Cracking in the asphaltic layer of pavement has been shown to be a major source of distress in roadways. Previous studies in asphaltic mixture cracking have typically not considered the material heterogeneity. A numerical method of analysis is presented that is based on the theory of fracture mechanics, in which the binder and the aggregates are treated as distinct materials. The simulations performed are verified and calibrated from simple and conventional laboratory tests. The study investigates crack evolution under monotonic loading, even though the method outlined can be further developed for the investigation of asphalt mixture fatigue. The approach discussed is part of a multiscale framework for pavement analysis, in which the damage due to cracking at the local scale can be considered in a global analysis at the actual pavement scale.

No abstract

<p>O trincamento da camada asfáltica em pavimentos é apontado como o principal defeito das rodovias brasileiras. Estudos experimentais e numéricos sobre este fenômeno vêm sendo realizados considerando o material como homogêneo. Este artigo apresenta uma abordagem numérica baseada na Teoria da Mecânica da Fratura na qual considera-se a heterogeneidade do material, sendo o ligante e os agregados tratados separadamente. As simulações realizadas são verificadas e calibradas através de ensaios laboratoriais simples e convencionais. O estudo trata da formação e propagação de trincas sob carregamentos monotônicos e aponta para uma nova forma de simulação do fenômeno de fadiga de misturas. É ainda discutida a utilização de uma abordagem multi-escala, na qual o dano observado na forma da propagação de trincas na escala local pode ser considerado numa escala global compatível com o pavimento real.</p>

Crack management has become a major focus for many gas and liquid transmission pipeline operators. Failures associated with crack-like features have been a concern for both pipe operators and regulatory agencies. As a result, pipeline operators are excavating large numbers of features for not only in-line inspection (ILI) validation purposes, but also to make repairs. Additionally, ILI technologies have advanced significantly in recent years and are identifying an increasing number of features with greater levels of accuracy. With increased data generation, operators are faced with an unprecedented amount of information that requires response prioritization. Because of high levels of conservatism associated with today’s assessment methods, pipeline operators are spending a significant amount of capital excavating crack-like features. There is a need for improved assessment methods that integrates testing simulated / synthetic crack-like features. This paper will provide details on a study funded to systematically generate crack-like features in pipeline materials with the application of cyclic internal pressure loading. Synthetic crack-like features were generated in 12.75-inch × 0.250-inch, Grade X42 pipe material using electronic discharge machining (EDM) to form notches. Notch depths were 10% of the nominal wall thickness and ranged from 1-inch to 3-inches in length. The pipe samples were then pressure cycled to achieve microcracking at the base of each notch. Initial stages of the program involved sectioning features to quantify crack growth levels. Once a systematic process for growing cracks from EDM starter notches had been validated, testing involved cyclic pressure fatigue to failure and burst testing. The advantage with the crack generation methodology used in this study was the ability to generate sharp, crack-like features without altering the microstructure of the pipe material in the vicinity of the feature. Programs such as the one presented in this paper are useful for both generating features in pipeline materials and quantifying behavior of pipeline materials subjected to cyclic pressure and burst loading.

This paper presents a case study of how a drilling contractor handled the implementation of Managed Pressure Drilling (MPD) equipment on 4 (four) drilling rigs, with focus on the impact on Well Control equipment and emergency disconnect while performing FMCD (Floating Mud Cap Drilling). The paper considers the effects of the rapid inflow of seawater from the bottom of the riser (water rush-in) during a possible emergency disconnect. Additionally, this paper discusses concerns about the subsea equipment when the drilling fluid level is close to the subsea BOP stack or below the seabed. Such scenarios can expose the drilling riser, riser adaptor, flexible joint, BOP annular preventer, BOP seals and gaskets to an inward-acting pressure differential. Restrictions that this inward-acting differential pressure may impose on the conventional equipment currently aboard the drilling units were taken into consideration to determine the feasibility of FMCD operations. This paper highlights the non-conventional considerations as well as challenges associated with this operation for the offshore drilling industry. Those challenges have also motivated technology innovation such as a reduced-friction, next-generation subsea flexible joint, which will operate equally in conventional or MPD conditions.