F. M. Sciammarella

Industrial Finishes of Ceramic Surfaces at the Micro-level and its Influence on Strength

The mechanical properties of ceramic materials are influenced by surface finishing procedures. This paper presents a brief introduction to an advanced methodology of digital moire contouring utilized to get surface information in the micro-range that is a generalization of a method developed for metallic surfaces [1]. Five types of surface treatments are considered. Two of the finishes utilize diamond grinding with a rough grit (100) and a smoother grit (800). The third type is laser assisted machining of the ceramic. The fourth type is simply applying the laser without machining. The final type is the as received ceramic resulting from the process of fabrication. A total of 63 specimens, nine of each kind were tested in four-point-bending. The strength of the specimens was statistically analyzed using the Gaussian and the Weibull distributions. The statistical strength values are correlated with the statistical distributions of surface properties obtained using this advanced digital moire contouring method. The paper illustrates the practical application of this method that was developed to analyze surfaces at micro level and beyond.

Light Generation at the Nano Scale, Key to Interferometry at the Nano Scale

The feasibility of recording optical information at the nanometric level was considered for a long time restricted by the wavelength of light. The concept of wavelength of light in classical optics is a direct consequence of the standard solution of the Maxwell equations for purely harmonic functions. Propagating harmonic light waves in vacuum or air satisfy the required mathematical conditions imposed by the Maxwell equations. Hence, in classical optics, the concept of wavelength of light was associated with that type of waves. Mathematically speaking, one can derive solutions of the Maxwell equations utilizing Fourier integrals and show that light generated in a volume with dimensions much smaller than the wavelength of light will have periods in the sub-wavelength region. Every oscillator, whether a mass on a spring, a violin string, or a Fabry–Perot cavity, share common properties deriving from the mathematics of vibrating systems and the solutions of the differential equations that govern vibratory motions. In this paper, some common properties of vibrating systems are utilized to analyze the process of light generation in nano-domains. Although simple, the present model illustrates the process of light generation without getting into the very complex subject of the solution of quantum resonators.

The Kinematics and Dynamics of 3-D Displacement Fields

In the last few decades Experimental Mechanics, helped by advanced technologies to gather 3-D spatial information in non-transparent media, has evolved into a very general tool. It has become possible to observe the internal volume of engineering materials and in the area of biomechanics living internal tissues. This paper contains a brief review of Continuum Mechanics mathematical models that are available to formulate problems in 3-D including large deformations. The extension of the experimental methods that measure displacements in 2-D to 3-D is presented. Two important cases are considered: (a) use of deterministic signals, (b) use of random signals. In order to separate the complexity of the subject of 3-D analysis from the difficulties that arise from the use of random signals, the connection between mathematical models and their experimental determination is presented utilizing deterministic signals. The extension of the use of random signals to the determination of displacements in 2-D to 3-D is outlined. A new method to extract displacement information from random signals is developed and an example of application is provided. Two methods to extract displacement information in 3-D, the classical method based on displacement projections and discrete image correlation (DIC) based on following gradients of intensities are compared. There are many complex steps involved in data processing aside the basic approach, this circumstance makes difficult a comparison between the two methods, however it is possible to conclude that the results are in fair agreement.

Merging Experimental Evidence and Molecular Dynamics Theory to Develop Efficient Models of Solids Fracture

Causes of failure mechanisms can only be found at the level of the dynamics of atoms and molecules. However, the subject of dynamics at the level of atomic structure is very complex, especially in terms of modeling and computations. An interesting way to better understand relationships between macro world and atomic realm is to develop Experimental Mechanics techniques that can provide a verification of developed models at the nanometric and subnanometric levels, guiding the derivation of comprehensive but manageable models. This paper will describe how to apply classical EM methods to establish a bridge between classical continuum mechanics variables and the atomistic analysis of solid mechanics. In particular, we analyze the role of the Cauchy-Born rule as standard tool applied in theoretical and numerical methods to describe the continuum utilizing atomistic arguments. Experimental evidence of the validity of the Cauchy-Born rule will be discussed for the case of SiC crystal including dislocations. Likewise, we will examine how to handle the onsets of plasticity and fracture.

Topography of Rough Dielectric Surfaces Utilizing Evanescent Illumination

The authors utilize optical evanescent fields to analyze the topography of metallic and non metallic surfaces. The methodology initiated with the phenomenon of planar surface waves produced by surface plasmon polaritons. By direct experimental observations in 2009 the method was extended to ceramic surfaces in the micron and sub-micron range. Since the ceramics are dielectric materials the plasmon polariton model cannot explain the observed phenomena. For almost a century researchers have analyzed surface electromagnetic waves observed in planar interfaces that involve metallic surfaces, or metallic surfaces and dielectric media. These studies resulted in the theory of surface-plasmon waves and surface-plasmon-polariton waves. Additional planar surface waves are the so called Dyakonov waves, Tamm waves, and Dyakonov–Tamm waves. These waves were originally theoretically derived by M.I. Dyakonov about 25 years ago and were observed for the first time in 2009. The Dyakonov–Tamm waves are generated in the interface of two dielectric materials with periodic internal structures.

Optical Head as a Gauge Device in Manufacturing

Numerous companies produce shape contouring devices based on the projection of an optical signal to obtain shape information. The basic principle for all of these devices is parallax determination. Parallax can be measured through projecting a small spot, a line, or a light pattern such as a grid. One application of this methodology is a gauge device in manufacturing processes where layers of materials are being deposited or removed to control the final geometry of the surface. The degree of accuracy achieved depends on the final required accuracy of the finished product. An essential aspect is measurement in real-time; real time stands for the time required by the controlling software to detect errors on the finished surface. The speed of the particular fabrication process dictates how quickly the software must be able to process information. The optical head must not reduce the speed of fabrication, and it should provide a warning of a faulty process fast enough to permit real-time corrections. In view of the real time requirement, the luminous signal processing must be reduced to a minimum. An optical head that projects a line is an excellent candidate for this operation because a line is the simplest form of the system that provides all of the required measurements in the case of the material deposition manufacturing process. This paper shows that very high precision and accuracy are achievable in conjunction with extremely low processing times in a unique laser line projection setup. The unique aspect of this system is the ability to make these measurements regardless of surface conditions.

High Accuracy Optical Measurements of Surface Topography

Surface characterization is a very important aspect of industrial manufacturing. All engineering parts are strongly affected in their performance by properties depending on surface topography. For this reason methodologies able to provide a functional representation of surface topography are of paramount importance. Among the many techniques available to get surface topography optical techniques play a fundamental role. A digital moire contouring technique recently proposed by the authors provides a new approach to the study of surface topography. This paper presents further developments in surface topography analysis particularly with respect to the resolution that can be currently obtained. The validity of the proposed approach is checked by analyzing existing standards for surface roughness determination. Optical results are compared with NIST certified standard specimen.

In Situ Modal Analysis of Gears

There has been a vast amount of work in the analysis of multistage gearbox housings and the effects vibrations can have on them. This subject is of concern in the aerospace industry and is handled by Finite Element Analysis (FEA). Often experimental verification is required, particularly when a new design or material is introduced. Holographic interferometry and speckle interferometry are optical tools that provide in-situ comprehensive solutions when investigating the modal analysis of gears. Both of these experimental techniques provide an output that determines the dynamic characteristics of the gear being analyzed which can be directly connected to the FEA solution. Experimentally it is possible to obtain the dynamic displacement and strains for all the points of the area of interest and hence can be utilized to modify the FEA in such a way that the results of the FEA agree with experimental values. This type of analysis is particularly critical when it is important to determine the in-plane vibration modes of large gears, known as the “oval modes”. These resonant modes are particularly important in aerospace applications because they can cause serious damage if left unchecked. The analysis of oval resonant modes were carried out on a spur gear to show the effectiveness and accuracy of this in-situ approach.

The Kinematics of Crystalline Arrays at the Subnanometric Level

This article presents additional developments in the analysis of displacement fields and strains around edge dislocations via electron microscopy. The goal of this work, which extends earlier work of the authors, is to provide additional information about the connection between the Continuum Mechanics model of the events taking place in a nanometric size region of a crystal and experimentally observed geometrical changes of the crystalline array.

Optical Fourier Transforms in the Nano Range

This paper highlights the recently developed technique of Nano-Holographic Interferometry via far field microscopy. The main difference between conventional lens holography of phase objects and the methodology presented in this paper is that the observations are made well beyond the classical limits of optical resolution. Going beyond the resolution limits becomes feasible by the use of evanescent wave fronts as a source of illumination. The objects to be analyzed enter an excited state that produces pseudo-non-diffracting wave fronts. These wave fronts travel well beyond the traditional limits and enable the observations of nano-particles via a far field microscope. These discoveries open up new possibilities for Experimental Nano-mechanics that were previously thought impossible.