The Loads tab is used to specify the loads that are applied to the FE model. EverStressFE is equipped to allow the user to specify a wide range of realistic loads that may be applied to a flexible pavement through a vehicle's tires. It is also possible for the user to create a custom nonuniform load file to simulate loads that can not be generated within the graphical user interface of EverStressFE. Note that changes made on the Loads tab may result in automatic updating of the mesh (i.e. increasing the size of the refined region). This is intended to serve as a safeguard so that the user does not inadvertently create a load that exceeds the refined region, which would likely cause an inaccurate solution.
The first step in selecting a load is to choose the type of Tire Contact to model. The Rectangular or Circular options allow the user to specify contact patches with a constant applied stress equal to the tire pressure. The User Defined option utilizes rectangularly shaped patches and the user specifies parameters for individual tire treads and non-uniform stress distributions. The final option is to select Load Custom, which will prompt the user to open a pre-existing .node file containing points and pressures.
After selecting the type of Tire Contact, the user must define the rest of the Load Parameters, as necessary. The Wheel Type can be selected as Single or Dual. The Axle Type can be selected as Single or Tandem. Depending on these selections, the user may also need to quantify the center-to-center C/C Tire Spacing (mm) and the center-to-center C/C Axle Spacing (mm). The Load per Tire (kN) and Tire Pressure (kPa)/Peak Pressure (kPa) must be quantified unless the user has chosen the Load Custom option. Finally, the user must quantify the Tire Width (mm) if a Rectangular or User Defined type of Tire Contact is modeled.
Figure 1: Screenshot of Loads Panel with Default Parameters
The graphics panel at the bottom of the Loads tab shown in Figure 1 displays graphics related to loading in addition to the main graphics panel. Other panels can be accessed by toggling between the Designer View radio buttons in the Nonuniform Tire Contact Plotting Options region, if applicable. The default view (and the only available view for Rectangular or Circular types of Tire Contact) is the Tire(s) view. This view simply displays a schematic of the tire(s) that are being simulated in the model. (Note that only 1/4 of the total wheel is applied in the FE model since it is 1/4-symmetric.) Thus, since the Load per Tire (kN) is specified, the load applied in the 1/4-symmetric FE model will be equal to 0.25, 0.5, 0.5, and 1.0 times the magnitude of this value for a single-single, dual-single, single-tandem, and dual-tandem [Wheel Type, Axle Type], respectively.
The Contact Pressures view is available for the User Defined and Load Custom types of Tire Contact. This view shows a color surface plot of the tire contact stresses as a function of plan view coordinates (example shown below in Figure 2). The name of the non-uniform tire contact file is also displayed in this view if the user has loaded a custom nonuniform load file. The user can choose to view the surface plot from a 3D or plan-view perspective (3D view shown in Figure 2).
Lastly, the user can choose the Tread Designer view (only for the User Defined option). The panel in this view provides tools for defining a non-uniform contact stress distribution and also accounting for individual tire treads (see Tread Designer for details).