Theoretical analysis on needle-punched carbon/carbon composites

© 2019, Springer Nature B.V. Needle-punched carbon/carbon composites (NP-C/Cs) are advanced materials widely used in aerospace applications. The needle-punching technique improves the integrality of carbon-fibre plies, however, it also introduces many defects, affecting the mechanical behavior of NP-C/Cs. A theoretical model of irregular beams is suggested to investigate the mechanical behavior of unidirectional needle-punched carbon/carbon composites. Stress distributions in punched and squeezed fibres and an effect of the needle-punching technology are assessed

Hybrid equilibrium finite element formulation for composite beams with partial interaction

Thanks to their various benefits, composite beams have been increasingly used in various applications. This study will focus on two-layer composite beams with a flexible shear interface between layers. The finite element method, in particular its displacement-based formulation, has been recognized as the most popular method for numerical analysis of composite beams. However, when applied to Timoshenko beams with partial interaction, the displacement-based formulation may suffer from the so-called shear-locking and slip-locking phenomena, leading to erroneous solutions. Hybrid and mixed finite element formulations have been viewed as competitive alternatives, since they naturally avoid locking effects. Special types of these formulations are the so-called equilibrium-based formulations, producing statically admissible solutions. This work introduces for the first time an equilibrium-based finite element formulation for the analysis of Timoshenko composite beams with partial interaction. The formulation relies on a variational principle of complementary energy involving only force/moment-like variables as fundamental unknown fields. The approximate field variables are selected such that all equilibrium equations hold in strong form. The inter-element equilibrium is enforced by resorting to the Lagrangian multiplier method. Unlike traditional displacement-based finite element formulations, the proposed scheme is naturally free from both shear- and slip-locking phenomena. The accuracy and effectiveness of the new formulation is numerically assessed through the analysis of several numerical examples. In particular, the ability of the formulation to model accurately both very flexible and very stiff shear connections is numerically shown

Plastic behaviour of microstructural constituents of cortical bone tissue: a nanoindentation study

A mechanical behaviour of bone tissues is defined by mechanical properties of its microstructural constituents. Also, those properties are important as an input for finiteelement models of cortical bone to simulate its deformation and fracture behaviours at the microstructural level. The aim of this study was to investigate a post-yield behaviour of osteonal cortical bone’s microstructural constituents at different loading rates, maximum load levels and dwell times; nanoindentation with a spherical-diamond-tip indenter was employed to determine it. The nanoindentation results revealed significant difference in stiffness values of cortical bone’s microstructural features − interstitial matrix and osteons. Similarly, interstitial matrix exhibited a stiffer post-yield behaviour compared to that of osteons that reflects the relationship between the post-yield behaviour and collagen maturity. In addition, both osteons and interstitial matrix demonstrated a time-dependent behaviour. However, in order to assess elastic-plastic behaviour accurately, an effect of viscosity on nanoindentation results was reduced by using a time-delay method

Finite element analysis of hypervelocity impact behaviour of CFRP-Al/HC sandwich panel

The mechanical response of CFRP-Al/HC (carbon fibre-reinforced/epoxy composite face sheets with Al honeycomb core) sandwich panels to hyper-velocity impact (up to 1 km/s) is studied using a finite-element model developed in ABAQUS/Explicit. The intraply damage of CFRP face sheets is analysed by mean of a user-defined material model (VUMAT) employing a combination of Hashin and Puck criteria, delamination modelled using cohesive-zone elements. The damaged Al/HC core is assessed on the basis of a Johnson Cook dynamic failure model while its hydrodynamic response is captured using the Mie-Gruneisen equation of state. The results obtained with the developed finite-element model showed a reasonable correlation to experimental damage patterns. The surface peeling of both face sheets was evident, with a significant delamination around the impact location accompanied by crushing HC core

Numerical modelling of impact fracture of cortical bone tissue using X-FEM

A cortical bone tissue is susceptible to fracture that can be caused by events, such as traumatic falls, sports injuries and traffic accidents. A proper treatment of bones and prevention of their fracture can be supported by in-depth understanding of deformation and fracture behaviour of this tissue in such dynamic events. Parameters such as damage initiation under impact, damage progression and impact strength can help to achieve this goal. In this paper, Extended Finite-Element Method (X-FEM) implemented into the commercial finite-element software Abaqus is used to simulate the actual crack initiation and growth in a cantilever beam of cortical bone exposed to quasi-static and impact loading using the Izod loading scheme. Izod tests were performed on notched bone specimens of bovine femur to measure its impact strength and to validate simulations. The simulation results show a good agreement with the experimental data

Dynamic properties of cortical bone tissue: impact tests and numerical study

Bone is the principal structural component of a skeleton: it assists the load-bearing framework of a living body. Structural integrity of this component is important; understanding of its mechanical behaviour up to failure is necessary for prevention and diagnostic of trauma. Bone fractures occur in both low-energy trauma, such as falls and sports injury, and high-energy trauma, such as car crash and cycling accidents. By developing adequate numerical models to predict and describe the deformation and fracture behaviour up to fracture of a cortical bone tissue, a detailed study of reasons for, and ways to prevent or treatment methods of, bone fracture could be implemented. This study deals with both experimental analysis and numerical simulations of this tissue and its response to impact dynamic loading. Two areas are covered: Izod tests for quantifying a bone’s behaviour under impact loading, and a 3D finite-element model simulating these tests. In the first part, properties of cortical bone tissue were investigated under impact loading condition. In the second part, a 3D numerical model for the Izod test was developed using the Abaqus/Explicit finite-element software. Bone has time-dependent properties – viscoelastic – that were assigned to the specimen to simulate the short term event, impact. The developed numerical model was capable of capturing the behaviour of the hammer-specimen interaction correctly. A good agreement between the experimental and numerical data was found

Finite element simulations of ultrasonically assisted turning

Finite element simulations of ultrasonically assisted turnin

Dynamic bending behaviour of woven composites for sports products: experiments and damage analysis

© 2015 Elsevier Ltd. Carbon fabric-reinforced polymer (CFRP) laminates employed in sports products are usually subjected to large-deflection quasi-static and dynamic bending deformations during service. Such loading conditions induce damage within the material affecting its strength, stiffness and energy-absorbing capability. To study this, mechanical behaviour of woven CFRP composites in on- and off-axis orientations is first quantified by carrying out large-deflection quasi-static bending tests followed by dynamic ones employing an Izod type impact tester. CFRP laminates of various orientations were tested at loads increasing up to failure to determine their energy-absorbing capability. On-axis laminates demonstrated better strength and stiffness whereas off-axis laminates exhibited good energy-absorbing capability. However, for applications demanding strength, stiffness and energy absorption as in sports products, a combination of both types of plies, as in a quasi-isotropic layup, is an optimum choice. Micro-computed tomography (micro-CT) analysis of the tested specimens showed that matrix cracking, delamination and tow debonding were the dominant damage modes at the specimen's impact location, whereas fabric fracture occurred at the bending location. Further, a catastrophic brittle fracture was observed in the on-axis laminates whereas the off-axis laminates exhibited pseudo-ductile behaviour thanks to matrix cracking and fibre trellising before their failure at higher energies

Damage response of steel plate to underwater explosion: Effect of shaped charge liner

© 2017 Elsevier LtdA shape of charge liners has a great effect on formation of a metal jet and its penetration into a target. In this paper, three different shapes of a charge liner, namely, conical, hemispherical and spherical-segment, are chosen to investigate their effect on damage response of a plate to underwater explosion. A Smooth Particle Hydrodynamic (SPH) method based on mesh-free Lagrange formulation is applied to simulate an entire process of a shaped-charge detonation, formation of a metal jet as well as penetration on a steel plate. Initially, a SPH model of the shaped charge with a spherical-segment liner is developed, and its results are compared with experimental data to verify the effectiveness of this method. Then, numerical simulations of shaped charges with different liners are performed to study the damage characteristics of a steel plate subjected to underwater-explosion shock loading and the metal jet. It was found that for the shock wave the peak value of the radial pressure is larger than that of the axial pressure during the detonation process; the level of pressure in the spherical-segment case was higher than that of the other two cases. After the detonation, the metal jet was gradually produced under the effect of the detonation wave. Three types of the metal jet - a shaped charge jet (SCJ), a jetting projectile charge (JPC) and an explosive formed projectile (EFP) – were formed corresponding to three cases with conical, hemispherical and spherical-segment liners. The obtained results show that the velocity and length of the SCJ in the conical case are greater than that of the other cases, and it therefore may lead to a larger penetration depth. In addition, the EFP has a better motion stability for a velocity difference in the spherical case is lower than that of the other two cases. Subsequently, the shock wave arrives at the plate earlier than the metal jet, which will cause deformation of the plate. Due to higher pressure, the shock wave in the spherical-segment case has a stronger damaging effect on the plate than that in the other two cases. Finally, the metal jet reaches the plate causing a hole. Because of a wider jet head, the EFP results in a more serious damage to the plate. The suggested analysis and its results provide a reference for structural design of shaped charge warheads

Indentation study of mechanical behaviour of Zr-Cu-based metallic glass

It has been well known that plastic deformation of bulk metallic glasses (BMGs) is localised in thin shear bands. So, initiation of shear bands and related deformation should be studied for comprehensive understanding of deformation mechanisms of BMGs. In this paper, indentation techniques are extensively used to characterise elastic deformation of Zr-Cu-based metallic glass, followed by a systematic analysis of initiation and evolution of shear bands in the indented materials. Our results, obtained with a suggested wedge-indentation technique, demonstrated initiation of shear bands in materials volume