Finite Element Wear Behaviour Modeling of AA7075 Coated with WS2/Cu Using ANSYS

Aluminium Alloys Are alloys in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin and zinc. Aluminium alloys are widely used in engineering structures and components where light weight, or corrosion resistance is required. Alloys composed mostly of aluminium have been very important in aerospace manufacturing since the introduction of metal-skinned aircraft. Aluminium alloys are widely used in automotive engines, particularly in cylinder blocks and crankcases due to the weight savings that are possible. Manufacturing techniques and metallurgical advancements have also been instrumental for successful applications in automotive engines. The addition of elements to the aluminium gives the alloy improved strength, workability, corrosion resistance, electrical conductivity, and/or density, compared with the pure metallic element. (I.J Polmear 1995)

Experimental study and FEM simulation of wear performance of different composite materials and metals are one of the major research fields in tribology. Pin on disc is one of the main experimental set up for wear analysis and for FEM analysis different software packages like ANSYS and ABAQUS were used.The first attempt to develop wear model to predict the wear performance made by Archard [11] and this model was incorporated in wide range of wear studies and results obtained shows good agreement with experimental wear studies. Firaol et al. 2015 studied about the detailed analysis of wear measurement and wear analysis of overhead line contact wire using ANSYS workbench software [13].The simulation of contact wire is performed on pin on disc model, where the model is used for sliding contact analysis. Researchers proposed a method of calculation of wear through FEM analysis and further, wear analysis is based on Archards wear model[14]. A study was carried out to investigate the sliding wear and calculation of wear is based on the Lim and Ashbys wear map, Archards wear law and selected the ANSYS software was used for analysis [14]. Sullivan developed a mathematical model to relate the applied load and the wear which also includes other factors collectively can assumed as Archards wear coefficient[15]. Authors have conducted the experiment of FE analysis of sliding wear in metals. Model is formulated in legrangian frame work. Archard law is used for the wear calculation. Model is validated using rotation of brass pin in steel disc [16]. Veenhuizen et al. 2006 carried out study of wear in both FEA and pin on disc experimental methods for CVT belt. FE analysis of wear is done in ABAQUS software and wear fracture of belt was analyzed using FE methods and suggested remedies. Experimental determination of wear life has both cost and time effect [17]. The simulation of wear and life prediction can helps product developers in many manners such as designing better products, propose better maintenance plans to hold off failures and prevent financial losses. In this paper, recently published work (Davanageri et al.2017) on wear behaviour of AISI2507 Super Duplex Stainless Steel results were tested [22]. The finite element simulation of the wear test is carried out in ANSYS using Archards FEA model.

MATERIAL AND METHODOLOGY

AA7075 is an aluminium alloy containing zinc, magnesium, copper, zinc and other metals. One of the most commonly used aluminium alloys for structural applications is 7075 Al alloy due to its attractive comprehensive properties such as low density, high strength, ductility, toughness and resistance to fatigue. It has been extensively utilized in aircraft structural parts and other highly stressed structural applications.

Table 1. Chemical composition of 7075 Aluminium Alloy

1. 1. FEA wear simulation and Finite element theory

The main task of the finite element method (FEM) in the wear calculations is to compute the fields of contact stresses. The structure to be analysed is discretised with a number of elements, assembled at nodes. In FEM the function in question (displacement, temperature, etc.) is piecewise approximated by means of polynomials over every element and expressed in terms of nodal values. The elements of different type and shape with com plex loads and boundary conditions can be used simultaneously. In the structural analysis the degrees of freedom are defined as nodal displacements. The equations for every element are assembled into a set, expressed in the structural level as.

The flow-chart of the FE wear simulation procedure, consisting of a series of structural solution steps combined with additional calculations, The initial parameters given define the model geometry, loads, constraints and wear model parameters. Along with the element and material data. Special sub routines were developed for every configuration to generate the FE model and define the loads and constraints automatically. A good discretization must be found for every particular geometry and loading case. The areas with expected high stress gradients utilize a finer node mesh. More elements in the model are likely to provide more exact results but contribute to an increased computing time and use of disk space. After the FEA iterative stress solution was obtained, the contact region was located. The status of every contact element (closed or not) was determined. The contact node coordinates of closed contact elements define the contact are allocation. The nodal stresses of the nodes in the contact region determine the contact pressure distribution. The Euler method is used to integrate the wear law with respect to time. For each wear simulation step the system parameters are assumed to be constant and contribute to the wear depth at every node according to the following discretized wear model.

Fig 1. Pin-on-disc rubbing contact and the FE model structure

RESULT AND DISCUSSION

The effectiveness of finite element analysis in prediction of wear is, its capability to consider accurately both the parameters i.e. the contact pressure and frictional stresses developed, and the relative progressive change occurred in the surface geometry due to material removal in three dimensional components. Many authors have reported the use of finite element analysis to simulate and predict the wear [11-19]. Feasibly the most conclusive way to authenticate the FEM results is to compare them with the known experimental results. FEM analysis of pin on disc wear test is carried out using ANSYS WORKBENCH-2021. Direct measurement of wear loss is not possible through the software. To determine the wear loss, the average value of contact pressure between pin (specimen) and disc, also frictional stresses during the rotation is determined by using ANSYS software. Further with help of Archard wear volume was calculated. In finite element analysis the wear phenomenon was considered as a nonlinear process. The solution for nonlinear problems was obtained by considering transient structural analysis. The various steps involved in transient analysis are listed below.

• Inputting the engineering data of the materials
• Modelling of the pin and disc geometry
• Meshing of the geometry.
• Identify the contact pairs.
• Designate contact and target surfaces.
• Define the contact surface.
• Define the target surface.
• Define/control the motion of the target surface.
• Apply necessary boundary conditions.
• Define solution options and load steps.
• Solve the problem.
• Review the results.

• Define the mechanical properties of AA7075 and the WS2/Cu coating.
• Gather data on wear coefficients, hardness, and other relevant properties.

Create the geometry of the coated AA7075 sample in ANSYS. Generate a finite element mesh with appropriate element size and type.

Fig 2. Material properties assign        

Fig 3. Meshed geometry of a pin wear test in ANSYS

Fig 5. Load and constraints

The model shown in Figure 4 (a and b) consists of two parts, the lower part is a steel (EN64) disc steel that rotates with predetermined velocity and upper part of it is a specimen (pin of 10 mm diameter) that stays stationary on rotating disc. For the application of load on the rotating disc a rigid contact surface is used. Here the famous Archard [11] approach taking into account the wear process is introduced to formalize the wear kinetics. The model was developed based on equal and steady state wear rate assumption. The geometric modelling can be done on Geometry of ANSYS Workbench for creating 3D prototypes that are used for wear simulation and contact analysis.

Table 2. Process parameters

The contact pressure developed in the pin surface increases with the increase in load as shown in Table 3 for solutions treated and for heat treated specimens. The contact pressure developed between the pin and disc is solely geometrical property and is dependent on applied normal force, contact area of the pin and the pressure distribution along the pin surface for a load of 10N shown in figure 5. From figure 5 it was observed that pressure distribution along the pin surface was minimum at the central portion of the pin and maximum at the edges of the pin and this trend found to be similar in all other heat treat specimens. Further the obtained contact pressure data can be used in Archard equation to determine the wear volume loss instead of analytical contact pressure calculation. It was also observed that FEM value of contact pressure is slightly on a higher side compared to analytical value of contact pressure.

Table 3. Values contact pressures

Fig 6. Frictional stress for 10N

Fig 7. Frictional stress for 20N

Fig 8. Frictional stress for 30N

Fig 9. Frictional stress for 40N

Fig 10. Frictional stress for 50N

Table 4. Analysis of Variance for Wear Rate and Coefficient of Friction