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Numerical Simulation of the Propagation of a Crack in Gearbox Crack

Lin Liu & Suri Ganeriwala
SpectraQuest Inc., 8227 Hermitage Road, Richmond, VA 23228
Published: August, 01 2005


In this technical note, fracture propagation is simulated using a finite element model for a gearbox which is designed for a rotor dynamic test rig. The circumferential plates of the gearbox are welded along the side as well as the bottom edges. Micro-cracks are usually generated at weld toes and the welding process will introduce residual stresses. The effect of the locations of initial fracture on fracture propagation path is studied.

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SpectraQuest Inc. specializes in design, development and fabrication of gearbox system for diagnostics and prognostics researches. Upon request from a custom, we have performed a numerical simulation of crack propagation in a gearbox. The gearbox is installed in the Gearbox Dynamic Simulator.

The gearbox is made of six aluminum plate. Each one of the four circumferential plates is welded with one another. Furthermore, the circumferential plates are welded to the bottom plate. The top plate is bolted to the circumferential plates.

Gearbox Model

The end plate of the gearbox facing the direction of the rotor "B" assembly is modeled in the work. The geometry of the plate is a 14 by 14 inches square with a 3 inches radius hole in the center. The thickness of the plate is 0.5 inches. Because of the small thickness of the plate, it can be considered as a plane stress problem and two dimensional finite element model is created using FRANC2D software.

The finite element model is displayed in figure 3. There are total of 800 Q8 quadrilateral elements. The bottom edge is constrained both in the x and ydirections. The assumed load is a node load applied at the uppermost node in the hole in the y direction with amplitude of 200 lb.

An edge fracture is introduced on the left side of the plate with different initial locations. The three fracture initial locations studied in the work are displayed in Figure 3. The lengths of three initial fractures are all 0.21 inches. And the initial crack direction is horizontal for all the three cases.


Fig 1: Gearbox in Gearbox Dynamic Simulator

Fig 2: Finite Element Model of Plate

Fig 3: Deformed Mesh for First Crack