USING DATA SCIENCE TO EVALUATE NANO-REINFORCED EPOXY SURFACES

Toughened composites reinforced with nanofillers show improved mechanical performance such as increased abrasion resistance, fracture toughness, and fracture energy. The degree of these improvements is influenced by the degree of dispersion of the nanofillers which can be analyzed using force microscopy (AFM), a technique that allows for mapping the local height and elastic modulus of a surface. However, current AFM apparatuses can only measure a narrow range of moduli according to the type of tip, which complicates the full-field measurement of moduli in nanocomposites with nanosilica (~72 GPa) embedded in epoxy (0.1 – 5 GPa). Moreover, height mapping can only visualize filler particles exposed at the surface. These limitations make it challenging to determine the 3D location of nanoparticles near the surface of a composite. To overcome these limitations of conventional AFM, we used a combination of data science, micromechanics, and experimental data from AFM to locate the centroidal position of nanosilica (NS) particles relative to the surrounding epoxy surface. Using finite element simulations, a theoretical dataset of modulus values as a function of particle position relative to the epoxy surface was created as a training set. Bayesian optimization determines the “best” particle position that results in minimum error between simulated and experimental modulus contours. The algorithm returns the 3D position of the fully or partially embedded NS particle relative to the epoxy surface. The algorithm has shown the ability to partially produce simulated modulus contours that resemble the experimental modulus contours.

Micro Vibration Measurement with Microscopic Speckle Interferometry Based on Orthogonal Phase

A micro-device vibration measurement method based on microscopic speckle interferometry combined with orthogonal phase is presented. This method utilizes the approximate linear distribution characteristics of orthogonal points (points satisfying the condition that the initial phase difference equal to π/2) to quickly obtain the vibration information of the measured object. Compared with common optical measurement methods, this method does not require scanning imaging and can realize real-time full-field measurement. Moreover, the measurement principle and equipment is simple, so there is no need to introduce a stroboscopic light source or heterodyne device.

Noncontact and Full-Field Measurement of Residual and Thermal Stress in Film/Substrate Structures

Residual stress and thermal stress of a film/substrate system are determined based on the curvature measurement with a 3D digital image correlation method (DIC) and calculation of the thin-film stresses by the extension of Stoney’s formula. A Ni film electroplated on a H62Cu plate is used to verify the proposed method. The full fields of nonuniform thin-film stresses are obtained in a room temperature to high-temperature environment of 200 °C, which can be potentially extended to higher temperatures. These results provide a fundamental approach to understanding thin-film stresses and a feasible measurement method for high temperature.

Measurements of Rotational Events Generated by Artificial Explosions and External Excitations Using the Optical Fiber Sensors Network

Measurements of artificial events can substantially confirm the data validity of constructed rotational sensors, as well as provide methods for simplifying the measurement process. The above task, especially with international cooperation, can provide full-field measurement results of the target object, which can deliver more significant data and sensor properties. The paper presents vertical rotational velocity recordings gathered during an international experiment that took place at the Geophysical Observatory of the Ludwig Maximilian University of Munich in Fürstenfeldbruck, Germany. Data were obtained during artificial explosions, as well as external excitations induced by a VibroSeis truck. The authors present data recorded by two prototypes of optical fiber rotational sensors. They have been specially designed for rotational seismology needs and are characterized by a theoretical sensitivity equal to 2 × 10−8 rad/s/√Hz and a wide measuring range both in amplitude even up to 10 rad/s, and a frequency from DC to 1000 Hz. Their self-noise investigation during the aforementioned experiment showed that both sensors have precision no worse than 2 × 10−6 rad/s/sqrt (Hz) in all desired frequency range from 0.01 to 100 Hz. A down-sampling and a spectral analysis of the recorded signals are also presented. The recorded data and their analysis confirmed the performance and reliability of the applied optical fiber rotational sensors. Moreover, the presented international experiment underlines a special necessity for specifying the sensors’ performance test methodologies in the rotational seismology.