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This paper aims to conduct a combined Eulerian/Lagrangian fluid/solid transient non‐linear dynamics computational analysis of the interaction between a single planar blast wave and a human head in order to assess the extent of intra‐cranial shock wave generation and its potential for causing traumatic brain injury.

Two levels of blast peak overpressure were selected, one corresponding to the unprotected lung‐injury threshold while the other associated with a 50 percent probability for lung injury caused death. Collision of the head with a stationary/rigid barrier (at an initial collision velocity of 5 m/s) was also analyzed computationally, since blunt‐object impact conditions may lead to mild traumatic brain injury (mTBI), i.e. concussion.

A comparison between the two blast and the single blunt‐object impact cases with the corresponding head‐to‐head‐collision results showed that, while the von Mises stress‐based head‐to‐head collision mTBI thresholds are not exceeded under blast‐loading conditions investigated, the high blast‐induced peak‐pressure levels within the intra‐cranial cavity may lead to mTBI.

While concussion is not generally considered as life altering/threatening, the associated temporary loss of situational awareness or consciousness may have devastating consequences in the case of common military tactical and battle‐field scenarios. This suggests that the head‐protection gear (primarily, the helmet) which are currently designed to withstand blunt‐object and ballistic impacts, should be redesigned in order to obtain the necessary level of head protection with respect to blast impact.

The paper provides a comprehensive computational investigation of impact on a human skull/brain assembly.

The purpose of this paper is to study mutual interaction between von Mises equivalent and hydrostatic stresses at the crack tip area of an elastoplastic material in order to obtain critical conditions for crack propagation under fatigue loading.

A5083-H111 aluminum alloy is used to obtain a Chaboche-type constitutive equation, which is introduced in a commercial finite elements package to evaluate stress distribution at crack tip area. A simplified three-dimensional (generalized plane strain) grid is used, resulting in fast and accurate results. Numerical simulations are performed to connect crack propagation rate with various combinations of fatigue stress amplitude, initial crack length and number of loading cycles. Distance between characteristic points of stresses distribution in the crack tip area are compared to experimental fatigue crack growth rates in order to assess the validity of the present approach.

It is found that saturation of plastic strains, i.e. maximization of von Mises equivalent stress, is a prerequisite for hydrostatic stress to take a critical-maximum value, outside the plastically saturated zone. At the point of maximum hydrostatic stress brittle fracture is initiated, driving to separation of the ligament up to crack tip, without formation of new plastic strains. The length of this ligament is defined as crack propagation step, showing good agreement with experimental data.

The present approach seems to constitute a reasonable and adequate method for the description of fatigue crack propagation in terms of continuum mechanics, not necessitating microscopic considerations or empirical criteria lacking theoretical or physical basis. In addition, it liberates from the notion of stress intensity factors, strongly disputed beyond linear elasticity. Improved constitutive equations and numerical models are expected to drive in a complete fatigue failure criterion similar to those of static loading.

A simulation framework that includes a finite element analysis (FEA) and computational fluid dynamics (CFD) model is generated to study the effect of unstable two-phase flow-induced vibrations at a vertical 90° pipe bend. The corresponding fluid-structure interaction (FSI) of an unstable flow may pose danger to the piping structure. This paper intends to discuss this interaction.

Four cases of flows under the slug flow and churn flow regimes were investigated. The flow regimes vary in superficial gas velocities with velocities from 0.978 m/s to 9.04 m/s, while the superficial liquid velocity is kept constant at 0.61 m/s. The pipe model consists of an internal diameter of 0.0525 m, a bend radius of 0.0762 m, and a stainless-steel pipe structure.

Results show that the average unstable void fractions increase with the superficial gas velocities, but the peak frequencies were constant at 13 Hz for three of the cases. The total displacement and von Mises stress increase with a declining rate in each subsequent case, while the RMS of von Mises stress begins to stall at superficial gas velocities between 5 m/s and 9.04 m/s. The peak frequencies of von Mises stress decrease in each subsequent case.

The proposed model can be used to investigate the FSI effect of unstable void fractions at pipe bends and could assist in the development of piping systems in which the use of piping elements arranged close together are unavoidable.

The present paper aims to explore a computational homogenisation procedure to investigate the full geometric representation of yield surfaces for isotropic porous ductile media. The effects of cell morphology and imposed boundary conditions are assessed. The sensitivity of the yield surfaces to the Lode angle is also investigated in detail.

The microscale of the material is modelled by the concept of Representative Volume Element (RVE) or unit cell, which is numerically simulated through three-dimensional finite element analyses. Numerous loading conditions are considered to create complete yield surfaces encompassing high, intermediate and low triaxialities. The influence of cell morphology on the yield surfaces is assessed considering a spherical cell with spherical void and a cubic RVE with spherical void, both under uniform strain boundary condition. The use of spherical cell is interesting as preferential directions in the effective behaviour are avoided. The periodic boundary condition, which favours strain localization, is imposed on the cubic RVE to compare the results. Small strains are assumed and the cell matrix is considered as a perfect elasto-plastic material following the von Mises yield criterion.

Different morphologies for the cell imply in different yield conditions for the same load situations. The yield surfaces in correspondence to periodic boundary condition show significant differences compared to those obtained by imposing uniform strain boundary condition. The stress Lode angle has a strong influence on the geometry of the yield surfaces considering low and intermediate triaxialities.

The exhaustive computational study of the effects of cell morphologies and imposed boundary conditions fills a gap in the full representation of the flow surfaces. The homogenisation-based strategy allows us to further investigate the influence of the Lode angle on the yield surfaces.

To provide an approach to fleXBGA design and reliability analysis.

A two‐dimensional (2D) plane strain finite element analysis model is established to simulate the thermo‐mechanical behaviour of fleXBGAs which are subjected to thermo‐cyclic loading under different temperature cycling conditions. The model has been used to consider the effects of printed circuit board (PCB) thickness, die size, package size, ball count, pitch and substrate configuration. The Anand constitutive model is adopted to simulate creep and plastic deformation of the solder joints. A fatigue life prediction model based on plastic shear strain range is then applied to predict the fatigue life of different kinds of fleXBGA.

Comparison of fatigue life predictions and experiments show that the maximum prediction errors are mostly within ±50 per cent, and it can be concluded that a smaller die size, a thinner PCB, a smaller solder ball diameter, more balls, a smaller temperature range and a faster ramp rate are all helpful in improving the package fatigue life.

Not all properties of the packaging materials are available for design and reliability analysis. Advanced research should be focused on determining the mechanical properties of the packaging materials to improve the analysis accuracy.

Design optimisation was used to determine the effect of structural parameters for the fleXBGA assembly on the von Mises equivalent stresses in the solder joints, which is one of the most critical factors for package reliability. The calculation results indicate that the equivalent stress in solder joints can be decreased about 19.7 per cent comparing with the initial structure and the fatigue life can be greatly enhanced.

The suggested approach is very useful for fleXBGA assembly design. The reliability of the package can be greatly improved by using the modified geometric parameters.

It has been observed from the history of failed dies used in local extrusion industry that after certain press cycles, severe die damage occurs by using more number of in‐house recycled billets. The purpose of this paper is to focus on the effect of billet quality on the extrusion die service life, based on using microstructural and finite element analyses.

Numerical solution of stress distribution in extrusion die using microstructural and finite element analyses.

Simulation results demonstrate that extrusion die experiences high stresses and strains at critical locations by running secondary billets. Billet deformation behavior also shows that secondary billet has more resistance to flow during extrusion cycle, which results in such high stresses and strains in the die.

The study includes a particular die used to extrude the aluminum alloy billets. It may need to generalized including materials other than aluminum alloy.

The findings are original and believed to be useful for engineers working in the extrusion dies. Since it is shown that secondary billets (recycled billets) have more resistance to flow in the dye, a care should be taken when estimating the die life for the practical applications.

It is an original work. It deals with the comparison of new and recycled billets's performance in terms of stress formation in the die during the extrusion cycle.

The purpose of this research is to establish a robust numerical framework for the calibration of macroscopic constitutive parameters, based on the analysis of polycrystalline RVEs with computational homogenisation.

This framework is composed of four building-blocks: (1) the multi-scale model, consisting of polycrystalline RVEs, where the grains are modelled with anisotropic crystal plasticity, and computational homogenisation to link the scales, (2) a set of loading cases to generate the reference responses, (3) the von Mises elasto-plastic model to be calibrated, and (4) the optimisation algorithms to solve the inverse identification problem. Several optimisation algorithms are assessed through a reference identification problem. Thereafter, different calibration strategies are tested. The accuracy of the calibrated models is evaluated by comparing their results against an FE2 model and experimental data.

In the initial tests, the LIPO optimiser performs the best. Good results accuracy is obtained with the calibrated constitutive models. The computing time needed by the FE2 simulations is 5 orders of magnitude larger, compared to the standard macroscopic simulations, demonstrating how this framework is suitable to obtain efficient micro-mechanics-informed constitutive models.

This contribution proposes a numerical framework, based on FE2 and macro-scale single element simulations, where the calibration of constitutive laws is informed by multi-scale analysis. The most efficient combination of optimisation algorithm and definition of the objective function is studied, and the robustness of the proposed approach is demonstrated by validation with both numerical and experimental data.

An analysis model has been developed for the elasto‐viscoplastic analysis of continuous fibre‐reinforced composite structures. Elastic deformation of fibre and elasto‐viscoplastic deformation of matrix are considered in the analysis model because the yield strength of matrix is, in general, substantially lower than that of fibre. A finite element formulation is derived for the proposed analysis model. If matrix is assumed homogeneous and isotropic, the von Mises yield criterion is used for viscoplastic yielding. As numerical examples, a parametric study has been performed for elasto‐viscoplastic analysis of unidirectional composite plates subjected to inplane loads.

This study’s investigation aims to clarify the effect of an additional geometry, i.e. a fillet radius, to the blades of a single-stage transonic axial compressor, NASA Stage 37, on its aerodynamic and structural performances.

Applying the commercial simulation software and the one-way fluid–structure interaction (FSI) approach, this study first evaluated the simulation results with the experimental data for the aerodynamic performances. Second, this paper compared the structural performances between the models with and without fillets.

This research analyses the aerodynamic results (i.e. total pressure ratio, adiabatic efficiency, stall margin) and the structural outcomes (i.e. equivalent von Mises stress, total deformation) of the single-stage transonic axial compressor NASA Stage 37.

This paper mentions the influence of blade fillets (i.e. both rotor hub fillet and stator shroud fillet) on the compressor performances (i.e. the aerodynamic and structural performances).

This paper aims to describe a shape optimization for hyperelastic axisymmetric structure with an exact sensitivity method.

The whole shape optimization process is carried out by integrating a closed geometric shape in the real space R2 with boundaries defined by B-splines curves. An exact sensitivity analysis and a mathematical programming method (SQP: Sequential Quadratic Programming) are implemented. The design variables are the control points' coordinates which minimize the Von-Mises criteria, with a constraint that the total material volume of the structure remains constant. The feasibility of the proposed methods is carried out by two numerical examples. Results show that the exact Jacobian has an important computing time reduction.

Numerical examples are presented to illustrate its performance.

In this work, the sensitivity performance is computed using two numerical methods: the efficient finite difference scheme and the exact Jacobian.