Richard Hathaway

1 – TRANSDUCERS AND DATA ACQUISITION

This chapter addresses the sensors, sensing methods, measurement systems, data acquisition, and data interpretation used in the experimental work that leads to fatigue life prediction. A large portion of the chapter is focused on the strain gage as a transducer. Accurate measurement of strain, from which the stress can be determined, is one of the most significant predictors of fatigue life. Prediction of fatigue life often requires the experimental measurement of localized loads, the frequency of the load occurrence, the statistical variability of the load, and the number of cycles a part will experience at any given load. A variety of methods may be used to predict the fatigue life by applying either a linear or weighted response to the measured parameters. Experimental measurements are made to determine the minimum and maximum values of the load over a time period adequate to establish the repetition rate. If the part is of complex shape, such that the strain levels cannot be easily or accurately predicted from the loads, strain gages will need to be applied to the component in critical areas. Measurements for temperature, number of temperature cycles per unit time, and rate of temperature rise may be included. Fatigue life prediction is based on knowledge of both the number of cycles the part will experience at any given stress level during that LEE: FATIGUE TESTING AND ANALYSIS Final Proof 22.6.2004 2:54pm page 1

Gear Root Stress Optimization Using Photoelastic Optimization Techniques

An important factor influencing the strength of spur gear teeth is the fillet profile. In the fillet area bending stress and local geometry changes result in stresses and stress concentrations that can, under high loading conditions, lead to failure. This study was conducted to determine if an optimum fillet profile existed, what the shape of the optimum profile is, if the profiles are similar for different pressure angles and the magnitude of improvement that could be expected. New manufacturing techniques such as full-form grinding, near net formed gear blanks and powered metallurgy technology allow the gear designer to put different forms in the root area than the usual trochoid produced by the tip of a hob generating the gear. With the application of these techniques the fillet profiles could be optimally formed leading to strength improvements of up to 40%, with reductions in rotating mass

Resonance detection and acoustic behavior in polymer intake manifolds using holographic interferometry techniques

Major emphasis on the use of lightweight components in engines has lead to widespread use of polymer intake manifolds. The pulsed flow through these manifolds combined with the lower elastic modulus materials can result in excessive noise under certain speed load conditions. Using full-field optical techniques allowed for the detection and analysis of the resonance behavior in polymer intake manifolds. The test procedures involved techniques including time-averaged holography, with variable excitation sources to identify resonating regions and associated critical frequencies. The results clearly indicate the development of an efficient test methodology to analyze manifold designs for resonance and structural characteristics.

Residual stress evaluation using shearography with large shear displacements

A newly developed optical method for the qualitative and quantitative evaluation of residual and live-load stresses is presented. The method utilizes shearography employing a large angle shearing prism which results in large shear displacements. The large angle shearing prism allows the surface speckle pattern to be referenced and mapped onto a remote, separately positionable, surface. Changes on the object surface are initiated between exposures by means of a spherical impression made into the surface. The impression is made by impacting a hardened ball into the surface producing local stresses approximately three times the magnitude of the yield stress for the material. The deformation pattern is recorded and related to the stress that was initially present in the specimen.