PML specifications, it's important to deter- rine whether the small variations that aze inevitable in the manufacturing pro cess will aus a percentage of production Duilds to squeal Although all brake squeal causes are ot fully understood, it is commonly accepted that such noise is initiated by instability due to the fiction force, lea ing to self-excited vibrations. This proc: ess is inherently more complex than a typical simulation problem that con: sists of applying a measurable load to a structure. Simulating brake squeal has typically required a tedious mesh gener ation process of manually creating cou plings between the brake pads and discs. Dynamic analysis is used to analyze the elgentrequencies of the system to deter rine whether or not squeal will cca Aig weakness ofthis method is that factors such as deflection may change the ‘way that the pad and dise surfaces come together. They may contact each other at an angle or with greater or lss force than. 's expected. With the traditional method, the uncertainty in the contact conditions js addressed by building and testing a physical prototype and comparing the ‘measurements against simulation pre Aictons to tune the model. The frst try is often a poor match, necessitating thal the simulation be run over and over again, adjusting the contacts each time until the predicted results accurately match the physical tests. This approach is both, expensive and time-consuming DEVELOPMENT OF NEW ‘SIMULATION METHOD TRW’s engineers wanted the ability to accurately simulate brake squeal without having to spend extra time and money on validation testing. The TRW team worked with ANSYS technical services staff to accurately define contact conditions prior to physical testing by using a non linear static solution to establish the Initial contact and compute the sliding contact between pads and disc. ANSYS software enabled the entire brake-squeal simulation process to be incorporated within the ANSYS Workbench envicon- ‘ment, which allowed automating the abil ty to simulate expected manufacturing variation and determine if the design met robustness requirements. The new simulation process — jointly developed by TRW and ANSYS — begins ‘One ofthe joint interfaces between rotor and hub TRW engineers wanted to accurately simulate brake squeal without having to spend extra time and money on validation testing. | with importing the CAD model into Workbench. The production intent para metic CAD model of the brake assem bly incorporates component-level models such as the pad assembly, caliper, rotor and knuckle. Additionally, the compo nent models are created to incorporate ‘manufacturing variability. After the ini tial import, the software automaticaly otects and performs setup for the com tacts or joints between parts of an assem bly. ANSYS meshing technology then provides multiple methods to gener ate 2 hex-dominant mesh or a tet mesh, depending on analysts requirements. Successfully simulating brake squeal ‘then requltes capturing the linear behav- {or of the structure based on its prior in ear or nonlinear pre-loaded status. The ‘TRW team uses near perturbation anal- ysis to solve a linear problem from this pre-loaded stage —a process thats essen- tially automated in ANSYS Mechanical Next, engineers employ a nonlinear static solution to establish the initial contact andl compute the sliding contact between pads and disc. The applied stresses and rotation ofthe dis create the pre-loaded effect, and friction contact generates an asymmetric stiffness matrix during static structural analysis. Im the second phase of the linear per turbation analysis, TRW engineers perform a QR-damped or unsymmetric modal analysis. The eigensolver uses the ‘unsymmetric stiffness matrix generated fn the contact elements and may produce complex elgenfrequencies. The results of a perturbation analysis then show the damped frequencies foreach mode num: ber along with the stability or eal part of, the eigenvalues. When the coupled mode shows a positive real value, it indicates instability in the system that may be a source of brake noise or squeal. The anal ysis results also include the mode shapes, which often provide useful diagnostic {information that helps in changing the design to eliminate instability