A constitutive equation for the behaviour of a mountaineering rope under stretching during a climber's fall

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microstructural numerical modeling of al2o3 ti composite

Abstract The present work focuses on the study of a numerical model of a ceramic/metal particle reinforced composite material that has the potential to be used in challenging engineering applications. The composite has been developed combining the specific properties of ceramic and metal in order to improve the overall mechanical characteristic compared to the characteristics of the individual materials only. In particular, the purpose of the composite is to improve the fracture toughness of the single ceramic in order to use it as protection against impact. Finite element modeling and analysis of a microstructure-based model have been used to analyze the mechanical behaviour of the particle reinforced composite in a virtual tensile test. The microstructure-based model has been created from scanning electron microscopy (S.E.M.) images identifying the areas and the edges of the two components present in the composite. The microstructure-based approach has been chosen for calculating the elastic properties starting from the material behaviour at the grain level in the ceramic and metal particles. The properties of the different individual particles have been used separately as the input to define the global mechanical properties of the composite. The aim of this work is to create and validate the microstructure-based model by replicating the results available from experimental data for the elastic properties of the composite. Furthermore, the numerical results have been compared with analytical models for particle reinforced composites to have a wider knowledge of the capability of the model created

a comparison of state based peridynamics and solid mesh to sph conversion techniques to reproduce fragmentation of a ceramic tile subject to ballistic impact

Abstract This paper presents a comparison of two present meshfree approaches for modelling brittle material in case of ballistic impact, where extensive cracking and fragmentation is present. These phenomena are very unfeasible to simulate with a standard Lagrangian technique thus alternative methods have been considered in the last years. A comparison between two methods is the main aim of the present article. Smoothed Particle Hydrodynamics (SPH) is an almost consolidated method that exploit the description of a continuum by means of discrete elements whose properties are "smoothed" by a Kernel Function. In this paper a procedure that exploits the transition from finite elements (FE) to SPH particles, following the onset of an erosion criterion is used. This approach and its results are then compared to the recent state-based Peridynamics. Peridynamics method is based on integral equation and allow a direct application to discontinuities and fractures. The results from both methods are critically compared with experimental data and show that the damage morphology is reproduced similarly by both approaches; however less computation efforts are required when peridynamics are used

Effect of cold driving process on fatigue life of helicopter fuselage joints

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the effect of mesh morphologies on the mesoscale finite element modelling of woven composites

Abstract Mesoscale Finite Element (FE) modelling methods of woven and braided composites have attracted great attention in recent years as they can provide high accuracy, especially in describing damage behaviour. One of the key factors that affects the results of such kind of simulations is the choice of the mesh morphology. The two most widely-applied meshing approaches at present are the voxel- and the volume-mesh; however, these two models have not been compared in detail with experimental data. Therefore, in the present work, both volume- and voxel-mesh models have been used to build a composite Representative Volume Element (RVE) made of glass-fibre woven fibre with Epoxy Ampreg 26. These FE models have been built in order to investigate the effects of the mesh morphology on the simulations under quasi-static tensile and shear loading conditions. The volume-mesh model provides a well correlated stress-strain relationship in comparison with the test results, while the voxel-mesh model predicts higher tension and shear properties. However, computational issues, such as negative volume and the stress concentration caused by the mesh, are observed in the volume-mesh model while the voxel-mesh is computationally more efficient, i.e. less time-consuming, in replicating the tension and shear tests with acceptable results

Numerical Simulation of High‐Velocity Impact on Fiber‐Reinforced Composites using MAT_162

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an enhanced material model for the simulation of high velocity impact on fiber reinforced composites

Abstract Composite MSC (MAT_161 and MAT_162) is an enhanced material model for fiber-reinforced composites implemented in the software LS-DYNA which considers different failure modes in tension, compression and shear, with a progressive failure model. It allows to model delamination without the necessity of physical interface between the layers. Furthermore, it considers the effect of strain rate on the strength and moduli properties of the materials by means of a logarithmic function. Several studies can be found in the literature where the material model Composite MSC is implemented for modeling glass fiber-reinforced composites while it is difficult to find studies related to aramid fiber-reinforced composites. Aramid fibers are used in the manufacturing of ballistic shields since they are characterized by high tensile strength and resistance to impact damage. In this study the predictive accuracy of the material model Composite MSC (in particular MAT_162) for aramid fiber-reinforced composites is assessed simulating the high-velocity impact of a .357 Magnum projectile considering different impact velocities and therefore different scenarios from the arrest of the projectile to the full penetration of the target. MAT_162 is compared with MAT_058 which is a simpler material model which needs less input materials parameters and is therefore easier to be implemented. Furthermore, a parametric study on input parameters which are considered to be relevant is performed

Numerical simulations of normal and oblique impact on single and double-layered aluminium Al6061-T6 plates

Studies of ballistic penetration into metal plates and their numerical simulation currently present an important topic in ballistics, however, no congruent results have been presented so far, especially when it comes to impacts on multi-layered plates. Presently, as far as ballistic limits are concerned, the choice between layered and monolithic structures is not completely straightforward and unproblematic. The effect of introducing air gaps between metallic layers is not fully understood and explained either. Furthermore, these issues are more investigated for normal impacts than for oblique impacts for which only limited results are available. Therefore, the aim of this paper is to conduct a numerical analysis in order to evaluate the effect on the ballistic limit on layered targets for both normal and oblique impacts. A validated numerical methodology will be used, though validated with a limited number of experiments. The target material is an Al6061-T6 aluminium alloy the mechanical behaviour of which (hardening, strain rate, failure, etc.) is already known and described. Several configurations will be numerically tested and the results critically evaluated

Numerical simulations of an explosion confined inside a cylindrical pipe made of aluminium alloy Al6061-T6

Simulation of the behaviour of structural components subjected to high explosive detonation is one of the current challenges in the field of numerical simulation. Along with experimental tests, numerical analysis is necessary to give an in-depth insight of this event, as well to reduce costs for some further experimental tests. High values of strain rate, temperature and pressure, together with failure phenomenon, govern the complex interaction between the explosion and the structure involved. In a scenario of this type, capabilities and performance of the numerical software used are crucial to the quality and the outcome of the simulation. Besides the simulation itself, this paper provides a comparison between different finite element programs such as ABAQUS, AUTODYN and LS-DYNA in an explosion event. In the event descibed in the paper, the behaviour of tube made of aluminium alloy Al6061-T6 and filled with explosive material is under investigation. A fully coupled Eulerian and Lagrangian formulation is used together with a complete mechanical behaviour and constitutive equations of all the materials involved in the simulation (aluminium alloy Al6061-T6, explosive C4, air). Finally, results and comparison between the mentioned numerical solvers will be reported and critically discussed

Four-point bending test on a middle strength rock: Numerical and experimental investigations

Developing a reliable numerical modelling technique is considered as challenge for fracture assessment of the geological materials, which are much subjected to hydrostatic pressure. For this purpose, the mechanical behaviour and the fracture pattern of a middle strength rock material, called Pietra Serena sandstone, is investigated both numerically and experimentally under a Four-Point Bending (also called Flexural) testing program. For the numerical approach, an innovative method, namely FEM-coupled to-SPH, is exploited due to its capabilities in dealing with rock mechanics related issues. Two different material models, which are the Karagozian and Case Concrete (KCC) and the Extended (Linear) Drucker-Prager, are exerted to assess their capabilities. The Flexural strength and the crack initiation area are studied based on the state of the stress in various parts of the specimen in both models, and finally the results obtained from the numerical models are compared with the data obtained from the experimental tests in order to assess the capability of the modelling approach