A Novel Implementation of the LDEM in the Ansys LS-DYNA Finite Element Code

In this paper, a novel implementation of the Lattice Discrete Element Method (LDEM) is proposed: in particular, the LDEM is implemented in the Ansys LS-DYNA finite element code. Such an implementation is employed to evaluate the fracture behaviour of sandwich panels under bending. First, the novel hybrid model proposed is validated by simulating some three-point bending experimental tests carried out at the University of Parma, and then it is used to model the fracture behaviour of sandwich panels under four-point bending. Failure mechanisms, damage locations, and load-deflection curves are numerically determined by employing such a novel model, and the results show a good agreement with the available experimental findings.

BUCKLE PROPAGATION OF SANDWICH PIPES UNDER EXTERNAL PRESSURE

Buckle propagation of local collapse appearing in the damaged pipes is one of the failure modes that are of particular interest for deepwater application. The local collapse can propagate along the pipeline for long distances in both directions when the external pressure magnitude is up to the propagation pressure. In this paper, the buckle propagation pressure of sandwich pipes (SP) with different material properties and geometric characteristics is investigated by numerical simulation using Python programming language based on general finite element code. The results of the pressure history data obtained are verified by comparing those published previously. The effect of material properties, geometric characteristics and adhesion conditions on the propagation pressure are analyzed.

Design Optimization of Composite Lay-up Sequence and Orientation to Achieve Minimum Weight for Racing Seat

Composites have proved their usefulness in the automotive industry during recent years. Many automobile companies use them in different parts to reduce weight without hampering strength. In a composite material, Lay-up sequence and orientation highly affects the properties of the laminate. Therefore, it is important to perform design optimization on a component to achieve high strength in minimum weight. This paper deals with the optimization of lay-up for composite Racing Seat using finite element analysis. Different lay-up sequences for laminates including, cross-ply [0/90]n, angle-ply [±α]n, and [0/90/±α]n are analysed. The lay-up sequence, orientation and ply number are optimized using composite material carbon fibre/Epoxy. Driver’s ergonomics and impact sustainability are considered constraints for weight optimization. Driver’s ergonomics were based on 95th percentile male and 5th percentile female rule. Force analysis is performed on the seat according to SFI 39.2 to evaluate the strength requirement. Finite element analysis of composite racing seat is performed via commercial finite element code ANSYS and using the capabilities of ANSYS Composite PrepPost (ACP) to form desired composite lay-up. A finite element code is based on classical lamination theory; including Puck’s failure criterion for first-ply failure. The seat is divided into three portions with a different number of layers considering the values and specific nature of acting forces; which resulted in different thicknesses in different regions. The optimization results show that for all the angles of Angle-ply laminate considered, Angle-ply laminates with an angle of 45⁰ provides a more optimum design. The minimum weight obtained is 10.15 kg.

Development of Line-to-Line Contact Formulation for Continuum Beams

A line-to-line beam contact formulation in the framework of the absolute nodal coordinate formulation (ANCF) is introduced in this paper. Higher- and lower-order ANCF beam elements employ the introduced beam contact formulation. The higher- and lower-order ANCF beam elements are compared in terms of their accuracy and performance in a large deformation contact problem. Efficiency of numerical integration of contact energy variation contribution to the system’s equations of motion is studied. The contacting elements’ surfaces of the ANCF beam elements are parameterized by segmentation of integration over the contact patch. Numerical results investigate the accuracy, robustness and efficiency of the developed line-to-line contact formulation by comparing against a solid element type using commercial finite element code. According to the numerical results, the higher-order ANCF beam element’s solution is closer than the lower-order ANCF beam element’s in accordance with the reference solution provided by a solid element type using commercial finite element code ABAQUS. Furthermore, the higher-order beam element is found to be more efficient than the lower-order beam with respect to the numerical integration of the contact energy variation. Expectedly, the higher-order ANCF beam element is able to capture the cross-section deformation in a large deformation contact problem, while the lower-order element fails to exhibit such cross-sectional deformation.

Rift jump and microcontinent formation in back-arc settings

<p><span>Back-arc basins often present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. In some cases, rift jumps can create continental fragments or microcontinents (e.g., Coral Sea, Central Mediterranean, Scotia Sea). The processes controlling rift jumps and possible formation of continental fragments are still not fully understood, but they are certainly related to the dynamics of subduction. </span></p><p><span>In this work, we show how episodic trench retreat shapes the morphology of back-arc basins and can produce rift jumps. We use the finite element code ASPECT to model the rifting of continental lithosphere in 2D with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically vary the duration of different extensional phases, simulating episodes of trench retreat. Our results show that when extension is continuous, continental break-up occurs and a spreading centre develops. On the other hand, rift jump occurs in models with multiple extensional phases resulting in more complex morphologies that go from a hyperextend margin, to microcontinent formation, to spreading centre jumps within the newly formed oceanic lithosphere. In the first two cases (i.e., hyperextended margin and microcontinent), the length of the rift jump ranges from about 40 to 100 km and the timing varies from about 2 to 6 Myr. In the latter case (i.e., spreading centre jump within oceanic lithosphere) the length of the jump is significantly lower, 10-15 km, and the time needed for the ridge jump to occur is <2 Myr. These values depend on the rheological properties of the lithosphere, but, importantly, we show that the resulting scenario is controlled by the duration of the first extension stage and of the break before the next one.</span></p>

Steady-state heat transfer analysis in a spherical domain revisited

The paper discusses the numerical solution of the one-dimensional radially axi-symmetric non-linear second-order differential equation to model the conduction and radiation transfer through a spherical domain as a result of an exothermic heat source. The equation is transformed to a non-dimensional form. The dimensionless numbers emanating from the transformation represent the effect of the reaction rate, reaction type, activation energy, radiation and the convection on the temperature. The non-dimensional differential equation for the temperature distribution was previously solved using the Runge-Kutta-Fehlberg method coupled with a Shooting technique. In this paper the solution of the non-dimensional differential equation using an iterative Galerkin finite element method approach employing the Picard method is described. The commercial finite element code Comsol is also employed to solve the non-dimensional differential equation. The current study was motivated by inconsistencies that were observed in the previous results that were presented. Although the assumed underlying physics is used to evaluate the results, the study focuses purely on the numerical solution of the non-dimensional differential equation. The results obtained by the Galerkin finite element code and Comsol were found to be in exact agreement and also exhibit no inconsistencies.

Sensitivity analysis, identification and validation of the dislocation density-based model for metallic materials

Microstructure evolution model based on the differential equation describing evolution of dislocations was proposed. Sensitivity analysis was performed and parameters with the strongest influence on the output of the model were revealed. Identification of the model coefficients was performed for various metallic materials using inverse analysis for experimental data. The model was implemented in the finite element code and simulations of various hot forming processes were performed.

Numerical Assessment of the Performance of Elastic Cloaks for Transient Flexural Waves

A relevant application of transformation elastodynamics has shown that flexural waves in a Kirchhoff-Love plate can be diverted and channeled to cloak a region of the ambient space. To achieve the goal, an orthotropic meta-structural plate should be employed. However, the corresponding mathematical transformation leads to the presence of an unwanted strong compressive prestress, likely beyond the buckling threshold of the structure, with a set of in-plane body forces to warrant equilibrium. In addition, the plate must possess, at the same time, high bending stiffnesses, but a null twisting rigidity. With the aim of estimating the performance of cloaks modelled with approximate parameters, an in-house finite element code, based on a subparametric technique, is implemented to deal with the cloaking of transient waves in orthotropic thin plates. The tool allows us to explore the sensitivity of specific stiffness parameters that may be difficult to match in a real cloak design. In addition, the finite element code is extended to investigate a meta-plate interacting with a Winkler foundation, to confirm how the subgrade modulus should transform in the cloak region.

Modeling solvent dynamics in polymers with solvent-filled cavities

Dynamics of solvent release from polymer gels with small solvent-filled cavities is investigated starting from a thermodynamically consistent and enriched multiphysics stress-diffusion model. Indeed, the modeling also accounts for a new global volumetric constraint which makes the volume of the solvent in the cavity and the cavity volume equal at all times. This induces a characteristic suction effect into the model through a negative pressure acting on the cavity walls. The problem is solved for gel-based spherical microcapsules and microtubules. The implementation of the mathematical model into a finite element code allows to quantitatively describe and compare the dynamics of solvent release from full spheres, hollow spheres, and tubules in terms of a few key quantities such as stress states and amount of released solvent under the same external conditions.

Development and Validation of Overpressure Response Model in Steel Tunnels Subjected to External Explosion

This study employed C4 explosives to evaluate the overpressure response in steel tunnels subjected to external explosions. The explosive scaled distance of the C4 charge from 2.15 to 3.26 m/kg1/3 was evaluated by experiments and the hydrodynamic finite element code LS-DYNA. The numerical results are in agreement with the experimental results. A simple way to estimate the overpressure in steel tunnels was proposed in this paper. The proposed methodology is both useful and efficient and can be further developed for designing protection for military structures and other facilities against explosion.