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This paper reports on the experimental study of carbide and polycrystalline diamond (PCD) drills used for drilling composite/titanium stacks. Materials systems used in this study were multi-directional carbon fiber in an epoxy matrix and titanium 6Al-4V. The drill materials included tungsten carbide (WC; 9%Co ultra fine grain) and polycrystalline diamond (PCD; bimodal grade). Torque and thrust force were measured during the drilling experiments. Tool wear of both drills was periodically examined during the drilling tests using various microscopic techniques such as optical and Scanning Electron Microscope (SEM). Effect of tool materials and process condition on hole quality parameters such as hole diameter, surface roughness, and titanium burrs, were examined. Dissimilar mechanical and thermal properties of the stacks affected the tool life and resulted in the decreased hole quality for both cutting tool materials, although to a differing degree.

A device has been designed and built to allow one to systematically investigate the dynamical behavior of a wide variety of torsional vibration absorbers (TVAs). These are devices that can passively absorb the torsional vibration of a wide range of rotating systems. The testing device allows different operating conditions to be studied and similarities and discrepancies between theoretical predictions and experimental results can be made. The manuscript emphasizes the design and capabilities of the device and discusses the instrumentation of the system. It also presents a limited number of experimental results along with the associated theoretical predictions.

Many engineering systems create unwanted noise that can be reduced by the careful application of engineering noise controls. When this noise travels down tubes and pipes, a tuned resonator can be used to muffle noise escaping from the tube. The classical examples are automobile exhaust and ventilation system noise. In these cases where a narrow frequency band of noise exists, a traditional engineering control consists of adding a tuned Helmholtz resonator to reduce unwanted tonal noise by reflecting it back to the source (Temkin, 1981). As long as the frequency of the unwanted noise falls within the tuned resonator frequency range, the device is effective. However, if the frequency of the unwanted sound changes to a frequency that does not match the tuned resonator frequency, the device is no longer effective. Conventional resonators have fixed tuning and cannot effectively muffle tonal noise with time-varying frequency.

A device consisting of a mass-loaded cantilever and a striker block mounted on an electromagnetic shaker can be used to create a wide variety of mechanical rattle sounds. The construction of the rattle mechanism is described and illustrated with diagrams. Examples of the different qualities of rattles that can be produced are presented as plots of microphone waveforms. The applications of such a device are primarily in support of the development, testing, and evaluation of rattle detection systems based on human experts or computers.

Effects of changing ambient humidity and temperature have been studied on the performance and emissions of a hand-held two-stroke and a hand-held four-stroke engine. The main effect of changes in ambient conditions is to change the intake air density and therefore the air-fuel ratio metered by the carburetor. Trends in the effects of humidity and temperature on emissions are predicted reasonably well by theoretical thermodynamic models. They suggest an improved correction for the dependence of NOx on ambient conditions, as a function of both humidity and operational air-fuel ratio, which appears to collapse NOx production data better than the existing KH correction factor. They also suggest a simple procedure for tuning engines to design air-fuel ratios using the measured exhaust-gas %CO, which takes into account the prevailing ambient conditions.

In this paper results are presented from a study that investigates the use of centrifugally driven pendulum vibration absorbers for the attenuation of engine torsional vibrations. Such absorbers consist essentially of movable counterweights whose center of mass is restricted to move along a specified path relative to the rotational frame of reference. These devices are commonly used in light aircraft engines and helicopter rotors. The most common designs use a circular path for the absorber, tuned to a particular order of rotor disturbance, although more recent developments offer a wider variety of paths. Our goal here is to evaluate the system performance for a range of path types with different types of tuning. This analytical study is carried out for a simple mechanical model that includes a rotor and an absorber riding along a quite general path. Approximate solutions are obtained using a perturbation scheme and compared with detailed computational results.

This paper presents the results of a combined theoretical and experimental study to find the relationship between a system's parameters and the sound generated when the system impacts against a rigid fixture. Although the particular physical structure investigated is a flexible cantilever beam, the approach adopted is such that the results are valid for a more general class of problem.

Squeak and rattle has become a primary source of undesired noise in automobiles due to the continual diminishment of engine, power train and tire noise levels. This article presents a finite-element-based methodology for the improvement of rattle performance of vehicle components. For implementation purposes, it has been applied to study the rattle of a glove compartment latch and corner rubber bumpers. Results from the glove compartment study are summarized herein. Extensions to other rattle problems are also highlighted.

This study analyzes methods of comparing SEA model results with experimental results for key traits. These qualitative traits provide the basis for correlation of model results with experimental results through the development of a comparison index. This paper formulates a comparison index and illustrates the application to SEA models. A customized data structure was designed around the comparison index to store all necessary aspects of the modeling, experiment and comparison results. This data structure was then implemented using relational database software. These new tools; the comparison index and the SEA database, will create a common language and a forum for SEA model results that will aid and stimulate dialog in the SEA modeling community and in tern, advance the science of SEA modeling.

The exhaust-gas emissions of a small four-stroke, carbureted, single-cylinder spark-ignition engine have been studied as functions of ambient conditions, using gasoline as the fuel. In steady-state dynamometer tests at fixed engine speeds/loads, carried out under different climatic conditions, the concentrations of exhaust-gas components have been measured. Their dependence on ambient conditions has been analyzed principally in terms of the influence of ambient temperature, pressure, and humidity on the air-fuel ratio metered by the carburetor. While the air-fuel ratio of carbureted utility engines at fixed loads varies by only a small percentage during modest changes in ambient air conditions, these changes can correspond to significant changes in the production of regulated pollutants. Using a correction for air mass flow and fuel density at wide open throttle, the scatter in observed air-fuel ratio and % CO data could be reduced by about one third.

The location of the pelvis in the seated automobile operator is critical for proper packaging and seat comfort design. The pelvis is the skeletal structure which contains the hip joint (H-point) and ischial tuberosity (D-point). The orientation of the pelvis largely determines the curvature in the low back which is supported by lumbar supports in the seat back. A methodology has been developed that uses onboard video and pressure measurement systems to locate the pelvis. This system has been used in a mid-sized vehicle on seated operators driving the vehicle on the highway. This paper describes the methodology and the location of the pelvis in seated automobile operators.

Statistical Energy Analysis (SEA) is a useful tool for predicting the transmission of noise and vibration through the structures of automotive vehicles. This work discusses the identification of SEA internal loss factor parameters from experimental measurements of vehicle sound pressure levels and structural accelerations. A simple automotive vehicle SEA model can be constructed from elements idealized as uniform beams, flat plates and acoustic volumes. Such an SEA automotive vehicle model can accurately predict the vibro-acoustic response of an automotive vehicles when appropriate equivalent SEA parameters are identified from in situ experimental data. This paper will present an algorithm for identifying internal loss factors for SEA models. The paper will include an example of the application of the algorithm to identification of automotive vehicle internal loss factors from measured vehicle response data.