Ali Mkaddem

Multiscale approach including microfibril scale to assess elastic constants of cortical bone based on neural network computation and homogenization method

The complexity and heterogeneity of bone tissue require a multiscale modeling to understand its mechanical behavior and its remodeling mechanisms. In this paper, a novel multiscale hierarchical approach including microfibril scale based on hybrid neural network (NN) computation and homogenization equations was developed to link nanoscopic and macroscopic scales to estimate the elastic properties of human cortical bone. The multiscale model is divided into three main phases: (i) in step 0, the elastic constants of collagen-water and mineral-water composites are calculated by averaging the upper and lower Hill bounds; (ii) in step 1, the elastic properties of the collagen microfibril are computed using a trained NN simulation. Finite element calculation is performed at nanoscopic levels to provide a database to train an in-house NN program; and (iii) in steps 2-10 from fibril to continuum cortical bone tissue, homogenization equations are used to perform the computation at the higher scales. The NN outputs (elastic properties of the microfibril) are used as inputs for the homogenization computation to determine the properties of mineralized collagen fibril. The mechanical and geometrical properties of bone constituents (mineral, collagen, and cross-links) as well as the porosity were taken in consideration. This paper aims to predict analytically the effective elastic constants of cortical bone by modeling its elastic response at these different scales, ranging from the nanostructural to mesostructural levels. Our findings of the lowest scales output were well integrated with the other higher levels and serve as inputs for the next higher scale modeling. Good agreement was obtained between our predicted results and literature data.

Application of response surface method for FEM bending analysis

The bending of metal parts is subjected to a variety of process parameters. In this paper, a numerical investigation into the bending process was carried out. The aim was to study the effects of the interaction between the clearance and the die corner radius on the evolution of the bending force, the maximum damage within the part, the springback and the Mises stress. Designed experiments are an efficient and cost-effective way to model and analyse the relationships that describe process variations. The numerical simulation of the damage evolution has been modelled by means of continuum damage approach. The Lemaitre damage model, taking into account the influence of triaxiality, has been implemented into ABAQUS/Standard code, in order to predict the risk to external fibres during the process and the changes in material characteristics after bending. The results of the proposed investigation show the strong dependence between the inputs and the responses.

A pure thermal model to evaluate heat-affected zone when milling E-glass fiber-reinforced polyester composites

This paper aims at investigating the resistance-to-vitrification of glass fiber-reinforced plastics when milling. A three-dimensional thermal model using volumetric heat source with Gaussian distributed cylindrical flux was developed as DFLUX subroutine and implemented into Abaqus/Standard code. The wheel feed was simulated by the source motion at 250 mm min−1 with spindle speeds of 11,460, 15,280, and 19,100 rpm. Milling tests using abrasive wheel with 10 mm in diameter were conducted on the composite specimens of dimensions 100 × 25 × 4 mm3 with fibers oriented both parallel and perpendicular to the milling direction. Four equidistant thermocouples were embedded within the medium plane of the specimen in order to measure the temperature histories. Each series of tests was repeated four times under identical conditions. Predictions confronted to measurements demonstrated the validity of the proposed model. Cutting perpendicular to fibers was found favoring in-depth heat dissipation. However, the fibers a...

Extension of the Slip Band Area under Magnetization during Steel Machining

This work discusses the machinability of AISI–1045 steel in a magnetically assisted environment. Physically, magnetization causes suppression of Bloch walls in ferromagnetics, which enhances the dislocation paths within the Weiss domains of the matrix material. From a material point of view, the changes were manifested through an enhancement in steel plasticity, resulting in (i) a widened slip band area within the primary shear zone (PSZ) and (ii) improved plastic flow at tool-steel interfaces along the secondary shear zone (SSZ). From a mechanical point of view, the modifications can be summarized as a neat drop of the thrust force component due to the magnetic action generated by the external source, i.e., the current coil. The changes observed in the local diagram of forces cause alterations in the tribological properties at the tool-material interfaces. These alterations act to accelerate formation of the chip and lead to save energy because of the decrease in the cutting period, which should significantly improve the operating lifetime of the tool.

Optimisation of Springback Predicted by Experimental and Numerical Approach by Using Response Surface Methodology

Bending has significant importance in the sheet metal product industry. Moreover, the springback of sheet metal should be taken into consideration in order to produce bent sheet metal parts within acceptable tolerance limits and to solve geometrical variation for the control of manufacturing process. Nowadays, the importance of this problem increases because of the use of sheet-metal parts with high mechanical characteristics (High Strength Low Alloy steel). This work describes robust methods of predicting springback of parts in 3D modelling subjected to bending and unbending deformations. Also the effects of tool geometry in the final shape after springback are discussed. The first part of this paper presents the laboratory experiments in wiping die bending, in which the influence of process variables, such as die shoulder radius, punch-die clearance, punch nose radius and materials properties were discussed. The second part summarises the finite element analysis by using ABAQUS software and compares these results with some experimental data. It appeared that the final results of the FEM simulation are in good agreement with the experimental ones. An optimisation methodology based on the use of experimental design method and response surface technique is proposed in the third part of this paper. That makes it possible to obtain the optimum values of clearance between the punch and the die and the optimum die radius which can reduce the springback without cracking and damage of product.

Modeling of Viscoelastic Behavior of Flexible Polyurethane Foams Under Quasi-Static and Cyclic Regimes

This paper discusses the reliability of two approaches in modeling the Flexible Polyurethane Foam (FPF) behavior. FPFs are cellular polymers characterized by highly complex mechanical behavior including nonlinearity, viscoelasticity, hysteresis, and residual deformations. The review of this topic reveals that several studies have developed models based either on hereditary or on fractional derivation formulations. However, the viscoelastic behavior of the material integrates both short and long memory effects, which needs the combination of the two mathematical approaches to cover the full behavior of such a material. This work compares the two methodologies in identifying the parameters of foam behavior using the combined model. The approaches are based on experimental observations of the FPF behavior on compression (short memory effects) and cyclic (long memory effects) loadings. The relative inefficiency of the force difference method widely addressed in modeling processes was specially discussed.

Sensitivity of GFRP Composite Integrity to Machining-Induced Heat: A Numerical Approach

This paper aims at investigating the temperature effects during abrasive milling of glass fiber reinforced plastic composites (GFRP). A 3D thermal model using volumetric heat source with Gaussian distributed cylindrical flux was developed as DFLUX subroutine and implemented into Abaqus/Standard code. The model employs linear power law for simulating the temperature variation during tool advance. The composite plate is made of glass fibers oriented perpendicular to the tool trajectory. The tool feed was simulated by the source constant motion while speed was taken variable. Four equidistant thermocouples were simulated within the medium plan of the specimen in order to record the temperature evolution. The predictions highlighted the sensitivity of temperature histories to cutting speed. The conductivity and heat capacity played for controlling heating and cooling phases of the curves. The peak temperature exhibited maximum value at TC3 irrespective to speed value. The pure thermal analysis showed sufficient ability to predict the heat affected zone in the GFRP, which is, in turn, a function of tool spindle speed.

On the Elementary Wear Mechanisms of UD-GFRP Composites Using Single Indenter Scratch Test

This paper deals with the investigation of friction and wear mechanisms involved when scratching parallel to fiber orientation of unidirectional glass fiber reinforced polymers (UD-GFRP) composite. A single indenter scratch test (SST) was performed at room temperature and constant sliding speed, using high speed steel conical indenter. The dominant damage modes owing to SST were inspected at different attack angle and load using scanning electron microscope (SEM). The apparent friction and the damage modes were investigated as function of the test parameters, particularly, the attack angle and the normal load. The experimental findings reveal that the attack angle has a most important role in controlling apparent friction if compared with applied normal load. However the wear mechanisms were more sensitive to both attack angle and normal load. The correlation between wear modes and tribological parameters was emphasized and the scratch map was parallel to fiber orientation built. Six domains were identified and the different wear mechanism transitions were detailed.

Friction Model for an Intermediate Orientation and Density of Fibres in Dry Cutting of Composites

This paper discusses a numerical analysis of polymer-matrix composites cutting. Focus is put on the sensitivity of friction to both the fibre orientation and fibre volume fraction. Firstly, a theoretical model based on decomposition technique was proposed for predicting the evolution of friction coefficient with the parameters considered. Secondly, the numerical model was built, for orthogonal cutting configuration and equivalent homogeneous material assumption, using Abaqus/Explit FE code. For enhancing the simulation of chip formation, adaptive mesh technique with kill element option was used in the dynamic explicit analysis. The model assumes plane stress state and orthotropic behaviour. Hashin damage model was considered for simulating the damage initiation mechanisms and material failure modes. The results showed an increase of both the thrust and cutting force with fibre volume fraction. The predictions confirmed the high dependency of chip formation on reinforcement percentage. The advantage of adaptive mesh on predicting the damage localization was further proved.Copyright