Laser surface profilometry

Figure 8. Laser surface profilometry scan. The gage section profile of a precision ground and lapped tensile specimen shows that relatively large valleys persist.

Laser-based profilometry is now being applied to a wide variety of both NDT and Quality Control gauging applications. In the world of NDT, the primary interest is in the details associated with surface topography or deformation of a particular component. Laser-based profilometry systems are commonly used to inspect surfaces for defects such as pitting, corrosion, deformation and cracking. Quality control gauges are used for absolute measurement of dimensions, such as the diameter and thickness of a given part. 

One of the earliest NDT applications for laser-based profilometry systems was for the inspection of marine boiler tubes. Under funding from the U.S. Navy", several systems were developed that were capable of rapidly and accurately mapping the inside surface of 25 mm and 50 mm diameter boiler tubing. Features such as internal pitting and corrosion can be located and quantitatively assessed using computer-graphic analysis. The system employs an... 

As described previously, laser-based profilometry uses a reflected signal to map a surface. In... 

Laser-based profilometry systems have also been adapted for unique applications in nuclear power generating plants. Applications where quantitative information with regard to surface condition for mechanisms such as surface pitting and flow-assisted corrosion are candidates for this NDT method. 

Another application of laser-based profilometry is the inspection of rocket and missile components. The U.S. Air Force has funded work to develop a non-contact laser-based profilometer for the inside surface of solid rocket motors. Over time, these devices are subject to slumping and cracking, which could potentially render the rocket motor ineffective and hazardous. When fully implemented, this system will provide a meaningful screening method for evaluating the condition of aging rocket motors. 

Other examples of government and military applications of laser-based profilometry include the evaluation of rocket thruster nozzles to locate and measure flame erosion remote inspection of hypervelocity test track and the measurement of sludge deposits on tube internal surfaces. 

Measurement of the power necessary to move an object on the skin surface mechanically laser-controlled profilometry of a skin-surface replica... 

Non-contact laser profilometry has been used to obtain roughness parameters and surface fractal dimension (Ds) of erythromycin acistrate tablets It was expected that tablet surface fractal dimension (Ds) will depend on the compression force used for tabletting. However, tablet surface fractal dimension was found independent of the compression force ranging from 4 to 22 kN. Instead, a surface roughness parameter Rp, which is the maximum distance between the highest point and the average height of the surface profile, indicated the variation of tablet friability as a function of compression force (Fig. 7). 

The taking of tooth impressions to assess wear in vivo has become popular in recent years, as silicone impression materials are available with excellent detail reproduction and good dimensional stability. Several authors [35-38] have reported the use of these materials to capture the dimensions of selected teeth (or teeth surfaces) over a period of time. The silicone impressions are scanned using a profilometry system, typically a laser profilometer, to build an electronic image of the tooth surface. Several scans of the same tooth or surface, taken over a period of time, can then be electronically overlaid and subtracted, to calculate the change in surface contour, or the volume of material removed. This technique can only work if the two scans are precisely overlaid. To avoid... 

Hence, based on the parameters available, three different ablation rates were studied corresponding to a weak, a medium, and a full ablation according to laser profilometry (Fig. 20.5). The weakly ablated surface possesses the same surface roughness as an untreated sample (Sa=0.6pm). On the contrary, the medium and the fuUy ablated ones exhibit partial and total removal of the polymer layer at the surface of the composite, respectively. In the case of total ablation, the resulting roughness is directly related to the kind of fiber weaving used for reinforcement. 

Fig. 20.5 S urface profilometry and surface roughness of glass/epoxy laser treated composites, (a) weak ablation (Sa = 0.6 p.m).

Microstructural analysis using SEM is requisite for examining surface details and features such as film pore structure and thickness or the crystallites formed by the EP surface activation process [81, 186]. AEM can be used to probe micro- to nanoscale surface topography and determine critical parameters such as surface roughness, (arithmetical mean deviation of the profile) [70, 154, 187] or the size and distribution of surface activation particles [188]. Nanoparticles formed during surface activation [147, 189] and the dislocation substructure of palladium [90] have been studied by TEM. Optical or laser profilometry is used to quantify surface roughness or to measure film thickness on a flat surface [190]. 

The polyester material has been analysed using 3D-Laser profilometry. The laser profilometer measures the texture, form and topography profile of the fabric, creating 3D images of the fabric surface. (Fig. 3) This technique can be used to compare the surfaces of treated textiles and visualise the effect that the finishes have on the surface profile of the polyester. 

Standard roughness values of an SLA and a Thermanox surface and of different positions on the roughness gradient measured by laser profilometry... 

D profiles do not, however, adequately describe 3-D properties, particularly in the ease of anisotropic surfaces. The next step in the application of the wavelength-depen-dent roughness concept will therefore be an extension to 3-D evaluation, as discussed in Section 3.5. Another frequent limitation in applications is related to the limits of lateral and/or vertical resolution and to instrumental artefacts. In comparison to the laser profilometry technique, interference microscopy, AFM and stereo-SEM are able to resolve finer structures and surface features, although — in the case of AFM — problems in ease of contacting envelope may be critical for strongly corrugated surfaces. A comparative study of different teehniques will be published separately. 

For measuring the topology of the fracture surface (i.e. roughness), direct contact profilometry, laser profilometry, or the atomic force microscopy are available (6). With the help of a coordinate system, contour maps of the fracture surface can be drawn based on roughness data or through-focus procedures for the light microscope. 

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