Life Prediction of a Refuse Truck Cab for Automatic Side Loading operation using Inertia Relief

Refuse Trucks are used to pick up garbage from houses. These trucks have huge robotic arms connected to the frame which are operated by hydraulic mechanism operated by the driver sitting inside the cab of the truck. The operator of the truck controls the robotic arm using a lever. Once the truck is positioned aside the garbage can, the operator moves the robotic arm outwards, grabs hold of the garbage can, picks up the garbage can and dumps the garbage into the truck. During this operation, the frame articulates and moves due to the frame suspension causing the cab to move along with the frame. This operation is performed about 1000 times a day, 5days a week for 12 years which could result in some amount of damage to the cab over its life. Since the time rate of application of the forces during the Automatic Side Loading operation is small compared to the lowest flexible mode of the cab, modal amplification is considered unlikely. Global displacements of the cab mounts were measured using string pots during the Automatic Side Loading operation which were used to calculate the input loads at the cab mounts using a Volvo In-house tool CVM-D (Complete Vehicle Modeling-Diamondback). The loads at the cab mounts were than used with Inertia Relief using MD NASTRAN to calculate high stress areas in the cab. A Static method like Inertia relief is used instead of the conventional Dynamic transient FEA due to substantial cost and time savings. The Inertia Relief method takes the dynamic effect into account without the added cost and time of the dynamic transient method. nCode DesignLife was used to create the duty cycle file and the stresses obtained from the Inertia Relief analysis were cycled to obtain the cumulative damage and Life of the cab. Critical areas seeing damage were identified and correlated to field failures. Good correlation was obtained with regards to cracks seen on the cab in the field.