3D Optical Topography Research Articles

Influence of machining damage generated during trimming of CFRP composite on the compressive strength

Machining of composite materials is a challenging task due to the heterogeneity and anisotropy of composite structures. The induced defects reduce integrity of the machined surface as well as the loading capacity of the composite structure in service. Therefore, it is necessary to quantify the damage induced during trimming and correlate the quality of the machined surface to mechanical properties. The correlation of the surface roughness criteria, widely used in literature, to the mechanical behavior raise several contradictions. For this reason, new parameters for the characterization of the machined surface are proposed and correlated to the mechanical behavior under compressive loading. In this context, carbon fiber-reinforced plastic laminates are conventionally trimmed, and the machining damage is characterized using scanning electron microscope observations, X-ray tomography, and 3D optical topography. The results reveal that crater volume and maximum depth of damage quantify the machining damage more realistic compared to the classical surface roughness criteria.

Surface integrity while trimming of composite structures: X-ray tomography analysis

The aim of this paper is to study the influence of the process parameters (cutting speed and feed) of the conventional trimming on cutting forces, machining temperatures, tool wear and machining quality of Carbon Fibers Reinforced Plastics (CFRP) using PCD tool. The machining quality was characterized using three different techniques such as Scanning Electron Microscopy (SEM), 3D optical topography and X-ray tomography. The originality of this work is based mainly on the multi-scale characterization of the machined surfaces. In fact, a new parameter based on the measurement of the volume of craters is proposed and compared to the surface roughness criterion (Sa) and the X-ray tomography images. The obtained results show that, with the crater volume criterion as well as the X-ray tomography images, the effect of the machining parameters and the wear of the tool on the textured surfaces are well correlated to surface roughness criterion (Sa). In addition, it was observed that the feed speed and tool wear were the major factors affecting the cutting forces and the machining temperatures.

Influence of laser peening without coating on microstructure and fatigue limit of Ti-15V-3Al-3Cr-3Sn

In the present study, Ti-15V-3Al-3Cr-3Sn (Ti-15-3), a beta titanium aerospace alloy in solution treated condition (850 °C/1 h) was subjected to Laser Peening without Coating (LPwC) with a wavelength of 532 nm and power density of 8.96 GW cm−2. Surface roughness was analysed using 3D optical topography. Curiously, in the near peened surface, peening induced precipitation (i.e. 19% of α precipitation) and increased fraction of low angle boundaries (∼123%) was revealed through the Electron Back Scattered Diffraction (EBSD) analysis. Through depth nanohardness measurement was carried out along the cross-section of the peened sample right from the near peened surface. Peak hardness of 4.6 GPa is observed at a depth of 100 µm from the peened surface while the base/bulk hardness of the material is 4 GPa. In addition, X-Ray Diffraction (XRD) based analysis confirmed the presence of compressive residual stress in the near surface region of the peened sample. To understand the effect of the peening induced microstructural changes and residual stresses in fatigue behaviour, staircase method of fatigue analysis was adopted and observed that the more number of run out samples belonged to laser peened condition when compared to the unpeened condition. Despite this favourable indication, fatigue limit remains more or less unaltered even after peening. Fractography studies revealed the least influence of the surface roughness induced by laser peening over the crack initiation. Irrespective of the condition (i.e. unpeened and laser peened), crack initiation was predominantly influenced by the stress concentration co-existing at the sharp corners.

Evaluation of Cutting Tools Secondary Adhesion Wear Using 3D Optical Topography Techniques — Application to Dry Turning of Al-Cu Aerospace Alloy

The combination of specific properties, cost, reliability and predictable behavior, guarantee that the aluminium alloys will be kept as one of the materials used in aerospace industry. When aluminium alloys are machined, transfer of cutting material to cutting tool is related with the secondary or indirect adhesion wear mechanism, which can be presented in form of Built-Up Layer (BUL) and Built-Up Edge (BUE), located in two defined zones of the tool, cutting edge and rake face respectively. The material adhered involve tool properties, geometrical and physicochemical alterations which modify the initial cutting conditions, in accordance with currently concept of tool wear. Until now, a generalized lack is observed in methodologies to assessment the secondary adhesion wear in machining of aluminium alloys, mainly due to the difficulty found in characterizing and quantify thereof. In this paper, based in Focus-Variation Microscopy (FVM) techniques, a methodology is proposed through high-resolution optical 3D topography measurements obtained from WC-Co worn tools tested in the dry turning of UNS A92024-T3 alloy, in order to obtained information about effects and intensity of secondary adhesion wear.

Cortical mapping of 3D optical topography in infants.

Precise localisation of cortical activation in the early development of the infant brain remains unclear. It is challenging to co-register haemodynamic responses during functional activation in infants with the underlying anatomy of the brain. We used a multispectral imaging algorithm to reconstruct 3D optical topographic images of haemodynamic responses in an infant during voice processing. In this chapter, we present a method for co-registering 3D optical topography images reconstructed from functional activation data in infants onto anatomical brain images obtained from MRI structurals of the individual infants.

Three-dimensional optical topography of brain activity in infants watching videos of human movement

We present 3D optical topography images reconstructed from data obtained previously while infants observed videos of adults making natural movements of their eyes and hands. The optical topography probe was placed over the temporal cortex, which in adults is responsible for cognitive processing of similar stimuli. Increases in oxyhaemoglobin were measured and reconstructed using a multispectral imaging algorithm with spatially variant regularization to optimize depth discrimination. The 3D optical topography images suggest that similar brain regions are activated in infants and adults. Images were presented showing the distribution of activation in a plane parallel to the surface, as well as changes in activation with depth. The time-course of activation was followed in the pixel which demonstrated the largest change, showing that changes could be measured with high temporal resolution. These results suggest that infants a few months old have regions which are specialized for reacting to human activity, and that these subtle changes can be effectively analysed using 3D optical topography.