In this two-part paper we introduce a new formulation for modeling progressive damage in laminated composite structures. We adopt a multi-layer modeling approach, based on Isogeometric Analysis ...(IGA), where each ply or lamina is represented by a spline surface, and modeled as a Kirchhoff–Love thin shell. Continuum Damage Mechanics is used to model intralaminar damage, and a new zero-thickness cohesive-interface formulation is introduced to model delamination as well as permitting laminate-level transverse shear compliance. In Part I of this series we focus on the presentation of the modeling framework, validation of the framework using standard Mode I and Mode II delamination tests, and assessment of its suitability for modeling thick laminates. In Part II of this series we focus on the application of the proposed framework to modeling and simulation of damage in composite laminates resulting from impact. The proposed approach has significant accuracy and efficiency advantages over existing methods for modeling impact damage. These stem from the use of IGA-based Kirchhoff–Love shells to represent the individual plies of the composite laminate, while the compliant cohesive interfaces enable transverse shear deformation of the laminate. Kirchhoff–Love shells give a faithful representation of the ply deformation behavior, and, unlike solids or traditional shear-deformable shells, do not suffer from transverse-shear locking in the limit of vanishing thickness. This, in combination with higher-order accurate and smooth representation of the shell midsurface displacement field, allows us to adopt relatively coarse in-plane discretizations without sacrificing solution accuracy. Furthermore, the thin-shell formulation employed does not use rotational degrees of freedom, which gives additional efficiency benefits relative to more standard shell formulations.
In this two-part paper we introduce a new formulation for modeling progressive damage in laminated composite structures. We adopt a multi-layer modeling approach, based on isogeometric analysis, ...where each ply or lamina is represented by a spline surface, and modeled as a Kirchhoff–Love thin shell. Continuum damage mechanics is used to model intralaminar damage, and a new zero-thickness cohesive-interface formulation is introduced to model delamination as well as permitting laminate-level transverse shear compliance. In Part I of this series we focus on the presentation of the modeling framework, validation of the framework using standard Mode I and Mode II delamination tests, and assessment of its suitability for modeling thick laminates. In Part II of this series we focus on the application of the proposed framework to modeling and simulation of damage in composite laminates resulting from impact. The proposed approach has significant accuracy and efficiency advantages over existing methods for modeling impact damage. These stem from the use of IGA-based Kirchhoff–Love shells to represent the individual plies of the composite laminate, while the compliant cohesive interfaces enable transverse shear deformation of the laminate. Kirchhoff–Love shells give a faithful representation of the ply deformation behavior, and, unlike solids or traditional shear-deformable shells, do not suffer from transverse-shear locking in the limit of vanishing thickness. This, in combination with higher-order accurate and smooth representation of the shell midsurface displacement field, allows us to adopt relatively coarse in-plane discretizations without sacrificing solution accuracy. Furthermore, the thin-shell formulation employed does not use rotational degrees of freedom, which gives additional efficiency benefits relative to more standard shell formulations.
The increasing popularity of composite materials in aerospace applications is creating the need for a new class of predictive methods and tools for the simulation of progressive damage in laminated ...fiber-reinforced composite structures. The unique challenges associated with modeling damage in these structures may be addressed by means of thin-shell formulations which are naturally developed in the context of Isogeometric Analysis. In this paper, we further validate our recently developed Isogeometric Analysis-based multi-layer shell model for progressive damage simulations using experimental data for low-velocity impact on a 24-ply flat panel. The validation includes a careful comparison of delamination and matrix damage patterns predicted by the Isogeometric Analysis-based simulation and those obtained from post-impact non-destructive evaluation of the damaged coupon. The Isogeometric Analysis-based formulation is then deployed on two additional examples: a stiffened panel and a full-scale UAV wing, to demonstrate its suitability for, and ease of application to, typical aerospace composite structures.
On the timing performance of thin planar silicon sensors Akchurin, N.; Ciriolo, V.; Currás, E. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
07/2017, Letnik:
859, Številka:
C
Journal Article
Recenzirano
Odprti dostop
We report on the signal timing capabilities of thin silicon sensors when traversed by multiple simultaneous minimum ionizing particles (MIP). Three different planar sensors, with depletion ...thicknesses 133, 211, and 285µm, have been exposed to high energy muons and electrons at CERN. We describe signal shape and timing resolution measurements as well as the response of these devices as a function of the multiplicity of MIPs. We compare these measurements to simulations where possible. We achieve better than 20ps timing resolution for signals larger than a few tens of MIPs.
Hundreds of concurrent collisions per bunch crossing are expected at future hadron colliders. Precision timing calorimetry has been advocated as a way to mitigate the pileup effects and, thanks to ...their excellent time resolution, microchannel plates (MCPs) are good candidate detectors for this goal. We report on the response of MCPs, used as secondary emission detectors, to single relativistic particles and to electromagnetic showers. Several prototypes, with different geometries and characteristics, were exposed to particle beams at the INFN-LNF Beam Test Facility and at CERN. Their time resolution and efficiency are measured for single particles and as a function of the multiplicity of particles. Efficiencies between 50% and 90% to single relativistic particles are reached, and up to 100% in presence of a large number of particles. Time resolutions between 20 ps and 30 ps are obtained.
This work describes a fluid–structure interaction (FSI) design optimization framework and applies it to improving the structural performance of a water brake used to stop aircraft landing on short ...runways. Inside the water brake, a dissipative torque is exerted on a rotor through interactions between rotor blades and a surrounding fluid. We seek to optimize blade shape over a parameterized design space, to prevent potentially-damaging stress concentrations without compromising performance. To avoid excessive numbers of costly simulations while exploring the design space, we use a surrogate management framework that combines derivative-free pattern search optimization with automated construction of a low-fidelity surrogate model, requiring only a handful of high-fidelity FSI simulations. We avoid the difficult problem of generating fluid and structure meshes at new points in the design space by using immersogeometric FSI analysis. The structure is analyzed isogeometrically: its design geometry also serves as a computational mesh. This geometry is then immersed in an unfitted fluid mesh that does not depend on the structure’s design parameters. We use this framework to make significant improvements to a baseline design found in the literature. Specifically, there is a 35% reduction of von Mises stress variance and a 25% reduction of maximum of stress, while the resisting torque and mass of the optimized blades remain uncompromised.
•A fluid–structure interaction design optimization framework is proposed.•Structures are discretized isogeometrically and immersed in an unfitted fluid mesh.•Changes to the structure design do not require any mesh (re-)generation.•Surrogate modeling prevents excessive model evaluations during optimization.•The framework is applied to optimization of a hydraulic arresting gear.
Ditching, which is a controlled landing of an airplane on water, is an emergency condition to be investigated in order to improve the aircraft global crashworthiness. The complex hydrodynamic ...phenomena involved in ditching events are difficult to simulate and the accuracy of the results depends on the capability to reproduce the forces related to the interaction of the fuselage with the water surface. In the first part of the paper, the vertical impact on water of a rigid sphere is analysed using the explicit solver LS-DYNA in order to compare different modelling strategies. Four models of the fluid domain are presented: Lagrangian, arbitrary Lagrangian-Eulerian, smoothed particle hydrodynamics and hybrid Lagrangian-smoothed particle hydrodynamics. In the second part, the ditching of a scaled simplified airplane is simulated considering two different models for the water region. Experimental data from the literature are used to validate the simulations. The analysis, where the water and the air are modelled with the arbitrary Lagrangian-Eulerian method, shows a better correlation with the experimental data because this formulation can reproduce the suction force which acts on the fuselage and affects significantly the ditching dynamics.
We extend a recently-developed framework for isogeometric analysis of composite laminates to drive material damage evolution with a smoothed strain field. This builds on ideas from gradient-enhanced ...continuum damage modeling, and is intended to limit the dependence of damage predictions on the choice of discrete mesh. The resulting enhanced framework models each lamina of a composite shell structure as a Kirchhoff–Love thin shell. To account for the anisotropic damage modes of laminae, we smooth a tensor-valued strain by solving an elliptic partial differential equation (PDE) system on each lamina. This strain-smoothing PDE system is formulated to be independent of the choice of coordinates and is applicable to general manifold shell geometries. Numerical examples illustrate the enhanced damage model’s validity, mesh-independence, and applicability to complex industrial geometries.
•Developed a gradient-enhanced continuum damage model for thin shells.•Tensor-valued strain smoothed by solving an elliptic PDE system.•PDE system formulated to be independent of the coordinate choice.•Numerical examples illustrate mesh-independence.•Impact on geometrically complex composite laminates is simulated.
Combined measurements of the production and decay rates of the Higgs boson, as well as its couplings to vector bosons and fermions, are presented. The analysis uses the LHC proton–proton collision ...data set recorded with the CMS detector in 2016 at
s
=
13
Te
, corresponding to an integrated luminosity of 35.9
fb
-
1
. The combination is based on analyses targeting the five main Higgs boson production mechanisms (gluon fusion, vector boson fusion, and associated production with a
W
or
Z
boson, or a top quark-antiquark pair) and the following decay modes:
H
→
γ
γ
,
Z
Z
,
W
W
,
τ
τ
,
b
b
, and
μ
μ
. Searches for invisible Higgs boson decays are also considered. The best-fit ratio of the signal yield to the standard model expectation is measured to be
μ
=
1.17
±
0.10
, assuming a Higgs boson mass of
125.09
Ge
. Additional results are given for various assumptions on the scaling behavior of the production and decay modes, including generic parametrizations based on ratios of cross sections and branching fractions or couplings. The results are compatible with the standard model predictions in all parametrizations considered. In addition, constraints are placed on various two Higgs doublet models.
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