Recep Ekici

Effects of Random Particle Dispersion and Particle Volume Fraction on the Indentation Behavior of SiC Particle-Reinforced Metal-Matrix Composites

The present composite structure models assume that reinforcement particles are located in a repeated arrayed order through metal matrix. This study investigates the effect of both random particle distribution and particle volume fraction on the indentation behavior of Al 1080/SiC particle reinforced metal—matrix composites under a spherical indenter. The ceramic particles were distributed randomly in a certain particle volume fraction through aluminum matrix in order to achieve a similar structure to a real particulate composite structure as possible. The particle volume fraction strongly affects permanent indentation surface profiles and indentation depths. The indentation profile becomes smoother, and the peak indentation depth increases as the particle volume fraction decreases. The random particle distribution has a small effect on the peak indentation depth but affects strongly the permanent indentation profiles as well as the residual stress and strain fields in the indentation region. A small increase appears in the local particle concentration in the indentation region and is affected considerably by the random particle distribution. The hardness tests as well as the scanning electron microscopy micrographs of the indentation regions of specimens with different particle volume fractions are in good agreement with theoretical analysis.

Free vibration analysis of an adhesively bonded functionally graded double containment cantilever joint

In this study, Genetic Algorithms (GAs) combined with the proposed neural networks were implemented to the free vibration analysis of an adhesively bonded double containment cantilever joint with a functionally graded plate. The proposed neural networks were trained and tested based on a limited number of data including the natural frequencies and modal strain energies calculated using the finite element method. GA evaluates a value generated iteratively by an objective function and this value is calculated by the finite element method. The iteration process restricts us apparently to use directly the finite element method in our multi-objective optimisation problem in which the natural frequency is maximised and the corresponding modal strain energy is minimised. The proposed neural networks were used accurately to predict the natural frequencies and modal strain energies instead of calculating directly them by using the finite element method. Consequently, the computation time and efforts were reduced considerably. The adhesive joint was observed to tend vertical bending modes and torsional modes. Therefore, the multi-objective optimisation problem was limited to only the first mode which appeared as a bending mode. The effects of the geometrical dimensions and the material composition variation through the plate thickness were investigated. As the material composition of the horizontal plate becomes ceramic rich, both natural frequency and modal strain energy of the adhesive joint increased regularly. The plate length and plate thickness were more effective geometrical design parameters whereas the support length and thickness were less effective. However, the adhesive thickness had a small effect on the optimal design of the adhesive joint as far as the natural frequencies and modal strain energies are concerned. The distributions of optimal solutions were also presented for the adhesive joints with fundamental joint lengths and material compositions in reference to their natural frequencies and corresponding modal strain energies.

Elastic Stresses in an Adhesively Bonded Functionally Graded Double Containment Cantilever Joint in Tension

This study investigates the three-dimensional stress state of an adhesively bonded double containment cantilever joint in tension. The plate is composed of a functionally graded region between ceramic (Al2O3) top layer and metal (Ni) bottom layer. The mechanical properties of the graded region were defined based on a power law distribution and modeled with a layered three-dimensional finite element. Stress concentrations occur inside the adhesive fillets along the free edges of the adhesive layer and through the corresponding plate and support regions. The peak adhesive stresses are observed at the free edge of the containment—adhesive interface. The von Mises stress through the graded plate thickness increases uniformly from the metal layer to the ceramic layer. The stress profiles peak around the adhesive free edges. The stress levels change suddenly near the ceramic layer in the metal-rich graded plate whereas the through-the-thickness stress profiles become uniform in the ceramic-rich graded plate. The layer number has a small effect on the through-the-thickness adhesive and plate stress profiles but on the peak stress levels. This effect becomes negligible after a layer number of 20. The compositional gradient exponent considerably affects both the through-the-thickness plate stress profiles and levels. As the material composition is enriched with the ceramic the stress profiles become uniform. The effects of the geometrical parameters and the compositional gradient exponent on the strain energy of the adhesive joint are investigated using the artificial neural networks. Consequently, the plate thickness and the compositional gradient exponent are the most dominant design parameters affecting the strain energy, and the adhesive thickness, the support length, and thickness are others in sequence. The strain energy increases drastically with increasing plate thickness whereas it decreases with increasing support length and thickness and as the material composition of the graded plate enriches with the ceramic. An optimum joint design requires that the plate thickness and the adhesive thickness be minimal, the support length, and thickness be maximal, and the material composition consist of the constituent with higher modulus as possible.

Free Vibration Analysis and Design of an Adhesively Bonded Corner Joint with Double Support

This study carries out the three dimensional free vibration analysis of an adhesively bonded corner joint and investigates the effect of an additional horizontal support to the adhesive corner joint with single support on the first ten natural frequencies and mode shapes. In the presence of a horizontal support the effects of the vertical support length, the adhesive thickness, the plate thickness, and the joint length on the natural frequencies and modal strain energies of the adhesive joint were also investigated using the back-propagation Artificial Neural Network (ANN) method and the finite element method. The natural frequencies and modal strain energies increased with increasing plate thickness, whereas an adverse effect was observed for increasing joint length. Both horizontal and vertical support lengths exhibited similar effects but the adhesive thickness had a negligible effect. The plate thickness and the joint length are dominant geometrical parameters in comparison with both horizontal and vertical support lengths. The proposed ANN models were combined with the Genetic Algorithm in order to determine the optimal corner joint in which the maximum natural frequency and minimum elastic modal strain energy are achieved for each natural frequency and mode shape of the adhesive corner joint and the optimal dimensions were given versus one geometrical parameter.

Optimal design of an adhesively-bonded corner joint with single support based on the free vibration analysis

This study investigates the three-dimensional free vibration behaviour of an adhesively-bonded corner joint with single support. The modulus of elasticity, Poissons ratio and density of adhesive were found to have negligible effects on the first 10 natural frequencies and mode shapes of the corner joint. The effects of the geometrical parameters, such as support length, plate thickness, adhesive thickness and joint length, on the natural frequencies, mode shapes and modal strain energies of the adhesive joint were also investigated using both the finite element method and the back-propagation artificial neural network (ANN) method. The free vibration and stress analyses were carried out for the corner joints with various random geometrical parameters so that a suitable ANN model could be trained successfully. The support length, plate thickness and joint length all played important roles in the natural frequencies, mode shapes and modal strain energies of the corner joint, whereas the adhesive thickness for the range of adhesive thickness studied had only a minor effect. The Genetic Algorithm was also combined with the present ANN models in order to determine the optimum geometrical dimensions which satisfied the maximum natural frequency and minimum modal strain energy conditions for each natural frequency and mode shape of the adhesively-bonded corner joint.

Low-velocity impact behavior of Al 6061/SiC particulate metal matrix composites

This study addresses the effects of impact velocity (impact energy) and particle volume fraction and particle size on the impact behavior of particle-reinforced metal matrix composites (Al 6061/SiC). Their effects on the contact force and plastic dissipation histories, the residual stress, and plastic strain distributions were also analyzed. The impact velocity and particle volume fraction and particle size were found to have a significant effect. The contact forces and durations increased significantly with increasing impact velocity. The predicted peak contact forces were in minimal errors for lower impact velocities, whereas the predicted impact durations were slightly longer. The composite structures become stiffer when the particle volume fraction is increased. Consequently, the contact force was increased, whereas the impact durations were shortened. However, a larger particle size resulted in lower contact forces, but longer impact durations. Particle reinforced composites can dissipate more kinetic energy in case the particle volume fraction decreases and the particle size increases. Increasing impact velocity and particle volume fraction increased residual stress levels and the plastic strain. Increasing the particle size resulted in the residual stress distributions to become non-uniform but increases in the plastic deformations.

Determination of Structural Damping and Optimal Vibration Control of an Adhesively-Bonded Double Containment Cantilever Joint

In this study, the loss factors of an adhesively-bonded double containment cantilever joint were determined for different plate and support lengths. The response of the adhesive joint subjected to a transverse excitation force was measured with a contactless eddy-current sensor and the first bending natural frequency was determined using the Fast Fourier Transform method. The loss factor was calculated using the half-power bandwidth method based on the power spectrum of the joint vibration. After an excitation force was applied to the joint, the damped free vibration analysis was carried out using the finite element method and its measured loss factor. The transverse vibration attenuation was actively controlled with different numbers of actuators located on the top surface of the plate. The optimal control of the vibration attenuation was achieved based on a performance index by considering the strain energy, the kinetic energy, the work done on the adhesive joint by the actuators as well as the vibration attenuation time. Genetic Algorithm was implemented to this optimization problem in which the optimal control force histories, the optimal locations and the optimal numbers of the actuators were searched. Eight actuators exhibited the best control force history minimizing the performance index to 3.34 × 10–2. Thus, the attenuation time was reduced from 16 s to 0.15 s and the absolute displacement was decreased from 13.1 mm to 17.15 × 10–3 mm for 0.15 s. In addition, the modal strain energy and kinetic energy were found to be at lowest levels. As the actuator number was increased only a minor decrease in the performance index was observed after four actuators.

Thermoelastic analysis of temperature-dependent functionally graded rectangular plates using finite element and finite difference methods

ABSTRACT Two-dimensional thermoelastic analyses of fully clamped functionally graded rectangular plates (FGRPs) by applying a constant in-plane heat flux from one edge were studied by using Finite Difference Method (FDM) and Finite Element Method (FEM) with temperature-dependent material properties. Some differences about 1.5 to 2 times between FDM and the FEM solutions in terms of normal strain, equivalent strain, shear stress, and equivalent stress levels are observed. However, similar distribution characteristics from FDM and FEM analyses are obtained for temperature, displacement, strain, and stress components.

Effect of Composite Patch Geometry in Notched Plates Under Low Velocity Impact

The repair technique of the composite patch with bonding adhesive are used with the purpose of repairing materials and increasing working life of the materials. In this study, the impact strength of notched metal materials repaired by composite patch investigated by numerically. Fiber reinforced laminated composite patch was modeled by using finite element model. Composite patch was bonded to damaged materials, and this structure was subjected to impact test. The geometrical and material non-linearities were considered in the explicit dynamic analysis. The notched plate was made of aluminum 6061-T6. The effects of design parameters, such as composite patch geometry, on the impact energy absorption of the plates were investigated. The metal notched plates were modeled as a Johnson-Cook material model and the composite patches were modeled orthotropic elastic material model and Hashin damage. In the analysis results, the damage mechanisms of composite patch were exhibited and strength of damaged materials was exhibited in terms of contact force, kinetic energy and stress distributions. The effect of patch geometries was also investigated in terms of absorbing impact energies. As the plates without patch perforated, repaired metal notched plates with composite patch did not perforate.

Free Vibration Analysis and Design of an Adhesively Bonded Composite Single Lap Joint

In this study the three dimensional vibration analysis of an adhesively bonded cantilevered composite single lap joint was carried out. The first four bending natural frequencies and mode shapes were considered. The back-propagation Artificial Neural Network (ANN) method was used to determine the effects of the fiber angle, fiber volume fraction, overlap length and plate thickness on the bending natural frequencies and the mode shapes of the adhesive joint. The bending natural frequencies and modal strain energies of the composite adhesive lap joint were calculated using the finite element method for random values of the fiber angle, the fiber volume fraction, the overlap length and the plate thickness. Later, the proposed neural network models were trained and tested with the training and testing data. The fiber angle was more dominant parameter than the fiber volume fraction on the natural bending frequencies and corresponding bending mode shapes, and the plate thickness and the overlap length were also important geometrical design parameters whereas the adhesive thickness had a minor effect. In addition, the present ANN models were combined with Genetic Algorithm to search a joint design satisfying maximum natural frequency and minimum modal strain energy conditions for each natural bending frequency and mode shape.© 2007 ASME