the final damage leading to failure. For cracks which induce little variation of specimen stiffness, the classic “Compliance method” could not be used to compute energy release rate. Hence, we present here a new procedure based on the estimation of heat source fields to calculate the energy release rate associated with transverse weft cracking. The results are then compared to those computed with a simple 3D inverse model of the heat diffusion problem and those presented in the literature

A modelling technique for calculating stress intensity factors for structures reinforced by bonded straps. Part II: Validation

In this second part of the two-part paper validation of the 2D FE modelling technique described in the first part is presented for a range of test configurations. Each mechanism that influences crack growth behaviour of strap reinforced structures is modelled for different substrate geometries, strap materials and dimensions in order to test the accuracy and robustness of the methodology. First, calculated through-thickness strain energy release rate distribution is compared with the result of a 3D FE model to validate this 2D model. Second, calculated disbond areas, thermal residual stresses and their redistribution with crack propagation are validated against experimental measurements. Third, influence of geometric nonlinearity and the need to use the alternate analysis method described in part I are demonstrated by examples, and errors generated by not following this analysis rule are given. Finally, using the 2D model calculated stress intensity factors, fatigue crack growth rates and lives are predicted for different specimens, strap materials and applied stress levels and are compared with the experimental tests. Good or acceptable agreement has been achieved for each case

Modelling the influence of machined surface roughness on the fatigue life of aluminium alloy

The influence of machined surface roughness on the fatigue life of 7010 aluminium alloy has been investigated. Four-point bending specimen have been machined according to various machining conditions and tested in fatigue. In order to explain the high dependence of SN curves on the surface roughness of the specimen, an approach based on the finite element analysis of measured surface topography is proposed. Surface grooves due to machining are supposed to generate stress concentrations that are so calculated. A model of fatigue life prediction is developed, using this definition of local Kt

Development of a Finite Element Analysis Methodology for the Propagation of Delaminations in Composite Structures

Analysing the collapse of skin-stiffened structures requires capturing the critical phenomenon of skin-stiffener separation, which can be considered analogous to interlaminar cracking. This paper presents the development of a numerical approach for simulating the propagation of interlaminar cracks in composite structures. A degradation methodology was applied in MSC.Marc that involved modelling the structure with shell layers connected by user-defined multiple point constraints (MPCs). User subroutines were written that apply the Virtual Crack Closure Technique (VCCT) to determine the onset of crack growth, and modify the properties of the user-defined MPCs to simulate crack propagation. Methodologies for the release of failing MPCs are presented and are discussed with reference to the VCCT assumption of self-similar crack growth. Numerical results applying the release methodologies are then compared with experimental results for a double cantilever beam specimen. Based on this comparison, recommendations for the future development of the degradation model are made, especially with reference to developing an approach for the collapse analysis of fuselage-representative structures

Inspection scheduling based onreliability updating of gas turbinewelded structures

This article presents a novel methodology for the inspection scheduling of gas turbine welded structures, based on reliability calculations and overhaul findings. The model was based on a probabilistic crack propagation analysis for welds in a plate and considered the uncertainty in material properties, defect inspection capabilities, weld geometry, and loads. It developed a specific stress intensity factor and an improved first-order reliability method. The proposed routine alleviated the computational cost of stochastic crack propagation analysis, with accuracy. It is useful to achieve an effective design for manufacturing, to develop structural health monitoring applications, and to adapt inspection schedules to airplane fleet experience.We are grateful to the Mechanical Technology Department of ITPAero (R) for supporting and helping us with this study. The invaluable guidance and feedback from Jose Ramon Andujar is recognized with great appreciation

Cyclic J-integral using the linear matching method

The extended version of the latest Linear Matching Method (LMM) has the capability to evaluate the stable cyclic response, which produces cyclic stresses, residual stresses and plastic strain ranges for the low cycle fatigue assessment with cyclic load history. The objective of this study is to calculate ΔJ through the LMM and suggest future development directions. The derivation of the ΔJ based on the potential energy expression for a single edge cracked plate subjected to cyclic uniaxial loading condition using LMM is presented. To extend the analysis so that it can be incorporated to other plasticity models, material Ramberg-Osgood hardening constants are also adopted. The results of the proposed model have been compared to the ones obtained from Reference Stress Method (RSM) for a single edge cracked plate and they indicate that the estimates provide a relatively easy method for estimating ΔJ for describing the crack growth rate behaviour by considering the complete accumulated cycle effects

Cyclic J integral using linear matching method

The extended version of the latest Linear Matching Method (LMM) has the capability to evaluate the stable cyclic response, which produces cyclic stresses, residual stresses and plastic strain ranges for the low cycle fatigue assessment with cyclic load history. The objective of this study is to calculate ΔJ through the LMM and suggest future development directions. The derivation of the ΔJ based on the potential energy expression for a single edge cracked plate subjected to cyclic uniaxial loading condition using LMM is presented. To extend the analysis so that it can be incorporated to other plasticity models, material Ramberg-Osgood hardening constants are also adopted. The results of the proposed model have been compared to the ones obtained from Reference Stress Method (RSM) for a single edge cracked plate and they indicate that the estimates provide a relatively easy method for estimating ΔJ for describing the crack growth rate behaviour by considering the complete accumulated cycle effects