Hydrogen embrittlement of an X70 pipeline steel assessed by slow strain rate tensile tests

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Fully-coupled continuum damage model for simulation of plasticity dominated hydrogen embrittlement mechanisms

The mechanical properties of steel are degraded due to the presence of hydrogen, also known as hydrogen embrittlement (HE). Simulations of hydrogen embrittlement at a continuum level can assist in characterizing the detrimental effect that is associated with the introduction of hydrogen regarding the structural integrity of steel structures. Such simulations require the implementation of both hydrogen diffusion and hydrogen assisted material degradation. The present study presents a framework for finite element simulations combining these aspects in a fully coupled way, with diffusion driven by hydrogen concentration, stress triaxiality gradient and plastic strain rate, and damage based on the ductile damage model known as the Complete Gurson Model (CGM). Hydrogen assisted degradation is modeled through acceleration of void growth, nucleation or coalescence, based on the HELP or HESIV mechanisms as underlying physical basis. The proposed model is the first fully-coupled continuum micromechanics-based damage model that accounts for the plasticity dominated HE mechanisms. The effect of element size and time increments is evaluated, establishing guidelines to use the model. Moreover, results of simulations of a tensile test on a hydrogen charged notched specimen are given, to provide an illustrative example of the capabilities of the framework. The well-known ductility loss due to hydrogen is observed in the simulation results

Control of Magnetic Spring Assisted Drivetrains

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A two-level Iterative Learning Control scheme for the engagement of wet clutches

This paper discusses the application of Iterative Learning Control (ilc) algorithms for the engagement of wet clutches. A two-level control scheme is presented, consisting of a high level ilc-type algorithm which iteratively updates parameterized reference trajectories which are tracked by the low level tracking control. At this low level, two standard ilc controllers are used to first track a pressure reference in the filling phase and afterwards a slip reference in the slip phase of the clutch engagement. The performance and robustness of the presented approach are validated on an experimental test setup. It is shown that both levels are crucial to achieve good engagement quality during normal machine operation. Through the use of this ilc control scheme, it is possible to avoid time-consuming and cumbersome experimental (re)calibrations, which are nowadays used to achieve and maintain good performance despite the complex and time-varying dynamics of wet clutches.status: publishe

Iterative optimization of parameterized trajectories for complex mechatronic systems

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Influence of weld porosity on crack size estimations in Single Edge Notched Tension (SENT) testing of steels : a numerical study

The acceptance of weld volumetric imperfections such as porosity from the perspective of structural integrity is guided by workmanship criteria. However, there is a lack of knowledge on how and to what extent volumetric imperfections can affect the outcome of fracture toughness tests. The small size of laboratory test specimens potentializes the relative impact of such imperfections. This study numerically investigates the influence of porosity on two crack sizing techniques commonly applied to single specimen fracture toughness testing, namely Unloading Compliance (UC) and Direct Current Potential Drop (DCPD). The investigation focuses on Single Edge Notched Tension (SENT) specimens, commonly used to characterize fracture behavior in low crack tip constraint conditions. An extensive finite element parametric study was performed where single pores and random porosity distributions were generated by element deletion. The results show that both UC and DCPD crack size estimations are influenced by pores of sizes within workmanship criteria acceptable limits, which in some cases might induce (or contribute to) crack size errors superior to validity limits set by fracture toughness test standards

ℋ2 optimal vibration control using tuned mass dampers and inertial actuators: comparison of passive and active control effects

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