Experimental and numerical investigation on draping behaviour of woven carbon fabric

In the liquid composite moulding (LCM) process, fabric is draped over the mould surface and a resin is injected under pressure to develop a composite laminate. Wrinkling is one of the most common flaws that occurs during the draping of the fabric. Wrinkling of the fabric within the composite could severely reduce the quality of the finished composite laminate. Thus, to develop a high-quality composite laminate, exact prediction of fabric wrinkling behaviour is necessary. The aim of the paper is to investigate the draping behaviour of carbon fabric. Carbon fabric with an areal density of 245 g/m2 is used in the study. Both experimental and numerical investigations were performed. An experimental setup was developed to predict the draping behaviour of the carbon fabric used in the study. LS-DYNA/Explicit solver is used to achieve macro level draping simulation. Material model MAT_REINFORCED_THERMOPLASTIC [MAT_249] offers the possibility to simulate the forming behaviour of a thermoplastic material. To simulate dry fabrics using MAT_249, a very low properties are used for the matrix in the material model. To capture the forming behaviour of fabric, an intensive material characterization has been performed. Tensile and shear properties of the fabrics were determined using uniaxial and picture frame tests, respectively. Influence of the position of the integration points from the mid surface on bending behaviour is studied and calibrated using a simple test.

Industrial Fe-Simulation of Roughing Using an Automatic Solver Shifting Technique

Roughing has been simulated with the Finite element software AbaqusTM to replicate an industrial-scale process. The model has been made to be as close as possible to its real counterpart. For this purpose, an automated controlling logic has been created to simulate the multiple passes as well as inter-pass times for roughing. Simulating multiple passes with FEM is computationally very demanding, so new methods to reduce computing times are worth considering. During a roll pass an explicit solver is necessary due to high deformation amounts and rates. An explicit solver is tied to a very small time increment, so it takes a long time. On the other hand, inter-pass periods do not include any deformation or roller contact, so an implicit solver is quite capable of computing this portion of the simulation. An implicit solver can speed up the time increment considerably when compared to the explicit solver, so using it potentially saves a significant amount of computing time. Unfortunately, Abaqus does not include any methods to change the solver during a single simulation. Instead it is possible to communicate between the two solver types by manually importing data from a completed simulation to a new simulation model. A new method to change solvers automatically using a self-made Python code is proposed in this paper.

Improving the Blast Resistance of Large Steel Gates—Numerical Study

Blast resistant gates/doors are essential for sensitive infrastructure, such as embassies, ministries, or parliaments. Lightweight gates equipped with ‘energy absorbing systems’ have better operational performance than the traditional costly and bulky design. Graded auxetic structures have not yet been used as potential passive damping systems in the supporting frame of blast resistant gates. Consequently, this study tries to test if a uniaxial graded auxetic damper (UGAD) proposed by the authors in a recent article, namely the development of a new shock absorbing UGAD, could maintain a 3000 mm × 4500 mm steel gate operable after high blast peak reflected overpressure of 6.6 MPa, from 100 kg TNT at 5 m stand-off distance. The blast-induced response of the gate was assessed, with and without the proposed UGAD, using Abaqus/Explicit solver. Results showed that the attachment of the proposed UGAD to the gate led to a dramatic decrease in permanent deformations (a critical factor for gate operability after a blast event). Hence, a lighter, more economical gate (with 50% reduction in mass) was required to satisfy the operability condition. In addition, 49% of peak reaction forces were diminished, that have a direct impact on the supporting frame. Moreover, the results revealed that, in the numerical model, 56% of the achieved plastic dissipation energy was from the UGADs, and 44% from the gate. The outcomes of this research may have a positive impact on other sectors beyond academia, such as industry, economy, and public safety.

Calibration of the material parameters of a CFRP laminate for numerical simulations

The aim of present paper is to show a procedure to calibrate mechanical properties to be used in a finite element model for a carbon fibre-reinforced plastic laminate that use solid elements. A reduced experimental programme including tensile test, tensile test on specimen with a central hole, three-point bending test and three-point bending test on short beam test were carried out. Every test was numerically reproduced by means of an explicit solver. Properties are determined from the tensile test and unmodified for the other load scenarios which are used as validation benchmarks. Finally, it is demonstrated that the properties determined with the simple tensile tests can guarantee accurate results when adopted to simulate much more complicated stress patterns.

Numerical Simulations of MitraClip Placement: Clinical Implications

Mitral regurgitation (MR) is the most common type of valvular heart disease in patients over the age of 75 in the US. Despite the prevalence of mitral regurgitation in the elderly population, however, almost half of patients identified with moderate-severe MR are turned down for traditional open heart surgery due to frailty and other existing co-morbidities. MitraClip (MC) is a recent percutaneous approach to treat mitral regurgitation by placement of MC in the center of the mitral valve to reduce MR. There are currently no computational simulations to elucidate the role of MC on both the fluid and solid mechanics of the mitral valve. Here, we use the Smoothed Particle Hydrodynamics (SPH) approach to study various positional placements of the MC in the mitral valve and its impact on reducing MR. SPH is a particle based (meshless) approach that handles flow through narrow regions quite efficiently. Fluid and surrounding anatomical structure interactions is handled via contact and hence can be used for studying fluid-structure interaction problems such as blood flow with surrounding tissues/structure. This method is available as part of the Abaqus/Explicit solver. Regurgitation was initiated by removing targeted chordae tendineae that are attached to specified leaflets of the mitral valve and, subsequently, MC implants are placed in various locations, starting from the region near where the chordae tendineae were removed and moving away from the location towards the center of the valve. The MC implant location closest to where the chordae tendineae were removed showed the least amount of residual MR post-clip implantation amongst all other locations of MC implant considered. These findings have important implications for strategic placement of the MC depending on the etiology of MR to optimize clinical outcome.

Numerical Simulation of a Supersonic Ejector for Vacuum Generation with Explicit and Implicit Solver in Openfoam

Supersonic ejectors are used extensively in all kind of applications: compression of refrigerants in cooling systems, pumping of volatile fluids or in vacuum generation. In vacuum generation, also known as zero-secondary flow, the ejector has a transient behaviour. In this paper, a numerical and experimental research of a supersonic compressible air nozzle is performed in order to investigate and to simulate its behaviour. The CFD toolbox OpenFOAM 6 was used, with two density-based solvers: explicit solver rhoCentralFoam, which implements Kurganov Central-upwind schemes, and implicit solver HiSA, which implements the AUSM+up upwind scheme. The behaviour of the transient evacuation ranges between adiabatic polytropic exponent at the beginning of the process and isothermal at the end. A model for the computation of the transient polytropic exponent is proposed. During the evacuation, two regimes are encountered in the second nozzle. In the supercritic regime, the secondary is choked and sonic flow is reached. In the subcritic regime, the secondary flow is subsonic. The final agreement is good with the two different solvers, although simulation tends to slightly overestimate flow rate for large values region.