ParisTech

About: ParisTech is a education organization based out in Paris, France. It is known for research contribution in the topics: Finite element method & Residual stress. The organization has 1888 authors who have published 1965 publications receiving 55532 citations. The organization is also known as: Paris Institute of Technology & ParisTech Développement.

What is the impact of a spinal fusion on acetabular implant orientation in functional standing and sitting positions

Abstract: Background This study used EOS imaging of primary total hip arthroplasty (THA) patients, with and without predating spinal fusion, to investigate (1) the impact of spinal fusion on acetabular implant anteversion and inclination, and (2) whether more extensive spinal fusion (fusion starting above the thoracolumbar junction or extension of fusion to the sacrum) affects acetabular implant orientation differently than lumbar only spinal fusion. Methods Ninety-three patients had spinal fusion (case group), and 150 patients were without spinal fusion (controls). None of the patients experienced dislocation. The change in sacral slope (SS) and cup orientation from standing to sitting was measured. Results Mean SS change from the standing to sitting positions was -7.9°in the fusion group vs -18.4°in controls (P = .0001). Mean change in cup inclination from the standing to sitting positions was 4.9°in the fusion group vs 10.2°in controls (P = .0001). Mean change in cup anteversion from standing to sitting positions was 7.1°in the fusion group vs 12.1°in controls (P = .0001). For each additional level of spinal fusion, the change in SS from standing to sitting positions decreased by 1.6(95% confidence interval [CI], 2.2073-1.0741), the change in cup inclination decreased by 0.8(95% CI, 0.380-1.203), and the change in cup anteversion decreased by 0.9(95% CI, 0.518-1.352; P Conclusion Patients with spinal fusion demonstrated less adaptability of the lumbosacral junction. Longer spinal fusion or inclusion of the pelvis in the fusion critically impacts hip-spine biomechanics and significantly affects the ability to compensate in the standing-to-sitting transition.

Hybrid constitutive modeling: data-driven learning of corrections to plasticity models

Abstract: In recent times a growing interest has arose on the development of data-driven techniques to avoid the employ of phenomenological constitutive models. While it is true that, in general, data do not fit perfectly to existing models, and present deviations from the most popular ones, we believe that this does not justify (or, at least, not always) to abandon completely all the acquired knowledge on the constitutive characterization of materials. Instead, what we propose here is, by means of machine learning techniques, to develop correction to those popular models so as to minimize the errors in constitutive modeling.

Growth of small cracks and prediction of lifetime in high-temperature alloys

Abstract: The lifetime to initiate an engineering crack is usually predicted from S–N curves in high cycle fatigue or Coffin–Manson curves in low-cycle fatigue. This paper investigates how to predict the engineering life to initiate an engineering crack from the growth of small cracks. Small cracks can nucleate from defects and especially ceramic inclusions in superalloys produced by powder metallurgy. The behavior of short cracks nucleated from artificial defects was investigated under small scale yielding. A deterministic prediction of the life of smooth specimens was made using the growth law measured in air or in vacuum. The distribution of real defects was then used in a probabilistic life prediction model. The growth of small cracks under large scale yielding was investigated in stainless steels. A modified Tomkins equation can account for the behavior of small cracks and provide an estimate of the lifetime under low-cycle fatigue or thermal fatigue. A damage model based on the propagation of micro-cracks originating at casting defects has been developed for single crystal turbine blades, operating under thermo-mechanical creep–fatigue conditions. The model used the process zone concept introduced by Mc Clintock. Weakening of material due to localized oxidation embrittlement is shown to account for oxidation–creep–fatigue interactions. The model gives satisfactory life predictions under various thermo-mechanical loading conditions. A local approach to fracture is proposed for fatigue crack growth using a fracture criterion as a post-processor of a finite element model, for two-dimensional long cracks.

Method for small signal stability analysis of VSC-MTDC grids

Abstract: This paper deals with small signal stability analysis of Voltage Source Converter based Multitermial HVDC grids (VSC-MTDC). First, a simplified model is used to predict the voltage dynamic behavior. Next, a modular method to build the state space model of the overall MTDC system is described. Model validation is achieved in time domain by a comparison with an electromagnetic simulation in EMTP-rv. As concrete example of effective application, a parametric study on the droop value is carried on a 3-terminal meshed HVDC grid. This example attests to the effect of the droop parameter on the stability of the overall system.