Gordon M. Brown

Fringe analysis for automotive applications

Abstract The capabilities of Ford USAs Computer Aided Holometry (CAH) system for stepped phase interferometry are presented. Holographic test equipment and facilities are briefly reviewed. Fringe analysis algorithms and procedures for practical semi-automated processing of stepped phase interferograms of complex real life structures for quantitative measurement of deformation and shape are discussed. Several automative applications illustrating the fringe analysis technique are presented, including: (1) the use of CAH combined with Finite Element Analysis (FEA) methods to study frictional effects of the thermal insertion of a wrist pin into a connecting rod; (2) a study of engine deformation due to hydraulic loading of the cylinders; and (3) the computation of sound pressure from CAH measured vibration amplitude/phase and shape using the Rayleigh integral and SYSNOISE TM methods. In the past, holometry methods have been used primarily for problem solving in structures that were already in production, often where limited opportunities existed to make expensive modifications to existing tooling. Infrequently holometry was used by knowledgeable engineers to develop optimized components in the prototype stage even without the current CAE methods. The opportunity and challenge of our day is to closely couple CAE (FEM, EFA) methods and experimental methods (CAH, modal, etc.) to optimize structural performance in the upstream product development process where necessary tooling modifications can and will be made.

Measurement of shape and vibration using a single electronic speckle interferometry configuration

Shape and vibration measurements of structures are required in many automotive product development and manufacturing processes. Optical measurement methods are attractive because they do not require contact with the structure and offer high precision and accuracy. Nevertheless optical techniques also suffer from a number of limitations which prohibit wide application. Typically the object is viewed and illuminated from two different points making objects situated in confined areas difficult to measure. In addition, most optical techniques are not easily scaleable in measurement range. Finally, most shape measurement techniques cannot measure vibration without a change in configuration. This paper presents a single electronic speckle interferometry (ESPI) method to measure both surface shape and vibration. A two-wavelength approach is used to measure shape and a stepped strobed phase technique is employed to measure vibration amplitude and phase. The technique requires only one line of sight to the object and can be scaled to measure surface roughness as well as large surface contours. The technique features the ability to coincidentally measure shape and dynamic behavior for structural design, modification, and optimization. The theory of the technique along with results of an experiment are presented.

Practical phase unwrapping of holographic interferograms

Although fully automated phase unwrapping of stepped phase interferograms is a worthy goal and is receiving considerable attention, this Utopian circumstance has not yet been uniquely achieved in a reasonable time on complex real life structures such as an automotive powertrain. The method presented here uses a binary bad spot mask and a seed point mask to phase unwrap the underlying modulo 2(pi) phase map of very complicated structures. Fringe amplitude, modulation, and triangular unit cell path dependence are used to automatically create a portion of the mask. Partition lines are added manually to the mask to separate sheared fringe systems, structural boundaries, and regions of sampling theorem violation.

Computer Automated Holometry For Automotive Applications

Current methods and equipment developed for computer automated holometry are described. Several applications including holo-photoelasticity of planar models, holographic interferometry of crankshaft bearing cap distortion due to bolt torquing and cylinder bore distortion due to head bolt torquing are discussed. Comments are made on future automotive applications.

Current applications of hologram interferometry at Ford USA

Testing of vehicle components with holometry to improve their structural characteristics is a proven methodology. Full field, high sensitivity holometric measurement capabilities are used for the iterative improvement of prototype structures (static and dynamic). The combination of modeling methods and Computer Aided Holometry (CAH) is just beginning to impact structural design. Current examples of studies of static and dynamic behavior of vehicle components using continuous wave CAH techniques are presented.

Holographic interferometry and its application in brake vibration and noise analysis

Brake roughness and brake squeal are important issues/concems of customer satisfaction in the automotive industry. Brake roughness is a low frequency vibration while brake squeal is a high frequency noise. Some fundamental root causes of brake roughness are rotor runout, rotor surface flat spots, etc., which cause brake torque variation that in turn produces unwanted low frequency vibration. Brake squeal is a dynamic instability and nonlinear phenomenon that occurs in a frequency range of lKHz to 15KHz, which is in the range of sensitivity for the human ear. Squeal is usually caused by excitation of brake components brought on by slip-stick of the brake caliper pad material and rotor surface during brake actuation. This paper will provide an overview of examples that illustrate the application of holographic interferometry methodology to identify the root causes of brake concerns and verify engineering solutions.

Comparison of holographic interferometry to other test methods in automotive testing

Hologram interferometry is one of many testing techniques used to study and improve vehicle structures and subsystems. Other test methodologies serve to provide data on component loadings and input conditions for holometric testing or serve to correlate holometric results at discrete locations. This paper includes applications that show the benefits of holometric testing and its ability to predict the in-vehicle behavior of a wide variety of automotive components.

Computer-aided holometry in the automotive industry

In the past, holometry methods have been used primarily for problem solving in structures that were already in production, often where limited opportunities existed to make expensive modifications to existing tooling. Infrequently holometry was used by knowledgeable engineers to develop optimized components in the prototype stage even without the current CAE methods. The opportunity and challenge of our day is to closely couple CAE (FEA, EFA, BEA) methods and experimental methods (Computer Aided Holometry (CAH), modal, etc.) to optimize structural performance in the upstream product development process where necessary tooling modifications can and will be made. Holometry is used by American, European and Japanese automobile manufactures and several commercial sources for equipment and software are now available. The capabilities of Ford USA’s CAH system for stepped phase interferometry are presented. Holographic test equipment and facilities are briefly reviewed. Fringe analysis algorithms and procedures for practical semiautomated processing of stepped phase interferograms of complex real life structures for quantitative measurement of deformation and shape are discussed. Several automotive applications illustrating the fringe analysis technique are presented.

Nanomeasurements by heterodyne hologram interferometry

Continued demands for higher performance and safer vehicles mandate use of new technologies for development of automotive structures. These structures are not only mechanical in nature, but also involve electronics. Durability of automotive electronics depends on their response to environmental and other loads that they encounter. Typically this response is characterized by force-displacement characteristics. Since displacements in electronic components are small, their determination is difficult. In this paper, analytical and empirical methodologies for determination of displacements of electronic components are outlined. It is shown that, using heterodyne hologram interferometry, displacements of electronic components can be measured on the scale of nanometers.

Hologram interferometry in automotive component vibration testing

An ever increasing variety of automotive component vibration testing is being pursued at Ford Motor Company, U.S.A. The driving force for use of hologram interferometry in these tests is the continuing need to design component structures to meet more stringent functional performance criteria. Parameters such as noise and vibration, sound quality, and reliability must be optimized for the lightest weight component possible. Continually increasing customer expectations and regulatory pressures on fuel economy and safety mandate that vehicles be built from highly optimized components. This paper includes applications of holographic interferometry for powertrain support structure tuning, body panel noise reduction, wiper system noise and vibration path analysis, and other vehicle component studies.