Low-velocity impact behaviour and failure of stiffened steel plates

The behaviour and failure of stiffened steel plates subjected to transverse loading by an indenter is studied in this paper. Low-velocity dynamic and quasi-static tests of stiffened plates with geometry adopted from a typical external deck area on an offshore platform were conducted. The results show that the quasi-static tests provide a good reference for impact loading situations, although they displayed a larger displacement at fracture. Finite element simulations of the steel panel tests were performed, using the elastic-viscoplastic J2 flow theory and a one-parameter fracture criterion. A relatively fine spatial discretization in the load application area was needed to capture accurately the onset of fracture. In order to locally refine the mesh, a method for automatic mesh refinement based on damage driven h-adaptivity was implemented and evaluated against results obtained with fixed meshes of various element sizes.acceptedVersio

Sandwich Panels with Polymeric Foam Cores Exposed to Blast Loading: An Experimental and Numerical Investigation

Sandwich panels have proven to be excellent energy absorbents. Such panels may be used as a protective structure in, for example, façades subjected to explosions. In this study, the dynamic response of sandwich structures subjected to blast loading has been investigated both experimentally and numerically, utilizing a shock tube facility. Sandwich panels made of aluminium skins and a core of extruded polystyrene (XPS) with different densities were subjected to various blast load intensities. Low-velocity impact tests on XPS samples were also conducted for validation and calibration of a viscoplastic extension of the Deshpande-Fleck crushable foam model. The experimental results revealed a significant increase in blast load mitigation for sandwich panels compared to skins without a foam core, and that the back-skin deformation and the core compression correlated with the foam density. Numerical models of the shock tube tests were created using LS-DYNA, incorporating the new viscoplastic formulation of the foam material. The numerical models were able to capture the trends observed in the experimental tests, and good quantitative agreement between the experimental and predicted responses was in general obtained. One aim of this study is to provide high-precision experimental data, combined with a validated numerical modelling strategy, that can be used in simulation-based optimisation of sandwich panels exposed to blast loading

A pragmatic orthotropic elasticity-based damage model with spatially distributed properties applied to short glass-fibre reinforced polymers

This article presents a simple progressive damage model for quasi-brittle materials, combining orthotropic elasticity with a scalar damage model including spatial variation of the damage initiation strain and the crack band method for softening regularization. The model’s performance is first analyzed from a numerical point of view and then demonstrated for tensile tests (, and ), open-hole tensile tests () and three-point bending ( and ) tests of short fibre-reinforced polypropylene with 15 wt.% and 30 wt.% glass fibres. Despite its simplicity, the model captures the anisotropic elastic and inelastic behaviour observed in experiments. The model is applicable for orthotropic brittle or quasi-brittle materials, where the variability in elastic properties is negligible and the orientation dependency of the fracture strain is small or not relevant for the application

Sandwich panels with polymeric foam cores exposed to blast loading: An experimental and numerical investigation

Sandwich panels have proven to be excellent energy absorbents. Such panels may be used as a protective structure in, for example, façades subjected to explosions. In this study, the dynamic response of sandwich structures subjected to blast loading has been investigated both experimentally and numerically, utilizing a shock tube facility. Sandwich panels made of aluminium skins and a core of extruded polystyrene (XPS) with different densities were subjected to various blast load intensities. Low-velocity impact tests on XPS samples were also conducted for validation and calibration of a viscoplastic extension of the Deshpande-Fleck crushable foam model. The experimental results revealed a significant increase in blast load mitigation for sandwich panels compared to skins without a foam core, and that the back-skin deformation and the core compression correlated with the foam density. Numerical models of the shock tube tests were created using LS-DYNA, incorporating the new viscoplastic formulation of the foam material. The numerical models were able to capture the trends observed in the experimental tests, and good quantitative agreement between the experimental and predicted responses was in general obtained. One aim of this study is to provide high-precision experimental data, combined with a validated numerical modelling strategy, that can be used in simulation-based optimisation of sandwich panels exposed to blast loading

Void nucleation and growth in mineral-filled PVC - An experimental and numerical study

The nucleation and growth of voids in mineral-filled PVC have been investigated through experimental and numerical studies. Uniaxial tensile specimens were deformed in tension to different elongation levels and then unloaded. The macroscopic strain fields were recorded by use of digital image correlation. After the test, the microstructure of the deformed specimens was investigated in a scanning electron microscope. It was found that the observed volume strain on the macroscale is related to void growth on the microscale. In addition, finite element simulations were performed on unit cell models representing the microstructure of the material in a simplified manner. The numerical simulations demonstrate macroscopic dilation as a result of void growth. Moreover, the numerical simulations indicate that the experimentally observed stress-softening response of the PVC composite material may result from matrix-particle debonding

CO2 pipeline integrity: A coupled fluid-structure model using a reference equation of state for CO2

We present a coupled fluid-structure model to study crack propagation and crack arrest in pipelines. Numerical calculations of crack arrest, crack velocity and pressure profiles have been performed for steel pipes with an outer diameter of 267 mm and a wall thickness of 6 mm. The pipe material and fracture propagation have been modelled using the finite-element method with a local ductile fracture criterion and an explicit time-integration scheme. An in-house finite-volume method has been employed to simulate the fluid dynamics inside the pipe, and the resulting pressure profile was for each time step applied as a load in the finite-element model. Choked-flow theory was used for calculating the flow through the pipe opening as the crack propagated. Simulations were performed with both methane and CO2, pressurized at 75, 120 and 150 bar. Initial results indicate that crack arrest does not necessarily occur with CO2 under circumstances where it would occur with methane

Coupled fluid-solid modelling of the valve dynamics in reciprocating compressors

A novel method coupling computational fluid dynamics (CFD) and finite element method (FEM) was developed to account for the complex physics of the reciprocating compressor. The developed method is based on data exchange between the two solvers at each time step. We address the challenges related to valve dynamics, where the motion of solid components is not prescribed as for pistons, but result from the combined interactions between pressure, velocity, spring forces and impact forces during each revolution. The coupling method enables accurate computation of the solid-fluid interaction, where at each time step the pressure acting on the valve computed by CFD is transferred to the FEM simulation, and the three-dimensional valve motion computed by FEM is transferred to the CFD simulation. It is demonstrated on the dynamics of a ring plate discharge valve in a reciprocating ammonia compressor to quantify the effect of impact damping which arises from the gas dynamics, leading to reduced forces on the valve. The results from the coupling simulations are compared against novel experimental measurements obtained by instrumenting a real compressor. The coupled CFD-FEM simulation gives detailed insights into the valve behaviour and was used also to investigate pressure inhomogeneities, which can lead to tumbling motion of the valve ring.Coupled fluid-solid modelling of the valve dynamics in reciprocating compressorsacceptedVersio

Coupled fluid-solid modelling of the valve dynamics in reciprocating compressors

A novel method coupling computational fluid dynamics (CFD) and finite element method (FEM) was developed to account for the complex physics of the reciprocating compressor. The developed method is based on data exchange between the two solvers at each time step. We address the challenges related to valve dynamics, where the motion of solid components is not prescribed as for pistons, but result from the combined interactions between pressure, velocity, spring forces and impact forces during each revolution. The coupling method enables accurate computation of the solid-fluid interaction, where at each time step the pressure acting on the valve computed by CFD is transferred to the FEM simulation, and the three-dimensional valve motion computed by FEM is transferred to the CFD simulation. It is demonstrated on the dynamics of a ring plate discharge valve in a reciprocating ammonia compressor to quantify the effect of impact damping which arises from the gas dynamics, leading to reduced forces on the valve. The results from the coupling simulations are compared against novel experimental measurements obtained by instrumenting a real compressor. The coupled CFD-FEM simulation gives detailed insights into the valve behaviour and was used also to investigate pressure inhomogeneities, which can lead to tumbling motion of the valve ring

CO2 pipeline integrity: A new evaluation methodology

A coupled fluid-structure model for pipeline integrity simulations has been developed. The pipe material and fracture propagation have been modelled using the finite-element method with a local fracture criterion. The finite-volume method has been employed for the fluid flow inside the pipe. Choked-flow theory was used for calculating the flow through the pipe crack. A comparison to full-scale tests of running ductile fracture in steel pipelines pressurized with hydrogen and with methane has been done, and very promising results have been obtained. It is suggested that the current method may be useful in the design and operation of safe and cost-effective CO2 transport systems