Thermo-Mechanical Analysis of Aluminium Silicon Carbide Composite Materials

In recent years, composite materials have dominated the electronics industries and other manufacturing industries. Hence, composite materials like aluminium silicon carbide (AlSiC), has been employed to produce heat sinks, which are used mainly to manage heat in electronic devices. However, thermal fatigue of such composite material is a major challenge in maintaining reliability of the device. This paper investigates the thermomechanical effect of AlSiC composite materials. Finite element method (FEM) was used in the analyses of the composite materials based on the particulate inclusions between 10 – 50% compositions. The thermal profile (-40C to 85C) employed in this study is used commercially for consumer products. The fatigue life of the composite material which is based on the stresses and strains parameters were obtained and evaluated. The results from this investigation suggests that the deformations, strains, and stresses reduced with increase in the percentage of particulate inclusions. Also, the fatigue life of the composite material showed that the reliability of the material is increased with higher inclusions. This investigation demonstrated that 50% particulate inclusions has a better number of cycles to fatigue failure (5.09E+04) when compare to other inclusions. While 10% inclusions has the least fatigue life (4.39E+04) based on this investigation. DOI: https://dx.doi.org/10.4314/jasem.v24i6.3 Copyright: Copyright © 2020 Ekpu. This is an open access article distributed under the Creative Commons Attribution License (CCL), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Dates: Received: 11 April 2020; Revised: 15 May 2020; Accepted: 05 June 2020

In order to improve thermal management in electronic devices, the traditional materials initially used for managing heat has to be revolutionized. Copper and Aluminium are the most commonly used materials for heat management (Ekpu et al 2011). However, the use of composite materials have considerably enhanced heat management in electronic applications. Hence, the need to investigate the thermo-mechanical behaviours of composite materials are indeed necessary. Researchers such as (Babalola et al 2018;Xiao-min et al 2012;Wang et al 2009) have studied composite materials to determine their electrical, physical and mechanical properties. Babalola et al (2018), presented a study of the electrical and mechanical properties of AlSiC composite material produced by stir casting method. In their study, the experimental results gotten was infused into an Artificial Neural Network (ANN) to predict the properties of the composite material. The essence of the work was aimed at reducing the high cost of carrying out experiments and its related challenges. Kumar et al (2019), studied the integrity of the surfaces of aluminium based composite materials machined by Electrical Discharge Machine (EDM). Their study suggested that the surface defect of pure AlSiC composite materials were less than AlSiC composite materials that B4C particles were added to. Hassan and Hussen (2017), investigated the mechanical properties of AlSiC composite material. In their study, it was observed that the weight loss and wear rate of the AlSiC were lower than the pure aluminium after 5 minutes, for temperatures of 300 o C and 400 o C. Also, the Vickers micro-hardness of the AlSiC composites were higher than that of the aluminium.
Composite materials has been developed over the years by researchers with the help of numerical and finite element modelling techniques (Cao et al 2013; Wu and Yao 2010;Yvonnet et al 2008). This will help reduce several experimental works on composite materials development. Issues related to thermal reliability of composite materials can be found in literature (Heimann and Pohl 2014;Li et al 2014). Not much works are available in literature on thermal fatigue of composite materials used for thermal management in the electronic industries. Hence, it is imperative to study the thermal fatigue of AlSiC metal matrix composite material using finite element method. This research will give an insight on the reliability capabilities of different compositions of Aluminium Silicon Carbide composite materials.

MATERIALS AND METHODS
The model adopted in this research work, is centred on the simplicity of creating circular shaped particulates Thermo-Mechanical Analysis of Aluminium Silicon…..

EKPU, M
in virtual squared matrix domain. This was necessary for simulation purposes. Table 1 presents the geometric parameters used in developing the finite element design. The multiple inclusions for different composite models were created with ANSYS workbench simulation software. The design of the models were based on volume fraction, to ensure that a near practical solution is obtained. 1 µm to 200 µm are the average sizes of particles obtained from most practical situations (Zhang et al 2007;Sahin and Acilar 2003;Sahin 2003). A two dimensional model was created for each of the multiple inclusions studied. It is assumed that the particles are uniformly distributed. The different composite models are presented in Fig.  1.
C is a non-dimensional constant, which is dependent on thermal cycling conditions characterized by the Biot modulus (β): Where E is the Young's modulus, v is Poisson's ratio, α is the coefficient of thermal expansion, ∆T is the temperature difference, "a" is the dimension of the material involved in the study, k is the thermal conductivity of the material and h is the heat transfer coefficient. The sub-script "e" is the effective properties of the composite material, "c" denotes to critical and σt is the material's tensile strength.
For crack to be initiated, a composite material will have to reach the critical temperature difference (∆Tc). The resulting critical induced thermal tensile stress (σts,c) is given in Equation 3. The thermal shock resistance parameter (R) is equal to the critical temperature difference (∆Tc) of the material before crack is initiated, as presented in Equation 4 (Jones 2001). Also, crack propagation resistance (R') is dependent on available elastic energy in the material, as given in Equation 5 (Jones 2001).

RESULTS AND DISCUSSIONS
The results from this research work are presented in this section.
Multiple Inclusions Analysis: The study of multiple particle inclusions in a metal matrix composite was necessary because in practice composite materials have multiple inclusions. This study shed more light on the distribution of equal volume fraction of particles for multiple inclusions. The individual components of the composites are analysed and presented.
Particles Inclusion: Figs. 2 and 3, shows the distribution of the plots of stresses and strains against time. Figs. 2 and 3 showed that the stress and strain on the 10% particulate inclusions were higher than the other inclusions. In addition, there was a slight increase in the stresses and strains around the highest and lowest regions of the thermal cycle time.   Fig. 6, it was observed that an increase in the percentage of inclusions reduces the stress of the composite material. In addition, the inclusions showed a significant reduction in the stresses as compared to the stresses of the matrix. The lowest stresses were recorded at 50% inclusion while the highest stresses were recorded at 10% inclusion. In Fig. 7, the strains were observed to be higher in the matrix as compared to the strains of the inclusions. However, there is only a slight difference in the strains of the matrix at the highest and lowest thermal cycle temperature. A similar behaviour was observed for the inclusions as well. The deformations of the metal matrix composites for the multiple particle inclusions are presented in the form of contour plots in Fig. 8. Fig. 8 showed that majority of the metal matrix had low deformation as compared to the inclusion particles. In addition, the bond area between the particle inclusions and the matrix had the highest amount of deformation. This will lead to delamination of the particle/matrix interface as shown in Fig. 9 (Zhang et al 2007). Also, it was observed that the deformation was affected by the arrangement of the particulate inclusions. Therefore, an evenly spaced inclusion is likely to have lower deformation than randomly spaced inclusions. This study showed that 50% inclusion recorded the lowest deformation. It could be inferred that the delamination between the inclusion particles and the matrix is a major issue affecting the production of composite materials for thermal management improvement in microelectronics applications. This issue could be reduced by increasing the number of particles in a composite material as shown in this study. Where σa is the stress amplitude (von-misses stress extrapolated from research), E is the modulus of elasticity, ∆εe/2 is the elastic strain amplitude, is the fatigue strength coefficient given as 558 MPa by (Rohatgi et al 2007), Nf is the number of cycles to failure, and b is the fatigue strength exponent (Basquin's exponent) which varies between -0.05 and -0.12 for most metals. The value of b used in the fatigue calculation is given as -0.1145 (Rohatgi et al 2007). Fig. 10 presents the fatigue life of the multiple inclusions composite material. It was observed that as the percentage of inclusions were increased, the fatigue life of the composite material also increased. This conclusion is consistent with the results presented by Koh et al (1999). In addition, the 50% SiC particulate inclusions have the highest fatigue life (5.09E+04) as compared to the other percentage inclusions studied. While 10% particulate inclusions have the least fatigue life (4.39E+04) based on this study. Therefore, it is recommended that a composite material with 50% SiC inclusions will have better reliability for microelectronic heat sink used for commercial purpose.